Correct selection of working oil
Due to the high power of hydraulic transmission machinery, poor operating conditions and large and frequent load changes, the requirements for working oil are high.
The power of hydraulic transmission is directly proportional to the weight of working oil. Therefore, when the transmission power remains unchanged, the hydraulic components can be relatively small by using working oil with large weight. 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 working oil changes little with temperature. At low temperature, the viscosity should not be too high to maintain high transmission efficiency and improve low-temperature starting performance. Generally, the kinematic viscosity of hydraulic transmission working oil is 55 ~ 70cst. For viscosity temperature property, it is generally required that the smaller the ratio of Wo / Woo is, the better, which is generally less than 4.5 (e.g. 8# hydraulic transmission oil is less than 3.60). If expressed by viscosity index, the viscosity index is required to be greater than 170 (up to 210 abroad). High viscosity index means that the viscosity changes less with temperature.
The allowable working temperature of hydraulic transmission device can reach 70 ~ 110 ° C, and even about 120 ° C if it works in low efficiency area for a long time. Therefore, the flash point of hydraulic transmission working oil shall be greater than 180P and not less than 155 ℃. The freezing point of working oil varies with different regions and seasons, which is generally higher than - 20p. Generally, the acid value should be lower than 0.15mg (KOH) / g. too high will aggravate the corrosion of metal, but it should not be too low, because some additives of hydraulic transmission working medium are composed of high molecular organic acids, which will increase the acid value of working oil. If water-soluble acid or alkali is found in the working oil, it will strongly corrode the metal. At this time, the working oil must be replaced.
In addition, the critical load value, anti-oxidation safety, anti emulsification, anti foaming, water content and mechanical impurities shall be guaranteed according to relevant performance indexes.
American Society for testing and materials and petroleum society divide hydraulic transmission oil into three categories. Ptf-1 type: high and strict requirements for low temperature viscosity, abrasion resistance and foam resistance. Ptf-2 type: it has high requirements for anti-wear and extreme pressure. It is suitable for full-automatic and semi-automatic hydraulic transmission systems with heavy load, and the requirements for low temperature viscosity are relaxed. Ptf-3: it is used for machinery with low speed and high load. It has high requirements for anti-wear and strict requirements for low temperature viscosity.
China has produced a variety of hydraulic transmission oils. 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), N46 hydraulic transmission oil (equivalent to the original 8# torque converter oil), n46d ordinary hydraulic oil and N68 anti-wear hydraulic oil. See table 1-130
N32 hydraulic transmission oil is used for diesel locomotives, off-road vehicles, construction machinery, etc. its color is light yellow transparent liquid, which is equivalent to foreign ptf-2. This oil is mainly based on 22# turbine oil and other additives.
The state of working oil often changes during use, so it should be observed frequently to prevent the use of deteriorated oil. Special attention should be paid to working oil bubbles, water oil mixture, pollution, etc. The service life of working oil depends on the cleanliness, which is related to the operating conditions of the machine, the quality of working oil, oil temperature and filtration accuracy. New oil and filter precision is 40; ZM, replace it after 100h of use; Filtering accuracy: 20; ZM shall be replaced immediately after 500h of use. For construction machinery, the interval between oil changes is about loooh. When the acid value reaches 2mg (KOH) / g, it must be replaced. For hydraulic coupling, the maximum oil temperature for continuous operation is about 90 ° C; For hydraulic torque converter, the maximum oil temperature is not more than 120 ° C. When the oil temperature exceeds the specified value, it shall be unloaded immediately for idling, and the operation shall be carried out 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 discharging the oil from the hydraulic system, the oil should be warm. At the same time, replace or clean all filters and strainers, and check whether there are metal slag particles or carbon deposits caused by high-temperature operation in the working oil. When draining the transmission oil, first remove the oil drain plugs at the transmission pipe joint and the housing respectively, then remove the filter and clean it with a soft brush in non-volatile mineral oil. Oil drain of hydraulic components means that part of the oil should be drained into the transmission. Just remove the oil inlet pipe of hydraulic oil, start the engine and run at the speed of 1000r / min for 20 ~ 30s. Oil filling of hydraulic system: start the engine after injecting appropriate working oil through the oil filling hole of the transmission. After the transmission runs at neutral and idle speed for 2min, add enough specified oil.
