The hazards and causes of excessively high oil temperature in the hydraulic system of construction machinery

The main consequences when the oil temperature is too high

1) The viscosity of the hydraulic oil decreases

When the viscosity of the hydraulic oil decreases, the leakage of oil in hydraulic components and systems will increase, and the volumetric efficiency of the hydraulic pump will decline. The increase in the flow rate of the oil through the throttle hole or the slot-type valve port causes a change in the originally adjusted working speed. This is particularly important for hydraulic servo systems, as it affects the working stability and reduces the working accuracy. When the viscosity decreases, the lubricating oil film on the surface of the relatively moving parts becomes thinner, which will increase mechanical wear.

2) Accelerate the oxidation rate of the oil

This causes the hydraulic oil to deteriorate and reduces its service life. The precipitated asphalt and other sediment can also clog small holes and gaps, affecting the normal operation of the hydraulic system.

3) Cause thermal deformation of hydraulic components

When heated, hydraulic valve components expand, reducing their fit clearance, which affects the movement of the valve core, increases wear, and may even get stuck.

4) It causes the sealing device to age and deteriorate rapidly, losing its sealing performance.

2. Reasons for excessively high oil temperature

There are many reasons for excessively high oil temperature. Some are caused by incorrect design of the hydraulic system, such as a too small volume of the hydraulic oil tank and insufficient heat dissipation area. There is no unloading circuit in the hydraulic system, and the oil pump is still overflowing at high pressure when it stops working. Improper selection of hydraulic components leads to excessive pressure loss. The oil pipe is long and thin, with too many bends, etc. There are also manufacturing issues, such as low processing and assembly accuracy of hydraulic components, excessive friction and heat generation between relatively moving parts, or severe leakage and excessive volumetric loss, etc.

From the perspectives of usage and maintenance, the reasons for excessively high oil temperature are as follows:

1) The oil level in the hydraulic oil tank is relatively low, resulting in insufficient circulation and cooling conditions for the oil in the hydraulic system.

2) The viscosity of the hydraulic oil is inappropriate or the hydraulic oil has deteriorated. If the viscosity is too high, the resistance to oil flow will be large, energy loss will be significant, and the temperature will rise. Low viscosity, poor viscosity-temperature characteristics, increased leakage, difficulty in forming an oil film on the surface of moving parts lubricated by hydraulic oil, decreased lubrication characteristics, and increased movement resistance. The deterioration of the oil reduces the volumetric efficiency of the oil pump and damages the oil film between the surfaces of the relatively moving parts, increasing resistance, friction loss and raising the oil temperature.