Montreal Metro Uses Wood Blocks on Their Braking System
Since its inauguration in 1966, the Montreal metro has been using yellow birch wood brake shoes, an idea inspired by the technology of the Paris metro. Indeed, the pneumatic-tired subways used wooden braking systems then.
According to the expert firm Knorr-Bremse, wooden shoes are less damaging than composite shoes, which wear out the iron of the wheel. They are also known for their quiet braking.
That is why, of the older technologies, the Bombardier-Alstom consortium, working together on the $1.19 billion contract, decided to keep the wooden brake system. It was the only option to meet the specifications – to have silent brakes that would not wear the iron of the wheels. Goodfellow then became their sole supplier of brake shoes. They use the same ones as on the previous models, only the mounting system has changed.
“All the brake shoes used on the Montreal metro are made here,” says Yves Duplessis, a mechanical engineer with the Société de transport de Montréal (STM).
Yellow birch blocks are cut to length, then the shoes are cut to their final shape and a serial number indicating the cutting date is printed on them. They undergo a double impregnation process: first they are immersed in pressure tanks of peanut oil – it is more tolerant of the high temperatures observed during braking – then they sit in the open air to allow the oil to impregnate them evenly. After a month, they are impregnated with fireproof salt to make the shoe more difficult to burn.
Thanks to this double process the wooden brakes can withstand trips of up to 80 000 km before needing to be replaced, explains Mr. Duplessis.
On a complete 9-car train, there are 144 shoes, for a consumption of 18 to 20 000 per year – their 80 000 km lifespan corresponds to about one year. The production cost of a wooden shoe is about $11, which makes it a more economical choice than the composite shoe, which would cost about $20.
After their disposal the old brakes show little wear and tear, as the Montreal metro mainly uses its electric motors for braking. In fact, they are only used in the last mile, when the motor can no longer ensure braking, below 9 to 10 km/h. On the other hand, emergency braking is done by wooden shoes alone. This gives off a distinct smell of wood and peanuts.