At present, there are mainly two forms of hydraulic external leakage.
One is interface leakage, which refers to the leakage of hydraulic oil through the gap of the sealing surface under the action of pressure difference. This is the most common leakage phenomenon of hydraulic components; the other is leakage. , refers to the leakage of the hydraulic medium through capillary gaps under the action of surface tension or pressure difference, such as leakage caused by loose tissue, pores, sand holes and other parts of castings.
External leakage can lead to fluid waste and environmental pollution, and can also affect the appearance of hydraulic components. In the design and manufacture of high-end hydraulic components, it is required that the performance of each sealing part is stable, the sealing is excellent, and there is no leakage at the static sealing part, and it is developing towards zero leakage. The entire sealing system must achieve the requirements of stability, reliability, long service life, and easy maintenance.
Hydraulic component leakage analysis and measures
Strict quality management of each sealing part is one of the keys to ensure the sealing performance. Insufficient quality assurance of each link may lead to unstable sealing and leakage. The control is mainly carried out through the following links: selection of hydraulic component shell materials, design of sealing parts, manufacturing accuracy, selection, and quality of seals, assembly methods and other links.
Selection of hydraulic component housing materials
Many shells in hydraulic components, such as hydraulic pumps, motors, valve shells and end covers, etc., are basically ferrous metal castings. The selected materials should have high tensile and compressive properties, and have a certain degree of elasticity. , has hardness and the ability to recover from deformation, has high bending strength and small deformation. The main materials are gray cast iron and nodular cast iron. When choosing gray cast iron materials, compressive strength, flexural strength and elasticity should be considered, and HT250 and HT300 are mostly used. Ductile iron mainly requires tensile strength and elongation, and can better adapt to the impact of the hydraulic system. Generally, QT450-10 or QT500-7 is selected.
Seal failure of hydraulic components
In many cases, it is due to the material of the hydraulic component housing. Taking the O-rings flat static seal as an example, the reason for the leakage is the gap. The shell of the hydraulic component will deform under high pressure. This deformation will cause a gap in the sealing part, and the O-rings will make up for its through deformation. However, when the gap is too large, the O-rings will be trimmed and damaged, resulting in short-term sealing failure. Although such a small deformation under high pressure has little effect on the seal, if the deformation is too large to produce a visible gap, it can be measured with a feeler gauge. In the application of hydraulic components, if the gap is greater than 0.02 mm, it is easy to cause leakage. In the case of long-term use, if the shell material has insufficient bending strength or poor elasticity, it will also deform under alternating high pressure, so that a gap will slowly form on the joint surface of the parts. After the gap becomes larger, it will The O-rings seal may be trimmed or damaged, resulting in seal failure.
Design and production of external sealing parts
When designing the sealing structure, it is first necessary to determine the use of the hydraulic components, whether the seal is a dynamic seal or a static seal, the pressure, medium, temperature, etc. Relevant dimensions, geometric accuracy, surface roughness, etc. In addition, the specifications, distribution, and tightening torque of the tightening bolts need to be fully considered. Taking the flat static seal of the O-rings seal as an example, eliminating the gap on the sealing surface is the primary measure to solve the leakage, improving the flatness and roughness of the joint surface of the sealing system parts, and controlling the joint surface gap within the allowable range. Generally, the flatness within 100mm2 is required to be within 0.01 mm, and one-time processing should be used as much as possible during processing to avoid the occurrence of knife-joining marks, which cannot be detected by roughness meters. In addition, the entire mating surface must be polished to remove bumps and burrs.
