Whether hydraulic oil is good or bad depends mainly on this.
发布时间：2022年03月14日 14:47
Viscosity is one of the primary factors that must be considered in hydraulic systems for construction machinery. Viscosity is an indicator of a fluid's flow performance, reflecting the magnitude of frictional resistance between molecules during fluid flow. If the viscosity is too high, it will increase the flow resistance in pipelines, leading to greater energy losses during operation, increased no-load losses in the main unit, and a rise in temperature. This could even result in cavitation at the suction port of the main pump. On the other hand, if the viscosity is too low, it will fail to ensure adequate lubrication conditions for mechanical components, accelerating wear and tear on parts and increasing system leakage, thereby reducing the volumetric efficiency of the pump.
Hydraulic oils with the same viscosity grade still differ from one another! Viscosity-temperature characteristics refer to the degree to which the viscosity of a fluid changes with temperature fluctuations, typically expressed by the viscosity index (VI). The higher the viscosity index, the less the fluid's viscosity varies with temperature during operation, thus preventing excessive internal leakage in the system. Since construction machinery generally operates under relatively harsh conditions, the oil temperature within the system fluctuates with changes in load and ambient temperature during operation; therefore, the viscosity index must not be lower than 90.
The ideal operating temperature for most hydraulic oils is between 30°C and 80°C, as the service life of hydraulic oil is closely related to its operating temperature. This is because high temperatures accelerate oxidation. Under atmospheric pressure, every liter of oil contains slightly less than 0.1 liter of air. In fact, oxygen is always present; it reacts with the hydrocarbons in the oil, causing the oil to gradually oxidize, turn darker in color, and increase in viscosity. Eventually, the oxidation products no longer dissolve in the oil but instead deposit as a brown, viscous layer somewhere within the system. This can lead to valve sticking, increased friction in components such as ball bearings, valve spools, and hydraulic pump pistons, and—more seriously—corrosive acids generated during oxidation that damage various hydraulic components.
Hydraulic oils used at high temperatures are required to have excellent oxidation stability, and the type of base oil significantly influences this property.
IV. Good hydrolytic stability and emulsion resistance
Hydraulic oils with good hydrolytic stability maintain relatively stable performance when they come into contact with water. However, this does not mean that hydraulic oils are immune to water. During use, it is crucial to ensure that no moisture or impurities enter the oil.
V. Good air release properties
If incompatible, hydraulic oil can cause swelling, softening, hardening, and other changes in the sealing elements it comes into contact with, thereby compromising the sealing performance of the sealing materials. Hydraulic systems may experience leakage and seal failure, leading to the escape of hydraulic oil. If this hydraulic oil is incompatible with the surrounding environment, it could result in environmental pollution.
7. Corrosion Resistance
The purpose is to reduce mechanical friction and ensure the service life of the main unit.
9. Good flame retardancy
Hydraulic fluids should have a high flash point to prevent spontaneous combustion and fire. For applications requiring fire resistance, specially formulated fire-resistant hydraulic fluids should be used.
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