Initial curvature

  • coil curvature
  • initial curvature range
  • initial curvature
  • spool curvature

The initial curvature is the curvature displayed by the product to be straightened before it enters the straightener.

A product to be straightened does not have a single initial curvature but several, which together form the initial curvature range. The difference between the minimal initial curvature and the maximal initial curvature is the curvature range.

How do the different initial curvatures arise?

Different initial curvatures are formed, for example, during the spooling process. The inner layers of a material wound on a spool have a bigger curvature than the outer layers. Whether the material undergoes elastic or plastic bending depends on many factors such as the material, geometry and dimensions of the product, the inner and outer diameter of the spool, and the temperature during winding.

Different initial curvatures of the product to be straightened also arise from its incorrect processing or deflecting. Helicities result in addition from changes to the directions of curvature in various curvature planes.

Internal stresses

  • internal stresses
  • internal stress conditions
  • causes of stress
  • stress conditions

In production processes such as casting, rolling and drawing, the outer shape of a workpiece is preserved only if it is adjusted and clamped before the process is started so that any twisting of the workpiece is prevented. Alternatively, the workpiece has to be straightened again at the end of the process. When the external loading is discontinued and the temperature compensation completed, the workpiece adopts an intrinsic shape which continues to exist without the application of any external forces and moments. The only explanation for this condition is that the sum total of internal forces and moments, i.e. internal stresses, is in equilibrium.

An analysis of the longitudinal internal stresses in a drawn wire reveals tensile stresses in the core and compressive stresses at the edge. Any change of a wire's parameters, such as curvature or helicity, over its length will result in changes of its internal stresses. Straightening has been shown to change the internal stresses so that the internal stress conditions existing in the material in the unstraightened state are eliminated. The magnitude and distribution of internal stresses existing after the straightening process depends on the design of the straightening system and particularly on the adjustment of the straightening rolls. With technology from WITELS-ALBERT it is possible to minimize the internal stresses arising during the straightening process while leaving the straightened material in optimal shape.