Selection of hydraulic media, the first should meet the environmental conditions of the hydraulic system, such as temperature changes in the environment, mechanical equipment and pumping station near the fire or high temperature heat source, the degree of humidity in the environment as well as environmental protection requirements, etc.; secondly, also to meet the working conditions of the hydraulic system, such as working pressure, temperature, hydraulic components used in the metal, coatings, load cycling, etc.; the third is that the fluid's physicochemical performance and Thirdly, the physical and chemical properties of the fluid and the use of performance should be suitable for the environmental conditions and working conditions of the system; Finally, the economic requirements should be analyzed. At the same time to meet the above conditions and performance indicators is more difficult, but the viscosity is an important factor in the selection of hydraulic media.
First, the choice of hydraulic medium
Specifically choose which hydraulic medium is more appropriate, according to the following four methods to determine:
① according to the type of pump selection. Pumps are very sensitive to the viscosity of the hydraulic medium and viscous temperature performance of one of the components, and the lubrication conditions of the requirements are particularly high, so the choice of pumps often become one of the main basis for the selection of hydraulic media. Generally speaking, gear pumps on the anti-wear performance requirements of hydraulic oil than vane pumps, piston pumps to be lower, so if the gear pumps can be considered to choose HL or HM oil, while the vane pumps, piston pumps should generally choose HM oil.
② according to the working environment of the hydraulic system and working conditions to choose. For example, the working environment for the outdoor, cold or cold areas; working conditions for the pressure is less than 7MPa, the temperature is less than 50 ℃, select HR or HV type hydraulic oil.
③ Selection based on the compatibility of hydraulic media and materials. Selection of hydraulic media, pay attention to analyze the compatibility of all metals, sealing materials, coatings, etc. in the hydraulic system with the fluid.
④ according to the use of machinery and equipment, working conditions, the working environment and its requirements for the hydraulic pump system to choose. For example, forging equipment hydraulic system, cold processing equipment hydraulic system used in the fluid usually use mineral oil; and on the hot processing equipment such as forging hydraulic press, taking into account the production environment, you can use flame retardant liquid.
Second, the rational use of hydraulic media and maintenance
A large number of domestic and foreign statistics show that the hydraulic system failure, 70% -80% is due to improper management of the use of hydraulic media. In order to ensure that the hydraulic system and components of long-term effective and reliable work, it is necessary to rationally use and manage the hydraulic medium, that is, to prevent deterioration of the fluid due to overheating, intense oxidation and pollution.
① Regular sampling and inspection and replacement of the fluid. Fluid acidity, viscosity, moisture and impurities, etc. is to determine whether it is necessary to replace the important indicators, usually requires the viscosity change shall not exceed 20%, the acid value shall not be greater than 1, the hydraulic piping, components, etc. should not appear corrosion, otherwise it should be replaced with new oil. Hydraulic oil replacement indicators shown in the table above.
② control temperature. High operating temperature of the fluid will make it oxidize violently and deteriorate; and its operating temperature is too low, but also increase the pump suction resistance, so that the pump noise increases and cause damage to the pump. Therefore, the starting temperature of the fluid to 15 - 30 ℃ is appropriate; working temperature of 40 -55 ℃. Therefore, the hydraulic system must be set up with sufficient cooling area of the tank and heater, if the tank alone is not enough natural cooling, but also need to set up a cooler.
③ pollution control. The new fluid is not clean, so it must be used before the main performance and pollution testing. The degree of contamination does not meet the requirements, must be filtered and purified to prevent water, air, solid impurities mixed into the hydraulic system. The degree of contamination of the new fluid should be lower than the permissible degree of contamination of the hydraulic system 1-2 levels. In addition, the new system for the first time and just before the maintenance of the system into use, need to be thoroughly cleaned; oil filter should be cleaned and replaced in a timely manner; the oil in the tank should be replaced regularly; general cumulative work 1000 h should be replaced after the oil change.
④ Oil can not be mixed at will. There is no sufficient scientific basis, shall not be arbitrarily mixed with different viscosity grade oil or the same viscosity grade but not the same manufacturer's oil.