Tests There are four tests specified for measuring the quality of the carbon black master batch produced by the supplier. 1.Durometer. The durometer test is used to measure the hardness of the rubber. A sample is placed against an indentor point, which pushes back into the casing against a spring. The harder the sample, the farther the indentor point will push back against the spring and the greater the reading on the dial. 2.Tensile strength. Tensile strength measures the maximum tensile stress reached in stretching a sample to its breaking point. The strength is written as the force per unit of the original cross section of the sample length 3. Elongation. Elongation measures the expansion created by a tensile force. The measurement criterion is the percentage of the original cross section of the sample length. Ultimate elongation is the elongation at the point of breaking. 4.Tensile modulus. Tensile modulus is a combination of tensile strength (stress) and elongation. It measures the stress required to achieve a certain elongation. Tensile tests are used to indicate the effect of various compounding materials The tests are sensitive to shifts in manufacturing conditions. They can be used to identify Under- or overvulcanization. Poor blending. The presence of foreign materials. An example of a testing machine for tensile stress-strain can be seen in Figure C22.4