1. The main cause of failure
● Improper design of sealing groove
● The o-rings are incompatible with the media used
● The size selection of o-ring seal is not correct
● O-rings are not fully lubricated
In addition, because of the complex force of the seal ring, it is difficult to diagnose and determine it due to some reasons. If necessary, the material and the use environment of the sealing ring should be tested.
2. Common failure forms and solutions
(1) O-ring is flat after use
▲ Reason: The sealing ring has poor elasticity and heat resistance. When the O type seal ring is used in the working medium of hydraulic system for a period of time, it often appears that the seal ring is over expanded and the compression force is increased. It is due to the rubber is not fully vulcanized during the production process of the seal ring. Under the effect of pressure, the three sides of the sealing ring section are pressed into a flat shape.
▲ Solution: Rubber materials with low solidification properties should be used. Under normal conditions, heat resistant rubber materials are selected (because of friction during work to generate heat) such as nitrile rubber and chloroprene rubber. It is confirmed that the sealing ring material should be compatible with the medium used, and the physical properties of the seal should be tested in accordance with the design requirements.
(2) O-ring wear
▲ Reason: This kind of failure occurs mostly in the seal with relative movement and vibration. It can be judged by observing the wear amount of the contact area between the seal ring and the sliding surface. The main reasons are: the sliding surface of the seal is rough, which leads to the premature wear of the seal ring, and the seal sliding surface is too smooth to make the seal lubricate badly; the oil liquid system contains contaminated particles.
▲ Solution: According to the recommended machining roughness to ensure that the sliding surface and the seal ring are lubricated fully during the movement (mainly internal lubrication), ensures the filter precision in the system, and to use the O type sealing material, such as polyurethane rubber, and so on.
(3) O-rings are hardened and oxidized by heat
▲ Reason: Because of the working temperature exceeds the normal range of use, the elastomeric is hardened, the plasticizer evaporation and oxidation, resulting in the sealing ring and the direction of action of the pressure perpendicular to the small surface of the crack, and thus the local dent or cracking phenomenon. This failure is mainly caused by static and dynamic seals that are exposed to air or seals that come into contact with other air pollutants.
▲ Solution: Use materials with good oxidation resistance and high temperature resistance to reduce the operating temperature of the system oil.
(4) Protruding and spiral failure of O seal ring
▲ The main reason of the bulge: the seal gap is too large, the system pressure exceeds the seal bearing strength or the retaining ring is not added, the material of the seal ring does not meet the design hardness requirements, the seal ring groove processing size does not conform to the standard, and the seal ring is not suitable (relative to the seal groove size is too large). The main causes of spiral failure: the parts of the concentricity is too low, insufficient lubrication, the seal ring material is too soft, when some parts of the seal ring is sliding and the other part is rolling, causing distortion or crack;
▲ Solution: Reduce the sealing gap and use O-ring seal with appropriate size to ensure that the concentricity of the part meets the design requirements; the sealing groove is processed strictly according to the standard, and the reinforced composite seal is used, such as the compound gasket, and the sealing ring conforming to the design requirements is adopted. Material or additional retaining ring that prevents the O-ring from being pushed out.
(5) O-rings are damaged during installation
▲ Reason: this case often occurs in dynamic and static seals. The main reason is that there is a sharp angle corner on the seal groove or the chamfered angle that does not conform to the standard, and the lubricating oil is not applied during installation , so that the sealing ring is cut by sharp edge, distorting or stuck, the surface produces concave (or convex) marks, peeling or peeling phenomenon.
▲ Solution: Accordance with the design requirements to process sealing groove, cannot retain a sharp edge, installation in the groove and sealing ring on the lubrication oil, when the O-ring through the thread, the thread on the thread metal sheet or belt, in order to smooth the sealing ring.