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How we make an unbreakable rubber-to-metal bond

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Rubber-to-metal bonded parts must be able to withstand significant shear and tensile stress, day-in, day-out. So there can be no weak link between the two materials that come together to make it. Here we explore how the rubber is mechanically bonded to the metal using a rigorous five-stage process.

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Rubber-to-metal How it works 2 min read

1 Choosing the right rubber compound

Since rubber-to-metal parts are exposed to many different elements - varying forces, temperatures, chemicals etc – they must perform differently too. Choosing a material that can withstand all these requirements is critical. This is why we carefully blend our rubber compounds, using many different ingredients, to get the right performance characteristics and physical properties for the application.

2 Preparing the surface

For the perfect bond between rubber and metal, all oils, lubricants and other contaminants must be removed from the steel surface, using either solvent degreasing or an alkaline cleaning. Because rubber-to-metal parts operate in harsh conditions, we also apply a special chemical treatment to the surface to protect the bond’s integrity and help prevent corrosion.

3 Primer and adhesive application

Once the surface has been properly cleaned, we use a two-coat adhesive system, to bond the rubber to the metal. Consisting of a primer and an adhesive topcoat, it is applied in a fine, even layer using an automated spray line. The adhesive coated metal must be molded as soon as possible, as any surface contamination at this stage, can cause performance issues further down the line.

4 Moulding

Moulding is one of the most important steps in the bonding process, as this is where the rubber vulcanizes and the adhesive cures simultaneously. During this process, the adhesive on the metal component reacts to the high-temperature, high-pressure and elastomer viscosity to create a powerful bond between the rubber component and metal. Even the smallest of variations in any one of these critical parameters and the bond will ultimately fail.

5 Tested to the limits

Our rubber-to-metal parts are pushed to breaking point, literally. To ensure each part performs to OE specification, a sample piece from each batch undergoes a destructive test, where we try our very best to break it. Whilst this might sound like a strange thing to do, on a part we’ve just made, it’s the only way we can ensure a high quality product. Very simply, the rubber should tear before the bond breaks – if not, the parts are rejected, and the rubber-to-metal bonding process begins again.

Through this painstaking five-step process  – rubber compound formulation, surface preparation, primer and adhesive application, moulding, and testing – we know that our rubber-to-metal parts will deliver an unbreakable bond. So, on your next steering job, you can fit Delphi’s parts with confidence, for a bond that will last just as long, with your customers.


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