Hardness is a very important physical property parameter for TPEs and TPRs. Different test methods and conditions may lead to certain deviations in test results! In this article, Shibu analyzes some of the causes of TPE/TPR hardness deviation.

　　1. The influence of specimen thickness

　　Shore A hardness value is determined by the depth of the pressure needle pressed into the specimen, so the thickness of the specimen directly affects the test results. The specimen is deformed by the pressure thickness, the part under pressure becomes thinner and the hardness value increases. Therefore, the specimen thickness is small hardness value is large, the specimen thickness is large hardness value is small.

　　2. The impact of the pressure needle length on the test results

　　The standard Shore A hardness tester pressure needle exposed to pressure surface height of 2.5mm, in the free state when the pointer should point to zero. When the pressure needle in a smooth metal plate or glass, the instrument pointer should point to 100 degrees, if the indication is greater than or less than 100 degrees, the pressure needle exposed to a height greater than

　　or less than 2.5 mm or less than 2.5 mm, in this case should stop using, for correction. When the pressure needle exposed height is greater than 2.5mm, the measured hardness value is high.

　　3. The influence of the shape of the end of the pressure needle on the test results

　　Shore A type hardness tester pressure needle end in the long-term role, resulting in wear, so that its geometric size changes, affecting the test results, the diameter of the worn end becomes larger measured results are also large, which is due to its unit area of the pressure is different. The diameter is large, the pressure is small measured hardness value is large, and vice versa is small.

　　4. Influence of temperature on test results

　　Rubber is a polymer material, its hardness value changes with the environment, and high temperature reduces the hardness value. The degree of influence is different for different rubber materials, such as natural rubber with slow crystallization speed, where temperature has less influence, while neoprene and styrene-butadiene rubber have significant influence. For thermoplastic elastomers, the effect of temperature is also more significant. Usually in the summer, the same model of TPE, TPR material, than in the winter to soft 5 degrees (A) or so!

　　5. Influence of reading time

　　Shore A hardness tester in the measurement of the reading time on the test results have a great impact. The pressure needle and the specimen under pressure immediately after reading and pointer stability and then read, the results obtained from a big difference, the former high, the latter low, the difference between the two up to about 5 to 7 degrees, especially in the synthetic rubber test is more significant, which is mainly due to creep in the rubber under pressure. So when the specimen should be read immediately after the pressure data.