How to filter hydraulic oil and dehydrate lubricating oil
2020/4/2??????view:
How to filter hydraulic oil and dehydrate lubricating oil
1、 Main physical properties of hydraulic oil
Hydraulic transmission uses hydraulic oil (usually mineral oil) as working medium to transmit power and signal. Therefore, the quality (physical and chemical properties) of hydraulic oil, especially the mechanical properties have a great influence on the work of hydraulic system. Therefore, in the study of the hydraulic system, it is necessary to have a deeper understanding of the hydraulic oil and its performance, so as to further understand the basic principles of the hydraulic transmission.
1. density
The mass of a unit volume of liquid is called the density of the liquid:
(=m/v) (8-1)
Where V is the volume, M is the mass of the liquid with volume V, and P is the density of the liquid.
Density is an important physical parameter of liquid. With the change of temperature or pressure, its density will also change, but the amount of change is generally small and can be ignored. The density of general hydraulic oil is 900kg / m3.
2. Compressibility
The compressibility of a liquid is defined as the change in volume caused by pressure. If air is mixed in the hydraulic oil, its compressibility will increase significantly, which will seriously affect the working performance of the hydraulic system. Therefore, the content of gas and other volatile substances (such as gasoline, kerosene, ethanol and benzene) in the hydraulic system shall be minimized.
3. viscosity
(1) Meaning of viscosity. When the liquid flows under the action of external force, the cohesion between the liquid molecules will hinder the relative movement of the molecules, that is to say, there is an internal friction force between the molecules, which is called the viscosity of the liquid. Viscosity is an important physical property of liquid, and also the basis of choosing hydraulic oil.
Because the liquid has viscosity only under the action of external force, the liquid does not show viscosity at rest. The viscosity of liquid is expressed by viscosity.
(2) The viscosity of the liquid. The specified quantity represents the quantity of viscosity. There are three kinds of viscosity commonly used, namely dynamic viscosity, kinematic viscosity and relative viscosity. Generally speaking, the brand of oil is actually kinematic viscosity.
1) Dynamic viscosity μ. In China's legal measurement system and SI system, the unit of dynamic viscosity μ is pa · s (PA · s) or n · s / m2 (n · s / m2).
In CGS, the unit of mouth is DGN · s / cm2 (dyne · s / cm2), and the fork is called P (poise). 1% of P is called CP (centipoise). The conversion relationship is as follows
1Pa·s=10P=l03cP
2) Kinematic viscosity v. The ratio of dynamic viscosity μ to density ρ of the liquid is called kinematic viscosity.
V= / / (82)
2、 Physical properties of water:
Usually a colorless, odorless liquid.
Boiling point: 99.975 ℃ (when the air pressure is a standard atmospheric pressure, that is 101.375kpa).
Freezing point: 0 ℃
Three phase point: 0.01 ℃
Temperature at maximum relative density: 3.982 ℃
Specific heat capacity: 4.186kj / (kg · ℃) 0.1MPa 15 ℃ evaporation latent heat: 2257.2kj / (kg) 0.1MPa 100 ℃
Density: the maximum density of water is 1 × 103kg / m3 at 3.98 ℃, 0.99987 × 103kg / m3 at 0 ℃, and 0.9167 × 103kg / m3 at 0 ℃ for ice.
Critical temperature: 374.2 ℃
Thermal conductivity: at 20 ℃, the thermal conductivity of water is 0.006 J / s · cm · K,
The thermal conductivity of ice is 0.023 J / s · cm · K,
When the density of snow is 0.1 × 103 kg / m3, the thermal conductivity of snow is 0.00029 J / s · cm · K.
Buoyancy classification: floating, floating, sinking, floating, sinking.
3、 Pollution of water to hydraulic oil:
For the particle pollution, now we pay more attention to it. Generally, we take corresponding measures to control it (for example, filter with filter element). However, there is not enough attention paid to other pollution, such as water, air, microorganism and so on. After particle pollution is effectively controlled, the harm of other pollutants to the system will be more prominent. People pay more and more attention to the harm of water to hydraulic and lubrication system.
In practice and research, people realize that one of the main reasons for the deterioration of hydraulic oil performance is that water enters into the hydraulic oil. As one of the main pollutants in oil, water also causes many problems. The entry of water, especially a large amount of free water, destroys the formation of lubricating oil film in the hydraulic system. The lubricating performance of oil products drops sharply, resulting in wear, adhesion and metal fatigue on the moving surface, resulting in some metal abrasive particles. However, the existence of these small metal particles, especially copper or iron particles, will become the catalyst for the oxidation and decomposition reaction between water and oil products, resulting in the reaction Speed up. The reaction will generate acid corrosive products, insoluble pollutants and other harmful substances, which will cause parts to be corroded, valves to be stuck or oil sludge to be formed; water will increase the viscosity of oil or thin the oil film; in addition, water in hydraulic oil will react with oil under high working temperature, which will cause oil oxidation and deterioration, and reduce the service life of oil; When the water enters the oil, it increases the compressibility of the oil, leading to unstable operation; under the low temperature working condition, the water droplets in the oil condense into ice particles, blocking the gap or small hole of the control elements, causing system failure; it is easy to breed bacteria in the system, reducing the service life of the oil, and increasing the oil change cost; The additives in the oil are dissolved in the water, resulting in loss, reducing the performance of the hydraulic oil; reducing the lubricity of the oil, resulting in unstable operation of the equipment; accelerating the surface fatigue of the metal, insufficient protection of the metal parts, easy to rust or be corroded, reducing the service life of the metal parts; blocking the filter, reducing the filtering efficiency
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