Maintenance skills of grader:

　　1. Requirements for hydraulic oil performance

　　In the hydraulic transmission, the hydraulic oil is not only the medium to transmit the power, but also the lubricant. It also plays the role of sealing in some components. The heat in the system is also diffused through the oil, so it also plays the role of heat dissipation. Therefore, in order to ensure the reliable, effective and economic operation of the hydraulic system, the following requirements must be met for the hydraulic oil:

　　1) proper viscosity. Viscosity is the amount of friction resistance between molecules when oil flows. When the viscosity is too high, the resistance of oil flow 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 "cavitation" phenomenon is easy to appear at the oil suction end of the main pump. If the viscosity is too low, the good lubrication condition of the hydraulic components will not be guaranteed, the wear of the components will be intensified, the leakage will be increased, and the efficiency of the hydraulic system will be reduced.

　　2) good viscosity temperature characteristics. Viscosity temperature characteristic refers to the degree that the viscosity of oil changes with temperature, usually expressed by viscosity index. The larger the viscosity index is, the smaller the viscosity of the oil will decrease with the increase of temperature, so that the internal leakage of the hydraulic system will not be too large. Viscosity index shall not be less than 90 generally.

　　3) good wear 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. It has been proved that the chemical reaction rate of the oil increases by about twice for every 10 ℃. The hydraulic oil with good oxidation resistance and stability is not prone to oxidation deterioration after long-term use, which can ensure the normal circulation of hydraulic oil.

　　5) the quality shall be pure, and the content of mechanical impurities, moisture and dust shall be minimized.

　　6) the impact on the seal shall be small.

　　7) emulsion resistance is good, not easy to cause bubbles. Demulsibility refers to the ability that oil is mixed with water and does not become emulsion after agitation and water is separated from it. Anti foaming property refers to the ability to separate air into oil and stir it without producing emulsion and separating bubbles from oil. After mixing with water or air, the volume modulus of the hydraulic oil is reduced, the compressibility is increased, and the hydraulic components are slow to move, which is easy to produce shock and vibration.

　　8) good rust resistance. The hydraulic oil covers the surface of the parts to avoid oxidation and corrosion.

　　9) good shear stability. In order to improve the viscosity index of oil, high molecular polymers such as polymethylpropylene ester and polyisobutylene are often added to the oil. These substances have long molecular chains. When the oil flows through the slit of the hydraulic components, it is subject to great shear effect, which often causes the molecular chain to break and the viscosity and temperature characteristics of the oil drop.

　　10) the ignition point and flash point shall meet the ambient temperature, and the volatility shall be small to ensure the safety of hydraulic oil.

　　2. Causes and hazards of hydraulic oil pollution

　　2.1 sources of pollutants

　　1) pollutants in new oil. Although the hydraulic oil is refined and processed under cleaner environmental conditions, it is polluted by pipelines, oil barrels and oil tanks during transportation and storage. Some dust, sand, rust, water and other liquids will be mixed in the oil.

　　2) residual pollutants in components and systems. In the process of processing, assembling and cleaning, some pollutants will remain in the hydraulic components and hydraulic system due to the incomplete cleaning work.

　　3) external invasion of pollutants. During the working process of hydraulic components and machinery, some pollutants, such as dust, sand, moisture, etc., are invaded from the outside of the system due to the imperfect sealing of oil tank, damage of component sealing and protective device, etc.

　　4) pollutants generated in the hydraulic system. In the work of hydraulic system, some solid particle pollutants will be generated, including metal particles or rubber powder caused by wear and corrosion of hydraulic components, as well as pollutants caused by oil oxidation.

　　2.2 hazards of hydraulic oil pollution

　　1) pollutants often block the throttle valve and pressure damping hole, or even block the valve core, causing the working pressure and speed of the hydraulic system to change from time to time, affecting its normal operation.

　　2) accelerate the wear of hydraulic pump, motor and valve group, resulting in the increase of internal leakage.

　　3) the water mixed into 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, crawling, cavitation and impact, which will worsen the working performance of the hydraulic system.

　　3. Maintenance of hydraulic oil

　　3.1. Prevent oil pollution

　　Among the various pump 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 slot type control valve ports in the hydraulic components. If the oil is mixed with dirt, blocking phenomenon will occur, even scratch the matching surface, increase leakage, or even block the valve core, resulting in component action failure. Therefore, to keep the oil clean is the key to maintain the hydraulic system.

　　1) the hydraulic oil must be strictly filtered. When filling the hydraulic oil tank, it shall pass through an oil filter with more than 120 meshes.

　　2) regularly check the cleanliness of the oil and replace it according to the working conditions. When replacing, try to discharge about 40L of the oil in the hydraulic system. Among them, the method of using system external circulation is more operable. The method is to drain the waste oil in the oil tank and radiator, 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. In particular, the change of oil level in the oil tank shall be observed in time to ensure the safe height of oil level. When replacing with new oil, replace the filter element at the same time.

　　3) the hydraulic components shall not be disassembled easily. If it is necessary to disassemble, the parts shall be cleaned with kerosene or diesel oil and placed in a clean place to avoid the mixing of impurities during reassembly.