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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 |
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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 |
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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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