Copper question

I've melted copper only once and poured it into a sand mold, so no direct experience here, but I've read that the copper alloys are hot enough that they will braze themselves to steel or iron and cannot be removed. You might throw this question over to rec.crafts.metalworking since I believe that's where I read this.

-- Gary Brady Austin, TX

I thought there was a mold release spray that you could use to prevent it brasing to iron or steel,,, I saw someone using something on that order casting brass pieces in a polished steel mold once long ago,, not sure of the difference in melt points between brass and copper though, or if the product only worked on alloys or anything else,, it was a long strange trip ago,, well over 30 years. How high of temp can silicone mold release go? I've only used it for plastics at work and lead at home casting fishing sinkers and jig heads.

Make sure the mold is thick enough so it won't get hot enough for the copper to bond. As long as the steel stays relatively cool and the surface is very smooth then the copper shouldn't bond.

PAM cooking spray makes an OK mold release.

It SOUNDS to me as if you are trying to create an inlay effect. If this is the case, then, yea, you will have to undercut a bit to get it to stay, or, go back and solder it in place afterwards. Have you considered plating instead? That might well produce the same effect you want with considerably less effort and challenge. Regards Dave Mundt

I'm sorry, I misread your question, please ignore my reply above, I thought you were wanting to make many identical castings from a permanent mold. Bear

Back when pennies were made from copper, the "penny weld" was a euphemism for using a penny to repair a missed weld in a bar shoe. Re-welding a bar shoe is often not an option after the shoe is fitted because the attendant hammering changes the fit.

Using copper to affix jar calks and toe grabs to steel shoes is still a fairly common practice amongst farriers who can work a fire.

If you want to inlay copper into steel, undercut the perimeter slightly, place the necessary amount of copper in the vacancy, heat to red, flux, heat to melting, remove from fire, allow to cool, then sand/rasp the excess copper away from the inlay.

This is easier done in a gasser than in a coal fire because the workpiece needs to be kept level.

Another good bet as a mold release would be something like Hoppe's Dri-Lube with Teflon. You would have to have good ventilation with this because you MUST NOT breath the fumes from this when the hot metal hits it.

Funny those are together. :) Pam used to be pressurized by a freon and ecthed the hell out of an aluminum skillet that was on the burner when anther pan was being sprayed. (phosgene and HCl)

The first guy to make teflon was trying to make another freon for DuPont and something went haywire. ;)

Seems to me teflon would be great unless it's exposed to those high temperatures then... after it forms phosgene gas etc, what good is it? Might as well start with talcum powder which is sorta like asbestos.

Alvin in AZ (but still I don't know squat about it, just guessing)

I'm just guessing myself, and would recommend trying teflon on a test piece of metal before risking it on a good piece. However, teflon - poly(perfluoroethylene) - doesn't give off phosgene - COCl2 - or HCl when heated, because it doesn't contain chlorine (unlike freon). That's why the insulation on plenum rated cable is made of teflon rather than PVC. Teflon might give you some HF when it decomposes, but fluoride is much less corrosive to steel than chloride.

I agree that Pam is also a real good bet, tho. Whatever floats your boat.

It sounds to me that the OP _wants_ it to adhere not that he is looking for a release. In that case, I would point out that blacksmiths frequently use pure copper for brazing filler on steel. You shouldn't have trouble getting it to stay put.

Ted

When the old style Pam (with freon) was sprayed into the air while the gas stove was on... the fumes produced would choke you down and send you outside for fresh air. I wonder which it was? ...the HF, HCl or phosgene gas that was so irritating?

Alvin in AZ

"TomNBanderaTx" wrote in news:60OWc.5510$ snipped-for-privacy@newssvr24.news.prodigy.com:

Is there a particular reason for casting copper?. Copper alloys such as everdur are easier to cast. If you need to pour into rigid molds I would also recomend using the lost wax method. The wax molds can easily be created in quantity and take on the precision of the master.

brad

I'm making a memorial cross with twin dragons on either side of the cross, I was wanting to pour the melted copper or brass into the eye and let it trickle down in a golden tear. I've since cut a piece of the disc I've got and I don't think its copper or brass but bronze. I bought some stuff at an auction to do melting and such, and the only thing that melted was the the bottom of the damn thing. So I'm searching other ways of doing what I'm wanting.

Hum...not sure how well this would work to pour it in place. Actually, having thought about it a couple of minutes (and ONLY a couple, so it might be "half-baked") why not make the tears out of gold? Unless they are really HUGE tears, it should not be a serious expense and it should be easier to form the tears, then, silver solder them to the statue. THe problem I see with using something that is NOT gold is that after some time...those tears will tarnish and dull down. Gold is the only thing that will stay looking "good" without care. Regards Dave Mundt

Okay, I tried melting and casing copper long ago and discovered that it takes on gasses when molten that are released when the phase change takes place from liquid to solid, leaving you a casting with holes in it, lots of holes. I think you will need an inert gas environment when it is melted to avoid this. When copper is alloyed, there isn't this problem. I would bo with brass, bronze, or as suggested, gold. my 2 cents Rick

It wasn't HF (hydrofluoric acid? - from Teflon at +400(?)centigrade) - unless you died in agony over the course of 5-7 days drowning in the remains of your own internal organs.

PLEASE don't mix Teflon (ptfe) and red-hot iron.

There is a story about a couple of (electrician) apprentices who put put some PTFE/teflon insulation inside their (tutor/master/gaffer)'s pipe for "a laugh" - he took a week to die.