Calibration chains, also called test chains, are made from carbon steel rollers and may or may not have a brass bushing. The steel roller type is steel-on-steel and requires oiling before applying chain. When the test chain is new you should get good repeatability but after some time has passed, especially when outside in the elements, the chain will start to rust. The rollers can stop turning freely or even stop rolling, which I have witnessed many times.
Recently, I went to a cement plant where the conveyor and test chain were in a building but because there was so much cement dust and moisture built up over time, the conveyor and chains had locked up the rollers and the chain could not be used anymore.
The best repeatability when using a test chain is to mark the chain and the conveyor. Also, make sure you line up the marks each time to ensure the chain is always positioned on the conveyor in the same place. By placing the chain in the same place, you are more likely to get repeatability.
Here is what you need to do before you use a test chain:
For safety, do not stand near the chain or cable while the belt is running. If a cable or chain were to break they could cause serious damage or injury.
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