Sometimes we see a crusher that tried to crush “tramp steel” and the result is something like the divots you see on the crusher head in the top picture. Rock crushers don’t crush metals well.
Although cone crushers are typically equipped with “tramp relief systems” to allow some uncrushable materials to pass without damaging the crusher, that system only offers so much relief. If the relief bottoms out, crushing forces are sent into the internals of the cone crusher and can cause very expensive damage. For example, a very thin film of oil normally separates the internal parts from each other. In a tramp event, the film is squeezed out of the cone crusher and metal parts contact each other directly, often with disastrous results within seconds.
To prevent this type of damage, we recommend metal detectors, or magnets, which are much less expensive than a crusher repair.
Typically, you can buy three or four magnets for the price of one crusher rebuild!