Quality Control

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.

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.

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

Corrosion protection is vital for preserving the integrity of metal structures by preventing the gradual deterioration caused by environmental factors and corrosive chemicals. Effective corrosion resistance measures not only extend the lifespan of materials but also contribute to maintaining structural stability and safety. Equally crucial is wear resistance, ensuring durability against friction and abrasion, minimizing the impact of mechanical stress and preserving the functionality of components over time. To fulfill its intended function, the rubber lining or coating must maintain its integrity, guaranteeing that any substance it comes into contact with does not penetrate it and cause corrosion to the underlying substrate.

Have you ever wondered how we inspect the integrity and ensure there are no holes or voids in the rubber lining or paint coating? One method is called holiday detection. It is a technique used to identify defects in the protective coatings and linings applied to metal surfaces. Many of these defects are difficult to visually see, hence the necessity for mechanical means like a holiday detector. Holiday detection testing can be categorized into two groups: low-voltage testing and high-voltage testing.

Both groups involve applying an electrical voltage to the coated or lined surface and using a probe or electrode to detect any electrical current flow or spark indicating the presence of a defect or a holiday in the liner. The choice between low-voltage and high-voltage testing depends on the thickness of the lining or coating and the specific requirements of the inspection.

Low-voltage testing

Low-voltage testing is a holiday detection method employed to inspect protective coatings thinner than 500 microns or 20 mils. This method typically uses a voltage of 9 volts for testing coatings under 12 mils in thickness and a voltage higher than 9V for those with a layer from 12 to 20 mils. Thinner coatings require a lower voltage because they have a lower dielectric breakdown voltage, an electric potential at which an insulating material becomes conductive. If the voltage is too high for a thin coating, it may lead to premature dielectric breakdown, causing the coating to become conductive even in areas without defects, which can result in false readings.

At Abtrex, we use a low-voltage detection testing procedure to inspect the proper coverage of paint and to make sure that there are no pinholes or leaks in the lining. This procedure involves using a detector with a damp cellulose sponge attached to one end of the tester with a metal clamp on the opposite end, used as an electrical ground. Ensuring the sponge lies flat on the surface, the inspection is carried out by moving it at a moderate speed over the coated surface. If there is a defect or a holiday in the paint coating, the moisture in the sponge will facilitate the flow of electrical current to the steel substrate, enabling the detection of the flaw. The detector signals the identification of a defect with a sound alarm. All identified holidays are then repaired by grinding or abrading the area, and applying new layers of the specified coating. Once the repair is completed and the coating dries, the testing procedure is repeated to ensure the area is defect-free.

Holiday Sponge Test Video

High-voltage testing

This quality inspection is conducted with a use of a high-voltage device called spark tester. The purpose of a high-voltage tester is to detect pinholes, leaks or voids in rubber linings and coatings thicker than 500 microns, or 20 mils. This spark testing technique requires use of a higher electric potential device, because the dielectric breakdown voltage increases with the thickness of the lining material. Use of a high-voltage detector will ensure an electrical current will effectively pass through the thicker lining, making it possible to identify any potential flaws.

Our quality technicians use a high-voltage tester to effectively detect and locate any pinholes or leaks in the rubber linings. This inspection procedure requires the use of a probe attached to the detector. Like the low-voltage testing procedure, the test is conducted by moving the probe over the rubber-lined area continuously. If a leak is found, the device will discharge a visible white spark from the probe to the metal surface through the air path, indicating the presence and location of a holiday in the lining. Any detected leak will then be repaired by grinding the defected area and applying a lining patch as necessary. When the rubber repair is completed, the testing process is repeated to confirm that the area is free of pinholes and holidays.

Spark Test Video

Ensuring the integrity of protective coatings and linings of industrial assets through comprehensive holiday testing is paramount for longevity and safety.

At Abtrex, we specialize in corrosion and abrasion resistance. If you are seeking expert solutions for rubber linings or coatings inspection, don’t hesitate to reach out. Contact us to discuss your specific needs and discover how our services can enhance the performance and durability of your industrial infrastructure.