introduction
Silicon O-rings are essential parts in industrial applications to guarantee sealing systems’ dependability. Even such high-performance seals, nevertheless, are not immune to failure. Maintaining proper operation of equipment and prolonging the service life of seals need an understanding of the primary reasons of silicone O-ring failure and the implementation of suitable preventive measures. Multiple causes of failure include mechanical stress, chemical attack, climatic conditions, and incorrect installation. Silicone O-rings can be made to operate and last far longer by carefully examining these possible issues and creating practical preventive measures.
Silicon O-ring failure causes mainly
Compression rate, stretching, and O-ring material permanent deformation: a relationship
Under compression, the several rubber compositions utilized to construct O-rings will release compressive stress, which eventually reduces. The longer the use duration, the more compression rate and stretching, and the more stress decrease brought on by rubber stress relaxation, the more elastic the O-ring becomes and the less effective it is at sealing. Thus, it is wise to try to lower the compression rate under the permitted usage conditions. Reducing the compression rate can be done most simply by increasing the O-ring’s cross-sectional size, although this will make the structure larger.
It should be mentioned that often the decrease in cross-sectional height brought on by the O-ring stretching during assembly is disregarded when computing the compression rate. Changes in the circumference of the O-ring are inversely proportional to changes in its cross-sectional area. The O-ring’s cross-sectional form will likewise alter as a result of the tension action, and this will show up as a drop in height. The O-ring’s outer surface flattens and its cross-sectional height somewhat drops when surface tension acts. Furthermore demonstrating the relaxation of the O-ring compression stress is this.
Hardness of the O-ring material also affects the degree of deformation of the cross-sectional shape of the O-ring. Additionally lowered under the same stretching amount is the high hardness O-ring’s cross-sectional height. From this angle, low hardness materials must to be chosen as much as feasible based on the intended use. The cross-sectional height of an O-ring composed of rubber material would eventually drop due to plastic deformation caused by liquid pressure and tension, thereby losing its sealing capacity.
The connection of the O-ring relaxation process with temperature
An other crucial element influencing the O-ring’s persistent deformation is the operating temperature. Rubber materials will age faster in high temperatures. The O-ring will permanently deform more in compression the higher the working temperature. An O-ring leaks when its persistent distortion is more than 40%. With O-ring relaxation and temperature decline, the initial stress value created by compression deformation in the rubber material of the O-ring will progressively drop and vanish. The rapid temperature drop may cause the initial compression of O-rings operating at sub-zero temperatures to reduce or even disappear. Rubber materials resistant to low temperatures will totally lose their initial stress at -50 to -60°C; even for such materials, the initial tension at this point will not be more than 25% of the initial stress at 20°C. This is so because the linear expansion coefficient determines how much the O-ring compresses at first. As such, it is critical to choose the initial compression so that, once the stress reduces as a result of the relaxation process and temperature reduction, there is still enough sealing ability.
Note the following during the design phase to avoid O-ring distortion damage:
Easy processing and no distortion should be the two criteria used to evaluate the concentricity of the O-ring installation groove.Every installation should include a full application of lubricating oil or grease to the sealing component and uniform cross-sectional dimensions of the O-ring. Sometimes you can also use an oiling tool of the felt ring kind that is drenched in lubricating oil.Increase the O-ring’s cross-sectional diameter. Generally speaking, an O-ring for dynamic sealing should have a bigger cross-sectional diameter than one for static sealing. Moreover, a big-diameter piston should not be sealed with an O-ring.The retaining ring can be protected by a seal ring when distortion damage happens even at low pressure.Polish the piston rod and barrel of the cylinder.Make O-rings out of materials having low friction coefficient.Seals resistant to distorting can take the place of O-rings.
Phenomenon of aggressive wearing.As the piston rod reciprocates during a relative motion of the sealed gap, dust and sand from the working environment stick to its surface and are carried into the cylinder along with the oil film. This causes the O-ring to wear out more quickly and lose its sealing ability. Use of a dust ring at the extended shaft end of the reciprocating seal mechanism is necessary to prevent this scenario.
Effect of the sliding surface on the O-ring
One of the main causes of the friction and wear on the O-ring surface is the roughness of the sliding surface. In general, less friction and wear result from a smoother surface, hence the roughness value of the sliding surface is frequently quite low (Ra0.2~0.050μm). But experiments have demonstrated that friction and wear will be negatively impacted by too low surface roughness (Ra less than 0.050μm). This is so because the essential lubricating oil coating can be maintained by the slight surface irregularity. It is therefore imperative to choose suitable surface requirements.
The O-ring life is influenced by the sliding surface material as well. The life of the O-ring is increased with increasing sliding surface material hardness, wear resistance, and smoothness maintenance ability. The surface of the hydraulic cylinder piston rod is chrome-plated for a reason as well. Comparably, it explains why a sealing ring with low hardness and high compression is less durable than one with high hardness and low compression, and why a sliding surface composed of copper and aluminum alloy with the same roughness causes more significant friction and wear on the sealing ring than a steel sliding surface.
Thermal impact Joule
The phenomena of rubber in a stretched condition shrinking when heated is known as the Joule thermal effect of rubber material. Usually, the O-ring is kept somewhat stretched during installation to avoid it from moving in the sealing groove and from twisting when employed as a reciprocating motion seal. But this installation technique will yield unfavorable outcomes if it is applied to rotating motion. Because of the friction heat produced by the rotating motion, the O-ring that is clamped on the spinning shaft shrinks and the clamping force is then increased. In this approach, friction heat is produced → shrinkage → tightening force rises → friction heat is produced…, and this repeating cycle considerably accelerates the aging and wear of the rubber.
Methods of prevention and control
Check that the material of the sealing ring and the contacting medium are compatible chemically.
Temperature control: Do not let the sealing ring to operate for extended periods of time in an environment that is warmer than its resistance range.
Using suitable coatings or lubricants can help to reduce friction and hence wear.
Installation should be done as directed by the manufacturer to prevent twisting or stretching the sealing ring.
Frequent inspection: Timely replace damaged sealing rings and check the state of the sealing rings.
Environment protection: Take action to shield the sealing ring from ozone and UV radiation.
Reasonably lubricated: To lessen wear, use lubricants that work well with the sealing ring material.
Control of quality: To guarantee the homogeneity and purity of the sealing ring material, choose providers of dependable quality.
Method for handling failures
Analyse the failed sealing ring in great detail to identify the reason of failure.
Better design: Depending on the reason of failure, optimise the sealing ring’s design.
Replace materials: Think about substituting other materials if the present one is inappropriate for the application setting.
Improve production and vulcanization procedures to raise seal quality.
Provide users thorough installation and usage instructions to prevent incorrect operation.
linde say
Silicone O-rings have many benefits, although for a variety of reasons they might still fail during use. The performance and dependability of the seal can be much increased, and possible maintenance costs and system failure risks can be decreased, by implementing suitable preventative measures and post-failure response plans.
