7. Manipulation of Chains
Symptom
Possible Causes
Remedy
(1) Static fracture. Stretching the link plate with a tensile load beyond its breaking load will cause it to stretch and then break. Cracks in the link plates (fatigue), which are perpendicular to the direction of pull. Deformation in the link plate holes.
(2) Fatigue fracture. By repeatedly applying a load past its fatigue limit (fatigue strength), the fatigue will start at holes and then suddenly break.
(3) Offset plate fatigue. Offset plates are bent at the center, and the result- ing concentration of stress at the bend can cause a fatigue break. Avoid using offset links in high-stress applications.
Remove all large or excessively repeating loads. Otherwise, increase the size or number of chains. Replace with a new chain.
Loads are greater than allowable.
Remove the cause of the excessive load. Replace with a new chain.
Excessive load.
Corrosion stress cracks appear, usually as bow-shaped cracks in the link plate.
Install a casing to protect the chain from the environment. Consider a chain with a high resistance to corrosion stress cracks. Replace with a new chain.
The chain is being used in an acidic or alkaline environment. (This is not caused by a repetitive load.)
Figure 7.14 (ii) Link Plate (Cont.)
Symptom Breakage of pin.
Remedy Reduce shock loads by making the start-up, stopping, and other actions smoother. Remove the large repetitive load. Otherwise, increase the size or number of chains.
Possible Causes Excessively large shock load. Subject to a repetitive load greater than the fatigue limit of the pin. Corrosion.
Install a casing to protect the chain. Periodically clean and lubricate the chains.
(1) Static fracture. The type of fracture found when subjecting the chain to the break- age test. Occurs when chain is subjected to a load greater than its breakage strength.
(3) Shock-induced bending fracture. The pin is subjected to a large shock load.
(2) Fatigue fracture. Occurs when the pin is repetitively subjected to loads greater than its fatigue limit. Recheck the size of the peak load and formulate a countermea- sure.
Apin is especially susceptible to this when the surface is corroded.
Figure 7.14 (iii) Pin
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