Q. What is the difference between vacuum degassing and pressurizing?

A. Vacuum de-gassing expands the air trapped during mixing or pouring, causing the bubbles to grow, rise to the surface, and in most cases, release. After a period of time the amount of trapped air decreases. The material’s viscosity and surface tension will determine how easily the air will escape. Certain materials appear to bubble indefinitely until the vacuum pump is turned off. In order to maximize the vacuum’s potential for air removal, the pump must be capable of pulling 29.6 inHg.

Degassing

Vacuum Degassing using the X-Vac™ Chamber

When placed under pressure, any air bubbles entrapped from the mixing and pouring process shrink to the point where they are no longer visible. Pressure ranging from 60-80 psi significantly reduces the chances of visible air bubbles. For pressure to be effective, the liquid thermoset material must remain under pressure until it has reached its gel time, otherwise the bubbles may expand once the pressure is relieved.

Pressure Casting using Hapco's Molding ChamberPressure Casting using the X-11 Molding Chamber

Q. Is one method preferred over the other?

A. One method really isn’t preferred over the other. Whether you choose to use vacuum or pressure depends on the application, your capabilities, and budget. In fact, we often recommend vacuum degassing your product after hand mixing, pouring into the mold, and then using pressure to make sure all parts of the mold are filled. When using dispensing equipment, there is no air introduced during mixing. That doesn’t mean air cannot be introduced while shooting into your mold, especially one with many thin walls, sharp corners, or intricate details.

If you find yourself in a situation where you absolutely need a bubble free part (e.g., using a plaster mold or a large quantity of expensive material) it’s best to play it safe and employ both methods. If neither option is in your budget and you need a void free surface, we recommend using low viscosity materials, mixing slowly and thoroughly, and brushing a thin coat onto the mold or pattern’s surface. Using a hair dryer while brushing the thin coat will help to ease surface tension and reduce bubbles.

Use Hair Dryer or Heat Gun to Pop Air Bubbles

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