Taking a hard look at rubber

Taking a hard look at rubber

Assessing the quality of any given sample of rubber is notoriously difficult, thanks to commercial secrecy, crude recycling processes and a lack of reliable visual clues. To help address quality concerns in the marine industry, Trelleborg has developed a test for rubber fenders used in dock protection systems.

When Charles Goodyear patented the vulcanization process in 1844, he transformed soft rubber into a hard and useful material. Today, industrial rubber is so ubiquitous that its many roles go unnoticed, says Mishra Kumar, Global Technical and Market Support Manager at Trelleborg’s marine operations within Trelleborg Offshore & Construction. “Rubber has found its application in almost everything from the iPhone to the Airbus A380. Its uses fall into three broad areas of use: to seal, damp and protect.”

Like its many and varied applications, rubber compounds come in an array of variations, with each manufacturer having its own unique formulations. Besides using natural rubber as the starting raw material, synthetic forms derived from petrochemical products are also used. “Each raw rubber has its own inherent advantages or disadvantages and is application dependent,” Kumar says. To provide different functions and to be endowed with specific properties other chemicals are added, such as fillers that can reinforce or bulk the material, aging protectors and softeners that regulate material hardness. Then there is the mixing process itself, the mixing cycle, the timing of each part of the process and the temperatures used for mixing and curing – all of which make a contribution to the final makeup of the rubber.

Designing a rubber compound is often considered to be a black art. Many manufacturers jealously guard their formulations, but Kumar believes that more openness about the composition of rubber is required, that there is a need to set technical standards in the industry and to work toward the development of better-engineered materials that can be assessed against those standards. He wants rubber to be seen as an engineered material selected for its performance, characteristics and long life rather than regarded as a commodity and bought on price alone. One way to transform customer perceptions is to develop methods to better assess rubber quality in a consistent way.

This is because in some major industrial applications – the marine industry, for example – the influx of producers and suppliers has led to poor-quality rubber based on recycled material. Kumar explains that current methods of recycling, while laudable in principle, are not environmentally sound. “The recycling process is aggressive, very intense and highly polluting,” he warns. Furthermore, the rubber’s original properties are not restored, resulting in an inferior material. “The unique properties of rubber come from its long chain molecules, but recycling shortens the molecular chains, thus degrading the material,” he says. This has a consequent effect on component performance and operating life.

Kumar points out the difficulty customers experience in trying to assess rubber quality. After all, most industrial rubber contains carbon black, an additive that helps reinforce or strengthen the material. It also gives rubber its black color, so the overall appearance of a good-quality or an inferior material cannot be gauged by visual inspection alone. What makes good rubber is an extremely difficult question, as rubber quality has been notoriously difficult to define. Kumar offers a definition of poor rubber as a substance “that fails to do the job for which it was intended.”

As a step toward answering the question of rubber quality in the marine industry, where a major application is for fenders that are used as part of dock protection systems, Trelleborg has developed a specific test regime for rubber fenders. The test to analyze the consistency and chemical composition of the rubber avoids the need for destructive testing of the product in order to establish the quality and performance of the material. Instead from only a 50 gram sample an indication of performance in application and the lifetime of the fender in use can be gauged.

Previously, such large components would have had to undergo destructive testing to determine quality and performance, so the ability to use a small sample to provide a reliable indication of quality is a major step forward for marine applications. In addition, Kumar points out that for some producers there was no guarantee that any testing was carried out prior to delivery or that the rubber compound conformed to the specification. This test removes that uncertainty.

For many of the applications for which Trelleborg develops solutions, Kumar believes that customers need to appreciate that the rubber material is part of an engineered solution. Such advanced materials as steel have clearly defined specifications, he says, and rubber components that work alongside steel in marine protection systems should meet their own clearly efined standards. Trelleborg’s testing system is an important step in that regard. “It is all about setting standards and making sure those standards are met,” he says.

Measuring quality for the marine industry

Millions of dollars are being invested in establishing ultramodern port facilities around the world. Protecting ships and berthing facilities is the job of fenders, highly engineered steel and rubber components that take the impact of the ship as it docks. Although there are specifications for the performance of the fender related to the velocity of impact and to temperature variations, reliable testing for rubber-quality without destruction of the fender was not available until Trelleborg developed its analytic method.

The analysis method requires only a small number of test samples that undergo chemical analysis. A Fourier Transfer Infrared spectrophotometer and a thermogravimetric analyzer are used on a 50 gram sample to identify the composition of the rubber component and the proportion of polymer to filler.

The test shows that the factors that determine the best-performing rubber compounds for fender application require a polymer-to-filler ratio greater than 1.2 and a density of less than 1.2. The life of a poorly formulated rubber compound may be 10 times less than that of a high-performance one, which can have a lifetime approaching 60 years. The importance of understanding rubber quality therefore takes on crucial significance when choosing a supplier.

This is an article from Trelleborg's T-Time magazine. To download the latest edition, go to: www.trelleborg.com/t-time 

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