Position Brakes vs Torque Brakes
Any torque arm can be equipped with several positioning brakes or with one torque brake.
What are Positioning Brakes for Torque Arms?
Positioning Brakes or ‘drag brakes’ are typically mounted on the 1st and 2nd Axes of the torque arm and act to hold the arm in one position so that it will not drift away. These brakes are usually very light and can be overcome by pushing with some force against the nutrunner or the end of the arm. Many torque arms are not equipped with positioning brakes at all, and are expected to drift away when the operator releases the nutrunner.
Positioning brakes are not meant to hold against a torque; they merely prevent arm drift.
What are Torque Brakes for Torque Arms?
Torque Brakes, on the other hand, are meant to withstand the torque exerted by the nutrunner. While it is theoretically possible to mount the torque brake on the 2nd Axis, typically they are mounted on the 3rd.
In the photo below right, the nutrunner is equipped with a disk and 2 heavy caliper brakes. These brakes are normally off until the time the nutrunner begins to spin. Torque brakes will have a safety factor against slippage of about 2:1.
The Benefits of Using Torque Brakes over Positioning Brakes
Torque brakes are generally air-operated and are much more powerful than positioning brakes. If a torque brake is not present when it should be, the arm will begin to turn unexpectedly when torque is applied, possibly resulting in injury.
When Do I Need a Torque Brake?
Usually, torque brakes are only needed when the fasteners to be tightened are vertical (or semi-vertical) and the nutrunner must be repositioned at the 3rd Axis.
Example 1: All fasteners are horizontal: typically, no torque brake is required because the arm geometry withstands the torque.
Example 2: All fasteners are vertical and the nutrunner has an in-line shape. There is no reason to spin or reposition the nutrunner at the end of the arm and no torque brake is required. The nutrunner can be fixed at the end of the arm and the arm geometry withstands the torque.
Example 3: Several fasteners are significantly off vertical (but are not horizontal) and are arranged in a long row. In this case, the nutrunner has to be twisted slightly with respect to the arm as each fastener is engaged and a torque brake at the 3rd Axis is required.
Example 4: All fasteners are vertical and arranged around the perimeter of a hub. The nutrunner has a right-angle shape. The operator must reposition the nutrunner at the 3rd Axis with each fastener to avoid interfering with the hub, and a torque brake is required.
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