Decoil-straightener

  • accumulator
  • dancer
  • pay-off
  • store
  • unwinding
  • wire store

The decoil-straightener is a combination of a decoiling/unspooling unit and a straightening unit used in conjunction with a material store. The endless material to be straightened is decoiled/unspooled from a coil/spool and directed to the straightening unit via several deflections (store) and a bending roll, always maintaining constant directions of deflection and curvature. Apart from the bending of the material around the bending roll, all the deflections around the pairs of pulleys are performed only elastically.

The coil/spool is rotatably mounted to enable the material to be paid off dynamically (preventing additional torsional stresses and helicities such as occur with static pay-off set-ups). The coil/spool is driven by an electric motor whose speed is controlled in accordance with the dancer position. A sensor scans the dancer position (height), producing an electric signal which is evaluated by a controller and relayed to the motor electronics.

The pull-off force acting on the material to be straightened is constant, consisting only of the straightening force and a variable dancer weight. Additional tensile forces caused by acceleration and deceleration, particularly in discontinuous processes, are minimized by the store function.

Equipped with the right mounting arrangement, users can change over quickly between various straightening devices, helix straighteners and killing-straighteners to suit the different types of material to be straightened. An additional stretch-bend-straightening effect can be produced by using a bending roll with brake, around which the material can wrap itself at least once. To produce a higher tensile stress in the material, on the other hand, a bending roll with brake should be placed in front of the straightening devices. The straightening unit normally takes the form of a straightening system with two straighteners.

Deflecting

  • bending radius
  • change of direction
  • defined deflection
  • deflecting roll radius
  • deflecting roll
  • deflection
  • rewinding

During the production and processing of wire the process material has to be deflected many times. To prevent disadvantageous changes to the initial curvature and material parameters, the material needs to be deflected elastically in the direction of its initial curvature. Elastic deflection depends on the diameter of the deflecting roll, which in turn depends on the process material's geometrical dimensions, modulus of elasticity, elongation limit and initial curvature. The permissible minimal value for the deflecting roll diameter is calculated with an equation.

The decoil-straightener from the WITELS-ALBERT range allows for elastic deflection in the direction of the initial curvature during the decoiling process. Decoil-straighteners for specific process materials can be built to order with adapted deflecting rolls. 
Minimal deflecting roll diameter:

D minimal deflecting roll diameter [mm]
d wide diameter or material thickness [mm]
E modulus of elasticity [N/mm2]
Rp0,2 stretching limit [N/mm2]
This equation applies only when the product is straight prior to deflection.

Deflection

  • arc height
  • arrow height
  • bend
  • camber
  • curvature
  • deviation from the straight
  • wire deflection

The deflection h of a product to be straightened is the maximal distance between the chord a and the arc of the product. The deflection is expressed as mm/reference length.

The permissible deflection values for bars and wires are specified by DIN EN 10 21 8-2.

Drawing direction in the straightening process

  • drawing direction in the straightening process
  • image of microstructure
  • production direction
  • pull-through direction
  • steel wire

Wire is formed on drawing machines to the required final diameter. The microstructure of the original wire is changed by the forming process. The image of the ensuing microstructure is also known as the "drawing texture". The draw ratio is derived from the quotient of the cross sectional reduction and the initial cross section. The higher the draw ratio, the greater the stretching of grain in the direction of the wire axis. Plastically formable components of the microstructure (e.g. tough ferrite crystals in iron and steel wires) follow the forces in forming direction. Brittle components (e.g. pearlite crystals) are crushed under the action of the forming force and then aligned in drawing direction.

Straightening tests have shown that final curvatures differ when the material is drawn through the straightener in different pull-through directions. With wires that are difficult to straighten, it is an advantage to perform the straightening in drawing direction.

Drive unit

  • advancing mechanism
  • caterpillar pull-off
  • drive unit
  • drive
  • driver stand
  • driver
  • feeding device
  • feeding

Endless material must not only be straightened, it must also be transported, pulled or pushed.
Generally this is the job of the actual processing machine. Where a process is divided into various steps, drive units may be integrated upstream and downstream from the process. Dividing the process into several steps also helps to reduce process stress.

Drive units are feeding devices which clamp the material to be pulled or pushed between two or more pairs of rolls or caterpillars, using motor power to apply a tensile force. Any type of controlled or uncontrolled motor may be used according to the application. The contact force of the drive rolls or caterpillars is applied pneumatically, hydraulically, by electric motor, or manually. The level of contact force depends on the tensile force needed to move the material by frictional locking. On the one hand it must be selected high enough to move the material without slippage. On the other hand it must not be too high in order to prevent plastic deformations and surface damage.

Drive rolls are generally made of hardened steel, although other materials such as plastic, Vulkollan(r) or the like are possible. Roll profiling depends on the geometrical shapes of the materials to be transported.

Users are also free to specify any V-belt coating from the range on offer.

Different drive units have been developed for various areas of application: 

  • one driven pair of rolls with unilateral bearing  NA
  • one driven pair of rolls with bilateral bearing NAB
  • two driven pairs of rolls with unilateral bearing NAD,NADV
  • two driven pairs of rolls with bilateral bearing  NADB
  • two drive belts with unilateral bearing NAK

Drive units are easily combined with other components, e.g. straighteners, roll-type guides, hydraulic units and pneumatic units. The resulting machine modules support existing production lines.