Correct selection of working oil
Due to the high power of the hydraulic transmission machinery, the harsh operating conditions, and the large and frequent load changes, the requirements for working oil are high.
The power of the hydraulic transmission is proportional to the weight of the working oil. Therefore, under the condition that the transmitted power is unchanged, the use of heavy working oil can make the hydraulic components relatively small. Generally, the weight of hydraulic transmission working oil is (8.00 ~ 9.50) X 103N / m3.,
In order to meet the needs of different working conditions, it is required that the viscosity of the working oil changes little with temperature. At low temperatures, the viscosity should not be too high to maintain high transmission efficiency and improve low-temperature starting performance. Generally, the hydraulic viscosity of hydraulic transmission working oil is 55 ~ 70cSt. Viscosity and temperature, generally require a smaller wo / woo ratio, the better, generally less than 4.5 (such as 8 # hydraulic transmission oil is less than 3.60). As indicated by the viscosity index, the viscosity index is required to be greater than 170 (more than 210 in foreign countries). A high viscosity index means that the viscosity changes little with temperature.
The allowable value of the working temperature of the hydraulic transmission device can reach 70 ~ 110 ° C. If it works in the inefficient area for a long time, it can even reach about 120 ° C. Therefore, the flash point of hydraulic transmission working oil should be greater than 180P, not less than 155 bar. The freezing point of working oil varies with different regions and seasons, and is generally higher than 20P. The acid value should generally be less than 0.15mg (KOH) / g, too high will aggravate the corrosion of the metal, but it should not be too low, because some additives of the hydraulic transmission working medium are themselves composed of high molecular organic acids Increase the acid value of working oil. If water-soluble acids or alkalis are found in the working oil, it will strongly corrode the metal, and the working oil must be replaced at this time.
In addition, the critical load value, anti-oxidation stability, anti-emulsification, anti-foaming, water content and mechanical impurities should be guaranteed according to the relevant performance indicators.
American Society for Testing and Materials and Petroleum Institute classify hydraulic transmission oils into three categories. PTF-1 type: It has higher and stricter requirements for low-temperature viscosity, and stricter anti-wear and anti-foam properties. PTF-2 type: high requirements for anti-wear and extreme pressure, suitable for heavy-duty fully-automatic and semi-automatic hydraulic transmission systems, and the requirements for low-temperature viscosity are relaxed. PTF-3: It is used for low-speed, high-load machinery, which has high requirements for anti-wear and strict requirements for low-temperature viscosity.
China has produced a variety of hydraulic transmission oil. In the past, it was divided into 6 # and 8 # according to the kinematic viscosity at 100 ° C. Now it is divided into N32 hydraulic transmission oil (equivalent to the original 6 # torque converter oil) and N46 hydraulic transmission oil (equivalent to the original 8 # torque converter) Oil), N46D ordinary hydraulic oil and N68 anti-wear hydraulic oil,
N32 hydraulic transmission oil is used in diesel locomotives, off-road vehicles, construction machinery, etc., and the color is light yellow transparent liquid, which is equivalent to the PTF-2 category abroad. This oil is mainly based on 22 # turbine oil, and then added with other additives.
The state of the working oil often changes during use. It should be observed frequently to prevent the use of metamorphic oil. Special attention should be paid to the working oil bubbles, water-oil mixture, and pollution. The working life of the working oil depends on the degree of cleanliness, which is related to the working conditions of the machine, the quality of the working oil, the oil temperature and the filtering accuracy. The new oil has a filtration accuracy of 40; when zm is used, it should be replaced after 100h; when the filtration accuracy is 20; when zm is used, it should be replaced immediately after 500h. For construction machinery, each oil change interval is about 1000h. When the acid value reaches 2mg (KOH) / g, it must be replaced. For the hydraulic coupling, the maximum oil temperature for continuous operation is specified to be around 90 ° C; for the torque converter, the maximum oil temperature is specified to not exceed 120 ° C. When the oil temperature exceeds the specified value, it should be immediately unloaded for idling, and then operate after the oil temperature is normal. If necessary, check the cause of overheating and eliminate it.
Pay attention to the following points when changing the working oil: When the hydraulic system drains the oil, the oil should be warm. At the same time, replace or clean all the filters and screens to check whether there are metal slag particles or high temperature operation Coke. When draining the transmission, first remove the drain plugs at the transmission couplings and the housing, then remove the filter, and clean them with a soft brush in the non-volatile mineral oil. The oil draining of the hydraulic component means that part of the oil should be drained into the transmission, as long as the inlet pipe of the hydraulic oil is removed and the engine is started to run at 1000r / min for 20 ~ 30s. Lubrication of hydraulic system: Inject appropriate working oil through the oil filling hole of the gearbox and start the engine. After the transmission is in neutral and idle for 2 minutes, add enough oil.
