If you have discussed vacuum impregnation with us before, then you’ve probably heard about superior impregnation results being all about process control – deep, consistent vacuum (less than 5 torr) and clean, dry parts.
Deep, Consistent Vacuum
Water, or should I say, the evaporation of water from the surface and/or porosity of parts being impregnated, increases the time it takes to reach deep vacuum.
When water boils, going from a liquid to gaseous state, it expands approximately 1,700 times. That expansion means there is more volume for the vacuum pump to evacuate from the vessel in order to reach the desired set point.
- 5cc of water (1 teaspoon) on the surface of a part will expand to approximately 8,500 cc (0.3 cubic feet) of gas when the vacuum level drops below 20 torr.
- If the water is in the pores (porosity) of the part, the evaporation process could take several seconds more than evaporating from the surface, depending on size of the migration path.
Bottom line, if you do not get the air out of the parts, then the sealant will not fill and/or stay in the porosity.
Clean, Dry Parts
It is very important that your parts come to impregnation free of surface impurities. Surface impurities, such as oils and solvents, can impede the sealant’s ability to penetrate the casting and worse, contaminate the sealant and inhibit its ability to seal the porosity.
- Below is a transmission case where oil (circled in red) is pooling out of the rings.
- The oil will need to be completely removed prior to vacuum impregnation so that the porosity can be filled.
In conclusion, when considering or preparing for a coupled manufacturing process/operation where machining and parts washing is directly upstream of impregnation, be sure and include the appropriate drying process. Ensuring that your vacuum impregnation system receives clean dry parts every time will help guarantee that they are impregnated efficiently.
To discuss your specific system or situation, contact us at 330-562-1440 or send us an email.