After prolonged use, the chain may experience some failures. What are the specific ways?

1. Wear failure

Wear is often the main failure mode of chain transmission in open transmission or for chains with the lowest quality and poor material. After the chain is worn out, the chain links and the total length of the chain elongate. When meshing, the meshing point moves towards the tooth top along the working edge of the tooth profile, ultimately causing tooth jumping or chain detachment. Wear mainly occurs in the outer chain links. When the outer surface of the pin shaft and sleeve inner ball wears out, the hinge clearance increases, thus causing the outer chain link to elongate. The pitch of the inner chain link depends on the same side busbar of adjacent rollers. Due to the minimal wear on the outer surface of the inner and outer circles of the rollers and the sleeve, the inner chain link will hardly elongate. When the elongation of chain wear reaches 3%, the chain will fail due to chain detachment, and the elongation rate of the outer link can reach 6%. In order to improve the wear life of the chain, it is necessary to pay sufficient attention to smoothness and limit the effective circumferential force within the allowable working load range.

2. Fatigue failure

Chains with good smoothness and wear resistance often fail due to fatigue damage. Due to the presence of tight and loose edges in the chain, the chain components are subjected to alternating loads of varying sizes. In each rotation of the chain link, the force state of the chain plate is tension and bending, the force state of the pin shaft is shear, compression and bending, the roller is subjected to compression and impact, and the sleeve is subjected to compression, shear and impact. Cracks occur in parts under alternating loads, leading to fatigue fracture due to crack propagation. The number of chain impacts can be regarded as the number of stress cycles of chain components. In practical calculations, during each rotation of the chain, only the impact of the hinge during meshing is often considered, so the number of revolutions per minute of the chain is considered as the number of impacts per minute.

In order to improve the fatigue strength of the chain, the manufacturing plant has adopted various methods to strengthen the parts, such as using chemical heat treatment to carburize the surface of the parts, using extrusion holes on the chain plate to resist stress concentration, widening the waist width of the chain plate to alleviate stress concentration in the holes, and stopping shot peening of the parts.

3. Destruction of connection strength

During the use of the chain, under the action of working load, the connection between the outer chain plate and the pin shaft, as well as the connection between the inner chain plate and the sleeve, becomes loose, resulting in wear of the chain plate hole and rapid elongation and failure of the chain. Due to the loosening of the riveting part at the head of the chain pin shaft, the detachment of the chain plate, or the scattering of chain links caused by the cutting of the toothed pin or the flying of the snap spring, the chain will fail.

4. Chain bonding

When the running speed of the chain is too high and the smoothness is poor, the pin shaft and sleeve are scratched, stuck and cannot be used.

5. Static tensile fracture

At low speeds and heavy loads, the load peak exceeds the allowable breaking load, causing the chain to break.

6. Other

Repeated starting of the chain, multiple breakages caused by braking, forward and reverse rotation, thinning of the chain plate due to side wear, wear and plastic deformation of the sprocket teeth, and different surfaces of the sprocket device may all lead to chain failure.

The above 6 points are common failure modes of chains.