Handling Conveyor Chain / Sprocket Maintenance and Inspection
Guideline for Replacement
Chain components wear as they are used, and the degree of wear can be used as a guideline for when to replace a chain.
(1) Link Plate Wear
The undersides of link plates are worn down by contact with the load and casing. Wear is also caused by contact between inner and outer link plates, and between the inner face of the inner links and the sides of the rollers.
|When the chain is subjected to lateral loads.|
|When the link touches the guide rail.|
(2) Pin and Bush Wear
Chains flex where they mesh with sprockets, causing sliding wear between pins and bushings, which leads to pitch extension.
|Component||Guideline for replacement
For carburized materials
|Guideline for replacement
For hardened or tempered materials
|There is a risk of pin fracture when its cross-sectional area has fallen to half.|
|When wear of the inner diameter has reached 0.025b.|
(3) Roller Wear
R type and F type rollers suffer increasing frictional resistance against the link plates and rails as their wear increases, increasing chain tension. That situation should be the guideline for replacement.
For S type rollers, the limit of use is reached when the roller becomes pitted or cracked.
(4) Chain Pitch Extension
With long-term use, wear to chain pins and bushes causes the chain to lengthen, so that it runs poorly on the sprockets. Therefore, the guideline for replacement is when pitch extension reaches 2~3% of the standard dimension.
Measure chain length across four or more links, as shown in the diagram on the right.
(5) Sprocket Wear
As sprocket wear progresses, it reaches the state shown in the diagram on the right, which causes the chain rollers to catch in area (A), so that it tends to wind around the roller (chain separates poorly from the sprocket). Wear at the base of the tooth varies with the size and speed of the chain, but the sprocket should be replaced or repaired when wear reaches 3~10㎜.
Inspection of Conveyor Chains and Sprockets
(1) Running Inspection
- Are the chains and sprockets attached correctly ?
- Are the T pins etc. correctly attached at chain joints ? (Note the degree of pin bending).
- Is chain take up tension appropriate ? (Is the chain too slack or too tight ?).
- Are there any foreign bodies that impede the motion of the chain ?
- Is the chain properly oiled ?
- Does the chain make any abnormal sound (vibration, noise, etc.) when it moves ?
(2) Daily Inspection
- Is there any abnormal vibration or noise ?
- Is the chain visibly corroded, dirty etc. ?
- Are there any abnormalities in the chain components ? (Particularly damage, deformation, uneven wear, breakage etc. of link plates and rollers).
- Do the chains and sprockets mesh smoothly ?
- Does the chain flex and the rollers roll smoothly ?
- Is there any wear extension in the chain ?
- Is there any abnormally uneven wear at points of contact between the chains and sprockets (inner faces of inner plates, sides of sprockets) ?
- Is chain tension appropriate ?
- Is the chain oiled appropriately ? (Is meshing with sprockets noisy ?)
(3) Regular Inspection
- Carry out visual and measurement inspections as described in (1) and (2) above while the chain is running, at rest and removed.
- Regular inspection should be tailored to the environment and conditions of use. Increase the frequency of inspection when conditions are harsh.