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About Silicone

  • What is silicone?
    Silicone is a synthetic polymer, derived from silicon metal. The nature of its origin gives it a number of significant advantages over conventional rubber polymers. Silicone is available in the form of rubbers, greases, and fluids.
  • Does the outside environment affect silicone?
    No. Silicone is not affected by extremes of weather – hot, cold, dry, wet, or humid. It also has excellent resistance to UV and ozone degradation.
  • Silicone seems to be more expensive than other rubber, why is this?
    Silicone is more expensive than most rubber types because it is a speciality high performance polymer with outstanding qualities. It is made in relatively low quantities and requires expensive and complicated primary manufacturing facilities.
  • In what colours is silicone available?
    Silicone can be supplied in a very wide range of colours, including fluorescents, metallics, and even those that change colour with heat!
  • What equipment do I require to process silicone compound?
    Silicone rubber compounds can in general be processed on conventional rubber processing machinery.
  • What is the shelf life of a silicone product?
    The effective shelf life of silicone rubber compounds is dependant largely on what is required from the compound in processing terms. The material tends to stiffen with age but this can be overcome by freshening on a two-roll mill. In general terms most compounds have a declared shelf life of at least 6 months.
  • How do I store silicone compounds?
    Silicone compounds should be stored in a dry environment away from direct sunlight and heat, and at a temperature of less than 30C.
  • How do I dispose of silicone rubber?
    Silicone rubber cured or un-cured is not considered as hazardous waste and therefore can be disposed of in accordance with the local regulations regarding waste disposal.
  • Is silicone toxic?
    Silicone is considered to be a very safe polymer with virtually no toxic effects in most environments. Also, as silicone is not considered as hazardous waste it can be disposed of in accordance with the local regulations regarding waste disposal.

Silicone Durability

  • What is the temperature range of silicone products?
    Broadly speaking, the service temperature range of silicone is within the region of -110C to +315C.
  • Is silicone volatile?
    Silicone is not normally considered as volatile. However, it can lose a fraction of its weight as the temperature rises.
  • Is silicone thermally conductive?
    By the addition of carefully selected chemicals, silicone can become a good conductor of heat.
  • Is silicone electrically insulating OR conductive?
    By the addition of carefully selected chemicals, silicone can become a good conductor of heat.
  • Is silicone rubber flame retardant?
    Silicone is not inherently flame retardant but can be modified to give good flame retardant properties. Indeed, because of its excellent biomedical properties, silicone is widely used in the fire protective clothing industry.
  • Is silicone suitable for underwater submersion?
    Parts made from silicone are not adversely affected by immersion in fresh, or seawater.
  • Can I paint on silicone?
    Products made silicone are very difficult to paint. Special surface treatments can help but in general silicones resist paint application.

Silicone Uses

  • Can silicone be used in clean room environments?
    Silicone is suitable for use in most clean room environments. The polymer itself does not support microbiological growth.
  • Is silicone safe for applications involving rapid decompression?
    Silicone is very permeable to most gases and as such would not be ideal for use in applications involving rapid decompression.
  • Can silicone be used for high traffic surfaces?
    Products made from silicone should not be used in high traffic applications because even the best high strength compounds have a relatively modest resistance to abrasion wear.
  • What environment is silicone rubber NOT suitable for?
    Conventional silicone rubber is not suitable in environments where it comes into contact with oils fuels and solvents. Fluorosilicone however, performs excellently under such conditions. Silicone rubbers in general also have poor resistance to steam and super heated water.
  • Is silicone rubber suitable for long- term medical implantation?
    Silicone rubber has been used for long-term medical implantation. An example is finger joints. The recent bad publicity about breast implants has meant that the major silicone manufacturers do not recommend their products be used for more than 28 days.
  • Why is silicone used in food applications?
    Silicone rubber is among a number of rubber types that can be used in contact with food. It has the advantage of being a low taint non-toxic material.
  • Is silicone safe for baby products?
    Specific grades of silicone rubber are used widely in the production of baby bottle teats due to their cleanliness aesthetic appearance and low extractable content.

Technical Questions

  • Why are some silicones specified as "addition cure"?
    Some silicones are described as addition cured because the cure mechanism is a catalyst reaction between the component ingredients within the compound. These components need to be added together for the compound to cure hence the term addition. Addition cure compounds can be supplied as one, two or three component systems.
  • How long does it take to cure silicone?
    The time taken to cure a silicone compound depends on a number of factors. These include temperature, section and cure mechanism. In practice a typical cure time for a compression moulded part is in the region of 5 minutes at 180C.
  • What is the difference between 'curing' and 'vulcanisation'?
    The terms curing and vulcanisation essentially describe the same thing - the transformation of the polymer into a cross-linked rubber.
  • Can I accelerate the cure time for my silicone compound?
    The cure time can be accelerated to a certain extent by a combination of the following - higher temperatures, mould design, processing method, and changing from a peroxide cured compound to a addition cured compound.
  • Does silicone release PCBs during curing?
    There is a possibility that certain compounds (usually those used for extrusion purposes) can evolve very low quantities of PCB''s. These are derived from the peroxide used to cross-link the silicone. It is therefore wise to ensure that adequate ventilation and extraction is provided in the areas where such compound is being processed.
  • Can I thicken a silicone?
    Silicone liquids can be thickened to a certain extent by the addition of silicas.
  • Can I thin a silicone?
    Silicone polymers can be dispersed in solvents to decrease their viscosity. ue to environmental and health and safety concerns however, this practice is seldom carried out today.
  • Can I 'bond' other substrates to silicone rubber?
    Silicone rubbers can be bonded to a range of substrates including common metals and plastics with the use of special primers and surface preparation techniques
  • Can you make silicone change colour with temperature?
    Silicone can be made to change colour with temperature by the addition of special thermachromic pigments.
  • What is the biggest silicone moulding that can be made?
    The maximum size of a silicone moulding is theoretically limited by the size and capacity of the processing and curing equipment.

Glossary

  • What does thermoset mean?
    Silicone rubber is a thermoset so once the material has cross-linked it cannot be practically de polymerised by heat as in the case of a thermoplastic.
  • What does RTV mean?
    Room Temperature Vulcanisation. RTV means that the silicone in question is capable of curing at room temperature. These materials tend to be supplied in a liquid or semi liquid form.
  • What does HTV mean?
    High Temperature Vulcanisation. HTV means that the silicone in question is cured with the application of heat. These materials tend to be supplied in a thick putty type form and thus are processed used moulds and extruders.