Silicone rubber operating temperatures

Silicone rubber exhibits excellent hot-air resistance. At 180 °C, it can be used in long-term operation and with the appropriate formulation, its rubber elasticity can be maintained over several 1000 h even at 250 °C. In the short term, e.g., under the influence of heat shock, silicone rubber withstands temperatures of 300 to 400 C [13]. 

Also termed glass temperature or Tg. The temperature at which the stiffness of an elastomer subjected to low temperatures changes most rapidly. If the glass temperature is close to the operational temperature the material will be leathery in its behaviour rather than rubber-like. Approximate glass transition temperatures for different polymers are NR -70 °C SBR -52 °C HR -75 °C PCP -40 °C and silicone rubber -85 °C. 

Silicone rubbers bum if the temperature of the flames exceeds 600-700 °C. However, their combustion does not release toxic products, and there is an isolating layer of carbon dioxide on the product. If this rubber is sealed in a glass or asbestos shell, the cable can endure operating voltage and ensure normal functioning of the electric circuit even in a fire. These properties help to reduce the requirement for wires and cables in most cases by 20% and noticeably increase the safety of operation in case of overloads and fires. 

One of the most essential spheres of their application is aircraft engineering. Silicone rubbers are used as seals, membranes, profile parts, flexjoints, etc. and operate at veiy low temperatures at high altitudes, in large concentrations of ozone and under various weather effects. 

Silicone rubbers have proven to be successful inserts for sea projectors. These inserts are meant to keep coal projector electrodes dry. In harsh conditions of the Arctic Sea no insert from organic rubber can stand the test, because the ambient temperature is well below zero, whereas the insert is heated by the voltage arc to 300 °C. Only an insert from silicone rubber successfully operates at such temperature changes. 

Silicone rubber in combination with asbestos fibre can be used in pressure reducers in receivers. In comparison tests all diaphragms from organic rubbers and asbestos cease operation due to aging after 200-360 thousand cycles on the other hand, diaphragms from silicone rubber are still in perfect state after 1 million cycles. We should also mention the use of silicone rubbers in industrial furnaces and various apparatuses operating at high temperatures (oil cracking towers, gas pipelines, recuperation installations). 

See Chapter 12 for information about gas chromatography. A Carbowax column works best, although any other nonpolar phase such as silicone rubber should work as well. With a nonpolar column packing the products cU e expected to come out in the order of their boiling points. A typical set of operating conditions would be column temperature 100°C, He flow rate 35 mL/min, column size 5-mm dia x 2 m, scunple size 5 microliters, attenuation 16. 

Silicone rubbers play a huge role in automotive applications due to their low temperature characteristics, thermal and chemical resistance, and general purpose use. From Table 8.1, we can see that the useful temperature range goes from -50 to 250°C. For automotive applications, this range covers all the operating system temperatures that a vehicle will see. Table 8.2 shows service life at continuous use for silicone rubbers. The time durations shown here are extensive for an elastomer and represent a great improvement over unsaturated carbon-based elastomers. 

The most frequently used insulating compounds are PVC, XLPE and EPR. For most onshore applications PVC and XLPE are preferred because of economic reasons, and XLPE is becoming more popular than PVC. Marine and offshore applications tend to prefer XLPE and EPR. EPR is usually more expensive than XLPE. Both compounds have the advantage that they permit the conductors to operate at higher temperatures (85 to 90°C) than those of PVC (70°C). PVC compounds can be specially manufactured to tolerate conductor temperatures up to 85°C. Silicon rubber can be specified if high conductor temperatures (up to 180°C), and for even higher temperatures (up to 260°C)... 

Special adhesives are required for high temperature use. Silicone rubber is an excellent flexible adhesive with a temperature limit of 250 °C. For higher operating temperatures, one must resort to inorganic adhesives and cements. These are usually based on silicates (water glass), phosphates (phosphoric acid), and Portland cement. 

Figure 10.21 shows the structure of the hardware of a single cell. Research by Zhang s group [77,78] revealed that when the cell was operated at a temperature <200 °C, the composite graphite material SGL BBP4 could be used for flow-field fabrication, and silicone rubber (Fuel Cell Store 590,363) could be used as the sealing material. But when the cell temperature was 200-300 °C, stainless steel 430 was more suitable as the flow-field material, while silicone rubber only... 

The sealing of the bipolar plates in a fuel cell stack is very important for avoiding fuel and oxidant leaks. O-rings are usually used in fuel cell stacks. For LT-PEM fuel cells, there are many choices of sealing materials, but the majority cannot be used at higher temperatures. For example, if the fuel cell is intended to operate at 180 °C, only those materials with a tolerance >200 °C can be used—silicon rubber, tetrafluoroethylene-propylene, perfluoroelastomer, and so on [97]. 

Silicones polymers which can take the form of fluids for lubrication, rubbers or plastics. Silicone resins are employed in electrical insulation applications, including component encapsulation. Silicone rubber is unique among synthetic elastomers being the only one with useful operating temperature, and resistant to weather, ozone, chemicals, with a non-stick surface. Silicones are used as release agents, because of incompatability with most materials, and as lubricants and additives. 

Since the early 1980s, membrane technology has advanced rapidly and continues to advance. In addition to cellulose acetate and polysulfone, the polymers used in making gas separation membranes include polyimides, polyamides, polyaramid, polydimethylsiloxane, silicon polycarbonate, neoprene, silicone rubber, and others. Today membranes can be designed to withstand a 2,000 psi pressure differential. Membranes used in hydrogen or carbon dioxide applications operate at temperatures up to 200°F, while those used in solvent applications can operate at temperatures up to about 400°F (Baker, 1985). 

Silicone rubber is often used where operating temperatures are high as they retain much of their tensile strength and compression set resistance at temperatures up to 200 °C. Typical applications include oven door gaskets, high-temperature hoses and... 

Due to the high operating temperatures of silicone rubber, cyanoacrylates are not always suitable and RTV silicones may be the only adhesive option if the operating temperature is >150 °C. Silicones have a low surface energy and so will benefit hugely from surface treatment prior to bonding (Table 4.12). 

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