Several important factors in choosing an O-ring
When choosing a seal, the first thing we should consider is its tensile strength, tensile stress, elongation, elongation at break, permanent deformation, and stress-strain curve. These are collectively referred to as tensile strength. The so-called tensile strength is actually the maximum tensile stress when the sample is stretched to break. The tensile stress is the stress that is reached when the elongation is specified. Elongation is the deformation of a specimen caused by tensile stress and is expressed as a percentage of the ratio of elongation to original length. The elongation at break is the elongation at which the sample is broken.
In addition to this, hardness is the ability to express rubber against external pressure. The hardness of the rubber is partly related to other properties. For example, the rubber has higher hardness, higher strength, less elongation, good wear resistance, and poor low temperature resistance. High hardness rubber resists crushing and damage under high pressure. Therefore, the appropriate hardness should be selected according to the working characteristics of the part.
We all know that rubber seals are usually in a compressed state, so in addition to these, we also need to consider the compression properties of the seal. Due to the viscoelasticity of the rubber, the compressive stress after compression decreases with time, and the compressive stress relaxes. After the pressure is removed, the original shape cannot be restored, and the expression is a compression permanent. These phenomena are more pronounced in high temperature and oily media. They can affect the sealing properties and can also affect the important properties of the sealant.
It is well known that the choice of O-ring material is important for its sealing performance and service life. The performance of the material directly affects the performance of the O-ring. In addition to the general requirements for the material of the sealing ring, the O-ring should also pay attention to the following conditions:
(1) Flexibility and resilience;
(2) Appropriate mechanical strength, including expansion strength, elongation and tear strength.
(3) The performance is stable, it is not easy to swell in the medium, and the heat shrinkage effect (Joule effect) is small.
(4) Easy to process and maintain precise dimensions.
(5) Does not corrode the contact surface, does not contaminate the medium, etc.
The most suitable and most commonly used material to meet the above requirements is rubber, so O-rings are mostly made of rubber. There are many varieties of rubber, and there are new varieties of rubber. When designing and selecting, you should understand the characteristics of various rubbers and make reasonable choices.