Re: risers chills and sand casting, question.


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Posted by Kurt Schaefer on April 05, 1999 at 14:13:43:

In Reply to: risers chills and sand casting, question. posted by Rob Frink on April 04, 1999 at 15:04:34:

Well I don't know the details of the pattern, but I can

tell you a few things you can try. First if you have long

pieces attached to a large mass you have to do something to

promote directional solidification. Are you having

some shrinkage in the small sections as well as in the central

mass? Things to try: Place risers long the thin sections

at about 4 * thickness intervals. (Well I'm taking that number

from a steel casting referance, so I don't know exactly what

the best spaceing should be for your material.) With a chill

at the very end.

You can try insulating your main riser with a investment plaster

shieth. That will keep it juicy for longer.

If you're main riser is skinning over so thickly that

atmospheric pressure can no longer push on the molten center you

won't have it feeding the casting so you can try a number of

things: If it's an open riser you can sprinkle some thing

over the top of it to insulate it. (Rice hulls for example)

If it's a blind riser you can make a little pin shaped sand

core that projects into the center of the riser. This acts like

a pin "popping" the solidified metal "ballon" that froms as

the riser cools.

Does you're riser show a lot of shrinkage? If not it's clearly

failing to feed for some reason. I don't suppose you can

post a picture of the pattern, and some of the failed

castings? :-)

Good luck! (Sorry about the spelling folks, when I post

through this form there's no spell checking. *sigh*)


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