This can be sub-divided into two distinct categories:

  • Testing of unvulcanized compound.
  • Testing of vulcanized compound.

Testing of Unvulcanized Compound

Testing of Unvulcanized Compound

Test Measuring Instrument Significance
Viscosity Moony viscometer It gives idea about processing performance of the rubber compound in moulding.
Scorch time Moony viscometer Optimum cure time can be obtained.

Testing of Vulcanized Rubber Compound

No tests should be performed until at least 16 hours after vulcanizing as significant post vulcanization changes in structure of the material may occur during this period.

Tensile Test – These tests are most widely used test in the rubber industry. They are used to determine rate of cure and optimum cure, quality check on the compound, effect of immersion in liquids etc.

Hardness – Hardness, as applied to rubber, may be defined as the resistance to indentation under conditions that the rubber is not punctured. Hardness is one of the most useful and often quoted properties of rubber. However the values mentioned can be misleading due to mechanical limitations of the instruments and personal error.

Rebound Tests – Resilience is the ability of a rubber vulcanizate to return the energy used to deform it during its recovery from deformation. It is expressed in percentage. The simplest test for resilience is the falling ball rebound. If the drop height of the steel ball is divided into 100 equal parts, the rebound height is equal to resilience.

Abrasion Tests – Abrasion is the progressive wearing away of a rubber article in service. In many applications, resistance to wear is one of the most important properties of a rubber article, although, it is one of the most difficult property to measure. The type of wear undergone by an automobile tyre on a road is very different from the wear on a hose used for sand blasting. Laboratory tests consist of rubbing the test piece against abrasive surface. These conditions are difficult to correlate with actual service conditions.

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Ageing Test – Tests for heat ageing are carried out for two purposes. Firstly to establish changes in physical properties at elevated service temperatures. Secondly they serve as accelerated ageing tests at high temperatures which try to predict the long term life at low temperature. The test consists of ageing tests pieces for a given period at a specified temperature and then measuring the physical properties such as tensile strength, moulds, elongation at break and hardness. Comparison is thereafter made with non- aged test pieces.

Resistance to Liquids – Elastomers when in contact with a liquid may absorb the liquid or the liquid may extract some soluble constituent from the elastomers or there may be chemical reaction between the two. Absorption is normally greater than extraction resulting in increase in volume which is called swelling.

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