Hardness of rubber depends on the static load applied. There are number of methods to measure the toughness of rubber rollers. The two prominent methods are Durometer, it is an international standard for measuring the hardness of rubber in industries like printing, coating, laminating, etc. In today’s modern world there are number of instruments used to measure the hardness and these are based on Shore scale durometers found in the year 1920s. Shore scale instruments are available in 12 different types ranging from very soft to very hard. The range is between 0-100 and the higher the measurement the harder the rubber.
Another method used to measure the hardness of rubber include Pusey & Jones Plastometer instrument. The method is prominently used in paper industry. The range is 0-300 and the lower the measurement, the harder the material.
Factors attributing to the roller hardness
- The specimen should be tested in room temperature, as rubber is sustainable to temperature change. It softens when heated and hardens when cooled.
- While testing the base of the durometer should be parallel to the roller journal. The operator must apply uniform force in a manner the base touches the surface of the roller paralleled as the indenter advances into the material.
- In the case of P&J Plastometer, there is a spirit leveled bubble placed on the mounting frame to ensure the indenter contacts the roller perpendicularly. At this point the load is applied without shocking the instrument.
- Using different instruments and operators will result in different outcomes. Therefore it is important to standardize the procedures based on the instruments and operators
- If the material thickness is less than 0.250”, it will result in higher durometer reading.
Remember that durometer is dimensionless and has no relationship with the material’s durometer for one scale to another to test the hardness.