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ELASTOMERS
An elastomer, more commonly referred to as rubber, is a polymer that has been modified to create cross-linking between polymer chains. This cross-linking changes the polymer from a plastic-like material to an elastic material.
An elastomer usually exhibits the following behavior at room temperature:
- It does not break when stretched approximately 100%.
- After being held for five minutes at 100% stretch, it returns to within 10% of its original length within five minutes of release
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What is an elastomer? |
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Types of Rubber Materials
Solids
Solid Structure - Hardness - Compression Set
Sponges & Foams
Cellular Structures - Density - Compression Load Deflection - Compression Set - Compression Load Retention - Flammability to UL 94
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SOLIDS
- Solid rubber is manufactured in molded sheet or calendared rolls.
- Solids are commonly used for liquid and gas seals due to their non-cellular structure.
- Solids are the preferred material when dealing with high compressive forces and vibration isolation.
- Solids may be reinforced with material such as nylon (i.e. ASMS 3235) for dimensional integrity.
HARDNESS
- A solid’s resistance to indentation is measured in durometer.
- Thermoset materials (rubber) are measured on a Shore “A” scale, using a Shore durometer gauge.
- Thermoplastic materials are measured on a Shore “A” or Shore “D” scale.
- Durometer is measured in increments of five or ten (i.e. 30, 40, 60, 70, 80, 90) with a tolerance of +/- 5.
DUROMETER IN APPLICATION
- Softer materials often work better as low pressure seals on irregular sealing surfaces. (Increasing material thickness may also work).
- Harder materials usually have a higher modulus, thus harder materials tend not to extrude under high pressure.
- Compounds can be formulated to enhance certain physical properties including extrusion resistance.
SPONGES & FOAMS
SPONGES
- Open & closed cell structures
- Generally, sponges are tougher than foams.
- Closed cell sponges can be used as liquid, gas and vacuum seals.
- Open & closed cell sponges can be used for thermal insulation, noise and vibration damping, and cushioning.
FOAMS
- Open cell structure
- Foams should not be used as water or vacuum seals.
- Foams can be used for light duty sealing applications such as light and dust seals, cushioning, sound and vibration dampening and thermal insulation.
DENSITY
- The weight of material per unit volume, usually expressed in pounds per cubic foot.
COMPRESSION LOAD DEFLECTION
Compression Deflection is the amount of force required, usually measured in lbs/in²
(PSI), to compress a material a specific percentage of its’ original thickness.
COMPRESSION LOAD RETENTION
- Compression load retention indicates a material’s ability to exert a countervailing force against compressive stresses without relaxing.
- This information is not readily available in manufacturers’ literature.
COMPRESSION SET
- Compression Set is the percent of original thickness that an elastomer fails to recover after being compressed for a fixed time period under specified pressure and temperature.
- The Compression Set indicates the ability of a material to retain its’ elastic properties after prolonged compressive stresses.
TEMPERATURE RANGE (see Temperature Chart)
- Continuous temperature range indicates the maximum and minimum continuous long-term operating limits of a material.
- Intermittent temperature range indicates the short-term operating limits of a material.
- Operating temperatures outside the recommended ranges may affect the material’s physical properties.
HOW TO SELECT AN ELASTOMER
Six Environmental Questions
1) What is the temperature range that this gasket will be subjected to?
2) Are these temperatures constant or intermittent?
3) Is this an environmental seal?
4) Is this a gas or liquid seal?
5) What types of chemicals, gases, oils or fuels will this gasket come in contact with, and what are their concentrations?
6) Does the material require UL approval?
Six Physical Questions
1) Will this gasket be subjected to cycles of compression, i.e., door gasket?
2) How much compression force will this gasket receive?
3) Will this material need flexing, tear strength or abrasion resistance?
5) Does this material need to meet any agency criteria such as: ASTM, Mil-spec, FDA, NSF, UL or N.A.S.A.?
6) Does adhesive have a temperature range?
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Durometer Scale |
 10 Shore "A"
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40 Shore "A" |
60 Shore "A" |
75 Shore "A" |
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TYPES OF ELASTOMERS
Neoprene (Chloroprene, Polychloroprene)
- Temperature Range : -40 ° F to +240 ° F
- Good ozone and weather resistance
- Good resistance to oil and petroleum based solvents
- Not recommended for degreaser solvents.
Nitrile (NBR, Butadiene-acrylo-nitrile)
- Temperature Range : -60 ° F to +300 ° F
- Excellent resistance to fuels and petroleum oils
- Good resistance to aliphatic hydrocarbons, vegetable, mineral and animal oils
- Not recommended for ozone, aromatic solvents and ketones
- Meets ASTM-D-2000
- SAE Specifications
Ethylene Propylene (EPR, EPM, EPDM)
- Temperature Range : -40 ° F to +250 ° F
- Excellent resistance to hot water and steam, weak acids, alkalis, silicone oil and grease, brake fluids, hydrogen-sulfide, alcohols, ketones and esters
- Resistant to ozone, aging and weather
- Not recommended for mineral oil products, oils, greases and fuels
- Meets ASTM-D-2000
Natural Rubber (Gum, Natural Polyisoprene)
- Temperature Range –60 ° F to +180 ° F
- Good tensile strength, tear resistance, low compression set
- Excellent resilience
- Not recommended for ozone, acids, fats, oils, grease, most hydrocarbons
Urethane (Polyurethane Diisocyanate)
- Temperature Range -65 ° F to + 240 ° F
- Excellent resistance to abrasion
- Greatest tensile strength
- Good resistance to oils, fats, ozone and gasoline
- Not recommended for heat, acids and alkalies
Contact us for other elastomers available. |
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