1. Foreword
This paper analyzes seven aspects of the bridge crane that can cause mechanical failure, such as wire rope, drum and wire rope pressure plate, hook, reducer gear, brake, wheel and rail and safety accessories, and puts forward measures and suggestions to prevent the mechanical failure of the crane.
Bridge crane in the enterprise production process to bring efficient, convenient, fast at the same time, because of mechanical insecurity, frequent accidents, to the country, the people caused economic losses, to the parties and their families caused pain. The main cause of the accident is the mechanical failure and misoperation of the machine itself. Study of mechanical failure, analysis of the causes, the development of preventive measures are the main measures to reduce the bridge crane mechanical accidents, which requires special equipment management personnel in the operation of the operator at the same time, pay attention to the hidden dangers of crane mechanical failure, according to the crane situation to develop a careful and feasible preventive measures to ensure the safe operation of the crane. Through the production practice, the mechanical failure and preventive measures of the bridge crane in the operation process are analyzed as follows.

2. wire rope
1 Fault analysis
During the operation of the wire rope, the force of each wire rope is very complicated, because the position of each wire in the rope is different, some are in the outer layer, and some are in the inner layer. Even by the most simple tensile force, the force distribution between each wire rope is also different, in addition to the wire rope around the coil, pulley bending stress, steel wire and steel wire between the extrusion force, so accurate calculation of its force is more difficult, generally using static calculation method.
The maximum static tension in the wire rope shall meet the following requirements:
Pmax≤pd/n
In the formula: Pmax-the maximum static stress that the wire rope can withstand during operation;
Pd -- Breaking stress of wire rope;
N-safety factor.
Pmax=(Q q)/(ah)
Where: Q-rated lifting weight of crane;
Q -- Weight of image hanging group;
a -- Total number of rope branches carried by the pulley block;
η-Total efficiency of the pulley block.
The calculation formula of the maximum allowable working tension of the wire rope is:
P=Pd/n 
Where: P-maximum rated static stress of wire rope during operation
P≥ Pmax is safe. From this, it can be seen that the main reason for wire rope breakage is overload, and it is also related to the number of winding times on pulleys and drums. Each time the wire rope is wound, the process of bending from straight to straight will occur. The more winding times, the easier it will be to damage and break. Secondly, the breakage of wire rope is related to the diameter, working environment, working type and maintenance of pulley and drum.
2 Preventive measures
The lifting weight of the 2.1 crane during operation shall not exceed the rated lifting weight.
The wire rope of the 2.2 crane should be selected according to the type of work and the environment.
2.3, the wire rope should be lubricated regularly (the lubrication cycle is determined according to the working environment).
2.4 the crane in the operation do not make the wire rope by sudden impact.
The wire rope 2.5 in the environment of high temperature and corrosive medium must have isolation device.

3. drum and wire rope pressing plate
The drum is an important force component of the crane, and there will be thinning of the barrel wall, holes and fracture faults during use. The reason for these failures is that the drum and the wire rope are in contact with each other, squeezing and rubbing. 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 occurrence of such mechanical accidents, according to national standards, the drum wall wear reaches 20% of the original or cracks should be replaced in time. At the same time, attention should be paid to the sanitation of the operating environment and the lubrication of the drum and wire rope.

4. hook
The hook is the bridge crane with the most fetching device, it bears the lifting of all the load, in the use of the process, the hook once damaged fracture easily cause major accidents. The reason for the damage and fracture of the hook is that the hook has cracks, deformation, damage and fracture due to friction and overload. In order to prevent the hook from malfunctioning, overload lifting is strictly prohibited during use. In the inspection process, attention should be paid to the opening degree of the hook and the wear of the dangerous section. At the same time, the hook should be annealed regularly. Once cracks are found, the hook should be scrapped according to the GB10051-88, and the hook should not be welded and patched. The special equipment management personnel shall check the hook according to the requirements of the GB10051-88 to determine whether the hook can be used.

5. reducer gear
1 Fault analysis
The reducer is an important transmission component of the bridge crane. The torque is transmitted through gear meshing, and the high-speed operation of the motor is adjusted to the required speed. In the process of transmitting torque, the gear will have gear teeth broken, tooth surface pitting, and tooth surface glue., Tooth surface wear and other mechanical failures, the causes of gear failure are as follows:
A. short time overload or impact load, repeated bending caused by fatigue fracture;
B. The tooth surface is not smooth, there is a convex point of stress concentration, or the lubricant is not clean;
C. due to high temperature caused by lubrication failure;
d. Wear due to hard particles entering the friction surface.
2 Preventive measures
a. The crane shall not be used for loading, and the starting and braking shall be slow and stable. It is forbidden to reverse the crane suddenly under non-specific conditions;
B. Replace the lubricant in time, clean the shell, and select the appropriate type of lubricant;
c. Always check whether the lubricating oil is clean; if the lubrication is not clean, replace it in time.

6. brake
1 Fault analysis
Brake is an important safety component of bridge crane. It has the functions of preventing suspension objects from falling and parking. Only intact brake can guarantee the accuracy and safe production of crane operation. In crane operation, the brake will have mechanical faults such as insufficient braking force, sudden failure of brake, excessive brake wheel temperature, smoke of brake pad, and failure of brake arm. The causes of these mechanical failures are analyzed as follows:
a. The brake belt or brake wheel is worn too much; the brake has small parts and falls off; the main spring is adjusted too loosely; there is grease between the brake belt and the brake wheel; there is a stuck place outside the living hinge or There are parts with excessive wear; the lock nut is loose and the whole pull rod is loose; the impeller of the hydraulic push rod loosening brake is not flexible;
B. The brake pads are severely or large parts fall off, or the long-stroke electromagnet is stuck, the main spring fails, or the main parts of the brake are damaged;
C. the gap between the brake and the gasket is too large or too small;
d. The hinge is stuck or the braking torque is too large, or the hydraulic push rod looser cylinder is short of oil and mixed with air, or the grease used in the hydraulic push rod looser does not meet the requirements, or the brake There is dirt between the pad and the brake wheel.
2 Preventive measures
Check and maintain the brake regularly. The brake of the lifting mechanism must be once per shift, and the brake of the operating mechanism must be once a day. The main contents are as follows:
a. Whether the hinge is stuck and worn, and whether each fastening part is loose;
B. Whether the movement of each moving part is normal;
c. Whether the hydraulic system is normal;
d. Whether the wear between the brake wheel and the brake belt is normal and clean.
According to the inspection to determine whether the brake is normal, resolutely put an end to the operation of the disease, while the brake to regular lubrication and maintenance. 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.

7. wheel and track
The common faults of the wheel and track in the operation of the crane are the gnawing of the wheel and the unequal height and skidding of the trolley. Among them, there are many reasons for gnawing, and the forms of gnawing are diverse. The life of the crane is affected by the light gnawing road, and the heavy one will cause serious casualties. Therefore, the management personnel of special equipment should pay enough attention to the gnawing road. The main reason for gnawing the road is that the braking is not synchronized due to the non-conforming error, uneven friction, excessive wear of parts in the cart transmission system and excessive key connection clearance during installation. Therefore, the competent department of special equipment of each unit must find a qualified unit for installation and maintenance when installing and maintaining the crane, so as to ensure the safety and operation life of the equipment; at the same time, the management personnel of special equipment should strengthen the inspection and management at ordinary times to avoid the mechanical failure of the crane gnawing road. In the process of inspection, the cause of gnawing road should be carefully and carefully found out, and corresponding measures should be taken. The unequal height of the trolley wheels is a very unsafe factor in the operation of the crane. The unequal height of the trolley makes a wheel hanging or the wheel pressure is too small during the operation of the trolley 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. Therefore, the failure of the unequal height of the trolley should be comprehensively analyzed and the problem of the unequal height of the trolley should be solved.
During the operation of the crane, the trolley produces a slip ring image due to the unclean track, excessive starting, uneven track of the trolley, elliptical wheels and unequal wheel pressures between the driving wheels. This requires the management personnel of special equipment to be careful in the inspection process and solve the problems found in time to avoid the skid of the trolley.

8. safety accessories
The safety accessories of the bridge crane are completely set up from the perspective of the protection equipment and the operator. The management of the safety accessories must be in accordance with the requirements of the "Special Equipment Safety Supervision Regulations" to strengthen the management and supervision of the safety accessories, so that The safety accessories are in good condition to ensure the safe operation of the bridge crane.
Bridge crane mechanical failure is more complex, the prevention of mechanical failure needs to strengthen equipment management, at the same time to the local special equipment management and supervision department on time to apply for annual examination, through the special equipment supervision department inspection guidance, the equipment of unsafe factors in the bud, so as to ensure the safety of equipment and personnel.