Bridge Crane Common Fault Analysis

Introduction  

The bridge crane is analyzed from seven aspects that can cause mechanical failure, such as steel wire rope, drum and steel wire rope pressure plate, hook, reducer gear, brake, wheel and track, and safety accessories, and puts forward measures to prevent mechanical failure of the crane and suggestions.

Hook

The hook is the most frequently used pick-up device for bridge cranes. It bears all the loads for hoisting. During use, once the hook is damaged and broken, it will easily cause major accidents. The reason for the damage and fracture of the hook is that the hook is cracked, deformed, damaged, and broken due to friction and overload. In order to prevent the failure of the hook, it is strictly forbidden to overload the lifting during use. During the inspection process, attention should be paid to the hook’s opening and the dangerous section’s wear. At the same time, the hook should be annealed regularly. If cracks are found, it should be scrapped according to GB10051-88, and the hook should not be repaired by welding. The inspection of the hook by the special equipment management personnel shall judge whether the hook can be used according to the requirements of GB10051-88.

Steel wire rope

Failure analysis

During the operation of the steel wire rope, the stress of each steel wire rope is very complicated, because the position of each steel wire in the rope is different; some are in the outer layer, and some are in the inner layer. Even under the simplest tensile force, the force distribution between each steel wire rope is different. In addition, when the steel wire rope goes around the coil and pulley, bending stress, extrusion force between steel wires, etc. are generated, so the force is accurately calculated. It is more difficult, and the static calculation method is generally used.

The maximum static tension in the wire rope should meet the following requirements:

     Pmax≤Pd/n

In the formula above: Pmax - the maximum static stress that the wire rope can bear during operation; Pd - the breaking stress of the wire rope; n - safety factor.

     Pmax=(Q+q)/(aη)

In the formula above : Q - the rated lifting capacity of the crane; q - the weight of the hook group; a - the total number of rope branches carried by the pulley block;η- the total efficiency of the pulley block.

The formula for calculating the maximum allowable working tension of the wire rope is:

     P=Pd/n

In the formula above: P - the rated maximum static stress of the wire rope during operation.

P≥Pmax is safe. It can be seen from this that the main reason for the breakage of the wire rope is overload, and it is also related to the number of windings on the pulley and drum. Every time the wire rope is wound, it will change from straight to curved and then from curved to straight. The greater the number of windings It is easily damaged and broken; secondly, the breakage of the wire rope is related to the diameter of the pulley, the drum, the working environment, the type of work, and the maintenance situation.

Precautions

• The lifting capacity of the crane should not exceed the rated lifting capacity during operation.

• The steel wire rope of the crane should be selected according to the type of work and the environment.

• The steel wire rope should be lubricated regularly (determine the lubrication period according to the working environment).

• Do not subject the wire rope to sudden impact when the crane is in operation.

• The steel wire rope in the environment of high temperature and corrosive medium must have an isolation device.

 Reducer gear

Failure analysis

The reducer is an important transmission part of the bridge crane. The torque is transmitted through the meshing of the gears, and the high-speed operation of the motor is adjusted to the required speed. Mechanical failures such as wear and tooth surface wear, the causes of gear failures are as follows:

• Fatigue fracture caused by short-term overload or impact load, repeated bending.

• The tooth surface is not smooth, there are raised points to generate stress concentration, or the lubricant is not clean.

• Lubrication failure due to excessive temperature.

• Wear is caused by hard particles entering the friction surface.

Precautions

• The crane cannot be used for loading, and the start and brake should be slow and stable. It is forbidden to reverse the car suddenly under non-specific circumstances.

• The lubricant should be replaced in time, and the shell should be cleaned, and the appropriate type of lubricant should be selected at the same time.

•  Always check whether the lubricating oil is clean; if the lubricating oil is not clean, replace it in time.

Reel and wire rope pressing plate

The reel is an important stress-bearing part of the crane, and the drum wall will be thinned, holes and fractures will occur during use. The cause of these failures is that the drum and the wire rope are in contact with each other and rub against each other. When the drum is thinned to a certain extent, it breaks because it cannot withstand the pressure exerted by the wire rope. In order to prevent the mechanical accident of the reel, according to the national standard, the wall of the reel should be replaced in time when the wear of the wall reaches 20% of the original or cracks appear. At the same time, pay attention to the sanitation of the operating environment and the lubrication of the reel and wire rope.

Brake

Failure Analysis

The brake is an important safety component of the bridge crane. It has the functions of preventing the hanging objects from falling and realizing parking. Only a good brake can guarantee the accuracy and safe production of the crane. During the operation of the crane, the brake will have insufficient braking force, The brake suddenly fails, the temperature of the brake wheel is too high, the brake pad smokes, the brake arm cannot be opened and other mechanical failures. The reasons for these mechanical failures are analyzed as follows:

• Excessive wear of the brake belt or brake wheel; small parts of the brake belt fall off; the main spring is adjusted too loosely; there is grease between the brake belt and the brake wheel; there is a stuck place or wear outside the living hinge Parts that are too large; the lock nut is loose and the whole tie rod is loose; the impeller of the hydraulic push rod brake release device does not rotate flexibly.

• The brake pads are severe or large pieces fall off, or the long-stroke electromagnet is stuck, the main spring fails, or the main parts of the brake are damaged.

• The gap between the brake and the gasket is adjusted too large or too small.

• The hinge is stuck or the braking torque is adjusted too large, or the cylinder of the hydraulic push rod brake release is short of oil and mixed with air, or the grease used for the hydraulic push rod release does not meet the requirements, or the brake pads and brake There is dirt between the drive wheels.

Precautions

Regularly inspect and maintain the brakes. The brakes of the lifting mechanism must be once a shift, and the brakes of the operating mechanism must be once a day. The main inspections are as follows:

• Whether there is stagnation and wear at the hinge, and whether there is any looseness at each fastening point.

• Whether the action of each movable part is normal.

• Whether the hydraulic system is normal.

• Whether the wear between the brake wheel and the brake band is normal and whether it is clean.

Determine whether the brake is normal according to the inspection situation, resolutely put an end to running with a disease, and at the same time lubricate and maintain the brake regularly. In order to ensure the safe operation of the crane, the brake must be adjusted frequently to ensure the working requirements of the corresponding mechanism.

Wheels and tracks

During the operation of the crane, the common faults of the wheel and the track are the gnawing of the wheel and the unequal height and slipping of the trolley. Among them, there are many reasons for gnawing, and the forms of gnawing are various. If the gnawing road is light, it will affect the life of the crane, and if it is heavy, it will cause serious casualties. Therefore, special equipment managers should pay enough attention to the gnawing road. The main reason for the gnawing road is that the installation does not meet the required error, uneven friction, excessive wear of parts in the transmission system of the cart, and excessive key connection clearance, resulting in asynchronous braking. Therefore, the special equipment authorities of each unit must find qualified units for installation and maintenance when installing and maintaining cranes, so as to ensure equipment safety and operating life; at the same time, special equipment management personnel must strengthen the usual inspection and management to avoid cranes. During the inspection process, it is necessary to carefully and carefully find out the cause of the road gnawing, and take corresponding measures. The unequal height of the wheels of the trolley is an extremely unsafe factor in the operation of the crane. The unequal height of the trolley makes one wheel suspended in the air or the wheel pressure is too small during the operation of the trolley, which may cause the vibration of the trolley body. The factors causing the unequal height of the trolley wheels are caused by many reasons, but the main reason is that the installation error does not meet the requirements and the weight of the trolley design itself is uneven. High problem solved.

During the operation of the crane, due to the unclean track, excessive starting, uneven track of the trolley, ellipse of the wheels, and unequal wheel pressure between the driving wheels, the trolley has a slipping ring phenomenon, which requires special equipment management personnel to check during the inspection process. You must be careful and careful during the operation, and solve the problems in time to avoid the phenomenon of trolley slipping.

Safety accessories

The safety accessories of bridge cranes are completely protective devices set up from the perspective of protecting equipment and operators. The management of safety accessories must follow the requirements of the "Special Equipment Safety Supervision Regulations" to strengthen the management and supervision of safety accessories to ensure safety. The accessories are in good condition to ensure the safe operation of the overhead crane.

The mechanical failure of bridge cranes is relatively complicated. To prevent mechanical failure, it is necessary to strengthen equipment management. At the same time, it is necessary to submit an annual review application to the local special equipment management and supervision department on time, and eliminate the unsafe factors of the equipment through the inspection and guidance of the special equipment supervision department. In the bud, so as to ensure the safety of equipment and personnel.

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