The quality of vacuum pump oil is mainly distinguished through the following aspects:
1. Extremely low vapor pressure: This is the most important performance indicator of vacuum pump oil. The lower the vapor pressure, the higher the vacuum degree. Since the rotary vane vacuum pump requires a vacuum degree of 0.06Pa, and the highest requirement is less than 1.33×10-4Pa, the evaporability of the vacuum pump oil is required to be extremely low. Generally, paraffin-based narrow fraction lubricants are used. For diffusion vacuum pumps, silicone oil or other synthetic oils with very low vapor pressure can also be used.
2. Appropriate viscosity and good viscosity-temperature characteristics: The vacuum system utilizes the continuous changes in the volume of the pump cavity to form an exhaust effect, which requires the lubricating oil to have appropriate viscosity and good viscosity-temperature characteristics. (The viscosity-temperature characteristics mean that the viscosity of the vacuum oil will change as the temperature inside the pump increases or decreases. The vacuum oil with good viscosity-temperature characteristics will have smaller changes in viscosity with temperature.)
3. Good thermal oxidation stability: Vacuum pumps continue to develop at high speeds. Due to the high-speed friction between the sliding vane and the pump body, the oil temperature increases, which intensifies the heat and oxidation of the oil. Diffusion pumps often work at very high ambient temperatures, and poor thermal oxidation will cause the vacuum pump oil to oxidize and deteriorate. This results in low vacuum degree, so the vacuum pump oil is required to have good thermal oxidation stability.
4. Good corrosion resistance and anti-emulsification: If the vacuum pump inhales corrosive gases, it will corrode the metal parts and oil in the pump and cause chemical changes. In addition, the inhaled air often contains water vapor, which causes the vacuum pump oil to emulsify, so it requires good corrosion resistance and emulsification resistance. The emulsification of vacuum pump oil used in the vacuum dehydration process is more prominent.
5. Higher flash point: It is required that the vacuum pump does not carry light components to avoid affecting the saturated vapor pressure of the oil. (When the volatile vapor of a flammable liquid is mixed with air and reaches a certain concentration, it will burn briefly when exposed to an open flame, or when a combustible solid is heated to a certain temperature, a flash-on combustion phenomenon will occur when exposed to an open flame, which is called flash combustion. Occurrence The lowest temperature of a solid during flash combustion is called the flash point)