Large Scale Central

White metal/pewter casting

Tools and Tips
#1

I have a question about getting pewter to flow well into fine detailed areas of your mold. I have used silicone molds to pour various pewter parts. One thing I am having trouble doing is getting consistent flow into all parts of an detailed mold. Where thin parts are it solidifies before it flow all the way through even with big air relieves cut into it. I have used talc which helps. I also know that when the mold warms up it helps. but what are the tricks to getting metal into all the fine areas of your mold consistently.?

One thing I have not done is invest in high temp RTV for the molds. I always thought this was for the longevity of the mold. But I am wondering does preheating the mold help keep the metal flowing? Can one heat a high temp RTV mold to at or near the melting point of pewter and get some working time with the metal and allow it to settle in? What about heating it up to the melting point and then using a vacuum pump like oyu would some resins? I am spit balling here.

How do say Ozark and the likes casting their parts with such fine detail? Spin casting?

#2

Hi Devon,

I have the same problem at times. I use Roto Metals pewter 98 and Smooth On high temp RTV. Have had great pours then using the same mould later nothing but junk. Check out Roto Metals web site and ask them. Someday I am going to work up a spin caster.

Don’t give up

Noel

#3

I don’t know about metal, but I know that for resins, vibrating the mold helps get the material into the nooks and crannies.

Also, if you heat the metal hotter then just its melting point, it will stay liquid longer.

#4

Noel Crawford said:

Hi Devon,

I have the same problem at times. I use Roto Metals pewter 98 and Smooth On high temp RTV. Have had great pours then using the same mould later nothing but junk. Check out Roto Metals web site and ask them. Someday I am going to work up a spin caster.

Don’t give up

Noel

I use the same metal. And with regular low temp silicon (I was just messing around) I had some really nice pours and now nothing. But I also ruined the mold with all the heat. I was hoping high temp would cure this.

#5

David Maynard said:

I don’t know about metal, but I know that for resins, vibrating the mold helps get the material into the nooks and crannies.

Also, if you heat the metal hotter then just its melting point, it will stay liquid longer.

I want to build a vacuum pot for resin. Its very easy make a cheap one out of an old pressure cooker. You just unscrew the pop off valve and thread in a connection to a automotive hand operated vacuum pump (I think they are for breaks?). Then you can suck it down and pull all the air out of the mold and the resin settles in. Now what I was thinking is if that vacuum container is heated up tot he melting point of the pewter and your using high temp silicone could the same thing be done with metal. Pour it and then vacuum all the air out of it then turn the heat off and let it cool. Would it work?

The thing with white metal that I am finding is that it burns when heated to hot. It pours a little nicer but is discolored. Not sure if that makes a hoot of difference or not.

I am sure the very best way to do it is spin casting but I ain’t going down that road.

#6

Spin casting is the trick! All large volume white metal manufacturers own one. You will get closer to 100% perfects but at if there are any rejects, they go back into the melting pot.

#7

But is getting set up for spin casting worth it for a low volume hobbyist making a few one off parts? I would love to do it but doesn’t sound cheap unless your into production.

#8

Try sling casting first … the flask and crucible are stacked and tied together on a rope, so that when the metal is liquid, you grab the other end of the rope and swing the contraption in a big arc moving the metal into the flask. Rope was short enough that the ground was cleared on the swing through…

About 1977 I saw this done to cast silver… I know it can be done. Forgive me if the instructions are thin.

John

#9

Well now there is an idea. For the small amounts of one off stuff I want to do this could be the ticket. I might have to research that one.

Do you know how to rig up the flask and crucible? Do you do it the same way as lost wax investment casting?

I like this idea a lot.

#10

Here is what I do with great success;

1st: use only a hight temp RTV for the molds. There should be a minimum of 1/2" thickness at the thinest spot on the side of the mold ( added mass). Talc is a must, for each pour.

2nd: I heat my molds in the oven to 350 deg. before pouring. Using gloves is a must.

3rd: Analyze the last pour. Add small vents as needed at all unfilled areas of the mold.

4th: Have “Oversized” sprues that act as overhead liquid reservoirs to push the liquid down and out the vents, and contraction reserves as the metal cools and shrinks.

5th: With a hot mold, it will take longer for the liquid to solidify, so just let it set without handling. De-mold when solid.

6th: Clean any spare flashing, re talc, assemble the mold, and re-heat for the next pour.

Caution: DO NOT OVERHEAT the metal, It will burn, and (depending on the alloy) may be ruined.

#11

Dave Taylor said:

Here is what I do with great success;

1st: use only a hight temp RTV for the molds. There should be a minimum of 1/2" thickness at the thinest spot on the side of the mold ( added mass). Talc is a must, for each pour.

2nd: I heat my molds in the oven to 350 deg. before pouring. Using gloves is a must.

3rd: Analyze the last pour. Add small vents as needed at all unfilled areas of the mold.

4th: Have “Oversized” sprues that act as overhead liquid reservoirs to push the liquid down and out the vents, and contraction reserves as the metal cools and shrinks.

5th: With a hot mold, it will take longer for the liquid to solidify, so just let it set without handling. De-mold when solid.

6th: Clean any spare flashing, re talc, assemble the mold, and re-heat for the next pour.

Caution: DO NOT OVERHEAT the metal, It will burn, and (depending on the alloy) may be ruined.

Dave,

You answered my main question about heating the molds up. I have been using the talc and that does make a big difference (thanks you gave me that tip once before and it sure does make a difference).

How large are you making the vents? I think this is something I am not doing well enough or have enough of.

#12

I found this on sling casting. Excellent tutorial.

http://www.brynmorgen.com/samples/pdfs/PracticalCasting.pdf

I just bought the whole book for $9.99 on Amazon (Kindle Version) some pretty good stuff for the DIY home budding caster.

#13

Use the toe of a nylon stocking to hold a ball of talc, just a tap and it will leave a layer behind. blow off excess, you want a very thin layer of talc.

John