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joelhains

"De-gassing" plastic

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Joel, that's pretty much how it works. Here's a copy paste that explains it a little better. Frank may be along to tell you how much vacuum you have to pull. I just buy the degassed stuff from Baitjunkys. Leonard has good prices, anyways.

"Vacuum degassing is the process of using vacuum to remove gases from compounds which become entrapped in the mixture when mixing the components."[2] To assure a bubble-free mold when mixing resin and silicone rubbers and slower setting harder resins, a vacuum chamber is required. A small vacuum chamber is needed for de-airing (eliminating air bubbles) for materials prior to their setting. The process is fairly straight forward. The casting or molding material is mixed according to the manufacturers directions.

ProcessEdit

Since the material may expand 4-5 times under a vacuum, the mixing container must be large enough to hold a volume of four to five times the amount of the original material that is being vacuumed to allow for the expansion; if not, it will spill over the top of the container requiring clean-up that can be avoided. The material container is then placed into the vacuum chamber; a vacuum pump is connected and turned on. Once the vacuum reaches 29 inches (at sea level) of mercury, the material will begin to rise (resembling foam). When the material falls, it will plateau and stop rising. The vacuuming is continued for another 2 to 3 minutes to make certain all of the air has been removed from the material. Once this interval is reached, the vacuum pump is shut off and the vacuum chamber release valve is opened to equalize air pressure. The vacuum chamber is opened, the material is removed and is ready to pour into the mold.

Though a maximum vacuum one can theoretically achieve at sea level is 29.921 inches of mercury (Hg,) this will vary significantly as altitude increases. For example for a mold making in Denver, Colorado, which sits at 5280 feet above sea level, one can only achieve a vacuum on the mercury scale of 24.896 Hg in their vacuum chamber.

To keep the material air-free, it must be slowly poured in a high and narrow stream starting from the corner of the mold box, or mold, letting the material flow freely into the box or mold cavity. Usually, this method will not introduce any new bubbles into the vacuumed material. To ensure that the material is totally devoid of air bubbles, the entire mold/mold box may be placed in the chamber for an additional few minutes, this will assist the material in flowing into difficult areas of the mold/mold box.

Vacuum dryingEdit

Water and other liquids may accumulate on a product during the production process. "Vacuum is often employed as a process for removing bulk and absorbed water (or other solvents) from a product. Combined with heat, vacuum can be an effective method for drying."[3] [4]

 

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14 hours ago, Apdriver said:

The thing about the chamber being 4-5 times as large as what you are degassing should be pointed out and recognized. It expands tremendously during degassing. So to degas a gallon of plastic you should have a five gallon chamber.

 

Sounds like it swells like a politician's head!  Hahaha

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Ap driver nailed it.  4 or 5 times the size is needed. 

If you get it big enough you can set a small container inside to transfer the liquid. I put valves and stuff in my big pots, so I dump in the top, valve off the bottom.

Best value vacs is what I have. I got 5 Big ones. I use a little better pump tho.

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Make sure and get one that pulls a vacuum down to 29.4 or lower. You will not get the air out unless it is at least that much. If you get one that may be a little small you could always get a resin trap. When it over flows it will fall in the resin trap and not go up in your pump.  It's not real exciting just put what you want to use in the pot and turn it on. A short time later it will grow and bubbles will pop and go back to normal.  

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