HOW DO YOU MAKE A ROUND STEEL BAR STRAIGHTER?

To answer this, we need to have in mind two concepts that apply to metals: stress and strain. Stress is the internal force exerted by two adjacent parts of a body upon the other across an imagined plane of separation. Strain is any forced change in the dimensions of a body by adding pressure.

Metal strain in a body will rise and fall proportionally with the stress within limits. As a result the body will deform under load and then spring back to its original shape when the load is removed. This is referred to as elastic behavior. If the body is deformed past its yield strength, it will still spring back, but not to its original shape. This is referred to as plastic behavior.

To improve the straightness of a metal bar, we must increase the stress level of some portion of its cross section above the yield strength by applying a sufficient load. When the bar springs back after the load is removed, it will have improved straightness quality, provided that the proper load has been applied and sufficient plastic behavior has occurred.

In the case of a two roll straightener, forces are applied to a round metal bar, and stresses above the yield strength can be induced. By compressing the bar between the concave, and straight roll, and the action of the concave roll forcing the bar around the straight roll, and by the guides, both above and below the rolls they keep the bar on a horizontal centerline. The higher the yield strength of the material and the smaller the cross section, the more curvature is required on the concave roll to induce plastic behavior, by the action of rolling and bending a bar. For most applications, it is desirable to achieve plastic behavior through the bending action of the rolls, not the crushing action, as this will take away from the lifespan of your rolls.

Generally you will attain consistent straightness improvement in round bars with a two roll straightener. Providing that the processes used to manufacture the bars are under control and your material quality does not vary. This of course assumes that your straightener set ups are consistent for each individual bar product straightened. That is why we recommend the use of set-up cards or a recipe-type book,  and that your straightener and rolls are properly maintained.