Shore Hardness – What Is It & Do I Need To Know About It.

CIPP Lining Certification Class, June 22, 2017, Pipe Lining Supply Office, Anaheim, CA.  We will hold the same training at our Batavia, IL office on July 27, 2017 as well. Call 888-354-6464 for more information or to sign up for one of the classes.

So, let’s talk about Shore Hardness. Hardness may be defined as a materials resistance to permanent indentation. The durometer scale was defined by Albert Ferdinand Shore, who developed a device to measure Shore hardness in the 1920s. The term durometer is often used to refer to the measurement as well as the instrument itself. Durometer is typically used as a measure of hardness in polymers, elastomers, and rubbers.

Shore’s device was not the first hardness tester nor the first to be called a durometer (ISV duro- and -meter; attested since the 19th century), but today that name usually refers to Shore hardness (other devices are simply called hardness testers).

Hardness may be defined as a material’s resistance to permanent indentation. The durometer scale was defined by Shore, who developed a device to measure hardness in the 1920s. The term durometer is often used to refer to the measurement as well as the instrument itself.

So, you ask, why do I need to know this for my industry, drain cleaning and repair? There are several devices with regard to lateral lining that use differing Shore hardness’s. One example is the gasket we use on the Quik Shot ™ lateral lining device. The gaskets we use to control the rear exhaust on the gun to regulate the venturi has a durometer or Shore hardness that is designed to be soft enough to open with our bat system, but strong enough to not deflect when air pressure in the unit changes. Any gasket material that you find in various pieces of equipment you use has a Shore hardness that optimizes the operation of whatever that gasket was designed for. Harder and softer materials may not perform as well as the one selected for that particular use. Moreover, the resin system you are using has a Shore hardness upon curing. The hardness levels can be adjusted to determine the finished product. Too hard can be too brittle, while too soft can allow materials to cut or destroy the hardened resin.

Here’s the ASTM that defines testing of rubber and plastic products:

ASTM D2240

4.1 This test method is based on the penetration of a specific type of indentor when forced into the material under specified conditions. The indentation hardness is inversely related to the penetration and is dependent on the elastic modulus and viscoelastic behavior of the material. The geometry of the indentor and the applied force influence the measurements such that no simple relationship exists between the measurements obtained with one type of durometer and those obtained with another type of durometer or other instruments used for measuring hardness. This test method is an empirical test intended primarily for control purposes. No simple relationship exists between indentation hardness determined by this test method and any fundamental property of the material tested. For specification purposes, it is recommended that Test Method D785 be used for materials other than those described in 1.1.

This test method covers twelve types of rubber hardness measurement devices known as durometers: Types A, B, C, D, DO, E, M, O, OO, OOO, OOO-S, and R. The procedure for determining indentation hardness of substances classified as thermoplastic elastomers, vulcanized (thermoset) rubber, elastomeric materials, cellular materials, gel-like materials, and some plastics is also described.

We also pointed out hardness levels to resist indentation, which is referred to as Rockwell hardness and is often performed on many of the same materials tested for durometer. This test moves beyond Shore hardness in determining how much permanent deflection is made to the material under pressure., but that’s another discussion.

The bottom line for you in the field and aren’t interested in the million dollar words of the test is that for various materials used in our industry there are various hardness levels. Each of those hardness levels were designed to perform certain tasks and while there may be variables to each product, there is a range that each application needs to perform correctly when installed. So there you have it. We’ve explored what Shore (durometer) hardness of a rubber or plastic materials is and how it applies to the lateral lining industry.