Vacuum Equipment

Last modified by Hypno Harem on 2022/07/19 17:54

A vacuum pump is used during degassing to remove bubbles and dissolved gasses from silicone.  The silicone is placed in a container and into the chamber which the pump pulls a vacuum on. This is an important step in producing a toy. Silicones that are "no vacuum required" do not produce bubble free castings acceptable for use in a person's body. They produce castings that are bubble free enough for making molds. Pumps and chambers are available from many sources and need not be prohibitively expensive for start up.

Choosing a pump and chamber can be a little confusing, so here are some pointers: 💚

  1. Just start with a cheap 5 gallon chamber and >3CFM single stage pump. Don't overthink it too much. They are less than $200 and will make their money back for you pretty fast. You'll have a better idea of what you don't like in a chamber by the time you are ready for an upgrade.
  2. See above
  3. How many containers of silicone do you want to degas at one time? Try laying them out on a table to get an idea of how much room they will take up when stacked together. Measure this and look at the ID (inner diameter) published for the chambers to match up.
  4. Get a chamber with a side entry air port if possible. Top entry ports will blow air down into the cups of silicone, splattering silicone around and becoming a source of foreign matter inclusions in your pours.
  5. Look for an acrylic top over a glass tops. Glass top chambers are VERY heavy and silicone will try to adhere to them.
  6. Get a >5 CFM duel stage pump to pull down to lower pressures for deeper degas and less flops.
  7. Do not buy an overly large chamber. Get only the size you need for the amount of silicone you like to pour at one time. A 10 gallon chamber used to degas two cups will take so long to evacuate the air that it will start to eat into your pot life.
  8. Buy a chamber from a company that also sells replacement gaskets for the lid, and buy two when you purchase the equipment.

Speeding Up Degas 💚

How fast you can degas is a function of the viscosity and surface tension of the silicone and the pump down characteristics of your equipment. You can lower viscosity through the addition of silicone oil, but this will change the firmness of the silicone; so it is generally preferable to focus on the equipment characteristics. The brute force approach is to buy the biggest and baddest 2 stage >8CFM pump available, often with disappointing results. Better approaches include:

  • Remove headspace in the chamber. If the full chamber has 2" of space between the top of the cups and the lid it could be doubling the amount of air in the chamber that must be removed. You can use a large piece of any solid non-porous material to fill the dead space. For example, the cup scrapings can be poured into the chamber to slowly create a large puck in the bottom that uses up the dead space, or you can cut a thick piece of acrylic.
  • Replace the fittings and hoses with the next size up. A 1/4" hose, three feet long will throttle a 9CFM pump down to the same speed as a 5CFM pump on a 1/2" line.
  • Keep up on maintenance! Check pump oil level and color and keep the lid gasket clean.

When looking to purchase an upgraded setup, BVV is a well known company selling a large selection of equipment. Double check that you are not purchasing a GlassVac as these have glass lids.


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