Thread Content
Coal Mill Maintenance Procedures 1 Equipment Overview These procedures apply to steel ball coal mills (referred to as ball mills) used in coal-fired boilers in chemical enterprises. 1.1 Equipment technical performance. Model: DTM250/390 Power: 10t/h Maximum ball loading capacity: 22t Rotation speed: 20r/min 1.2 Motor technical specifications Model ； JSQ157—8 Power: 320kw Voltage: 6000v Current: 40A Speed: 740r/min 1.3 Equipment operating conditions Spindle temperature: < 55℃ Spindle return oil temperature: < 40℃ Lubricating oil temperature: < 60℃ Spindle vibration: < 0.10mm Reducer oil flow rate: 25L/min Reducer oil supply pressure: 0. 63MPa Spindle oil supply volume: 63L/min Spindle oil supply pressure: 0. 5-0.6MPa 2 Maintenance cycle and maintenance contents: The maintenance cycle and the number of days the ball mill is out of service are determined in accordance with the regulations for the maintenance of the boiler itself. 3 Maintenance Contents 3.1 Minor Repairs 3.1.1 Inspect the wear of the cylinder linings, end linings, fixing wedges, and tightening wedges, and make minor replacements as necessary. 3.1.2 Check the bolts of the cylinder liner and end liners, as well as the bolts of the sound-insulating and heat-insulating enclosures. 3.1.3 Check the wear condition of the inlet and outlet hoppers as well as the seals at the inlet and outlet of the cylinder. 3.1.4 Check the integrity of all anchor bolts, coupling rubber rings, rod pins, and coupling bolts. 3.1.5 Check and address leaks in the lubricating oil pipelines and cooling water pipelines. 3.2 Major Overhaul 3.2.1 Main Body Section 3.2.1.1 Measure the radial clearance and penetration length of the inlet and outlet hopper sections and the hollow shaft sleeves. 3.2.1.2 Remove steel balls with a diameter of less than 25 mm or those that are damaged or incomplete. 3.2.1.3 Measure the horizontal error of the cylinder, the contact angles between the inlet and outlet bearing shells and the diameter of the hollow shaft, as well as the expansion clearance and thrust clearance of the bearings. 3.2.1.4 Check the shaft bearings at the inlet and outlet of the cylinder for defects such as flaking or cracks, and measure the thickness of these shaft bearings. 3.2.1.5 Grind and scrape the bearing bushings of the inlet and outlet bearings of the cylinder. 3.2.1.6 Check the roundness, conicity, and surface finish of the hollow shaft diameters at the inlet and outlet of the measurement cylinder. 3.2.1.7 Check the contact surfaces between the inlet and outlet bearing bushes and the supports, as well as the position of the positioning pins. 3.2.1.8 Check the wear condition of the hollow shaft sleeve and the helical thread, examine the fit between the hollow shaft sleeve and the hollow shaft, and measure the clearance. 3.2.1.9 Clean the cooling water chambers and cooling water pipelines of the inlet and outlet bearings of the cylinder. 3.2.1.10 Check the explosion-proof doors at the inlet and outlet of the cylinder. 3.2.1.11 Replace the sealing felt of the inlet and outlet bearings of the cylinder. 3.2.1.12 Check the oil supply pipe holes of the inlet and outlet bearings of the cylinder, and clean the lubricating oil pipeline and oil filter. 3.2.1.13 Inspect and replace damaged cylinder linings, end linings, and lining bolts, and repair the soundproof and heat-insulating enclosures. 3.2.2 Transmission mechanism 3.2.2.1 Check and measure the gaps at various points of the engagement between the large and small gears, as well as the degree of engagement (area). 3.2.2.2 Check the large and small gears for missing teeth, cracks, and wear. 3.2.2.3 Measuring the tooth pitch at the joint surface of the large gear ring ； Check whether the fastening bolts at the mating surfaces of the large gear ring and the cylinder flange are loose. 3.2.2.4 Clean the large and small gears as well as their housings. 3.2.2.5 Check the bearings of the pinion shaft or repair/scrape the shaft bushings. 3.2.2.6 Measure the fit tightness (clearance) between the bearing (bushing) of the pinion shaft and the shaft as well as the bearing housing. 3.2.2.7 Measure the hardness of the pinion and the straightness of the pinion shaft if necessary. 3.2.3 Reducer 3.2.3.1 Check and analyze the quality of the lubricating oil. 3.2.3.2 Measuring the clearance or tightness between each bearing and the reducer housing ； Clean and inspect each bearing. 3.2.3.3 Check each gear for cracks, missing teeth, and wear ； Check the meshing condition of each gear, and measure the meshing clearance of each gear if necessary. 3.2.3.4 Clean the reducer housing and oil level indicator. 3.2.3.5 Inspect and clear the oil cooler and cooling water pipes. 3.2.3.6 If the gear is equipped with counterweight blocks, their firmness should be checked. 3.2.4 Couplings 3.2.4.1 Elastic couplings Check the couplings for wear, deformation, and cracks. Check the integrity of the coupling connection bolts, the conical holes of the bolts, the nuts, and the split pins. Measure the gap between the two opposite couplings, as well as the axial and radial deviations. Inspect and replace the large and small rubber rings of the coupling. 3.2.4.2 Rod and pin coupling (Boiler No. 3): Check whether the shaft sleeves and outer casings are worn or cracked ； Inspect and replace the rod pins. Measure the gap between the two opposite couplings, as well as the axial and radial deviations. 3.2.5 Lubricating Oil System 3.2.5.1 Inspect and analyze the quality of the lubricating oil. 3.2.5.2 Inspect and clean the oil filter and cooling water piping. 3.2.5.3 Flush the lubricating oil pipeline ； Check the stop valves and check valves of the lubricating oil system. 3.2.5.4 Check and clean the high and low fuel tanks as well as the fuel level gauges. 3.2.5.5 Service the oil pump. 3.3 Special Overhaul Items 3.3.1 Special Items 3.3.1.1 Repair (metalworking or other processes) of the main bearing housings and the spherical surfaces of the supports for the cylinder body. 3.3.1.2 Locally weld the shell that has peeled off, at the bearing bush of the outlet bearing. 3.3.1.3 Replace the cylinder gear or turn the gear over. 3.3.1.4 Replace the reducer gears. 3.3.1.5 Replace more than 1/2 of the cylinder linings or all the end linings. 3.3.1.6 Grind the hollow journal. 3.3.1.7 Rerouting of component foundations. 3.3.2 Major Special Projects 3.3.2.1 Modification or replacement of ball mills. 3.3.2.2 Cylinder liner modification. 4 Daily maintenance of equipment Table 1 Common faults of ball mills and their solutions Phenomenon Cause Solution Unstable pressure difference at the inlet and outlet of the ball mill as well as unstable system negative pressure; large fluctuations in the current of the exhaust fan; unstable air pressure after the powder discharge fan (spontaneous combustion in the coal grinding system). Accumulation of coal within the coal grinding system, improper ratio of coal types, high volatility of the raw coal, or the raw coal being too dry ； The outlet temperature of the ball mill was above the specified limit and was not adjusted in a timely manner ； Coal contains flammable and explosive materials such as oils, wood chips, and *tubes ； The coal supply to the ball mill was interrupted for an excessive period of time, and no action was taken promptly. The coal supply rate should be increased; the high-temperature air valve at the inlet of the ball mill should be closed slightly, while the low-temperature air valve or the recirculation valve at the inlet should be opened. If necessary, the cold air valve can also be activated in order to reduce the temperature at the outlet of the ball mill. Turn off the air lock on the return powder pipe of the coarse powder separator, stop the return of powder, and extinguish the fire. When using steam to extinguish a fire, the condensate water in the pipeline should be drained first, and it is necessary to prevent steam from entering the coal powder bin. Determination of the location of the fire: When a fire breaks out inside the ball mill, the temperature of the air and powder rises abnormally, sparks are emitted from the inlet and outlet of the ball mill, and there is a burnt smell ； When other areas catch fire, the system air temperature behind the burning area rises abnormally. Wear, peeling, cracks, and local flaking of the main bearing bushings. A fault in the lubricating oil supply system has led to a reduction in the amount of lubricating oil supplied, resulting in its interruption ； The poor quality of the lubricating oil damaged the oil film in the bearing shells, resulting in semi-dry friction between the hollow shaft journal and the bearing shells ； The meshing condition between the large and small gears is poor, which causes vibration, leading to cracks and eventual separation of the gears. Check whether the oil lines are blocked or open ； Is the valve damaged? ； Is the oil filter (filter element, screen) clogged, and is the filter element installed in the wrong direction? ； Is the gap between the gears of the oil pump and the housing too large? ； Check for any short circuits between the cooling water and the lubricating oil ； Check whether the oil seal of the main bearing or the seals in other areas are damaged ； Check whether the filter screen or filter element of the oil filter is damaged ； Check and adjust the meshing clearance of the large and small gears ； Check the fit between the large gear and the ring gear, as well as whether the bolts connecting the ring gear to the cylinder flange are loose ； Check whether the anchor bolts of the pinion bearing housing are loose ； Check whether the center of the pinion shaft and the coupling of the reducer are aligned. 5 Maintenance methods and quality standards 5.1 Maintenance steps and methods 5.1.1 The main body part 5.1.1.1 Inspect the inlet and outlet sealing devices of the cylinder, and remove the sealing material. 5.1.1.2 Measure and record the axial clearance, radial clearance (or center deviation), and penetration length of the inlet and outlet hopper sections and the hollow shaft sleeve (screw sleeve). 5.1.1.3 Remove all the connection bolts of the pipes connected to the inlet and outlet hoppers. 5.1.1.4 Remove and inspect the inlet and outlet hopper bodies. 5.1.1.5 Remove the steel balls. 5.1.1.6 Remove the coupling connection between the pinion shaft and the reducer. 5.1.1.7 Remove the bearing caps of the inlet and outlet bearings of the cylinder. 5.1.1.8 Measure and record the horizontal error of the cylinder, as well as the contact angles and expansion (thrust) clearances between the bearing shells and the hollow journal at the cylinder’s inlet and outlet bearings. 5.1.1.9 Inspect and replace the cylinder liner, end liners, and liner bolts. 5.1.1.10 Check the connection between the hollow journal and the cylinder. 5.1.1.11 Check the wear condition of the hollow shaft sleeve and the fixing bolts, and measure and record the clearance between the hollow shaft sleeve and the hollow shaft journal as well as the expansion clearance with the end shield. 5.1.1.12 Remove and clean the sealing covers of the cylinder gear and the drive pinion. 5.1.1.13 Clean and inspect the bolts at the junction of the large gear ring, as well as the bolts connecting the large gear to the cylinder flange. 5.1.1.14 Check the large gear teeth for wear, cracks, broken teeth, and other defects ； Measure the hardness of the teeth if necessary. 5.1.1.15 Measure and record the meshing clearance and meshing area at one or several locations of the large and small gears, and mark the measured locations. 5.1.1.16 Use a jack to lift the cylinder body by at least 100 mm, lift the inlet and outlet bearings respectively, rotate them 180° along the hollow journal, and then remove them. Place them with their contact surface (spherical surface) facing down on the sleepers on the ground. 5.1.1.17 Inspection of the bearing shells at the inlet and outlet ； Clean the cooling water chamber. The methods for dealing with defects in bearing bush bodies are as follows: a) Wear and peeling of the bearing bush ； Grind and scrape to smoothness ； b) Bearing shell cracks: Small holes can generally be drilled at each end of the crack to prevent it from spreading ； Alternatively, use a chisel to carve a V-shaped groove along both sides of the crack, then weld on bearing alloy of the same specification using gas welding, and finally polish it smooth ； c) Local flaking of the bearing shell: Remove the bearing alloy from the flaked area, use carbon tetrachloride to clean the oil from the bearing lining, and polish the cleaned surface of the bearing lining (including the dovetail grooves). Apply a uniform layer of fluxes such as zinc chloride or stannous chloride (or tin chloride) onto the surface of the bearing lining. Heat the bearing bush at the stripped area using an acetylene flame, and apply pure tin while heating, until the entire surface of the stripped area is covered with a tin layer. The thickness of this tin layer should be 0.2–0.4 mm; it must be uniform, smooth, and free of any imperfections. During the tinning process, care must be taken to ensure that the temperature of the bearing bush does not exceed 200°C. Bearings alloy is surfaced welded using an acetylene flame; the welding should be carried out in layers, with each layer having a thickness of 2–3 mm. Grind and scrape the surfaced bearing alloy using normal methods ； d) Method for removing welding stresses in surfaced bearing alloys: During welding, use segmented reverse welding; after each pass, wait until the bearing alloy has fully solidified, then gently tap the weld metal with a hammer. After welding is complete, the surfaced bearing alloy is evenly heated to a temperature of 125–150°C. 5.1.1.18 Check the hollow journal at the inlet and outlet of the cylinder. 5.1.1.19 After inspecting, cleaning, measuring, and servicing (or replacing) each component, reinstall it in the reverse order of disassembly, and record all the data obtained from the reinstallation measurements. Inspect the explosion-proof doors at the inlet and outlet of the cylinder, and postpone putting the steel balls back into the cylinder. 5.1.2 Transmission Mechanism 5.1.2.1 Removing the Pinion Bearing Cover a) Bearing shells: Remove the inlet and outlet lubricating oil pipes as well as the measuring devices. Attach the upper bearing shell (the upper cover of the bearing), measure and record the clearance between the upper bearing shell and the pinion shaft, as well as the thrust clearance of the bearing shell at the coupling end and the expansion clearance of the bearing shell at the other end. Remove the shims from the mid-plane of the bearing seats at both ends, measure and record the total thickness of the shims on each side, make marks, and store them separately ； b) Rolling bearings: Remove the bearing cover and temperature sensing device, and measure and record the clearance or tightness between the bearings at both ends and the bearing cover, as well as the thrust clearance of the bearing at the coupling end and the expansion clearance of the bearing at the other end. Remove the shims from the mid-plane of the bearing seats at both ends, measure and record the total thickness of the shims on each side, keep proper records, and store them separately. 5.1.2.2 Lower the pinion shaft. 5.1.2.3 Clean and inspect the pinion shaft and bearing housing. Inspection items include: a) straightness of the shaft ； b) Check for wear, cracks, and other defects on the teeth; measure the hardness of the teeth if necessary ； c) Whether there are cracks or other defects in the bearing housing and end caps. 5.1.2.4 Inspect the bearings or bushings and address any defects. 5.1.2.5 Check the fit between the bearing and the shaft, as well as between the pinion and the shaft. 5.1.2.6 Check the coupling and the fit between the coupling and the shaft. 5.1.2.7 After each component has been inspected, cleaned, measured, and repaired (or replaced), reinstall it in the reverse order of disassembly, and record all the data measured during reinstallation. 5.1.3 Reducer 5.1.3.1 Transfer the lubricating oil inside the box into a dedicated oil tank, and take samples to analyze the oil quality. 5.1.3.2 Remove the oil inlet and outlet pipes, the cooling water inlet and outlet pipes of the oil cooler, and the temperature measurement devices. Remove the bearing end cover and the box top cover. 5.1.3.3 Measure and record the longitudinal and lateral horizontal errors of the partition plane in the lower housing, the clearance or tension between each bearing and the housing, as well as the meshing clearance of the gears; check the meshing area of the gears, make marks at the gear meshing points, and lift out the gears using a coupling. 5.1.3.4 Check for wear, cracks, or missing teeth on the gears, and ensure that the balance weights are securely fastened. 5.1.3.5 Check the fit between the bearings and the shaft, as well as between the gears and the shaft, and address any issues. 5.1.3.6 Check the coupling and the fit between the coupling and the shaft. 5.1.3.7 Inspect and clean the lower tank, the tank cover, and the oil level indicator; clear the cold oil cooler and the cooling water pipes. 5.1.3.8 After each component has been inspected, measured, repaired (or replaced), reinstall it in the reverse order of disassembly, and record all the data measured during reinstallation. 5.1.4 Lubricating oil system 5.1.4.1 Transfer the lubricating oil in the tank into a dedicated container, and take samples to analyze the oil quality. 5.1.4.2 Inspect and clean the high and low oil tanks, oil filters, oil coolers, and oil level gauges. 5.1.4.3 Inspect the stop valves and check valves in the oil pipelines and cooling water pipelines, and clear and clean these pipelines. 5.1.4.4 Overhaul the oil pump. 5.1.4.5 After all maintenance work is completed, fill the high and low oil tanks with qualified lubricating oil. 5.1.5 Final Assembly 5.1.5.1 Align the pinion according to the specified clearances between the tooth tops and tooth backs of the gear teeth. 5.1.5.2 Align the pinion shaft with the reducer, and the couplings between the reducer and the motor. 5.1.5.3 Test run of the ball mill system, install the steel balls. 5.1.5.4 Tighten the newly installed gasket bolts again, and check the existing gasket bolts. 5.2 Quality Standards Generally, the provisions of the manufacturer and **relevant standards shall be followed; in the absence of specific provisions, the requirements of this clause shall apply. 5.2.1 Main body section 5.2.1.1 Inlet and outlet hoppers a) When the wear over a large area exceeds 2/3 of the original steel plate thickness, it should be replaced ； For local thinning or penetration, remedial excavation can be employed ； b) When the wear resistance plate is worn to more than 2/3 of the original plate thickness or is worn through and cannot be repaired by digging out, it shall be replaced ； c) The linings made of gabbro slabs or other wear-resistant materials shall be free from damage, defects, and detachment ； d) The radial clearance, axial clearance, centering error between the hopper body and the hollow shaft sleeve, as well as the length by which the hopper body extends into the hollow shaft sleeve, shall comply with the specifications in Table 3 ； Table 2 mm Position Axial Clearance Radial Clearance Centering Error Penetration Length Inlet (Expansion Side) 15～20 2～4