Up to 15 different kinds of rubber compounds go into a truck tyre. Which ones are best for which components for specific models is accurately tested at Continental using every method you can think of, lots of experience, and even more sweat.
A clack-clack-clack noise fills every corner of the basement. It sounds like hundreds of sewing machines on an endless loop. Countless pistons fitted with black strips are moving back and forth in glass boxes as quick as lightening. Rubber test pieces are being put through the mill here. They are bent a hundred times a minute – two million times a week. Continental material testers are observing how cracks form – a sign of fatigue in the material. "One test piece holds the tread strip record," says Ronald Wildt with a grin. The rubber strip completed over 90 million revolutions and the trial lasted almost two years. On the road, a tyre would have to roll forever and still not produce a comparable result. Only in a testing laboratory can the exact same conditions be implemented.
Ronald Wildt has been working for seven years in physical material testing, which is carried out at Continental's research and development department in Hanover-Stöcken. The 45-year-old proudly shows off the huge "vehicle fleet" he and his 40 colleagues use to perform tens of thousands of material trials and analyses every year. Countless presses, stamping machines, and tractor trucks are distributed throughout several rooms. One pricks a needle into a round piece of rubber to measure the hardness, while another stretches a rubber ring to test for extensibility. The third checks the rebound resilience – important for rolling resistance, which is a deciding factor when it comes to fuel consumption for truck tyres. In addition, there are high-tech devices such as the "aircraft carrier," as employees respectfully call it. It simultaneously performs a hundred different tests on rebound resilience and hardness automatically. Then there are the "Ferraris" – eight testing systems, each costing a quarter of a million euros, that distort rubber in every way possible using their robotic arms. And finally, the "Lamborghini": a massive high-speed linear friction tester that simulates grip on various surfaces at high speeds – Continental makes its own snow and ice in the cold chamber.
"Rubber has a memory"
Measured with precision that comes down to fractions of millimeters and seconds, all data is directly assimilated by the computer and sent to the material developers. They invent the recipes for rubber compounds at Continental. "Between 15 and 20 tests are required for each compound depending on which component the material is meant for," says Fred Waldner. He has a doctorate in chemistry and has worked in research and development at Continental for twelve years and has headed physical material testing since 2009. Just pick up worn tyres off the street and see how to make the material better? "This is the 21st century," he chuckles, his eyes twinkling behind his distinctive glasses.
Today the goal is to find the perfect rubber compound – before it even becomes a tyre. Trials are becoming ever more sophisticated and comprehensive. "In recent years, the number of dynamic tests with high-frequency deformations has multiplied by eight and the number of tear strength tests by five," says Fred Waldner. To make development move even faster, material testing requires a lot of machines – and efficient processes.
Fred Waldner's team processes around 12,000 recipes per year, approximately 25 of which eventually end up in tyres. The compounds are constantly being refined in numerous improvement cycles. "Rubber has a memory," he explains. "Unlike steel, rubber is always different depending on what was done with it before."
A test piece must be as pristine as it would be if it had just come off of the manufacturing belt.
That's why the material testers also produce the test pieces themselves in the laboratory.
In the rubber bakery
Wearing trainers, Fred Waldner jogs with a spring in his step to the "bakery". It's warm here, but instead of smelling like cookies, it smells like rubber, and all the employees are wearing black Conti polo shirts instead of chefs' hats. One of them is Alberto Sabor – with 22 years at the company, a real Continental legend. The 40-year-old carefully weighs the ingredients – natural rubber, filler, plasticiser, sulfur, oil – strictly according to the recipe. Precision is key. He pours everything into the mixer in the prescribed order and then selects the right temperature and mixing time on the computer. A soft mass emerges, which Alberto rolls out into a slab. With a steady hand, he stamps this into circles and right angles which are then vulcanised in the press – the "oven".
Ten minutes later he puts on a pair of blue protective gloves and with a beaming smile pulls out a metal tray: The rubber cookies are ready! The employees from the inspection laboratory are now ready to test them out.