Silicone

tappiIn comparison with other elastomers, Silicone-based rubber types are different because they are not purely organic compounds. They also have a polymer chain which includes silica and oxygen atoms.

Silicone rubber mixtures are quite simple in their composition: apart from rubber, they contain inorganic extenders, often pigments and a curing agent, mostly a peroxide or a catalyzing agent. Silicone-based oils characterized by a heavy molecular weight can be used as plasticizers to obtain very soft rubber types.
The kind of silicone rubber you should choose depens on the features required of the cured rubber product, since there are countless different silicone rubber mixes.
Indeed, the different properties of these compositions make them suitable for quite different applications – and explain their different prices.
ALL silicone parts made by STAMPAGGIO GOMMA SNC are made using high-quality PURE SILICONE; for some special compositions developed for the WINE-MAKING and MEDICAL industry we we have been granted a “food-grade certificate” from a well-known research and analysis laboratory.

Warm curing is achieved heating the material together with organic peroxydes. As in the case of FPM fluorinated rubber (Viton®, Fluorel®, Tecnoflon®), cross-linking is a two-stage process:

1. Pre-vulcanization until dimensional stability is attained, either under pressure (in a press, a boiler, a steam tunnel) or not (hot air)
2. Post-vulcanization to malleableize rubber and achieve optimal properties, carried out in non-pressurized containers through the circulation of hot air and the introduction of cool air.
Post-vulcanization also has two effects:
* Removing volatile substances created when peroxydes were being split off during the pre-vulcanization stage;
* Achieving optimum technological properties.
Vulcanized silicone rubber only becomes odorless after all byproducts have been eliminated; the lack of odor is however an “INDISPENSABLE” property for pharmaceutical items and staple commodities.

Properties

  • Hardness: Shore rating: 30 to 80
  • Impact strength: 40 to 60% (only marginally related to temperature changes)
  • Extensibility: 100 to 400%
  • Heat resistance: up to 200°C; temperatures in excess of 230° can be acceptable for a short time only. We also offer silicone rubber for special applications that can withstand 300 to 350° quite well.
  • Resistance to irradiation: usually lower than that of other elastomers like NR, SBR and NBR.
  • Resistance to bacteria and fungi: decidedly higher than that of other elastomers.
  • The surface of objects made of silicone-based rubber does not cling to the sticky surfaces of other materials it may come into contact with; it is also water-repellent, so that water drops cannot spread on it.
  • Vulcanized silicone products are flavorless and odorless because they do not contain any extractable ingredients such as plasticizers or antiaging extenders.
  • Resistence to chemicals:
    • Good resistance to:
      Aliphatic lubricating and fuel oil
      Animal and vegetable oils and fats
      Glycol-based brake fluidsand hydraulic fluids not likely to catch fire belonging to the HFD-R and HFD-S group
      Chlorinated aromatic hydrocarbons with heavy molecular weight (such as Clophen) Water, up to 100°C.
      Diluted saline solutions
    • Does not withstand:
      Aromatic mineral oil (except for some peculiar silicone rubber types)
      Fuels (except for some peculiar silicone rubber types)
      Superheated steam exceeding 120°C.
      Acids and alkalis, that can destroy this kind of rubber.
      Silicone-based oils nand fats (they cause substantial swelling because silicone oils and silicone rubber have a similar chemical structure).
  • Resistance to water and steam
    As a rule, silicone elastomers show good resistance to water up to 100°C. However, this depends upon the kind of extender. High-value extenders that contain no electrolytes provde the best resistance to water and steam.
    Special compositions can be used to make rubber types that do not swell more than 1% even after several weeks in boiling water. In superheated steam, silicone elastomers are destroyed above 120°C after a long time. For short-term heating (e.g. sterilization or autoclaving) no damage occurs.


Applications

Silicone-based elastomers are used whenever great heat resistance must be combined with excellent elastic properties at low temperatures.

  • Ideal for all sorts of gaskets, e.g. for cockpit canopies, aircraft doors and windows, freezers, airtight containers, shaft gaskets, O-rings, etc.
  • Molded or drawn technical parts such as ingition system hoods, warm air or oxygen ducts, section bars for hot air furnaces.
  • Electrical insulation for ships, planes, containers likely to be heated.
  • Coating layers for belt conveyors to be used with warm and sticky materials or food.
  • Medical and pharmaceutical articles, wine gaskets for the wine-making industry, silicone plugs for casks and barrels, gaskets for glass cask-fillers of small, medium and large size.
  • Syringe caps, blood transfusion tubes, silicone hose for food processing machinery, artificial heart valves, oxygen masks, underwater masks and mouthpieces.
  • Cylinder lining, e.g. for glue-like materials.
  • Lighting fixture and general plant engineeering gaskets, etc.



   

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