Innovation: Recycling model for brake blocks avoids waste and saves raw materials.

Knorr-Bremse is the first company to develop a process for recycling worn brake blocks from the London Underground, avoiding large-scale waste and cutting consumption of raw materials.

“Our savings on raw materials are in the region of 70 to 80 tonnes a year—from one customer alone!” says Dr. Nicolas Lange, Member of the Management Board and Head of Sustainability at Knorr-Bremse Knorr-Bremse Rail Vehicle Systems. He and his colleagues on the Knorr-Bremse Sustainability Committee had decided to put their energies into something nobody had ever tried before.

Lord of the mixers, mills and presses: Paul Eeles from the Knorr Bremse branch in Manchester, UK, where the brake blocks are manufactured.

Testing with the London Underground

The London Underground was an ideal test case. The Manchester-based Friction division of Knorr-Bremse supplies all the brake blocks required by the biggest metro network throughout Europe—all of which are Type 697. “The brake blocks have a special marking that shows when they need to be replaced,” explains Paul Eeles, Friction Products Business Development Manager in Manchester. “The rail operator knows that new blocks are needed when only 30 percent of the material remains.”

Recycling for brake blocks

In the past, old blocks had simply been thrown away. “Now we’ve developed an extremely advanced technology that enables us to recycle the material from these worn blocks,” says Eeles. First huge shredders strip the brake compound from the metal backing plates. These scraps are returned to the plant for milling into powder or granulate, which is then mixed with new compound and hot-pressed or “baked” onto a new backing plate to produce a new brake block.

Lots of test loops: Markus Seidl and his team have produced the perfect recipe for “baking” brake blocks.

Recycled brake blocks must deliver flawless performance

So far, so simple—but as Markus Seidl, Director Friction Material, explains, that simplicity is deceptive. “The recyclate is actually a raw material in itself. In the engineering and compounding* processes, we have to ensure that brake blocks containing recycled material deliver the same friction profile as new blocks. The recycled material must not impair braking performance.” Seidl compares the complex process with making a cake. “Right from the start, when liquid resin is blended with the powdered compound, I have to make sure the mixture is smooth and that all the materials are evenly distributed.” The milling and granulation process is repeated one more time before the final press and cure stage that results in the finished block. Here the presses apply pressure of up to 600 tonnes on the raw material, which is then cured at around 200 degrees for between 10 and 40 minutes depending on the “recipe.” When recycled materials are used, the challenge is to produce a smooth mixture from a substance that has previously already undergone curing.

Testing the recycled blocks in Manchester

In the early days, the engineers tested the recycled brake blocks on their dynamometer test rig, over and over again. Would the recycled blocks be able to match the braking distance of new blocks? “We and our colleagues in Manchester had to complete a whole series of engineering processes and test loops,” recalls Markus Seidl. “But now, after many, many tests, we’ve developed the perfect manufacturing process for recycled brake blocks, including all test documentation.” Conveniently, Manchester is joining forces with the center of Friction Material operations in Pamplona, Spain, to add a new mixing facility to its production line. Dr. Nicolas Lange is looking forward to the upcoming field tests with the rail operator.

"We’ve advanced a long way against our competition by developing these innovations."

Dr. Nicolas Lange – CEO and Head of Sustainability at Knorr-Bremse Rail Vehicle Systems

Is recycling brake blocks really worthwhile?

He admits that developing the process has involved effort and costs, but points out that the operator now saves on recycling costs while Knorr-Bremse can cut the costs of purchasing new raw materials. “Taken across the entire life cycle, brake block recycling ends up cost-neutral for us; but the project is an excellent test case and sends out a powerful signal.” Lange believes the brake block recycling concept for the London Underground will attract the interest of other customers that also use single-material brake blocks. “We’ve advanced a long way against our competition by developing these innovations in our Friction Materials sector. Sustainability is a great sales pitch.”

* Compounding = mixing raw materials in the “recipe” for the recycled brake blocks

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