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RTV casting tools...looking for advice

5360 Views 16 Replies 7 Participants Last post by  rkapuaala
I'm looking for recommendations regarding what I should be looking for to develop a casting capability using RTV molds. I have the mold master...so I'll need to be able to make the mold and then make the parts with the mold. I'm not interested in what materials to use...yet. I know RTV comes in a variety of "qualities". But this request is about the tools needed.

I think I need three "tools":

a. Paint pot, in which to do the mold making or part making

b. Vacuum pump
[*]to pull air out of the RTV when making the mold from RTV and [*]When using the finished mold, to pull air out of the resin after it's poured/forced into the mold [/list] c. Presure pump to force the resin into the RTV mold

Is this correct? If so, then what are the specs I'm looking for?
[*]How many inches of vacuum dose the vacuum pump need to pull? [*]How much capacity does the vacuum pump need?...How fast does it need to pull the air out of the paint pot....10 seconds...or 10 minutes? [*]Same for the pressure pump....how much pressure does it have to put out....how fast does it need to pressurize the paint pot? [*]I've found paint pots up to 2.5 gal in size. What size is used by most modelers? Where does one find one in larger sizes...say 5 gal? [*]What gauges are needed on the paint pot to measure vacuum or pressure. What kind of valves? Where does one get the valves. [/list] I'd LOVE to see a photo or drawing on how one of these things is set up. Does anyone have one?

Lastly...some questions related to size. If I wanted to cast a 3' long passenger car side, how does one size this stuff up? What kind of paint pot would work and how much bigger do the pumps need to be.
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OK...I'm back to my questions...about TOOLS. The info and videos were fantastic...and I thank you Richard for being specific on the pumps. The TAP plastic device I saw in the video (thanks Russ) might be a whole lot easier to just buy....versus building this rig...it all depends on the cost.

I've been thinking through the mold making part of the process...

OK...the paint pot. Do you guys use a regular paint pots? At 29" hg, do they hold the vacuum? Paint pots are designed to hold pressure...often 100 psi...so I don't see that there would be a strength issue since 29" hg of vacuum is about -15 psi. Is that thinking right?

Question 2...how long does one have to pump the pot down to -15 psi? This goes to the capacity of the pump...and I know the pumps initially pump air out fast...then the pressure drop speed flattens out. A 2.5 gal paint pot has about 2.5 times the volumn of the TAP system...so I would expect it to take AT LEAST 2.5 times as long to evacuate the cavity to the same pressure using the same vacuum pump...assuming no leaks in the larger seal area. I have a hunch that "expectation" about the 2.5 times has a gotcha I don't understand...and it would take a lot longer. Is my thinking of pump down time correct?
Richard you said suck on the RTV for 17 minutes if you got bubbles in it while mixing the RTV. I am assuming that is AFTER it reaches 22" hg (what you stated later...versus the 29' hg you stated first....I'm a bit confused on that). Is the 17 minutes critical...because it means a vacuum pump that has at least 2.5 the capacity of the TAP rig. Thoughts?
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Richard...woof....a photo would be worth a thousand words. And....you have a rig like I first understood I needed....vacuum AND pressure. Please post a photo.

Burl...thanks. I saw the long thin stream on the TAP video...looks like a winner to me...cause it's simple. Thanks.
Posted By rkapuaala on 11/01/2008 2:06 AM

"if the wife doesn't figure out something else for me to do."

Hah....same everywhere. Is that possible??
Thanks Richard....the clay as pipe dope was a sure surprise. I always use teflon tape...and not pipe dope. Another surprise was the 3/4" birch ply box...I would NOT have thought it would be strong enough to handle the vacuum.

Question...is the other paint pot used as a pressure pot...for forcing resin into molds? I see you have both pressure and vacuum present at your work location.
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