Zinc shrinkage

[Double D]

Does anyone know the shrinkage rate for zinc?

I other words if I make a mould to cast a zinc round ball what diameter does the mould have to be to drop a 1.68 diameter ball.

[GGaskill]

Depends on the alloy but looks like about .007"/".  See Eastern Alloys' properties page.

[Double D]

So for a 1.68" diameter ball total shrinkage is going to be slight less than .012".

Dose that  mean our mould diameter has  be 1.691"?

[GGaskill]

Yeah, more or less.  I would suggest making the mould first and measuring its products, then boring the barrel to match.  It shouldn't be much different in any case and real golf balls are so low mass that you could shoot them with less than standard windage and still be safe.

[Double D]

Yeah, more or less.  I would suggest making the mould first and measuring its products, then boring the barrel to match.  It shouldn't be much different in any case and real golf balls are so low mass that you could shoot them with less than standard windage and still be safe.

sorry this is for existing barrels, just don't want to get them to big.

[GGaskill]

Well, if you made the cavity 1.680", the ball would be about 1.668" which really wouldn't make much difference.  I would try 1.690" or 1.687" for the first one and see what you get.  You can always cast hot and get a little larger ball.

[Double D]

1.69 it shall be.

[little seacoast]

While you're set up to make that, how about making a couple to sell?

[armorer77]

When I get the design right , they will be for sale .

[guardsgunner]

Don't forget that you have heat expandision of the mold material. It can be big differnce when going up a thousand degrees. In steel that could be as much as .006 If memory serve's.

Bob

[armorer77]

Having a little experience with casting I would say this will be minimal . I had my first mold cut for me at 1.690" . I took a guess on shrinkage and got lucky . Cast perfect 1.680" lead balls . Normal casting temp. for the mold is 350 degrees , since lead melts at 620 degrees and zinc melts at 740 , I don't think the difference will be that great . This is the reason for testing before marketing , I may be wrong . Ed

[little seacoast]

You are not wrong, let me know when you are ready to market them!

[GGaskill]

Steel expands at the rate of 6 millionths of an inch per inch per °F, and the mould will be approximately 400°F above the machining temperature which would amount to about .004" expansion (.000006 X 1.68 X 400).

[armorer77]

Here is the prototype GB mold . Made from 4.5" HRS



Cast a lead ball today to check my dimensions


Had to add a locator pin.

I always get that little flash at the bottom . All dimensions check + - .005"

[Cornbelt]

  Just curious, but how do you avoid shrink cavities using zinc without more sprue or riser volume?

[GGaskill]

Just curious, but how do you avoid shrink cavities using zinc without more sprue or riser volume?

At CBC² I, we played a propane torch over the sprue area to keep it molten until the metal in the cavity had finished shrinking.  It worked well but we needed a raised casting table instead of on the ground on the knees.

[Double D]

Just curious, but how do you avoid shrink cavities using zinc without more sprue or riser volume?

At CBC² I, we played a propane torch over the sprue area to keep it molten until the metal in the cavity had finished shrinking.  It worked well but we needed a raised casting table instead of on the ground on the knees.

CBC¹

[GGaskill]

What was the proper name of the cannon shoot in 2009?