Rubber is a truly fascinating material to work with and exhibits viscoelastic behaviour. In its original, unvulcanised state, it can be shaped plastically like modelling clay. Once it has been vulcanised, however, its elastic properties come to the forefront, allowing it to stretch and then return to its original shape when the stress is removed. Depending on the composition of the compound, rubber can show either elastic resilient behaviour or energy-absorbing behaviour. Consequently, the rubber compound recipe is key to a tyre’s functionality, influencing both braking performance and rolling resistance. A balance must be struck between maximising braking performance in the interests of safety and minimising rolling resistance in order to reduce fuel consumption.
The Compound Testing Lab investigates new rubber recipes to determine how well they are able to reconcile these conflicting priorities. A wide range of testing techniques are employed to establish whether the material developers’ recipe ideas are on the right track: Do the new materials fulfil the physical criteria that the development department has specified for the tyres?
The Compound Testing Lab investigates new rubber recipes to determine how well they are able to reconcile these conflicting priorities.
The tests typically carried out in the Compound Testing Lab include microabrasion tests, strength tests, tear, compression and impact strength tests, and tests to investigate the material’s elasticity, dimensional stability and viscoelastic behaviour. Special equipment is used to analyse friction mechanisms on a wide range of different surfaces, providing a deeper insight into the phenomenon of rubber friction. One of these testing machines carries out extremely precise measurements of the friction coefficients of rubber test pieces on different substrates – such as asphalt, concrete, snow and ice – in a test environment that can be set to a wide range of temperatures. Once the rubber test piece has been mounted on the machine, it can be moved over the substrate at high speeds.
This allows local slip velocities occurring at the tyre contact patch during braking and traction testing to be simulated in the laboratory. High acceleration values can also be achieved. The test piece can be pressed against the different substrates at high pressures so that the real-world stresses encountered by the full range of tyre types (motorbike, car, bus and truck tires) can be replicated in the lab. These tests make it possible to predict the outcome of traction-focused tire tests (e.g. on ice and snow) and rank the effectiveness of different compound variants. The High-Speed Linear Friction Tester (HSLFT) provides the technological basis for the Automated Indoor Braking Analyser (AIBA) at our Contidrom test facility. The HSLFT enables precise control of surface and temperature conditions, while the AIBA provides the link between controlled test conditions and the real world.
The High-Speed Linear Friction Tester (HSLFT) provides the technological basis for the Automated Indoor Braking Analyzer (AIBA) at our Contidrom test facility.
