Several Common Failure Forms of Chains

Chains are essential components in various mechanical systems, but after prolonged use, they can fail in several ways. Understanding these failure modes is crucial for maintenance and prevention. Here are six common failure forms of chains:

1. Wear Failure: Typically, wear is the main failure mode in chain transmissions, particularly in open transmissions or with low-quality chains made from inferior materials. As the chain wears, the links elongate, causing the meshing point to shift towards the tooth top along the tooth profile’s working edge, potentially leading to tooth jumping or chain detachment. Wear usually affects the outer chain links most severely, as the outer surface of the pin shaft and the inner surface of the sleeve wear out, increasing the hinge clearance and causing elongation. Interestingly, the inner chain links elongate less due to minimal wear on the rollers’ outer and inner surfaces. Chain failure often occurs when elongation reaches 3%, although the outer link can elongate up to 6%. Enhancing the chain’s smoothness and keeping the effective circumferential force within permissible limits can significantly improve wear life.
2. Fatigue Failure: Even chains that are well-lubricated and wear-resistant can succumb to fatigue failure. This is due to alternating loads on the chain’s components, where chain plates undergo tension and bending, pin shafts experience shear, compression, and bending, and rollers and sleeves are subject to compression, shear, and impact. These alternating loads can initiate cracks that propagate and lead to fatigue fractures. Manufacturers often adopt methods like carburizing the surface of parts or using extrusion holes on the chain plate to improve fatigue strength.
3. Destruction of Connection Strength: Over time, the connections between the outer chain plates and pin shafts, as well as between inner chain plates and sleeves, may loosen under working loads. This loosening leads to rapid wear and elongation of the chain plate holes, resulting in chain failure. Other issues such as loose riveting at the chain pin shaft head, detachment of chain plates, or scattered chain links due to severed toothed pins or ejected snap springs also contribute to this failure mode.
4. Chain Bonding: High running speeds combined with poor lubrication can lead to the pin shaft and sleeve getting scratched and stuck, rendering the chain unusable.
5. Static Tensile Fracture: When chains operate under low speeds and heavy loads, the peak load may exceed the chain’s allowable breaking load, causing it to snap.
6. Other Causes: Various other factors can lead to chain failure, including repeated starts, multiple breaks due to braking, forward and reverse rotations, side wear thinning of the chain plate, wear and plastic deformation of sprocket teeth, and inconsistencies in the sprocket device’s surface.

By recognizing these failure modes, you can better maintain your chains and extend their operational lifespan.