The hydraulic system uses oil as the working medium, uses oil to transfer pressure, and controls the hydraulic actuator through the control valve and other accessories. The hydraulic system is mainly composed of five parts, namely, power components, executive components, control components, auxiliary components and hydraulic oil.
The power element refers to the oil pump in the hydraulic system, which can convert the mechanical energy of the prime mover into the pressure energy of the liquid to provide power to the entire hydraulic system. The role of the actuator, such as the hydraulic cylinder and the hydraulic motor, is to convert the pressure energy of the liquid into mechanical energy and drive the load for linear reciprocating or rotating motion. Control elements, namely various hydraulic valves, control and regulate the pressure, flow and direction of liquids in the hydraulic system. Auxiliary components include fuel tank, oil filter, tubing and fittings, sealing ring, quick change fittings, high pressure ball valve, hose assembly, pressure gauge, oil level gauge, oil temperature gauge, etc. Hydraulic oil is the working medium of transmission capacity in hydraulic system. At present, mineral oil, emulsion and forming hydraulic oil are commonly used.
The hydraulic system usually has the characteristics of small size and light weight, so the inertia force is small, and when suddenly overloaded or stopped, there will be no big impact; The traction speed can be adjusted smoothly and automatically within a given range, and the speed can be adjusted; The commutation is easy, and the rotation of the working mechanism and the linear reciprocating motion can be realized conveniently without changing the rotation direction of the motor. The hydraulic pump and the hydraulic motor are connected by tubing, and the space arrangement is not strictly limited to each other; Because the oil is used as the working medium, the relative moving surface of the component can lubricate itself, and the wear is small and the service life is long. Simple operation and control, high degree of automation; Easy overload protection.
However, in the working process of the hydraulic system, there are also the following problems: the use of hydraulic transmission has high maintenance requirements, and the working medium should always be clean; The manufacturing precision of hydraulic components is high, the process is complex and the cost is high. The maintenance of hydraulic components is complicated and requires a high technical level; Mineral oil working medium, fire hazard.
Hydraulic oil is a working medium that plays a role in transmission capacity, heat dissipation, lubrication and corrosion inhibition, and is the "blood" of the hydraulic system. According to statistics, about 70% of hydraulic system failures are caused by hydraulic oil, which seriously affects normal production and work and causes great economic losses. Therefore, how to scientifically choose, use and maintain hydraulic oil is particularly important. At present, there are many kinds of hydraulic oil, according to the chemical composition, mainly divided into mineral oil type, emulsion type and synthetic hydraulic oil.
Mineral oil hydraulic oil refers to the hydraulic oil with the base oil extracted from petroleum by physical distillation method as the main component, good lubrication and low price. However, mineral oil type hydraulic oil is easy to burn, poor high temperature performance, low risk resistance. Mineral oil in the refining process can not be removed clean impurities, so this type of hydraulic oil pour point is high, not suitable for low temperature operation. The composition of mineral oil hydraulic oil is complex, the viscosity decreases at high temperature, the lubrication becomes poor, and the oil mud is easy to be produced.
Emulsion type hydraulic oil usually refers to water-in-oil or oil-in-water type hydraulic oil, due to the existence of water, usually has a high flash point, ignition point, but with the evaporation of water in the process of use, the performance and quality will change.
Synthetic hydraulic oil is a kind of hydraulic oil which is composed of chemical compounds processed by chemical synthesis and supplemented by various functional additives. Synthetic hydraulic oil has the following characteristics: it can meet the use requirements that mineral fats or natural fats can not meet, such as low temperature, high temperature, high load, high speed, strong oxidizing medium and long life. Synthetic lubricating oil has a wide range of applications, it can be said that where the use of mineral oil parts can be replaced by synthetic oil. In addition, because synthetic oil has many special properties that mineral oil can not, some parts can only use synthetic lubricating oil.
As a kind of synthetic hydraulic oil, synthetic ester hydraulic oil was developed in the mid-1930s. It is a lubricating oil prepared by synthetic method and has a certain chemical structure and special properties. Synthetic ester flash point, high ignition point, low evaporation loss, high viscosity index, strong corrosion resistance, good lubricity, excellent adaptability to non-metallic materials, biodegradation rate of 80% to 100, according to CEC-L-33-AA) method, low toxicity, no need to replace the material of the system when replacing the traditional mineral oil lubricating oil, harmless to the human body, does not pollute the environment, It is a green lubricant that meets the requirements of environmental protection. Compared with mineral lubricants, it has a wide range of use, can adapt to the increasingly demanding requirements of modern mechanical equipment for good lubricity, long oil change period and low energy consumption, and its price is higher than mineral lubricants, but it has excellent performance, long service life and low mechanical wear. Therefore, synthetic ester as a base oil for mining lubricating oil has advantages.
At present, there are some brands of synthetic ester hydraulic oil on the market, but there are still problems to be solved for lubricity, stability, rubber compatibility, hydrolysis and so on. In order to meet the requirements of modern industrial development on the working medium, and to meet the performance requirements of high temperature, high speed, high load, fire resistance, environmental protection, etc., it is particularly important to develop a new generation of synthetic ester hydraulic oil suitable for national conditions. In the research of synthetic ester hydraulic oil, how to further improve its flash point, ignition point and high temperature fire resistance is a topic that researchers pay attention to. In addition, with the wide use of lubricating oil, people will pay more and more attention to its impact on the environment, and the study of environmentally friendly synthetic ester hydraulic oil will become an important development trend.
