Bubbles in PR...

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gothycdesigns

gothycdesigns

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Joined
Nov 27, 2005
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192
Location
Vancouver, WA, USA.
So I'm working on some bottle stoppers. I am casting some small skulls in some clear PR.
I'm using a 1" i.d. PVC pipe for the molds and only pouring about 5/8" - 7/8" thick. I'm trying to mix the PR and cat. as smoothly as possible but I expect some bubbles. The question is, can using a butane torch with light passes over the PR help pull and rid some of the bubble? a guy at the local TAP plastics says it could get rid of most, not all bubbles. as long as you use quick passes and low setting.

Just curious if anyone has any experience on this or advise. I do not have a vacuum chamber
so was thinking this for an alt. option til then.

ThX

Ray
 
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I don't think an open flame close to the pr would be a good idea, but I could be wrong. You can get a toaster oven from goodwill or salvation army for $10.00 and use it to heat your pr before you add the catalyst. I heat at 150 for about 8 minutes, then add the catalyst and stir slowly. With the heated pr, it will have a thinner consistency and any bubbles will float out easier and faster. Hope this helps.
 
The flash point for polyester resin is 88 degrees F so the torch is definitely not a good idea. There is an article in the library entltled 'bubble free casting'. Maybe a quick read would be helpful. Show the MSDS sheet to that guy at TAP plastic...if he still is working there.
Do a good turn daily!
Don
gothycdesigns said:
So I'm working on some bottle stoppers. I am casting some small skulls in some clear PR.
I'm using a 1" i.d. PVC pipe for the molds and only pouring about 5/8" - 7/8" thick. I'm trying to mix the PR and cat. as smoothly as possible but I expect some bubbles. The question is, can using a butane torch with light passes over the PR help pull and rid some of the bubble? a guy at the local TAP plastics says it could get rid of most, not all bubbles. as long as you use quick passes and low setting.

Just curious if anyone has any experience on this or advise. I do not have a vacuum chamber
so was thinking this for an alt. option til then.

ThX

Ray
Click to expand...
 
i've only cast a few molds so far, but i've been putting them on my scroll saw table and vibrating them for around a minute. I haven't had any bubble so far. might be worth a shot...
 
Does vibration really get rid of the bubbles? If it does could you build a small board with the vibrator from one of these recliners that vibrate and mount it to the bottom of the board. Then mount the board on some rubber legs. Build a small box or rails on the board to keep your mold from vibrating off. Then just set the mold on the board and flip a switch and vibrate.
 
I don't know how well this works only try it once. will try it some more today and let you know how it works. I poured the pr through a piece of window screen with real small holes and the results came out with very few bubbles.
 
PR and open flames are the recipe for disaster.

The flash point of PR (fiberglass) resin is less than 90 degrees. Additionally, depending on the addatives in mix, ignited vapor fumes are likely to be toxic. Having ANY open flame (and yes that includes your kerosene heater over in the corner) is pure INSANITY.

In layman's terms that means if the fire doesn't kill you, the fumes will. PR really should be cast WITHOUT FLAME and outdoors in a well ventilated area.

If bubbles are a big problem and pressure is not an option, you can use a small "toaster over" set at approximately 120 -150 F to heat the resin before adding MEKP. Vibrating will also work as will straining the mixture through window screen when filling the mold.

OPEN FLAMES AND PR ARE LETHAL, but could be fun to watch as all the big red trucks and men with high pressure hoses arrive.:)
 
If you are mixing small batches of resin a small crock-pot is what I use it will heat the resin to a temp of up to 200 degrees. I quit using plastic cups to mix resin in and started using shot glasses (cheep at yard sales and thrift stores) after pouring a wipe with paper towel and second wipe with acetone wet paper towel. I marked the side of the shot glass for the resin saver molds by a scratch. My resin saver 2 cavity holds one ounce.
I also vacuum the resin before pouring. For an inexpensive vacuum pump go to medical supply stores I got mine for ten dollars. (the pump will pull about 25 hg)

Mark
 
tommyd said:
I don't know how well this works only try it once. will try it some more today and let you know how it works. I poured the pr through a piece of window screen with real small holes and the results came out with very few bubbles.
Click to expand...
never mind tried it again with no luck.
 
ThX everyone. I understand about the flammable part...so I was curious to ask....lol. well. I did try it the other night. Actually it seemed to work. Keep in mind I'm not doing a steady flame over the batch. total amount poured was just about less than 1oz. The setting on the torch was so low it was wanting to shut off. So the flame wasn't straight out. I made even passes about the speed of as quick spray of paint would go. It took out most of the bubbles. But I'm sure they all can't be rid of in this manner. I probably won't do the method again because it does seem like a time waster.

I like the ideas of the toaster ovens. I have even thought of making a small hotbox to help with curing time in cold weather. But anyways, I'm still alive...hehe. Even still have the eyebrows, so no flashing happened. Smells really couldn't tell because the flame didn't touch the mixture at all. But also understand the concerns of harmful vapors.
One of those had to try to see...

Thx for the support.
 
Seems like most of the info you need is here.. read Don's article on bubble free
casting, it's good. You don't need fancy equipment.

There's two sets of bubbles you need to worry about.. the ones in porous
materials (doesn't sound like your issue) or the ones introduced by mixing.
Those are suspended in the resin. Warming the resin or vibrating it (or both)
clear these bubbles very well.
You can warm the resin with hot tap water.. just get your container of resin
into a warm bath and let it get thin.

http://content.penturners.org/articles/2009/casting_bubble_free.pdf

there's a lot of good info in this article.
 
Great, I'll def. check it out. I have tried vibrating the mixture. The best thing I have is a Porter Cable orbital sander. I just cover the cup lightly and hold everything. Works ok. But I'll try the hot water aswell. ThX
 
sander jig

I just set the sander upside down on a piece of scrap and traced it. I then cut it on the bandsaw and fastened it to another scrap the same size.

I use it to finish sand small pieces. I use it to finish sand the ends of blanks. and now I use it to vibrate out bubbles.

Works so far.
 
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Thank you.

leestoresund said:
I just set the sander upside down on a piece of scrap and traced it. I then cut it on the bandsaw and fastened it to another scrap the same size.

I use it to finish sand small pieces. I use it to finish sand the ends of blanks. and now I use it to vibrate out bubbles.

Works so far.
Click to expand...
 
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