Stickman Baits

Foam inquiry

22 posts in this topic

I've been researching rigid foams, considering it for making crankbaits. My question is what are your recommendations for a vacuum source ?? I've seen a vacuum "pump" that uses compressed air but I'm curious if my air brush compressor would power it or if vacuum "pump" could be created/modified to utilitize my small compressor. I don't think I'd be working with any more than 2 to 3 ozs. at a time. What do you guys think is this attainable??? Thanks Vern :huh:

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I don't understand the need for the vacuum. Are you talking about the 10Lb expanding foam, often talked about on TU, or something different?

Dave

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Well Dave, I believe I really botched this inquiry. :huh: I saw a video about the foam but after I read your reply I think the vacuum was used to make the mold for the foam to be used in. :huh: Anyway I still like to know more about vacuum pumps. Vern

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OK, for de-gassing RTV. Instructions for RTV often recommend vacuum de-gassing, but they never stipulate the vacuum required. I guess any vacuum is better than none.

I can think of a couple of vacuum systems on the non-specialised market, fish tank pumps and clothing storage bags. I've never used a vacuum, but plan to in the near future. So would be interested too, in what others find useful.

Dave

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Vacuum can be a tricky thing. Here are two good sites on vacuum products. I use vacuum on some of the custom equipment will build at work.

www.piab.com

www.smcusa.com

The simplest vacuum equipment to use (and least expensive) are air ejectors.

An air ejector is simply a venturi valve. They mount inline on

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Are you asking about a vacuum chamber to de-gas the rtv? Is that what you mean by a container to contain the mixture cup?

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Very good question, had not considered that one yet.

I am thinking an open box, made of 1/4" acrylic. Glued together with neoprene, fish tank style. The fillet of glue on the outside, so that the air pressure cannot blow out the seal. Fit a nipple for hose attachment.

A flat rubber sheet, glued to a board. Place the mold box on the rubber board and pour RTV. Place the open box over the mold box and start pump. Press down on box until vacuum takes hold.

Would be interested to hear what others use.

Dave

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That sounds loke a good idea but it creates another question for me...........the box would be quite large for the quantity of liquid being de-gassed. Can a hole be into a glass jar?? I'm still waiting for others provide insight. Vern:)

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For degassing just build a simple box or rectangle out of 1/2 to 3/4 MDF (its cheap and plenty strong) liquid nails/screw the box together. The liquid nails or caulk will act as the sealer. leave the top open to put a lid on (mdf or Lexan). I would use a MDF top with a small hole to view through, if you go to large you may compramise the boxes/plastic lid integrety. Screw/liquid nails a fitting into the top or side of the box for the vacuum fitting. Use simple stick on weather stripping from Home depot for the top sealent.

Sometimes if you don't pull a strong enough vacuum (27lbs if I remember) you can do more damage than good because the air bubbles will actually expand as you start to draw vacuum (less atmospheric pressure), and if the vacuum is not strong enough the air bubble will not be able to surface due to the tension in the material itself. Similar to scuba diving the deeper you go the more the air compresses, you rise and oxygen expands. Hope I made sense.

There is some good information and FREE how to videos on www.freemansupply.com (silicone, RTV, wax molds, Two piece molds ect.). Way cool:yay:

If your garage is wired for 220 Volts take a look at www.surpluscenter.com the used to have a GAST 220 rotary vacuum moter for about $90 which I think is cheap Gast's are excelent pumps.

Let me know if you need any other links for moldmaking supplies, I have a bunch.

Sorry for rambling on!:yawn::twocents::spam:

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Good video, even though it is basically a sales pitch. It was impressive how much gas was removed.

28" of mercury is a serious amount of vacuum and will require a serious chamber to hold it. I don't think my 1/4" plastic plate box is capable of those specs.

If I build anything like this myself, I will be using it out doors, away from windows and observing from a long distance.

One thing not mentioned so far, is a vacuum release valve. Some way of releasing the vacuum slowly. Why not add a vacuum gauge while we are at it.

Would still like to hear from someone who has built a chamber. Maybe this is not a suitable project for the home constructor.

Dave

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I have seen pictures and video of home made chambers and I want to say they were built out of MDF. They were not that big so there was not much of a span. There is another site I fogot to mention because it is geared towards woodworkers for veneering but it is www.veneersupplies.com They have some vacuum kits, valve and other ideas on making vacuum a press. Maybe they could be used to modify a chamber.

If MDF is questionable, I sure you could have a box welded up cheap at a local metal shop or weld it your self. :twocents: I made a few molds out of silicone and cast some stuff similar to alumilite but does not shink as much. The casts/mold were not very think (I was making a few pistol grips) so degassing was not a huge issue. Degassing really matters when you start casting with clear or transparently died plastics.

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I guess a soft vacuum bag would be a much safer option. Just place a sheet of acrylic over the pour, to stop contact with the vacuum bag.

The uses I would put the vacuum to are, de-gassing PoP, bondo etc, also sealing light wood bodies in propionate, for penetration. May get back to some RTV work in the future.

I believe Palmetto balsa has also been involved with vacuum, might be worth a PM to him, give him a heads up to this thread, see if he can contribute.

Dave

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As far as a hole being cut into a jar, don't know if this is what your looking for... buuuut could you cut a hole into the lid of the jar and screw it on tight???:twocents:

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Thanks for the insight everyone. After reading :oooh: trying it out the 1st time outside from afar, that itty bitty light came on :lol: . Never thought about a relief valve either :yay:. This is why I like this site & all you guys, it really helps avoid those redneck jokes that begin with "watch this" :worship: . Still like to know more. :)

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vodkaman, Since I had the available supplies, becouse I use vacuum systems at work from time to time, I tried an experiment with de-gasing PoP awhile back. I made a box almost identicle to what you explained. (Great minds think alike) At the time I was not sure what pressure I needed to hit to get the PoP to "boil". So I made this plexiglass box w/ a neoprene gasket base. I put a vacuum gage on the top and used the vacuum ejector I described earlier in the post. I put a manual flow control in before the ejector to be able to sneak up on the vacuum. I also put an adjustable flow control that was just ported to the vacuum chamber to act as a manually adjustable relief valve. I hit 16 in of merc and pop went the box. (Your basic implosion):eek:. Scared the PoP out of me. I have not had time to make a stronger vacuum chamber at work to continue the experiments. But consider this in vacuum. 1 in of merc is the same as .5lbs per square in of pressure(roughly) so if you generate 27 in of merc on a 12" square panel you will see almost 2000lbs of force on that panel. (check the math it is late) You start to realize why pressure chambers tiny view windows that are several inches thick. Food for thought. I would be happy to help size the vacuum equipment if someone is interested in moving forward with this.

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Yes, I did the sums too, just the numbers caused me extra laundry.

My innitial intention was never to go to such a deep vacuum, claimed by the RTV video, of 28". I intended using a aquarium pump. But, as your experience has shown, as little as 16"Hg can cause failure.

I am definately leaning towards the soft bag approach now and abandoning the rigid structure idea.

Thanks for this valuable fedback and glad you were not hurt.

Dave

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At 16 in of mercury I still had not got the PoP to "boil". I know that when urethane is poured they have to de-gas the the mixture before pouring it into a mold, and they hit about 29 in of mercury on that stuff. Also remember this safety tip. The material you are degasing will rise like a cake. So make sure the container you mix in is at least twice as tall as the fluid in it. Otherwise you might get a volcanoe effect all over mama's kitchen table. Then she might cut off your science experiments.

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I would think in terms of pressure vessel shapes. Like air or propane tank shapes. If you could get a pressure cooker pot, I bet you could modify that pretty easy. Most already have pressure gauge on them just swap it out with a vacuum gauge. Probably just need to drill and tap a hole in the lid for a vacuum line.

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