Or, how a small push can generate high torque
There is not much room to maneuver in a nacelle 60m up so when bolt tightening is the task at hand, Norbar Torque Tools, Inc., of Willoughby, Ohio says torque multipliers can be a better and safer alternative to a long wrench. A torque multiplier increases the torque that can be applied by hand. Of course, output power cannot exceed the input power, so the number of output turns will be fewer than the number of input turns. A brief equation shows how the mechanical parameters relate.
Power = torque x rpm
Handtorque multipliers use and epicyclic or planetary gear train with one or more stages. Each stage of gearing increases the torque applied by a factor of 5. Norbar Handtorque multipliers typically come in ratios of 5:1, 25:1, and 125:1.
In the planetary-gear design, a tech applies torque to the input gear or sun gear. The action rotates three or four planetary gears whose teeth are engaged with the sun gear. The outside casing of the multiplier (an annulus or ring gear) also engages the plant gear teeth, and normally rotates in the opposite direction to the sun gear. A reaction arm prevents the casing from rotating, and this causes the planetary gears to orbit around the sun gear. The planetary gears are held in a planetary carrier which also holds the output square drive. Therefore, as the planetary gears orbit around the sun gear, the carrier and square drive turns.
Without the reaction arm to keep the casing stationary, the output square will not apply torque.
Other reasons to use a torque multiplier include:
- It’s safer in the nacelle. Use of long levers can be dangerous. In the confines of a nacelle, long torque arms are impractical. Torque multiplier allows reducing the lever length or operation effort by a factor of 5, 25, or 125.
- Torque Multipliers are especially useful breaking loose stubborn or frozen bolts, and are widely used for a 10% verification of bolted joints.
- Accuracy of the torque value improves when applying torque smoothly and slowly. Torque multipliers do this by removing much of the physical effort from the tightening task.
Torque-output calculations are a matter of simple arithmetic with little risk of incorrect bolt loading due to conversion errors. Other manufacturer’s multipliers often require graphs or formulae to calculate the input torque to achieve a particular output.
Norbar says its comprehensive multiplier range of Handtorque torque multipliers includes standard products in up to 47,500 Nm (35,000 lbf-ft) devices and specials to 100,000 Nm (73,000 lbf-ft). Accessories include ‘nose extensions’ for reaching difficult to access bolts and torque transducers for highly accurate torque monitoring.
Filed Under: O&M