Understanding Shore Hardness

March 7, 2014
Understanding Shore Hardness

The solidity and toughness of plastics is usually measured using the Rockwell hardness test or Durometer test. Both these methods can accurately quantify how well a plastic item can resist indentation and provide a practical hardness value. This value does not automatically correlate with basic characteristics of the plastic. Shore Hardness is generally applied to softer types of plastics such as elastomers and rubbers. With these plastic types, the appropriate shore hardness scale would be shore A. Other kinds of softer plastics where shore A can be applied include vinyls, polyolefins, and fluoropolymers. The Shore D scale is used for harder ones. Other Shore hardness scales are Shore O and Shore H but they are rarely used within the plastic industry.

When measuring the hardness value of certain plastics, the Durometer indenter foot is inserted into the plastic sample. A needle is placed against the plastic and pressure is applied. If the gauge has been pressed on the material and the needle has entered into the plastic as far as it can go, the hardness gauge measurement needle will show the matching hardness measurement. Depending on the flexibility of plastics and rubber, the indentation reading on the Durometer may change in time. That is the reason why the time the measurement was taken is usually written down together with the hardness number. As was already discussed, there are various shore hardness scales used in gauging the hardness of different materials. These scales were designed to create a common point of reference for people dealing with plastics.

The shore A hardness scale is used to measure the solidity of bendable rubbers that vary from very soft and very flexible, medium and hardly flexible, and hard with almost zero flexibility. Even half-rigid plastics can be gauged using the high level of the shore A scale. The data you can get from the test can be used as a helpful measure of comparative resistance to indentation of different polymers grades. Nevertheless, you have to keep in mind that the shore hardness test with the Durometer cannot be used as an accurate judge of other plastic properties including resistance to scratches and abrasion, strength, or speed of wear which means they should not be used alone when making product specs and designs. Shore hardness is generally used as a substitute for flexibility when making the specs for elastomers. Studies prove that there is a correlation between flexibility and shore hardness in similar materials, especially when you are dealing with the same product line.

Shore hardness is an important feature to consider when choosing the original rubber mold that you need to create another mold.