A holding or e-stop brake is used to keep a drive system from moving once the variable frequency drive has reached a near stop (i.e., near zero RPM shaft speed). In a holding or e-stop braking application, the brake generally isn’t used to stop the system except for emergency situations. The brake is always fail-safe, meaning that it is spring applied and will set itself in the event of a power failure.
Below is a summary of how we determine the best fail-safe holding or e-stop brake for our customers’ industrial applications:
Establish Torque Requirement
The first step in sizing of the fail-safe brake is to establish the torque required to prevent rotation of the shaft. The required torque may be determined by studying either the external load on the system or the input power being applied to the system during operation. For instance, if the input horsepower and rated RPM of the motor are known, the rated torque can be determined.
Similarly, if the line pull and rope drum pitch radius are known, the torque required to hold this load can be calculated. Once the required torque is established, the next step is to determine the maximum drum or disc diameter that will fit into the available space. Using the maximum drum or disc diameter will reduce the size of the brake due to use of the maximum moment radius.
Disc vs. Drum
Knowing the required torque and maximum available drum/disc diameter for the brake, the type of brake, “drum” or “disc,” must be decided.
If at all possible, a drum brake should be used for holding/e-stop applications due to its low relative cost, zero overhung load applied to the shaft, and compact configuration. It should be noted that drum brakes are limited to a rubbing speed of 40 m/sec at the drum surface and a maximum torque level of 9400 N-m on a 710mm diameter drum.
Disc brakes are capable of much higher rubbing speeds, up to 90 m/sec, as well as higher maximum torque level and disc diameter. Disc brakes are also able to handle higher disc/pad surface temperatures during an e-stop and dissipate heat faster while running than industrial drum brakes.
With the required torque, drum/disc diameter, and brake type specified, the last step for choosing the brake is the method of release actuation. There are four types of release mechanisms for spring applied drum and disc brakes:
In weighing the cost of spring applied brakes, electromagnetic brakes are generally the most expensive, followed by thruster brakes, hydraulic brakes, with pneumatic brakes being the least expensive option.
Usually, the external environment will be the deciding factor in selecting the method of release actuation for a spring applied brake. It is common to default to using whatever is easiest to get power to the brake in the installation area. Other times, unique environmental factors (e.g., avoiding hydraulic fluid leaks) are the prime consideration.
Select a Fail-Safe Brake
Having established required torque, drum/disc diameter, drum or disc brake type, and means of release actuation, you are now ready to select your industrial holding/e-stop brake.
We’ve developed our Industrial Fail-Safe Brakes page with a dynamic search function to help you weigh these different considerations and hone in on a brake you think may be best for your application.
At any point in your search for the best fail-safe brake for your application, we’d encourage you to speak with our engineers at Hindon. After understanding your application, we can help you weight the trade-offs you face, suggest industrial brake options you perhaps hadn’t considered or that we’ve used in a similar application, and perform technical analysis to ensure the holding/e-stop brake will work as intended (e.g., perform a heat load calculation to ensure the system will not overheat in the event of a e-stop).