rubber types - materials

Rubber is understood to be elastic polymeric materials that are processed by vulcanization.

We prefer to use standard qualities for our products. Depending on the requirements of our customers, special materials are also used for individual items.

NR

natural rubber

advantages

  • high static and dynamic strength
  • very low attenuation
  • very good setting behavior
  • very good low temperature behavior

disadvantage

  • low resistance to aging
  • low ozone resistance
  • no oil resistance

SBR
Styrene-butadiene rubber
Buna

advantages

  • better heat resistance than NR
  • moderate aging resistance
  • medium elasticity
  • good abrasion and wear properties

disadvantage

  • no ozone resistance
  • low oil resistance

NBR
Nitril-butadiene-rubber
Perbunan

advantages

  • resistant to petrol and oil
  • good setting behavior
  • good damping (increasing with nitrile content)
  • good drive and wear properties

disadvantage

  • moderate aging resistance
  • poor ozone resistance
  • bad cold properties

EPDM

advantages

  • very good heat and weather behavior
  • high resistance to ozone
  • very good cold behavior
  • resistant to aqueous chemicals

disadvantage

  • no oil resistance

CR
Chloropren-rubber
Neoprene

advantages

  • Heat, weather and ozone resistance better than NR or SBR
  • medium oil resistance

disadvantage

  • problematic processability
  • strong hardening at temperatures below 0 °C

FPM
Fluor-rubber
Viton

advantages

  • extremely good resistance to
  • Heat, chemicals, solvents, oil, gasoline, weather

disadvantage

  • elaborate processing
  • bad cold properties
  • price

VMQ

silicone

advantages

  • extreme heat resistance
  • excellent low temperature behavior

disadvantage

  • complex processing
  • low strength

Typical material properties of rubber

The hardness of rubber is usually measured in “Shore” according to DIN 53505.

A rounded needle is pressed into the test piece against a spring force. The resistance to this penetration (in percent) is the measure of the Shore hardness. (Therefore the Shore hardness can only assume values ​​between 0 and 100.)

An extremely soft material (with the theoretical hardness of 0 Shore) does not offer any resistance to the spring. At 100 Shore the needle cannot penetrate the material, the spring is compressed to the maximum.

A distinction is made depending on the needle shape

  • Shore A    Needle with a blunt end    soft materials (rubber)
  • Shore D    Sharp ended needle   hard materials (plastic)

We mainly process materials between 35 and 90 Shore A.

Abrasion resistance

The abrasion resistance of rubber can be measured according to DIN 53516. In this experimental setup, a piece of rubber is pressed against a rotating roller which is covered with smear paper. The amount of material that has been removed after a specified time is used as a measure of the abrasion resistance.

The value is therefore given as follows: Abrasion resistance according to DIN 53516: ### mm³

The usual values ​​are between 70 mm³ (very good) and 600 mm³ (unsatisfactory).

The value of the abrasion resistance decreases with increasing hardness; softer types of rubber have poorer abrasion resistance than harder types.
For statements about the service life of a component, however, this value for abrasion resistance cannot be considered alone. Especially with freely rotating rollers, other properties of the rubber (surface aging, elasticity, …) have a significantly greater influence on the service life that can actually be achieved.

Coefficient of friction µ0 (Coefficient of friction)

The classic laws of solid-state friction do not apply to elastomers, or only with severe restrictions. The reason for this is that elastomers do not have a rigid surface, but adapt to the opposing surface depending on their hardness and creep behavior.

It is therefore not possible to specify a specific coefficient of friction (e.g. for rubber / steel), but this must always be determined in tests, adapted to the practical case. With favorable material pairings, values ​​of more than 1.5 can be achieved.

In general, the following applies: the higher the Shore hardness and the better the abrasion value, the lower the coefficient of friction.

Tensile strength, elongation at break, modulus of elasticity

Tensile strength and elongation at break can be determined by means of a tensile test according to DIN 53504.

The tensile strength of elastomers is much lower than that of solid materials. It is approx. 5 – 20 N / mm²

The elongation at break is strongly dependent on the hardness of the material and is approx. 100% – 800%.

The modulus of elasticity E is the ratio of stress σ to elongation ε and is determined by evaluating the tensile test. The modulus of elasticity can be read in the stress-strain diagram as a rise in the diagram line.

For metals, the modulus of elasticity (for smaller deformations) is a constant value. Hook’s law applies: σ = E × ε

For rubber, however, the stress-strain diagram is a curved line. It is therefore not possible to give a general value for the modulus of elasticity.

The tension value at 300% elongation (100% for hard materials) is therefore often used as a measure of elasticity: Tension value 300% σ300