1 Requirements for hydraulic oil performance
In hydraulic transmission, hydraulic oil is both a medium for transmitting power and a lubricant, and it also plays a sealing role in some components. The heat in the system is also diffused through the oil, so it also plays a role in heat dissipation. Therefore, in order to ensure that the hydraulic system works reliably, effectively and economically, the hydraulic oil must ensure the following requirements:
1) Appropriate viscosity. Viscosity is the magnitude of the frictional resistance between molecules when oil flows. When the viscosity is too large, the resistance when the oil flows is large, the energy loss is large, and the system efficiency is reduced. In addition, the no-load loss of the main engine increases, the temperature rises fast and the working temperature is high, and the phenomenon of "cavitation" easily occurs at the oil suction end of the main pump. If the viscosity is too small, the good lubrication conditions of the hydraulic components cannot be guaranteed, the wear of the components is increased, the leakage is increased, and the efficiency of the hydraulic system is also reduced.
2) Good viscosity-temperature characteristics. Viscosity-temperature characteristics refer to the degree to which oil viscosity rises and falls with temperature, and is usually expressed by viscosity index. The greater the viscosity index, the smaller the decrease in oil viscosity as the temperature rises during operation of the hydraulic system, so that the internal leakage of the hydraulic system is not too large. The viscosity index should not be lower than 90.
3) Good abrasion resistance and lubricity. The purpose is to reduce mechanical friction and ensure sufficient oil film strength under different pressure, speed and temperature conditions.
4) High chemical reaction stability, not easy to oxidize and deteriorate. Practice has proved that for every 10 ° C increase in oil temperature, the chemical reaction rate increases about twice. The hydraulic oil with good anti-oxidation stability is not prone to oxidative deterioration after long-term use, which can ensure the normal circulation of hydraulic oil. [!-empirenews.page--]
5) The quality should be pure, and the content of mechanical impurities, moisture and dust should be reduced as much as possible.
6) The impact on the seal should be small.
7) The anti-emulsification property is better, and it is not easy to cause foam. Anti-emulsification refers to the ability of oil mixed with water and after stirring, it does not become an emulsion and water is separated from it. Anti-foaming resistance refers to the ability of mixing air into the oil and not generating emulsions and bubbles from the oil after stirring. After mixing with water or air, the volume modulus of the hydraulic oil is reduced, the compressibility is increased, the hydraulic components act slowly, and they are prone to shock and vibration.
8) Good anti-rust performance. The hydraulic oil covers the surface of the parts to prevent them from being corroded by oxidation.
9) The stability of shear resistance is good. In order to improve the viscosity index of the oil, polymer polymers such as polymethacrylate and polyisobutylene are often added to the oil. These substances have long molecular chains, and the oil is greatly sheared when it flows through the slit of the hydraulic element. The effect will often break the chain of the molecule and reduce the viscosity-temperature characteristics of the oil.
10) The ignition point and flash point should meet the ambient temperature, and the volatility should be small to ensure the safe use of hydraulic oil.
In addition, the choice of grader hydraulic oil should also consider the different environments and regions of use. The oil used in winter and summer is also different. The brand and type of oil recommended by the manufacturer should be strictly followed.
2 Causes and hazards of hydraulic oil pollution
2.1 Sources of pollutants
1) Contaminants in new oil. Although hydraulic oil is refined and processed under relatively clean environmental conditions, it is contaminated by pipelines, oil drums and oil storage tanks during transportation and storage. Some dust, sand, rust, Moisture and other liquids.
2) Residual contaminants in components and systems. Hydraulic components and hydraulic systems may leave some contaminants due to incomplete cleaning during processing, assembly and cleaning.
3) Intrusion of pollutants from outside. In the process of hydraulic components and mechanical work, due to imperfect sealing of the fuel tank, damage to the component sealing and protective devices, some contaminants such as dust, sand, and moisture invade from the outside of the system.
4) Contaminants generated inside the hydraulic system. The hydraulic system itself will generate some solid particulate pollutants in the work, including metal particles or rubber powder produced by the wear and corrosion of hydraulic components, and pollutants produced by the oxidation of oil. [!-empirenews.page--]
2.2 The hazards of hydraulic oil pollution
1) The contaminants often cause the throttle valve and pressure damping hole to be blocked at times, and even block the valve core, causing the hydraulic system working pressure and speed to change from time to time, affecting its normal operation.
2) Accelerate the wear of hydraulic pumps, motors, and valve blocks, causing an increase in internal leakage.
3) The water mixed in the hydraulic oil corrodes the metal and accelerates the aging and deterioration of the hydraulic oil.
4) The air mixed into the hydraulic oil will cause noise, vibration, creeping, cavitation and impact phenomena, thereby deteriorating the performance of the hydraulic system.
3 Maintenance of hydraulic oil
3.1 Prevent oil pollution
Among the various pumps and valve components used in the grader, the matching clearance and working surface between the relative moving parts are small, and there are many damping holes and slit-type control valve ports in the hydraulic components. If the oil is mixed with dirt If it is blocked, it may even scratch the mating surface, increase leakage, or even jam the spool, causing component failure. Therefore, keeping the oil clean is the key to the maintenance of the hydraulic system.
1) The hydraulic oil must be strictly filtered. When filling the hydraulic oil tank, it should pass through an oil filter of more than 120 mesh.
2) Regularly check the cleanliness of the oil and replace it regularly according to the working conditions. When replacing, the oil in the hydraulic system should be discharged as much as 40l. Among them, the method of using the outer circulation of the system is more operable. The method is to drain the waste oil in the fuel tank and radiator first, and then add new oil. Remove the oil return pipe into the oil tank, start the engine, and let the waste oil flow out of the oil return pipe completely. It is particularly emphasized that changes in the oil level in the fuel tank should be observed in a timely manner, and the safety level of the oil level should be ensured. When changing to new oil, the filter element of the filter should be replaced at the same time.
3) The hydraulic components should not be easily disassembled. If they must be disassembled, the parts should be cleaned with kerosene or diesel oil and placed in a clean place to avoid mixing of impurities during reassembly.
3.2 Prevent air from entering
The air dissolved in the oil will escape from the oil when the pressure is low, generating bubbles and cavitation.
3.3 Prevent moisture from entering
Take measures such as filtration and oil-water separation to prevent water from mixing into the oil and emulsifying.
3.4 Prevent excessive oil temperature
The working temperature of the hydraulic oil of the grader is generally in the range of 60 ~ 80 ℃. If the oil temperature is too high, the viscosity of the oil will decrease, the volumetric efficiency of the oil pump will decrease, the lubricating film will become thinner, mechanical wear will increase, and the seals will deteriorate and lose. Sealing performance. [!-empirenews.page--]
3.5 Regular inspection of hydraulic system
It is necessary to regularly check the pressure of each detection point of the hydraulic system to prevent the hydraulic system from working under abnormal pressure for a long time. It can also reduce the wear of the hydraulic system and ensure the normal operation of the hydraulic system.
The py180 grader produced by China Foreign Construction Development Co., Ltd. adopts hydraulic transmission, and its motion transmission is smooth and uniform, and it is easy to obtain large forces and moments. The unit power is light in weight, small in size, compact in structure, responsive, and has long component life. Such advantages have won the mass market. However, due to its harsh environment and poor working conditions, it will often fail. According to the data, 75% of the failure of the grader hydraulic system is caused by the contamination of hydraulic oil, and 20% is caused by the improper selection of hydraulic oil. Therefore, the reasonable selection and correct maintenance of hydraulic oil are the prerequisites for exerting the working performance and economic performance of the grader and prolonging the service life of the hydraulic system and its components. Our company purchased two py180 graders in 1998, and now we share with you the accumulated experience of hydraulic system maintenance.
1 Requirements for hydraulic oil performance
In hydraulic transmission, hydraulic oil is both a medium for transmitting power and a lubricant, and it also plays a sealing role in some components. The heat in the system is also diffused through the oil, so it also plays a role in heat dissipation. Therefore, in order to ensure that the hydraulic system works reliably, effectively and economically, the hydraulic oil must ensure the following requirements:
1) Appropriate viscosity. Viscosity is the magnitude of the frictional resistance between molecules when oil flows. When the viscosity is too large, the resistance when the oil flows is large, the energy loss is large, and the system efficiency is reduced. In addition, the no-load loss of the main engine increases, the temperature rises fast and the working temperature is high, and the phenomenon of "cavitation" easily occurs at the oil suction end of the main pump. If the viscosity is too small, the good lubrication conditions of the hydraulic components cannot be guaranteed, the wear of the components is increased, the leakage is increased, and the efficiency of the hydraulic system is also reduced.
2) Good viscosity-temperature characteristics. Viscosity-temperature characteristics refer to the degree to which oil viscosity rises and falls with temperature, and is usually expressed by viscosity index. The greater the viscosity index, the smaller the decrease in oil viscosity as the temperature rises during operation of the hydraulic system, so that the internal leakage of the hydraulic system is not too large. The viscosity index should not be lower than 90.
3) Good abrasion resistance and lubricity. The purpose is to reduce mechanical friction and ensure sufficient oil film strength under different pressure, speed and temperature conditions. [!-empirenews.page--]
4) High chemical reaction stability, not easy to oxidize and deteriorate. Practice has proved that for every 10 ° C increase in oil temperature, the chemical reaction rate increases about twice. The hydraulic oil with good anti-oxidation stability is not prone to oxidative deterioration after long-term use, which can ensure the normal circulation of hydraulic oil.
5) The quality should be pure, and the content of mechanical impurities, moisture and dust should be reduced as much as possible.
6) The impact on the seal should be small.
7) The anti-emulsification property is better, and it is not easy to cause foam. Anti-emulsification refers to the ability of oil mixed with water and after stirring, it does not become an emulsion and water is separated from it. Anti-foaming resistance refers to the ability of mixing air into the oil and not generating emulsions and bubbles from the oil after stirring. After mixing with water or air, the volume modulus of the hydraulic oil is reduced, the compressibility is increased, the hydraulic components act slowly, and they are prone to shock and vibration.
8) Good anti-rust performance. The hydraulic oil covers the surface of the parts to prevent them from being corroded by oxidation.
9) The stability of shear resistance is good. In order to improve the viscosity index of the oil, polymer polymers such as polymethacrylate and polyisobutylene are often added to the oil. These substances have long molecular chains, and the oil is greatly sheared when it flows through the slit of the hydraulic element. The effect will often break the chain of the molecule and reduce the viscosity-temperature characteristics of the oil.
10) The ignition point and flash point should meet the ambient temperature, and the volatility should be small to ensure the safe use of hydraulic oil.
In addition, the choice of grader hydraulic oil should also consider the different environments and regions of use. The oil used in winter and summer is also different. The brand and type of oil recommended by the manufacturer should be strictly followed.
2 Causes and hazards of hydraulic oil pollution
2.1 Sources of pollutants
1) Contaminants in new oil. Although hydraulic oil is refined and processed under relatively clean environmental conditions, it is contaminated by pipelines, oil drums and oil storage tanks during transportation and storage. Some dust, sand, rust, Moisture and other liquids.
2) Residual contaminants in components and systems. Hydraulic components and hydraulic systems may leave some contaminants due to incomplete cleaning during processing, assembly and cleaning.
3) Intrusion of pollutants from outside. In the process of hydraulic components and mechanical work, due to imperfect sealing of the fuel tank, damage to the component sealing and protective devices, some contaminants such as dust, sand, and moisture invade from the outside of the system. [!-empirenews.page--]
4) Contaminants generated inside the hydraulic system. The hydraulic system itself will generate some solid particulate pollutants in the work, including metal particles or rubber powder produced by the wear and corrosion of hydraulic components, and pollutants produced by the oxidation of oil.
2.2 The hazards of hydraulic oil pollution
1) The contaminants often cause the throttle valve and pressure damping hole to be blocked at times, and even block the valve core, causing the hydraulic system working pressure and speed to change from time to time, affecting its normal operation.
2) Accelerate the wear of hydraulic pumps, motors, and valve blocks, causing an increase in internal leakage.
3) The water mixed in the hydraulic oil corrodes the metal and accelerates the aging and deterioration of the hydraulic oil.
4) The air mixed into the hydraulic oil will cause noise, vibration, creeping, cavitation and impact phenomena, thereby deteriorating the performance of the hydraulic system.
3 Maintenance of hydraulic oil
3.1 Prevent oil pollution
Among the various pumps and valve components used in the grader, the matching clearance and working surface between the relative moving parts are small, and there are many damping holes and slit-type control valve ports in the hydraulic components. If the oil is mixed with dirt If it is blocked, it may even scratch the mating surface, increase leakage, or even jam the spool, causing component failure. Therefore, keeping the oil clean is the key to the maintenance of the hydraulic system.
1) The hydraulic oil must be strictly filtered. When filling the hydraulic oil tank, it should pass through an oil filter of more than 120 mesh.
2) Regularly check the cleanliness of the oil and replace it regularly according to the working conditions. When replacing, the oil in the hydraulic system should be discharged as much as 40l. Among them, the method of using the outer circulation of the system is more operable. The method is to drain the waste oil in the fuel tank and radiator first, and then add new oil. Remove the oil return pipe into the oil tank, start the engine, and let the waste oil flow out of the oil return pipe completely. It is particularly emphasized that changes in the oil level in the fuel tank should be observed in a timely manner, and the safety level of the oil level should be ensured. When changing to new oil, the filter element of the filter should be replaced at the same time.
3) The hydraulic components should not be easily disassembled. If they must be disassembled, the parts should be cleaned with kerosene or diesel oil and placed in a clean place to avoid mixing of impurities during reassembly.
3.2 Prevent air from entering
The air dissolved in the oil will escape from the oil when the pressure is low, generating bubbles and cavitation. [!-empirenews.page--]
3.3 Prevent moisture from entering
Take measures such as filtration and oil-water separation to prevent water from mixing into the oil and emulsifying.
3.4 Prevent excessive oil temperature
The working temperature of the hydraulic oil of the grader is generally in the range of 60 ~ 80 ℃. If the oil temperature is too high, the viscosity of the oil will decrease, the volumetric efficiency of the oil pump will decrease, the lubricating film will become thinner, mechanical wear will increase, and the seals will deteriorate and lose Sealing performance.
3.5 Regular inspection of hydraulic system
It is necessary to regularly check the pressure of each detection point of the hydraulic system to prevent the hydraulic system from working under abnormal pressure for a long time. It can also reduce the wear of the hydraulic system and ensure the normal operation of the hydraulic system.
