Silicone rubber is a synthetic polymer that has a backbone of silicon oxygen linkages. This rubber has similar bond structure as found in glass, sand and quartz. This is a unique synthetic elastomer which is made from a cross-linked polymer that is reinforced with silica. The characteristic of this rubber is such that it provides the perfect balance of mechanical and chemical properties which is required in today's most demanding applications.
Properties of Silicone Rubber:
- The outstanding property of this form of rubber is its very wide temperature range. It offers excellent resistance to extreme temperatures, the range of which can be from minus 100°F to plus 500°F.
- It has better oil and water resistance than the others.
- Because of its compatibility with varied temperature range, the tensile strength, elongation, tear strength and compression set of this rubber can be far superior to conventional rubbers.
- It is susceptible to ozone, UV, heat and other aging factors.
- This rubber is resistant to steam.
- It is metal detectable.
- It glows in the dark.
- It is electrically conductive.
- It is resistant to chemical/oil/acid/gas resistance.
- It has low smoke emission and flame retardant
These rubber can be extruded into tubes, strips, solid cord or any custom profiles according to the size specifications of the manufacturer. Cords can be joined to make o-rings. Extruded profiles can be joined to make seals. Silicone Rubber can also be moulded into custom designs and shapes. This form of synthetic rubber is available for making molds that are poured, brushed or sprayed on to a model and has performance characteristics that is not available in other molded rubber. High temperature resistance makes this rubber the only mold rubber suitable for casting low melt metal alloys like lead, tin, pewter. It is also used in the production casting of resins.
- High and low temperature stability
- Inertness, that is no taste or smell
- Translucent and easy to color
- Wide hardness range
- Chemical resistance
- Sealing performance
- Electrical properties
- Compression set resistance
- These rubber is generally high in cost.
- It is sensitive to substances like sulfur clay that may prevent the silicone from curing which is known as cure inhibition.
- This rubber is usually very thick, having high viscosity.
- It must be vacuum degassed before pouring to minimize bubble entrapment.
Forms of Silicone Rubber
This rubber is available in the following forms:
- Compounds: These are ready to use materials which can be pigmented and catalyzed for your processing equipment and end application.
- Bases: These silicone polymers contain a reinforcing filler. The bases can be further compounded with additives and pigments that produce a compound which meet your color and other fabrication needs.
- Liquid silicone rubber (LSR): This rubber system can be pumped into a suitable injection molding machine which then can be heat cured to produce molded rubber parts.
- Fluorosilicone rubber compounds and bases: They maintain many key properties of silicone, but also has other characteristics of superior chemical, fuel, and oil resistance.
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Butadiene rubber is supposed to be the most elastic rubber type. The chemical name of this rubber is Polybutadiene. This rubber is polymerized butadiene and usually used in combination with other rubber types. This rubber is the second largest volume synthetic rubber produced, after styrene-butadiene rubber (SBR).
Application of Butadiene Rubber
A typical application is a blend of BR and natural rubber in truck tires. The major use of butadiene rubber is in tires with over 70% of the polymer produced going into sidewalls and treads. This rubber is usually combined with other elastomers like natural rubber or SBR for tread compounds. It also has a major application as an impact modifier for acrylonitrile-butadiene-styrene resin (ABS) and polystyrene with about 25% of the total volume going into these applications. Typically about 7% of this rubber is added to the polymerization process to make these rubber-toughened resins. Due to its outstanding resiliency, it is estimated that about 20,000 metric tons worldwide of “high cis” polybutadiene is used every year in golf ball cores. This application is widely growing because the golf ball industry seems to be moving away from the traditional wound ball technology to the two-piece, solid core construction, made of BR, in combination with other rubbers
Properties of Butadiene Rubber:
- High Elasticity
- Low temperature properties
- Wear resistance
- Low hysteresis
- Good flexibility at ambient temperatures
- High abrasion resistance in severe conditions
- Low rolling resistance
The butadiene rubber is and will continue to be a high volume rubber for use in toughened plastics, tires, and golf balls due to its low cost, availability and unique properties.
This is a class of synthetic rubber designed for very high temperature operation. FKM provide extraordinary levels of resistance to chemicals, heat and oil, while providing useful service life above 200°C. FKM are not a single entity but a family of fluoropolymer rubbers. Fluoroelastomers or FKM can be classified by their fluorine content, 66%, 68%, & 70% respectively. This means that FKM rubber having higher fluorine content have increasing fluids resistance derived from increasing fluorine levels.
Properties of Fluoroelastomers (FKM):
- They have excellent resistance to chemical attack by oxidation, by acids and by fuels.
- They have good oil resistance.
- They have limited resistance to steam, hot water, methanol, and other highly polar fluids.
- The outstanding heat stability and excellent oil resistance are due to the high ratio of fluorine to hydrogen, the strength of the carbon-fluorine bond, and the absence of unsaturation.
- The latest FKM polymers have a much broader fluids resistance profile than standard fluoroelastomers.
- They are able to withstand strong bases and ketones as well as aromatic hydrocarbons, oils, acids, and steam.
- Peroxide cured fluoroelastomers have inherently better water, steam, and acid resistance
FKM provides premium, long-term reliability even in harsh environments. A list of its applications is given below:
- O-ring seals in fuels, lubricants
- Valve stem seals
- Fuel hoses
- Fuel Injector O-rings
- In tank and quick connect
- Flue duct exp. Joints
- Valve liners
- Roll covers
- Sheet stock/cut gaskets
- Shaft seals
- Check valve balls
- Military flare binders
- Electrical connectors
- Tire valve stem seals
- Clips for jet engines
- Lathe cut gaskets
- Hydraulic o-ring seals and hydraulic systems
- Manifold gaskets
- Fuel tank bladders
- Firewall seals
- Engine lube siphon hose fuel system seals
- Gaskets (valve & manifold)
Viton® is a registered trademark for fluroelastomer by DuPont Performance Elastomers L.L.C. This fluoroelastomer was introduced in 1957 to meet the requirements in the aerospace industry for a high-performance elastomer. The use of Viton® has spread quickly to many other industries, including the fluid power, automotive, appliance and chemical industries. Viton® is the most specified fluoroelastomer, well known for its excellent heat resistance, excellent resistance to aggressive fuels and chemicals. This popular fluroelastomer has worldwide ISO 9000 and ISO/TS 16949 registration.
FKM is of high value in use as a class of synthetic rubber which provides extraordinary levels of resistance to chemicals, oil and heat. This type of rubber can be fabricated into seals, o-rings, and hoses for a variety of high performance applications in the automotive, aerospace, and petrochemical industries.