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flux when melting pewter?


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#1 noir

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Posted 03 August 2009 - 07:42 PM

I'm hoping there's someone here experienced with casting pewter....

I've been trying to do some home pewter casting but I'm still a long way from perfecting it. It seems like every time I skim the dross from the surface of the molten metal a new skin of off-colour non-shiney metal forms. I keep trying to scrape it all back but I think some is getting into the pour as I'm getting deeply pitted dirty areas on the surface of my cast objects.

I've been trying to think how else I could do it and came up with a couple of ideas.

I've been around people casting silver and they always add a powdered flux to the crucible as they melt the silver. In all the instructions I've found online for casting pewter I've seen nothing to say you need to use a flux. Now I'm beginning to wonder.... are you supposed to use a flux with pewter?

Also, I'm thinking of trying to get a lead melting pot as sold by gun shops that pours from the bottom of the pot so the dross stays in the pot when you fill your ladle.

Just wondering if anyone who's more experienced can tell me if I'm on the right track with these ideas or if there's something simple that I'm doing wrong at the moment. Thanks.

#2 PTsideshow

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Posted 04 August 2009 - 04:07 AM

add a powdered flux to the crucible as they melt

Short answer is no, there is no need to.

I skim the dross from the surface of the molten metal a new skin of off-colour non-shiney metal forms

You will never get ahead of it, as it is a form of oxidation.

get a lead melting pot as sold by gun shops that pours from the bottom of the pot so the dross stays in the pot when you fill your ladle.

Problem it will form as you fill the ladle

You can make a divider for your ladle that has slots in the lower part so as you pour the dross stays behind on one side. A piece of sheet copper, cut to conform to the bottom of the melting container. At this time I can't seem to find mine. I generally make a new one each time as I can never seem to find them. they are held in place by bending ears from the sheet metal over the sides of the ladle.

Since the temp of pewter melts at 450' to 500' F depending on the alloy.
You can use a soft pine shim or other piece of wood to skim the dross off.
when the pine starts to char it is ready to pour.

You can collect and return the dross to the melting process if you are dealing with quantities. Also after it is cooled in the ladle you can tap it out on a brick and dispose of.

One note of caution, as the airborne dross particles can be toxic.

something simple that I'm doing wrong at the moment.....

No its just the way it is, and the articles that are cast will develop the oxide skin after casting. One of them can't mess with mom nature moments.

Here are a couple of the better books on pewter casting.
Tim McCreight's pratical casting

Jay D Kain's Cast pewter jewelry
The second is a long time library standard on jewelry and casting
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#3 Brad S

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Posted 04 August 2009 - 08:32 AM

"deeply pitted dirty areas on the surface of my cast objects." That doesn't sound like a dross problem....It sounds like a porosity problem. Which most likely is a venting problem, alloy problem or metal temp problem. What are you casting into? ie. rubber molds, invested flasks, ect. What is your casting method? direct pour, vacuum assist, spin cast? Add the word porosity to pewter casting and google it. Brad

#4 ranprodig

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Posted 04 August 2009 - 10:44 AM

I had the same problem trying to cast parts onto a knife blade. I decided the problem was that there was too much temperature difference between the liquid and the blade. I preheated everything that the pewter was going to touch with a mapp torch. that seemed to improve things considerably.

#5 Brad S

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Posted 04 August 2009 - 12:41 PM

Right, you heated the blade and prevented chill. Bi-metal casting, casting one metal into or over another,
has lots of possibilities. http://www.hooverand...og/archives/11/
Chill can happen most commonly with cold metal molds, or cold invested flasks. Flask temperature is one of the variables. Pewter is usually cast into vulcanised rubber molds. Venting becomes a greater issue than metal temp or chill. Pewter is a very different metal from golds, silvers, brasses and bronzes. The obvious difference is one of melting temp. The other difference is that pewter will not flow as thin as far as the others. In other words the detail possible with the others is much greater, actually in descending order as I've listed them. Models made to be cast in gold could be cast in the others but not cast in pewter. The other thing to consider is the tensile strength and durability of the metals. Pewter is not very strong. Therefore cast pewter items are much thicker than castings made in the four dominate materials. This gets into considering the use of the finished item. Pewter handles may work fine, while pewter forks might not be such a good idea. Just some thoughts. Brad




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