The use and precautions of vacuum pump oil
Requirement one: tightness
The pump oil in the vacuum pump accessories must have a suitable viscosity, which can enable the vacuum pump to start quickly at low temperature, and the pump oil can have good sealing performance at high temperature, and the pump oil in the pump has a low temperature rise. Does not contain light volatile components, reducing the oil return rate of the vacuum pump during operation.
Requirement 2: Saturated vapor pressure
Saturated vapor pressure is one of the more critical indicators of pump oil. In a constant temperature airtight container, the pressure when the vapor-liquid two phases reach dynamic equilibrium is called the saturated vapor pressure.
The saturated vapor pressure of the oil should be as low as possible. At the maximum working temperature of the pump, it still has a sufficiently low saturated vapor pressure and is lower than the ultimate pressure of the vacuum pump regulations. At least 6.5 × 10-5 kPa at a temperature of 60 °C (since the temperature rises by 20 °C, the saturated vapor pressure will drop by about an order of magnitude).
Requirement 3: Ultimate Total Pressure and Ultimate Partial Pressure
Ultimate total pressure: The sum of the pressure generated by all substances (gases) in the vacuum pump is measured by a Pirani gauge or a thermocouple vacuum gauge. At present, foreign countries pay attention to the test index of full pressure.
Ultimate partial pressure: the ultimate air partial pressure of the pump measured by a mercury compact vacuum gauge (McFurnier), the partial pressure of the two-stage rotary vane pump should be ≤6×10-5kPa. The difference between the ultimate total pressure and the ultimate partial pressure The request is no larger than an order of magnitude. The greater the difference between the two, the more volatile components the pump oil contains, and the worse the oil properties.
Requirement 4: The smoothness of the pump oil in the vacuum pump accessories
The friction wear, surface fatigue wear and corrosion wear of the friction surface are all related to the smooth conditions. Pump oil with good performance is beneficial to inhibit corrosion and wear; it can effectively reduce adhesive wear and surface fatigue wear; fluid lubricants have a cleaning effect on friction surfaces and can also reduce friction and wear. Reduce frictional resistance to save energy and reduce wear to extend mechanical life.
Requirement 5: Cooling and cooling performance
Reducing the temperature of the friction surface is an important function of smoothness. When the friction surface moves, it is necessary to restrain the friction force and do work, and all the work spent in restraining the friction force is converted into heat, which will cause the temperature of the friction surface to rise. The magnitude of frictional heat is related to the smooth state, the heat of high viscosity is the largest, the heat of low viscosity is the smallest, and the heat of border friction is between the two. It can be seen that using pump oil of suitable viscosity can not only complete the smoothing of the liquid and reduce the generation of frictional heat, but also can bring the frictional heat out of the pump in time.
Requirement 6: Cleanliness
Prevent contact with surrounding media during friction, causing corrosion, rust and damage. The pump oil with excellent performance cleans and removes the scale on the friction area as much as possible.
Requirement 7: Oxidation stability of pump oil
Oxidation stability indicates the anti-aging performance of lubricating oil, and this special performance is required for pump oil in industrial assembly line operations. All lubricating oils have different levels of auto-oxidative tendencies depending on their chemical composition and external conditions. In the presence of air (or oxygen) and metal catalyst, the pump oil will show the acid value of the oil, the change of viscosity and the formation of sediment during the oxidation time at a certain temperature. Oxidation occurs with the use process, so some aldehydes, ketones, acids, colloids, asphaltenes and other substances are gradually generated.
Requirement 8: Thermal stability
Indicates the high temperature resistance of the oil, that is, the resistance of the lubricating oil to thermal synthesis, that is, the thermal synthesis temperature. Some harsh vacuum application environments will require thermal stability of vacuum oil.
Natural mineral oil has its inevitable defects, the heat resistance is worse than that of synthetic oil, the composition is easily deteriorated with thermal oxidation synthesis, the ultimate pressure stability is poor, and the pumping speed also decreases with the use time. Ordinary pure mineral oil oxidation test method D943 is about several hundred hours, while D943 of synthetic oil can be extended to more than 3000 hours. It can be seen that its service life has been extended.
Requirement 9: Demulsibility
During the operation of the vacuum pump, the water and cold air in the system will be discharged into the pump oil. If the anti-emulsification is not good, it will form an emulsion with the mixed water, so that the water is not easy to be released from the bottom of the circulating oil tank, which may form a vacuum. Degree drop and poor smoothness.
Therefore, demulsibility is a very important physical and chemical property of industrial lubricating oil. Especially in the vacuum drying process of pharmaceutical, food, ceramics and other industries, the anti-emulsification performance is more important. The pump with good anti-emulsification has strong oil-water separation ability, and the water vapor and condensed gas will discharge local water vapor after opening the gas ballast valve. In addition, low viscosity demulsibility is better than high viscosity pump oil.
Requirement 10: Anti-foaming
During the operation of the vacuum pump, due to the presence of air, foam is often generated, especially when the oil contains additives with surface activity, it is more likely to generate foam, and the foam is not easy to disappear. The generation of foam in the use of lubricating oil will damage the oil film, not only cause the friction surface to sinter or increase wear, but also promote the oxidative transformation of lubricating oil. The air in the vacuum system in operation is discharged from time to time through the sealed pump oil layer. The discharged air will produce a large number of air bubbles on the surface of the oil layer and overflow from the exhaust hole of the pump, resulting in oil loss and equipment pollution. The pump oil with anti-foaming agent has obvious improvement in anti-foaming effect.
In a word, vacuum pump oil is a part of vacuum pump accessories and plays a vital role in the equipment. Certain requirements must be followed when selecting it.
The pump oil in the vacuum pump accessories must have a suitable viscosity, which can enable the vacuum pump to start quickly at low temperature, and the pump oil can have good sealing performance at high temperature, and the pump oil in the pump has a low temperature rise. Does not contain light volatile components, reducing the oil return rate of the vacuum pump during operation.
Requirement 2: Saturated vapor pressure
Saturated vapor pressure is one of the more critical indicators of pump oil. In a constant temperature airtight container, the pressure when the vapor-liquid two phases reach dynamic equilibrium is called the saturated vapor pressure.
The saturated vapor pressure of the oil should be as low as possible. At the maximum working temperature of the pump, it still has a sufficiently low saturated vapor pressure and is lower than the ultimate pressure of the vacuum pump regulations. At least 6.5 × 10-5 kPa at a temperature of 60 °C (since the temperature rises by 20 °C, the saturated vapor pressure will drop by about an order of magnitude).
Requirement 3: Ultimate Total Pressure and Ultimate Partial Pressure
Ultimate total pressure: The sum of the pressure generated by all substances (gases) in the vacuum pump is measured by a Pirani gauge or a thermocouple vacuum gauge. At present, foreign countries pay attention to the test index of full pressure.
Ultimate partial pressure: the ultimate air partial pressure of the pump measured by a mercury compact vacuum gauge (McFurnier), the partial pressure of the two-stage rotary vane pump should be ≤6×10-5kPa. The difference between the ultimate total pressure and the ultimate partial pressure The request is no larger than an order of magnitude. The greater the difference between the two, the more volatile components the pump oil contains, and the worse the oil properties.
Requirement 4: The smoothness of the pump oil in the vacuum pump accessories
The friction wear, surface fatigue wear and corrosion wear of the friction surface are all related to the smooth conditions. Pump oil with good performance is beneficial to inhibit corrosion and wear; it can effectively reduce adhesive wear and surface fatigue wear; fluid lubricants have a cleaning effect on friction surfaces and can also reduce friction and wear. Reduce frictional resistance to save energy and reduce wear to extend mechanical life.
Requirement 5: Cooling and cooling performance
Reducing the temperature of the friction surface is an important function of smoothness. When the friction surface moves, it is necessary to restrain the friction force and do work, and all the work spent in restraining the friction force is converted into heat, which will cause the temperature of the friction surface to rise. The magnitude of frictional heat is related to the smooth state, the heat of high viscosity is the largest, the heat of low viscosity is the smallest, and the heat of border friction is between the two. It can be seen that using pump oil of suitable viscosity can not only complete the smoothing of the liquid and reduce the generation of frictional heat, but also can bring the frictional heat out of the pump in time.
Requirement 6: Cleanliness
Prevent contact with surrounding media during friction, causing corrosion, rust and damage. The pump oil with excellent performance cleans and removes the scale on the friction area as much as possible.
Requirement 7: Oxidation stability of pump oil
Oxidation stability indicates the anti-aging performance of lubricating oil, and this special performance is required for pump oil in industrial assembly line operations. All lubricating oils have different levels of auto-oxidative tendencies depending on their chemical composition and external conditions. In the presence of air (or oxygen) and metal catalyst, the pump oil will show the acid value of the oil, the change of viscosity and the formation of sediment during the oxidation time at a certain temperature. Oxidation occurs with the use process, so some aldehydes, ketones, acids, colloids, asphaltenes and other substances are gradually generated.
Requirement 8: Thermal stability
Indicates the high temperature resistance of the oil, that is, the resistance of the lubricating oil to thermal synthesis, that is, the thermal synthesis temperature. Some harsh vacuum application environments will require thermal stability of vacuum oil.
Natural mineral oil has its inevitable defects, the heat resistance is worse than that of synthetic oil, the composition is easily deteriorated with thermal oxidation synthesis, the ultimate pressure stability is poor, and the pumping speed also decreases with the use time. Ordinary pure mineral oil oxidation test method D943 is about several hundred hours, while D943 of synthetic oil can be extended to more than 3000 hours. It can be seen that its service life has been extended.
Requirement 9: Demulsibility
During the operation of the vacuum pump, the water and cold air in the system will be discharged into the pump oil. If the anti-emulsification is not good, it will form an emulsion with the mixed water, so that the water is not easy to be released from the bottom of the circulating oil tank, which may form a vacuum. Degree drop and poor smoothness.
Therefore, demulsibility is a very important physical and chemical property of industrial lubricating oil. Especially in the vacuum drying process of pharmaceutical, food, ceramics and other industries, the anti-emulsification performance is more important. The pump with good anti-emulsification has strong oil-water separation ability, and the water vapor and condensed gas will discharge local water vapor after opening the gas ballast valve. In addition, low viscosity demulsibility is better than high viscosity pump oil.
Requirement 10: Anti-foaming
During the operation of the vacuum pump, due to the presence of air, foam is often generated, especially when the oil contains additives with surface activity, it is more likely to generate foam, and the foam is not easy to disappear. The generation of foam in the use of lubricating oil will damage the oil film, not only cause the friction surface to sinter or increase wear, but also promote the oxidative transformation of lubricating oil. The air in the vacuum system in operation is discharged from time to time through the sealed pump oil layer. The discharged air will produce a large number of air bubbles on the surface of the oil layer and overflow from the exhaust hole of the pump, resulting in oil loss and equipment pollution. The pump oil with anti-foaming agent has obvious improvement in anti-foaming effect.
In a word, vacuum pump oil is a part of vacuum pump accessories and plays a vital role in the equipment. Certain requirements must be followed when selecting it.