The operating factors are overloaded. During the operation of the belt conveyor, the actual load exceeds the rated load of the main drive roller, causing the connecting bolt to be cut. The bolts are loose. The impact and vibration of the belt conveyor during operation make the connecting bolt gradually loose. Due to the limitations of the structure of the belt conveyor, the loose bolt cannot be tightened in time and is cut off during operation.
The pre-tightening force of the connecting bolt is small. During installation, the pre-tightening force of the connecting bolt does not meet the technical requirements, so that the torque transmitted by the main drive roller is less than the rated torque, and the bolt is cut during operation.
Manufacturing factors During the manufacturing process, the connecting bolts are cut off during use due to the poor machining of the components.
(1) The barrel processing is super poor. There are three main aspects in the processing of the barrel that causes the connecting bolt to be cut: the full end of the web end is out of tolerance; the web spacing is out of tolerance; the end surface roughness of the web is not satisfactory.
If the full runout of the web end face is too large, the joint surface of the flange end face and the web is small or only partially close after assembly; if the gap between the webs is too large, there is a gap between the flange and the web after assembly. Or the drum has axial sway; the surface roughness is too large or too small, reducing the friction between the web and the flange end face.
(2) Flange processing is super poor. There are three main aspects that affect the normal operation of the flange of the drum: the verticality of the end face of the flange is out of tolerance; the dimension of the inner end to the small end face is B-poor; the end face roughness does not meet the requirements. The cause of the failure of the cutting bolt caused by the excessive machining of the flange is the same as that of the barrel machining.
(3) The shaft machining is out of tolerance. The shaft machining tolerance is mainly referred to as the shoulder size C. If the shoulder size is too large or too small, it will cause axial sway or gap between the inner end surface of the flange and the end surface of the web.
Remedy In the inspection of the cut-off bolt drum, some simple measures are taken to remove the bolt and reassemble. However, this method sometimes does not really solve the fault. During the overhaul, the fault drum should be thoroughly and carefully tested to find out all the unsafe factors that may cause the bolt failure again, and the corresponding repair measures should be made.
After the failure of the cutting bolt of the drum, it is impossible to stop the operation immediately due to the mechanical failure. The flange end faces of the drum web will have different degrees of scratches, wear and deformation. After the actual inspection, if dimensional tolerance, shape tolerance, and surface roughness are found. The degree cannot meet the assembly requirements and the parts of the drum should be reworked. Dimensional tolerances and geometrical tolerances shall be determined according to the size of the drum, and the surface roughness shall be 63/ or 32/.
In the overhaul, the strength check of the joint screw inspection should also be carried out according to the actual load. If the safety factor of the original connecting bolt is found to be low, bolts with larger specifications or higher strength may be used. For the drive roller that is subjected to shock vibration and can not be tightened frequently, the method of using the elastic pad to prevent loosening is anti-loose but unreliable. It is recommended to use a retaining washer to prevent loosening or a thread-locking agent to prevent loosening.
Conclusion By adopting the above-mentioned method for the main drive roller, the probability of re-cutting bolt failure in normal production is significantly reduced, and the inspection time and maintenance cost are also significantly reduced.
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