When the crane is working, the pulley working system of the crane plays a very important role. The winding steel wire rope can rotate to transmit the tension, and can change the direction of the tension, and can achieve the purpose of labor saving. If the pulley of the crane fails, the wire rope will fall out of the groove or slide, which will cause serious consequences. Therefore, the failure analysis of crane pulley is of great significance in safety and economy.
In the working process of crane, the working system of crane pulley bears the tensile force from the steel wire rope. After working for a period of time, it will produce fatigue wear, which is contact fatigue. When two contact bodies slide or roll relatively, the cyclic stress formed in the contact area exceeds the fatigue strength of the material, cracks appear and continue to expand, resulting in the process of wear. And wear is the main reason of crane pulley failure.
After a certain degree of pulley indentation, the problem of pulley indentation failure will occur. The main reasons include:
(1) During the long-term use of the crane pulley, the indentation of the pulley will initiate cracks, and the gap will gradually expand. The plastic deformation of the pulley groove occurs under the reciprocating action of tensile force, leaving marks on the surface of the pulley groove and forming a deep slip band in the groove.
(2) The mechanism of cyclic wear on the surface of pulley groove. When the crane lifts an object, the object will shake slightly, and the wire rope and pulley will swing to a certain extent, resulting in friction and wear of the wheel groove. When the crane moves laterally, it will aggravate the degree of wear.
In addition to the bending stress caused by the movement on the pulley, the wire rope also bears the radial pressure caused by its contact with the pulley. This pressure will cause shear stress in the wire rope, change the structure of the wire rope, and affect the wear rate of the pulley groove. Therefore, the pressure and the anti-wear property of pulley material should be considered when selecting the appropriate wire rope structure, such as hot rolling pulley with better quality.
Failure analysis and preventive measures of crane pulley
(1) Corrosion is also a common factor of crane pulley failure. In some complex working environment, corrosion atmosphere often appears, which has a great impact on the life of crane pulley.
(2) Overload in use will make the instantaneous force on the crane pulley seriously exceed its bearing range, which is very easy to cause failure and damage.
(3) If the crane pulley is at too high or too low temperature, it will reduce its wear resistance and become more brittle.
The impact load is an important reason for the indentation of wheel groove. In the process of lifting and transportation, the contact stress caused by acceleration or lifting is (1 ~ 2) times of the uniform stress, so it is very important to study the wire rope winding system. In the process of practical application, the acceleration should be properly controlled to reduce the impact load on the pulley and the friction coefficient between the wire rope and the groove.
By analyzing the operation principle of the wire rope and pulley in the working process of the crane, it can be concluded that the indentation of the pulley is mainly because the main stress point of the pulley block is concentrated at the bottom of the pulley groove. When the spreader lifts heavy objects, due to the influence of shaking and other factors, the alternating friction of the wire rope will produce fatigue wear on the pulley groove and produce obvious indentation at the bottom of the pulley, When crack propagation and fracture occur, there will be serious consequences. Therefore, according to the surface area, the liner matched with the diameter of the wire rope can be installed to strengthen the contact stress between the wire rope and the pulley and reduce the friction between the wire rope and the pulley groove.
The long-time working of lifting machinery will inevitably cause wear between the wire rope and the pulley groove of the crane. The impurities produced by the surface wear of the pulley groove will be mixed into the grease, which will increase the resistance between the wire rope and the pulley groove and aggravate the degree of wear. Therefore, grease should be replaced in time to reduce wear consumption.
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