There are three types of vacuum impregnation processes:
- Dry Vacuum and Pressure (DVP)
- Dry Vacuum (DV)
- Wet Vacuum (WV)
Dry Vacuum and Pressure (DVP) is the most commonly used process in Godfrey & Wing equipment. To better understand the DVP process, this blog will discuss the process step by step, and its advantages. The following example illustrates engine blocks being impregnated in a traditional batch system.
What is the "Dry Vacuum and Pressure" Impregnation Process?
Parts are loaded into a dry impregnation chamber, and the vacuum is applied until a predetermined setpoint is achieved. This vacuum setpoint has been specified in US military specifications to be no less than 29” of mercury (23.4 Torr or 31mbar). There is no liquid present in the vessel to impede air removal from the porosity. All parts see a uniform vacuum pressure that originates from the vacuum pump. This is the "Dry Vacuum" portion of the process.
When the vacuum end point is reached, the transfer valve is opened. The sealant (shown in green) is de-gased and pulled from the reservoir to the impregnation vessel while the vacuum is maintained.
Next, the vacuum is released, and overpressure is applied (typically between 70-90 PSI) from above. The pressure is then held to allow the sealant to penetrate the porosity. The transfer valve is re-opened and the sealant is transfered back to the storage reservoir. The parts are removed to be washed and cured.
What are the Advantages of Dry Vacuum and Pressure Impregnation?
Removing air from the leak path (porosity) is one of the four key characteristics in vacuum impregnation. If casting pores contains air, sealant cannot enter the pores to seal the leak path. The dry vacuum process ensures the air is removed allowing sealant to penetrate deep into the casting.
Bottom line, Dry Vacuum Pressure impregnation is the most thorough and robust form of vacuum impregnation and delivers that highest possible rate of leak free components.