WITELS-ALBERT GmbH

Three main factors have an influence on the number of straightening rolls: the initial curvature range, the pemissible final curvature (i.e. the tolerance of the final product), and material parameters such as the stretching limit, the modulus of elasticity, internal stresses and hardening.

Four simple and intelligible rules of thumb can be derived accordingly:

• The bigger the initial curvature range, the higher the number of rolls.
• A constant initial curvature requires few rolls.
• The higher the strength, the higher the number of rolls.
• The softer the material, the lower the number of rolls.

A further two rules can be derived from these four rules of thumb:

• The higher the number of rolls, the flatter the angle of straightening conicity and the less aggressive the curvature course during straightening. This applies in particular to material with rising straightened material parameter.
• The lower the number of rolls, the steeper the angle of straightening conicity and the more aggressive the curvature course during straightening. This applies to material with low material parameters.

As a general rule, the final quality of a straightened product (decrease of the final curvature range) increases with the number of rolls (alternate bends).

The right strategy - not only in terms of the environment and energy conservation - is “as little as
necessary” rather than “as much as possible”.