Types of Silicone Rubber

There are many basic differences between liquid silicone rubber, room temperature vulcanizing silicone and the high temperature vulcanizing variant which influences their potential use.

Silicone rubber is a man-made elastomer that is composed of silicone with carbon, hydrogen and oxygen. This inorganic rubber-like material is used extensively across various industries - rail, aerospace, automotive, food/beverage and artworks to name a few. The superior benefits of resistance to high temperatures, weather and abrasion coupled with chemical stability and electrical insulation make it a popular and commonly-used rubber for varied applications.

It is manufactured in three different forms with varying viscosity and curing temperatures:

  • Liquid Silicone Rubber (LSR) – As the name goes, this is in liquid form with good viscosity and flows well. It is a two-part silicone and the curing occurs only when the base material comes in contact with the catalyst. This is a thermosetting material and cannot be restored to its original form after curing. The range of hardness is wide, from 5 to 90 Shore A. The excellent liquidity ensures that the rubber can easily fill the most complex parts of the mold, making it perfect for automated injection molding, compression molding, transfer molding and other molds that have complicated designs or demand tolerance.
  • Room Temperature Vulcanizing Silicone Rubber (RTV) – This rubber is also in liquid state, but comes in both one-part and two-part formulations. The two-part variant is again of two types - condensation cure and addition cure. The former uses tin salts as a catalyst while the latter relies on a platinum-based catalyst to turn the liquid silicone into a solid form. It should be noted that these types of RTV silicone rubbers are not only quite different from each other, but also not even compatible with each other. However, all RTVs will cure at room temperature when they come into contact with air.

In general, RTVs cure to a soft or medium hard finish ranging from 15 to 40 Shore A. They have low shrinkage and can capture details well, making them suitable for injection molding, gravity casting and vacuum casting. They enjoy varied applications including mold making, casting, prototype-making, prosthetics and encapsulation. The tin-cured silicones have food safe, skin safe and transparent versions too.

High-Temperature Vulcanizing Silicone Rubber (HTV) –
This is also known as Solid, Milliable or High Consistency Silicone Rubber. It is usually in the form of solid, gummy rubber blocks which are partly vulcanized, though liquid forms are also formulated. It goes without saying that the rubber has to be heat-cured at high temperatures to get the finished product. It is used for compression and resin-transfer. Silicone tubing and other shapes are often extruded from HTV silicone rubber.

EnvironMolds offers a great selection of high quality RTV silicone mold rubbers that can be used to make a silicone mold or cast. This popular art supplier also provides skin-safe, food-safe and translucent silicone rubber formulations. Apart from this, other related materials, supplies, tools and equipment are also available.

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