Question Bank for Power Coal Transportation 1

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1. Briefly describe the production process of a thermal power plant. Answer: The production process in a thermal power plant can be summarized as follows: The chemical energy of fuel is converted into thermal energy through combustion, which is used to heat water into steam at a certain pressure and temperature. This steam then drives a turbine, converting thermal energy into mechanical energy that causes the rotor to rotate; finally, a generator converts this mechanical energy into electrical energy. 2. What are the main systems, auxiliary systems, and facilities involved in the production process of a thermal power plant? Answer: The main production systems involved in the operation of a thermal power plant are the steam and water system, the fuel system, and the electrical system. In addition, there are various auxiliary systems such as water supply systems, chemical systems, coal conveying systems, and thermal automation systems, as well as corresponding facilities such as workshops, buildings, and structures. 3. What is a coal transportation system in a power plant? What equipment is generally included? Answer: The coal transportation system in a power plant encompasses the entire production process, from transporting coal directly from the unloading equipment to the raw coal silo in the boiler room, as well as transferring the coal to the raw coal hopper via a coal storage area. A coal transportation system generally includes fuel transport equipment, coal unloading machinery, coal volume measurement devices, coal yard facilities, coal conveying equipment and screening/crushing devices, centrally controlled or programmatically controlled equipment, as well as other auxiliary equipment and auxiliary buildings. 4. What equipment does the coal transport system in thermal power plants consist of? Answer: The coal transport system is mainly composed of coal unloading equipment, coal feeding equipment, coal loading equipment, coal blending equipment, coal plant-related equipment, and auxiliary equipment. 5. What are the reasons for oil leakage in reducers? Answer: The reasons for oil leakage in reducers are: (1) Rough machining of the mating surfaces. (2) The reducer housing deforms after long-term operation, resulting in a loose fit at the joint surface. (3) Excessive oil in the tank. (4) An excessive sealing gap between the bearing cover and the hole causes oil leakage from the bearing cover. The main reason for oil leakage from the end cover is the blockage of the oil return groove inside the bearing cover; there being a certain gap with the end cover, oil leaks out through this gap. (5) The joint surface of the observation hole is uneven; the paper gasket at the joint surface is damaged, resulting in poor sealing and oil leakage at the joint surface. 6. What are the requirements for assembling rolling bearings? Answer: Generally speaking, the degree of fit for bearings should be determined based on the application requirements; a tighter fit is required in situations where there is high rotational speed, large loads, and significant vibration ； Conversely, use a looser fit. The fit between the inner ring of the bearing and the shaft is a transition fit based on the hole system, while the fit between the outer ring of the bearing and the hole is a transition fit based on the shaft system ； When assembling large bearings, a static fit or a transitional fit based on the hole system should be used. 7. What is the significance of the clearance in rolling bearings? Answer: The clearance in rolling bearings includes radial clearance and axial clearance; it refers to the maximum amount of movement of one bearing ring in the radial and axial directions, with the other bearing ring being fixed. For a certain type of bearing, the radial clearance and the axial clearance influence each other, and there is a specific conversion relationship between them. 8. What are the quality requirements for tape bonding? Answer: The quality requirements for tape bonding are as follows: (1) The unevenness in the equal division of various sections of the tape shall not exceed 1 mm. (2) The surface of the cut area must be smooth, with no cracks present. (3) When using a wire wheel to remove residual adhesive, clean it thoroughly. (4) The edge of the tape at the joint should be a straight line, with a straightness of less than 0.3%. (5) The quality of the joint must ensure its usability for over one year, during which no defects such as holes, delamination, or cracked edges shall occur. 9. What is the function of a belt coal conveyor? Answer: Its function is to transport the coal from the coal unloading chute to the boiler’s raw coal hopper. 10. Briefly describe the advantages of ring coal crushers. Answer: Ring coal crushers have the following advantages: (1) High crushing capacity, low power consumption, and high efficiency. (2) It has a simple and compact structure, occupies little space, possesses high stiffness, and is lighter in weight than hammer and impact types. (3) Ensure that the discharge particle size is below 30 mm and the discharge is uniform. (4) Since the hammer ring can swing freely, when it encounters a harder object, the ring hammer automatically retracts and is reflected into the magnetic separation chamber by the material shifter. (5) It has a low blower effect due to the hammer ring, a small machine size, low air volume, and less coal dust leakage. (6) It has reliable operation, is easy to adjust, convenient for maintenance, requires minimal upkeep, and exhibits strong adaptability to changes in coal type. (7) Low operating noise. (8) The unit has low vibration. (9) The materials used in the unit are appropriate, ensuring a long service life. 11. Briefly describe the principle of electric actuators. Answer: After the motor starts, it reduces speed through a pair of gears, thereby driving the screw to rotate. The nut that is meshed with the screw moves along the guide rails fixed on the inner wall of the guide sleeve. The push rod is connected to the nut by screws; as the nut moves forward, it pushes the push rod outward. Conversely, when the motor rotates in the opposite direction, the push rod retracts. In this way, after the motor is slowed down by this pair of gears, it drives a screw-nut assembly to convert the motor’s rotational motion into linear motion of the push rod; the forward and reverse rotation of the motor is used to carry out the pushing action. The push rod is equipped with an automatic overload protection system; when the push rod is overloaded or reaches its maximum travel distance, the limit switch automatically shuts off, stopping the push rod and thus providing overload protection to prevent damage to the motor and other components. 12. Briefly describe the components of an impeller coal feeder. Answer: An impeller coal feeder is mainly composed of a main drive mechanism and a crane drive mechanism. The main drive mechanism includes: electric motor, coupling, reducer, bevel gear reducer, impeller, etc ； The vehicle transmission mechanism includes a motor, reduction gearbox, coupling, worm gear reduction gearbox, wheels, coupling, control system, etc. 13. Briefly describe the components of a belt conveyor. Answer: A belt conveyor is mainly composed of the belt (ordinary belts and steel cable belts), idlers (including grooved, parallel, cushioned, and automatically adjusting idlers), as well as the frame. It also includes a driving mechanism (in which an electric motor drives the drums through a coupling and a reducer), a tensioning device (which can be of the weight-type or screw-type), direction-changing drums, braking devices (such as belt brakes, roller brakes, electro-hydraulic brakes, and electromagnetic brakes), and a cleaning device. 14. What causes the pusher to make a “whooshing” sound? How should it be dealt with? Answer: The radial clearance of the main bearing is too large. Check the gap; if it exceeds the limit, it should be replaced. 15. Why does vibration occur when the gears of a loading/unloading bridge skip teeth? How to solve it? Answer: The gears are severely worn or damaged. A new gear should be replaced. 16. What are the reasons for the hydraulic system pressure to exceed the specified value? How should it be handled? Answer: The reasons for the hydraulic system pressure to exceed the specified value are: (1) The main valve of the relief valve is stuck. (2) The oil holes are blocked. The solution is: shut down the machine for maintenance. 17. What are the advantages of gear transmission? Answer: The advantages of gear transmission are its compact structure ； Wide range of applications ； It ensures that the gear ratio remains constant ； High mechanical efficiency ； It operates reliably and has a long service life, with relatively low stress on the shafts and bearings. 18. What are the criteria for selecting bearings? Answer: The main criteria for selecting bearings are the magnitude and direction of the load, as well as the nature of use. 19. What are the components of a hydraulic system? Answer: A hydraulic system consists of a power unit, an actuating unit, a working fluid, and auxiliary components. 20. Into which categories can lubrication be divided? Answer: Lubrication can be divided into three categories: hydrodynamic lubrication, elastohydrodynamic lubrication, and boundary lubrication. 21. What is the function of lubrication? Answer: It reduces frictional losses between moving and stationary parts of mechanical equipment, minimizes wear on the contact surfaces, reduces vibrations, provides sealing, and helps with heat dissipation. 22. What are the main components of the coal transport system in a thermal power plant? Answer: The coal transport system in a thermal power plant mainly consists of coal unloading equipment, coal feeding equipment, coal loading equipment, coal blending equipment, coal yard equipment, and auxiliary equipment. 23. The belt deviates when loaded but not when unloaded. What is the reason? How can it be eliminated? Answer: The reason is that the coal dropping point is not in the correct position. Eliminate the issue by adding baffles and adjusting the coal falling point. 24. What are the reasons for abnormal wear of the adhesive surface of the tape? How to address it? Answer: The reasons are: (1) There are debris between the adhesive sheet of the guide groove and the tape. (2) The glue sheet of the material guide groove is too hard. The solution is: (1) Stop the machine and remove debris. (2) Replace the soft rubber pad. 25. Why do the traveling wheels of the impeller coal feeder severely damage the rails? How to deal with it? Answer: Because: (1) Uneven gauge. (2) The traveling wheel is skewed. The solution is: (1) Adjust the gauge. (2) Solve the problem of skewed walking wheels. 26. Describe the cold adhesive bonding process for tapes. Answer: The cold adhesive bonding process for tapes is as follows: (1) First, preheat and dry the damp tapes. (2) Line drawing, trimming. Then, use a wire grinding wheel to remove the residual glue from the surface of the core layer until the canvas becomes slightly fuzzy, and clean it up. (3) Apply glue. Apply a layer 0.4 mm thick in the first pass, and dry it using an iodine-tungsten lamp. Apply a second coat of glue once the surface is no longer sticky to the touch. Apply a slightly smaller amount of glue on the second application, then dry it; once the surface of the glue is sticky but not too sticky, the pieces can be joined together. (4) When closing the joints, the corresponding steps should be aligned, and then the area should be struck with a hammer from the center outward to expel air and ensure a strong bond between the joints. The hammering force should be even, and this process should be carried out across the entire joint area. (5) Repair the interface edges. 27. What is the role of screening equipment in the coal transportation system? Answer: To improve the efficiency of coal mills and reduce their wear and tear, it is necessary to crush the raw coal before it enters the mills, reducing it to an appropriate particle size. To enhance the crushing efficiency of the crushers and save electrical energy, screening is carried out first; coal with the correct particle size goes directly into the crushers, and after being crushed to the desired size, it is then sent to the coal mills. 28. What is the function of an iron remover? Answer: An iron remover is used to remove various shapes and sizes of metal particles mixed in coal during transportation, thereby ensuring the safe operation of coal conveyors, coal crushers, and coal grinders. 29. Briefly describe the working principle of a belt conveyor. Answer: When a belt conveyor is in operation, the motor drives the drive roller of the conveyor; through the friction between this drive roller and the belt, the belt moves forward. Materials such as coal are placed on the belt, and they travel together to the discharge point where the coal is unloaded. 30. What are the different types of tensioning devices? What are their characteristics? Answer: There are three types of tensioning devices: tensioning using a weight attached to a tail car, tensioning using vertical rollers with weights, and screw-type tensioning. (1) The weight block type tensioning of the tail car can maintain a uniform tension in the conveyor belt at all times. (2) The helical tensioning arrangement is compact and requires little space, but it cannot maintain a constant tension. (3) Vertical drum-type weight tensioning device, capable of maintaining constant tension. 31. What are the main components of a screw coal unloader? Answer: The main components of a coal unloader are: (1) the metal frame section. (2) The moving part of the truck. (3) Screw lifting section. (4) Spiral rotating section. 32. What is the method for replacing the surface roller? Answer: Remove the foot screws, lower it using a crane, position the new roller properly and level it, then tighten the screws. 33. What is the purpose of installing a sieve on the coal drop tube in front of the coal crusher? Answer: It is to ensure that coal with the appropriate particle size is sent directly to the coal grinder, while coal that does not meet the requirements is passed through the sieve and sent to the coal crusher for crushing before being fed into the coal grinder. This improves the crushing efficiency of the coal crusher and saves electrical energy. 34. What is the overall structure of a ring coal crusher? Answer: A ring coal crusher consists of a housing, a cover, crushing plates, rocker arms, a screen plate regulator, a coal shifter, toothed ring hammers, screen plates, a main shaft, an annular shaft, ring hammers, and impact plates. 35. What are the allowable angular displacement and radial angular displacement of a coupling? Answer: When there is no radial displacement between the centerlines of the two shafts, the difference in alignment between the couplings represents the allowable angular displacement; when there is no tilt between the centerlines of the two shafts, the radial displacement between the couplings is referred to as the radial angular displacement. 36. What are the structural features of planetary cycloidal pinwheel reducers? Answer: The greatest advantage of planetary cycloidal pinwheel reducers is their high gear ratio and efficiency; under the same gear ratio conditions, their weight is 1/2 to 1/6 lower than that of conventional reducers. 37. What is the operating clearance of a rolling bearing? What is the relationship between the operating clearance and the fit clearance? Answer: The operating clearance of a rolling bearing refers to the clearance present when the bearing is in use. When the bearing is in operation, the operating clearance is smaller than the fit clearance due to the temperature difference between the inner and outer rings ； Furthermore, due to the effect of rotational centrifugal force, elastic deformation occurs between the inner and outer rings of the rolling elements, resulting in a working clearance that is larger than the fit clearance ； Under normal circumstances, the working clearance is greater than the fit clearance. 38. What are sealing and sealing devices? Why is sealing necessary? Answer: Sealing refers to the use of appropriate measures to prevent the leakage of liquids or gases at the interface between two parts. A complete assembly designed for sealing is known as a sealing device. Hydraulic machinery, chemical processing equipment, etc. often experience leaks during operation, which leads to waste of resources and energy as well as environmental pollution. It also causes unstable operation of the equipment and endangers the safety of both people and the equipment itself; therefore, sealing measures must be employed. 39. What is standard coal? Answer: Coal with a base lower calorific value of 7000×4.1868 kJ/kg is called standard coal. 40. What is combustion? Answer: Combustion is a process in which the combustible components in a fuel undergo a vigorous chemical reaction with oxygen in the air, releasing heat in the process. 41. What are the elemental analysis components and industrial analysis components of coal? Answer: The elemental analysis of coal includes seven elements, namely carbon (C), hydrogen (H), oxygen (O), nitrogen (N), sulfur (S), moisture (W), and ash (A). 42. What is spontaneous combustion of coal? Explain its causes and outline the main measures that can be taken to prevent spontaneous combustion of coal stored in stockpiles. Answer: When coal comes into contact with air and undergoes slow oxidation, the heat generated must be dissipated promptly; otherwise, the temperature will rise, accelerating the oxidation of the coal and generating more heat. When the temperature reaches the ignition point of the coal, combustion occurs, and this phenomenon is known as spontaneous combustion of coal. To prevent spontaneous combustion of coal stored in coal yards, it is primarily necessary to improve the management of such stored coal. According to the storage period specified by coal quality standards, the coal should be stored in batches and retrieved in sequence. Additionally, the coal piles should be compacted as much as possible. For coal that is stored for extended periods, heat dissipation measures should be taken based on the specific conditions, such as installing ventilation pipes, regularly turning over the pile, and compacting it to seal it off. 43. What is the basic principle for setting up interlocks between various devices in the coal transportation system? Answer: The basic principle is that, under normal conditions, the operation of devices must be stopped in the direction of the coal flow ； At startup, start the equipment in the opposite direction to the coal flow. 44. What does the inspection and acceptance of belt conveyor systems mainly involve? Answer: It mainly refers to the inspection and acceptance of gears, pulleys and sprockets, bearings, couplings, brakes, reducers, idlers, motors, and belts. 45. What is standard coal? Answer: Coal with a base lower calorific value of 7000×4.187 M/kg is called standard coal. 46. What are the composition benchmarks for coal? Express the percentage content of carbon using each benchmark. Answer: The basis values for the composition of coal include the as-used basis, the analytical basis, the dry basis, and the combustible basis. The percentage content of carbon can be expressed as Cr, Cf, Cs, and Cl respectively. 47. Describe the characteristics of anthracite, bituminous coal, subbituminous coal, and lignite. Answer: Bituminous coal has a high carbon content, low volatile matter, is difficult to ignite, and does not tend to caking. Bituminous coal has a lower carbon content and a higher volatile matter content; most bituminous coals ignite easily and produce long flames. However, low-quality bituminous coal has a high ash and moisture content, resulting in a low calorific value and difficulty in ignition; most bituminous coals also exhibit strong caking properties. Bituminous coal has characteristics that lie between lignite and anthracite: it has a low volatile matter content and is difficult to ignite, but it is slightly better than anthracite. Lignite has a low carbon content and high volatiles, making it very easy to ignite with a long flame. It has high oxygen content, moisture, and ash content, as well as a low calorific value. 48. List several types of gearboxes used in coal conveying systems and indicate their codes. Answer: There are cylindrical gear reducers, arcuate toothed cylindrical worm reducers, worm gear reducers, planetary gear reducers, and cycloidal pinwheel reducers. Taking gear reducers as an example, there are three types: single-stage (9ZD), two-stage (ZL) reducers, and three-stage (ZS) reducers. Lb3C3038: Describe the role of lubrication. Answer: Lubrication plays an important role in the proper operation and maintenance of mechanical equipment. It can control friction, reduce wear, cool down, prevent rust and corrosion on the friction surfaces, provide sealing, transmit power, and reduce vibrations. 49. What is the principle of self-aligning of auto-aligning idlers? Answer: When the belt deviates from its path, the edge of the conveyor belt comes into contact with the vertical rollers that are suspended outside the return frame. When these vertical rollers are subjected to the force exerted by the belt edge, they exert a torque on the rotating frame, causing it to rotate by a certain angle, thereby achieving self-aligning. 50. What are the characteristics of the herringbone-grooved drive drum? Answer: The herringbone-grooved drive drum has a high friction coefficient, which reduces belt tension and extends its service life. The grooves prevent water films from forming, ensuring good driving performance even in particularly humid environments. Additionally, the drum’s bonding process is simple, making on-site maintenance easy. 51. Explain the reasons why the entire belt shifts to one side and the methods for dealing with it. Answer: The reasons and solutions are: (1) The center of the drive drum is not perpendicular to the center of the belt. Solution: Move the bearing housing position to adjust the center. (2) The idler bracket is not perpendicular to the belt. Solution: Adjust the bracket. (3) The center of the driven drum is not perpendicular to the center of the belt. Solution: Adjust the center. (4) Coal accumulation is adhered to the surfaces of the driving or driven drums and idler rollers. Solution: Remove the accumulated coal. (5) The belt joint is misaligned. Solution: Reconnect the joint. (6) The material falls off at a position offset from the center of the belt. Solution: Modify the coal discharge pipe or install baffles to ensure that the material falls at the center of the belt. (7) Debris is jammed. Solution: Remove debris. 52. Describe the inspection criteria, quality standards, inspection methods, and instruments used for the construction and installation of belt conveyor drums. Answer: The error in the longitudinal and transverse centerlines shall be ≤5 mm, measured using a steel ruler ； Axis center elevation error: ±10mm, measured using a glass level ； Levelness ≤ 0.5 mm, to be checked with a level ； The center line of the drum shaft must remain perpendicular to the center line of the conveyor belt; this should be checked using a steel ruler after tensioning the cable. 53. Describe the inspection criteria, technical standards, inspection methods, and instruments used for the construction and installation of belt conveyor frames. Answer: Centerline error: ≤0.5% per segment of the frame length, to be measured using a steel tape ； Elevation error: ±10mm, measured with a glass level ； Lateral and longitudinal levelness: ≤2‰; for the length (width) of the frame and the total length, it should be ≤10 mm, with measurement carried out using a steel ruler after tensioning the cables. 54. Describe the inspection criteria, quality standards, inspection methods, and instruments used for the construction and installation of idler rollers in belt conveyors. Answer: The error in center distance is ±20 mm, to be measured using a steel ruler ； Levelness of upper and lower idler rollers: ≤0.5mm, to be checked with a level ； Height error of the working surfaces of adjacent idlers: ≤2mm, to be measured using a glass level tube ； The bolts connecting the idler frame to the belt frame should be located in the middle of the long holes, and wedge washers and anti-loosening washers should be used; observe this ； Check that the groove of the idler frame and the shaft head of the idler are fitted tightly and securely, with no looseness. 55. Explain the working principle of a hammer-type coal crusher. Answer: The working principle of a hammer-type coal crusher is as follows: The high-speed rotating hammers move in a radial pattern due to centrifugal force. When coal enters the machine tangentially, some of the coal pieces are crushed by the impact of the high-speed rotating rotor hammers, while in other cases, the impact force generated by the hammers is transmitted to the coal pieces, which are then crushed by the guard plate located at the upper part of the crusher. Thereafter, the particle size required for grinding between the hammer and the screen plate falls through the apertures in the screen plate. 56. Describe the quality standards, inspection methods, and instruments for the construction and installation of the vertical and horizontal centerlines of hammer-type and counterattack-type coal crushers, as well as the levelness of the machine shaft. Answer: The error in the vertical and horizontal centerlines shall be ≤10 mm; a steel tape is used for measurement ； Axle levelness: ≤0.1mm, to be measured with a precision level. 57. What functions does the program control of the coal conveying system have? Answer: Generally, there are mainly 6 functions: (1) The program starts or stops the coal conveying system. (2) A fault triggers a chain reaction that stops the coal conveying system. (3) Procedural coal blending. (4) Automatic position switching. (5) Repeat coal blending. (6) Change procedure. 58. Describe the functions of belt idlers and tensioning devices. Answer: The function of idlers is to support the belt, reduce the resistance to its movement, and ensure that the sag of the belt does not exceed a certain limit, thus allowing the belt to move in a balanced manner. The function of the tensioning device is to ensure that the belt has sufficient tension, thereby creating the required friction between the drive drum and the belt ； Another function is to limit the sag of the belt between the supporting idlers, thereby ensuring the stable operation of the belt conveyor. 59. Explain the working principle of a belt conveyor. Answer: The working principle of a belt conveyor is as follows: The belt wraps around the drive drum at the head end and the idler drum at the tail end, forming an endless loop. Both the upper and lower sections of the belt are supported by idlers, and a tensioning device applies the necessary tension to the belt to ensure its proper operation. During operation, the drive drum drives the belt through friction between it and the belt, and materials such as coal move along with the belt. 60. What are the different types of belt conveyors? Answer: Belt conveyors can be classified according to the type of belt used: ordinary belt conveyors, steel cord belt conveyors, and steel rope-driven belt conveyors ； It can be divided into: TD62 type and TD75 type. 61. What types of self-aligning idlers are generally used on belt conveyors? What are the characteristics of each type of self-aligning idler? Answer: Belt conveyors typically use trough-type, unidirectional, self-aligning idlers. Grooved bidirectional reversible self-aligning idlers and flat self-aligning idlers. Sleeve-type self-aligning idler rollers and flat-type self-aligning idler rollers have a simple structure, making them easy to install and maintain ； But it can easily wear out the edges of the belt. Slung reversible self-aligning idlers do not wear the edges of the belt, but they have a complex structure and require significant maintenance effort. 62. What is the principle of self-aligning of auto-aligning idlers? Answer: When the belt deviates from its path, the edge of the conveyor belt comes into contact with the vertical rollers that are suspended outside the rotating frame. As these vertical rollers experience friction from the belt edge, they exert a rotational torque on the rotating frame, causing it to rotate by a certain angle. This in turn generates a force in the opposite direction on the belt that has deviated from its path, thereby achieving self-aligning. 63. What are the main components of a belt conveyor for coal transportation? Answer: A belt conveyor is mainly composed of the conveyor belt, idler rollers and frame, drive mechanism, tensioning device, direction-changing drums, cleaner, etc. (7) 64. At what angle above 4° does a belt conveyor require a braking device to be installed? What are the common braking devices used in power plant coal transportation systems? Answer: When the inclination angle of a belt conveyor exceeds 4°, a braking device is generally necessary to prevent reverse rotation in the event of a shutdown under heavy load. Common braking devices used in power plant coal conveying systems include belt check valves, roller check valves, electro-hydraulic brakes, and electromagnetic brakes. 65. Why are cleaners installed on belt conveyors? Answer: After the belt unloads, fine coal particles often stick to its surface; in order to keep the belt clean, cleaners must be installed to clean the surface of the belt. 66. What is belt deviation? Answer: During the operation of a belt conveyor, sometimes the center line of the belt deviates from the center line of the conveyor and moves to one side; this phenomenon is known as belt deviation. 67. What are the advantages of wire rope-driven belt conveyors compared to ordinary belt conveyors? Answer: The advantages of wire rope-driven belt conveyors over ordinary belt conveyors are: (1) Each unit can handle long transportation distances and has a high transport capacity. (2) Low power consumption and less steel required. (3) It operates smoothly without any deviation. (4) It has a large single-unit length, few unloading operations during processing, is simple to operate, and facilitates automatic control. 68. What components does a hammer-type coal crusher consist of? Answer: A hammer-type coal crusher is composed of a rotor (main shaft, partition plates, discs, bushings, shaft pins), screen plates, screen plate support adjustment devices, and the frame portion (cover, base). 69. What are the main tasks of coal management in the fuel sub-factory (workshop)? Answer: Ensuring a continuous supply of coal to the raw coal silo is the main task of the fuel sub-factory (workshop). 70. How does a boiler convert the chemical energy of fuel into the thermal energy of steam? Answer: The fuel burns in the furnace, releasing chemical energy which is transformed into thermal energy in the form of flames. This thermal energy is then transferred to the boiler’s feed water; the feed water absorbs this heat and evaporates, eventually turning into superheated steam at a certain pressure and temperature, which is then sent to the turbine to generate power. 71. What are the main technical specifications of electronic rail scales? Answer: The main technical specifications of electronic rail scales include: measurement range and the objects to be weighed, measurement accuracy, dynamic weighing speed, and the measurement process. 72. What are the main components of an electronic belt scale? Answer: An electronic belt scale is mainly composed of a scale frame, weight sensors, speed sensors, and various instruments for signal processing. 73. What is the significance of implementing centralized control for the coal conveying system? Answer: By using centralized control for the coal conveying system, it is possible to improve the working conditions for operators, reduce their workload, and enhance labor productivity. At the same time, it also increases the safety and reliability of equipment operation. 74. What equipment is included in the control of the coal conveying system? Answer: The control system for coal conveying equipment can be divided into four parts: the control of belt conveyors (including screening, crushing, iron removal, and wood removal equipment, etc.), the control of coal unloading equipment, the control of yard machinery (including bucket trucks or loading/unloading bridges, etc.), and the control of equipment in the coal blending system. The control methods include local manual control, centralized manual control, and centralized program control. 75. What safety measures should be taken when working on electrical equipment that is completely or partially de-energized? Answer: The following measures must be implemented: (1) De-energize the equipment. (2) Test for electricity. (3) Install a ground wire. (4) Hang signboards and install barriers. 76. What are the main types of motor protection devices? Answer: The main ones include inter-phase protection, single-phase grounding protection, overload protection, and low voltage protection. 77. What is volatile matter? Does it include the moisture in coal? Answer: In the industrial analysis of coal, when coal is heated under conditions free from air, moisture evaporates first. When the temperature rises to 104°C and is maintained for 7 minutes, the organic substances break down into various gases that are released into the atmosphere. These released gases are known as volatile matter; therefore, volatile matter does not include moisture. 78. What are higher and lower heating values? Which heating value is commonly used in power plant boilers? Answer: The higher heating value refers to the maximum possible heat output per unit mass of fuel; it includes the latent heat released when the water vapor produced during combustion condenses into liquid water. Lower calorific value is the heat released when a unit amount of fuel is completely burned, with the combustion products H2O remaining in a vapor state. Power plant boilers mostly use low calorific value fuels. 79. What are the fuel basis of application, analysis, drying, and combustibility? Answer: They refer to the different baseline conditions for fuel used when analyzing its various components. Application basis: Based on the coal fed into the boiler equipment. Analysis basis: Coal that has been naturally dried and had its surface moisture removed is used as the reference. Dried basis: Based on coal after removal of surface and inherent moisture. Combustible base: Based on the residue remaining after all moisture and ash have been removed from coal. 80. What are the effects of air entering a hydraulic system? Answer: When air enters a hydraulic system, since the volume of gas is inversely proportional to pressure, the movement of the hydraulic actuator is also affected as the load changes. Additionally, air is the main cause of hydraulic oil degradation and heating; therefore, any air that enters the system should be promptly removed. 81. Briefly describe the meaning of the “five fixities” in lubrication management. Answer: The “five fixities” in lubrication management are: (1) Fixed quality—Use only the lubricants specified for the equipment; when changing or cleaning the lubricants, ensure that the cleaning is done properly. All lubrication devices on the equipment must be in good condition, and the tools used should be kept clean. (2) Quantitative — Add oil and grease in the specified amounts. (3) Positioning—Determine the parts and lubrication points of the equipment that require lubrication. (4) Regularly—refuel and change oil at scheduled times. (5) Assign responsibility – Designate a specific person to be in charge for the specified lubrication areas and points. 82. What should be noted regarding the operation and maintenance of the impeller coal feeder? Answer: The following points should be taken into account for the operation and maintenance of the impeller coal feeder: (1) The oil temperature in the gearbox should not exceed 75°C, and the temperature of the rolling bearings should not exceed 80°C℃ ； Vibration is within acceptable limits, the quality of the lubricating oil is good, the oil levels in all reduction gears are at the specified levels, and there is no oil leakage. (2) There is no shaft shifting, and the shaft seal is tight. The couplings are firmly connected and the protective covers are in place; there is no friction or knocking sound between the moving and stationary parts. (3) The foundation nuts are not loose or detached. (4) The voltage and current are stable and within the rated values, with no arcing at the slip ring. (5) The impeller ensures uniform coal feeding, stable speed regulation, and good operation of the crane. (6) Carry out tasks such as refueling, cleaning, and regular testing in a timely and thorough manner as required by the procedures. Electrical components should be cleaned and wiped once a week, while debris on the impeller should be removed once per shift. (7) Slip motors should not operate at low speeds for long periods; they generally need to operate at speeds above 450 r/min, otherwise the excitation coil will overheat. 83. What are the general components of a data processing system for electronic rail scales? Answer: A data processing system for electronic rail scales typically consists of an input zeroing device, an analog-to-digital converter, arithmetic circuits, logic control circuits, a digital display for the weight value, and a digital recorder. 84. What is the function of a screw unloader? Answer: Its function is to use the rotation of the augers on both sides, as well as their up-and-down movement and forward/backward movement, to unload coal from trucks into the coal chute. 85. Describe the control ranges for temperature and vibration values of the main equipment in the coal conveying system during operation. Answer: (1) The bearings of coal conveying machinery must be adequately and properly lubricated. During operation, the vibration should be within 0.1–0.15 mm, while the axial movement should not exceed 2 mm. During operation, the bearing temperature should not exceed 80°C; for plain bearings, it should not exceed 60°C. (2) When the reducer is in operation, the gear meshing should be smooth without any noise; vibration should not exceed 0.1 mm, and shaft play should not exceed 2 mm. The oil temperature of the reducer should not exceed 60°C. (3) During the operation of the coal crusher, the amplitude should not exceed 0.1 mm; otherwise, the cause should be identified and the vibration eliminated. (4) There is no oil leakage at the various hydraulic components and pipe connections in the hydraulic system; the moving rod is not deformed and functions smoothly; the seals have no longitudinal cracks, and the hoses show no signs of aging. The oil pump is oriented correctly, operates without noise, and its vibration does not exceed 0.03–0.06 mm. 86. What are the main types of interlocks for coal conveyor belts? Answer: (1) The coal conveyor belt is equipped with interlocks that prevent the mechanical equipment intended to start from doing so if the audible signal is not activated, or if it does not sound for the required duration. (2) Interlock to prevent mechanical equipment from starting in the wrong sequence. For example: the interconnection between the upper belt and the lower belt, starting from the raw coal bin; if the upper belt does not start, then the lower belt cannot start either (except for the coal crusher). (3) Accident interlock, which means that when any piece of mechanical equipment in the system undergoes an emergency shutdown due to an accident, the coal conveyor belt from the accident point to the coal receiving section automatically stops. 87. What are the commonly used accident audible signals in the programmed control of coal conveying systems? Answer: The commonly used accident audible signals include: when the equipment is in operation, issues such as belt misalignment, belt slippage, blockage in the coal chute, motor failure resulting in tripping, longitudinal tearing of the belt, false coal level readings in the coal bunker, or unexpected shutdown due to on-site faults occur; in such cases, the corresponding indicator lights on the mimic panel illuminate, and the affected equipment flashes on the mimic panel. Simultaneously, an electric siren emits the accident audible signal. 88. What is the basic principle for setting up interlocks on various devices in the coal transportation system? Answer: The basic principle is that, under normal conditions, the devices must be stopped in the direction of the coal flow ； At startup, start the equipment in the direction opposite to the coal flow. 89. What is the policy for safe production? Answer: The policy for safe production is “safety first, prevention first”. 90. What is the three-level safety education for enterprises? Answer: The three levels of education are: plant-level education, workshop-level education, and team/group-level education. 91. What is the policy for fire protection work in our country? Answer: The policy for fire protection work is “to give priority to prevention and use suppression as a supplementary measure”. 92. What are the three types of safety inspections stipulated by the State Council? Answer: Safety inspections come in three forms: regular inspections, specialized inspections, and seasonal inspections. 93. What is an absolutely safe voltage? Answer: An absolutely safe voltage is one below 12V. 94. What are the different forms of electric shock? Answer: There are the following forms of electric shock: (1) Single-phase electric shock. (2) Two-phase electric shock. (3) Step voltage electric shock. 95. What is working at height? Answer: Any work carried out at a height of more than 2 meters above the ground should be considered as working at height. 96. What is a equipment accident? Answer: Losses resulting from the damage to mechanical and electrical equipment, pipelines, buildings, etc., caused by various reasons are referred to as equipment accidents. 97. What are the “three wastes” in industry? Answer: The “three wastes” in industry refer to industrial wastewater, waste gas, and solid waste. 98. What are the health standards for industrial noise? Answer: For newly established or expanded enterprises, the allowable noise level during 8 hours of work is 85 dB; for existing enterprises, this limit is temporarily set at 90 dB for 8 hours of work. 99. What is noise? Answer: Any sound that people do not need is called noise. Internationally, decibels are commonly used as the unit to measure the volume and intensity of sound. 100. What is safety management? Answer: Safety management refers to a series of management activities carried out to ensure that production can take place in a favorable environment and with proper order, in order to prevent accidents involving people and equipment, and to safeguard the personal safety of workers as well as the safety of equipment during the production process. 101. What is an occupational disease? Answer: An occupational disease refers to a disease that occurs in workers during their productive work, as a result of their exposure to toxic and harmful factors. 102. Which personnel shall bear the responsibility for work safety? Answer: (1) The work order issuer. (2) Work permit issuer. (3) Person in charge of the work. 103. What are the advantages and disadvantages of grease compared to lubricating oil? Answer: Compared to lubricating oil, grease has the following advantages: it does not easily leak away or slide off, it has good compressive resistance, excellent sealing and dust-proof properties, good resistance to emulsification, and good corrosion resistance. In addition to serving as a lubricant, grease can also protect metal surfaces from corrosion; it is widely used in industry. Compared with lubricating oils, it has the following disadvantages: (1) High viscosity, which increases mechanical resistance and results in poor lubrication performance. (2) Poor fluidity and inadequate heat dissipation. (3) Poor adsorption and wedging ability. (4) It is difficult to replace and replenish during operation. 104. What are the main types of general-purpose components? Answer: The main types of general-purpose components include gears, pulleys and sprockets, bearings, couplings, brakes, reducers, etc. 105. What are the contents of the external inspection and acceptance for electrical equipment? Answer: The contents of the external inspection and acceptance for electrical equipment are: (1) The grounding wire of the motor should be in good condition and firmly connected. (2) Manual turning is smooth and effortless, with no jamming or resistance, and there is no friction between the rotor and the stator. (3) The end covers, end shields, and base show no cracks or damage; the fan is intact with firm connections, and the guards are properly installed without any deformation. (4) The leads show no signs of aging; the fuse is intact. (5) The slip ring connections are secure, with good electrical conductivity; the brushes and brush holders show no damage, and the contact is tight. (6) The buttons reset properly, all switches make good contact and allow for smooth start/stop operations, the indicator lights are in good condition, and the emergency button functions well. 106. What is the working principle of relay protection devices? Answer: When a fault occurs in electrical equipment or circuits, it often results in a significant increase in current, as well as a sharp drop in voltage near the location of the fault. These fault currents or voltages are transmitted to the relay through current transformers or voltage transformers. When they reach a predetermined value, which is the operating current or voltage for the protection device, the relay activates and sends a trip signal to the circuit breaker, causing it to disconnect quickly thereby protecting the equipment and the system. 107. What are the main types of motor protection devices? Answer: There are interphase protection, single-phase grounding protection, overload protection, and undervoltage protection, etc. 108. What are the basic deformations of bars? How is the stress distribution in cases of tension and compression deformation? Answer: The basic deformations of bars include tension and compression, shear, torsion, and bending. Under the action of tensile force, a rod will undergo elongation deformation; under the action of compressive force, it will undergo compression deformation. 109. Under what conditions does a member undergo torsional deformation? Answer: The indicator of torsional deformation is the relative angle of rotation between two cross-sections around the axis; when the maximum torsional angle per unit length exceeds the allowable value, the member experiences torsional deformation. 110. What are the various forms of beams? What are the reaction forces at the supports? Answer: There are three forms of beams: simply supported beams, overhanging beams, and cantilever beams. The direction of the reaction force at the support is opposite to that of the load acting on the beam, while their magnitudes are equal. Because the external forces acting on the beam include loads and support reactions. 111. What is work hardening? Answer: The phenomenon in which the hardness and strength of a metal increase during cold plastic deformation is called work hardening. 112. What is normalizing of steel? Answer: The main purpose of normalizing steel is to refine the grain structure, eliminate structural defects resulting from forging and rolling, and improve the mechanical properties of the steel, etc. 113. What is carbon steel? How is carbon steel classified based on its carbon content? Answer: An iron-carbon alloy with a carbon content of 0.02% to 2.11% is generally referred to as carbon steel, also known as plain carbon steel. Based on the carbon content of steel, it is classified as follows: (1) Low-carbon steel: Steel with a carbon content of ≤0.25%. (2) Medium-carbon steel: Steel with a carbon content of 0.25% to 0.6%. (3) High-carbon steel: Steel with a carbon content > 0.6%. 114. What marks the failure of brittle materials and plastic materials? Answer: The failure of brittle materials is marked by fracture, while the failure of plastic materials is marked by plastic deformation of the material. 115. What are the characteristics of a throttle valve? Answer: A throttle valve is used to regulate the flow rate, thereby changing the operating speed of the cylinder ； The throttle valve can control the amount of bidirectional flow: a one-way throttle valve acts as a check valve when the oil flow is in the reverse direction, allowing the reverse-flowing oil to pass through freely without being controlled by the throttle valve. 116. What is the purpose of centering rotating machinery? Answer: Centering, also known as alignment, refers to the process of adjusting and aligning the relative positions of various components, as well as leveling them. In general machinery, centering refers to adjusting the centerlines of the drive shaft and the driven shaft to be on the same straight line, thereby ensuring smooth operation. This goal is achieved by measuring and adjusting the relative position of the two half-couplings that are properly mounted on the drive shaft and the driven shaft, respectively. 117. What is static imbalance? What is dynamic imbalance? Answer: On a rotating component, the centrifugal forces resulting from all the unbalanced masses can be combined into one force; therefore, when the component rotates, only one centrifugal force is generated. This type of imbalance is called static imbalance. When the rotor rotates, periodic vibrations occur due to the eccentric weight caused by static imbalance, or because, even though the rotor is statically balanced, the masses responsible for that balance are not located in a plane perpendicular to the rotor’s centerline. This phenomenon is known as dynamic imbalance. 118. Under what circumstances should worm gears and worms be repaired or replaced? Answer: Worm gears and worms should be replaced when the surface roughness of their teeth exceeds △6.3. The circular contact deviation should be no less than 65% in terms of length for worms with precision grade 7, and no less than 60% in terms of height; for worms with precision grade 8, it should be no less than 50% both in terms of length and height. Otherwise, they need to be repaired or replaced. Furthermore, after wear occurs on the worm gear and worm surfaces, if the wear amount of the tooth thickness is no more than 10% of the original thickness, it can still be used after repair; otherwise, it must be replaced with a new part. For worm gears and worms used in precision transmissions, they should be repaired or replaced whenever they no longer meet the original design requirements. 119. What is the strength limit? What happens when a specimen reaches its strength limit? Answer: As the material’s resistance to deformation increases until it reaches its maximum value, the stress at that maximum point is known as the strength limit. When the test specimen reaches its strength limit, a significant contraction occurs in a certain part of its cross-section, a phenomenon known as \"necking\". 120. What are the stress characteristics of a member under shear? Answer: The stress characteristics of shear are that the two forces acting on the member are equal in magnitude and opposite in direction, and their lines of action are quite close to each other. The deformation characteristic of shear is that when a member is subjected to shear force, once the force reaches a certain limit, it will break along a certain section; in other words, internal forces are generated at all sections between the two external forces. 121. What is the critical transition temperature for brittleness? Answer: The impact toughness of a material is related to temperature; some materials exhibit good toughness at room temperature of around 20°C, but become brittle at lower temperatures. The impact toughness of the material decreases significantly, and there is a temperature at which brittleness occurs; this temperature is known as the \"brittleness critical transition temperature\". 122. Into how many categories can internal stress be divided? What impact do they have on the properties of metals? Answer: During plastic deformation of polycrystalline metals, the degree of deformation varies from one grain to another, resulting in highly uneven deformation across different areas. When the external force is removed, residual stresses are generated within the material, also known as internal stress. Based on the range of influence of these residual stresses, they can be divided into three categories: The first category of internal stress is also known as macroscopic residual stress. The second type of internal stress is also known as micro-residual stress. The third type of internal stress is also known as lattice distortion stress. The presence of internal stresses not only affects the load-bearing capacity of materials, but also causes metal deformation due to the subsequent relaxation or redistribution of these stresses, thereby affecting the dimensional stability of machine parts or components. Furthermore, residual internal stress also reduces the corrosion resistance of metals. 123. What is the purpose of tempering steel? Answer: The purposes of tempering are: (1) to reduce the brittleness of quenched steel, eliminate and reduce internal stresses, and prevent deformation and cracking of the workpiece. (2) Stabilize the workpiece dimensions. (3) Obtain the mechanical properties required for the workpiece. 124. What is cast iron? What is the effect of graphite on the properties of cast iron? Answer: An iron-carbon alloy with a carbon content of more than 2.11% is generally referred to as cast iron. The effects on the properties of cast iron are: (1) excellent casting properties. (2) Excellent anti-friction properties. (3) Good shock absorption. (4) Low notch sensitivity. (5) Good machinability. 125. What is a tolerance fit? What are its various forms? Answer: Tolerance refers to the allowable range of error for a part’s dimensions, that is, the difference between the maximum limit dimension and the minimum limit dimension. That is, the difference between the upper deviation and the lower deviation, always taking a positive value. Parts with the same nominal dimensions that are assembled together and meet certain operating conditions are referred to as a fit, and the dimensions of these fitting parts are called fit dimensions. Due to the different requirements for the degree of fit in terms of usage, there are three possible types of fit: (1) Loose fit – when two parts fit together and the actual size of the hole is larger than that of the shaft, a gap is created after assembly; such a fit allows free rotation, which is why it is called a loose fit. (2) Static fit — When two parts are fitted together, the actual size of the hole is smaller than that of the shaft, resulting in interference after assembly. This fit is forced in by external force and cannot rotate freely; therefore, it is called a static fit. (3) Intermediary fit – It lies between loose fit and tight fit; there may be a small clearance or a slight interference, which is why it is called an intermediary fit. 126. What are the advantages and disadvantages of worm gear drives? Answer: Worm gear drives have the following advantages: (1) A large transmission ratio can be achieved with just one stage of transmission; in applications requiring high power transfer, the value of i is usually between 70 and 80, while in indexing mechanisms this value can exceed 50. (2) The operation is smooth with no noise. (3) It can self-lock, which is very useful for certain lifting equipment. The disadvantages of worm drive are: (1) low transmission efficiency, with the efficiency of self-locking worms being less than 50%. (2) Due to low efficiency and high heat generation, it is not suitable for applications where high transmission power (generally not exceeding 100 kW) is required for long-term continuous operation. (3) Relatively expensive bronze is required to manufacture the worm gear ring. Based on the shape of the worm drive, it can be divided into cylindrical worm drives and arc-shaped worm drives. Cylindrical worms are widely used in mechanical transmissions due to their simplicity in manufacturing. Arc-shaped worm drives offer good lubrication conditions and high efficiency, but they are more difficult to manufacture and are thus used primarily in power transmission applications. 127. What is the working principle of a gear pump? Answer: When the motor drives the two gears to rotate, the oil suction chamber sees the meshing teeth sequentially coming out of contact; the space between these teeth that are no longer in contact creates a small area of free space, which increases the volume of the oil suction chamber and thus generates a local vacuum. Therefore, the oil in the tank enters the suction chamber under external pressure, filling the small spaces between the teeth. As the gears rotate, the oil is carried from between the teeth to the pressure chamber; when the teeth mesh with each other, the oil is forced out, thereby gaining pressure and being pushed out from the pressure chamber. This process repeats continuously, and this is how a gear pump operates. 128. What conditions must a basic hydraulic circuit meet? Answer: A basic hydraulic circuit must satisfy the following fundamental conditions: (1) To improve the efficiency of the hydraulic circuit, appropriate hydraulic components must be selected, sources of heat generation must be eliminated as much as possible, and power losses must be reduced. (2) In the hydraulic circuit, hydraulic shock should be prevented as much as possible. In response to load changes, it is necessary to maintain stability while minimizing shocks and noise, in order to ensure the safety of the hydraulic circuit. (3) Use standardized components as much as possible, and simplify the oil circuit as much as feasible. 129. What is the impact of hydraulic oil viscosity on mechanical operation? Answer: (1) Effects of excessive viscosity: Internal friction increases, leading to a rise in oil pressure; fluid resistance rises as well, resulting in increased pressure losses. Hydraulic actions become less efficient, and mechanical efficiency declines due to increased power losses. (2) Effects of too low viscosity: Increased internal and external leakage, reduced volumetric efficiency of the pump, increased wear on all moving parts, and failure to operate properly due to the inability to achieve the necessary pressure in the circuit. 130. What are the common types of seals? What are their uses? Answer: The common seals and their uses are as follows: (1) O-ring – mainly used for static sealing, and can also be used for dynamic sealing in reciprocating motions. (2) Y-type seal ring – commonly used for sealing between the piston and cylinder barrel of hydraulic cylinders; it can also be used on sealing surfaces with relatively high speeds. During installation, its lip should face the pressurized oil chamber. (3) V-type clip fabric sealing ring—commonly used in cylinder pistons and similar components where the relative movement speed is not high. (4) L-shaped seal ring — used for sealing between the cylinder piston and the cylinder barrel. (5) Skeleton seal ring — mainly used for sealing rotating shafts. 131. Compare the advantages and disadvantages of belt drives and chain drives? Answer: The main advantage of belt drives is a wide range of allowable center distances ； Simple structure, smooth transmission, capable of buffering, and can serve as a safety device ； The manufacturing cost is low. Main advantages of chain drive: a large range of center distance variations, accurate average transmission ratio, and higher overload capacity compared to belt drives. Main disadvantages of belt drives: large external dimensions and high stress on the shafts ； The gear ratio cannot be strictly guaranteed, and the service life is low. Main disadvantages of chain drives: they cannot be used in precision indexing mechanisms, and their lifespan is significantly reduced under vibratory and impact loads. 132. What is the procedure for alignment in machine assembly? Answer: The procedure for alignment is as follows: (1) Based on the reference parts selected during assembly, determine a reasonable and easily measurable alignment reference surface. (2) First, correct the levelness and perpendicularity of reference components such as the fuselage, housing, and base in the longitudinal and transverse directions. (3) Adopt reasonable measurement methods and procedures to identify the actual positional deviations during assembly. (4) Analyze the factors affecting the machine’s operating accuracy, consider the necessary compensations, and determine the adjustment amount and direction. (5) Decide on the adjustment steps and methods, and make adjustments based on the measured deviations. (6) Return to the original position; after meeting the requirements, secure it firmly. 133. What are the key points for aligning a coupling? Answer: The key points for aligning a coupling are as follows: (1) Place a straight edge at the relative positions of the coupling; after identifying the direction of the deviation, make rough adjustments to bring the centers of the couplings closer together and to ensure that their end faces are aligned, thereby laying the foundation for precise alignment of the coupling. (2) Install the alignment tool and measure the relative position of the center. (3) Fix the position of the driven motor, then adjust the motor to align the centers. After adjustment and measurement, the specified requirements are met. (4) Based on experience, when aligning, it is easier and quicker to adjust the end face first and then the center. Once one becomes proficient, the adjustment of both the end face and the center can be done simultaneously. 134. Explain the relationship between dynamic and static balance. Answer: The static balance of a rotating body refers to its static equilibrium when the rotational speed is zero; however, this does not guarantee that in any plane perpendicular to the axis, the mass distribution of the rotating body is symmetric about the center. In other words, the planes are unbalanced; when the rotor rotates, an additional couple is generated, causing the rotor to vibrate. The purpose of dynamic balancing is to eliminate such couples of forces. For rotors where the ratio of length L to diameter D is less than 1.0 (i.e., L/D < 1.0), only static balancing is required. For rotors with 1.0 < L/D < 2.0, dynamic balancing is necessary for precision machinery; for machines with less stringent requirements, static balancing suffices. Rotors with an L/D ratio greater than 2.0 require dynamic balancing. 135. What are the various control methods for the coal transfer system? Answer: There are three ways to control coal transfer equipment: (1) Local manual control: This involves the operators on site using the start/stop buttons on the control panel beside the machine to operate the equipment. (2) Centralized manual control: All coal conveying equipment, as well as some of it, is under centralized control, with the duty personnel manually operating the equipment to start and stop it. (3) Centralized automatic control: This involves automatically starting and stopping the relevant equipment, as well as making necessary operational adjustments, in accordance with the sequence and conditions required by the production process. 136. What are the common faults of gears and what are their causes? Answer: The common faults of gears include the following: (1) Tooth fracture. Reasons: ① When the teeth are under load, the bending stress at the tooth root is maximum, and there is stress concentration ； ②Overload fracture caused by short-term overload or shock overload ； ③Fatigue fracture occurs due to repeated loading. (2) Pitting on the tooth surface. During the operation of the tooth, the contact stress at a certain point on the tooth surface varies in a pulsating cycle, from low to high. When this contact stress exceeds the material’s limit for contact, surface cracks appear after repeated actions; these cracks spread and grow until the material peels off, resulting in pitting. (3) Gluing. In heavy-duty transmissions, when lubrication fails due to temperature rise or difficulty in forming an oil film, the two tooth surfaces come into contact and stick together; the softer tooth surface is then torn away along the direction of sliding, resulting in grooves – this is what is known as seizure. (4) There are usually two types of tooth surface wear: one is abrasive wear caused by dust and hard particles entering the tooth surface ； Another type is running-in wear caused by friction on the tooth surfaces. (5) Plastic deformation of the tooth surface. In transmissions with low speeds, overload, and frequent starting, softer tooth surfaces undergo local plastic deformation. 137. Describe the acceptance criteria for the maintenance of cylindrical gear reducers. Answer: The acceptance criteria are as follows: (1) The oil level gauge is visible, clear, and accurate; there is no oil leakage, and the lubricating oil has not changed color. (2) The gear runs smoothly, without any impact noises or uneven sounds. (3) After a 30-minute trial run, the bearing showed no abnormal noises and its temperature was within the specified range. (4) The vibration of the cabinet is within acceptable limits; if cooling water is used, the water pipes must be unobstructed, and the valves must operate smoothly and easily. (5) The reducer housing should be clean, with no oil leakage at the joint surfaces and bearing end caps. (6) The records are complete, true, and accurate. (7) Clean up the site after the maintenance is completed. 138. What are the advantages of planetary cycloidal pinwheel reducers? Answer: In addition to having a high gear ratio, a compact structure, small size, light weight, and high efficiency, planetary cycloidal pinwheel transmissions also offer the advantages of smooth operation, reduced tooth wear, and a longer service life, thanks to the large number of teeth that can be supported simultaneously and the rolling friction between the tooth profiles. 139. Why does the oil level in the main clutch of the coal pusher drop sharply? How can this be resolved? Answer: It is because of oil leakage from the seal on the driving gear in the transfer case. It should be repaired or replaced. 140. What are the reasons for abnormal operating noise in the steering clutch of a coal pusher? How can it be made to operate normally? Answer: The abnormal noise is caused by the powder metallurgy components of the friction plates coming loose or being damaged. Replace the friction pads. 141. Why does a ring coal crusher have pressure in the pump but no oil output, or is its volumetric efficiency reduced? How can this be resolved? Answer: The reasons are: (1) Damage to the sealing components inside the pump. (2) Dirt has been inhaled, and the sliding parts are severely worn. The solution is: (1) Replace the seal. (2) Remove debris or replace worn parts. 142. Why does the bearing temperature rise after repairs are done on the high-speed end of the impeller coal feeder reducer? How can this be resolved? Answer: The reasons for the increased temperature are: (1) Damaged bearings. (2) The bearing clearance is small. The solution is: (1) Replace the bearing. (2) Adjust the bearing clearance. 143. What are the reasons for the rupture of the accumulator oil pipe in a car dumper? How should it be handled? Answer: The reasons are: (1) The oil pressure in the accumulator is too high. (2) The low-pressure relief valve is malfunctioning. The treatment method is: (1) Adjust the accumulator oil pressure to no more than 5 MPa. (2) Replace the low-pressure relief valve. 144. What are the common faults of electric motors? Answer: Common faults of electric motors include motor vibration, motor overheating, and operation of the motor with two phases. The motor experiences increased temperature, vibration, humming, and failure to rotate. 145. Why does the reducer experience severe vibration and abnormal noises? Answer: The reasons are as follows: (1) The foot screws are loose. (2) The clearance between the two end surfaces of the coupling does not meet the requirements. (3) The alignment does not meet the quality standards. (4) Shaft bending or gear breakage. (5) There are miscellaneous items inside the machine. (6) Bearing damage. 146. Why doesn’t the electromagnetic vibration coal feeder vibrate after power is connected? How to solve it? Answer: Because: (1) The power fuse has blown. (2) Short circuit in the coil wire. The solution is: (1) Replace the fuse. (2) Check whether the coil connections are properly made to eliminate any short circuits. 147. Explain the reasons for the small amplitude and excessive current of the electromagnetic vibrating coal feeder when it is running without a load, as well as the solutions. Answer: The reason is an excessive air gap; the solution is to reduce the air gap. 148. Why is the temperature of the motor and reducer in the drive unit of a belt magnet separator high? How to solve it? Answer: The reasons are: (1) The belt is too tight and the bearings are damaged. (2) Damaged reducer and lack of oil. The solution is: (1) Loosen the tape and replace the bearing. (2) Service the reducer and refuel it. 149. How many types of fire extinguishers are there? Which fire extinguishers are not suitable for extinguishing electrical fires? Answer: There are several types of fire extinguishers: (1) Acid-base fire extinguishers. (2) Foam fire extinguisher. (3) Carbon dioxide fire extinguisher. (4) Dry powder fire extinguisher. (5) Carbon tetrachloride fire extinguisher. (6) 1211 fire extinguisher. Among them, acid-base fire extinguishers and foam fire extinguishers cannot be used for electrical fires. 150. When were China’s fire safety regulations issued and implemented? Answer: They were issued by the State Council on May 13, 1984, and came into effect on October 1 of the same year. 151. What are high voltage and low voltage? Answer: (1) Equipment with a voltage relative to ground of 250V or more is considered high voltage. (2) Equipment with a voltage to ground of 250V or less is considered low-voltage. 152. What is an absolutely safe voltage? Answer: A voltage of 12V or less is considered an absolutely safe voltage. 153. How to prevent electric shock accidents? Answer: (1) Strictly implement electrical safety regulations. (2) Earnestly carry out electrical safety education and publicity work. (3) Regularly check for violations and disciplinary issues as well as the condition of electrical equipment. 154. What are the reasons for overheating of the ring-type coal pulverizer oil pump? How to deal with it? Answer: The reasons are: (1) Poor plot ratio. (2) Burns to the sliding part. The treatment method is to shut down the machine and disassemble it for inspection. 155. What are the reasons why the main clutch of the coal pusher cannot engage? How to solve it? Answer: The reason is that the adjustment ring has been adjusted too much, resulting in a small gap between the friction plates. The solution is to loosen the adjustment ring to adjust the gap. 156. What is the reason for the shock noise when shifting gears in the coal pusher’s gearbox? How to deal with it? Answer: The reason for the shock noise is clutch slippage. The solution is to adjust the small brake. 157. Why does the gear on the loading/unloading bridge experience tooth skipping vibration? How to solve it? Answer: It is due to gear wear and severe damage. The solution is to replace it with a new gear. 158. What are the reasons for the crane grab falling to the ground during loading and unloading? How should it be handled? Answer: The reason is that the key is damaged. The solution is to carry out timely maintenance and replacement. 159. Explain the purposes and functions other than coal. Answer: The purpose of coal cleaning is to remove metal particles from the coal conveyed by the coal transport belts, thereby ensuring the safe operation of the coal transport belts, coal crushers, and coal grinders. 160. Discuss the situations that occur during the operation of coal conveying equipment that require immediate shutdown Answer: The coal conveying equipment should be stopped immediately in the following situations: (1) The belt breaks or slips severely ； (2) The motor is smoking or making severe abnormal noises ； (3) The reducer experiences severe vibration or loud abnormal noises ； (4) Situations posing a threat to personal safety ； (5) When the temperature of the motor, reducer, and various drive bearings reaches above 80 degrees Celsius ； (6) When the coal crusher experiences severe vibration or the bearing temperature reaches 65 degrees ； (7) Impurities in coal are difficult to remove, posing a threat to the safety of personnel and equipment ； (8) Severe belt deviation can pose a risk to the safety of the equipment ； (9) Failure of the tensioning device endangers equipment safety ； (10) Idler roller falls off and drops into the return section of the belt ； (11) Debris found; iron objects scratched the belt ； (12) When it is found that the adhesive joint has separated or broken, posing a serious threat to safety ； (13) Belt caught fire on site ； (14) Breakage of the drum shaft, fracture of the shaft. 161. What are the basic principles for equipment interlocking among various devices in the coal conveying system? Answer: The basic principle is that in the event of a fault, the operation of the equipment must be stopped in the direction of coal flow. Upon startup, the equipment must be started in the direction opposite to the coal flow; otherwise, it cannot be guaranteed that all components of the coal conveying system will operate normally. 162. What are the characteristics of the traveling mechanism of the stacker-reclaimer? Answer: The traveling mechanism consists of two sets of driven trolleys and a driving trolley. The drive trolley is equipped with a two-speed motor; when not engaged in stacking or retrieving operations, the speed of the bucket wheel stacker-reclaimer when moving without load can reach 30 m/min, while its speed during such operations is 7 m/min. 163. Why are interlock devices installed in the coal conveyor belt system? Answer: 1. To reduce the number of starts and stops of the system conveyor ； 2. Ensure that the coal conveying belts in the system start and stop in sequence ； 3. When a critical device in the system fails, the system stops automatically. 164. What are the characteristics of the bucket wheel in a bucket wheel stacker-reclaimer? Answer: The bucket wheel adopts a semi-format structure, and such buckets wheels operate smoothly, with high efficiency and excellent unloading performance in coal yard operations. The edges of the bucket wheel are welded with wear-resistant teeth, which allow it to extract coal from frozen layers with a thickness of no more than 100 mm during winter. 165. What is the main function of the bucket wheel luffing mechanism? Answer: The luffing mechanism of the bucket wheel conveyor is primarily used to enable the pitching motion of the cantilever, thereby adjusting the picking height of the bucket wheel during material pickup and the drop height of the material during dumping. 166. Briefly describe the advantages and disadvantages of rotary tipplers? Answer: Advantages: high unloading efficiency, low power consumption, large rotation angle ； Disadvantages: Large amount of earthwork is required, with the foundation reaching a depth of 13 M. 167. Briefly describe the structure of the car dumper body? Answer: Rotor, clamping device, backing plate assembly, idler roller device, vibrator, end stop, material guiding device, transmission device, hydraulic system. 168. Concrete weights are installed in the front beam of the turntable rotor; what is their purpose? Answer: Balance the load on the rotor, thereby reducing the unbalanced torque, lowering the driving power, and minimizing the flipping impact. 169. What are the reasons for inaccurate alignment of the car dumper platform? Answer: 1. Coal accumulation at the support seat end. 2. Brake failure. 3. Shift of the pinion housing. 4. The travel switch disconnects prematurely. 5. Eddy currents are abnormal. 6. Fault in the main control unit. 170. Why is it generally not allowed to start a belt conveyor under heavy load? Answer: This is because during start-up with no load, especially on inclined conveyors, the instantaneous current required for start-up **exceeds several times the current limit allowed by the motor. If the conveyor starts under heavy load, the motor may overheat and get damaged as a result; therefore, it is not permitted to start the conveyor under heavy load under normal circumstances. 171. What are the advantages and disadvantages of roller screens? Answer: Advantages: Simple structure, stable operation, reliable performance, screening efficiency of 80%, low maintenance requirements, and easy installation ； Disadvantages: Excessive moisture can cause coal clogging, it makes a lot of noise during operation, and its production capacity is low. 172. What is the working principle of a ring coal crusher? Answer: A high-speed rotating rotor is used to drive the ring hammers to impact and crush the material; the impacted material is then subjected to compression, shearing, and grinding actions between the ring hammers, the crushing plates, and the screening plates, thereby achieving the desired particle size. 173. What are the high calorific value and low calorific value of coal? Answer: The heat released when 1 kg of coal burns completely, with the water in the combustion products remaining in liquid form, is known as the high calorific value. The calorific value when the water in the combustion products remains in a vapor state is the lower calorific value. 174. What is the sequence for switching fuel pumps? Answer: First, start the standby pump; once it is operating properly, set it to the “interlock” position. Stop the originally operating pump again and move it to the standby position. 175. What should be done if an alarm is triggered due to high oil and gas concentration in the oil pump room? Answer: Reset it, clean the area and open doors and windows for ventilation, and rinse with water to reduce the concentration. 176. What are the causes of oil pump vibration? Answer: 1) There is air in the pump ； 2) The oil pump inlet filter is clogged or the oil level in the tank is too low ； 3) Damaged bearing or unbalanced impeller. 177. The oil level in Tank #2 has been found to be dropping abnormally; how to determine the cause? Answer: 1) Check whether there are any leaks in the oil circuit system and valves associated with tank #2 ； 2) Check whether the oil from #1 oil tank flows to #2 oil tank ； 3) Check the oil level in the sludge tank to see if the oil from Tank #2 has flowed into it ； 4) Check the ground and drains for oil, and identify the cause, such as an unclosed drain valve. 178. What are the regulations regarding the bearing temperature of motors? Answer: (1) Sliding bearing: shall not exceed 800°C (temperature rise of 400°C) ； (2) Rolling bearings: Must not exceed 1000°C (temperature rise of 600°C). 179. How should the operating mode of the impeller coal feeder be selected, and what actions should the operator take if the coal in the coal chute is unevenly distributed? Answer: 1) The operation mode is controlled via the “Programmed/Local” switch on the local control cabinet ； 2) If the coal in the coal chute is uneven, a feeding method that combines fixed-point feeding with moving feeding should be adopted. 180. How does the on-site operator adjust the coal feeding amount of the impeller coal feeder? Based on what for the adjustment. Answer: The operator should turn the operation mode button to the “local” setting, and use the “Increase impeller speed” or “Decrease impeller speed” buttons to adjust the coal feeding rate. The speed gauge of the impeller motor should be adjusted based on the belt output and the coal flow on the belt, while also paying attention to the readings on the current meter of the impeller motor. 181. When there is coal in one section of the coal unloading chute and no coal in another, how should the operator adjust the operation of the impeller feeder? Answer: With coal remaining in the sealed section, the impeller in the coal-free section should operate at a lower speed and be adjusted so that normal coal feeding can occur in the section with coal; the coal level in the coal channels should be kept as consistent as possible. 182. What is the ash content of coal? Answer: Ash is a general term for the solid residues formed after complete combustion of fuel. 183. What safety measures should be taken during the maintenance of impeller coal feeders? Answer: 1) Shut off the control and power supply, then conduct a check ； 2) Stop the control and power supply of the corresponding belt conveyor ； 3) The programmed duty operator should place a maintenance flag at the operator station, set the equipment interlock to the “local” mode, and keep records of this ； 4) The operating mode is set to “local”; a warning sign reading “Do not close – persons are working” should be placed on the local control panel. 184. What is the working principle of a conveyor belt? Answer: The tape wraps around the rollers at the head and tail ends to form a continuous loop; the tape is supported by parallel idlers and trough idlers, and a tensioning device provides sufficient tension. When the drive roller rotates, the friction between the drive roller and the tape drives the tape to move horizontally, thereby achieving the purpose of transporting materials. 185. What are the various layout types of belt conveyors? Answer: The basic layout patterns of fixed conveyors include horizontal, upward inclined, with convex arc sections, with concave arc sections, with both convex and concave arc sections, as well as layouts with intermediate unloading. 186. What aspects should the operator pay close attention to during the operation of the impeller coal feeder? Answer: 1) The coal flow is normal, the motor operates smoothly, the impeller runs properly without any jamming or abnormal noises, and its movement is smooth ； 2) Each protection switch operates reliably ； 3) The track is level, free of debris and deformation ； 4) All motors and reducers are operating normally ； 5) The coal drop pipe is unobstructed, with no coal spillage or leakage. 187. What tasks should the duty officer carry out when a belt conveyor needs to be tested in operation locally as a single unit? Answer: 1) Inspections before equipment startup should be carried out in accordance with the procedures ； 2) Inform the program-controlled operator to disable the \"interlock\" and pay attention to monitoring the current value ； 3) The operation mode switch of the local control box is in the “local” position ； 4) After checking that the starting conditions are met, press the “Pre-start” button to sound the alarm, then press the “Start” button to activate the belt. 188. What protective devices does a conveyor belt have? Answer: Tear resistance ； Slipping, deviation, fire prevention, material flow sensors, emergency pull-cord switches, etc. 189. What are the reasons why a belt cannot be started? Answer: 1) The motor loses power or the operating power supply is lost ； 2) The protection devices have not been reset after activating ； 3) Interlock condition restrictions ； 4) Excessive load ； 5) Too low tension, causing the belt to slip. 190. What are the advantages of rubber lining for drive drums? Answer: Rubber-coated rollers have the advantages of a high friction coefficient and resistance to coal sticking, making them particularly suitable for use in applications with high power requirements and harsh working conditions. 191. What are the advantages of belt conveyors? Answer: Compared with other types of conveying equipment, belt conveyors offer high production efficiency, stable and reliable operation, uniform material transfer, low operating costs, easy maintenance, and the ability to achieve automatic control and remote operation. 192. What are the characteristics of herringbone groove drive drums? Answer: The herringbone groove drum has a high coefficient of friction (μ=0. 5) It can reduce belt tension and extend the belt’s service life. Furthermore, the grooves can cut off the water film, enabling good driving performance in humid environments. 193. What components make up a vertical mud pump? Answer: A vertical slurry pump is composed of components such as an electric motor, base, bearing housing, pump body, impeller, guard plate, suction pipe, and discharge pipe. 194. What is a hydraulic coupler? Answer: A hydraulic coupling is a hydraulic component composed of a pump impeller and a turbine, filled with fluid; it serves to connect the power unit to the transmission mechanism, which is why it is called a hydraulic coupling. 195. What are the main components of an electronic belt scale? Answer: An electronic belt scale consists of four components: the scale frame, the weight sensing element, the speed sensing element, and the measurement and display instrument. 196. What is the volatile matter in coal? Answer: When coal from which the moisture has been removed is isolated from air and heated at a certain temperature for a certain period of time, the gaseous substances released as a result of the decomposition of the organic compounds in the coal are known as volatiles. 197. What are standard coal and standard coal consumption? Answer: Standard coal refers to coal with a calorific value of 29.4 MJ/kg. The coal consumption required to produce one unit of electricity, as determined through conversion to standard coal, is known as standard coal consumption. 198. What are the characteristics of electric drums? Answer: The electric drum is a driving device for belt conveyors. It features a compact structure, small size, neat appearance, safe operation, light weight, low consumption of metal materials, and low cost; however, its maintenance is complex. 199. What should be done after the machine stops due to belt misalignment? Answer: 1) Disengage the deviation protection, transport the coal on the belt out, and then stop the belt from operating. 2) Analyze the reasons: a) If it is due to an incorrect coal dropping point, insufficient weight, or improper jointing. b) If the frame is deformed or the widths of the sealing seals on both sides are different, maintenance should be contacted for adjustment ； c) If coal sticks to the metal drum, safety measures should be taken to clean it off ； Additional adjustment can also be achieved by adjusting the deviation correction idler rollers. Under what conditions is a 200.42.6Kv high-voltage motor equipped with a heater? How long is the investment time under normal circumstances? Answer: 1) It should be used when water accidentally enters the junction box or the area becomes humid, when the motor’s insulation test fails, when the room temperature is below -50°C, or when the motor has been out of use for more than 5 days ； 2) Under normal circumstances, run it for 5 minutes. 201. What damages can occur if a steel-ring type spiral cleaning idler does not rotate for an extended period of time? Answer: Worn belts reduce cleaning efficiency. In severe cases, it is possible to scratch or cut the belt ； The sticky coal gets caught in the drum or weights, causing the belt to deviate from its path. 202. The belt does not deviate when idling, but it deviates when coal is fed in. What is the reason? Answer: 1) The belt is too loose ； 2) Incorrect coal dropping point: 3) Deflected guide chute ； 4) Coal sticking to the drum. 203. What type of idler rollers are installed within the operating area of the iron remover, and why? Answer: Magnetic-resistant drums and magnetic-resistant idlers ； If non-magnetic idlers are used, the idlers become magnetized and are attracted by magnetic separators, which affects safe operation ； Magnetizing the idler rollers increases the iron removal resistance of the iron remover. 204. Do brakes and regenerators serve the same purpose? What belts have brakes installed on them, and on which belts are brakes mounted? Answer: They are not the same. Brakes are generally used for inertial braking; they are installed between the motor and the hydraulic coupling, as well as on horizontally arranged conveyor belts (they can also be installed on belt conveyors with dual drive units at both ends) ； The function of a check valve is to prevent the belt conveyor from reversing after it stops, and it is generally installed on belt conveyors that are arranged at an angle. 205. What type of idler rollers are used at the head of the conveyor belt, and why? Answer: Transition idler. Transition idlers are used to gradually change the belt from a troughed shape to a flat one, thereby reducing belt bending fatigue, increasing the wrap angle between the belt and the drum, and ensuring sufficient friction. 206. What is the function of the clearance cleaner, and where is it usually installed? Answer: It is used to remove material stuck on the non-working surface, preventing it from entering the rear drum or the tensioning drum of the vertical tensioning device. It is generally welded to the intermediate frame in front of the rear drum and the tensioning drum of the vertical tensioning device, with the length of the suspension chain being adjusted accordingly. 207. Under normal circumstances, why is it not allowed to stop the coal crusher from operating? Answer: To prevent substandard coal particles from entering the raw coal bin directly in their large pieces, without being crushed or removed first, which could damage the coal grinder or affect its normal operation. 208. What protections does a coal crusher have? Answer: Over-vibration and over-temperature protection are provided, and the hydraulic coupling has a fuse-based overload protection. 209. What are the consequences of clogged screen elements in a roller screen? Answer: 1) Reduce screening efficiency and increase the output of the coal crusher ； 2) It can cause the sieve to overload and shut down, leading to the shutdown of upstream equipment due to excessive load ； 3) In severe cases, it can damage the screening motor, and even cause the screening plates to fall off, leading to equipment damage. 210. The duty officer noticed that the particle size of the coal on belt #5 had increased significantly. Please analyze the reasons. Answer: 1) The baffle of the roller screen is not in place, resulting in a gap on the bypass side ； 2) The sieve plates of the roller screen are severely worn or have fallen off ； 3) The ring hammers of the coal crusher are severely worn ； 4) Improper adjustment of the sieve plate gap in the coal crusher ； 5) The grid holes of the coal crusher screen are broken. Why are herringbone rubber-covered drums used for the drive drum at the head of the conveyor belt? If the rubber surface is worn 211., what harm does this cause to the belt in severe cases? Answer: Herringbone rubber-covered rollers are used to increase the friction coefficient between the belt and the rollers, thereby breaking up any water film and preventing the belt from slipping. The friction coefficient of the rubber surface decreases, causing the belt to slip. 212. What are the hazards of a conveyor belt weight hammer being too light or too heavy? Answer: 1) The weight of the belt counterweight is too low, causing the belt to drift and slip, as well as preventing the belt from starting ； 2) An overly heavy belt weight can cause excessive tension in the belt, leading to its rupture and increasing the load on the motor. 213. When carrying out maintenance work on-site, can a pull-cord switch be used as a safety measure to control the equipment during maintenance? Why? Answer: No ； The pull-cord switch can only be used for emergency shutdown in case of an accident. If it is used for shutdowns during maintenance, it does not meet safety regulations; the pull-cord switch for shutdown will generate an alarm signal, preventing other devices in the system from operating. If the reset function of the pull-cord switch fails, the conveyor belt remains in standby mode, which can lead to incorrect operations by operators and pose a risk to maintenance personnel. 214. After maintenance, the belt needs to be tested in operation on a single machine – what tasks should the duty officer carry out? Answer: 1) Conduct pre-startup inspections of the equipment in accordance with the procedures ； 2) Switch the local control box switch for the belt to the “local” position, inform the programming staff to “unlock” the belt, press the “pre-start” button, and then start it ； 3) Operation should be stopped immediately if any abnormal conditions are detected. 215. What is the reason why the water bath dust collector results in the discharged air containing a large amount of dust? Answer: 1) The relief valve is damaged, causing the water level to be too high ； 2) There is no water in the dust collector or the water level is too low ； 3) The sewage discharge valve does not close properly, preventing the water level from reaching the operating level ； 4) Air intake duct leakage ； 5) The water baffle has fallen off. 216. What are the reasons for ash emission from the exhaust duct of a bag filter? Answer: 1) The cloth bag is worn out, with holes appearing ； 2) Severe dust accumulation in the bag ； 3) Holes appeared in the corrosion of the steel plate supporting the bag cage. Which areas are prone to belt tearing accidents, and why is it necessary for the programmed duty officers and inspectors to pay attention to checking these areas? 217 Answer: Conveying trough, coal dropping pipe, coal distributor, tensioning drum, tail drum. 218. What safety measures must be taken when entering the coal bunker to clean the coal? Answer: 1) Close the outlet baffle of the coal bin, cut off the power to the corresponding conveyor belt, and hang a warning sign. 2) Staff should wear masks and gloves, tie up their sleeves and trouser legs, and use a safety belt when entering the coal bin. The rope of the safety belt must be attached to an external fixing device, with at least two people monitoring from outside. Once inside the coal bin, the safety belt should remain slightly tightened by the supervisor, and staff should use ladders to go up and down. 3) If coal accumulates on one side of the coal hopper and forms a steep slope, that slope should be removed before the coal enters the hopper. 4) Take safety measures to prevent foreign objects from falling into the coal bin through grates or manholes. 5) Detect the concentration of harmful gases and oxygen level in the coal bin. 219. What should a bucket wheel loader operator do when a collapse at the coal yard presses down on the bucket wheel? Answer: Operating the tilting mechanism and slewing mechanism is strictly prohibited. If there isn’t much coal accumulated under the bucket body, immediately stop the bucket wheel and then withdraw the trolley. If buried in large quantities, manual cleanup is required. 220. What are the limit protections available for bucket conveyors, and what is the purpose of these limits? Answer: The bucket wheel conveyor is equipped with protection against belt deviation, slippage, and tearing ； Protections against collisions for the forearm frame, limits for rotation and movement within the track area, limits for the upward and downward movement of the cantilever, as well as limits for forward and backward movement. 221. Why must the rotation of the bucket wheel conveyor be within specified limits? Answer: 1) To prevent damage to the railings, floor conveyors, and coal yard facilities ； 2) Prevent the central cable from being twisted off due to excessive rotation ； 3) Prevent damage to the rear vehicle’s facilities. 222. Why is it required that the angle between the cantilever frame and the belt conveyor on the ground be less than 300 degrees when the bucket wheel conveyor is used for rapid shunting? Answer: To ensure the stability of shunting operations and prevent the bucket wheel loader from derailing or tipping over. 223. Inspection requirements for the cable reel mechanism of stacker-reclaimers. Answer: Regularly inspect the cable reel mechanism; check whether its surface is scratched, crushed, or fractured, whether there is any jamming in the reel, and whether the reel rotates smoothly and in sync with the movement. 224. Parking requirements for bucket wheels. Answer: 1) Place the bucket wheel facing the wind on top of the coal pile; it is strictly prohibited to have it suspended above the ground conveyor belt or with its arm in the air ； 2) Deploy the rail clamps and anchors ； 3) Cut off the control power supply and stop the oil heater ； 4) The cab doors and windows are closed and locked. 225. Why is it strictly prohibited to start conveyor #3 during the process of replacing the tail car of the bucket wheel conveyor in the limited liability company? Answer: To prevent the tail car from hitting and damaging the equipment due to tension when starting the belt. 226. What effects will an overly loose or overly tight brake in the traveling mechanism of a bucket wheel conveyor have on its operation? Answer: 1) If it is too loose, the brake will lose its effectiveness, and the conveyor’s bucket wheel will be unable to pick up coal ； 2) Excessive tightness makes it difficult for the entire machine to move; the increased resistance can overload or even burn out the drive motor, and may also cause the machine to get stuck on the tracks or tip over. 227. What does the programmed duty operator use to determine the system operation mode? Answer: Based on the operation of equipment in the coal transportation system, its availability, the status of equipment defects, coal quality requirements, the economic efficiency of the operating mode, and arrangements from higher-level authorities. 228. What is the spontaneous combustion of coal? Answer: When coal oxidizes in air, the heat generated cannot dissipate and accumulates within the pile of coal. As a result, the temperature inside the pile rises continuously, and when it reaches the ignition point, the coal begins to burn on its own; this phenomenon is known as spontaneous combustion of coal. 229. What is the function of lubrication? Answer: Lubrication plays an important role in the proper operation and maintenance of mechanical equipment. It helps to control friction, reduce wear, cool down the components, prevent rusting of the friction surfaces, provide sealing, transmit power, and reduce vibrations. 230. What are the high calorific value and low calorific value of coal? Answer: The heat released when one kilogram of coal burns completely, with the water in the combustion products remaining in liquid form, is known as the high calorific value. The calorific value when the water in the combustion products remains in a gaseous state is called the lower calorific value. 231. What is the function of the emergency pull-cord switch in the coal conveying system? Answer: The emergency pull-cord switch is a device designed for on-site operators to use in order to stop the operation of equipment at any time when a fault is detected or when there is a threat to human safety. 232. What is the proportion of coal in power generation costs? Answer: Coal is the main fuel for thermal power plants, and the cost of fuel accounts for about 70% of the electricity generation costs. 233. What is gear transmission? Answer: Gear transmission is a type of meshing transmission in which two or more gears working together transmit the power and motion from the driving shaft to the driven shaft through mutual meshing. 234. What is the function of a bearing? Answer: Bearings are components used to support shafts; sometimes they can also support components that rotate around a shaft.