Is The Standard O Rings Compression The Better?

- Aug 11, 2017-

Is the Standard O Rings compression the better?
 The traditional view that the more Standard O Rings is squeezed (ie, deformation relative to its "squeeze" state), the tighter the seal. More squeeze is equal to the Standard O Rings, which fits the greater force between the hardware - that is, the flow of liquid, gas and dry powder from the rubber seal and the fit between the hardware.
This is subject to squeezing more and also a Standard O Rings tends to keep its force (and hence better seal) than the lesser the Standard O Rings that is squeezed less. The elastomer does not maintain its "push back" force over time and is called compression set. The elastomer with a high compression set (usually more than 80%) no longer returns to its original uncompressed shape when it is not squeezed. However, assuming that increasing the extrusion on the Standard O Rings will result in a better seal that may not always be correct, depending on other factors. These include:
Installation is damaged
In the installation process more forcefully you squeeze the Standard O Rings when you are more likely to pinch them because of the leakage generated by the way. It is found that when Parker is used to predict the installation of a finite element model of 40% and 25% of the extrusion (Figure 1 and 2, respectively) Standard O Rings. At 40%, the pinch-fitting parts between the Standard O Rings are difficult to avoid, while in 25% of the mounting clamps are actually eliminated.
Mating hardware is damaged
As shown in Fig. 3, the relationship between the amount of non-squeezing and the compressive load force required to keep the squeeze is linear. In fact, the compressive load force rises by more than 30% of the squeeze much faster. Standard O Rings require almost two and a half times the load to compress to 40% to 25% of it. This level of compression load can be flattened or deformed with light or fragile fit parts.
Standard O Rings material
The data shown in these figures are 70 Shore hardness nitrile rubber. Other materials, such as perfluoroelastomers and compounds with low elongation (ie, they only stretch "so far"), squeeze more than 30% may break. Other materials can experience accelerated compression of the permanent deformation, reducing the service life of 40% in the extrusion.
While many variables affect the form, fit and function of the seal, the back of the leakless seal is the most important parameter that is the amount of extrusion applied. However, since these data show that the squeeze in the ideal amount itself is subject to many factors. You can not just assume that the more is better.
Keep in mind that other factors can lead to Standard O Rings to poor performance, such as thermal degradation, chemical interactions, gas infiltration, mechanical damage such as extrusion or wear, or elasticity of low temperature loss. In these cases, adjusting the amount of extrusion can not solve the problem.
(1) to improve the viscosity of the media can reduce the leakage, the greater the better viscosity. Of course, increased viscosity will increase the power loss. At present, lubrication is often used to increase the medium viscosity method to reduce leakage. Such as semi-fluid grease, the viscosity between the oil and fat, fat oil and so on.
(2) reduce the gap, increase the width of the joint surface. The size of the joint gap is the main cause of leakage, it is not only with the metal surface processing accuracy, but also with the flatness. The effect of flatness is often greater than the machining accuracy, flatness is poor, the gap increases, and its relationship with the leakage is greater than the third-party form increases, that is, the gap increased by 1 times the leakage will increase more than 7 times The To reduce leakage, the most important research object is to reduce the gap and increase the width of the joint surface.
(3) to reduce the pressure inside and outside, so that the box with the outside world. This method is applied more, such as in the gear box above the lid has a filler hole, when the gear in the high-speed rotation, the box temperature, the box pressure gradually increased, the oil to speed up the leak. If the oil hole in a tube connected with the outside air, so that the pressure difference between the two, the leakage will be better.

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