- adjustment angle
- adjustment philosophy
- defined straightening
- distance between straightening rolls
- exponential adjustment
- individual adjustment
- roll adjustment
- roll setting
- setting of the straightening rolls
- straightening conicity
- straightening roller positions
- straightening gap
- straightening angle
- type of adjustment
- wedge adjustment
For the characteristics of a material to be changed by alternating forming on a straightener, the straightening rolls have to be adjusted relative to each other. This adjustment is understood to be the absolute position of a straightening roll relative to a specific zero line. Technologically there are various ways of making such adjustments. Rail adjustment and individual adjustment are two relevant options. With the rail adjustment method, a least one row of rolls is fastened to a rail which can be positioned by rotation and translation. Being able to rotate the rail the operator can obtain various pitches between the straightener's rolls according to the angle of rotation. With the individual adjustment method it is possible to position each single roll. Commonly used types of straighteners include those with one row of fixed rolls while the other rows can be individually adjusted, and those on which all the rolls can be separately positioned. The highest degree of roll adjustment freedom exists, of course, when all the rolls of a straightener can be individually adjusted. In this case it is possible, for example, to change the initial curvature exponentially to the final curvature.
For the effective changing of initial curvatures in the initial curve zone it is recommended to select large adjustments in the front - pre-bending - section of the straightener. This results in a maximal curvature which is then reduced to the required final curvature by alternating forming in the follow-up straightening section using smaller adjustments.
Analysis of straightened material production
- analysis of straightened material production
- straightened material production process
A correct straightening process set-up depends on an analysis of the straightened material production process as well as on an analysis of the product to be straightened and an analysis of the final product.
A product's material characteristics are constantly affected from the production of the original material, e.g. its melting, to the final processing operation. The history of these effects adds up to the material's memory.
Each individual process creates stresses in the product. Incorrect handling of the product to be straightened has a negative impact on the constantly changing state of internal stress, whereas its correct handling helps to prevent additional stress factors, keeping the internal stress conditions practically constant throughout the processing.
The stress factors active during the production of a straightened material can be divided into “avoidable” and “unavoidable” stresses. Needless to say, it is far easier to design a constant straightening process and thus achieve continuously better straightening results and hence final products of reproducible quality if steps are taken to prevent the avoidable stresses.
Processes with unavoidable stress factors should be followed as directly as possible by corrective measures in order to reduce or neutralise the stresses. If not, the stresses will be increased by a multiple.
The only way to obtain constant conditions of internal stress is with selective corrective measures. Uniform directions of rotation and defined deflections with unchanged curvature courses ultimately lead to constant input parameters for the resulting controlled straightening process.
Analysis of the final product
- analysis of the final product
A correct straightening process set-up depends on an analysis of the final product as well as on an analysis of the material to be straightened and an analysis of the straightened material production process.
A final product's characteristics are defined above all by its specified tolerance fields, i.e. final curvature, final helicity, stretching limit and tensile strength. These are supplemented by quality features which result from the mechanical and physical requirements imposed on the final product. It is essential, therefore, for the straightened product to fulfil these preconditions and to display these quality features.
The objective of a final product's quality features must be to meet realistic requirements. Its tolerances should not be set any closer than is justified, nor should they be subordinated to process-oriented targets. Quality-oriented and environment-friendly production is likewise an important basis of any sensible improvements. Energy consumption has an important role to play in this connection.
Quality enhancement takes on special significance in economic terms, too.
Analysis of the product to be straightened
- analysis of the product to be straightened
- analysis of the material to be straightened
A correct straightening process set-up depends on an analysis of the product to be straightened as well as on an analysis of the straightened material production process and an analysis of the final product.
In an analysis of the product to be straightened conducted in connection with setting up the correct straightening process, efforts are first concentrated on recording the product's geometrical parameters, regardless of the material parameters which need to be determined.
Basically speaking, the product remains in constant directions and zones of curvature during the most diverse process transitions in the course of its production. It is important to scan and measure these parameters:
- Constant curvature on one plane
- Curvature zone on only one curvature plane
- Curvature zone with a pronounced increasing or decreasing radial offset on only one curvature plane
- Constant curvature and or curvature zone on the same or different curvature planes (helicities)
Case 1 provides good conditions for a constant follow-up process. All the other cases require a more elaborate follow-up process with what are sometimes less constant results. Each non-constant process input will give rise to different outputs, no matter how elaborate the applied corrective measures are.
The use of so-called helix straighteners or killing-straighteners can exert only a limited effect on the quality of the final product.
An analysis of the product to be straightened should include a definition of the straightened material parameter.
Automatic roll positioner
- adjusting tool
- automatic roll positioner
- computerized tool
- electronic positioner
- roll positioner
- straightening positioner
- straightening roller positioner
The automatic roll positioner for the individual positioning of at least one straightening roll is an innovation combining well-known conventional and semi-automated straightening technology from WITELS-ALBERT. The high effort required with semi-automated systems is reduced by using just a single actuator with a corresponding sensor to position several rolls. It also makes no difference whether the rolls are on one and the same straightener or straightening system or on different straighteners or systems.
The use of a single intelligent tool to perform the roll adjustment functions flexibly on numerous systems, including those of different types, has resulted in a new category of wire straightening. With the automatic roll positioner it is possible to position straightening rolls objectively, exactly, reproducibly, flexibly and cost-effectively. Information about the materials in contact with the rolls and about the boundary and ambient conditions of the rolls themselves is taken into account for the positioning. Adjustments have to be specified. Data on positions, roll identification and the actual process are automatically scanned, saved, documented, visualized and made available to higher-order systems.
- automatic straightening unit
- defined straightening
- intelligent straightener
- verified straightening
We understand the automation of straightening to be the use of offline and online data, a basic automation system, at least one straightener, a geometry operator, a stretching limit operator and an adjustment operator. Information flow takes place in a loop using all the previously mentioned elements and is aimed at the automatic positioning of the straightening rolls with due consideration of the production, product and process data identified online and of the technology, equipment, product and quality data determined offline. Automatic straightening permits a straightened product to be manufactured in the quality required, regardless of any fluctuations in diameter and stretching limit over the length of the material to be straightened.
- alternate bending
- alternating loading
- Bauschinger effect
- Bauschinger modulus
- Bauschinger parameter
- Bauschinger strain
- primary loading
- secondary loading
The Bauschinger effect is a special case of forming behavior among metals. It is defined as a change of material parameters due to a reversal of loading direction between two consecutive loads (e.g. tension/compression). Because of the Bauschinger effect, loading against the initial loading direction results in a distinctly lower beginning of flow (stretching limit, elongation limit). Alternating tension-compression loads result accordingly in a shift of the flow limit. The reasons are to be found in a change of the material's microstructure. Factors affecting the magnitude of the Bauschinger effect include the material, its alloying elements (particularly carbon), the number of load cycles, and the dimensions of external deformation (actual strains).
A bend is the strain produced in long and endless bodies by external forces, resulting in internal bending moments over their cross sections. The original straightness or curvature of the bodies is changed either elastically or plastically as the result. The internal bending moments arising in every cross section as a reaction to these external bending moments lead to tensile and compressive forces, resulting in an equilibrium of forces and moments.
Bodies subjected to bending are shortened on the one side by compressive stresses while on the other side they are lengthened by tensile forces. There is a (practically Iinear) continuous transition from tensile stress to compressive stress over the cross section, with a neutral fiber that is neither stretched nor compressed and therefore stress-free.
The diagram opposite shows a wire cross section with an applied external bending moment and the resultant strain and stress characteristic.
- active-bending roll
- bending roll
A bendlng roll is a rotating roll (pulley) on which the product to be straightened is plastically deformed during a partial or complete wrap. The important point is that the product should only be bent in the direction of its initial curvature. In other words: the initial curvature, the bend and the final curvature should all lie in one plane. A change of plane along this course of curvature and bending during the straightening process will cause helicities (twisting of the product to be straightened).
Subjecting the curvature to several changes of plane has a particularly negative effect. It leads not only to curvature fluctuations, which are very difficult to eliminate, but also to extremely disadvantageous right/left helicities.
The magnitude of plastic deformation suffered by the product to be straightened depends e.g. on its material parameters and on the diameter of the bending roll.
- caliber gauge
- measuring wire
A caliber is a measuring instrument used as a gauge. In steel mills, gauges are used to determine the rolling gap. On straightening units, calibers are used to fix the distance between the straightening rolls.
When a caliber is placed between the open straightening rolls of a straightener, all the adjustable straightening rolls can be aligned on one line. The straightening rolls of the one row are thus parallel to the straightening rolls of the second row. It is then possible to set the zero line for the particular product to be straightened. The adjustable rolls are adjusted by an amount equal to the difference between the thickness of the caliber and the thickness of the product to be straightened. It should be note that the adjusting travel is also affected by the geometry of the product to be straightened and the geometry of the groove. Adjustment positions are reproducible at any time.
- alloy component
- carbon content
- image of microstructure
- steel wire
The carbon content of a steel wire is crucial for many of its properties. The higher the carbon content, the greater the tensile strength but the smaller the elongation to fracture. Wire with a very low carbon content is referred to as iron wire. Its tensile strength is low. Wire made of spring steel generally has a high carbon content of between 0.4 and 1.0%, resulting in high tensile strength values.
- cassette technique
- straightening roll
WICAS® - WITELS CASSETTE STRAIGHTENING SYSTEM
The rolling elements mainly used in straightening processes with roll-type straighteners suffer extreme wear as the result of the high roll adjusting forces and ever higher production speeds. At the same time, metal particles contaminate the bearings and contribute likewise to a drastic shortening of rolling element life. The WITELS Cassette Straightening System called WICAS(r) was developed specifically to improve this situation.
Notable features of WICAS®:
A) Expert installation of the rolling elements in a closed housing with an additional labyrinth seal prevents practically all soiling of the bearing system, resulting in a useful life up to 30 times longer than that of a conventional straightening roll.
B) The straightening sheave can now be produced in any form, type, quality and strength irrespective of the material used for the bearing system. Oval pressing of the rolling element outer ring, against which the product to be straightened runs, is ruled out with this design.
C) The use of smaller rolling bearings at high speeds of rotation increases the peripheral speed of the larger straightening sheave. Far higher production speeds are thus possible than with conventional straightening rolls.
D) In the case of miniature straightening rolls, cutting the groove in the relatively thin outer rings weakens the straightening roll to an unacceptable degree. This does not happen with WICAS(r) because the bearing shaft as well as the straightening sheave can be made with annular grooves of any shape and size.
E) Flexible use of needle and ball bearings gives the designer considerable scope with regards to the static and dynamic bearing values.
F) It is possible to use bearings with life-time lubrication as well as systems designed for relubrication.
The above-mentioned 30-fold longer useful life of WICAS(r) compared to conventional straightening rolls greatly minimizes the cost-intensive stoppage of individual machines and complete production lines - a benefit that should not be overlooked.
Causes of stress
- bending stress
- internal stresses
- origin of stress
- stress analysis
- tensile stress
- torsional stress
Stress is the reaction of a material/workpiece to an external load. It is defined as an internal force of resistance per unit of area. There is a fundamental correlation between the condition of stress and the condition of deformation of a workpiece. A plastic deformation produces internal stresses in a workpiece which remain after the load is removed. Stresses arising during loading of such a plastically deformed workpiece are superimposed on these internal stresses. The type of stress produced during loading is characterized by the type of load. Tensile forces (drawing, coiling) result in tensile stresses while bending forces (deflecting, straightening) result in bending stresses.
- wire coil
- wire ring
For logistical reasons, products to be straightened (wire, strip, rope, etc.) are wound into coils. This entails laying the product, winding for winding, in the direction of the coil axis. If the coil is not rotated simultaneously during the laying, helicities will be produced with each winding. The product will then behave accordingly when it is pulled off. Pulling off the product statically in the direction of the coil axis will cause it to twist and the quality of the straightened product will be negatively affected by additional helicities. These curvature fluctuations and helicities are difficult to eliminate and are therefore best avoided in the first place.
The beginning and end of a coil should always be marked in order to ensure its careful and correct further processing. Constriction-free securing of the ends prevents snap-back and avoids kinks.
- unwinding technique
- wire coiler
A coiler is a device for the winding or unwinding of a lengthy process material.
In direct or indirect interaction with other components it is also used to create tensile stress.
Important technological sub-functions such as guiding the process material are likewise performed by a coiler.
- coil curvature
- coil winding
- deviation from the straight
- free wire bypass
- spool curvature
- wire bend
- wire curvature
Curvature is understood to be a deviation from the straight.
When an endless material is wound onto a spool, the inner layers have a smaller radius of curvature and the outer layers a larger radius of curvature.
Whether or not a winding is elastic or plastic depends on the spool geometry, the properties of the endless material, and the degree of deformation.
Curvature is the reciprocal of the radius of curvature and has the dimension [1/mm].
Curvature course during straightening
- adjustment induced curvature
- bending up
- change of direction
- curvature course during straightening
- opposite direction
- reduction of curvature
- straightening triangle
The curvature course during straightening is understood to be the correct sequence of curvatures followed by the process material during the straightening process.
The initial curvature is always followed by the counter-curvature. The final curvature is the curvature remaining after spring back. This curvature sequence is repeated according to the number of straightening rolls.
A straightening process should be arranged so that, irrespective of the initial curvature, the last adjustment-induced curvature resulting after the last spring back in a final curvature corresponds to the desired straightening result.
- 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.
- bending radius
- change of direction
- defined deflection
- deflecting roll radius
- deflecting roll
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.
- arc height
- arrow height
- 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.
- advancing mechanism
- caterpillar pull-off
- drive unit
- driver stand
- feeding device
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.
- deviation from the straight
- find curvature
- level condition
- out of straightness
- permissible deviation
- quality criterion
- run-out curvature
- spring back
- straight-axis condition
- wire bend
- wire curvature
The result of a straightening process is expressed e.g. by the final curvature of the product to be straightened. Basically there can be two objectives: to create a straight product, i.e. a final curvature of zero within the set tolerances, or to produce a defined final curvature other than zero. Which of these two objectives applies will largely depend on the process which follows the straightening.
To guarantee final products of constant positive quality it is important to produce a final curvature that is as constant as possible. A changing final curvature goes hand in hand with varying process transitions and ultimately leads to final products of fluctuating quality.
- frictional coefficient
- frictional force
External friction is the inhibition of relative movement between touching bodies. In the case of solid bodies, friction is mainly based on microscopic unevenness. The frictional values of different materials relative to each requires special attention in this connection. Internal friction is the friction between parts of the same body. In liquids this friction is called viscosity.
During the straightening process, friction occurs mainly in the straightening rolls. It consists of the following components, which together add up to the total running resistance: rolling and sliding friction of the rolling elements and cages relative to each other, lubricant friction and seal friction. The aim must be to keep the friction as low as possible by ensuring an acceptable bearing load and optimal lubrication.
Friction leads to “losses”, i.e. kinetic energy is converted into frictional energy. This energy fraction is therefore no longer available for use in the production process.
- axial deflection
- axial offset. helical
- torsional stress
Helicity, also commonly referred to as torsion or twisting, is understood to be a curvature course adopted by wire radially rather than axially upon leaving the curvature plane. Such a curvature course can be intentional, as in the production of rope and cable where it is called the lay length, and in the production of springs where it is called the pitch.
Helicity is an undesirable condition for all follow-up processes if it is not specifically created for the product but arises unintentionally due to certain production factors. Frequent causes of helicity include overhead pulling off, static unwinding and unspooling, incorrect deflecting, frequent changes of direction, and any faulty process transitions with a negative effect on round material which rotates during processing.
Inconstant or indeed alternating helicities not only impede the process flow but also rule out final products of any required constancy.
Aids such as helix straighteners, killing-straighteners and additional straightening systems can go a long way in solving the problem. Above all, however, it is important to avoid the avoidable and to create a constant process.
- height-adjustable straightening roll
- helix straightening
A wire wound into a coil or onto a spool should have only one curvature - that of the spool or coil - in one plane if the follow-up process is to proceed without difficulty. Changing preliminary processes with sometimes inconstant process transitions create helicities, i.e. twisting, in the wire.
Helicities need to be avoided or, where constant helicities are concerned, eliminated by means of a helix straightener. A helix straightener can produce as well as remove helicities.
Like a standard straightener, a helix straightener has several straightening rolls which are partly or fully arranged in familiar manner so that they can be adjusted relative to each other.
In addition to this, one or more straightening rolls can be adjusted in height. The groove of the height-adjusted straightening roll thus forces the wire unilaterally from its zero line, bending it with unequal flank pressure into a second curvature plane. Helicities are thus removed or created by force-feeding the wire through these adjustable positions.
- 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 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.
- killing straightener
A wire with fluctuating initial parameters, e.g. fluctuating material parameters, initial curvature and alternating internal stresses, will be left with varying final curvatures after straightening. The wire is therefore “killed” by severe bending with straightening rolls in at least one plane in order to produce a final curvature in a single plane.
This “killing” is performed by special straighteners of type TR and TRV. Through the application of severe alternating bends with small bending radii the curvature fluctuations are reduced and the wire's internal stresses changed.
If a TR or TRV straightener is used in combination with a conventional straightening system, a semi-automatic straightening system, or a straightening system with an automatic roll positioner, then the straightening result will be affected by the resulting reverse tension.
- bearing load
- life-time equation
- load rating
The more precisely the operating conditions of a straightening roll are known or can be calculated, the more exactly and reliably its useful life can be determined.
Three different equations are available: for nominal life-time according to ISO, for modified nominal life according to ISO, and for modified nominal life-time based on a new life theory.
The simplest approach is to determine the nominal life-time according to ISO using the relevant equation.
Calculation of the nominal life-time using the equation is sufficient for conventional bearing applications.
In other applications it may be wise to take detailed account of other life-affecting factors as well. This led in 1977 to the introduction of the modified life-time equations.
In a third equation - modified nominal life-time according to the new SKF life theory - a life-time coefficient is added to take account of a fatigue load limit and various other factors affecting the lubricating conditions and the degree of soiling.
The life-time value calculated with the third equation is regarded as the period of use actually covered by a straightening roll in its life-time. As a rule this value deviates slightly from the calculated nominal life-time.
Location of the straightener
- arrangement of straighteners
- choosing a location
- distance to the straightener
- location of the straightener
- placement of straighteners
The distance between the straightener and the pay-off or final deflection of the product to be straightened has a major effect on the straightening result. A distance of A £ d p, where d is twice the initial curvature radius or the diameter of the last deflecting roll, guarantees that the initial curvatures will be effectively changed by the straightening process and that the product to be straightened will leave the straightening system with the required final curvature and enter the follow-up machine in a defined condition.
If this distance is exceeded there is a real risk of the product - still under the influence of its initial curvature - turning and twisting before it enters the straightener so that its forming takes place neither constantly nor in the plane of curvature requiring straightening.
- characteristics of the material to be straightened
- material characteristics
- material parameters
- material quality
- wire characteristics
Mechanical material characteristics describe a process material and largely determine its forming behavior. The modulus of elasticity, elongation or stretching limit, modulus of hardening, carbon content and the parameters of alternating forming used to derive the Bauschinger effect are the most important characteristics in connection with elastic-plastic cold forming.
Material model/material behavior
- material model/material behavior
With a material model based on mathematical and physical laws it is possible to produce a virtual image of a process material's behavior. Creation and development of the model are accompanied by tests aimed at its verification. A material model can be used, for example, to forecast the stresses arising in the process material in reaction to an applied forming force of a specific magnitude. A material model is essential for the simulation of processes such as the straightening process.
Mechanical model / straightening
- end-fixed beam
- mechanical substitute system
- mechanical model / straightening
- straightening triangle
- straightening force
For considerations and calculations concerning the product to be straightened it is an advantage to set up a mechanical model (a level substitute model) of the real straightening process. It is then possible to make (simplified) calculations and predictions.
The definition of straightening refers to three straightening rolls as a straightening triangle. The product to be straightened can be idealized as an end-fixed beam. In addition to the forces applied, bending moments (clamping moments M) are transmitted via both supports. As these forces and moments are not equal to zero, the result is a three-component statically indeterminate system. Mechanical variables are a central force (corresponding to the straightening force), two vertical supporting forces (FV), two horizontal longitudinal forces (FH) and two clamping moments. The product to be straightened bends as the result of the applied straightening force (FR).
Modulus of elasticity
- elastic characteristics
- elastic limit
- elastic straight line
- Hooke's straight line
- modulus of elasticity
The modulus of elasticity is a characteristic material parameter determined from the data collected in a tensile test. From the beginning of the tensile up to a specific load, steel deforms elastically, i.e. its length changes proportionally to the load. This proportionality is known as Hooke's law, and in connection with the stress-strain diagram we talk about Hooke's straight line or the elastic straight line. If the load is removed after purely elastic loading of the material or tensile test-piece, the Iatter will readopt its original shape.
The modulus of elasticity varies in size from material to material, but it is also dependent on the material's processing condition and production process. While hot-rolled steels generally have a modulus of elasticity of 210,000 MPa, this value is never reached by drawn wire.
Drawing speeds, cross sectional reductions and other factors have a major impact on the modulus of elasticity of steel wires.
Number of straightening rolls
- minimum number of straightening rolls
- number of rolls
- number of straightening rolls
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”.
- axis position
- coil axis
- horizontal straightening
- horizontal axis
- over the back
- parallel-axis straightening
- vertical axis
- vertical straightening
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
- 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
- production of strands and ropes
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
- 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.
- 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.
Reproducibility of straightening roller positions
- repetition of adjustments
- reproducibility of straightening roll positions
All straightening results, including the final curvatures of the material to be straightened, ultimately depend on the correct positions of the straightening rolls. It is vital, therefore, for the straightening process to display constant reproducibility.
In addition to being a precondition for constant results, reproducibility also minimizes unnecessary line stoppage times and it wastes less material during repeat set-ups. High speed and continuous availability also play a major role in minimizing costs.
Existing possibilities of achieving reproducibility differ in their use of reference points on the adjustable elements of a straightener and in the methods used to determine actual positions.
The most commonly used possibilities are:
1) Engraved veneer scales
2) Dial gauges
4) Screws; hex screws, slotted screws etc.
5) Knurled screws
6) Micrometer screws
7) Veneer scales on buttons
8) Collar screws with veneer scales
9) Machine knobs/tapered machine handles
11) Geared motors / stepping motors
12) Hydraulic / pneumatic cylinders
13) Automatic roll positioners
A solution is chosen which best meets the demands of local conditions and technical handling criteria. A combination of two of the above options is also possible, in which case the functions are divided into adjustment and position measurement.
Whatever option is selected it should not be forgotten that continuous documentation of the adjustment values is essential if reproducibility is to be achieved as planned.
- double straightener
- drag-type gripper bench
- drag-type straightener
- drag-type straightening set
- pre-straightening device
- roll unit
- roll-type straightener
- roll-type straightening device
- rope straightener
- sickle straightener
- single straightener
- straightening rotor
- straightening device
- straightening machine
- straightening mechanism
- strip straightener
- wire bending unit
- wire straightener
- wire straightening device
Using a roll-type straightener it is possible to change a process material's unidimensional initial curvatures, i.e. initial curvatures in one plane, so that defined final curvatures remain after the straightening process. The bending tools of such a roll-type straightener are straightening rolls arranged in two parallel, mutually offset rows. When the rolls are accordingly adjusted, the process material is subjected to alternating bends as it passes through the straightener. The number and magnitude of these alternating bends must be such that the initial curves are changed in defined manner over the complete length of the product to be straightened.
To straighten a product over its complete length it has to be transported relative to the straightener.
For this purpose, straightening machines are equipped with driven rolls. By contrast, the rolls on a straightener are not driven, i.e. additional devices such as drive units, pull-in units, drivers or the like are required to transport the product to be straightened.
In other words, a straightening machine has technical elements for transporting as well as straightening the product, whereas a straightener has only elements for straightening it. By this definition it is possible to use straighteners in straightening machines.
Straighteners can be classified in terms of their degree of automation. WITELS-ALBERT offers products for conventional straightening, semi-automatic straightening, and straightening with automatic roll positioners. Automatic straightening is currently the subject of intensive research.
Each sector should have a matching straightener with specific features that can be adapted to the cross section to be straightened and to the properties of the process material.
- roll crosses/roll guides
- roll material
Roller crosses/guides are used in the processing of endless material between the spool or coil, straightener, pull-off unit or processing machine. Their function is to guide and support the product to be processed.
The number and the arrangement of the roller crosses/guides in the material flow system are selected so that
- sagging of the material is prevented,
- sharp edges and deflections with small radii do not damage the surface of the material,
- the endless material enters the next apparatus or machine in central position.
The diversity of roll guides results in a wide range of different applications. Which roll guide is selected will depend on the particular requirements. Roll guides are available as rigid and adjustable types. Adjustable roll guides are used when dimensions change and when exact positioning of the material is essential.
Centrally adjustable roll guides are suitable for a range of dimensions. The center of the material is retained even when dimensions change. The material itself does not have to be adjusted for it to enter the line centrally.
Some roll guides are designed to completely enclose the material while they guide it. Others are open on one side for better insertion of the material.
Roll diameter, roll material and clear widths depend on the dimensions and geometry of the material.
Burnished and hardened steel rolls are used e.g. for firm materials. Softer rolls made of PETP can be used for sensitive surfaces. The following basic types of roll are available:
- with chromium-plating
- hardened (up to 64 HRC)
- with rubber coating
- with ceramic coating
- rolls made of PETP, PVC or polyamide
- alternate bending
- rotary straightening
- wire straightening
Unlike the roll straightening process, rotary straightening subjects the process material to alternating bends with a revolving bending axis.
The number of alternate bends depends on the speed of the product to be straightened and the number of rotations made by the spinner. Straightening blocks, straightening cheeks or straightening rolls are among the straightening tools used.
Rotary straightening is mainly performed in the production of rods or bars which permit a certain spring back of the material from the bending and torsion as the result of being cut to length.
It is sometimes wrongly assumed that two counter rotating straightening spinners neutralize the unwelcome stresses induced by torsion.
In view of the surface damage and sometimes severe impact on material parameters caused by the more aggressive forming of the product in the rotary straightening process, preference is being given more and more often to roll-type straighteners as the gentler alternative.
- basic automation
- control system
- positioning control system
- semi-automatic straightener. semi-automatic straightening
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.
- process data
- process simulation
- relative curvature
- simulation program
- 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
- 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 diameter
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.
- measuring instrument
- Status quo
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.
- binding wire
- composite wire
- enameled wire
- fine wire
- flat wire
- iron wire
- mesh wire
- packing wire
- profiled wire
- rectangular wire
- reinforced concrete steel
- split strip
- spring wire
- steel wire
- straightened product
- straightened material
- tie wire
- winding wire
- wire fabric
- wire mesh
- wire rod
- wire rope
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
- initial curvature
- material cross section
- 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
- Preforming heads
- Postforming apparatus
- adjusting spindle
- adjusting screw
- clamping lever
- dial gauge
- guide block
- height-adjustable guide roll
- micrometer screw
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,
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).
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.
- curvature 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
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.
- ball bearing
- cam roll
- dust seal
- grease lubrication
- grooved roll
- life-time lubrication
- lip seal
- miniature bearing
- radial ball bearing
- rolling bearing
- 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:
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
- 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
- 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
- seal arrangement
- elastic deformation
- 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
- make straight
- 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
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.
- 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.
- beginning of flow
- elongation limit
- flow limit
- proportionality limit
- 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
- 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.
- maximal endurable stress
- tensile strength
Tensile strength is a characteristic material parameter which can be derived form 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 a material's tensile strength the deformation of the workpiece or the elongation of the tensile specimen due to the external tensile load continues to increase while only the inner resistance decreases in relation to the cross sectional area prior to the loading. The visual result of the tensile test is that the tensile specimen constricts locally at the material's tensile strength, whereas up to this point it stretched over its entire length. This constriction is the reason for the specimen's failure by breakage if subjected to further loading.
Tensile strength is derived from the quotient of the maximal load and the cross sectional area prior to loading. A material's tensile strength thus denotes its maximal endurable stress.
- elongation to fracture
- material test
- tear test
- tensile force
- tensile loading
- tensile specimen
- tensile strength
- tensile stress
- tensile test
- tensile testing machine
- wire testing machine
- wire test-piece
The tensile test according to DIN EN 10 002 is a static test method. It is the most important test for determining a material's mechanical parameters. A standardized test bar is subjected to an increasing tensile load in its axial direction. The test-piece, which is clamped at both ends in suitable clamping fixtures, has a specific test length which is bigger than its measured length.
The test is performed on a testing machine, often continuing until the test-piece fails. Tensile force and the change of length are recorded and plotted in a diagram. This is followed by presentation in a stress/strain diagram using the initial values for the material cross section and the test length. From the stress/strain diagram it is possible to derive parameters which express the material's behavior under external loads. The parameters most often determined are:
- modulus of elasticity
- stretching limit
- tensile strength
- elongation to fracture
- dynamic pulling off
- dynamic spooling
- dynamic unwinding
- mobile reel
- pay-off unit
- pulling off
- rotatable reel
- rotatable coil
- static pulling off
- torsional stress unrolling
Basically the methods used to unspool or unwind a material which is to be straightened break down into two categories: static or dynamic.
With the static method the spool or reel is not moved. Material is paid off in axial direction so that a helix or twist is created in each winding as it is removed, with negative consequences for the follow-up process.
With the dynamic method of pay-off the spool or reel is rotated around its axis, which may be arranged vertically or horizontally, enabling the material to be paid off without suffering any torsion.
Windings are at risk of slipping only in vertical unspooling or unreeling set-ups, particularly in intermittent processes. A horizontal pay-off may be more elaborate technically, but it is the better solution with a view to follow-up processing operations.
- wire core
- zero line
- zero position
The term “zero line” is used in two contexts. The first is the zero line of the processing system and the second is the zero line in the straightener.
The term zero line of the processing system is understood to mean that the product to be straightened runs through the processing system without undergoing any additional bending, deflecting or guiding. It is an advantage therefore for wide spools to be axially adjustable in order to always obtain the required zero line. The zero line of the processing system includes the zero line in the straightener.
The term zero line in the straightener describes the situation when all the straightening rolls touch the product to be straightened but do not bend it. This setting is usually made with a caliber, hence the term calibration. The zero line in a straightener depends on the geometry of the product to be straightened and of the straightening roll groove.