Overhead cranes bring great efficiency, convenience, and speed to production, but due to the inherent safety risks of machinery, the influence of the on-site usage environment and frequency, malfunctions frequently occur. This paper mainly analyzes the common mechanical failures of overhead cranes to reduce the number of repairs and achieve practical benefits. The following is an analysis of common mechanical failures and problems of overhead cranes.
I. Wire Rope
1. Failure Analysis
During operation, the stress on each wire rope is very complex, as the stress varies depending on the position of each wire in the rope. Even under the simplest tensile force, the stress distribution among each wire rope is different. The main reason for wire rope breakage is overloading, and it is also related to the number of times it is wound around the sheaves and drums. Each winding of the wire rope involves a process of changing from straight to curved and then from curved to straight. The more times it is wound, the easier it is to damage and break; secondly, the breakage of the wire rope is related to the diameter of the sheaves and drums it passes over, the working environment, the type of work, and the maintenance conditions.
2. Preventive Measures
(1) During operation, the lifting weight of the crane should not exceed the rated lifting weight.
(2) The wire rope of the crane should be selected according to the type of work and the environment. Before rope making, the rope core is coated with lubricating oil to reduce the damage caused by friction between the wires. Double-wrapped ropes have better flexibility, are easy to manufacture, and are the most widely used.
(3) Regular lubrication of the wire rope is required.
(4) Avoid subjecting the wire rope to sudden impact forces during crane operation.
II. Drum and Wire Rope Pressure Plate
The drum is an important load-bearing component of the crane. During use, it may experience thinning of the drum wall, holes, and fracture failures. These failures are caused by the mutual compression and friction between the drum and the wire rope. When the drum is thinned to a certain extent, it will break due to the inability to withstand the pressure exerted by the wire rope. To prevent such mechanical accidents, according to national standards, the drum should be replaced in time when the drum wall wear reaches 20% of the original or cracks appear.
III. Gearbox Gears
1. Failure Analysis
The reducer is an important transmission component of the overhead crane. It transmits torque through gear meshing, adjusting the high-speed rotation of the motor to the required speed. During torque transmission, the gears may experience mechanical failures such as broken teeth, pitting on the tooth surface, tooth surface adhesion, and tooth surface wear. The causes of gear failure are as follows:
(1) Fatigue fracture caused by short-term overload or impact load, and repeated bending.
(2) Rough tooth surface, stress concentration caused by protrusions, or unclean lubricant.
(3) Lubrication failure due to excessive temperature.
(4) Wear caused by hard particles entering the friction surface.
(5) Preventive Measures
(6) The crane should not be used under load, and starting and braking should be slow and smooth. Reversing should be prohibited except under specific circumstances.
(7) Lubricants should be replaced promptly, the housing should be cleaned, and the appropriate type of lubricant should be selected.
(8) Regularly check the cleanliness of the lubricating oil; replace it promptly if it is found to be unclean.