Chain crack (mining)
The breaking of a chain or a chain lock is called a chain break or broken chain. In mining , a chain break in a coal plow or a tank conveyor leads to runtime interruptions.
Causes and effects
Chains are often subject to great stress. Due to the operation, there are signs of wear or the so-called consumption of the chain. Especially with chains that are exposed to high tensile loads, such as curb chains or plow chains, even small incorrect handling of the chain becomes noticeable. Moisture causes signs of corrosion on the chain links , which in turn means that the material thickness is reduced and the load-bearing capacity of the chain is reduced. Crushed or twisted chain links also weaken the strength of the chain. If the chain is now loaded, such chain links tear. In the case of pull chains with a return chain, it can happen that the unloaded side of the chain becomes too loose and a so-called hanging chain is formed. This hanging chain can get stuck on structural elements, block and then tear. The chain star or the deflector can cause crimps or bruises. But jerky loading of the chain can also lead to chain rupture. A chain pretension that is too high leads to premature chain destruction due to chain vibrations. These chain vibrations occur when the chain is overly tensioned due to the high tensile and dynamic loads. If several chains are used in parallel for a load, an uneven load distribution can lead to one of the chains breaking. As a result of the chain break, the remaining chains are excessively loaded and also break. Depending on the location of the break, the chain break can cause production interruptions of up to eight hours.
Prevention and Remedies
The best protection against a chain break is regular monitoring and maintenance. A chain card index in which all chains are entered is a good help so that one can keep track of the running time of an armored or plow chain. Depending on the condition and running time, the chains are checked for elongation. This measurement is made on individual pieces of chain. Test pieces are taken at regular intervals and checked on the test stand for elongation at break and breaking force . The determined measurement results are entered in the chain card index. This gives the specialist staff a good overview of the wear and tear on the chain and can replace it in good time if the chain's working capacity is exhausted. So that the chains are not too tightly pre-tensioned or too loose, the chains must be pre-tensioned with appropriate pre-tensioning devices that are suitable for the respective chain type. In order to prevent increased wear and tear or corrosion, chains must be well lubricated at least before being used for the first time. A suitable chain guide prevents excessive wear and damage. To avoid further damage, damaged chain links or chain locks must be replaced immediately. To repair a broken chain, the two chain ends are pulled together and reconnected with a fitting piece and chain locks. Then the correct tension is applied to the chain.
Individual evidence
- ^ A b c Walter Bischoff , Heinz Bramann, Westfälische Berggewerkschaftskasse Bochum: The small mining dictionary. 7th edition, Verlag Glückauf GmbH, Essen 1988, ISBN 3-7739-0501-7
- ↑ a b Heinz Kundel: coal production. 6th edition, Verlag Glückauf GmbH, Essen, 1983, ISBN 3-7739-0389-8