Author Topic: Pressure pot for casting resin  (Read 4821 times)

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sirenwerks

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Pressure pot for casting resin
« on: February 20, 2008, 10:00:39 AM »
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Has anyone who casts their own resin tried a "pressure pot", like the one featured here - http://alumilite.com/checkout/index.php?cPath=25. Does it work?
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diezmon

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Re: Pressure pot for casting resin
« Reply #1 on: February 20, 2008, 10:16:13 AM »
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Yep, that's exactly what I do.. I found a pot on craigslist.

I pressurize the rtv and the resin.. that way both mold and casting are created in the same "no bubbles" enviornment.  I've only had to use about 35-40psi to get perfectly bubble free molds :)

My pot leaks just a tiny bit.. so I just keep it hooked up to the compressor, which is set to 40psi.. and leave it in there all night.

sparky

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Re: Pressure pot for casting resin
« Reply #2 on: February 20, 2008, 11:29:56 AM »
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Yep, the pressure pot works well.  Don't buy it from Alumilite though.  It's just a pressure pot used for spray painting.  You can find them on eBay, or from any online auto paint equipment supplier much cheaper.  Harbor Freight has an import version on sale for $40.  That's the one I use for resin.  I also have a $250 Binks unit that I use for finishing in my cabinet shop, but I wouldn't use that one for resin!

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93119

sirenwerks

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Re: Pressure pot for casting resin
« Reply #3 on: February 20, 2008, 12:00:48 PM »
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Thanks guys. Just the recommendations I needed and the price hints help too.
Now seeking Pacific NW N scalers to create a Modutrak-style modular club featuring NP's shared mainline between Seattle and Portland. PM me if interested.

TrainCat2

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Re: Pressure pot for casting resin
« Reply #4 on: February 21, 2008, 10:27:50 AM »
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Bryan,

I'm switching from Pressure to Vacumm casting. I was using these 2.5Gal because of the size for price was great.
http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_42673_42673

With some of the upcoming complicated molds, I took the advise of Al Westerfield and began switching to vacumm casting. Simple vacumm chambers can be made from large OD PVC couplings, rubber seals and .375 plexiglass for covers.

Regards
Bob Knight

TrainCat Model Sales

randgust

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Re: Pressure pot for casting resin
« Reply #5 on: February 21, 2008, 10:22:36 PM »
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I went to simple injection molding in multi-part molds and 95% of my bubble problems went away, along with all the working time issues and also the waste.

I'm using fibreglass resin syringes from www.westmarine.com .  Without a doubt, the all-time best tip I've ever got on a forum, so I'm obliged to pay it forward.

The darn stuff still 'foams' when relative humidity goes over 62% by my meters, particularly in open molds.  Right now, at around 50%, it is smooth as glass.  If vacuum or pressure molding cures THAT phenomenon, tell me more.

diezmon

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Re: Pressure pot for casting resin
« Reply #6 on: February 22, 2008, 09:13:49 AM »
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I went to simple injection molding in multi-part molds and 95% of my bubble problems went away, along with all the working time issues and also the waste.

I'm using fibreglass resin syringes from www.westmarine.com .  Without a doubt, the all-time best tip I've ever got on a forum, so I'm obliged to pay it forward.

The darn stuff still 'foams' when relative humidity goes over 62% by my meters, particularly in open molds.  Right now, at around 50%, it is smooth as glass.  If vacuum or pressure molding cures THAT phenomenon, tell me more.

well, actually both could help you there.  But it sounds like pressure might be the easier, cleaner method.. the key is to have enough extra volume in your mold to put extra resin because when you pressurize and remove bubbles the volume will be a bit less and may not fill the entire mold, knowudimean?

Vacuum casting actually removes bubbles and air from your RTV, before you pour.. so you're bubble free in the mold.  What pressure casting does it make the bubbles SO small they essentially disappear.   some guys vacuum the rtv and pressurize the resin.   there are many schools of thought on the topic, and most of them DO work.  you have to pick what you can afford, and what works best for you.

pressure casting is definately cheaper, as a good vacuum is mucho bucks! Way more than a decent compressor.  You can build the chamber for cheap, but you need a very good pump to make things work right.. and to vacuum fast enough.

I pressurize my RTV and my resin.. I've had perfectly bubble free castings ever since.  I use a simple paint pot, and my cheap compressor from menardos.
 

sirenwerks

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Re: Pressure pot for casting resin
« Reply #7 on: February 22, 2008, 10:31:11 AM »
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diezmon,

You got any sort of how-to on your set-up? I already have a decent compressor, and a paint bucket is easy to find, considering my brother works in the auto coatings industry.
Now seeking Pacific NW N scalers to create a Modutrak-style modular club featuring NP's shared mainline between Seattle and Portland. PM me if interested.

fieromike

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Re: Pressure pot for casting resin
« Reply #8 on: February 22, 2008, 11:36:08 AM »
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I went to simple injection molding in multi-part molds and 95% of my bubble problems went away, along with all the working time issues and also the waste.

I'm using fibreglass resin syringes from www.westmarine.com .  Without a doubt, the all-time best tip I've ever got on a forum, so I'm obliged to pay it forward.

The darn stuff still 'foams' when relative humidity goes over 62% by my meters, particularly in open molds.  Right now, at around 50%, it is smooth as glass.  If vacuum or pressure molding cures THAT phenomenon, tell me more.
I don't know at what point your resin foams, but applying a vacuum will reduce the moisture inside the chamber.  That is one of the reasons that the serviceman evacuates (vacuums) your air conditioner before charging it with freon.
You could also purge then pressurize the chamber with nitrogen gas.  It, IIRC, will absorb moisture from its surroundings.

Mike

diezmon

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Re: Pressure pot for casting resin
« Reply #9 on: February 22, 2008, 01:13:54 PM »
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diezmon,

You got any sort of how-to on your set-up? I already have a decent compressor, and a paint bucket is easy to find, considering my brother works in the auto coatings industry.

yup, it's easy peazy  :)

I attached tire valve to the lid of my paint pot, and I have a nozzle that clamps on to that from my air compressor..  On the inside of the lid I epoxied a scrap piece of plastic to just inside the air intake.. so the air doesn't shoot straight down into the mold.

All I do is pour the RTV, or resin, place it in the pot, screw the top down, and attach the compressor.  Now, typically you'd just pressurize it and leave it.. but since mine leaks a bit, I keep the compressor hooked up.

On my compressor I just adjust the output pressure to be 40psi, that way it keeps a constant 40psi in the pot. 

here's how things look:



and with the compressor attached: