A DIY vacuum chamber ~ M.Koushyar

Summary

For those who mold RTV silicone or resins such as epoxy, degassing is important. In this project, I will introduce a DIY vacuum chamber that has been very useful to me. I used the following to make this vacuum chamber:

pneumatic hose
pneumatic fitting
3d printed gasket
silicone RTV2 for gasket sealer
wide-mouth big size glass bottle
Vacuum pump

Background

Two-component resins, or resins that require a hardener to set, produce air bubbles when mixing, as well as the RTV silicone that must be mixed to a 5 to 50 percent hardener depending on the manufacturer's brand.
For resin, we consider several different time periods.

Mixing time is when we normally have the time to mix two A and B parts. Mixing also has its own principles and rules. For example, we must be careful to mix them very evenly and not to skip any part. If we are mixing in a simple container, we should not neglect the bottom and walls of the container, because mixing is less tend to happen in these areas. Mixing is done either with a stick or mixing machine. The faster the mixing and the higher the viscosity, the more likely the bubbles will be trapped.

Working time is the time period in which we have respite to pour the material into the mold. At the end of working time, the resin starts internal chemical reactions and sets.

Since the working time of the resin may be short, mixing is done faster to extend the working respite. In workshops where the workload is high, there is more rush, so many bubbles will be trapped in the resin.
Definitely no one likes trapped air bubbles. In silicone, it reduces the life of the part and causes cracking and tearing. In addition, bubbles that come in contact with the outer walls of the piece reduce the quality of the surface.
So you have to somehow pull out the trapped bubbles. These methods are briefly as follows

No additional equipment:

Mix very gently, so that the mixing stick does not create waves and the waves do not land on top of each other.
Sprinkle a liquid like alcohol on the surface of the mixed resin; This reduces surface tension and bubbles close to the upper surface. This is suitable for low volume epoxy resin, for example less than 15 grams.
Using a toothpick and guiding the bubbles to the liquid surface; This method can be done in simple molds and low weight.

Pour the resin from a great height, such as 40 cm, until a strip drips from container and the bubbles burst while falling.

With equipment

There are positive pressure or negative pressure methods.

Place the mixed resin or silicone in a vacuum chamber during mixing time. With this card, the bubbles are pulled out.
Place the mixed resin or silicone in a high pressure chamber during working time. In this method, the air pressure is increased so that the trapped bubbles are completely compressed and disappear.
The difference with negative pressure method is that it must be done when the resin is poured into the mold. But the negative pressure method is done at mixing time.
The point negative method is that, immediately after degassing, the resin must be molded.

Designing of vacuum chamber

The vacuum chamber is an air tight chamber against vacuum. I got a wide-mouth big size glass bottle. The thickness of the glass should be high so that it does not break and does not pose a danger. The vacuum pressure will reach very low values. the vacuum pump is 1/4 HP.

The design is very simple. In the gasket part of the cap, I made an O-ring made of silicone, which automatically tightens in place when the vacuum pump is turned on and the air is sucked.