After a long time of use, the chain will fail. What are the detailed ways?
1. Wear failure
In the open drive or the chain with the lowest quality and poor material, wear is often the main failure mode of the chain drive. After the chain is worn, the chain link and the total length of the chain elongate. When engaging, the meshing point moves along the working edge of the tooth profile to the top of the tooth, resulting in tooth skipping or chain disengagement. Wear mainly occurs in the outer link. When the pin shaft and the outer surface of the sleeve inner block are worn, the hinge clearance increases, so that the outer chain link is extended. The pitch of the inner chain link depends on the busbar on the same side of the adjacent rollers. Since the outer and outer surfaces of the rollers and the sleeves are rarely worn, the inner chain link can hardly stretch. When the wear elongation of the chain reaches 3%, the chain will lose its effectiveness due to chain breaking, and the elongation of the outer chain link can reach 6% In order to improve the wear life of the chain, it is necessary to pay full attention to the smoothness and limit the effective circumferential force to the allowable working load.
2. Fatigue failure
Chains with good smooth conditions and wear resistance are often destroyed due to fatigue. Because the chain has tight edges and loose edges, the chain parts are subject to alternating loads. During each rotation of the chain link, the stress state of the chain plate is tension and bending, the stress state of the pin shaft is shear, extrusion and bending, the roller is subjected to extrusion and impact, and the sleeve is subjected to extrusion, shear and impact. Under the action of alternating load, the part produces cracks, — crack propagation, leading to fatigue fracture. The number of chain impacts can be regarded as the number of stress cycles of chain parts. In practical calculation, each rotation of the chain usually only considers the impact of the hinge when it is engaged, so the number of revolutions per minute of the chain is regarded as the number of impacts per minute.
In order to improve the fatigue strength of the chain, the manufacturer has adopted various methods to strengthen the parts, such as using chemical heat treatment to carburize the surface of the parts, using the chain plate to squeeze holes to resist stress concentration, widening the waist width of the chain plate to ease the stress concentration of the holes, and stopping shot blasting for the parts.
3. Destruction of connection strength
During the use of the chain, under the working load, the connection between the outer chain plate and the pin shaft and the connection between the inner chain plate and the sleeve is loose, so that the chain plate eyelet is worn, and the chain is rapidly extended and invalid. The chain will become invalid due to the looseness of the riveted part at the head of the chain pin shaft, the chain plate coming out, or the chain link loose frame formed by the shearing of the tooth opening pin and the flying off of the circlip.
4. Chain gluing
When the running speed of the chain is too high and the chain is not smooth, the pin shaft and sleeve are scratched, stuck and cannot be used.
5. Static tensile fracture
In case of low speed and heavy load, the load peak exceeds the allowable breaking load, causing the chain to break.
6. Others
Chain failure may be caused by repeated starting of chain, multiple breaking caused by braking, positive and negative rotation, thinning of chain plate due to side wear, or wear and plastic deformation of chain gear teeth, and different surfaces of chain wheel device.
The above six points are common failure modes of chains.
