Durometer is the hardness of a material. In our manufacturing process we use Shore A, Shore D and Shore 00 to gauge the different rubber polymers that we extrude by using a durometer gauge. Hardness may be defined as a material’s resistance to permanent indentation. Durometer gauges are also referred to as shore hardness testers, hardness testers, or durometer gauges. Durometer is an important property in how the material will react in the intended environment and application. Its measurement is a unique and valuable gauge to measure for consistency and quality control.
The final value of the hardness depends on the depth of the indenter after it has been applied for 15 seconds on the rubber material. If the indenter penetrates 0.100 inch or more into the material, the durometer is 0 for that scale. If it does not penetrate at all, then the durometer is 100 for that scale. It is for this reason that multiple scales exist. Durometer is a dimensionless quantity, and there is no simple relationship between a material’s durometer in one scale, and its durometer in any other scale, or by any other hardness test.
ASTM D2240 durometers allows for a measurement of the initial hardness, or the indentation hardness after a given period of time. The basic test requires applying the force in a consistent manner, without shock, and measuring the hardness (depth of the indentation). If a timed hardness is desired, force is applied for the required time and then read. The material under test should be a minimum of 0.25 inches thick. This gives you a nice solid piece of rubber to test the durometer of that rubber polymer against. Sometimes it is difficult to gauge the durometer of a profile depending on the shape of the profile.
There are several scales of durometer, used for materials with different properties. The two most common scales, using slightly different measurement systems, are the ASTM D2240 type A and type D scales. The A scale is for softer rubber and plastic, while the D scale is for harder ones. However, the ASTM D2240-00 testing standard calls for a total of 12 scales, depending on the intended use; types A, B, C, D, DO, E, M, O, OO, OOO, OOO-S, and R. Each scale results in a value between 0 and 100, with higher values indicating a harder material.
As part of our Quality Control process at Central Rubber Extrusions, the durometer is gauged for all production runs and this is monitored for consistency on the products that we ship.