1、the hardness of the O-ring
O-ring material hardness is the most important indicator to evaluate sealing performance. The hardness of the O-ring determines the compression of the O-ring and the maximum allowable extrusion clearance of the groove. Since the Shore A70 nitrile seal can meet most of the conditions of use, if the sealing material is not specifically stated, a nitrile rubber of Shore A70 is generally provided.
The maximum allowable extrusion gap gmax is related to the system pressure, O-ring section diameter, and material hardness. In general, the higher the working pressure, the smaller the value of the maximum allowable extrusion gap gmax. If the gap g exceeds the allowable range, it will cause the O-ring to squeeze out and even damage.
Another indicator of the O-ring sealing performance is the compression set of the selected material. Under the action of pressure, the O-ring as an elastic element is elastically deformed, and as the pressure increases, permanent plastic deformation also occurs.
4、the amount of pre-compression
The O-ring is installed in the groove. 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 also varies. Typically, it is about 15% to 30% in static seals and about 9% to 25% in dynamic seals.
5、stretching and compression
When installing the O-ring in the groove, it must be stretched or compressed. If the values of tension and compression are too large, it will result in an excessive increase or decrease of the O-ring cross-section, since stretching 1% correspondingly reduces the cross-sectional diameter W by about 0.5%. For the hole seal, the O-ring is preferably in tension and the maximum allowable elongation is 6%; for the shaft seal, the O-ring is preferably compressed in the direction of its circumference, and the maximum allowable circumference is 3 %.
6、O-ring used as a rotating shaft seal
O-rings can also be used as rotary shaft seals for low-speed rotary motion and shorter operating cycles. When the peripheral speed is less 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 elongated rubber ring must be considered to shrink after being heated, so the sealing ring should be selected. With the inner diameter being about 2% greater than the diameter of the shaft it seals, this phenomenon can be avoided. After the sealing ring is installed in the groove, the sealing ring is compressed radially, and the O-shaped ring forms a minute wave shape in the groove, thereby improving the lubrication conditions.
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