Semi-automatic straightening

  • basic automation
  • control system
  • PLC
  • positioning control system
  • positioning
  • semi-automatic straightener. semi-automatic straightening
  • semi-automation

Semi-automatic straightening is straightening with the use of offline and online data, basic automation equipment and at least one straightener. The offline and online data is relayed via the basic automation equipment to the straightener in order to achieve a defined and highly exact adjustment of the straightening rolls. A semi-automatic straightening system enables the reproducible adjustment of roller positions at any time.

The advantages of a semi-automatic straightener over a straightener with conventional roll adjustment are:

  • defined fine adjustment of the individual straightening rolls,
  • reproducibility of straightening roller positions within close tolerances,
  • application of high adjustment forces,
  • operation of the roll adjustment system from any location,
  • use of process data (data bases),
  • integration in a central control environment.


  • forecasting
  • identification
  • model
  • offline
  • online
  • pre-calculation
  • pre-determination
  • process data
  • process simulation
  • relative curvature
  • simulation program
  • Simulation
  • simulation calculation

Simulation is the representation of specific interesting properties of a system by the actions of a different system. By copying the behavior of a system in a simulation program it is possible to study behavioral characteristics or to examine variants. Simulation can be used at low cost and with little risk to identify behavioral patterns in time-consuming, costly, uncertain and hazardous processes.

With a simulation of the wire straightening process it is possible to pre-calculate the positions of the straightening rolls needed to prcduce a defined final curvature while taking due account of the parameters of the straightener (number of rolls, external roll diameter, roll pitch, groove width, groove angle) and of the wire (cross sectional geometry, elongation limit, modulus of elasticity, modulus of hardening, initial curvature, etc.). The simulation is based on a model of the elastic-plastic material characteristic under alternate bending and on the relationship between bending moment and curvature. Simulation of the wire straightening process also supplies data which can be used to determine the process forces.


  • drive unit
  • feeding speed
  • processing speed
  • pull-off speed
  • speed
  • straightening speed

In the forming processes employed in the wire producing and wire processing industry it is normal for the process material or workpiece to move relative to the tooling. Forming speed is one of the variables which characterize a forming process. It is derived from the degree of forming as a function of time.

Exemplary straightening tests conducted at different speeds of the process have proven that the final curvature and other parameters of the straightening process do not change significantly in the speed range up to approximately 10 m/s. At speeds above this limit, an identical adjustment of the straightening rolls results in a different deformation.


  • spool
  • spool diameter
  • Transport

Spools are used for the safe transportation of endless material. The material is wound onto the spool layer by layer so that it is difficult for individual windings to slip. Spools have a minimal (inner) and a maximal (outer) diameter. This has two important consequences: a difference in speed and a difference in curvatures.

Status quo

  • adjustment
  • caliber
  • measuring instrument
  • Status quo
  • testing

Latin for "the existing state".
To be able to design a straightening process in a defined manner it is first vital to identify the status quo as the starting point for producing the necessary change of state with the bending operations and tools available. For a reproducible straightening process it is essential, for example, to document the positions of the system's straightening rolls relative to the process material. This data can then be used at any time to produce specific straightening results under identical framework conditions.

Straightened material

  • binding wire
  • cable
  • composite wire
  • enameled wire
  • fine wire
  • flat wire
  • iron wire
  • mesh wire
  • packing wire
  • profiled wire
  • rectangular wire
  • reinforced concrete steel
  • rope
  • split strip
  • spring wire
  • stand
  • steel wire
  • straightened product
  • straightened material
  • strip
  • tie wire
  • tube
  • winding wire
  • wire fabric
  • wire mesh
  • wire rod
  • wire rope
  • wire

Straightened material is a workpiece whose properties have been changed by the straightening process. Its most important property is straightness or final curvature. Other properties, apart from straightness, changed by the straightening process include the material's internal stress condition.

A straightened material can be endless or finite. Rails and sheets are examples of finite straightened material. Wire, cable and rope are endless straightened material.

Straightened material parameter

  • diameter
  • dimension
  • initial curvature
  • material cross section
  • material
  • nominal diameter
  • nominal strength
  • straightened material analysis
  • straightened material cross section
  • straightened material parameter
  • wire analysis
  • wire characteristics
  • wire cross section
  • wire diameter
  • wire parameters

Straightened material parameters describe the characteristics of the straightened material. They can be classified in three groups:

  • Parameters of the material
  • Parameters of the cross sectional geometry
  • Parameters of the initial curvature

The straightened material parameters have an influence on the type, design and size of:

  • Straighteners and straightening systems
  • Drive units
  • Guides
  • Preforming heads
  • Postforming apparatus


  • accessories
  • adjusting spindle
  • adjusting screw
  • clamping lever
  • dial gauge
  • guide block
  • handwheel
  • height-adjustable guide roll
  • micrometer screw
  • straightener/accessories

The range of accessories available for a straightener or straightenrng system can be classified according to

  • application, size and surroundings,
  • safety and operating reliability
  • handling and use,
  • design,
  • maintenance.

For each of these categories WITELS-ALBERT offers a large selection of elements and devices which are well described in the company's documentation.

The handling of a straightener, for example, largely depends on the technical elements provided to position the straightening rolls. In addition to the conventional roller positioning method using an adjusting screw it is possible to use a micrometer screw, an adjusting spindle with knurled edge, or an actuator (hydraulic cylinder, pneumatic cylinder, stepping motor or servo motor). 


  • set-up
  • straightener/set-up

Rather than describe the straightener as a tool and its function, we want to draw attention here to its precise and modular design.

The “A” parts of a straightener's design, i.e. its basic load-bearing elements, are adapted in size to the number of rolls to be accommodated and serve as mounts for the “B” parts such as rails, grooved blocks, threaded bolts, pins and other standard parts.

The final block of this modular design are the straightening rolls. They are also the parts exposed to the greatest wear.

An approach based on the ideas of environmental management gives rise to a product and production engineering of outstanding accuracy, impressive ruggedness and durability, and
unique operability and results.

Straightening plane

  • curvature plane
  • plane
  • straightening planes

The commonly held idea that the position of a straightener's body corresponds to the straightening plane is wrong.

Basically, the straightening plane is defined by the axial position of the straightening rolls. If this is horizontal, then the straightening plane is horizontal. The same applies to the curvature plane in which the product to be straightened is fed in or bent.

With a vertical axis we speak of a vertical straightening and curvature plane.

The most frequently used arrangement is the double straightener, which eliminates the initial curvatures in two planes (horizontal/vertical).

You may well ask what happens with the other curvature planes lying outside the two straightening planes? Their processing is possible at best on a random and sporadic basis or not at all.

Hence it is important when producing wire to maintain a constant curvature course and not to leave the curvature plane.

A constant straightening plane can only produce constant final curvatures from constant curvatures in the same plane.

Where this is impossible for whatever reason, the use of killing-straightener, and helix straighteners in straightening systems can prove very useful.

Straightening process set-up

  • analysis of the straightening process
  • paying off during straightening
  • selecting a straightener
  • straightening process set-up
  • technology

A correct straightening process set-up depends on an analysis of the product to be straightened, an analysis of the straightened material production process, and an analysis of the final product. A specific procedure has to be followed in order to choose the correct straightening system, the correct number of straightening rolls, and the correct location of the one or more straighteners.

The purpose in setting up a straightening process is to determine the status quo from the essential analyses and to define the production steps and corresponding equipment needed to obtain the final product. Using our knowledge of the process we can create constant process transitions, i.e. output and input parameters, in order to produce constant final results.

Constant and reproducible straightening roll settings based on the constant input parameters known to us at the beginning of the straightening process result in a constant final curvature.

If all these aspects are duly considered, the straightener will provide optimal processing conditions for obtaining a final product of the required quality.

Straightening roll

  • ball bearing
  • bearing
  • cam roll
  • dust seal
  • grease lubrication
  • grooved roll
  • life-time lubrication
  • lip seal
  • miniature bearing
  • radial ball bearing
  • roll
  • rolling bearing
  • seal
  • straightening roll
  • straightening cylinder
  • track roller

A straightening roll is the last link in a straightener's modular design chain and the component exposed to the greatest wear. Its design, production and use thus deserves special attention.

The following criteria are particularly important:

A) Materials
The raceway of a straightening roll is subjected during roll-over to local loads which find
expression in high Hertzian surface pressures. The raceway material should be selected so that
ideally through-hardening but at least the necessary depth of hardness and a surface hardness
of 670-840 HV is achieved. The material normally used is through-hardening steel according to
DIN 17230, e.g. 100 Cr 6.

B) Bearing arrangement design
The bearing arrangement for a straightening roll is that of a locating bearing. The shaft or pin end provides radial support as well as axial guidance. Radial bearings able to absorb combined loads, e.g. radial ball bearings, angular contact ball bearings or track rollers, are suitable for use as straightening rolls. To enable the bearing's load capacity to be used to the full, the cylindrical contact faces need to be firmly and uniformly supported over their entire circumference and across the full width of the raceway. Perfect radial mounting is also vital.

C) Dynamic/static load rating
A straightening roll's dynamic load capacity depends on the fatigue behavior of its material. Fatigue time is an expression of useful life and depends on the straightening roll's loading and speed as well as on the statistical probability and random timing of the first incident of damage. Static load capacity, on the other hand, is limited by the plastic deformations produced in the raceways and rolling elements by a high resting load.

D) Bearing capacity and life-time
The size of bearing required for a specific straightening process depends firstly on the straightening range of the straightening roll. A further factor, however, is the magnitude of loading. This is expressed by the dynamic load rating C and the static load rating Co. A straightening roll's useful life is defined as the number of rotations made by its bearing before the first signs of material fatigue are noted on a raceway or rolling element.

E) Friction, speeds, and temperature
A straightening roll's frictional moment depends on many factors such as load, speed, condition of lubrication and seal friction. The maximum possible speed of a straightening roll is mainly defined by the permissible operating temperature of the rolling bearing. In other words, speed depends on the type of load, the conditions of lubrication and the conditions of cooling. A straightening roll temperature of 70°C is considered normal.

F) Dimensional, geometrical and bearing tolerances
A straightening roll's dimensional, geometrical and bearing tolerances comply with tolerance class PN conforming to DIN 620.

G) Installation and dismantling
The smooth and troublefree operation of Witels straightening rolls largely depends on the care with which they are installed and replaced. Inner rings have to be mounted on the shaft or pin so that the mounting force is evenly distributed over the front face of the inner ring. The mounting force must not be transferred to the rolling elements.

H) Lubrication, maintenance and corrosion protection
For straightening rolls to perform reliably they require sufficient lubrication to prevent direct metallic contact between the rolling elements, raceways and cage while at the same time reducing wear and protecting surfaces from corrosion. All straightening rolls are supplied with grease lubrication as standard.

J) Storage of straightening rolls
Although Witels straightening rolls are always delivered with life-time lubrication, they cannot be stored indefinitely. Under certain circumstances a straightening roll kept in storage for a long period may initially display higher frictional moments than one fresh from the factory. Nor is it possible to rule out deterioration or even gumming of the grease charge in the course of prolonged storage. Attention is drawn in this connection to the WlCAS cassette system, which finds use mainly in problematic applications for straightening rolls.

Straightening roll groove

  • angular groove
  • effective diameter
  • groove geometry
  • groove
  • notch
  • prism
  • profiling
  • slot
  • straightening roll groove

The profile cut into the outer ring of a straightening roll is called the straightening roll groove. Its purpose is to accommodate and guide the product to be straightened.

Angular grooves of 90°, 100° or 110° are normal for round, solid material. They are particularly advantageous for straightening ranges, i.e. wire of different diameters.

Profiled, soft or tubular material, on the other hand, is straightened in grooves which are adapted to the material to be straightened to produce a non-slip fit. Smooth, unprofiled rolls are used to flatten strip material.

Straightening roll life-time

  • durability of straightening rolls
  • life expectance
  • load rating
  • straightening roll life-time

The dynamic load capacity of a straightening roll depends on its material fatigue characteristics and wear. Useful life depends on the straightening roll's loading, speed, conditions of lubrication, soiling, installation and temperature, the statistical probability of the first incidence of damage, and diverse other factors. All too often the impact of dirt is underestimated.

The load capacity and useful life of straightening rolls from Witels are determined by the methods customary in rolling bearing practice. At the same time allowance is made for the fact that the outer ring undergoes elastic deformation through contact with the product to be straightened. Compared to a rolling bearing supported in a housing bore, there is a different distribution of load in the bearing and bending stress in the outer ring. We differentiate between internal and external factors with an influence on wear.

Contact between the product to be straightened and the outer ring results in the following external factors:

  • material of the outer ring
  • material and surface consistency of the product to be straightened
  • speed
  • slip
  • soiling and lubrication

Internal factors with an influence on straightening roll wear are:

  • lubrication of the bearing
  • type of bearing
  • dynamic and static bearing load
  • speed
  • seal arrangement
  • elastic deformation

Straightening system

  • combination of straighteners
  • helix straightener
  • straightening system
  • wire straightening system

A straightening system is understood to be a combination of straighteners which, duly adapted to the product to be straightened, transform difficult and sometimes alternating initial material parameters into constant values.

The constant process transition thus obtained is essential for designing controlled follow-up processes.

The simplest straightening system generally consists of two individual straighteners arranged in different planes and mounted using a connecting bracket. Acceptable, constant results are achieved in many applications using a simple straightening system of this type.

If the initial parameters of the product to be straightened change during the process and if, for example, curvature fluctuations or helicities arise, then it will be necessary to use problem-related tools and jigs such as helix straighteners, killing-straighteners, etc.

A straightening system set-up consists accordingly of a clearly structured straightening process sequence. Fluctuating initial parameters require greater structuring of the straightening process to achieve a defined and constant final curvature. Simply increasing the number of straightening rolls would have little effect in this case.

The first priority is to transform changing curvatures in different planes into a constant curvature in a single plane. This is the essence of a successful straightening process with constant final curvatures.


  • alternate bending
  • bending
  • dressing
  • make straight
  • pressing
  • straightening
  • wire straightening

The term “straightening” covers the actions and measures needed to eliminate process-induced curvatures in the process material in order to produce a condition of straightness, levelness or defined curvature


  • straightening
  • stretch-bend-straightening

The term “stretch-bend-straightening” is understood to be the bending of a material around rolls of small diameter with the simultaneous application of tensile stresses. Local plastic elongation occurs in those areas where bending tensile stresses are added to tensile stresses. Upsetting can occur, on the other hand, where the bending compressive stresses superimpose on the tensile stresses. However, the biggest part of the material's cross section is subjected to a tensile load. If such a process is performed by alternate bending, the product is stretched in steps, producing a final curvature in wire material and a flatness profile in strip material.

A stretch-bend-straightening system generally consists of an infeed unit for producing a reverse tension, a straightening unit for the bending or alternate bending, and an outfeed unit for applying a forward tension. For the purpose of straightening wire, the infeed unit can be e.g. a killing-straightener and the outfeed unit can be a drive unit. The straightening unit is either a conventional straightening system, a semi-automatic straightening system or a straightening system with an automatic roll positioner.


  • straightening
  • stretching
  • stretch-straightening
  • tensile straightening

In the stretch-straightening process the product to be straightened is subjected to a tensile force. This results in a tensile stress inside the workpiece, which superimposes on the existing internal stresses.

The tensile force is applied in sections and at a level of magnitude designed to produce plastic deformations in the material to be straightened.

Stretching limit

  • beginning of flow
  • elongation limit
  • flow limit
  • proportionality limit
  • strength
  • stretching limit
  • technical stretching limit

The stretching limit is a characteristic material parameter which can be determined in a tensile test. It is the stress defined as the internal force of resistance per unit of area perpendicular to the direction of load application with which a material reacts to an external tensile load of specific magnitude. At the stretching limit the deformation of the workpiece or the elongation of the tensile specimen due to the external tensile load continues to increase although the inner resistance remains constant or even decreases.

For process materials in the wire industry, where the materials used are preferable drawn wires, it is typical for the resistance to the load not to decrease at the stretching limit. Hence the stretching limit cannot be identified in the stress/strain diagram. DIN EN 10 002, the tensile test guideline for metallic materials, thus recommends determining an elongation limit at a non-proportional strain. Accordingly it is no longer the stretching limit, which is determined for drawn materials in the wire industry, but the elongation limit at a non-proportional strain of 0.2%. This is also referred to as the technical elongation limit.

The stretching limit or elongation limit at a non-proportional strain is a value used in the simulation of the WITELS-ALBERT wire straightening process for calculating the adjustments required to achieve a defined final curvature.


  • actual adjustment values
  • actual adjustment
  • adjustment value
  • elastic deformations of the straighteners
  • welling
  • way of adjustment

The loading of a body by mechanical variables (forces, moments) produces stresses in the body, causing the body to deform in accordance with its material characteristics. The magnitude of the load decides whether this deformation takes place in the elastic or plastic zone.

Swelling is understood to be an elastic deformation which is reverted when the external load is removed. It consists of strains, compressions and bends. Every straightener and every straightening machine swells under the action of the straightening forces. It is a characteristic of straighteners, therefore, that the adjustment of their straightening rolls becomes smaller and the straightening gap larger, leading to changing results.

Each straightener has its own force/swelling characteristic, meaning its own specific deformation behavior. This characteristic has to be determined for the straightener in question if constant straightening results are to be achieved regardless of swelling.