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What Are The Classification Of Seals?
Jul 06, 2019

The sealing ring includes dynamic seal and static seal. The sealing coupling parts of dynamic seal have uniform motion, and there is no relative motion between the sealing coupling parts of static seal. There are many differences in the requirements for rubber seals in these two different working conditions.


In addition to meeting the working medium pressure of the hydraulic system, dynamic seals also need to withstand the friction, wear (or wear) caused by the relative motion of the coupling parts; that is, to ensure certain sealing performance indicators, but also to consider the various requirements of the motion characteristics, including the support and guidance requirements of the moving parts. According to the sliding or rotating motion between the sealing coupling parts, the dynamic seal can be divided into reciprocating (moving) dynamic seal and rotating dynamic seal. The seals between cylinder block and piston, piston rod and guide sleeve in hydraulic cylinder are all reciprocating motion seals. According to the contact relationship between seal and sealing surface of coupling parts, reciprocating motion seal can be divided into hole seal and shaft seal. Seals for holes move relative to holes and seals for axles move relative to shafts.

seal

A) piston seal with radial seal

B) piston rod seal with radial seal


Static seals can be divided into plane static seals, radial static seals and angular static seals. Their leakage voids are axial and radial respectively. According to whether the pressure of the hydraulic working medium acts on the inner diameter or the outer diameter of the sealing ring, the plane static seal can be divided into internal pressure and external pressure. Hydraulic working media will leak from the inside to the outside, which is called internal pressure plane static seal (outflow type). Hydraulic working elements will leak from the outside to the inside, which is called external pressure plane static seal (inflow type), as shown in Figure 1-2. Radial static seal can refer to Fig. 

seals

A) Axial static seal under internal pressure b) Axial static seal under external pressure c) angular static seal


According to the shape and seal form of the hydraulic seal, the seal can be divided into forming filler (moulded product or moulded seal) seal and glue seal, belt seal and packing seal. Forming seal or filling seal generally refers to ring seal rings formed by moulding rubber, plastics and other materials, such as O-ring, Y-ring and V-shaped combination oil seal, etc. The utility model has the advantages of simple and compact structure, many kinds and specifications, wide working parameters, and convenient installation and use.


Dynamic seals can be divided into contact and non-contact seals according to the contact type of the coupling surface of the sealing coupling parts. Contact seals are closely attached to the sealing surface of coupling parts under the action of forced pressure. There is only a very thin layer of hydraulic medium between the sealing surface and the sealing parts. This sealing method has good sealing performance, but due to friction and wear conditions, the relative movement speed of the sealing surface can not be too high, which should be the case for most reciprocating dynamic seals of hydraulic components.


Contact seals are divided into compression seals and pressure-enabled seals: compression seals expand along the radial direction by extruding the sealing filler in the sealing groove, and are tightly pressed on the shaft or hole to achieve sealing; pressure-enabled seals are self-sealing seals, such as O-shaped rubber seals and Y-shaped seals. Sealing rings and so on should belong to this kind of sealing rings. Their design principle is to install rubber sealing ring in sealing groove and assemble with coupling parts, then apply a pre-pressure to the sealing parts through elastic deformation, i.e. couple parts. When the sealing parts are subjected to the pressure of sealing medium in one direction, the sealing parts further deform and the contact pressure of sealing surface increases. In order to apply to increase the pressure of sealing working medium and ensure the sealing performance. Pressure-enabled seals can be classified into extrusion type and lip type. The representative form of extrusion type is 0-shaped rubber seal ring, and the representative form of lip type is Y-shaped seal ring. Non-technical contact seal is a kind of clearance seal, such as piston clearance seal, because there is no contact and friction on the sealing coupling surface, so this kind of seal has less friction, wear, low starting pressure, long service life, but poor sealing performance.


According to the function of hydraulic seals in sealing devices, there are two main seals and auxiliary seals. The function of auxiliary seals is also to maintain the main seals from damage, increase the life of the main seals, and enhance the wear resistance of the seals. Such as dustproof ring, baffle ring, buffer ring, anti-fouling pressure ring, etc.


In addition, seals can also be classified according to different working media, sealing materials and working media pressure.


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