Silicone Rubber

Silicone, scientifically called polysiloxane, is one of the many rubbers used to make industrial components. It is a manmade elastomer that shares both plastic and rubber properties like flexibility and temperature resistance. It is offered in many forms like liquid, sheets, etc with a unique combination of chemical and mechanical properties. It is used in a range of applications from aerospace to electronics to demanding medical purposes. Silicone has a usual harness range of 50-90 Shore A and is suited well for temperatures between -80° F to 450° F.

Safety of Silicone Rubber

Since the approval by FDA in 1979 Silicone elastomer has been considered safe to be used in consumer cookware and medical equipment in the United States. It is also approved in Canada. Although, the EU has labelled some of the chemicals used in the production of silicone elastomers as a matter of concern and recent studies suggest that silicone products can drain away these chemicals under certain conditions.

Types of Silicone Elastomers

Silicone has a number of variants, each having different traits.

1. According to ASTM D1418 standard, the organic molecules in silicone rubber can be classified as:
   • Methyl Group– Also called as dimethyl silicone elastomer or just methyl silicone rubber. It’s also referred to as MQ. These are the principal silicone elastomers that were first developed.
   • Methyl and Phenyl Groups– Also known as methyl-phenyl silicone elastomer/rubber or phenyl silicone rubber. It is referred to as PMQ, and it has an excellent low-temperature performance
   • Methyl, Phenyl and Vinyl Groups– It’s also called as PVMQ and is recognized for its excellent low-temperature performance.
   • Methyl and Vinyl Groups– Also known as methyl vinyl silicone elastomer/rubber. It is also called VMQ. It features good compression traits. These are the foremost commonly used styles of silicone elastomer since the vinyl aids in vulcanization.
   • Fluoro, Vinyl and Methyl Groups– Also known as fluorinated rubber or fluorosilicone rubber. It is referred to as FVMQ, and they are highly chemically resistant to oil, fuel, and solvent.

 

2. Silicone Rubber can be classified into three types based on its viscosity and processing method:
   • Solid or High-Temperature Vulcanized (HTV) Silicone Rubber – This kind features long-chained polymers with a high molecular weight. As these generally comes in raw forms, these must be vulcanized as traditional rubbers prior to use.
   • Liquid Silicone Rubber (LSR) – This type has the shortest polymer chains with lower molecular weight. Extrusion machines can be used to extrude them. It is transparent in nature and offers good weathering resistance.
   • Room Temperature Vulcanized (RTV) – This type of silicone rubber is made by mixing one-part (RTV-1) or two-component (RTV-2) systems that harden at room temperature to very soft to medium hardness. Its uses include potting, encapsulations, sealants etc.

COR Manufacturing stock & sell high-quality Silicone Cord in Red and Translucent (clear) colour. Other colours are available only upon request. Durometers we carry include 30, 40, 50, 60, 65, and the standard on most parts we carry is 70D. Duro above 70 is available upon request.

70D Testing Specs (AMS 3304):

Original Physical Properties (ASTM D412 Die C tested at 20 inch/min crosshead speed)
	Test Sample	Requirements	Results
Durometer (Shore A)	68	70 ± 5	Pass
Specific Gravity	1.53	Report	Pass
Tensile Strength	1142.6	650 psi min	Pass
Elongation (%)	171.62	125% min	Pass
Heat-Aged Properties (ASTM D573, 70 hours @ 225 °C in a forced air oven)
Durometer Change (Shore A)	-3	±10 max	Pass
Tensile Change (%)	-22.1	-25% max	Pass
Elongation Change (%)	-24.8	-40% max	Pass
Tear Resistance (ASTM D624 Die B)
Tear Resistance, ppi	103	25 ppi	Pass
Compression Set (ASTM D395 Method B, 70 hours @ 150 °C, 25% deflection, 1/2 hour recovery)
Compression Set (%)	+40.4	25% max	Pass
Fluid Immersion (ASTM D471, 70 hours @ 150 °C in ASTM No. 1 oil)
Durometer Change (Shore A)	-14	-15 to +5	Pass
Tensile Change (%)	-14.6	-20% max	Pass
Elongation Change (%)	-16.4	-15% max	Pass
Volume Change (%)	6.01	+15% max	Pass
Low Temperature Resistant (ASTM D2137, 3 minutes @ -65 °C)²
	Non-brittle	Non-britle	Pass²

Please Note:

1. Testing not completed because limits are not specified within ASTM D2000-5
2. Lab testing completed at an outside lab because test cannot be performed in house.

 

Advantages of Silicone Elastomers

The advantages of Silicone Elastomer include:

• Excellent resistance to temperature
• Excellent dry heat resistance
• Good resistance to sunlight, ozone, weathering
• Moderate oil resistance
• Low compression set
• Highly physiological inert

Disadvantages of Silicone Elastomers

The disadvantages of Silicone elastomer include:

• Poor abrasion resistance or physical strength
• Poor resistance to petroleum fluids and ketones

Customization

COR can supply custom Silicone extrusion profiles in many sizes and shapes. Send us your requirements in a dwg., pdf or even on a napkin, with dimensions and we can try and quote according to your request. 

Applications of Silicone Elastomers

Silicone elastomers are used in a wide range of industries due to their unique properties:

• Medical: Silicone rubber, due to its unique biocompatibility and physical durability, is used in a countless number of healthcare applications like feeding pumps, diagnostic equipment, etc.
• Automotive: Due to silicone rubber’s resistance to sunlight, ozone, weathering, it is highly utilized in automotive parts.
• Construction: Silicone elastomers are used as adhesives, sealants, and coatings, because of their ability to bond with metals and their resistance to weathering.
• Electronics: Highly purified Silicone is used a lot in manufacturing electronic chips used in motherboards. It is also for insulation and other purposes in various electronic components.
• Consumer products: A lot of cookware these days is manufactured using silicone rubber due to its dry heat resistance. It is also used in toys, jewellery, shampoos, and deodorants, among other products.
• Aerospace: Silicone elastomer is used in manufacturing space capsules, aircraft, etc. Its unique properties offer support to engines that undergo high temperatures during liftoff and provides shelter to the exteriors against low temperatures and shock absorption within the atmosphere.

Check out other materials we offer. For any questions or more information, contact COR Manufacturing.