Causes and Solutions of O-ring Failure

The sealing ring is the most basic and important device to ensure the normal operation of the hydraulic system. In the hydraulic and pneumatic system, most of the leakage is caused by the failure of the sealing ring. The performance and reliability of the o-ring and sealing device are important indicators to measure the quality of system design and manufacturing. If the seal is improper, it will cause the internal and external leakage of the components and the system, which will not only reduce the volumetric efficiency of the system, but also make the system unable to work if the pressure is not established; in addition, the leakage will contaminate the equipment and pollute the environment. Therefore, the correct use of sealing ring is very important to ensure the normal operation of the machine.
    
The main reasons for the failure of O-ring:

1. Sealing groove design is unreasonable;

2.O-ring is incompatible with the medium used;

3. The size of the O-ring is not selected correctly;

4.O-ring seal is not fully lubricated.

In addition, due to the complex force of the sealing ring, it is difficult to diagnose and determine some reasons. If necessary, it is necessary to conduct experimental research on its materials and use environment.

Common failure forms and solutions:

1.O-ring is flat after use

① The main reason is that the material elasticity and heat resistance of the sealing ring are poor. O-ring seal in the hydraulic system working medium after a period of time,
Often appear excessive expansion of the sealing ring, the phenomenon of increased pressure. This is due to the sealing ring in the production process, rubber vulcanization is not complete,
Therefore, under the action of pressure, the three sides of the sealing ring section are pressed into a flat shape;

The solution should be low solidification properties of rubber materials. Under normal conditions,
Selection of heat-resistant rubber materials (due to friction in the work will generate heat) such as nitrile rubber, neoprene, etc;
Confirm that the sealing ring material shall be compatible with the medium used, and check that the physical properties of the sealing ring shall meet the design requirements.

2.O-ring seal is worn

① The reason for this failure mode is mostly in seals with relative movement and vibration,
It can be judged by observing the wear of the contact part between the sealing ring and the sliding surface. The main reason is: the sliding surface of the seal is rough,

Lead to premature wear of the sealing ring; The sealing sliding surface is too smooth, which makes the sealing lubrication poor; The oil system contains contaminated particles;

The solution is made in accordance with the recommended machining roughness to ensure that the sliding surface and the sealing ring are fully lubricated during the movement (mainly internal lubrication),
Ensure the accuracy of the filter in the system, with better wear resistance of the O-ring material, such as polyurethane rubber.

3.O-ring heat hardening and oxidation

① Because the working temperature exceeds the normal use range, the elastomer hardens, the plasticizer evaporates and oxidizes,
As a result, the sealing ring produces small surface cracks perpendicular to the direction of the applied pressure, resulting in local dents or cracks.
This failure is mainly exposed to the static and dynamic seal in the air or the sealing ring in contact with other air pollutants;

The solution is to use materials with good oxidation resistance and high temperature resistance to reduce the working temperature of the system oil.

4. Protruding, biting and spiral failure of O-ring

① The main reasons for protruding and biting failure: the sealing gap is too large, the system pressure exceeds the sealing pressure strength or no retaining ring is added,
The sealing ring material does not meet the design hardness requirements, and the processing size of the sealing groove of the sealing ring does not meet the standard requirements,
Sealing ring selection is not appropriate (relative to the sealing groove size is too large), etc. The main reasons for the failure of the spiral: the concentricity of the parts is too low, the lubrication is not sufficient, the sealing ring material is too soft,
When some parts of the seal ring are sliding and the other part is rolling, causing distortion or cracks;

The solution to reduce the sealing gap, choose the appropriate size
O-ring to ensure that the concentricity of parts meet the design requirements; sealing groove in strict accordance with the standard processing,
Use a reinforced composite seal, such as a combination gasket, use a seal material that meets the design requirements or add a retainer to prevent the O-ring from being extruded.

5.O-ring seal is damaged during installation

① This situation often occurs in dynamic and static seals. The main reason is that there are sharp edges and corners on the sealing groove or the imported chamfer does not meet the standard,
The installation is not applied with lubricating oil, so that the sealing ring is cut, twisted or stuck by the sharp cutting edge,
Concave (or convex) marks, peeling or peeling on the surface;

② solutions in accordance with the design requirements of the processing of sealing groove, shall not leave a sharp edge, installation in the groove and sealing ring coated with lubricating oil,
When the O-ring seal passes through the thread, a metal sheet or belt is set on the thread to insert the seal ring smoothly.


O-ring has the advantages of simple structure, convenient processing and reliable performance, and is widely used in hydraulic components and systems. The above is the analysis and summary of the working mechanism, failure forms, failure causes and solutions of O-ring seals made by Mingzhen Rubber and Plastic Products Factory. Only by accumulating experience in the work and constantly summarizing and analyzing the problems in use can the O-ring be better applied.