Preventing fretting of metals

[SRutter]

Is there anyone who has any knowledge of minimising fretting of metals. The problem is that our 300 tonne press has pins that fatigue which leads to the perf tool braking. The tool is made of 500/7 spheroidal cast iron, constinously cast and is induction hardened around the prefery of the tool to approx 40rc. The sheet material is 0.5 zintec or galvanised steel.

I would appreciate any info on the choice of tool metal or methods that would lead to a longer lifespan of the tool.

Thanks

 

[jbel]

This may be a good place to start.

http://www.asm-intl.org/

 

[unclesyd]

It is not clear what the specific problem is.
Can you come back with a little more information?

Are the perforating pins fretting first?

If so what material are they made from?

Are the pins held by the CI block or is the CI block the die?

 

[SRutter]

the pins are not the problem. the fretting is taking place on the bed.
The build up of particles causes an uneveness and when the press drops again, it snaps the tool.

 

[EdDanzer]

We typically see fretting occur when there is point contact that exceeds the tensile strength of one or both of the materials. This is common in machine tool spindle tapers. Both the spindle and the tool are subjected to compressive loads and there is always some point contact. To solve your problem will require some experimentation. Our experimentation shows that using a softer rougher finish material for one part will allow it to deform without point contact exceeding the tensile point of either material. Another way to describe this is like having a spring at each point of contact on the mating surface.

 

[CdotS]

As UncleSYD mentioned we need more info.

I would encourage not to use the term fretting without knowing the type of wear for sure. Fretting is due to vibratory motion of small amplitude. I do not know whether this is what happens in your die/punch situation.

Please describe the situation, materials (with treatment and propeties such as hradness)used, fracture / wear / corrosion pattern (just a note on damaged surface appearance), etc.

Where does the build up of particles occur? What kind of particles (e.g. sand)? Uneveness - in relations to what surface?

 

[eagle56]

It was not clear from your message where the fretting was occuring or where the pins were breaking. My experience is with bearing failure analysis. Fretting between a bearing and shaft is caused by slight relative movements of the parts due to herztian contact stress in the bearing ring. Small cracks form in the surface of the ring (from intergranular corrosion) that propagate and sometimes crack the ring. If the press fit cannot be increased to reduce the movements, then a more fracture tough material that inhibits crack propagation will eliminate the crack problem. Surface coatings such as thin dense chrome (satin chrome) sometimes are useful in reducing the onset of the fretting corrosion. If you can provide more details I might be able to more confidently determine the problem.