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#1
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What to use to make a mold?
I want to make a small mold I would later use to create a fiberglass
container to hold lead weight. It would be nice if mold material can withstand 500 degrees Fahrenheit so I can pour lead into it and then cover it by fiberglass. Alternatively I would use the mold to create a fiberglass container first and fill it up with lead pellets. So my question is what do I use to make a mold, gypsum if so what kind, anything else? Andrzej |
#2
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What to use to make a mold?
On Mar 22, 5:23*pm, AK wrote:
I want to make a small mold I would later use to create a fiberglass container to hold lead weight. It would be nice if *mold material can withstand 500 degrees Fahrenheit so I can pour lead into it and then cover it by fiberglass. Alternatively I would use the mold to create a fiberglass container first and fill it up with lead pellets. So my question is what do I use to make a mold, gypsum if so what kind, anything else? Andrzej High temp RTV rubber can withstand up to 1000deg F. It's not cheap stuff, but it will work quite nicely... If you use gypsum or plaster products, just make two molds, (after your first mold is made make a male model from it to cast new females off of...) as it would be difficult to get out your lead w/out breaking it, assuming it survives the thermal shock of the pour. Heat up your plaster mold in an oven to within 100deg of your pour first to avoid that pitfall, but you must very slowly heat the plaster up since it may have micro water in pores that will superheat and make it crack as the steam exits. Take at least 4 hrs to bring your mold up to temp (after 24 hrs minimum cure) , ramping up 100deg/hr until at 400ish... plaster is cheap and easy to work with, so it will probably be most practical. note-plaster expands 1-3% when cured, so take this into account for allowances if you have critical tolerances. If you need precision plaster/gypsum there is a product called Ultracal (in 30 or 60 minute cure versions) made by US gypsum that does not expand or shrink. it's cheap enough to use too at like $30/50# . It feels and mixes just like plaster of paris but is gypsum based so it cures like cement. Phenomenal product actually... There's always the option to just trap your lead shot in epoxy thickened with cabosil or microballoons etc, which seems much easier but will obviously not provide the same density as a solid block... -Paul |
#3
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What to use to make a mold?
sisu1a wrote:
There's always the option to just trap your lead shot in epoxy thickened with cabosil or microballoons etc, which seems much easier but will obviously not provide the same density as a solid block... It does avoid the breathing of lead vapors, something even a pilot should avoid. -- Eric Greenwell - Washington State, USA * Change "netto" to "net" to email me directly * "Transponders in Sailplanes" http://tinyurl.com/y739x4 * Sections on Mode S, TPAS, ADS-B, Flarm, more * "A Guide to Self-launching Sailplane Operation" at www.motorglider.org |
#4
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What to use to make a mold?
For a single pour mold, you can even carve it out of wood, like a 2 by 4.
It will smoke, burn the wood (you can blow out the fire), but it will hold up for a single lead weight making. How heavy a weight are you trying to make? And about how big? You could then make the glass cup from the lead part, or even from a block of foam that you cut to about the same shape. A friend once got in trouble with his wife by using one of her frying pans to make lead disks for putting in the seat pan of our old club two place! One thing to watch out for (may not be this way with the gypsm stuff that Paul mentioned), but anything that used water in its making, can trap water inside. Put molten lead in it, and it can be a bad thing. Happy slug making! Steve Leonard |
#5
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What to use to make a mold?
At 02:30 23 March 2009, Steve Leonard wrote:
For a single pour mold, you can even carve it out of wood, like a 2 by 4. It will smoke, burn the wood (you can blow out the fire), but it will hold up for a single lead weight making. How heavy a weight are you trying to make? And about how big? You could then make the glass cup from the lead part, or even from a block of foam that you cut to about the same shape. A friend once got in trouble with his wife by using one of her frying pans to make lead disks for putting in the seat pan of our old club two place! One thing to watch out for (may not be this way with the gypsm stuff that Paul mentioned), but anything that used water in its making, can trap water inside. Put molten lead in it, and it can be a bad thing. Happy slug making! Steve Leonard Lead has a melting temp of about 500 degrees C commercial moulds for casting batches are usually cast iron as are some pans. If you make a mould using sheet steel this would then encapsulate the lead after pouring and prevent the soft lead from deforming under pressure from the fastening bolts. |
#6
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What to use to make a mold?
On Mar 22, 5:23*pm, AK wrote:
I want to make a small mold I would later use to create a fiberglass container to hold lead weight. It would be nice if *mold material can withstand 500 degrees Fahrenheit so I can pour lead into it and then cover it by fiberglass. Alternatively I would use the mold to create a fiberglass container first and fill it up with lead pellets. So my question is what do I use to make a mold, gypsum if so what kind, anything else? Andrzej sand |
#7
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What to use to make a mold?
On Mar 23, 8:28*am, wrote:
On Mar 22, 5:23*pm, AK wrote: I want to make a small mold I would later use to create a fiberglass container to hold lead weight. It would be nice if *mold material can withstand 500 degrees Fahrenheit so I can pour lead into it and then cover it by fiberglass. Alternatively I would use the mold to create a fiberglass container first and fill it up with lead pellets. So my question is what do I use to make a mold, gypsum if so what kind, anything else? Andrzej sand http://en.wikipedia.org/wiki/Sand_casting not quite that simple in practice and would also req the purchasing of some specific setup materials which are not found at Home Depot etc... You should go the wood or plaster route.Wood is dead simple if your shape is not to complex. I saw that Steve quite rightly mention of worry of plaster and residual water/steam being an issue... hence the very specific directions I layed out for preheating/drying your plaster mold BEFORE lead is poured in. If it survives the 4 hr incremental ramp up to 400deg, it will not break from the pour since all the water will have been evacuated by then. If in doubt, leave it in the oven for an extra hr or 2 at 400ish... I dabble in investment casting, and the same methodology applies for pouring 1700-2100 deg metal (bronze, slver, gold, etc) into a plaster mold, except the heatup/dryout process brings it up to 1000deg over a 5, 7, or 12 hour ramp up (usually spending some an hr or 2 at 1300deg to vaporize out the wax remnants before ramping back down to 1000ish). -Paul |
#8
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What to use to make a mold?
On Mar 23, 12:12*pm, sisu1a wrote:
On Mar 23, 8:28*am, wrote: On Mar 22, 5:23*pm, AK wrote: I want to make a small mold I would later use to create a fiberglass container to hold lead weight. It would be nice if *mold material can withstand 500 degrees Fahrenheit so I can pour lead into it and then cover it by fiberglass. Alternatively I would use the mold to create a fiberglass container first and fill it up with lead pellets. So my question is what do I use to make a mold, gypsum if so what kind, anything else? Andrzej sand http://en.wikipedia.org/wiki/Sand_casting* not quite that simple in practice and would also req the purchasing of some specific setup materials which are not found at Home Depot etc... You should go the wood or plaster route.Wood is dead simple if your shape is not to complex. * I saw that Steve quite rightly mention of worry of plaster and residual water/steam being an issue... * *hence the very specific directions I layed out for preheating/drying your plaster mold BEFORE lead is poured in. If it survives the 4 hr incremental ramp up to 400deg, it will not break from the pour since all the water will have been evacuated by then. *If in doubt, leave it in the oven for an extra hr or 2 at 400ish... I dabble in investment casting, and the same methodology applies for pouring 1700-2100 deg metal (bronze, slver, gold, etc) into a plaster mold, except the heatup/dryout process brings it up to 1000deg over a 5, 7, or 12 hour ramp up (usually spending some an hr or 2 at 1300deg to vaporize out the wax remnants before ramping back down to 1000ish). -Paul Thank you a lot to all who responded, especially to Paul for the details he provided and Steve for the safety warning. I was already aware of safety issue, but I appreciate you mentioned it. |
#9
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What to use to make a mold?
For safety in an accident I would use the lead pellets
and make a containter. Plus you will be able to make adjustments to your weight if you use pellets in a containter. A big chunk of lead could become a very dangerous projectile in a hard landing or crash. Ray |
#10
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What to use to make a mold?
On 23 Mar, 02:01, Eric Greenwell wrote:
sisu1a wrote: It does avoid the breathing of lead vapors, something even a pilot should avoid. Is the sublimation rate of lead at room temperature significant? Church roofs seem remarkably resistant to evaporation after hundreds of years, as do the 120 year old lead water pipes in my house. Ian |
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