Re: lost foam casting


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Posted by bruce paul fink on May 18, 1999 at 20:31:36:

In Reply to: lost foam casting posted by John Odom on May 18, 1999 at 13:17:06:


Don't know where a technical manual is but have done it and have taught how to do it on the beginning levels. Hope this helps.

Since you have some casting and molding experience already here are some thoughts to tide you over til you find the real bookworks. And then please let us know where it was and how it goes.

Check out the post later down this line entitled: "Aluminum casting properties may surprise you" which is at:

The last part of that talks about the pouring and cooling and potential overheating that will in part be a real key to your success rate. Also explains in part why aluminum works better here than bronze which is about 1000 degrees hotter when poured, but solidifies even quicker.

Remember that the metal has to melt the channel of the filler styrofoam in order to take it's place so give it all the help you can. You can do this by slowly inserting a red hot rod down the sprue BEFORE you pour and maybe even do a second sprue or larger than normal air vent (also pre diminished with the hot rod) that can act as a second feed near the end.

Also make the pouring cup a larger than normal size so it acts as a reservoir to hold metal while the whole process gets started and then has a volume of it to drop down into the mold.

This will also let the cleanest metal drop down the sprues from the bottom of the filled cup instead of doing a series of belches and taking all the dross or what have you that is also floating and going down in spurts.

Next thought is to emphasis that while you can glue styrofoam together with Elmer's Glue (or such) it is a bad idea especially if it will not be fully dried. Aluminum does not melt Elmer's. We often use fine toothpicks instead. Aluminum does not melt wood either but the fine parts have more of a chance at not slowing the flow, of carbonizing to a charcoal ash and floating or locking in place in a less than obvious manner. Only glue's I found to work are minor amounts of wax... but that also creates another problem with more smell, more stink, and it becomes a flash fuel to boot so more gassing out is necessary.

So we stick with the toothpicks and keep to a minimum...

OR since you can prepare for this use snipped off sections of stainless steel welding rods of the fineness size, or even steel pins or needles. They hold the parts together and if the flow encases them you will never see them.

And lastly in this commentary on common sense... the thinner the sections are (like the pencil thin legs of a horse than one student did or the fineness of the wings on an angel by another) the more chance there is of it not making a complete casting. With this in consideration then figure the natural solution and make sure that is also covered by another adjacent and larger 'throwaway' section or feeder than will quickly spread it's mass heat to the same area and make the wings or such also castable.

See... it starts to get more interesting. You and they will have all the answers to this so just don't forget to define the questions and encourage each to learn from each others efforts, and mistakes, and all will progress even faster.

(That's the secret beauty of teaching John, I always learn more by teaching than by studying).

SAFETY EQUIPMENT and PRECAUTIONS are a real must here. Especially if the students are new to this and associate the 'hot' concept with their normal fare of knowledge. This is more than hot, it is also 'sticky' if it hits clothing, melty if that cloth is of a plastic combination, and blinding or panicky if it hits the wrong parts. It is also a bad fume to breath and is 'deadly' in the right proportions.

Good luck and let us know how you go.


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