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Re: Lost Foam,refractory coating,etc.
Posted by bpfink on October 12, 1999 at 21:18:43:
In Reply to: Lost Foam,refractory coating,etc. posted by Xandor on October 12, 1999 at 19:57:49:
I would think the hollow core with loose sand casting you mentioned would be dependent by the success of a chill factor in order to work. The metal surface would have to gain some inflexibility to hold it's shape in order to not shift the sand segments. Too hot metal and the sand core could start to float, too cool and it simply would not fill. So good luck but sure sounds uncontrollably risky to me.
As the pieces get larger, and the wall thickness gets more massive the problems would either surface or increase in appearance. Surface detail and mass would be the telltale indicators.
I would keep the walls of the pouring cup large to hold the most metal needed to both fill the piece but also have a reservior to keep any gas burps or slow metal drops in check before the final fill.
Not sure about this mention...
You also mentioned:
I should surmise that more sprues will not help the flow if they are solid prior to the pour so no gas can escape... but more will help if they have melted enough for an air channel to let the gas escape... so do a pre melt with that hot rod and get a jump on it.
And you can also do vents in the sand with either
I would tend to agree with your cohorts at San Diego U that a bonded sand would give much more control to your results and with these other mentions it should not slow the air / gas escape at all.
As for a BELOW sprue.... it would only tend to trap the gas all the more as the only way to vent is via both the sand and the sprue... and a longer burping could really disrupt the surface of the metal all the more... and 'wash' in more sand from the mold and inti the metal body.
PS. The graphite and alcohol is usually painted or sprayed on the surface of a bonded mold and then a match torch flames the liquid off before the cast.