Text 616, 52 rader
Skriven 2009-10-18 09:56:48 av Robert Bashe (2:2448/44)
    Kommentar till text 609 av Roy Witt (1:387/22)
Ärende: Foundry work
====================
Roy Witt wrote to Robert Bashe on Saturday October 17 2009 at 18:21:

RB>> It's amusing that when I was first interviewed for a job in a foundry
RB>> chemicals company, the manager told me that the products they made
RB>> had to bond sand as strongly as possible - and after the casting
RB>> operation must essentially disappear. At first glance, I thought the
RB>> idea ridiculous. But only at first glance.

RW> We knew there wasn't enough resin in the sand when it broke before it
RW> got placed in the mold. Sometimes they broke coming out of the sand
RW> core mold. Add more resin and try again.

Resin costs money - big money in comparison to sand. That's why foundries try
to use as little as possible for the application, and sometimes have problems
because of that. Green sand is much cheaper, but is not good for intricate
castings, just for the heavy stuff. If a resin core breaks when ejected from
the coremaking machine, or when it's set in the mold, the problem _may_ be too
little resin, but often there are other problems involved (gassing in the case
of gas-curing resins, heat distribution in the case of hot box resins and the
like). That' what makes the foundry business so interesting...

RW>>> Of course, the resin sand core molds were made of a mild steel and
RW>>> lasted a lot longer than the molds for casting brass.

RB>> Molds or copes and drags? Sand molds use the latter, and since they
RB>> are basically only hollow forms to hold the bonded sand, they
RB>> naturally last indefinitely. True permanent molds don't, but are
RB>> naturally much more expensive.

RW> Permanent molds don't use copes, or drags for that matter.

Of course not. I misunderstood you and read "resin sand" instead of "resin sand
_core_".

RW> I think my biggest challange was to design a sand core that was made
RW> in two pieces and fit in a permanent mold to cast a brass bathtub
RW> faucet. It worked the first time out.

That's pretty high-class work. Making cores is often hard, but designing them
even harder.

RW> Best part was the machine that was used to make sand cores was
RW> imported from Germany, as was the resin we used. That's because of the
RW> American chemical engineer who spent 30 some years at a German
RW> foundry.

Are you sure he was _still_ "100% American"? ;-)))

Cheers, Bob

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