Materials Question

I've been using some hammer faces (that are described hard white nylon) on some specialty hammers. A couple of users have reported that the nylon isn't standing up to their use, (chipping ice and snow from snowmobile track suspensions). It's not the ice, that's causing the damage but the edges on the parts.



I've made a pair out of Delrin for one of the folks to test. I'm only using Delrin as a test, since I have some on hand. I'm not sure if Delrin is a better or worse substitute material for the nylon.

So now my question, can anyone suggest a readily available 'plastic' that won't gouge in use or fracture
in the cold (below freezing temps)?

TIA

If Delrin doesn't hold up, try PEEK. Very tough, but more expensive than either Delrin or Nylon.

PEEK is the wrong suggestion for this - it's benefits are at very high temperature use, not low temperature.
As a matter of fact, the glass transition temperature for PEEK is in excess of +140deg C - which is what makes it so good for high temperature stability - whereas the glass transition temperature for (Delrin) Acetal is -35deg C.
Nylon, by comparison, is in the range of +50 to +80 deg C

For those who don't know, the glass transition temperature is the point at which a Polymer changes molecular state from a hard glass-like structure to a more flexible rubbery structure (in molecular terms of course...). Which is why Delrin/Acetal is a premier choice for bindings on Ski boots for example. However, the very stiffness of Acetal can also make it brittle. Conundrums..

The very best material choice would be a high-density polyethylene, or an UHMW polyethylene - the Tg on these is around -90 to -150deg C, which means they will still be relatively flexible at very low temperatures and unlikely to chip.
And also inexpensive.

What about a higher durometer rubber?

Peter Neill said:

PEEK is the wrong suggestion for this - it's benefits are at very high temperature use, not low temperature.

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Fair points, thanks for the correction.

Mtndew said:

What about a higher durometer rubber?

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+1 on this, FKM (Viton) 90 Shore A will get as hard as plastic in the cold, generally non-brittle down to -20°C which might be marginal for the application. I sure don't like to ride in sub-zero Fahrenheit temperatures but maybe some of the buyers might.

On the other hand, urethane is excellent at sustaining shock loads and is flexible down to -70°C but will maintain its rubber-like hardness (softness) until a similar -20°C as Viton's brittle point. Maybe a double-sided hammer?

In the oilfield, we will go to 60D nitrile for sub degree temperatures to keep packing elements from shattering when hit. 90 hard Viton in general, not made for sub zero temperatures. BUT, there are over 25 different compounds of Viton-Fluorel FMK compounds available, and some of them are made for sub-zero temperatures. The problem is, finding someone that will mold a certain compound for you. Most will require you to buy a minimum size lot of a given compound. For hammer faces, that could be as many as a 1,000 pieces! Ken

What about a cheapo horrible freight dead blow?

4GSR said:

In the oilfield, we will go to 60D nitrile for sub degree temperatures to keep packing elements from shattering when hit. 90 hard Viton in general, not made for sub zero temperatures. BUT, there are over 25 different compounds of Viton-Fluorel FMK compounds available, and some of them are made for sub-zero temperatures. The problem is, finding someone that will mold a certain compound for you. Most will require you to buy a minimum size lot of a given compound. For hammer faces, that could be as many as a 1,000 pieces! Ken

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I have... 81 on file, and counting! FKM won't seal worth a damn in any kind of sub-zero (because it gets too hard too fast), but it will remain non-brittle for another 15 degrees or so below that.

There are plenty of options that have good low temp flexibility, but that comes with them remaining rubberlike at those temperatures. FKM has the most cold-hardening effect of any common rubber material which is why I mentioned it.

PS: Rumor has it there are rubber molding companies out there that occasionally get involved in low-quantity projects if someone is able to pique the engineer's interest

(PM me if interested)