Parallel-axis straightening

  • axis position
  • axis
  • coil axis
  • horizontal straightening
  • horizontal
  • horizontal axis
  • over the back
  • parallel-axis straightening
  • vertical axis
  • vertical straightening
  • vertical

The curvature plane of the initial curvature decides the arrangement of the follow-up straightener. Spools, coilers or deflecting rolls with horizontal axes are followed by straightening rolls arranged on the same plane, those with vertical axes likewise.

The straightening and curvature plane is not altered until in the follow-up process. This applies for several straightening planes as well as for successive changes of direction.

To establish and maintain the correct curvature course during straightening it is necessary to observe the following order: initial curvature, counter-curvature, final curvature.

Two frequently made errors:

1) The first straightening device is not arranged with its axis parallel to the unspooling or deflecting roll axis but is turned through 90 degrees. Instead of the first essential counter-curvature being applied to the material to be straightened, the material is made to adopt additional lateral curvatures.

2) Although the first straightening device is arranged with its axis parallel to the unspooling or deflecting roll axis, the first and third straightening roll do not touch the material on the spool side but on the opposite side. Hence the second straightening roll does not create the necessary counter-bend but confirms or reinforces the initial curvature. In this case the first two straightening rolls of the straightening device perform no straightening function.  

Postforming apparatus

  • postformer
  • postforming apparatus
  • postforming unit

A postforming apparatus can be compared to a straightener in that its design is largely similar. Unlike a straightener, however, it is used solely to form process multi-wire type materials such as strands or ropes. The forming is called postforming because the apparatuses, which can be grouped together in postforming systems, are usually positioned downstream from the stranding point on the stranding line. Upstream from the stranding point the material is usually subjected to preforming by preforming heads. Both the preforming and postforming operations are performed for the express purpose of minimizing the recovery efforts of individual elements in the strand or rope structure as well as the internal stresses of the final product, which correlate with the forming conditions.

Preforming head

  • preforming head
  • preforming
  • production of strands and ropes
  • stranding

A wire rope is constructed from wires which are brought together as strands or legs and are formed into the structure of the rope. Wire ropes can be classified into single-bay and mufti-lay ropes according to how the outer wires are formed. The forming of the wires, strands or legs begins ahead of the actual stranding point with the preforming head and is co-defined by the stranding process parameters, namely the length of lay, the angle of lay and the direction of lay. The preforming head, which rotates around the longitudinal axis of the revolving rope, uses systems of bending rolls applied radially in one plane to produce the characteristic spiral shape of the wire, strand or leg so that these elements result in as little stress as possible in the rope structure after the stranding. The “Trulay” process is sometimes used to denote this preforming method.

Process forces

  • force
  • process forces
  • straightening force
  • tensile force

Straightening forces and tensile forces are the process forces of relevance during straightening. Straightening forces are understood to be the forces of reaction arising at the interface between the straightening roll and the product to be straightened and owed to the bending moments existing in the process material during forming. Straightening forces act in various directions and magnitudes according to the geometrical boundary conditions. Of the many proposals for calculating the straightening forces (Zelikow, Geleji and others), the approach proposed by Guericke has proven expedient in practice. As his central instrument Guericke uses the bending moment/curvature hysteresis, which incorporates all the relevant factors affecting the straightening process. The straightening forces correlate with the tensile forces which, affected by the boundary conditions, arise as forward tensile force or pull-off force and reverse tensile force.

The work of plastic deformation performed in the specific case has to be determined in order to calculate the forward tensile force or pull-off force needed to transport a process material relative to the straightening system.

If further technological operations are positioned upstream and/or downstream from the straightening process, the tensile force fractions during the individual operations have to be taken into account when determining the total pull-off force. It is an advantage to ensure as constant a tensile force as possible in the direct vicinity of the processing in order to achieve a final product of high quality on a processing line. This can be promoted by using a decoil-straightener.

Pull-off force

  • force
  • frictional force
  • frictional moment
  • inertial force
  • pull-off force
  • pull-through force
  • straightening force
  • tensile force

The material straightening process requires the application of forces and moments in order to move the material and to deform it.

Pull-off force is the force needed to pull the material to be straightened through a line, a machine or tooling.

The necessary level of pull-off force depends on the following factors:

  • the forces of acceleration for the coil/spool to overcome the moments of inertia,
  • the frictional forces needed to overcome the bearing friction of the coil/spool,
  • the tensile forces resulting from the bends and the bearing friction of the deflectors,
  • the tensile forces resulting from the bends and the bearing friction of the material wraps (particularly on killing-straighteners),
  • the tensile forces resulting from the bends (e.g. straightening force) and the bearing friction of the straightening device.

To determine the driving force it is necessary the calculate or estimate the variables affecting the pull-off forces.

Frictional forces in the bearings and between the deflecting, bending and straightening rolls and the material to be straightened depend on the type of bearing and are generally small enough to be neglected. In discontinuous processes and when dealing with large spool and coil masses the pull-off force is largely made up of the force of acceleration. The role played by tensile force from bends increases with the number of straightening rolls (and deflecting rolls) and the size of their adjustment.

For a better and more exact assessment of pull-off forces it is recommended to separate the processes involved. This requires separate drives for the spooling process and the straightening process.