How to choose the diameter of O-ring wire?
When selecting the wire diameter of the O-ring, the following key factors should be considered:
Compression rate:
Calculate the compression rate (w) based on the cross-sectional diameter (d0) of the O-ring in the free state and the distance (h) between the bottom of the groove and the sealed surface.
In static sealing, cylindrical static sealing devices generally take w=10%~15%; flat static sealing devices take w=15%~30%.
In dynamic sealing, the compression rate of reciprocating motion sealing is generally taken as w=10%~15%; rotary motion sealing needs to consider the Joule heat effect, and the compression rate is generally taken as w=10%~15%.
Sealing surface roughness:
The surface roughness should be within the range of 3.2-6.3μm to ensure good air tightness.
When the surface roughness exceeds 12.5μm, the O-ring has poor contact with the sealing surface and is prone to air leakage.
Seal groove shape:
The seal groove is generally rectangular, and the groove width should be larger than the wire diameter of the O-ring to leave enough space so that the O-ring will only deform without volume compression after installation.
Sealing ring material:
Common materials include nitrile rubber (NBR), fluororubber (FKM), silicone rubber (VMQ), ethylene propylene rubber (EPDM), chloroprene rubber (CR), etc.
The hardness should be around 70 Shore A hardness to ensure good bridging and sealing performance.
O-ring inner diameter selection:
Select the appropriate inner diameter according to the position of the O-ring and the air pressure it is subjected to. For example, the inner diameter of the O-ring at the inlet and outlet sleeve position should be 1%~3% smaller than the inner diameter of the groove; the outer diameter of the O-ring at the dynamic fit and explosion-proof valve position should be 1%~2% larger than the outer diameter of the groove.
Wire diameter specifications:
According to national standards GB1235-76, GB3452.1-88 and GB3452.1-92, the wire diameter specifications of O-rings include 1.9, 2.4, 3.1, 3.5, 5.7, etc.
According to the international standard ISO, the wire diameter specification of the O-ring is usually expressed as inner diameter × cross-sectional diameter, such as 7.5 × 1.8, 10.46 × 5.33, etc.
When selecting the wire diameter of the O-ring, factors such as compression rate, sealing surface roughness, sealing groove shape, sealing ring material, O-ring inner diameter selection and wire diameter specification should be considered comprehensively to ensure that the O-ring can meet specific sealing requirements.