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Crane in the pulley group for an important component, is also an important component of the crane lifting, its pulley group generally by the rolling bearing, pulley, pulley shaft, rolling bearing spacer, the structure to withstand radial force is better than bearing axial force. This structure in the use of rolling bearing retaining ring, support ring, spacer damage caused by the pulley can not rotate, wire rope wear serious, so that the normal construction.

Figure 1 and 2 above are the top structure of the crane and the specific installation structure of the lifting pulley respectively. Rolling bearings are installed in the pulley, using the lifting shaft to install the pulley on the upper section of the arm, the pulley and the pulley between the use of spacer to retain the appropriate gap to ensure that the work does not interfere with each other. If the bearing damage will directly affect the normal lifting of the crane, so share the common causes of damage to the crane pulley bearing and repair related methods.

Analysis of crane pulley bearing damage causes:

1. Crane overload

Crane have a load table, that is, the crane construction work must be in accordance with the load table marked load lifting heavy objects, it is strictly prohibited to exceed the load table limited data operation construction. Crane in the design are left with a safety factor, but the current domestic crane construction is generally overloaded, resulting in a relatively small safety factor reserved, or even offset the reserved safety factor. This crane local institutions may be damaged and failure, lifting heavy overload, directly causing the lifting pulley parts shaft bearing force increases, close to or beyond the range of forces, which is the most direct cause of bearing damage.

2. Pulley quality problem

Crane lifting pulley directly wrapped wire rope, wire rope to bear the weight of the object hanging all, so the weight of the object through the wire rope and pulley directly to the bearing. Lifting pulley set is composed of a pulley, two bearings, two bearings installed in the left and right sides of the lifting pulley, if the center of the pulley rope groove and the center of the pulley itself is not in the same plane, see Figure pulley analysis Figure 3. gravity will not be uniformly distributed in the two bearings, a small, or even a single pulley on the gravity is completely borne by a bearing, at this time the bearing to bear a large axial force. Due to the structure of the bearing itself determines its ability to withstand radial forces is much greater than its ability to withstand axial forces, so under the action of axial forces, bearing retaining ring is easy to destroy, and then bearing ball support frame damage, resulting in bearing can not rotate, wire rope, pulley wear and other problems, and ultimately the crane can not work properly.

3. The crane construction of heavy objects in the air is not stable, there is shaking

Due to the existence of shaking will also lead to uneven bearing force on the shaft, if the pulley is still rotating movement, bearing retaining ring bearing force significantly increased, in this case construction, bearing retaining ring is very easy to damage, resulting in ball left and right save, and then bearing retaining ring completely damaged, and ultimately damaged the entire bearing, affecting construction.

4. The crane design process

In the design of the pulley and the selection of bearings, must be based on the load, construction conditions and other circumstances, consider and set aside a safety factor. If you choose a small safety factor or a large error in the calculation of the load, resulting in a small calculation of the gravitational force borne by a single pulley will cause the choice of bearing is not appropriate, the bearing force can not meet the actual work needs. In addition, unfamiliar with the working conditions, only consider the static load work load does not test the impact load, will also cause the selected bearing does not meet the actual work needs, resulting in easy damage to the bearing, short service life. If the selection of the parameters are small bearings, even if there is no overload, pulley quality is not qualified, heavy lifting instability three situations, the bearing will be prematurely damaged.

Repair method

Construction machinery construction is generally about timeliness, time is benefit, cranes as a special mechanical equipment, in order to construction process continuous  uninterrupted, must be analyzed for the above situation to solve the problem of premature damage, after analysis, I crane lifting parts structure for some repair.

1.increase the overload limiting device: according to the load table to calculate the maximum bearing capacity, when the bearing bearing load force equal to the rated force to issue an alarm, prompting the operator. When the bearing bearing load force exceeds the rated load or exceed the safety factor, the crane action is locked under the action of the safety device, forcing the construction personnel to work in accordance with the crane load table, which in turn reduces the force on the bearing and plays a role in protecting the bearing and extending the service life of the bearing.

2.change the pulley structure, increase the thickness of the pulley, replace the bearing: pulley repair before the structure size thickness of 61.5mm, supporting the installation of bearing model GB/T276-19946217-Z. Bearing width of 28, after repair pulley size for the thickness of 83mm, supporting the installation of bearing model GB/T283-19942217EM, bearing width of 36.

GB/T276-19946217-Z deep groove ball bearing basic load rating Cr=83.2kN, Cor=63.8kN. GB/T283-19942217EM reinforced cylindrical roller bearing basic load rating Cr=205kN, Cor=272kN. As can be seen from the table, the basic dynamic load and static load have been greatly improved. The change of the bearing from deep groove ball to cylindrical roller type and the increase of the thickness B of the pulley have greatly improved the axial force that the bearing can withstand. In addition, NJ2217EM reinforced bearing has brass solid cage inside, and the retaining ring is not easily damaged. After repairing the actual application verification, the bearing service life is significantly extended.

3.Strictly control the quality of the pulley: repair the production process of the pulley and strictly control the inspection procedure of the pulley into the factory, control the center of the rope groove of the pulley and the flatness of the center of the pulley to meet the design requirements, in order to eliminate the phenomenon of bearing damage caused by the pulley.

4.Increase the pulley group without affecting the construction efficiency: increase the upper end of the pulley group, which can increase the pulley multiplier, thus can reduce the force on the single pulley and bearing. Due to the reduced force can improve the safety factor of the bearing, reduce the probability of damage and improve the service life.

5.Training users in accordance with the requirements of the equipment manual construction, strictly prohibit overload, in the process of lifting and lowering the weight to maintain the stability of the weight, to avoid the weight shaking resulting in uneven bearing force, axial force increases and damage. After the above method of repair, in the actual application of bearing damage phenomenon, basically eliminated. It proves that it is feasible to change the pulley structure, replace the bearing type and increase the overload limiting device.