When the hydraulic pressure creates bubbles, it's a dangerous signal
As the hydraulic oil into the air and lead to the emergence of hydraulic bubbles, will increase the temperature of the hydraulic system, and even greater harm. From the aspects of economy and quality of work, we sum up the harm caused by hydraulic bubbles.
System failure
In the hydraulic transmission system, the oil is the transmission medium of the power, in the absence of air mixing, the compression rate is about (5~7) x 10-10m3/N, that is, when the pressure increases by 10MPa, the volume is only compressed to reduce to 0.625%.
Therefore, in the general hydraulic system, the oil can be considered as a non compressible fluid without considering its compressibility. Once the oil mixed with air, the compression ratio will increase substantially, the oil itself has a very high stiffness or elasticity coefficient of large volume (reciprocal compression rate) is greatly reduced, seriously endangering the working reliability of the system, such as automatic control malfunction, working mechanism of producing intermittent motion and processing the rejection rate increases.
Machinery and personal accidents
Rising oil temperature. If the bubble is compressed immediately after the pump, the temperature will rise sharply. If the gas is not dissolved in oil, the approximate value of its adiabatic compression temperature is not difficult to calculate, for example, when the bubble is heated to 3.5MPa at 35 degrees Celsius, its temperature rise can reach 580 degrees celsius.
When the bubbles reach the high temperature, the oil around them will produce combustion, and become the main reason for the sudden rise of the system oil temperature. However, the air is difficult to heat conduction, when there is a bubble in the oil, its thermal conductivity is greatly reduced, seriously affecting the cooling effect of the oil.
Accelerate the oxidation of oil
The increase of oil temperature is the main reason to promote the oxidation of oil. According to the mechanism of oxidation, when the oil temperature is above 60 degrees Celsius, the oxidation rate increases exponentially when the temperature is increased by 10 degrees celsius. The oxidation of the oil usually increases the viscosity and produces acidic compounds, causing corrosion of metal parts in the system. Moreover, the chemical properties of oxides are generally more active than those of pyrolysis products, so it is easier to produce slag mud, and the mechanical impurities such as rust and metal filings are also used as catalysts for oxidation process to accelerate the oxidation of oil. Generally hope that the oil temperature can be below 90 degrees, so that it has good chemical stability.
The lubricating property of the oil drops. The oil with good properties can form a strong oil film on the metal friction surface. The strength and thickness of the oil film mainly depend on the quality of the oil.
The oil film modified by filtered advertisement is not strong enough to bear the pressure of the working load, which causes the metal surface to contact each other, which leads to a sharp increase in friction and accelerates the wear of the parts. Therefore, the lubricity of the oil is of great importance to the hydraulic device.
Accelerated aging of seals
The hydraulic system seals used by the different chemical composition of the material seal ring and gasket in various forms, not only has good compatibility with oil, but also requires the appropriate working temperature, as the temperature of the oil seal more than normal heat, it will make the accelerated aging, lose their elastic, and lead to premature loss of seal.
Lead to cavitation. Bubble in oil is the oil into the high pressure area, volume shrinking, the bubble again condensed into liquid, the local area to form a vacuum, at high speed around the liquid particle to fill the space, particles collide with each other and form local high pressure, hydraulic impact, the partial pressure increases up to hundreds or even thousands of atmospheric pressure. If the local hydraulic impact on the solid wall, it can cause the erosion of the solid wall, called cavitation phenomenon, it is very harmful to the system.
The bubbles in the oil can also increase the vibration and noise of the system and reduce the volume efficiency of the pump.
When the bubble appears in the hydraulic system, we must carefully select the right way to deal with, to avoid major accidents, the construction machinery home operating hydraulic pump components and hydraulic systems related maintenance, please refer to Mr. Zhang: 13705210834.
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