Qingdao AOD Rubber Products Co., Ltd.

How to choose the material of rubber sealing products?

How to choose the material of rubber sealing products?

Rubber sealing products are widely used, different application fields require different conditions, different working conditions, some require acid and alkali resistance, oil resistance; some requirements are purely waterproof and dustproof; in extreme environments, high pressure resistance and fire resistance are also required. , weather resistance, etc. This raises a general question: How do you choose the material for a rubber seal?

When we choose rubber sealing products, the primary considerations include tensile strength, tensile stress, elongation, elongation at break, permanent deformation, and stress or strain curves. We collectively refer to tensile strength. . The tensile strength is the maximum tensile stress at which the sample is stretched to crack. The tensile stress (the modulus of extension) is the stress (modulus) that arrives at regular elongation. Elongation is the deformation caused by the tensile stress of the specimen, and is expressed as a percentage of the ratio of the elongation increment to the original length. The elongation at break is the elongation at which the sample is broken. The torn permanent deformation is the residual deformation of the gauge length portion after the specimen is stretched and cracked.

Then, we consider the basic function of the rubber seal - hardness. The so-called hardness is the ability to indicate the intrusion of rubber against external pressure. The hardness of rubber is necessarily related to other functions. For example, the hardness of the material is relatively high, relatively speaking, the strength is large, the elongation is small, the wear resistance is good, and the low temperature resistance is poor. High hardness rubber can resist kneading damage under high pressure. Therefore, the appropriate hardness should be selected according to the working characteristics of the parts.

We know that rubber seals are often under tightening, so we need to consider the tightening function of rubber seals. Because of the viscoelasticity of the rubber, after the rubber is tightened, the tightening stress will decrease with time, which is manifested by the relaxation of the tightening stress; after the pressure is removed, the original shape cannot be recovered, and the permanent deformation is exhibited. These phenomena are more pronounced in high temperature oil media. They affect the sealing function of the sealing article and are one of the important functions of the material for sealing products.

The most commonly used is the brittle temperature, which refers to the highest temperature at which the sample will break when the temperature is subjected to a certain impact. It can be used to compare the low temperature function of different materials. However, because the operation of the rubber parts is different from the test conditions, the brittleness temperature of the rubber does not indicate the minimum operating temperature of the rubber parts, especially in the oil medium. Secondly, it is the low temperature retracting temperature. The test piece is stretched to a certain length at room temperature, then fixed, and sensitively cooled to below the freezing temperature. After reaching the temperature balance, the test piece is released, and the temperature is raised at a certain speed, and the test piece is recorded. The temperatures at which 10%, 30%, 50%, and 70% were retracted are indicated by TR10, TR30, TR50, and TR70, respectively. In the data specification, TR10 is generally adopted as a policy, which is close to the brittleness temperature of rubber. Another way to indicate the low temperature function of rubber is to determine its cold resistance. Generally, the sample is compacted to a certain amount of deformation at room temperature, and then frozen at a regular low temperature, and then the load is released to recover at a low temperature. The ratio of the amount of recovery to the amount of shrinkage is called the coefficient of tightening and cold resistance. The larger the coefficient, the better the cold resistance of the rubber.

The rubber-sealed products have a harsh living environment. Most of them are livelihoods in fuels, lubricants, hydraulic oils, etc., so they often come into contact with various oils, which inevitably requires oil resistance. In oil media, especially at higher temperatures, it will cause swelling, softening and lowering strength and hardness. Plasticizers or soluble substances in the rubber may be leached by the oil, resulting in reduced weight, reduced volume, and leakage. Therefore, the oil resistance of rubber is an important function of materials working in an oil medium. Generally, the component changes, volume changes, and changes in strength, elongation, and hardness are measured after immersing in the oil for a certain period of time at a certain temperature. Sometimes it can also be indicated by the oil resistance coefficient, ie the ratio of the strength or elongation after soaking in the medium to the original strength or elongation.

The above are some considerations for selecting rubber sealing products, welcome to add.

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