When we choose rubber seals, the first consideration is tensile strength. The so-called tensile strength is the maximum tensile stress when the specimen is stretched to fracture. Elongation is the deformation of a sample caused by tensile stress, expressed as a percentage of the ratio of the increment of elongation to the original length. Elongation at break is the elongation of the specimen at break. The permanent deformation at tear is the residual deformation of the scale part after tensile fracture.

Then, we consider the basic properties of rubber seals - hardness. The so-called hardness is the ability of rubber to resist the invasion of external pressure. The hardness of rubber is to some extent related to some other properties. For example, the higher the hardness of the rubber, relatively speaking, the greater the strength, the smaller the elongation, the better the wear resistance, and the poor low temperature resistance. High hardness rubber can resist extrusion damage under high pressure. Therefore, appropriate hardness should be selected according to the working characteristics of parts.

We know that rubber seals are often in a state of compression, so we have to consider the compression performance of rubber seals. Due to the viscoelasticity of rubber, the compressive stress will decrease with time after the rubber is compressed, which is manifested as compressive stress relaxation. After the removal of pressure, the original shape can not be restored, as a result of compression permanent deformation. In high temperature and oil medium, these phenomena are more significant. They will affect the sealing performance of the sealing parts, is one of the important properties of the sealant.

We most commonly use the brittleness temperature, which refers to the highest temperature at which the sample is cracked by a certain impact force at low temperature, which can be used to compare the low temperature performance of different rubber materials. But because the working state of rubber parts is different from the test condition, the brittleness temperature of rubber does not mean the lowest working temperature of rubber parts, especially in the oil medium.

The survival environment of rubber seals is poor, most of which are very survival in the fuel, lubricating oil, hydraulic oil and other systems, so they often contact all kinds of oil, naturally, it needs to have oil resistance. Rubber in the oil medium, especially at a higher temperature, will lead to expansion, softening and reduce strength, hardness, at the same time, the plasticizer or soluble substance in the rubber may be oil leaching, resulting in weight reduction, volume reduction, cause leakage. Therefore, the oil resistance of rubber is an important property of the rubber material working in the oil medium. Generally, after soaking in oil for a number of time at a certain temperature, the changes in weight, volume and strength, elongation and hardness are measured. Sometimes it can also be expressed by the oil resistance coefficient, which is the ratio of the strength or elongation after soaking in the medium to the original strength or elongation.

The above is a simple introduction to the main performance of rubber seals that should be considered.

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