O-ring is one of the most commonly used seals in sealing. However, due to improper selection, groove design, processing and assembly, oil leakage failure is often caused, which can be said to be a trivial matter.
My country's national standards regarding the size of O-rings include GB1235-76, GB3452.1-88 and GB3452.1-92. Among them, the cross-sectional diameter (also called wire diameter) of the O-ring specified in GB1235-76 is 1.9.2.3.3.5.5.7, etc., and the outer diameter of the O-ring is × Wire diameter marking method, generally called the old national standard; GB3452.1-82 is basically the same as GB3452.1-92, generally called the new national standard, which stipulates that the O-ring cross-sectional diameter is 1.8.2.65.5.5.3, etc. The new national standard adopts international practice, and the O-ring adopts the inner diameter × wire diameter marking method.
When selecting O-rings, first try to choose the most commonly used new national standard wire diameters of 2.65 and 3.55. If the outer diameter is greater than 30 and the structural size allows, try to choose an O-ring with a wire diameter of 3.55 to achieve larger compression and contact area.
O-rings are mainly made of nitrile rubber NBR and fluororubber FKM, with fluororubber more suitable for high-temperature working conditions.
In addition to the material, the hardness of the O-ring is a very important indicator. Generally speaking, Shore hardness ranges from 60 to 90. The larger the value, the higher the hardness. Under the same pressure, the higher the hardness, the stronger the ability to resist extrusion (deformation or even tearing). Therefore, O-rings with higher hardness should be selected.
However, common O-rings on the market are made of nitrile rubber, and their Shore hardness is generally around 70, which is difficult to meet the requirements of quite a few working conditions.
O-rings have three groove designs: transfer seal, axial static seal and radial static seal. O-rings such as flanges and box covers are axially compressed, making assembly easier and ensuring sealing performance. In addition, the groove size standards in my country's national standards have lagged behind. For example, in the national standard, the outer diameter of the O-ring is equal to the outer diameter of the O-ring, while the outer diameter of the O-ring of the PARKER flange joint is smaller than the outer diameter of the O-ring. The design should refer appropriately to foreign standards.
Do not use flat sealant on the sealing surface of the O-ring. Apply a small amount of butter on the O-ring to prevent it from falling off. During maintenance, the specifications of the O-ring should be determined according to the groove size. The thicker the wire diameter, the better.
