| What does "Dry-Vacuum-Pressure" impregnation mean?
The removal of air from all cavities within the casting prior to impregnation is extremely vital. Without this, the subsequent introduction of the impregnant into the porosity would be impeded or blocked. When the porous castings are placed in an empty impregnation vessel, (one that contains no impregnant), air in the pores is readily exhausted as soon as a vacuum is pulled on the castings, for at the time of evacuation there is no liquid present to impede removal of air from the pores. This is the "Dry-Vacuum" portion of the cycle. After evacuation for a specified length of time to remove air from the pores, the liquid impregnant is transferred into the vessel from a separate storage tank while parts are still under vacuum. As soon as parts are covered with impregnant, shop air pressure (80-100psi) is applied to the vessel forcing the impregnant into the evacuated porous cavities. This is the "pressure" portion of the "Dry-Vacuum-pressure" cycle.
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