Preparation of test pieces

The testing of rubber is either starting from uncured rubber or from cured rubber products. Testing can also apply to the uncured or cured state. The preparation of the test pieces is an extremely important part of the testing itself and it must not be the case that the test results reflect the effects of the preparation rather than the properties of the materials being tested.

Temperature conditioning of the test material is also an important part of the preparation.

Testing cured properties ISO 4661

In order to test cured properties, specimen test sheet and other test pieces need to be produced. Nearly all rubber testing is carried out on 2 mm ± 0,2 mm thick test sheets, which are vulcanised in a mould, often with four cavities, each 150 x 150 mm.

Cylindrical test pieces are used for compression set, relaxation, abrasion and compression testing and are also produced in a mould. There are two common sizes, the so called small test piece with a diameter of 13 mm and a height of 6,3 mm, and a large test piece 29 mm in diameter and 12,5 mm high.

Test pieces are punched out of the test sheets in order to perform tests for tensile strength, tear strength and tension set etc. It is important that sharp punching cutters or dies are used against a soft surface when punching out the test specimens. Punching cutters with poor cutting edges or nicks may cause rupture notches in the test piece and thus produce incorrect results.

Testing uncured properties

When testing uncured rubber, it is often sufficient to cut off a piece of rubber of the appropriate size using a pair of scissors. In certain tests, as for example, the determination of cure curves, the test must have a specific volume in order to be able to provide reproducible test results. In these cases, a volume press is used to provide test pieces with a constant volume.