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Formula Design of Heat-Resistant Rubber

Heat resistance refers to the ability of rubber and its products to maintain physical and mechanical properties or performance after a long time of thermal aging. The resistance to temperature indicates the sensitivity of the physical and mechanical properties of rubber to the temperature, that is, the mechanical properties of rubber will not decrease at high temperature. At high temperature, the difference between physical and mechanical properties is very small at room temperature, that is, good temperature resistance. It shows that the physical and mechanical properties of rubber vary with temperature. High temperature (heat resistant) rubber products are both good in heat resistance and good in temperature resistance.

There are various methods to evaluate the heat resistance, such as using Martin heat resistant and VEKA heat-resistant to evaluate the heat resistance, and to find the upper limit of the use temperature of the material by the thermal weight loss meter, or the temperature (Tn) - half life temperature (Tn) - half life temperature when the vacuum is heated from 40 to 45min. Evaluation of heat resistance

Heat resistant rubber is the vulcanized rubber that still maintains the original mechanical properties and use value for a long time under high temperature. The change of performance change (such as hardness), performance change rate (such as tensile strength, elongation), performance retention rate and aging coefficient are used to indicate the change of mechanical properties. In rubber seals, the heat-resistant properties of vulcanized rubber in the compressed state are called heat-resistant compression properties, which are often evaluated by the compression permanent deformation coefficient or the compression stress relaxation coefficient.

The rubber, which can still maintain the original performance and use value after a long time over 80 C, is attributed to the category of "heat-resistant rubber". The heat resistance and high temperature properties of rubber products are the most common properties of rubber special properties. The essential reason for the stability of rubber in this case is that it can resist the influence of oxygen, ozone, corrosive chemicals, high energy radiation and mechanical fatigue at high temperature. The molecular structure of rubber does not change and damage significantly, and it can maintain good performance.

Rubber suitable for temperature range / temperature

< 70 kinds of rubber

70~100 natural rubber and styrene butadiene rubber

100~130 chloroprene rubber, nitrile rubber, Chloroether rubber

130~150 butyl rubber, ethylene propylene rubber and chlorinated sulfonated polyethylene rubber

150~180 acrylic rubber and hydrogenated nitrile rubber

180~200 vinyl silicone rubber and fluorine rubber

200~250 two methyl silicone rubber and fluorine rubber

> 250 perfluoroether rubber, fluorosilicone rubber and borosilicate rubber.

The temperature resistance of national standard rubber can be divided into two categories and five categories.

Ordinary rubber A-70~-30 C/90~120 C, such as NR, IR, BR, 237SBR, CR.

Ordinary rubber B-40 to-20 degrees C/120 to 150 degrees C, such as NBR, IIR, EPDM, CSM.

Ordinary rubber C30 - 10 C / 80~90 C, such as T and U.

Heat-resistant rubber A-30~-10 C/150~200 C, such as ACM, ANM, EVA, CO, ECO.

Heat-resistant rubber B-70~-20 C/250~300 C, such as MQ, MVQ, FPM, FKM.

However, in the course of actual use, due to various internal and external factors, in order to ensure safe service life, generally diene rubber is controlled at about 100 C, oil resistant NBR is 130, and acrylate rubber is 180 C. Silicon and fluorine rubber are 200~250 degrees centigrade and can be used for 300~350 times in short time.

There are also 4 categories

The heat resistance of rubber products depends mainly on the type of rubber used. Therefore, when designing the formula, we should first consider the choice of raw rubber.

The heat resistance of rubber shows that rubber has higher viscous flow temperature, higher thermal decomposition stability and good thermochemical stability. The viscosity flow temperature of rubber depends on the polarity of its molecular structure and the rigidity of its molecular chain. The greater the polarity and rigidity, the higher the viscosity flow temperature. The polarity of the rubber molecule is determined by its polar group and molecular structure, and the rigidity of the molecular chain is also related to the polarity of the polar substituents and the regularity of the arrangement of the spatial structure. The addition of 238 cyanide, ester, hydroxyl or chlorine atoms and fluorine atoms to rubber molecules will increase heat resistance. The thermal decomposition temperature of rubber depends on the chemical bond nature of the molecular structure of the rubber. The higher the chemical bond energy, the better the heat resistance. The macromolecular chains of borosilicate rubber, silicone rubber and polyphenylene siloxane have higher bond energy and are superior in heat resistance.

In general, carbon chain rubber, in addition to FPM containing fluorine, is not high in heat resistance and can be used at 150~200 C for a long time; organic polymers with no carbon atom in the main chain, such as Q, have good heat resistance, and silica gel can be used for a long time at 250 or even 300.

The chemical stability of rubber is an important factor in heat resistance, because in the high temperature conditions, some chemicals, if exposed to oxygen, ozone, acid, alkali and organic solvents, can promote the corrosion of rubber and reduce the heat resistance. Chemical stability is closely related to the molecular structure of rubber. Low unsaturated butyl rubber, ethylene propylene rubber and chloro sulfonated polyethylene show excellent heat resistance. In addition, if the primary chain has a single bond linked aromatic structure, the molecular chain will also promote structural stability by means of conjugation.

Formulation design of heat resistant rubber, heat resistance of rubber, saturation of rubber molecular chain and rigidity of molecular chain.

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