One
tensile property
Tensile properties, including tensile strength, constant tensile stress, elongation at break and permanent deformation at break, are the first properties to be considered in sealing materials. Tensile strength is the maximum stress of specimen stretching to fracture. The tensile stress (elongation modulus) is the stress reached when the elongation is specified. Elongation is the deformation caused by the specified tensile force of the specimen, and the elongation increment is proportional to the original length. Elongation at break is elongation at break. The permanent deformation is the residual deformation between the marking lines after tensile fracture.

Two
hardness
Hardness indicates the ability of sealing materials to resist external pressure, and is also one of the basic properties of sealing materials. The hardness of the material is related to other properties to a certain extent. The higher the hardness, the greater the strength, the lower the elongation, the better the wear resistance, and the worse the low temperature resistance.

Three
Compression performance
Rubber seals are usually in a compressive state. Due to the viscoelasticity of rubber materials, the compression pressure decreases with time, showing compressive stress relaxation; after removing the pressure, the original shape can not be restored, showing compressive permanent deformation. This phenomenon is more evident in high temperature and oil media, and the performance is directly related to the durability of sealing products.

Four
Low temperature performance
To measure the cryogenic characteristics of rubber seals, two methods of testing low temperature performance are described below:
(1) Low temperature shrinkage temperature: the sealing material is stretched to a certain length, then fixed, quickly cooled to below the freezing temperature, after reaching equilibrium, the specimen is loosened, and the temperature is expressed as TR10, TR30, TR50 and TR70 respectively when the recording pattern shrinks by 10%, 30%, 50% and 70%. The material standard is TR10, which is related to the brittleness temperature of rubber.

(2) Low-temperature flexibility: after the specimen is frozen to a specified time at a specified low temperature, it bends to and fro at a prescribed angle to investigate the sealing ability of the seals after repeated dynamic loading at a low temperature.

Five
Oil resistance or dielectric resistance
Sealing materials in addition to contact with petroleum-based, diester, silicate grease oil, in the chemical industry, sometimes also contact acid, alkali and other corrosive media. In addition to corrosion in these media, at high temperatures will also lead to expansion and strength reduction, hardness reduction; at the same time, the plasticizer and soluble substances in the sealing material are extracted, resulting in quality reduction, volume reduction, resulting in leakage. Generally, the quality, volume, strength, elongation and hardness of the sealing material are measured after soaking in the medium for a certain time at a certain temperature to evaluate its oil or medium resistance.

Six
Aging resistance
Sealing materials by oxygen, ozone, heat, light, moisture, mechanical stress will cause performance deterioration, known as the aging of sealing materials. Aging resistance (also known as weatherability) can be expressed by changes in strength, elongation, hardness of the pattern after aging, the smaller the change rate, the better the aging resistance. Note: Weatherability refers to a series of aging phenomena, such as discoloration, discoloration, cracking, powdering and strength reduction, etc. of plastic products affected by sunlight, temperature changes, wind and rain. Among them, ultraviolet radiation is the key factor to promote plastic aging.