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Material combinations for star pumps, plates ect.


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#1 mabuse00

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Posted 13 September 2020 - 08:15 AM

What is in your opinion the most desirable combination of materials for such tasks?

 

Working with pumps, I encounter frequent jamming problems. Little grits of even the small 325mesh atomised aluminium get betwen piston and cylinder...

Or rather because it is small enough to get in there.

 

Also I found that aluminium sliding on another piece of aluminium likes to seize, or "gall", expecially with those little grits in between... Life expectancy isn't too good.

 

A question of money of course...

Steel on brass or brass on brass is obviously better, POM seems to be workable also, and cheaper to machine...


Edited by mabuse00, 13 September 2020 - 08:16 AM.


#2 Carbon796

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Posted 13 September 2020 - 04:31 PM

- 325 mesh AL shouldn't be seizing or galling your pumps up. Something else is probably going on.

Are you hand ramming or pressing ?
What water % and binder ?
What style or brand of pump ?

Brass on brass would be the better/safer choice.

#3 BetICouldMake1

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Posted 14 September 2020 - 08:40 AM

Regardless of the material used you will have issues with hard metal particles small enough to get between the pins and the hole plate. Usually aluminum doesn't cause problems, but Ti or FeTi certainly will. 

 

Aluminium tooling is typically anodized to prevent the galling you mention, but using delrin or brass/bronze pins works as well. Delrin is much cheaper. Steel seems common in commercial applications for its durability, but I personally would avoid it due to sparking risk. It would also need to be painted or otherwise treated to prevent rust.  



#4 mabuse00

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Posted 14 September 2020 - 09:01 AM

In this case it was D1, working with an untreated, bare aluminium pump.

 

I think the -325 aluminium is just to small, bigger stuff wouldnt get in there. And the pump itself is to soft.



#5 Bensmith

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Posted 14 September 2020 - 09:02 AM

Brass on brass is an excellent choice and will last nearly indefinitely. Bare aluminum will gall with coarse Ti or FeTi. I actually prefer to use aluminum in comps that typically call for Ti. Looks basically the same and is easier to work with. Hard anodized aluminum is incredibly tough and will last a lifetime as well. Cosmetically anodized aluminum isn't much tougher than bare aluminum and will easily gall and wear out. Plain steel should never be used for anything dealing with pyro. Not only is there a sparking issue, but it will corrode almost immediately when exposed to oxidizers. 

 

A simple trick to long tool life when using Ti and FeTi is to make up a small batch of comp (say 100grams) that contains no metal. Sprinkle a small amount of this comp over the metal containing comp prior to pressing. This will form a small "gasket" that prevents the coarse metals from migrating between your piston and cylinder wall. 


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#6 rogeryermaw

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Posted 14 September 2020 - 10:39 AM

i like delrin plastic (acetal) for the pin portion of a pump or plate. the softer material will give before the metal and the plastic is cheap to replace.





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