Abrasion Resistance
Abrasion properties of rubber are difficult to define. Many different abrasion machines have been designed but they do not always give similar results. The most common abraders are AKRON, Dunlop and DuPont. Results are recorded as volume loss per standard test piece, or as the difference in volume loss when compared with a standard material of known abrasion value. Indices of relative abrasion are also used.

ASTM REFERENCE: D394

BS REFERENCE: BS 903 Part A9

ISO REFERENCE: -

Accelerated Ageing
Heat ageing is widely used as a method of evaluating long term ageing properties. Hardness and dumbbell type tensile test pieces are placed in an air circulating oven for a specific period of time at a given temperature (e.g. 7 days at 70°C 0). The properties of the rubber are then tested and compared with the properties before ageing. The percentage retained for each property is recorded (change in hardness is recorded in degrees).

ASTM REFERENCE: D573

BS REFERENCE: BS 903 Part A19

ISO REFERENCE: /// ISO 188

Chemical Resistance
This is usually expressed as the change in properties (such as hardness, strength and elongation at break) caused by the presence of chemicals under defined conditions (including concentration, time and temperature).

Coefficient of Friction
Ratio of the force needed to move an elastomer over a given surface to the total forces pressing on the elastomer and surface.

Compression Set
A cylindrical button of rubber of known thickness is compressed to a fixed height (typically 70% or 75% of its original height) at a defined temperature for a specific period of time. The button is then released, allowed to recover (typically for 30 mins) and the thickness is measured. Compression Set is the height that is not recovered expressed as a percentage of the amount by which it was compressed.

ASTM REFERENCE: D395

BS REFERENCE: BS 903 Part A6

ISO REFERENCE: /// ISO 815

Dielectric Strength / Electrical Properties
The resistance of an elastomer to the conducting of an electrical current. Anti-static and conductive properties of rubbers are defined by measuring their electrical resistance. Typical measurements are obtained through the thickness of a sample by using 25mm sq. electrodes under a pressure of 45N and applying a voltage of 500V DC @ approx. 6mA. (Energy dissipated into the test piece is limited to 3W max.) The surfaces should be cleaned before measuring. Patterned surfaces should be wetted with a conductive solution or paint. Results should be recorded in ?, defining the conditions of testing.

ASTM REFERENCE: D991 & D257

BS REFERENCE: BS 2050

ISO REFERENCE: -

Elongation at Break
Elongation is defined as the length at breaking point expressed as a percentage of its original length (i.e. length at rest) e.g. if a rubber reaches twice its length before breaking its elongation is 100%.

ASTM REFERENCE: D412

BS REFERENCE: BS 903 Part A2

ISO REFERENCE: /// ISO 37

Flame Resistance
Flame resistance testing requires a standard burner and fuel which gives a flame of known characteristics. Rubber samples are then placed at a certain position in the flame and removed after an ignition period. The time taken for the rubber to self-extinguish is recorded with notes regarding afterflow and any hot particles emitted by the sample at any stage

ASTM REFERENCE: -

BS REFERENCE: BS 2011

ISO REFERENCE: -

Fluid Resistance / Volume Swell
Fluid resistance is commonly measured by the effect of the fluid on the volume of the rubber exposed as a volume change (e.g. +100% indicates that the volume of the rubber has doubled as a result of exposure to the fluid, -10% indicates that the volume of rubber has decreased as a result of exposure to the fluid). Volume change is measured by determining the weight of a sample in air and water before and after exposure to the fluid under defined conditions. The sample is normally totally immersed in the fluid.

Fluid resistance may also be defined in the same way as chemical resistance (above) i.e. by change in properties of the rubber. W1 Wt in air (initial) W2 Wt in water (initial) W3 Wt in air (swollen) W4 Wt in water (swollen)

ASTM REFERENCE: D471

BS REFERENCE: BS 903 Part A16

ISO REFERENCE: /// ISO 1817

Hardness
Measured in degrees and based on the penetration into the rubber of a defined indentor under a set load. Three scales are commonly used: IRHD (International Rubber Hardness Degrees), Shore A and Shore D for hard materials over 90° Shore A. IRHD is preferred for most specifications but Shore A is also in widespread use.

ASTM REFERENCE: D2240 & D1415

BS REFERENCE: BS 903 Part A26

ISO REFERENCE: // ISO 48 & // ISO 1400 & // ISO 1818

Hysteresis
The build up of heat in an elastomer sample caused by rapid deformation

Modulus
Modulus is measured as the force per unit area required to extend a rubber to a stated percentage of its original length e.g. to 100%, 200% or 300%. It is often written as M100 = 3.0 MPa (i.e. modulus at 100% = 3.0 Mpa).

ASTM REFERENCE: D412

BS REFERENCE: BS 903 Part A2

ISO REFERENCE: /// ISO 37

Ozone Resistance
Ozone causes cracking in rubber. Test pieces are usually placed under a small degree of tension e.g. by bending round a mandrel or stretching by 5%. The sample is exposed under static conditions to a controlled atmosphere containing ozone (typically 50 pphm). The cracks are graded by standard photographs, by measurement or by description, e.g. 'visible under 10 x magnification' 'visible to the unaided eye' etc. Results may be recorded as the time taken to reach a particular grade of cracking, or by the grade of cracking apparent after a fixed period of time.

ASTM REFERENCE: D1149

BS REFERENCE: BS 903 Part A43

ISO REFERENCE: /// ISO 1431/1

Rebound Resiliance
The measure of the rebound (bounce) of a metal ball dropped at a given height onto an elastomer sample. Resilience is measured on standard test equipment ( of which there are several types - e.g. Dunlop, Tripsometer, Lupke, Rebound). Standard test pieces are struck by the 'hammer' and the 'bounce back' of the hammer measured. This is expressed as a percentage of the flight path of the hammer.

ASTM REFERENCE: D1054 & D2632

BS REFERENCE: BS 903 Part A8

ISO REFERENCE: /// ISO/R 1767

Specific Gravity / Density
Density is defined as the mass per unit volume and is measured by weighing the rubber sample in air and water.

ASTM REFERENCE: -

BS REFERENCE: BS 903 Part A1

ISO REFERENCE: /// ISO 2781

Tear Strength
Tear Strength is measured as the force required to tear a standard piece. The standard test pieces are designed to produce weak points where a tear is initiated.

ASTM REFERENCE: D624

BS REFERENCE: BS 903 Part A3

ISO REFERENCE: /// ISO 34

Tensile Strength
This is measured in various units and is expressed as a force per unit area. A standard dumbbell type test piece of known cross sectional area is used which is stretched until it breaks. The force required to do so is then recorded and expressed as force per unit area.

ASTM REFERENCE: D412

BS REFERENCE: BS 903 Part A2

ISO REFERENCE: /// ISO 37

Thermal Conductivity
The ability of an elastomer to conduct heat.

Weather Resistance
Weather resistance is a fairly subjective test and it is necessary to state clearly the conditions under which the exposure took place i.e. dates, geographic location, angle and direction of exposure relative to the sun etc.

The properties of test pieces are measured before and after exposure and expressed as percentage changes (with exception of hardness changes which are usually recorded in degrees). The change in any property may be measured but the most common are hardness, tensile strength, elongation at break and modulus at 100% and 300%.

ASTM REFERENCE: D1171

BS REFERENCE: BS 903 Part A53 & BS 903 Part A54 & BS 903 Part A55

ISO REFERENCE: -