Slitting. High-speed slitting is the most economical way to cut wide mill coils into narrower strips. If the thickness varies significantly within the width of the coil, then during rewinding, the thicker, shorter coil segments will remain tight, and the thinner, longer ones will hang in a loop.
In some older slitter installations, 20- to 40-foot-deep pits were built to accommodate these loops. To keep a tension on all recoiled narrow strips and to eliminate the loop, cardboard pieces were placed between the wraps to increase the rewinded coil's diameter. Newer, better slitting equipment can rewind the strips under tension and eliminate the dangerous practice of inserting cardboard pieces.
As mentioned previously, slitting will not eliminate camber in the strip. Actually, dull slitting knives, applying more force, and/or creating burr may induce camber in the formerly straight material.
Conclusion
Choosing the right material at the right price is an important contribution to successful roll forming. To select the right material, an understanding of both the properties of the material and principles of roll forming is important.
Practically every material that can be formed with other processes can also be roll formed. However, the material's mechanical properties, thickness, straightness and flatness tolerances, surface quality, and finished-product requirements should influence the number of passes and shaft diameters selected and how the rolls are designed. To achieve the best results, cooperation among the customer, product designer, manufacturing plant, and suppliers is essential.
