1. Hardness of O-ring
O-ring material hardness is the most important index for evaluating sealing performance. The hardness of the O-ring determines the compression of the O-ring and the maximum allowable extrusion gap of the groove. Since the nitrile seal of Shaw A70 can meet most of the conditions of use, if the sealing material is not specified, the nitrile rubber of Shao A70 is generally provided.
2, extrusion gap
The maximum allowable extrusion gap gmax is related to the system pressure, the cross-sectional diameter of the O-ring and the hardness of the material. Generally, the higher the working pressure, the smaller the maximum allowable extrusion gap gmax. If the gap g exceeds the allowable range, it will cause the O-ring to squeeze out or even be damaged.
3, compression set
Another index to evaluate the sealing performance of the O-ring
is the compression set of the selected material. Under pressure, the O-ring, which is an elastic element, produces elastic deformation, and as the pressure increases, permanent plastic deformation will also occur.
4, the amount of pre-compression
O-ring is installed in the groove, in order to ensure its sealing performance, an initial compression amount should be reserved. For different applications, the amount of pre-compression relative to the cross-sectional diameter W is also different. Generally, it is about 15%-30% in static seals, and about 9%-25% in dynamic seals.
5. Tension and compression
When installing the O-ring
in the groove, it must be stretched or compressed. If the value of tension and compression is too large, it will cause the O-ring cross section to increase or decrease excessively, because 1% stretching will correspondingly reduce the cross-sectional diameter W by about 0.5%. For hole sealing, the O-ring is best in tension, and the maximum allowable stretch is 6%; for shaft sealing, the O-ring is preferably compressed along its circumference, and the maximum allowable circumference compression is 3 %.
6, O-ring is used as rotating shaft seal
O-rings can also be used as seals for rotating shafts with low-speed rotating motion and short operating cycles. When the peripheral speed is lower than 0.5m/s, the O-ring
can be selected according to the normal design standard; when the peripheral speed is greater than 0.5m/s, the phenomenon that the elongated rubber ring will shrink after heating must be considered, so choose the seal ring The above phenomenon can be avoided by making its inner diameter approximately 2% larger than the diameter of the shaft sealed by it. After the sealing ring is installed in the groove, the sealing ring is radially compressed, and the O-ring ring forms a slight corrugation in the groove, thereby improving the lubrication condition.