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Vacuum pump oil

Vacuum pump is a device to improve, generate and maintain vacuum in a closed space by various means. According to the working principle of vacuum pump, vacuum pump can be basically divided into two types, namely gas capture pump and gas transmission pump. It is widely used in metallurgy, chemical industry, food, electronic coating and other industries. How to correct vacuum pump oil is very important. How to select pump oil more effectively and the matters needing attention during selection?


What is vacuum pump oil?


Vacuum pump oil is a kind of lubricating oil specially developed for vacuum pump on vacuum equipment. It is divided into mineral oil and synthetic oil.

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10 characteristics of vacuum pump oil and matters needing attention during selection:


1. Tightness of vacuum pump oil


Vacuum pump oil needs to have appropriate viscosity, can make the vacuum pump start quickly at low temperature, vacuum pump oil can have good sealing at high temperature, vacuum pump oil has a low temperature rise in the pump. It does not contain light volatile components and reduces the oil return rate of vacuum pumps during operation.


2. Saturated vapor pressure of vacuum pump oil


Saturated vapor pressure is one of the key indicators of vacuum pump oil. In a constant temperature closed container, when vapor liquid two phase is in dynamic equilibrium, the pressure term is saturated vapor pressure. The saturated vapor pressure of oil products should be as low as possible. At the highest working temperature of the pump, the saturated vapor pressure should be sufficiently low and should be lower than the limit pressure stipulated by the vacuum pump. The saturated vapor pressure will drop by about an order of magnitude for every 20 C rise in temperature, at least 6.5 10 - 8 kPa at 60 C.


3. Limit total pressure and limit pressure of vacuum pump oil


Limit total pressure: The total pressure produced by all substances (gases) in the vacuum pump is measured by a Pirani gauge or a thermocouple vacuum gauge. Foreign countries now attach importance to the test target of full pressure.


Limit partial pressure: Limit partial pressure of the pump measured by mercury compression vacuum gauge (Maxwell gauge), the partial pressure of the two-stage rotary vane pump should be <6 *10-5 kPa. The difference between limit total pressure and limit differential pressure is not greater than one order of magnitude. The greater the difference between the two, the more volatile components in vacuum pump oil, the worse the nature of the oil.


4. The lubricity of vacuum pump oil


Frictional wear, surface fatigue wear and corrosive wear are all related to lubrication conditions. Excellent performance of vacuum pump oil is conducive to inhibiting corrosion wear; can effectively reduce adhesion wear and surface fatigue wear; fluid lubricants on the friction surface cleaning role, but also to reduce friction wear. Reduce friction resistance to save energy and reduce wear to extend mechanical life.


5. Cooling performance of vacuum pump oil


Lowering the temperature of the friction surface is an important function of lubrication. When the friction surface moves, the work must be done by overcoming the friction force. The work consumed by overcoming the friction force is converted into heat, and the result will cause the temperature of the friction surface to rise. The magnitude of friction heat is related to the lubrication state. The heat of high viscosity is the largest, the heat of low viscosity is the smallest, and the heat of boundary friction is between the two. Therefore, the vacuum pump oil with suitable viscosity can not only achieve liquid lubrication, reduce the generation of friction heat, but also can bring friction heat out of the pump in time.

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6. The detergency of vacuum pump oil


The friction pair inevitably contacts with the surrounding medium, causing corrosion and corrosion. Excellent performance of vacuum pump oil requires as far as possible to clean the friction area of the scale removal; corrosion resistance and rust prevention and protection of the friction surface from oil deterioration or external erosion.


7. Oxidation stability of vacuum pump oil


Oxidation stability shows the anti-aging property of lubricating oil, which has this special performance requirement for vacuum pump oil in industrial production line operation. All lubricants have varying degrees of automatic oxidation tendency depending on their chemical composition and external conditions. In the presence of air (or oxygen) and metal catalysts, vacuum pump oil will be oxidized at a certain temperature for a certain time, the acid value of the oil, viscosity changes and the formation of precipitates. Oxygenation will occur with the use of the process, and thus gradually produce some aldehydes, ketones, acids and resins, asphaltenes and other substances, oxidation stability is to inhibit the above-mentioned unfavorable to the use of oil generation of substances.


8. Heat stability of vacuum pump oil


It indicates the high temperature resistance of oil, that is, the resistance of lubricating oil to thermal decomposition, that is, the thermal decomposition temperature. Some harsh vacuum environment will require the thermal stability of vacuum oil products.


Natural mineral oils have their unavoidable shortcomings. Their heat resistance is worse than synthetic oils. The composition of pump oils is easily deteriorated with thermal oxidation decomposition. The stability of limit pressure is poor, and the pumping speed is also reduced with the use time. Generally speaking, the oxidation test method of pure mineral oil D943 is about several hundred hours, while synthetic oil D943 can be extended to more than 3000 hours. Its service life can be prolonged.


9. Emulsification of vacuum pump oil


During the operation of the vacuum pump, the water and cold gas in the system will be discharged into the pump oil. If the anti-emulsification of the vacuum pump oil is not good, it will form an emulsion with the mixed water, so that the water is not easy to be discharged from the bottom of the circulating tank, which may cause the vacuum degree to drop and poor lubrication. Therefore, emulsification is a very important physicochemical property of industrial lubricants. Especially in the vacuum drying process of medicine, food, ceramics and other industries, the anti-emulsification performance of pump oil is more important. Good anti-emulsifying pump oil-water separation ability, water vapor and condensate gas through the opening of the gas ballast, will discharge part of the steam. In addition, the emulsion resistance of low viscosity pump oil is better than that of high viscosity pump oil.


10. Anti foaming property of vacuum pump oil


Vacuum pump in the operation process, due to the existence of air, often produce foam, especially when oil contains surfactant additives, it is easier to produce foam, and foam is not easy to disappear. Foaming in lubricating oil will destroy the oil film, not only sintering or increasing wear on the friction surface, but also promoting oxidation and deterioration of lubricating oil. Gas in the running vacuum system will be continuously discharged through the sealed vacuum pump oil layer, the gas discharged will produce a large number of bubbles on the surface of the oil layer, and overflow from the pump vent hole, resulting in oil loss and equipment pollution. The anti foam effect of the pump oil is obviously improved.

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