1. Tensile properties Tensile properties are the first properties to be considered for sealing materials, including: tensile strength, constant elongation stress, elongation at break and permanent deformation at break. Tensile strength is the maximum stress at which a specimen is stretched to fracture. Constant elongation stress (constant elongation modulus) is the stress reached at specified elongation. Elongation is the ratio of the increment of elongation to the original length of the specimen when it is subjected to a specified tensile force. Elongation at break is the elongation of the specimen at break. Tensile permanent deformation is the residual deformation between the marks after tensile fracture of the specimen.
2, hardness hardness indicates the ability of the sealing material to resist external pressure, and is also one of the basic properties of the sealing material. The hardness of the material is related to other properties to a certain extent, the higher the hardness, the greater the strength, the smaller the elongation, the better the wear resistance, and the worse the low temperature resistance.
3, compression performance rubber seals are usually in a state of compression, due to the viscoelasticity of rubber materials, the pressure will decrease with time when compressed, manifested as compression stress relaxation; Can not return to the original shape after removal of pressure, as compression permanent deformation. This phenomenon is more obvious in high temperature and oil media, and the performance is directly related to the durability of the sealing ability of the sealing product.
4, low temperature performance used to measure the low temperature characteristics of rubber seals indicators, the following two methods to test low temperature performance: 1) low temperature retraction temperature: The sealing material is stretched to a certain length, and then fixed, quickly cooled to below the freezing temperature, after reaching the balance, release the test piece, and at a certain speed, the temperature of the record pattern is reduced by 10%, 30%, 50% and 70%, respectively, TR10, TR30, TR50, TR70. The material standard takes TR10 as an indicator, which is related to the brittleness temperature of rubber. Low temperature flexure: After freezing the sample at the specified low temperature to the specified time, reciprocating bending according to the specified Angle, to investigate the sealing ability of the seal after the repeated action of the dynamic load at low temperature.
5, oil or medium resistance sealing materials in addition to contact with petroleum-based, double ester, silicone 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, plasticizers and soluble substances in the sealing material are extracted, resulting in mass reduction, volume reduction, and leakage. Generally at a certain temperature, after soaking in the medium for a number of time to determine its quality, volume, strength, elongation, hardness changes to assess the sealing material oil resistance or medium resistance performance.
6, aging resistance sealing materials by oxygen, ozone, heat, light, moisture, mechanical stress will cause the performance of the deterioration, called the aging of sealing materials. Aging resistance (also known as weather resistance) can be expressed by the change in strength, elongation and hardness of the aging pattern after aging, and the smaller the change rate, the better the aging resistance. Note: Weather resistance refers to a series of aging phenomena such as fading, discoloration, cracking, powder and strength decline of plastic products due to the influence of external conditions such as sunlight exposure, temperature change, wind and rain. Among them, ultraviolet radiation is the key factor that promotes the aging of plastics.