Overload protection devices can be divided into automatic stop type, alarm type and comprehensive type according to their functions.

The automatic stop overload limiter can stop the crane from continuing to move in an unsafe direction when the lifting weight exceeds the rated lifting capacity, and at the same time allow the crane to move in a safe direction. The safe direction refers to the descent of the lifting load, the retracting of the boom, the reduction of the amplitude and the combination of these actions. The automatic stop type is generally a mechanical overload limiter, which is mostly used on tower cranes.

The alarm-type overload limiter can display the lifting capacity, and can send out an alarm sound and light signal when the lifting capacity reaches 95% to 100% of the rated lifting capacity.

The comprehensive overload limiter can send out an alarm sound and light signal when the crane reaches 95%~100% of the rated lifting capacity. When the lifting weight exceeds the rated lifting capacity, it can stop the crane from continuing to move in an unsafe direction.

According to the structure, the overload limiter can be divided into three types: mechanical, hydraulic and electronic. Mechanical overload limiters include lever type and bullet type.

The overload protection device is designed to consider the influence of the crane’s apparent load. Under the conditions of lifting, braking, and vibration, the speed change will produce an additional load, and the lifting dynamic load often reaches 110%~130% of the rated load. . Dynamic load is an inherent dynamic phenomenon of lifting operations, and is a feature of hoisting machinery operations. Therefore, the overload protection device has designed a delay circuit based on this feature to make it have the ability to judge and deal with such false loads, while preventing actual If the load exceeds the specified value, malfunctions will not occur.

The strands of the steel wire rope can also be made into compact strands by post-treatment methods such as rolling or die extrusion. After treatment, the diameter of the strands will be reduced, and the surface finish will be high. Therefore, the densely stranded wire rope can use thicker steel wires. Under the same diameter, the densely stranded wire rope has a higher filling factor and greatly improves the breaking force. When multi-layer winding is performed on the reel, the outer strands of ordinary strands of steel wire ropes are squeezed more severely between layers, and the surface of the wire rope wears quickly. The tightly stranded steel wire rope has higher abrasion resistance and anti-extrusion ability.

Wire ropes are commonly used on construction cranes, and are generally made of many high-strength steel wires braided and wound. It first consists of single steel wires wound together to form strands, and then some of the strands are wound into a rope core, and then outer strands composed of other strands are wound around the rope core to form a steel wire rope. Some imported steel wire ropes also contain a plastic ferrule inside, usually in the form of a plastic coating, which is covered on the rope core through a special treatment. Important steel wire ropes are filled with appropriate lubricants to reduce friction.

Domestic steel wire ropes are generally divided into organic matter (hemp core and cotton core), asbestos core or metal core according to the rope core material. There is usually no filler or lubricant inside the rope.

According to the mutual direction of the steel wire winding into strands and the strand winding into the rope, the wire rope can be divided into the winding rope and the cross winding rope, and according to the twist direction of the strand rope, it is divided into left and right twists in the same direction and left and right alternate twists; imported steel wire ropes Generally, the winding rope is used as the standard rope, and the direction of the wire rope is specified to be consistent with the direction of the outer strand helix relative to the longitudinal axis of the wire rope, which is divided into left-handed and right-handed. Correspondingly, the direction of the strands is also specified, that is, the direction of the helix of the outer filaments constituting the strands is the direction of the strands based on the longitudinal axis of the strands. When the ordinary steel wire rope is used in a single rope, it rotates in the opposite direction of the wire rope. When used in a pulley block, the lifting wire rope twists due to the rotation of the wire rope, which is commonly known as twisting. Compared with ordinary steel wire ropes, non-rotating steel wire ropes have begun to be widely used. The so-called non-rotating steel wire rope is based on the principle that the torsional moment of the rope and the strands are opposite and equal in magnitude: the imported non-rotating steel wire rope is different. The principle is to make the rotation direction of the rope core opposite to the rotation direction of the rope itself. When force is applied, the torque produced by the rope core is equal to the torque produced by the outer strands, and the direction is opposite.

The strands of the steel wire rope can also be made into compact strands by post-treatment methods such as rolling or die extrusion. After treatment, the diameter of the strands will be reduced, and the surface finish will be high. Therefore, the densely stranded wire rope can use thicker steel wires. Under the same diameter, the densely stranded wire rope has a higher filling factor and greatly improves the breaking force. When multi-layer winding is performed on the reel, the outer strands of ordinary strands of steel wire ropes are squeezed more severely between layers, and the surface of the wire rope wears quickly. The tightly stranded steel wire rope has higher abrasion resistance and anti-extrusion ability.

1. The service life of the wire rope has a great relationship with the method of use. Therefore, it should be used according to regulations, dragging and throwing are prohibited, overloading is not allowed during use, the wire rope is not allowed to bend at an acute angle, and the lifting speed is not allowed to change sharply. , Avoid shock load. 2. When the wire rope has rust and dust, use a wire brush to remove it and apply oil.
2. Oiling the steel wire rope every 4 months. It is best to soak the core of the rope with hot oil (about 50℃) and wipe off the excess grease.
3. After the wire rope is coiled, it should be placed in a clean and dry place, and should not be stacked to prevent sprains.
4. The end of the steel wire rope should be tied up with a steel wire or welded with a low melting point alloy. It can also be fastened with an iron hoop to avoid loosening the rope head.
5. During use, if oil droplets are squeezed out on the surface of the wire rope, it means that the wire rope has been subjected to considerable strength. At this time, the load should be stopped and the inspection should be carried out. If necessary, replace with a new wire rope.

Crane Hook rotation phenomenon

The hook rotation often occurs during the equipment hoisting operation without any warning. When the hoisting machinery lifts the heavy object, the hook rotates, and the wire rope passing through the hook and the pulley block on the top of the boom is twisted and twisted together. The hoisted heavy object also rotates with the hook, and at this time it is no longer possible to continue to hoist or put down the already hoisted heavy object. The rotation of the hook will affect the normal operation of the hoisting operation and seriously threaten the safety of the operators and equipment, so it must be avoided.

The crane hook rotation is related to the following factors:

(1) The larger the crane, the higher the lifting height, that is, the longer the wire rope between the top pulley block of the boom and the hook, the greater the possibility of the hook rotating;

(2) The singular matching of the hook wire rope is easier to make the hook rotate than the even number matching, and the number of matching wire ropes is less, the greater the possibility of the hook rotating;

(3) The greater the weight of a single wire rope, the greater the possibility of the hook rotating;

(4) The smaller the size of the hook assembly and the size of its pulley, the greater the possibility of the hook rotating;

(5) The speed of operating the crane hook is not stable, especially when the heavy object is off the ground, the possibility of the hook rotating increases.

In order to ensure the safety and reliability of the lifting operation, the crane is equipped with a more complete safety device to protect the machine parts or remind the operator to pay attention to safety protection in the event of an accident.

1. Relief valves in the hydraulic system: it can suppress the abnormal high pressure in the circuit to prevent damage to the hydraulic oil pump and motor, and to prevent overloading.
2. Boom luffing safety device: when an accident occurs and the high-pressure hose or tubing in the boom luffing cylinder circuit bursts or is cut off, the balance valve in the hydraulic circuit will work to lock the work from the lower cavity of the cylinder Oil, so that the boom will not fall, thus ensuring the safety of the operation.
3. Boom telescopic safety device: when accidents occur, the high-pressure hose or tubing in the boom telescopic cylinder circuit bursts or is cut off, the balance valve in the hydraulic circuit works to lock the working oil from the lower cavity of the cylinder, The hoist will retract by itself to ensure the safety of the operation.
4. Height limit device: After the hook is lifted to the specified height, touch the limit weight, turn on the travel switch, the indicator light will light up, and cut off the hook lifting, boom extension, and boom Ensure safety by waiting for the operation of the action. At this time, as long as the handle is operated such as lowering the hook, retracting the boom or raising the boom (that is, operating to the safe side), the limit weight is released from the restraint, and the operation returns to normal. In special occasions, if you still need to do a small amount of bypass operation, you can press the release button on the meter box, and the function of the limit will be released at this time, but the operation must be very careful at this time to prevent accidents.
5. Outrigger locking device: When an accident occurs and the high-pressure hose or tubing leading to the vertical cylinder of the outrigger is broken or cut, the two-way hydraulic lock in the hydraulic system can block the outrigger and block the pressure oil in the two chambers of the cylinder, so that the support The legs are not retracted or thrown out, so as to ensure the safety of lifting operations. 6. Lifting weight indicator: The lifting weight indicator is set on the closing side of the basic arm (that is, the right side of the control room). The operator can clearly observe when sitting in the control room, and can accurately indicate the boom The elevation angle and the rated lifting capacity allowed by the crane under the corresponding working.

(1) In order to enhance the rigidity of the connection between the main beam and the end beam, sometimes a steel plate (or large angle steel) is welded on the head and end beam of the main beam by a unit, which causes the end beam to bend outward.
(2) If the cart gnaws the rail severely, the end beam will also be deformed under the action of lateral force.
(3) Due to the deflection and deformation of the main beam in use, the end beam will also be deformed.