Power-Off Brake For Short Axial Shaft

Retrofit: Suitable Brake Power In a Limited Space

How Power Off Brakes Work

Power off brakes are also referred to as holding and fail-safe brakes. They are suitable for applications where a motion system component must be held stationary in the absence of an energizing source. If using electric power brakes, the brake would engage when electricity is intentionally shut off or disrupted by an unexpected power outage. Mach III power off brakes remain disengaged if compressed air pressure is supplied to the brake at the specified pounds per square inch. When air pressure is lost, springs activate to apply force to a series of metal drive discs and composite friction pads providing the torque required to hold the shaft stationary.

How Required Torque Is Determined

The holding power brakes can provide is referred to as torque capacity. Details about how the torque capacity is determined can be found in our Selection Guidelines. For this retrofit application, we used the specifications of the existing motor and the RPM at the brake to calculate that the minimum torque required to hold the shaft stationary was 600 pound inches. Applying a safety factor of 2:1 resulted in a total torque capacity requirement of 1,200 pound inches. Below are the formula and calculation.

Brake Torque Requirement Formula

(Horsepower of the Motor x 63,000/RPM at the Brake) x Safety Factor = Torque Required

Retrofit Brake Torque Requirement Calculation

(0.5 x 63,000/52.5) x 2 = 1,200 pound inches

Why Was A Custom Power Off Brake Required?

Mach III’s standard D6F3G-STH brake could satisfy the torque requirement but would not fit in the available space. The design challenge in this application came from the fact that the brake needed to attach to a shaft which extended only 2.125 inches beyond the frame of the machine. Additionally, the shaft had no keyway. A custom design was necessary to avoid the downtime and expense that would result from field modification of the machine.

The Resulting Custom Brake Design

Mach III took advantage of the radial space available to provide the required torque capacity while keeping total axial length of the brake to just slightly over 3 inches. The custom design allowed for quick and simple installation in the field. The brake housing attaches to the machine frame with six bolts on a 6.563 inch bolt circle. Instead of a traditional set-screw and key connection, a Ringfeder shrink disk connects the brake to the shaft.

Click Here to view the detail sheet for this custom power off brake.

To learn more about the Mach III custom design process, and see more custom brakes, Click Here.