Thanks to its strength, long fatigue life and elasticity, rubber is the engineer’s preferred material for the attenuation of vibration. However, rubber alone does not an anti-vibration solution make – to be successful, the perfect partnership between rubber and metal must be created. Conrad Hextall, our Principal Engineer, explains how it’s done.
“The bonding of rubber to a substrate has a history dating back over 150 years.
“In 1839, the self-taught chemist and engineer Charles Goodyear discovered that rubber could be ‘cured’ with the addition of sulphur – an accidental discovery that changed the way we thought about (and used) rubber. Within 25 years of this milestone, and after further development, it was found that under heat and pressure, natural rubber compounds formed a chemical bond with brass. This discovery made rubber even more useful resulting in a rapid growth of the rubber-to-metal bonding industry.
“For much of the first half of the 20th century, bonding rubber to brass-plated steel was the most common method of securing rubber to a metal substrate. The metals could be formed to any practical shape that suited the application giving the designer greater flexibility than ever before. Bonding rubber to brass is still used today in tire production where a bond is essential between the rubber and internal brass plated steel chords.
“Tyre production aside, rubber-to-brass bonding was phased out in companies like Trelleborg in the 1960s due to the advancement of bond paints which were more cost effective than having on-site brass plating shops. Further development of different kinds of bond paints meant that we could now bond almost any type of rubber to almost any type of substrate, even plastics – whereas with brass bonding, we were limited to only a few specific rubber types. That’s a significant drawback when you consider we have a portfolio of more than 300 rubber types!
“Bond paints, also known as cements or bonding agents, are applied to the metal substrate much in the same way as any paint. Firstly the metal surface is cleaned and prepared by either grit-blasting or phosphating. Secondly, the primer is sprayed onto the areas that required rubber bonding, then thirdly, a top coat is sprayed onto the primer. Under pressure and temperature in the moulding cycle, chemical reactions, atomic adsorption and cross-bridging occur between the metal, cement and rubber, creating a bond which is stronger than the rubber itself. Under shock conditions, some applications will see the rubber extend to many times its original dimensions meaning that a strong rubber-to-metal bond is crucial.
“The characteristics of an anti-vibration mounting or suspension system component is mostly defined by the geometry of the metal substrates, and the volume of rubber bonded to those substrates. Rubber bonding gives the designer great flexibility in allowing complex designs. Whatever practical shape the substrates are, the rubber will bond to it with the presence of a bonding cement.
“The most common method of testing bond strength in a laboratory environment is using a peel strength test on a length of rubber that has been bonded to a steel plate. As the name suggests, the rubber strip is peeled from the steel plate at an acute angle leaving a thin rubber layer on the plate. The presence of this rubber layer means that the bond between the rubber and metal has passed the test.
“Within the production environment, we have a set of rules to apply a shear force on the product that will impart a known stress on the bond interface. This gives absolute confidence in the quality of the bond between the rubber and substrate.”
To discover how we use this technology to create bespoke anti-vibration solutions for our customers, check out Conrad’s product engineering blog.