Whether the hydraulic system of the servo injection molding machine can work normally, in addition to the reasonable design of the system, the quality of component manufacturing and maintenance and use, the suitability and cleanliness of the hydraulic oil is a very important factor. As the working medium of hydraulic transmission, hydraulic oil not only transfers energy, but also protects the metal at the moving parts of the lubricating element from corrosion. In particular, the current hydraulic technology continues to develop toward high pressure, integration, and miniaturization. In addition to the application of electronic technology, the reliability, sensitivity, stability, and life of the hydraulic system have raised higher and higher requirements. Therefore, injection molding The hydraulic system of the machine should use hydraulic oil with good performance and high cleanliness. Relevant data statistics show that more than 70% of the failures of the hydraulic system are caused by the improper selection of hydraulic oil or the use and improper storage of the hydraulic oil, which has caused pollution of the hydraulic oil. Therefore, it is necessary to understand the various requirements of the hydraulic system for oil, and choose it reasonably and maintain it properly to ensure the normal operation of the hydraulic system, reduce failures, and improve production efficiency.
1. Requirements and selection of hydraulic oil
(1) Appropriate viscosity and good viscosity-temperature characteristics. If the viscosity of the hydraulic oil is too large, the pressure loss of the system is large, the efficiency of the sheep is reduced, and the wear is increased, reducing the service life of the pump; if the viscosity of the hydraulic oil is too small, the system is easy to leak and the efficiency of the system is also reduced. The viscosity of the oil should be selected reasonably, not too large or too small. The viscosity of hydraulic oil will change with the change of temperature. When the temperature increases, the viscosity of hydraulic oil will decrease. The performance of oil viscosity changing with temperature is called viscosity-temperature characteristic, which is usually expressed by viscosity index. The higher the viscosity index, the better the viscosity-temperature characteristics of the oil. When the temperature changes, the viscosity changes less. The viscosity index of hydraulic oil should generally be higher than 90.
(2) Under the working temperature and pressure, it has good lubricity, shear stability and certain oil film strength. When the hydraulic system works, the components always produce friction and wear. When the machine is stopped and started, the friction force is large, and the friction force is the largest when it starts, which is easy to cause wear. Therefore, the hydraulic oil should have good lubricity, lubricate the moving parts, and achieve the purpose of reducing wear and prolonging the service life. The hydraulic system working under the conditions of high temperature, high pressure and high speed requires the hydraulic oil to have good lubricity, that is, high oil film strength, that is, good wear resistance. When hydraulic oil passes through some valve ports and small holes in the gap, it must be subjected to a strong shearing action. In this case, the larger molecules will break and become smaller molecules, causing the viscosity of the oil to decrease. To a certain extent, the hydraulic oil can no longer be used, therefore, the hydraulic oil should have better shear stability.