Safety protection devices for cranes [Daily Question 20090401]

Common safety accessories: steel ropes, hooks, pulley blocks, drum sets, reducers, braking devices, wind and slip resistance devices, position limiting and adjusting devices, overload protection and alarm devices. To mention a few of them: 1. The various relief valves in the hydraulic system: they can prevent abnormal high pressures in the circuit, thus avoiding damage to the hydraulic pumps and motors as well as preventing overload conditions. 　　2. Boom swing safety device: In the event of an accident, if the high-pressure hoses or pipes in the boom swing cylinder circuit burst or get severed, the balance valve in the hydraulic circuit comes into action, locking off the working fluid coming from the lower chamber of the cylinder and preventing the boom from dropping, thereby ensuring the safety of operations. 　　3. Boom extension safety device: In the event of an accident, if the high-pressure hoses or pipes in the boom extension cylinder circuit burst or get severed, the balance valve in the hydraulic circuit comes into action, locking off the working fluid coming from the lower chamber of the cylinder and causing the boom to retract on its own, thereby ensuring the safety of the operation. 　　4. Height limit device: When the hook is raised to the specified height, it touches the limit weight, which activates the travel switch; the \"overtravel\" indicator light then turns on, and at the same time the operations of raising the hook, extending the boom, and lowering the boom are stopped to ensure safety. At this point, simply operating levers such as those for lowering the hook, retracting the boom, or raising the boom (that is, operating it in a safe direction) will release the restraint of the limit weight, and normal operation will be restored. On special occasions, when a slight amount of over-winding is still required, the release button on the instrument panel can be pressed; this will deactivate the limit function. However, such operations must be carried out with great care to prevent accidents. 　　5. Leg locking device: In the event of an accident, if the high-pressure hose or tubing leading to the vertical leg cylinders ruptures or is cut, the two-way hydraulic lock in the hydraulic system can seal off the pressure fluid in both chambers of the leg locking cylinders, preventing the legs from retracting or falling away, thereby ensuring the safety of lifting operations. 　　6. Lifting capacity indicator: The lifting capacity indicator is located on the side of the main arm (i.e., on the right side of the control cabin); it can be clearly seen by the operator sitting inside the control cabin, and it accurately indicates the elevation angle of the boom as well as the rated lifting capacity permitted by the crane under the corresponding operating conditions. 　　7. Lifting capacity table: Located on the lower front wall panel inside the control cabin, this table lists the rated lifting capacity and lifting height for various arm lengths and working ranges for easy reference during operation. When performing lifting operations, it is absolutely necessary not to exceed the values specified in the table. To ensure the safety and reliability of lifting operations, cranes are equipped with comprehensive safety devices that, in the event of an accident, serve to protect the machinery or alert operators, thereby providing a safety safeguard. This post was last edited by itdojust on 2009-4-1 08:38]

　　Learning together with everyone*: Crane safety devices – Devices that prevent cranes from being damaged in accidental situations. In addition to the common electrical protection devices, sound signals, and colored lights, cranes are equipped with a variety of other safety devices as well. 　　A travel switch is a safety device that prevents various moving components of the crane from exceeding their limit positions. When the various moving mechanisms reach their limit positions, the travel switch is activated, thereby cutting off the power supply. 　　Buffering and crash prevention devices are used to absorb the kinetic energy generated when the crane or trolley hits the end stop in the event of a switch failure. Such devices make extensive use of rubber, springs, and hydraulic buffers; the latter are used in cranes or trolleys with high operating speeds (such as those on bridge carriers), as they can absorb large amounts of energy in the event of a collision. Some cranes are also equipped with photoelectric collision avoidance systems to prevent two operating cranes on the same track from colliding with each other. Its simple principle (see diagram) is as follows: when the two cranes come within a certain safe distance, the light waves emitted by the transmitter of Crane A are detected by the receiver of Crane B. This generates an electrical signal through a phototube; after waveform shaping and amplification, the relay is activated, the buzzer emits an alarm sound, and the power supply to the operating mechanism is automatically cut off. Each of the two cranes needs to be equipped with a set, allowing them to interact with each other. 　　Wind protection devices: Devices that prevent cranes from being blown away or toppled by strong winds, mainly including crane track clamps and crane anchors. Large cranes operating at ports are usually equipped with both rail clamps and anchors at the same time. The rail clamps come into action when the crane is stopped or when the wind strength reaches a certain level ； The anchor is operated by the driver before a storm arrives. The wind-resistant effect of the rail clamps is inferior to that of the anchors. 　　A lifting capacity limiter ensures that the weight of the load being lifted does not exceed a specified value; it comes in mechanical and electronic types. Mechanical types utilize the spring-lever principle; electronic types usually use pressure sensors to detect the lifting weight, and the lifting mechanism will not activate when the allowable lifting weight is exceeded. The lifting capacity limiter can also serve as a lifting capacity indicator. 　　A lifting torque limiter can prevent the lifting torque of a boom-type crane (the product of the weight of the load and its reach) from exceeding a specified value, and it is capable of receiving signals indicating changes in the lifting load as well as changes in the reach. The two signals are combined and amplified using electronic instruments, and then electric interlocking is established with the lifting and luffing mechanisms to prevent the crane from toppling over. 　　Tilt limiter: In large-span cranes (usually over 50 meters long, such as bridge-carrying cranes and large gantry cranes used in shipbuilding), when the operating speeds on the two sides are not identical, tilting can occur, increasing operational resistance and placing additional loads on the connection structures between the bridge deck and the legs. At this time, a deflection limiter is usually installed at the upper part of the flexible leg. The relative rotation between the crane’s bridge and its legs can be achieved through the movement of arms or gear pairs, which cause cams or protrusions to act on the control switches; thus, the power supply can be cut off or the crane can be automatically corrected when it reaches a certain value of maximum deflection (usually 0.3% to 0.5% of the crane’s span).

An overload limiter, also known as a lifting capacity limiter, is a safety device for overload protection. Its function is to cut off the power supply to the lifting mechanism when the load being lifted exceeds the rated value, preventing the lifting action from taking place and thus avoiding overload. There are two types: mechanical and electronic. The mechanical type uses levers, springs, or cams to prevent the lifting mechanism from operating when overloaded. The electronic type consists of components such as sensors, operational amplifiers, control actuators, and load indicators, integrating display, control, and alarm functions into one. When a load is applied, the sensor deforms, converting the magnitude of the load into an electrical signal. After passing through an operational amplifier, this signal indicates the value of the load. A warning signal is issued when the load reaches 90% of the rated value, and the power supply to the lifting mechanism is cut off once the load exceeds the rated value. Overload limiters are widely used in bridge-type cranes and elevators. Some types of jib cranes (such as tower cranes and gantry cranes) use overload limiters in combination with torque limiters. 　　A torque limiter is an overload protection safety device for boom cranes. A jib crane uses its lifting torque characteristics to reflect the load condition, and the torque value is determined by various parameters such as the lifting capacity, amplitude (the product of the arm length and the cosine of the arm angle), and operating conditions; therefore, controlling it is quite complex. Electronic torque limiters address this issue effectively. The working principle is illustrated using the torque limiter of a mobile crane as an example. The torque limiter consists of a load detector, an arm length detector, an angle detector, a mode selector, and a microcomputer (see the schematic diagram of the torque limiter’s operation). When the crane enters operation, the detection signals of the actual parameters are input into the computer; after calculation, amplification, and processing, the corresponding parameter values are displayed and compared with the rated lifting torque value stored in advance. A warning signal is issued when the actual value reaches 90% of the rated value, while an alarm signal is sent in case of overload, causing the crane to stop moving in dangerous directions (lifting, extending the arm, lowering the arm, rotating). 　　Buffers are installed on track-mounted cranes. A safety device used to absorb kinetic energy and reduce impact when two or more cranes on the same track collide, or when the crane’s main frame (or trolley) reaches the end of its travel distance and collides with the stop at the end of the track. There are various types, including rubber buffers, spring buffers, and hydraulic buffers. 　　Wind protection device: A safety device that prevents cranes or crane trolleys from sliding along the tracks or toppling over due to strong winds; it should be installed on all track-mounted cranes used in outdoor environments. Wind protection devices include rail clamps, anchoring devices, and shoe blocks. 　　Track clamps use grippers to tighten the tracks, thereby fixing the position of the crane or lifting trolley. It can also improve the stability of certain cranes during operation. 　　An anchoring device is a mechanism that connects the crane to the track foundation, preventing it from sliding or toppling along the tracks under the effect of strong winds. 　　Interlock protection and operational limit position restriction devices. The interlock protection device is a type of interlock switch, including door switches for accessing the crane operator’s cabin from the building, hatch doors for going from the operator’s cabin to the main girder of the bridge, and walkway railing doors

1. Each relief valve in the hydraulic system: It can suppress abnormally high pressures in the circuit, thereby preventing damage to the hydraulic pump and motor as well as avoiding overload conditions； 2. Boom swing safety device: In the event of an accident, if the high-pressure hoses or pipes in the boom swing cylinder circuit burst or get severed, the balance valve in the hydraulic circuit comes into action, locking the working fluid from the lower chamber of the cylinder and preventing the boom from falling, thereby ensuring the safety of operations ； 3 Boom extension safety device: In the event of an accident, if the high-pressure hoses or pipes in the boom extension cylinder circuit burst or get severed, the balance valve in the hydraulic circuit comes into action, locking off the working fluid coming from the lower chamber of the cylinder, causing the boom to retract on its own and thus ensuring the safety of the operation ； 4 Height limit device: When the hook is raised to the specified height, it touches the limit weight, which activates the travel switch; the overload indicator light comes on, and at the same time the lifting of the hook is stopped. The extension of the boom as well as other related movements are controlled in order to ensure safety ； 5-leg locking device: In the event of an accident, if the high-pressure hoses or pipes leading to the vertical leg cylinders rupture or get severed, the two-way hydraulic lock in the hydraulic system can prevent the pressure fluid in both chambers of the leg cylinders from flowing, thus preventing the legs from retracting or falling away and ensuring operational safety ； 6 Lifting indicator: The lifting indicator is located at the front of the boom; it can be clearly seen by the operator sitting in the control cabin, and it accurately indicates the elevation angle of the boom as well as the rated lifting capacity permitted by the crane under the corresponding operating conditions ； 7. Lifting capacity table: Located on the front lower wall panel inside the control cabin, this table lists the rated lifting capacity and lifting height for various arm lengths and working ranges for easy reference during operation.

① Load display: a load-radius display or an automatic safety load display that can provide audible and visual warning signals. 　　② Control: It should be of the “dumb” type and have obvious indicators ； 　　③ Overtravel switch: A limit switch designed to prevent the hook or pulley block from being wrapped around by the wire rope ； 　　④ Access: Safe conditions for operators to enter and exit should be provided, and such conditions should also be available during maintenance, testing, and emergency situations ； 　　⑤ Operation position: It should provide a good line of sight to the hook and load, as well as facilitate control of the operation ； 　　⑥ Boom: The lifting rings, slings, cables, bolts, and hooks must all be inspected; they have to be free of defects and properly installed, with clear markings indicating the safe working load. They should also be used appropriately, without being used in areas with sharp edges or at abnormal angles.

Devices such as overload limiters, torque limiters, buffers, wind protection devices, rail clamps, anchoring devices, interlock protection systems, and limits for operational extreme positions.

Crane safety protection devices refer to the safety and protective devices installed on cranes, as well as other safety technical measures taken, with the main purpose of preventing various hazards that may arise during crane operation. The Safety Regulations for Lifting Machinery specify a total of 25 types of safety protection devices to be installed on various types of lifting machinery, which are classified into two requirement levels: \"must be installed\" and \"recommended to be installed\". Safety protection devices can be roughly divided into three categories: protection devices, display and indication devices, and safety devices. 　　Protective devices isolate people from hazards by creating physical barriers. For example, platform railings, protective covers for exposed moving parts, protective plates for conductive slides, rain shields for electrical equipment, and temporary fences set up within the area where lifting operations take place. 　　Display indicators are devices used to show the operating status of a crane; they serve as a means for people to observe and monitor the system’s operations. Some of these devices also have alarm functions, while others are interconnected with control and adjustment systems. Such devices include bias adjustment and display units, amplitude indicators, levels, wind speed and force alarms, boarding signal buttons, reverse movement alarm devices, and alarms for dangerous voltages. 　　A safety device refers to a single device that, through its own structural functions, limits or prevents a certain hazard, or a protective device used in conjunction with protective gear. Among them, the devices that provide limiting forces include overload limiters, torque limiters, buffers, and ultimate torque limiters, etc ； Devices that limit the movement range include an upper limit position limiter, a lower limit position limiter, a travel limit position limiter, a device to prevent the boom from tilting backward, and track end stops, etc ； The positioning device includes leg retraction locking devices, rotary positioning devices, rail clamps, and anchoring devices or shoe anchors, etc ； Others include interlock protection devices, safety hooks, track sweeping plates, etc. 　　In recent years, safety devices that utilize integrated circuit chips, offer a combination of various security functions, are reliable in performance, and are small in size and light in weight have emerged. With the advancement of science and technology, the safety of cranes will continue to improve. The following introduces several major safety devices. 　　An overload limiter, also known as a lifting capacity limiter, is a safety device for overload protection. Its function is to cut off the power supply to the lifting mechanism when the load being lifted exceeds the rated value, preventing the lifting action from taking place and thus avoiding overload. There are two types: mechanical and electronic. The mechanical type uses levers, springs, or cams to prevent the lifting mechanism from operating when overloaded. The electronic type consists of components such as sensors, operational amplifiers, control actuators, and load indicators, integrating display, control, and alarm functions into one. When a load is applied, the sensor deforms, converting the magnitude of the load into an electrical signal. After passing through an operational amplifier, this signal indicates the value of the load. A warning signal is issued when the load reaches 90% of the rated value, and the power supply to the lifting mechanism is cut off once the load exceeds the rated value. Overload limiters are widely used in bridge-type cranes and elevators. Some types of jib cranes (such as tower cranes and gantry cranes) use overload limiters in combination with torque limiters. 　　A torque limiter is an overload protection safety device for boom cranes. A jib crane uses its lifting torque characteristics to reflect the load condition, and the torque value is determined by various parameters such as the lifting capacity, amplitude (the product of the arm length and the cosine of the arm angle), and operating conditions; therefore, controlling it is quite complex. Electronic torque limiters address this issue effectively. The working principle is illustrated using the torque limiter of a mobile crane as an example. The torque limiter consists of a load detector, an arm length detector, an angle detector, a mode selector, and a microcomputer (see the schematic diagram of the torque limiter’s operation). When the crane enters operation, the detection signals of the actual parameters are input into the computer; after calculation, amplification, and processing, the corresponding parameter values are displayed and compared with the rated lifting torque value stored in advance. A warning signal is issued when the actual value reaches 90% of the rated value, while an alarm signal is sent in case of overload, causing the crane to stop moving in dangerous directions (lifting, extending the arm, lowering the arm, rotating). 　　Buffers are installed on track-mounted cranes. A safety device used to absorb kinetic energy and reduce impact when two or more cranes on the same track collide, or when the crane’s main frame (or trolley) reaches the end of its travel distance and collides with the stop at the end of the track. There are various types, including rubber buffers, spring buffers, and hydraulic buffers. 　　Rubber buffers absorb less energy and are generally used in cranes with lower operating speeds. 　　Spring buffers are widely used due to their simple structure and insensitivity to environmental conditions; they can rapidly convert most of the impact kinetic energy into the compressional potential energy of the spring, making them suitable for applications where the speed ranges from 50 to 120 m/min. The disadvantage is the high rebound force, which exerts stress on the crane. There are now two improved types to reduce this rebound force: one is a spring buffer equipped with a rebound-stop mechanism, and the other is a spring-friction buffer. 　　Hydraulic buffers do not rebound and can absorb much greater impact kinetic energy than spring buffers, making them suitable for situations with higher speeds. The disadvantage is its complex structure, and high ambient temperatures can affect its performance. 　　Safety checks mainly focus on whether the installation is firm and reliable, whether the components are in good condition, and their ability to absorb kinetic energy. 　　Wind protection device: A safety device that prevents cranes or crane trolleys from sliding along the tracks or toppling over due to strong winds; it should be installed on all track-mounted cranes used in outdoor environments. Wind protection devices include rail clamps, anchoring devices, and shoe blocks. 　　Track clamps use grippers to tighten the tracks, thereby fixing the position of the crane or lifting trolley. It can also improve the stability of certain cranes during operation. 　　An anchoring device is a mechanism that connects the crane to the track foundation, preventing it from sliding or toppling along the tracks under the effect of strong winds. 　　Interlock protection and operational limit position restriction devices. The interlock protection device is a type of interlock switch, including door switches for accessing the crane operator’s cabin from the building, hatch doors for going from the operator’s cabin to the main girder of the bridge, and walkway railing doors

Overload limiters, anchoring devices, interlock protection systems, and limits for operating extreme positions, etc.

Wind protection device, collision prevention device for two vehicles, overload detection device, height limiter, limit devices for the extreme positions of the large and small vehicles, overspeed detection device, alarm sound device, anti-rollover device, torque control device, and various audio and visual alarm devices.

Analysis and Prevention of Common Accidents in Crane Operations 1 Common Accidents with Cranes 1.1 Crushing Accidents A crushing accident occurs when workers are squeezed between two objects during crane operations, resulting in injuries. The reason is human factors such as the lack of safety supervision and command personnel at the crane site, the lack of safety awareness and self-protection consciousness among the personnel carrying out lifting operations, or the use of rough handling methods. Those who suffer from crush injuries are mostly lifting operators and maintenance personnel. Common crushing accidents include the following: ① Crushing accidents between lifting equipment or loads and objects on the ground. In indoor areas such as workshops and warehouses, where ground workers are situated between lifting equipment or loads and obstacles such as machinery, walls, and columns, crush injuries can occur when lifting, giving instructions, operating equipment, or performing other tasks, due to the violent swinging of the loads hitting the workers. ②Stranding accidents in lifting equipment. Accidents of crushing injuries occur when lift maintenance personnel or operators fail to follow operating procedures and get squeezed between the cage and the frame. ③Accidents of crushing injuries occur when the lifted objects are not placed stably and topple over. The main causes of the accident were improper placement or unstable positioning of the lifted objects, as well as chaotic on-site management. ④Falling accidents in flipping operations. When carrying out lifting, flipping, and turning operations, issues such as improper lifting methods, inadequate securing of the load, wrong selection of lifting equipment, and poor positioning of commanders and operators can lead to instability of the load or its swinging, which in turn results in various types of accidents including crushing, collision, impact, squeezing, and pressing during these operations. Crushing accidents involving lifting machinery are the most common type of injury or death incident that occurs during operations with such machinery; they are highly dangerous and have serious consequences. 1.2 Electric shock accidents Electric shock accidents refer to injuries or deaths that occur when workers engaged in lifting operations and maintenance tasks are struck by electric current. Most crane operations take place in an electrified environment, and electric shock is a common cause of injuries and deaths in such operations. The most common are electric shock accidents caused by leakage in electrical installations. 1.3 Falls from height Accidents involving falls from height refer primarily to injuries caused when workers operating lifting machinery fall from heights such as the machinery itself to the ground; they also include accidents in which tools or components fall from heights and injure workers on the ground. Falls from heights mainly occur during the installation and maintenance of lifting machinery. ①During the maintenance of the lift cage, or when the cage equipment is defective and causes it to fall. ②The maintenance worker failed to operate properly and did not take necessary safety precautions (such as wearing a safety belt), resulting in a fall. ③Personnel engaged in maintenance work fall when crossing the crane. ④Accident caused by falling maintenance tool parts injuring someone. 1.4 Accidents caused by the fall of lifted objects Equipment: An accident resulting from the fall of lifted objects or equipment using lifting machinery refers to incidents that cause injuries or deaths and damage to equipment as a result of such heavy objects falling from a great height during lifting operations. Common types of accidents caused by the fall of lifted objects include the following. ①A rope failure accident refers to an incident involving injuries, fatalities, or damage that occurs when a heavy object breaks free from its lifting ropes. ②A detachment accident refers to an incident in which a heavy object is dropped as a result of the lifting rope or specialized lifting device coming loose from the hook. ③A rope break accident refers to an incident in which heavy objects are dropped due to the rupture of lifting ropes or hoisting ropes. The main reasons for the breakage of the lifting rope are: a) the steel wire rope is broken due to overloading, as the operators are unaware of the weight of the load and proceed with lifting recklessly, resulting in overloaded lifting. b The lifting limit switch fails, resulting in over-winding that causes the wire rope to break; c the wire rope suffers from fatigue deformation, wear, damage, and broken strands due to long-term use and lack of maintenance, yet is still used even when it has reached or exceeded the standards for disposal. ④The main reasons for the breakage of the lifting rope are: a) an excessive angle between the lifting rope and the hook (>120°), along with the absence of a balance beam, which causes the tension on the lifting rope to exceed its limit and lead to breakage ； b Improper selection of the type and specifications of the lifting steel wire rope, or continued use of wires that have reached their end-of-life limit** Breakage of the lifting rope due to the weight being lifted ； c The lifting rope was cut by the sharp edges of the load due to the lack of protective measures such as padding at the contact points, resulting in a rupture of the lifting rope. 1.5 Hook breakage accidents: Hook breakage accidents refer to incidents in which heavy objects are dropped as a result of a broken hook. The main causes of hook breakage accidents: ① Defects in the hook material ； ②The hook has experienced prolonged wear, resulting in a reduced cross-sectional area that has reached the limit for disuse, yet it is still being used ； ③Frequent overloading leads to fatigue failure, which in turn results in fracture. 1.6 Over-winding accident An over-winding accident refers to an incident in which a load is dropped due to the hook hitting the top limit. The main reasons are: ① No upper limit position limiter was installed, or the limiter failed, allowing the hook to continue rising until the wire rope broke ； ②The main contactor of the lifting mechanism fails (such as the main contacts melting or operating slowly), and is unable to cut off the power supply in a timely manner. Accidents caused by the falling of loads (tools) lifted by lifting machinery mainly occur in the load-retrieval and winding system of the lifting mechanism. In addition to rope slippage, hook failure, rope breakage, hook breakage, and over-winding, securing both ends of each lifting wire rope is also very important. For example, it is necessary to ensure that there are at least 2 to 3 safety turns of the wire rope on the drum; there should also be a lower limit protection mechanism. The fixing plates on the drum device, as well as the way in which the wedges are fixed, must be safe and reliable. Additionally, accidents can occur when the wire rope slips out of its groove on the drum or falls off the pulley, leading to the loss of control over the load. The falling of loads is one of the most common types of injuries and fatalities that occur during crane operations, and it is a widespread problem across all types of lifting equipment. Its danger is extremely high, and the consequences are very serious. 2 Characteristics of lifting operation accidents 2.1 Accidents occur more frequently during the installation and maintenance of lifting machinery. The installation and maintenance of lifting machinery are tasks with a high degree of risk. Injuries such as crushing or collision by lifting equipment, or falls from heights, mainly occur during the installation and maintenance of lifting equipment. 2.2 The types of injuries in the accident were relatively concentrated. The direct causes mainly include falling loads, crushing or collision with objects, electric shock, and falls from heights; these account for 34%, 30%, 10%, and 8% of the total number of accidents involving lifting machinery respectively, with these four categories together accounting for approximately 82%. Among them, falling loads and crushing collisions are the most prominent, accounting for about 64% of the total. Accidents that occur during crane operations are indeed due to technical and equipment-related factors, but the primary cause is managerial issues. The main managerial problems include: ① a lack of safety training for personnel involved in crane operations, with unauthorized operation occurring from time to time. ②Management is lax, supervision and inspection are insufficient, and illegal operations continue to occur despite repeated prohibitions. ③Due to untimely maintenance, equipment operating while faulty is a common occurrence. ④There is a lack of systematic safety management for the design, manufacturing, installation, operation, and maintenance of lifting machinery. 3 Safety Measures 3.1 Improving Systems It is necessary to establish and improve systems such as responsibility frameworks for the safe management of lifting machinery, management systems for safety technical records related to such machinery, safety operation regulations for operators, supervisors, and maintenance personnel, as well as maintenance systems for lifting machinery. 3.2 Strengthen training and education: Safety and technical training and assessments should be provided for personnel who operate lifting machinery. In accordance with **relevant technical standards, safety and technical training and assessments should be carried out for crane operators, supervisors, and rigging personnel, so as to improve their safety and technical skills and ensure that they work with valid certificates. 3.3 Implementing system safety management: The safety management of lifting machinery is a complex systematic task that requires comprehensive management throughout the entire lifecycle of such machinery – including its design, manufacturing, installation, operation, and maintenance – to ensure that this process is carried out in a scientific, thorough, standardized, and orderly manner. 3.4 Strengthen safety inspections: Quality supervision departments at all levels shall, in accordance with the relevant safety regulations and standards, enhance the safety inspections of lifting machinery. ①Safety certifications are issued for the manufacturing qualifications of crane manufacturers, and safety and quality inspections are conducted on the crane products they produce to ensure that cranes meet the required standards before leaving the factory. ②Safety and quality certifications for installation and maintenance qualifications are issued to enterprises engaged in the installation and repair of lifting machinery; enterprises that do not possess the necessary expertise for such work are not allowed to carry out installation tasks. ③For newly installed/overhauled units whose important performance parameters have been altered, technical qualification verification must be carried out; for those subject to regular routine inspections, they must pass such inspections before they can continue to be used. ④Injuries and fatalities that occur during crane operations must be dealt with seriously.

Functions that safety devices for tower cranes should possess 1 Introduction Safety devices for tower cranes include limiters and restrainers. The limiters include travel limiters, amplitude limiters, rotation limiters, and height limiters ； Limiters include weight limiters and torque limiters. The function of the safety devices on tower cranes is to prevent serious accidents caused by improper or careless operation on the part of the crane operators. Their proper use has drawn significant attention from **relevant authorities and construction companies. In September 1998, the Bureau of Quality and Technical Supervision, the Ministry of Construction of the People’s Republic of China, and the ** Administration for Industry and Commerce of the People’s Republic of China jointly issued the \"Regulations on the Supervision and Management of Safety Protection Equipment and Machinery Used at Construction Sites.\" In 1999, the \"Safety Inspection Standards for Building Construction\" JGJ59-99 were issued. To help readers understand the requirements of the standards regarding the safety devices of tower cranes, as well as the functions that such safety devices should possess, the author presents the requirements for limiters and stop devices in tower cranes based on standards such as GB/T9462-1999 \"Technical Conditions for Tower Cranes\", GB5031-1994 \"Performance Tests for Tower Cranes\", GB5144-1994 \"Safety Regulations for Tower Cranes\", and GB/T7950-1999 \"General Technical Conditions for Lifting Moment Limiters in Boom-Type Cranes\". 2 Requirements for safety devices in fixed tower cranes 2.1 The device must enable the tower crane to stop moving in the lifting direction and to start moving in the direction of increasing the boom angle when the lifting torque exceeds its rated value but is less than 110% of that rated value ； 2.2 Cranes with a variable jib length can achieve the function of adjusting both the lifting capacity and the jib length separately ； 2.3 For cranes in which the maximum speed of the trolley’s amplitude variation exceeds 0.67 m/s, the limiter enables the trolley to move in the direction of increasing amplitude; when the lifting torque reaches 80% of the rated value, it automatically switches to a low-speed operation mode ； 2.4 It enables the tower crane to issue an automatic alarm when the lifting torque exceeds 90% of its rated value ； 2.5 It enables control of the weight-related parameters of tower cranes through gear-based speed limitation, that is, different speed gears are used to restrict different lifting capacities. In QTZ4007 tower cranes equipped with three-speed motors, when the lifting load exceeds 40%, it automatically switches from high speed to low speed operation ； 2.6 The variable amplitude mechanism is capable of automatically stopping its movement when the amplitude exceeds the maximum value or is below the minimum value ； 2.7 It is capable of achieving a lifting height exceeding the rated value, and the lifting mechanism can automatically stop working when it reaches the ground ； 2.8 It is capable of controlling the number of rotation cycles (1–3 cycles) within a specified range. Article 2.1 is taken from clause 4.5.2 of GB/T9462-1999 \"Technical Requirements for Tower Cranes.\" The author believes that there can be disputes regarding the interpretation of this clause. According to clause 3.3 of GB7950-1999 \"General Technical Requirements for Lifting Moment Limiters of Boom Cranes,\" the author thinks this clause should be understood as follows: 1) Tower cranes should be capable of performing lifting and luffing operations at their rated lifting moment values. 2) Tower cranes are not allowed to lift or change the amplitude in the direction of increase when the lifting moment is greater than or equal to 110% of the rated lifting moment. 3) The tower crane is allowed to stop its upward lifting and outward luffing actions at any value within the range greater than the rated lifting torque value and less than 110% of the rated lifting torque value. 3 Analysis of the settings for limiters and their control switches: The limiters of fixed tower cranes include lift height limiters, luffing angle limiters, and slewing angle limiters. Fixed tower cranes equipped with a central collector ring only require a lifting height limiter and a swing angle limiter. The limiter should be equipped with switches to control the maximum and minimum amplitude, maximum lifting height, height above the ground, and rotation angle. Fixed tower crane limiters include torque limiters and weight limiters. For a swing speed of less than 40 m/min ； A tower crane with only two lifting speeds requires 4 control switches, which are used to control the parameters of changing the luff angle at a constant radius, changing the radius at a constant luff angle, operating at 90% of the rated lifting torque, and operating at the rated lifting capacity. For tower cranes with a luffing speed greater than 40 m/min and three lifting speeds, 6 control switches are required to respectively control luffing at constant amplitude, changing amplitude at constant speed, 90% of the rated lifting torque, 80% of the rated lifting torque, high speed at the rated lifting capacity, and medium speed at the rated lifting capacity. 4 Performance analysis of current limiters and measures for improvement: At present, the quality, stability, and accuracy of the limiters used in tower cranes meet the requirements of national standards, so they will not be discussed here; however, the quality, stability, and accuracy of these limiters are not yet satisfactory. The following discussion focuses only on the tower crane limiters. Currently, the commonly used approaches that limit torque and weight parameters include: 1) a combination of a bowplate-type torque limiter and a tension ring weight limiter. 2) Multifunctional limiter. 4.1 Analysis of the combined approach using bowplate-type torque limiters and tension ring weight limiters, as well as measures for improvement. In the approach that employs bowplate-type torque limiters and tension ring weight limiters, weight control is achieved through the use of tension ring weight limiters, thereby meeting the **standard requirements. For torque control, bowplate-type torque limiters are used; these devices control the lifting torque by regulating the strain in the sections where the torque limiters are installed on the main members of the tower cap. Since the main members of a tower crane’s tower cap experience relatively simple stress conditions and are less affected by wind loads and rotational inertial forces, the principal strain ε in these members can accurately reflect the lifting load. In principle, this method is stable and reliable. However, the bow-type torque limiter currently in use has an insufficient number of microswitches, which prevents it from meeting the requirement specified in GB9462-88 \"Technical Conditions for Tower Cranes\" to control the lifting torque separately based on weight and amplitude ； On the other hand, by keeping the strain in the main member of the tower cap constant for lift moment control, and using equation (1) to determine its lift characteristic curve, this approach is feasible and relatively accurate for single-joint horizontal-arm tower cranes and short-horizontal-arm tower cranes. Using Equation 1 to determine the lifting characteristic curve for double-sling long-horizontal-arm tower cranes results in large errors, and it is very difficult to adjust the torque limiter. The improvement measures are: 1) Add several torque switches to meet the above 3 requirements. 2) The method for determining the lifting characteristic curve of jib cranes as given in Reference 1 is used: M = (Q1 + q) * (X1 – r) = (Q + q) * (X – r) --------------------------(1) Where: X1 – length of the basic arm, in meters; r – distance from the hinge at the base of the jib to the rotation center, in meters; Q1 – rated lifting capacity when the basic arm is at its full length, in KN; q – weight of the load being lifted, in KN; X – length of the arm, in meters; Q – rated lifting capacity corresponding to an arm length of R, in KN. 4.2 Analysis of multi-functional limiters and measures for improvement: Multi-functional limiters enable comprehensive control over torque, weight, and arm length, which facilitates separate manufacturing from the main crane unit and promotes the commercialization of related components. However, the multi-functional limiters currently in use have the following drawbacks: 1) The curves of the curved plates cannot be adjusted, resulting in poor adaptability, and it is difficult to meet the requirements of different tower cranes of the same model as well as those of different models ； 2) There are few limit switches, making it difficult to meet the requirements specified in 4.5.2-1 of GB9462-88 \"Technical Requirements for Tower Cranes\". 3) The tension of the luffing wire rope changes during use, resulting in insufficient stability of the luffing angle parameters. 4) The load sensing sensor and the multi-functional limiter are far apart, and wind loads and temperature effects result in insufficient stability of the weight parameters. 3) and 4) cause instability in the torque limiter. The improvement measures are illustrated in Figure 1, showing the structure of an adjustable multi-functional torque limiter. There are four microswitches on the pull plate, which allow for adjustment based on the lifting weight and amplitude. When the load exceeds the maximum lifting capacity but is less than 110% of that capacity, movement in the lifting direction as well as in the direction of increasing amplitude is stopped; when the lifting weight exceeds 90% of the maximum capacity, an automatic alarm is triggered; and when the lifting torque exceeds 80% of the maximum allowable torque, the luffing trolley automatically switches from high-speed operation to low-speed operation. B-spline curves are used to simulate the torque curve; by adjusting these curves, the requirements of different tower cranes of the same model as well as those of different models can be met, thereby enabling torque control. Installing one or two microswitches on the base plate can achieve stepped limiting of the lifting capacity. The bridge is equipped with two microswitches that enable control of the minimum and maximum amplitudes ； An automatic tensioning device has been added to ensure the accuracy of the amplitude parameters ； Changing the position of the speed wheel reduced the distance between the weight sensor and the torque limiter, thereby increasing the reliability of the weight measurement. At present, our factory has used this multi-functional limiter produced by Shandong Fuyou in tower cranes such as the QTZ40C, QTZ5013, and QTZ4007; it not only reduces costs but also delivers excellent results.

1 Overload limiter a. The overall error of the overload limiter shall not be greater than 8%； b. A warning alarm signal should be issued when the load reaches 90% of the rated lifting capacity ； c. After installing an overload limiter on the lifting machinery, it should be adjusted or calibrated based on its performance and accuracy; when the lifting load exceeds the rated capacity, it should automatically cut off the power supply for lifting and issue a warning signal to indicate that lifting is prohibited. 2 Torque limiter a. The overall error of the torque limiter should not be greater than 10% ； b. After a torque limiter is installed on a lifting machine, it should be adjusted or calibrated based on its performance and accuracy. When the load torque reaches the rated lifting torque, it shall automatically cut off the power source for lifting or luffing, and issue a warning signal to indicate that operation is prohibited. 3 Rising limit position limiter: It is necessary to ensure that the power source for lifting is automatically cut off when the lifting device reaches its limit position. For hydraulic lifting mechanisms, it is advisable to provide a prohibitive alarm signal. 4. Lower limit position restrictor: In working conditions where the lifting device might drop below its lower limit position, this device should ensure that the power supply for lowering is automatically cut off once the lifting device reaches that lower limit position, so as to guarantee that the wire rope is wound around the drum for at least the number of turns specified in the design. 5 The limit position regulator should ensure that, when the mechanism reaches its extreme positions of movement, the power supply for forward motion is automatically cut off and the movement stops. 6 The skew adjustment and display device shall ensure that for large-span gantry cranes and loading/unloading bridges, when the two support legs skew due to different moving speeds, it can indicate this skew to the operator so that the skew can be adjusted. 7 Amplitude indicators: Cranes equipped with a luffing mechanism must be able to accurately indicate the amplitude at which the lifting appliance is located. 8 Interlock protection device: a. An interlock protection device should be installed between the boom support stopper and the boom oscillation mechanism, so that the oscillation mechanism cannot be activated until the stopper ceases to provide support ； b. Interlock protection devices shall be provided for the doors leading into bridge cranes and gantry cranes, as well as for the hatch doors used to access the bridge deck from the cab. When the door is open, the crane’s operating mechanism cannot be activated ； c. When the driver’s cab is located on the moving part, an interlock protection device should be installed at the access entrance to the cab. When the door at the access opening is opened, the crane’s operating mechanism cannot be activated. 9 The level should have good performance for checking the tilt of cranes with outriggers. 10 The device to prevent the boom from tilting backward shall ensure that the boom cannot tilt backward in the event that the travel switch of the luffing mechanism fails. 11 The extreme torque limiting device shall ensure that sliding occurs to provide protection when the rotational resistance torque exceeds the torque specified in the design. The 12 buffers should have good performance in absorbing the energy of the moving mechanism and reducing shocks. 13 Track clamps and anchoring devices or shoes: For cranes that operate outdoors on tracks, their track clamps and anchoring devices or shoes must be able to withstand the maximum wind force in a non-operational state on their own, without being blown away. A wind speed alarm with a scale of 14 wind forces should ensure that cranes operating in outdoor areas emit an alarm signal when the wind force exceeds level 6, and it should also be capable of displaying the instantaneous wind speed and wind force level. Cranes operating in coastal areas can be equipped to emit an alarm signal when the wind force exceeds level 7. The 15 leg retraction locking device shall ensure that mobile cranes with extendable legs can be reliably locked once the legs have been retracted during operation. 16 The rotation positioning device shall ensure that the upper structure remains in a fixed position while the mobile crane is in motion. 17 The boarding signal button shall be installed on the crane at a location that is easily accessible and safe to reach. 18 The anti-tilt safety hook shall ensure that a single-girder crane with the hook mounted on one side of the main girder does not tip over during trolley maintenance. 19 The maintenance lift cage, used for maintaining the conductive slides at great heights, should have a reliability level no lower than that of the driver’s cab. 20 Scanning plate and support frame: the scanning plate should be no more than 10 mm above the rail surface, while the support frame should be no more than 20 mm above the rail surface ； When the two are combined, the distance from the rail surface should not exceed 10 mm. The end stops of track 21 should have good performance in preventing the crane from derailing. 22 Conductive slide wire protection plate. a. When the bridge crane operator’s cab is located at the end of the main girder slide rails, protective panels should be installed between the ladder and walkway leading to the crane and the slide rails ； b. A protective plate should be installed under the end beam at the trolley slide end of the bridge crane to prevent accidental contact between the lifting gear or wire rope and the slide ； c. When bridge cranes are arranged in multiple layers, the slide rails of the lower-level cranes should be equipped with protective plates along their entire length ； d. For other cranes that use sliding wires, protective devices should be installed at the parts where electric shock is likely to occur. 23 Reverse alarm device: When a mobile crane is moving in reverse, it shall emit a clear audible alarm signal as well as a flashing light signal. 24 On cranes, all exposed moving parts that pose a risk of injury to people, such as open gears, couplings, drive shafts, sprockets, chains, conveyor belts, pulleys, etc., must be equipped with protective covers. 25 For cranes operating in outdoor conditions, their electrical equipment shall be equipped with rain guards.

1. Upper and lower limit position restrictors (also known as over-winding restrictors or lifting height restrictors). The upper limit position restrictor is used to prevent the hook from reaching its maximum elevation, which could lead to the wires breaking, the hook falling, the pulleys being damaged, and thus equipment failures that may result in injuries or deaths. A lower limit position limiter is generally not required for cranes; its principle is the same as that of an upper limit position limiter. 2. Operate the limit position restrictors to prevent the main and auxiliary cranes from exceeding the track’s limit positions. 3. Overload limiter: The overload limiter is a device designed to prevent cranes from lifting loads that exceed their capacity; it comes in lever-type, spring-type, and digital load control versions. It is commonly used in the hoisting mechanisms of cranes with large lifting capacities and a high risk of tipping over, such as portal cranes and tower cranes. 4. Buffer: A buffer is a device that absorbs the energy generated when the crane collides with the impact post. It is an additional energy-absorbing device that comes into use when the brakes and end-stop switches fail, ensuring that the crane can stop smoothly without experiencing sudden shocks. Rubber buffers, polyurethane buffers, spring buffers, and hydraulic buffers are commonly used on cranes. 5. Conductive slide wire protective plate: A protective plate should be installed under the end beam at the slide wire end of the bridge crane’s main girder, to prevent accidental contact between the lifting gear or steel wire rope and the slide wire. When the bridge crane operator’s cab is located at the end marked for the main girder movement, protective panels should be installed between the ladder and walkway leading to the crane and the sliding rails. These days, enclosed and safe slip rings are generally used. 6. Interlock protection device: Interlock protection devices should be installed on the doors that lead into bridge cranes and gantry cranes, as well as on the hatch doors used to access the bridge deck from the driver’s cabin; the crane’s operating mechanism must not be activated when these doors are open. When the cab is located on the moving part, a interlock protection device should be installed at the access opening to the cab; similar interlock protection devices should also be provided for the railing doors of the end beams of bridge cranes. 7. Maintenance hoist: Used for the maintenance of high-altitude conductive pipelines, and is generally located below the walkway on the non-driving side of the bridge crane. 8. Track scrubbers: The wheels of cranes that move on tracks should be equipped with track scrubbers to remove obstacles from the tracks. The lower edge of these scrubbers should be no more than 10 mm away from the track surface. 9. End stop for the track: At the end of the tracks along which the crane’s trolley moves, a sturdy end barrier must be installed; this is commonly referred to as a stop. The height of the guard frame matches the height of the corresponding buffer on the crane. 10. Anti-slip devices: Cranes used in outdoor work must be equipped with devices to prevent them from being blown away by strong winds. Commonly used ones include: rail clamps. Derailers, rail-pressure anti-skid devices, and anchoring devices; among these, the anchoring device is a supplementary component to the anti-skid device and should generally be used in combination with other devices. 11. Others: Protective covers should be installed on all exposed transmission parts of cranes, and gantry cranes operating in outdoor conditions should be equipped with rain protection devices.

I agree with the opinion above; thank you all for your active participation.