SELECTING THE STRAIGHTENER
The material to be straightened must be subjected to constant stress conditions if good straightening result are to be achieved (see Analysis of the material to be straightened). If this can not be achieved, because of too great a range of initial curvature, varying stress conditions, or too much torsion (helix), then killing sets or helix straighteners must be added in front of or behind the straightener to counteract these influences.
THE NUMBER OF STRAIGHTENING ROLLS
Four factors determine the number of straightening rolls:
· the tensile strength and/or the yield
· the ranges of initial curvature
· the applied energy
The greater the tensile strength and/or the higher the yield stress, the greater the number of required rolls (see figure 10). The reverse is similarly true (see figure 9).
THE POSITIONING OF THE STRAIGHTENER
Experimentation has resulted in the following formula to determine the distance
between the spool, coil, or the position of the last direction change and the straightener:
A < π x d (see figure 7 and 8)
CURVATURE AND STRAIGHTENING ROLL ARRANGEMENT
Any straightening process is concerned with initial curvature, reverse curvature, and
residual curvature. Reverse curvature is applied via the second roll in the opposite mode to the spool, coil, or guide which is responsible for the initial curvature. The residual
curvature is progressively removed until the required final value has been achieved. In
principle, this is a parallel axis process whether it relates to spool-straightening or
straightening-spooling. Repetition in various planes is suggested.
STRAIGHTENING ROLL SETTINGS
With a small number of rolls, the reverse curvature is severe, the taper angle is large (see figure 9), and the straightening process is generally aggressive. High tensile materials
can not be straightened in this way. With such materials, the straightening process must be spread over a greater number of rolls (see figure 10). The required straightness is achieved by first submitting the material to be straightened to severe reverse curvature and, thereafter, to progressively gentler treatment (see figure 11).
Avoiding dirty conditions, particularly from metal particle contamination, and proper roll fit have a significant influence on the life of straightening rolls. Under highly clean conditions your WITELS straightening rolls can achieve a life-time of up to 30 times the norm. Improved WITELS straightening systems such as the WICAS cartridge system are designed specifically to prevent contamination from dirt and metal particles.
When fitting straightening rolls, always ensure that pressure is applied correctly so that bearing balls and races are not damaged. Always “seat” the inner-ring of the bearing by applying pressure evenly over its front facing surface. A press or similar tool should be used for this purpose (see figure 12).