The five most important indicators in the application of hydraulic transmission oil
November 02, 2022
There are many kinds, brands and brands of hydraulic transmission oil. China's hydraulic transmission oil includes the industrial standards JB/T 7282-2004, JB/T 12194-2015, and the enterprise standard Q/SY RH2042-2001 (2009) of PetroChina. Each product brand has more than ten quality indicators, such as viscosity, condensation point, copper corrosion, and bubble resistance. It can be said that each indicator on the product quality standard and analysis sheet is indispensable. For hydraulic transmission oil in use, in addition to the above special indicators, Emphasis is placed on monitoring moisture and mechanical impurities. Generally, moisture is required to be no more than traces, and mechanical impurities are required to be no more than 0.01%.
1. Oxidation stability Due to the high operating temperature of hydraulic transmission oil, the oil is prone to oxidation, which will produce sludge, paint film, corrosive acid and other substances. These substances will change the friction characteristics of the oil, causing the clutch or friction plate to slip. The acid substances will also corrode the components, and the sludge will block the hydraulic control system and pipelines; Oxidation may also cause changes in oil viscosity, resulting in poor transmission. Therefore, DKA oxidation, ISOT oxidation or THOT oxidation are generally used to determine the oxidation characteristics of hydraulic transmission oil. Taking TO-4 heavy load hydraulic transmission oil as an example, it is required that after the THOT oxidation test, the increase of 40 ℃ kinematic viscosity of the oil is not more than 100%, the increase of 100 ℃ kinematic viscosity is not more than 60%, the increase of acid value is not more than 4.0 mgKOH/g, and the difference of infrared absorption peak is not more than 0.75. 2. Shear stability Hydraulic transmission oil has high requirements for viscosity temperature characteristics of oil products, so it is necessary to improve the use demand of oil products for high and low temperature working environments by adding viscosity additives. In the process of use, due to the impact of mechanical equipment stress shearing, the performance of viscosity additives in oil products will often be reduced, resulting in irreversible viscosity loss of oil products, resulting in clutch slipping. Therefore, the oil products are required to have good shear stability. Generally, THCT bench, ultrasonic shearing, conical roller shearing and other methods are used to evaluate the shearing stability of hydraulic transmission oil. Among them, NB/SH/T 0845 conical roller shearing is the most commonly used. Taking ATF VI as an example, it is required that the reduction rate of the conical roller shearing at 100 ℃ kinematic viscosity after 60 ℃ for 40 hours is not more than 10%. 3. Low temperature characteristics Engineering machinery and equipment are often operated in the low temperature environment in the field. Oil products are required to have good low temperature performance, low freezing point (or pour point) or low low temperature apparent viscosity, which is conducive to the start of hydraulic components in the low temperature environment, and also brings convenience to production and transportation. The freezing point of No. 6 and No. 8 hydraulic transmission oil shall not be higher than - 30 ℃ and - 35 ℃ respectively, and the low temperature performance of No. 8D hydraulic transmission oil shall not be higher than - 50 ℃. The hydraulic transmission brake oil also specifies the low temperature apparent viscosity of the oil, requiring that the apparent viscosity at - 18 ℃ should not be greater than 4500mPa · s, and the apparent viscosity at - 34 ℃ should not be greater than 70000mPa · s; For ATF III, the apparent viscosity at - 40 ℃ shall not be greater than 20000mPa · s. 4. Antiwear property Hydraulic transmission device is usually composed of hydraulic torque converter, gearbox and hydraulic control system. It requires good anti-wear property of oil to prevent gear pitting and long-term stable operation of hydraulic pump. As the most important performance index of hydraulic transmission oil, the abrasion resistance is usually measured by the GB/T 3142 four ball tester, SH/T 0306FZG gear tester and GB/T 11144Timken tester. Taking hydraulic transmission dual-use oil as an example, it is generally required that the maximum non seizure load PB of the four balls shall not be less than 784N, the wear scar diameter shall not be greater than 0.5mm, the OK value of the anti scratch ability shall not be less than 112N, and the FZG failure level shall not be less than 10. 5. Friction characteristic Friction characteristics are the core and most important index of hydraulic transmission oil, which is the comprehensive balance performance of gear shifting feeling, torque load and friction durability. In the gearbox, shifting is accomplished through the engagement of the clutch. During shifting, the relative speed between the clutch plates changes from large to small until the relative speed is zero. In order to get a good shifting feeling, people hope that the clutch can transmit torque smoothly, which requires that the friction coefficient between the two clutch plates should not change with the speed and remain constant, and at the same time, in order to obtain greater transmission capacity, It is also required that the friction coefficient of the clutch plate should be as high as possible without increasing wear, and the friction durability should be better to ensure that the transmission of power will not be affected by the oxidation and decay of oil during the use of the gearbox. Generally, SAE No.2 friction testing machine and LVFA low speed friction testing machine are used to investigate the friction characteristics of oil products. Generally, hydraulic transmission oil requires that the ratio of dynamic and static friction coefficients of oil products be greater than 1 to improve the transmission efficiency. At the same time, there is a certain static friction coefficient to reduce clutch slip.
