Characteristics and Applications of Silicone Rubber
Silicone rubber polymer molecules are chain like structures formed by Si O (silicon oxygen) bonds, mainly composed of linear polysiloxanes with high molar mass. Due to the fact that Si-O-Si bonds are the basic bond type formed by them, silicon atoms are mainly connected to methyl groups, and a small amount of unsaturated groups are introduced on the side chains. The intermolecular force is small, and the molecules are in a helical structure. The methyl groups are arranged outward and can rotate freely, making silicone rubber have better heat resistance, electrical insulation, chemical stability, and other properties than other ordinary rubbers. A typical silicone rubber, polydimethylsiloxane, has a helical molecular configuration with low intermolecular forces, resulting in good resilience. At the same time, the formaldehyde group pointing outside the helix can rotate freely, giving silicone rubber unique surface properties such as hydrophobicity and surface anti adhesion.
Heat resistance: Silicone rubber has much better heat resistance than ordinary rubber, and can be used almost permanently at 150 degrees Celsius without any performance changes; Can be used continuously for 10000 hours at 200 degrees Celsius; It can also be used for a period of time at 350 degrees Celsius. Widely used in situations that require heat resistance: sealing rings for hot water bottles, heat-resistant handles for pressure cookers, etc
Cold resistance: Ordinary rubber has a delay of -20 ° C to -30 ° C, while silicone rubber still has good elasticity at -60 ° C to -70 ° C. Some special formulas of silicone rubber can also withstand extremely low temperatures.
Weather resistance: Ordinary rubber rapidly degrades under the action of ozone generated by corona discharge, while silicone rubber is not affected by ozone. Moreover, under long-term exposure to ultraviolet radiation and other climatic conditions, its physical properties only show slight changes. Sealing materials for outdoor use
Electrical performance: Silicone rubber has a high resistivity and its resistance value remains stable over a wide temperature and frequency range. At the same time, silicone rubber has good resistance to high-voltage corona discharge and arc discharge. High voltage insulators, TV high voltage caps, electrical components, etc.
Conductivity: When conductive fillers (such as carbon black) are added, silicone rubber has conductive contact points on the keyboard
Thermal conductivity: When certain thermal conductive fillers are added, silicone rubber has thermal conductivity heat dissipation fins, thermal sealing pads, photocopiers, fax machines, and thermal rollers
Radiation resistance: Silicone rubber containing phenyl greatly improves the radiation resistance of electrically insulated cables, connectors for nuclear power plants, etc
Flame retardancy: Silicone rubber itself is flammable, but when a small amount of flame retardant is added, it has flame retardancy and self extinguishing properties; And because silicone rubber does not contain organic halides, it does not emit smoke or toxic gases during combustion.
Breathability: Silicone rubber film has better breathability than ordinary rubber and plastic waxing film. Another characteristic is its strong selectivity for different air permeability.
Silicone rubber compound is a synthetic rubber with excellent comprehensive performance, which has excellent thermal stability, high and low temperature resistance, and can work for a long time in the state of -60 ℃ to+250 ℃. It is resistant to ozone, weather, good electrical properties, corona, arc, and electric spark. It has chemical stability, weather aging resistance, radiation resistance, physiological inertness, and good breathability, and can be widely used in aviation, cables, electronics, electrical appliances, chemical industry, etc Used in industries such as instrumentation, cement, automobiles, construction, food processing, and medical equipment for deep processing of machinery such as molding and extrusion.
Blended rubber is made by adding silicone rubber raw rubber to a double roller rubber mixer or a closed kneading machine, gradually adding white carbon black, silicone oil, and other additives for repeated refining.
The performance of silicone varies depending on the added fillers and additives. Mainly manifested in: physical properties (hardness, tensile strength, elongation, tear strength, shrinkage, plasticity, specific gravity), electrical properties, chemical stability (temperature resistance, weather resistance, acid and alkali corrosion resistance), and other aspects.
The molding of mixed rubber requires the application of a certain temperature and pressure under the action of a vulcanizing agent (only required in solid state to prevent the formation of bubbles). If HTV needs to be around 165 ℃, LSR needs to be around 140 ℃.