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Disc Brake Cooling
By Reid Penner
Disc brakes are a common mechanism used in almost every industry. From an engineering perspective, their primary purpose is to turn rotational energy into heat energy, with the end goal of controlling the speed of rotation. This leaves us with an overheating problem that if unchecked, can lead to the brakes failing.
Brakes in particular are a complex heating problem. They are hardly ever in a constant state for long periods of time, and quite often they rely on airflow to provide cooling, called convection. The convective cooling is directly related to the turning speed. This all makes it very hard to determine what will be required to keep brakes from overheating.
- Braking phase – where heat is applied to the system as the block is lowered
- Slow cooling phase – where the disc is stopped and work is done at ground level
- Fast cooling phase – where the discs are turning as the block is raised
- Slow cooling phase – where work is done at the top of the mast
In the braking phase, the calipers are clamping down on the disc, usually to control the rate of decent on the block under load. The amount of heat generated is directly related to the load on the block, and the speed the block is traveling. A larger load will generate more heat than a smaller one, as the caliper clamping force is greater. As well, a faster speed will reduce the time that the heat is applied to the brakes, as well as increase the cooling effect of the air flow.
In the slow cooling phase, the discs are not spinning, as the block is stopped at either the top or bottom of the mast. No heat is being generated, and the cooling is primarily from the hot air near the discs rising, causing an induced air flow. As the temperature difference between the discs and the surrounding air increases, this cooling effect also increases due to the increased buoyancy of the hot air near the discs.
During the fast cooling phase, the discs are spinning but the brakes are not applied as the block is raised up the mast. Again, no heat is being generated, and the cooling is primarily from convection. Inside the disc brakes used in drawworks, there are generally a set of cooling fins. These fins turn the disc into an impeller, forcing air through the discs and increasing the cooling effects of the air.
The combined effect of the heat-cooling phases on the discs means that during normal operation, the temperature of the brakes will alternate over a span of roughly 150°C, depending on the loading and the design of the brakes. In our designs, normal operational temperatures can be anywhere from 250°C to 350°C.
In the past, we have designed a few drawworks disc brake systems that have included air blowers to try and decrease this operational temperature range. However, the only times a blower is effective in adding cooling effects is in the slow cooling phases. Due to the cooling fins inside the discs, the disc itself acts as a giant fan with much more power than a typical blower of this size.
This means, as far as drawworks disc brake cooling goes, adding air blowers to your system is very dependent on how you are using the drawworks. For a heavy load and slow speed operations, a blower cooling system may be beneficial. For light load and fast speed operations, a blower system is probably not required.
In summary, drawworks brake heating is cyclic, with operational temperatures that can span a wide range. The majority of the cooling effects on the brakes comes from convection while the discs are spinning, and adding a forced-air cooling system to the drawworks would mostly be beneficial for heavy load, slow speed operations.