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Casting update - How to eliminate cracking


#1

Ron,

I used to run a production casting shop and we found that the

optimum safe time to leave the invested flasks undisturbed was 1
hour. If we moved them sooner than this we would start to have
problems. We also found that water to powder ratios and water purity
to have significant impact on the quality of the results we would
get.

Jim


#2

Hi Ron, I understand that one of your points was to allow the
investment to set long enough, However, with new casters, I don’t
recommend mixing by feel. When You look at the fact that I do approx
200 4x7" flasks per week, There is no other way to do it but with
exact formula’s ,time cycles, and burn out proceedures.We also have to
cast large numbers of hand carved waxes ( 1 off) for jewelry stores
and cannot afford the mistake of mixing by feel. the recommended
procedures for investing from the manufacturers do work
correctly…Most peoples investing problems come from procedure and
improper ratios/inccorect burn out as well as not allowing the
invested flask to dry long enough before loading into the oven. We
allow the flasks to sit unmolested for 1 1/2 to 2 hours before
loading into an oven. We do not have stop points in the burn out
process , but we do use a ramping digital control that allows us to
set the degrees /minute of climb which is 2.8 degrees / minute to
1350. then soak for the appropriate number of minutes before
decending to casting temp. No cracking will happen this way. as a
manufacturer of volume, we can’t let flasks sit for more than 2 hours
which is the recommendedtime.

when I used to sell investment( Kerr) for a large supply company, I
often was called in to figure out why the customer was having a
particular problem. Very rarely was it a problem with the
investment… 98% of problems were caused by improper procedure, bad
vacuum pump, a Lying vaccuum gauge(incorrect reading) which them
proved to be a pump problem, leaks in the vaccum system, bad mixing
procedures , mixing for too long or too little, and one time a
mechanical timer that was set up on a machine for the operator by an
engineer and the mechanical timer was off by 1 1/2 minutes in a 10
minute span…Saw these problems too often!

Any how, once anyone has it working and they are happy with their
results, continue doing it. Best wishes to all
Daniel Grandi Leaving for Thailand this sunday for a few weeks