How to Size Turning Rolls
The basic turning roll setup includes one (1) drive roll and a companion non-powered idler roll. The driver roll supports one end of the workpiece and imparts rotational motion to the work. The idler merely supports the other end of the work-piece as it rotates. The first factor in selecting any set of turning rolls is to determine the maximum weight capacity required. In a symmetrical work-piece, one of its ends and half the load is supported by the drive roll. The other half of the work is supported by the idler roll. Each driver and idler roll has separate load ratings and capacities.
Although most turning roll applications are primarily concentric loads, they are rated to handle a certain degree of eccentricity. Tractive pull ratings show the available turning power for a given Turning Roll. For eccentric loading, the available turning power must be compared to the force required to turn the eccentric load. To determine the required force to rotate an eccentric vessel, use the following formula.
The force required to rotate a vessel should never exceed 1/2 of the catalog rated Tractive Pull.
(Total load) x (distance CG is
located from center of rotation)
required to rotate the work must also be considered. The Drive Roll is rated in
terms of turning capacity. This rating refers to the power that is produced by the
driver, to rotate a smooth-walled, straight-sided circular cylinder.
For example, a Driver rated to support 30,000 lbs is also rated to rotate 90,000 lbs.
To support and rotate a 90,000 lb load (1) 30,000 lb driver and (2) 30,000 lb idlers are required to provide sufficient support and rotation power for the load. Vessel roundness, irregularities and roll alignment can all affect the rotation power required and must be considered.
When supporting a load on a set of turning rolls, the distance between the rollers is very important. A balanced symmetrical load should normally have an included angle between 30 degrees and 60 degrees. Although a greater included angle can provide more traction, it also requires additional torque and can stall the drive motor. Small included angles can produce unstable loads and unsafe conditions.