Author Topic: Questions for Zinc projectile casters (Read 1210 times)

BoomLover · « **on:** April 04, 2009, 07:54:04 PM »

I know that Zinc isn't too hard to cast, melting around 715 Degrees F., but should you always use pure Zinc? I read that pennies are 97 1/2% Zinc, and 2 1/2% copper...are they alright to melt down? Does the copper melt out into the Zinc, or seperate? I also read that it has an almost 3% shrinkage rate, so should the mold be slightly oversized? Thanks, BoomLover

GGaskill · « **Reply #1 on:** April 04, 2009, 11:03:46 PM »

Zinc die casting metal (Zamac) is an alloy of several metals besides the primary zinc. Do a web search on it if you are interested in the chemistry.

Forget the pennies unless you are willing to cut them in half; the copper melts at a much higher temperature than the zinc. There have been a couple of threads discussing this already.

Cat Whisperer · « **Reply #2 on:** April 05, 2009, 03:26:20 AM »

I suppose one could use pure zinc.

Most of what you find is an alloy formulated for one characteristic or another - ease of casting, perhaps thinness of some cast features, or functional features as strengths or corrosion resistance.

We used to injection mould to fill in around a shaft centered in a hub that would become a motor.

Double D · « **Reply #3 on:** April 05, 2009, 04:09:42 AM »

Go to the Cannon internet resource list in the stickies at the top of the forum. Scroll down the list to zinc suppliers and click on the links. A couple of the suppliers list the composition.

Pennies only need a notch with a file so you can see white metal to leak when heated. To work intensive. Where to find zinc. Wheel weights, visits to scrapyard, word of mouth. Go to the dock at Port Orford and ask for old anodes. Visit the ship yards in Coos Bay and Charleston and look for anodes.

Shrinkage? They shrink? I had Wes Pilley build my moulds. I don't know if he adjusted for shrinkage our not. The only mould Ihave used is the 6PDR. I haven't measured the 6 PDR balls. I will be building my furnace as soon it warms up. I don't want to build it if we still have any freezing weather.

I might build the burner this week. THe cricuble and pouring gear are done.

Thanks SouthPaw!

BoomLover · « **Reply #4 on:** April 05, 2009, 07:07:08 AM »

Thanks for all the info...I'll skip the pennies, sounds like too much labor for your results! I like your crucible, DD, I know that it will make pouring eaiser with a setup like that! I'll check the docks, too. BoomLover

Double D · « **Reply #5 on:** April 05, 2009, 07:52:44 AM »

Boom Lover,

Do you know if Bill Cobb is still alive. If he is still around, give him my regards. He helped me cast my first lead roundball with is cannon ball sinker mould. Bill use to be the "go to" for sourcing this this sort of stuff in PO. Monty was a good resource also, but not as Good a Bill. Seems to me there was some on in PO making anodes.

RocklockI · « **Reply #6 on:** April 05, 2009, 07:50:46 PM »

Why do you need to notch or cut the pennies in half ?
gary

DoktorD · « **Reply #7 on:** April 05, 2009, 08:49:30 PM »

I think since the copper melts at a higher temperature, the zinc core would melt but would be contained in the still solid jacket... Cutting em in half or notching them would leave a hole for it to leak out... or at least thats how I'm understanding it

GGaskill · « **Reply #8 on:** April 05, 2009, 11:31:01 PM »

Correct.

Max Caliber · « **Reply #9 on:** April 06, 2009, 06:08:11 AM »

Thought I would give the penny melting a try. I put about 35 zinc pennies in my lead ladle that has a skimmer built into it and melted the pennies with my furnace burner. Once the pennies started to melt they sort of slumped into a mass and the zinc ran out and the copper covering turned to crud. Once completely melted, I poured the clean zinc into one side on my GB mold. The skimmer prevents the crud from flowing into the clean metal. As I suspected, there's no need to cut the pennies before melting. The process yields some nice looking metal but leaves behind a bunch of crud. Don't see much use to do this unless in an emergency, zinc is cheap and easy to come by.

I read here awhile back that zinc could not be cast in aluminum molds. I gave that a try also and cast zinc in my aluminum GB mold and also in my 2"+ mold. The process worked fine and due to the higher melting point of zinc the balls came out with an excellent finish, even the first ones cast in cold molds. There appeared to be no more shrinkage then with lead. The zinc balls were a bit harder to extract from the molds due to them being harder than lead. Casting zinc in the aluminum molds did not cause a problem with casting lead into them later.

Double D · « **Reply #10 on:** April 06, 2009, 06:17:18 AM »

Nice to hear that the Aluminum mold worked...I was told not do it as the melting temperature of of aluminum was close enough to zinc that if you got your zinc to hot it would distort the aluminum mould.

Max Caliber · « **Reply #11 on:** April 06, 2009, 06:45:53 AM »

You might warp some of those shell type molds like fishing sinker molds. I make my molds on the hefty side to hold heat and they stay stable even when heated to a high temp.

BoomLover · « **Reply #12 on:** April 06, 2009, 07:42:10 AM »

Thanks to everyone for all the good info! Seems I won't have to try melting pennies just yet, found a close source for Zinc, so I'll try casting a few to see how it works. I'll keep in mind the process for the pennies, never know when a source might dry up! Kind of like powder, always good to have extra on hand! BoomLover

cannonmn · « **Reply #13 on:** April 07, 2009, 04:24:47 AM »

One question I'd have on the "marionette" type crucible pictured above: It seems the way it works requires the operator to be directly over the mould. Since sometimes you can get little explosions that spit molten metal forcefully out of the pour hole, does this type of crucible create a potential safety hazard?

Double D · « **Reply #14 on:** April 07, 2009, 06:45:25 AM »

This is a standard metal melting set up that is regularly used by backyard casters. http://www.backyardmetalcasting.com/crucibles2.html

Spitting metal with lead and zinc is reaction to impurities in the mould particularly moisture or improper venting especially in a large cold mould. Make sure the mould is clean and preheat the mould before pouring to drive moisture out and warm the air inside. Keep these impurities and moisture away from the mould. Make sure you don't pour too fast and your sprue hole is large enough to vent properly. If you pour stream is larger than your sprue hole you will trap air and it can blow out.

Use the same precautions you would use casting bullets and melting lead--keep in mind zinc melts hotter. Preheat metal before putting in Crucible. Wear safety glasses and/or face shield, gloves, long pants and leather shoes. Don't pour on cement pads or walkways. When casting zinc, watch your temperature, don't over heat and have good ventilation. Drink your milk.

cannonmn · « **Reply #15 on:** April 07, 2009, 09:57:51 AM »

Quote

This is a standard metal melting set up that is regularly used by backyard casters. http://www.backyardmetalcasting.com/crucibles2.html

Thanks, however that doesn't mean the use of such a rig isn't accompanied by avoidable safety hazards. Side-pour ladles are made in all sizes needed by hobby casters, the larger ones with two handles. When you pour with these your head isn't over the mould.

We put a video on you-tube about casting projectiles from Kirksite, using ladles, and got a few emails from apparently experienced casters criticizing us for taking unnecessary risks by having our heads within a couple of feet of being over the mould. Zinc at 750 degrees plus is pretty unforgiving if it hits you in the face. That's why if someone is determined to use the marionette crucible, heavy-duty protection including a full face shield is mandatory.

http://www.youtube.com/watch?v=y36zlWQJU9Y

Double D · « **Reply #16 on:** April 07, 2009, 11:56:46 AM »

Quote from: Double D on April 07, 2009, 06:45:25 AM

This is a standard metal melting set up that is regularly used by backyard casters. http://www.backyardmetalcasting.com/crucibles2.html
Use the same precautions you would use casting bullets and melting lead--keep in mind zinc melts hotter. Preheat metal before putting in Crucible. Wear safety glasses and/or face shield, gloves, long pants and leather shoes. Don't pour on cement pads or walkways. When casting zinc, watch your temperature, don't over heat and have good ventilation. Drink your milk.

And long sleeves and a properly constructed crucible.

Frank46 · « **Reply #17 on:** April 07, 2009, 05:43:16 PM »

Another little trick borrowed from the bullet casters. Get a hoplate and dial it up to 600 degrees and place a flat round piece of metal on the burner unit. This acts as a heat sheild and helps transfer the heat more thoroughly. Park your cannon ball mold on that puppy while you are waiting for your pot full of zinc to melt. Then when you are ready to pour the mould will be close to the temp of the metal poured this will help lessen the wrinkles, voids, and help the mold fill more evenlyWhen you are not using the mould but still in casting mode the hot plate will keep it hot until your ready. Frank

Double D · « **Reply #18 on:** April 07, 2009, 06:46:49 PM »

Now that is a solution to a question I have been pondering, Thanks Frank.

and7barton · « **Reply #19 on:** April 09, 2009, 12:53:13 AM »

Quote from: Double D on April 06, 2009, 06:17:18 AM

Nice to hear that the Aluminum mold worked...I was told not do it as the melting temperature of of aluminum was close enough to zinc that if you got your zinc to hot it would distort the aluminum mould.

Aluminium's melting point is around 300 degrees higher than zinc - It would take a good deal of over-heating of the zinc to even approach this.