Why do shredder hammers crack?

[clivej4555]

We have experienced elongation and cracking of cast Hadfields manganese steel hammers. Some hammmers are fine and some crack after a short service life. Can anyone shed any light on whether this is a problem with the casting or the operation of the shredder.

 

[Frederick]

It is hard to diagnose the problem with such little information. Have you done cross sections of the material near the cracks, or done a failure analysis of broken pieces? By the way, you can get a considerable increase in life by cryogenic treatment.

 

[Pressed]

A full metallurgical analysis would probably indicate what the issues are. Manganese steel has trouble with ammonia leading to stress corrosion cracking.

Do you have ammonia near the hammer or in the shredded material? Sabotage/accident is another possible cause, GALVALUME roofing and urine comes to mind.

Can you get a material spec which will lead you to the way it needs to be thermally stressed relived and test that?

Just some thoughts.

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[clivejones]

Thanks for your input guys. The hammers fractured at the eye about which they pivot. This hole extended from 130 to 160mm longitudinally during which time cracks propergated at 10 oclock and 2 oclock at the edges of the hole. This caused lateral spreading and work hardening to occur. The material was Hadfield's manganese steel.

 

[EdDanzer]

The cracking is probably being caused by pin and bushing clearance. The material you are using work hardens when impacted. Then it becomes brittle and any surface imperfection will propagate cracks. High hardness steels that are hard faced will probably work better.
You might get more information on the Metal and Metallurgy engineering forum.