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The importance of testing rubber hardness

Did you know that rubber linings can have different degrees of hardness? Why is this, and why does it matter for the protection of your equipment?

The hardness of rubber linings affects its performance in various applications. For example, in industrial conditions where rubber materials are used to provide abrasion or chemical resistance, the hardness can influence how well the lining withstands wear and tear over time. If the material hardness is not selected properly, it can wear out faster, leading to contact with corrosive or abrasive substances on the metal substrate. To ensure that rubber achieves the desired hardness, it must undergo a vulcanization process after application. Vulcanization aims to improve the chemical properties of the lining by introducing cross-links between individual polymer chains. This process transforms soft rubber, into a durable material with increased elasticity, resilience, and resistance to chemicals and temperature.

Hardness testing helps evaluate the durability of rubber linings and determine whether it will perform as expected under specific conditions, and to ensure that the vulcanization process was successful.

The required hardness of rubber lining depends on its purpose and the project specifications. Softer linings can be used in processes where flexibility and cushioning are important, such as in vibration dampening and impact absorption. The hardness of the rubber can also impact its chemical resistance. Specific compounds are formulated to provide optimal hardness for resistance to particular chemicals. Examining hardness with a durometer involves quantifying the depth of the penetration caused by the indenter. The lesser the indentation depth, the greater the material’s hardness.

Shore durometer testing

At Abtrex, we conduct rubber hardness tests using Shore durometers. The name “Shore durometer” comes from Albert F. Shore, the inventor of the device and the scales used to measure hardness values. The ASTM D2240 standard recognizes 12 Shore hardness scales: A, B, C, D, DO, E, M, O, OO, OOO, OOO-S and R.

At Abtrex, to measure the hardness of rubber linings, we use the Shore A and Shore D scales. The Shore A scale is used for measuring softer materials such as chlorobutyl, neoprene, or Hypalon. The values of these measurements typically range from 30 to 80 Shore A. For tests in this scale, the durometer has a blunt, conical indenter suitable for softer linings, preventing deep penetration that could damage or alter the test sample.

Shore A durometer test on a chlorobutyl rubber lining

Shore A durometer test on a chlorobutyl rubber lining.

The Shore D scale is used for measuring harder linings such as ebonites, graphite-loaded, or harder neoprene rubbers. The measurement range for this scale typically spans from 50 to 85 Shore D. This durometer has a sharper, more pointed indenter that can penetrate harder materials to measure their hardness accurately.

Test Method

A durometer measures hardness by testing the material’s resistance to indentation.  The tester is placed perpendicular to the material’s surface, and then the indenter is pressed into the material, applying pressure through a spring-loaded probe. This device then measures the depth of the indentation, which correlates with the material’s hardness. The reading should be taken from the dial or digital display after approximately one second and then compared to the specification value for the specific rubber or project. This process should be repeated multiple times to ensure the lining has been tested across its whole surface area.

Testing hardness of rubber lining with a Shore A durometer

Testing hardness of rubber lining with a Shore A durometer.

Overall, hardness testing of rubber linings is a crucial part of quality assurance and ensures that the linings will perform reliably in their intended applications, contributing to safety, durability, and efficiency. If your equipment requires protection from corrosion or abrasion, contact the Abtrex team for a custom solution. Abtrex’s professionals will help you select and install the appropriate compound for your specific needs.

Rubber Hardness Testing Video

Abtrex Industries Inc.

Author Abtrex Industries Inc.

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