ROLLING FLAT AND SHAPED WIRE...FERROUS WIRE HANDBOOK 814 Ferrous2_Ch1.qxp 3/14/2008 9:16 AM Page 814 elongation. The simplest example is the flat rolling of round wire (see Fig. 5),

Chapter 28

ROLLING FLAT AND SHAPEDWIRE

The Manufacturing Process of Rolling – Basic DefinitionsRolling is the technical process of transforming the cross section

of a feed stock that passes through a set of rotationally symmetrictools called rolls. Besides shape, the rolling process also changescharacteristics of the processed material such as strength, microstruc-ture, and surface.

The process of rolling is mainly used for either ferrous or nonfer-rous metal stock and is classified into cold, warm, and hot rolling ofwire or sheet. This chapter primarily covers the cold rolling of flatand shaped wires.

Flattening as the basic rolling operation for sheet or wire uses twocylindrical rolls with parallel axes (see Fig. 1). If the rolls are designedwith a profile groove, the material can be shape rolled. Rod-typestock, such as wire, can also be shaped using more than two rolls (seeFig. 2).

Those rolls that contact the feed stock are called work rolls. Insheet rolling machines where high rolling forces appear, backup rollsare used to support the work rolls (see Fig. 3). Typically backup rollsare not needed for wire rolling due to relatively low rolling forces.

If none of the rolls on the rolling machine are equipped with adrive, the rolling process is called undriven, or friction driven,because the rolls are indirectly driven by the stock being pulledthrough. In contrast, driven or power driven rolling machines featureat least one or more driven rolls. These systems can be operated asstandalone machines because pulling equipment is not required.

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Comparison with Alternative Manufacturing Methods

SlittingIf flat strip is required, it can either be made by rolling round wire

or by slitting a wide, flat sheet to multiple strips. Rolling is advanta-geous for narrow strips, while slitting is limited to strip widths widerthan 5 mm because shearing discs cannot be infinitely narrow.Another limitation for slitting is the length of the produced strip.

Fig. 2. Shaping process.

Fig. 1. Flattening process.

FERROUS WIRE HANDBOOK

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Each slit stripe is limited by the length of the coil, whereas roundwire rolling leads to virtual endless strips (see Fig. 4).

Also, unlike rolling, the shearing of strips in slitting machines cre-ates burrs and chamfers that are unacceptable in many applications.

DrawingFor round wire production the use of drawing dies and related

machinery is usually more economical, than rolling machines

Fig. 4. Rolling versus slitting.

Fig. 3. Sheet mill with small workrolls and three rows of backup rolls.

CHAPTER 28 — ROLLING FLAT AND SHAPED WIRE

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because the design of capstans is simple and dies with circular shapeare inexpensive.

When shapes more complex than simple rounds are needed,rolling is preferably applied because shaped dies are expensive andcan’t be refurbished after wear as rolls can be. Another reason forrolling instead of shaping with dies is the characteristic spreading ofthe rolled material that does not appear in the drawing process.Smaller feedstock sections can be used for shapes characterized by awidth-to-thickness ratio value of 2:1 or higher, unlike with the draw-ing process.

Rolling is the only applicable forming technology for some metalstock because these materials have a micro-structural layout thateither breaks during drawing or shows an unsatisfactory surface afterpassing the die.

Rolling generally creates a better surface quality than drawingbecause unlike drawing it proceeds without lubrication. As thedemand grows for read-to-use wire, the surface preparation used tomake the lubricant adhere to the wire surface is becoming unpopu-lar because it creates rough surfaces.

Design Criteria for Wire Rolling MachinesThe rolling machine’s design criteria are determined with regard

to finished wire requirements such as shape, size, dimensional varia-tion, strength, and production quantity.

Wire Shape and SizeTo configure the optimal rolling machine for a final given shape,

the first thing to determine is the shape and size of the feed stock.These affect the shape and size of the finished wire and the applica-ble rolling sequence. The availability of feed stock also has to be considered.

One very important parameter for selecting the appropriate feedstock is the wire’s elongation caused by rolling. The rolling processalways reduces the wire’s cross section and—due to volume constan-cy—increases its length. The rolls force the wire to align to the rolls’surface geometry in the contact zones between rolls and wire. As areaction, one portion of the material flows in an orthogonal plane tothe wire’s longitudinal axis into those areas that are not bounded bythe rolls. This movement is called spreading. Another portion flowsparallel to the wire’s longitudinal axis. This movement is called


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elongation. The simplest example is the flat rolling of round wire (seeFig. 5), which becomes thinner, wider, and longer by rolling.

The ratio between spread and elongation is difficult to predictdue to the large number of parameters that affect spread. Eventhough for some basic forming processes approximate calculationformulas are available, a precise calculation is not possible so far.

The following relations can be used to predict and influence thedegree of elongation. It has been theoretically and practically proventhat spread is higher when:

• The ratio of roll diameter to wire size is higher• The friction coefficient between roll and wire is higher

(rough roll surface, rough wire surface, low grease contentin lubricant)

• The wire’s tensile strength is higher• The width of the feed stock is smaller• The degree of forming per step is higher

Fig. 5. Thickness reduction,elongation, and spread in theflattening process.


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Once the size and shape of the feed stock is determined, the num-ber of rolling steps and the type of rolling machine for each step isdecided. This rolling sequence is designed either by experience withsimilar shapes, reference to literature, or computer-based simulation.At this point only the forming steps are considered without regard toany limitations given by the available machine equipment, wireformability, etc.

Separating ForcesRolling—as any forming process—is based on plastic flow.

Therefore, stress, which is higher than the material’s yield strength,has to be applied. During the rolling process the material’s yieldstrength usually increases by work hardening—especially when coldrolling is used. The average value of yield strength before and afterthe forming step is used to calculate separating forces. These valuescan be found in flow curves that are available for most steel grades.

The dimensions and shapes for each forming step are defined inthe rolling sequence. These parameters are used to determine thecontact zone’s area (A) between roll and wire. The separating forces(F ) that affect each roll and the supporting structure are calculated asthe product of this area and the average yield strength (YS ).

Eq. (1)

Because of relative movements between roll and wire surface,which are caused by spread and elongation, the effective separatingforces are higher than the theoretical values. The difference is incor-porated by introducing a grade of efficiency (η) into the calculationformula.

Eq. (2)

For some simple forming operations (e.g., flattening withoutspread limitation, see Fig. 6) the calculation formulas and efficiencygrades are provided in the literature.


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Eq. (3)

where: Ffl = Separating force for flatteningYS = Average yield strengthb0 = Width before rolling b1 = Width after rollingη = Grade of efficiency

Eq. (4)

where: ld = Contact lengthd = Roll diameterh0 = Thickness before rolling h1 = Thickness after rolling

Fig. 6. Calculation of separatingforce in the flattening process.


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It is more difficult to calculate complex processes such as shaperolling with four rolls. Recently the simulation with finite elementmethods (FEM) can predict the forces accurately. However, thesemethods require expensive, sophisticated computer hard- and soft-ware and are, therefore, seldom used.

Separating force is defined by the size of the contact zone area.Therefore, small roll diameters generate smaller separating forcesthan larger roll diameters in a given rolling process. In strip rollingmills, rolls with small diameters are used to reduce forces. As thesesmall rolls tend to bend, backup rolls are used for support (see Fig.3). In wire mills, the separating forces are lower due to smaller widthof the rolled material and support rolls are usually not found.

After identifying the separating force, a suitable rolling machineis selected based on:

• the machine’s break load and the static bearing capacity ofthe used roll bearings

• the lifetime of the bearings. This is calculated according tothe required production speed. Usually, the nominal lifetimeis 10,000 hours; however, in multi-roll machines (e.g., turks-heads) due to limited installation space for bearings thenominal lifetime sometimes reaches less than 2,000 hoursonly.

• the elastic deformation of the machine caused by theseparating forces. This can only be calculated if themachine’s spring constant, which represents the machine’sstiffness, is known. The higher the requirements on thedimensional constancy of the rolled wires are, the stiffer the machine should be. Alternating separating forces—caused by variations of the feed stock’s yield strength or its dimensions—will result in alternating dimensions after rolling. High stiffness makes the machine less sensible for variations of the separation force.

The maximum specific surface pressure is the criterion for select-ing the material grade of the roll, not the separating force. The roll’syield strength must be higher than the wire’s yield strength. For wireswith yield strengths up to 1000 to 1200 N/mm² the use of hardenedconventional tool steels is sufficient. However wear is lower if therolls are made from tungsten carbide materials.


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For higher grade wires the use of tool steel rolls is not possiblebecause the rolls will break due to the specific loads applied. Thesewires demand tungsten carbide rolls. Alternatives can be powdermetallurgical materials or, to a lesser extent, ceramic, which is sel-dom used because it was introduced recently into rolling technique.

Torque and Power to Drive the RollsTo perform the rolling operation, it is necessary to drive the rolls.

The required torque can either be created by connecting the rolls toa motor (power-driven machine) or by applying a pulling force to thewire (friction-driven machine).

Rolling machines with a combination of driven and undrivenrolls, such as four-roll designs (also called turks heads) with two driv-en and two undriven rolls, don’t need external wire-pulling equip-ment. In that case, the driven rolls drive the wire that subsequentlymoves the undriven rolls.

For the torque calculation the values of separating force (F ) andthe distance (a) between the connecting line of roll centers and thebalance point of the separating force are multiplied (see Fig. 7).

Eq. (5)

where: M = Driving torqueF = Separating forcea = distance from centerline to the balance point

of the separating force

The tangential force for each roll is calculated by dividing thetorque by the half-roll diameter. The pulling force needed for frictiondriven machines is the sum of the tangential forces of all rolls.

Eq. (6)

where: Ft = Tangential force


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The power (P ) needed for the rolling process is the product of thesum of the tangential forces of all rolls and the rolling speed (v).

Eq. (7)

where: P = Driving powerv = Rolling speed

Friction Between Wire and RollsDriven rolls basically have the ability to draw the wire into the

gap between the rolls and feed it through. This feature is limited bythe contact angle and the friction coefficient between roll and wire.With a given height reduction and roll diameter the contact angle (α)between roll and wire can be calculated as:

Eq. (8)

Fig. 7. Driving torque calculation.


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For feeding in the wire by driving the rolls, the required frictioncoefficient is:

Eq. (9)

To transport the wire through the rolls by driving them, therequired friction coefficient is smaller:

Eq. (10)

These formulas show why, even though a specific rolling processis operating successfully, the wire feeding process might not work atall. To ease the wire feeding process, the contact angle may bereduced by opening the rolls or by pointing the wire. Another possi-bility is to increase the friction coefficient by switching off the lubri-cation of the roll surface, degreasing the front end of the wire, orroughening the rolls.

Practice has shown and theory can explain that the friction coef-ficient depends not only on the surface of wire and rolls and the char-acter of the lubricant but also on the rolling speed. For this reason themaximum degree of forming is reached at low speeds. If high pro-duction speeds are required, usually more forming steps are appliedto avoid wire transportation problems.

If the actual friction coefficient is even smaller than µtrans, thewire will not move, even though the rolls are rotating. During thisstandstill, the lubricant between wire and rolls escapes, the frictioncoefficient increases, and the wire eventually starts moving again.

This alternating start-stop process affects the quality of the rolledwire. The wire surface is damaged and dimensions will vary becausewire tension between the rolling machines is not constant. Moreover,the escape of lubricant during the standstill of the wire creates eitheradhesive or abrasive wear on the rolls’ surfaces.

During the rolling process the cross-sectional area of the wire isreduced and the wire is elongated. This means that the wire is accel-erated on its way through the contact zone. As the roll’s surfacemoves with constant speed, therefore, a speed difference existsbetween wire and roll. It can be shown that the wire speed is slower


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at the entrance to the contact zone and is faster than the roll surfaceat the exit. There is only one point at which the speed of the wire isthe same as the speed of the roll.

The speed difference between roll and wire surface is a charac-teristic of the rolling processes and does not create wear as long asthe lubricant separates the surfaces of wire and rolls.

For this reason rolling without lubrication always creates weardue to relative motion between contacting surfaces.

The above considerations show that a non-slip rolling process,promoted by some rolling machine manufacturers, does not exist.Any speed synchronization between roll stands can only minimizespeed differences between rolls and wire.

Wire TemperatureDuring the rolling process a forming energy is applied to the

wire, and this energy is almost entirely converted into heat, elevatingboth the temperature of the wire and the rolls. The degree of heatingis related to the yield strength of the wire and its heat capacity as follows:

• High tensile wires providing high yield strengths getwarmer than those with low yield strength because theyrequire more energy for forming.

• If the same forming energy is applied, wires with low heatcapacity get warmer than those with high heat capacity.

The heating of the wire caused by rolling is independent of therolling speed, which is—at first sight—surprising, because the practicalwork with rolling machines shows that the wire temperature risesafter rolling with the increase of line speed. The explanation for thiscorrelation between wire temperature and line speed is that, contraryto the heating by rolling, the subsequent cooling is time-dependant.The longer the cooling processes are applied, the lower are the finalwire temperatures.

Cooling is mainly done by heat transduction from wire into rollsand cooling lubricant. As the calculation of rolling forces and therelated applied power is already difficult, the calculation of wire tem-peratures is even more challenging. Especially the cooling by lubricantcontact, as a complex heat transferring flow process is influenced bycountless parameters. Even FEM-based calculations can only pro-vide approximate results.


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Other than setup time, the most important machine parameter isproduction speed. To reach the required wire properties at an eco-nomic line speed, the wire temperature must be kept below criticalvalues because of the following:

• The yield strength of wire and the related separating forcesdrop with high temperature. Because of the machine’selasticity this leads to dimensional deviations.

• The degree of elongation changes with variations of yieldstrength and friction coefficient. This again leads todimensional deviations.

• Lubricant properties can change causing differences in wiresurface quality.

• The mechanical properties of the final wire can be differentwhen rolled at different temperatures.

• Roll dimensions can change due to heat expansion. As aresult the wire dimensions can vary.

• If the final wire is coiled on spools in warm conditions, thecooling is accompanied by shrinkage. This generates highloads resulting in surface damage and geometric failures,especially on the inner windings of the coiled wire. To avoidthis, maintain coiling temperatures below 60 to 70ºC.

Effective wire cooling is necessary on high-performace wiredrawinglines because of increased production spees, accuracy demands, orlarge per-step reductions. This can be achieved by:

• external cooling of rolls and wire in the contact zone byspraying cooling lubricant

• internal roll cooling with either lubricant or coolant• dip-cooling of the wire in special basins filled with coolant

located after each rolling step. Ideally the wire exits thebasin chilled to the coolant’s temperature to avoid heataccumulation from one rolling step to the next.

• use of a coolant with high heat capacity: Water (and water-oil-emulsion) is much more efficient than oil.

• controlling the coolant’s temperature by a re-cooling system


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As a machine typically cools to below the production tempera-ture during standstill-times, such as setup or weekends, high precisionlines usually are prepared for production by preheating the rolls andthe coolant to working temperature prior to the start of production.

Machines with lower production output typically do not requirespecial measures to reduce wire temperature.

Wire FormabilityAt the end of the wire shape and size section, a reference was

made to an occasional limitation of the rolling sequence by wireformability.

Material forming as it is applied by the cold rolling process isonly possible if the material is ductile, which means plasticallyformable without damaging the material’s internal structure. Thedegree of formability is a material parameter that varies for the dif-ferent steel grades. Basically the degree of formability decreases asthe content of carbon and alloys rises. The maximum degree offormability is often found in flow curves for the given steel grade.

After any warm forming—such as casting, hot rolling or forging—steel is ductile. Any applied force that creates tension beyond theyield point causes plastic flow. During plastic flow the material’s crys-tal lattice layers are displaced against each other. Defects in the crys-tal structure interfere with the crystalline motion. The number ofmovable crystal layers reduces and the force required for plasticforming increases. Finally, all crystals are blocked. No further form-ing is possible. The material’s character has changed from ductile tobrittle. Any further increase of the applied force will result in thematerial’s breakage.

To provide additional forming capability the crystalline structuremust be restored. This is done by a heat treatment called recrystalliza-tion annealing. Afterward, the material’s ductility is recovered.

When wire is cold rolled, the degree of deformation over thecross section usually is not uniform. Some portions of the section areformed more than others. In strongly deformed zones, the wire getsbrittle and starts cracking while other portions are still ductile. Thislack of ductility does not necessarily result in a wire break, but it maycreate wire defects that are the source for subsequent malfunctions ofthe final wire product.

A simple example is the flat rolling of round wire feedstock dur-ing which the round wire is elongated during the rolling process. The


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highest degree of longitudinal deformation is found in the lateralzones where the raw wire’s section is smallest. As a result, the flatwire shows cracks in the corners first if the degree of forming is toohigh. To avoid this, the degree of forming is reduced and the rolledwire is annealed before further flat rolling. To a certain degree moreflattening without annealing is possible by the use of edge rollingbetween flattening steps to reduce stress in the flat wire’s lateralzones.

Typical Designs of Cold Rolling Machines for Wire

Two-high Rolling MachineThe two-high rolling machine design is the simplest one, provid-

ing two rolls with parallel axes usually mounted horizontally. In mostcases the rolls are driven but, in combination with capstans, undriv-en types also are used.

The most common application for two-high rolling machines isflat rolling, often referred to as flattening, in which cylindrical plainrolls are used. By profiling the rolls it is also possible to use the two-high design for rolling shapes, but since the four-roll design has beenimproved, this application has become less important.

The main advantage of two-high design compared with four-rolldesign is its higher bearing capacity, which allows higher separatingforces, and higher degrees of forming. The basic capacity of turksheads is smaller due to space limitations for the bearings. Therefore,in today’s modern rolling mills, two-high machines are usually foundin flattening applications either for flat wire production or for pre-forming wires that are finally shaped in turks heads.

The two-high standard design (see Fig. 8) uses rolls with incorpo-rated bearing journals on both ends. Either taper roller bearings or acombination of radial cylinder bearings and axial needle bearings—often in high precision design—are used. While the bearing housingsof the bottom roll are fixed in the machine frame, those of the top rollare joined to a mechanical screw-down system consisting of two gear-boxes and a spindle.

Usually the wire widths are multiples smaller than the widths ofthe rolls. To use the whole roll width the standard two-high designusually provides the possibility to shift the entire stand and therebyuse several lanes on the roll surface.


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In case of roll change, the universal shafts that drive the rolls mustbe uncoupled and subsequently roll bearings and bearing housings canbe removed as complete units. To reduce machine downtime it is rec-ommended to have a complete second set of units on hand.

The two-high machine designs were improved (see Fig. 9) withregard to productivity and precision of the rolled wires. The rollerbearings moved inside the roll body, and the drive is realized by aset of geared wheels. The roll change is quicker, the roll is muchstiffer, and the roll body material can be selected with regard to itsrolling characteristics only, without limitations such as break restric-tions due to bending and torque.

Single horizontal shift of the top and bottom rolls is a character-istic of ideal designs (see Fig. 10) that compensates for the trapezoidaleffect which is commonly experienced on standard designs when therolling lane is changed. Motorization of the horizontal roll shiftallows for continuous roll traversing. As a result no wear tracks arecreated and the regrinding cycles are extended.

Fig. 8. Common two-high typerolling machine.


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Edge RollersEdge rollers provide two rolls with parallel axes as do the two-

high mills. However, unlike the two-high design, the rolls’ axes arevertical. Basically an edge roller (or edger) is a two-high rollingmachine that is twisted by 90 degrees. Edger machine design islighter than two-high machines because of the low-force applicationsfor which it is used, e.g., width adjustment of flat wires between two-high machines or the chamfering of pre-rolled shapes to prevent fins.

Fig. 10. Roll shift.

Fig. 9. Actual two-high design.


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Usually edge rolling machines are friction-driven. The wire ispulled through by downstream equipment—mostly driven rollingmachines. Only in some cases where tension sensitive materials suchas copper are processed, can it be advantageous to use driven edgers.

Edge rolling requires rolls with shaped grooves (see Fig. 11). Toreduce set-up times some designs allow the use of several groovesarranged beneath each other that can be adjusted to the wire passline by vertical roll shifting. Other designs provide a cantilever rollshaft to decrease roll change time. This design, however, is less stiffthan a system with bearings on both sides of the rolls.

Turks HeadsThe term turks head is often used for all variations of rolling

machine designs that feature four rolls with 90 degree displacementto each other. As this general specification can lead to confusionfuture references in this book will be made to standard or universallydesigned “profile rolling machines.”

Standard Profile Rolling Machines. The design of standard profilerolling machines is based on four rolls (see Fig. 12). The roll axes arepositioned in one common plane. The angle between neighboringroll axes is 90 degrees. Usually each roll can be adjusted separately;in the simplest design this is done manually. The roll adjustmentoperates along a vertical axis to the roll axis and directs through thewire’s pass line. This adjustment axis will be referred to as “radial”adjustment.

Fig. 11. Friction-driven edge rolling machine.


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Depending on the application, the wire is either pulled throughthe machine, by a capstan for example (so called undriven or fric-tion-driven type), or the machine itself moves the wire by drivenrolls. These driven machines (see Fig. 13) usually have a pair of driv-en and undriven rolls, because in most profile rolling applicationsthere is a significant difference in rolling force and required torquebetween the two-roll pairs. The pair of rolls, which does most of theforming, usually is the driven one. Only when shapes with a width tothickness ratio between 1:1 and 1:2 are rolled is the use of four-drivenrolls justified.

In general the use of driven profile rolling machines is advanta-geous compared with undriven machines. The degree of forming ishigher and the operation is easier as pointing is not required andunshaped wire is not wasted on a capstan’s drum. For a final calibra-tion step the combination of an undriven profile rolling machine andcapstan is beneficial because it enables the operator to do a skin passwith minimal transformation and without the risk of roll slippage.

Producing shaped wires with profile rolling machines requiresshaped rolls that are individually designed for each rolling step (seeFig. 14). To reduce the costs, many machine designs provide rolls thatare split into a basic roll body (often referred to as a “roll mountingdevice”) and a mounted ring. The roll mounting device is equippedwith bearing and shaft and those parts that are needed to connect theroll to the drive. For a quick machine set-up two sets are beneficial.

Fig. 12. Friction-driven standardprofile rolling machine.


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When one set is in operation, the second set can be prepared with theshaped rings for the next product.

In addition to economical benefits, another advantage of thebody and ring system is the ability to vary ring materials easily.

As mentioned previously, the precision of a rolling machinedepends on its stiffness. Due to the fact that profile rolling machineshave four rolls, the design space for each roll and its bearing, drive,and adjustment system is limited. Therefore, the stiffness of a four-roll profile rolling machine is less than that of a two-high rollingmachine with the same roll diameter. The maximum degree of form-ing is also lower than on a two-high rolling machine. Whenever pos-sible, two-high rolling machines should be used for pre-profiling andprofile rolling machines should follow downstream in the productionline to finish the shape.

Due to limited stiffness of older profile rolling machine designs,the interlocked roll system (see Fig. 15) was used to reach acceptablewire tolerances. This interlocked system uses precisely shaped rollsthat touch each other and are preloaded with a force that is higherthan the rolling force needed for the actual rolling process. As longas the rolling forces are below the pre-load force, the contact gapsbetween the rolls stay closed and the wire tolerances generallydepend on the precision of the roll profiling process (usually grinding).

Fig. 13. Driven profile rolling machine.


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The interlocked roll system compensates for machine elasticityand is not sensitive to roll expansion caused by heat. Even oldmachines with worn-out roll bearings can reach acceptable results ifprecise ground and interlocked rolls are used.

The interlocked system has the following disadvantages:

• The wire dimensions cannot be changed by roll adjustment.Often many trials are needed to find the correct roll shapebecause the springback expansion of the wire and thedeformation of the contact zone between the roll and wireaffect the process.

• The contact between the rolls is critical with regard toabrasive and adhesive wear. The use of hardened tool steelas roll material is acceptable. However, today’s increasedwire tensile strengths and demands on production speedsrequire different roll materials such as tungsten carbide. Thedirect contact between tungsten carbide rolls creates heavywear and ultimately results in breakage. Therefore, theinterlocked roll system is limited to applications in whichthe use of tool steel rolls is sufficient.

To overcome mechanical problems, actual profile rollingmachine designs have been improved, especially with regard to stiff-ness (see Fig. 16). Tightest tolerances in the range of +/-0.003 mm at

Fig. 14. Shaped rolls for standardprofile rolling machines.


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production speeds of up to 800 m/min. can be realized today with-out interlocking the rolls. Nevertheless, very tight gaps are usedbecause many shapes require sharp corners, and gaps between therolls would result in finned wires. The most modern machines areequipped with a computer-controlled roll calibration and set-up sys-tem to achieve a balance between the need for minimum gap with-out the pre-loaded contact of the rolls.

Fig. 16. Modern design of a standard profilerolling machine.

Fig. 15. Interlocked roll system.


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Universal Profile Rolling Machines. Basic profile rolling machinesrequire a specific set of shaped rolls to produce the special shapesdictated by each wire profile.

A variation of the basic profile rolling machine was developed inthe past for production of rectangular shapes, which accounts for thelargest production volume of shaped wires. The design of thismachine extends the basic design by the axial adjustment of each rollresulting in a universal rolling machine profile (see Fig. 17).

The combination of radial and axial roll adjustment provides aroll set-up that allows for the production of rectangular wires of dif-ferent dimensions with one single set of rolls (see Fig. 18).

Even trapezoidal shapes of different sizes can be made in a certainrange as long as the trapezoidal angle does not need to be changed.

To simplify set-up and operation, the axial adjustment of one rollis linked to the radial adjustment of the neighboring roll. When rec-tangle dimensions are changed, only the radial adjustments need tobe moved.

Some universal profile rolling machines also provide a “Standardprofile rolling machine” mode in which the linked operation of axialand radial adjustments are disconnected and the axial adjustmentsystems are fixed in a central position.

Due to limited axial bearing capacity it is not possible to close thegap between the rolls with pre-load forces in the linked universalmode. This means that an interlocked system, in order to increasewire accuracy as used in standard profile rolling machines, is not pos-sible here. For this reason, the old and elastic designs of universalprofile rolling machines cannot meet today’s tolerance requirements.This elasticity also complicated the use of tungsten carbide as rollmaterial because it was almost impossible to prevent roll contact inthe gap zones due to elastic roll deflection during operation.

The actual designs of driven and undriven machines in differentconfigurations have improved stiffness to keep the adjusted gapsbetween the rolls constant (see Figs. 19 and 20). Another develop-ment is the computer-controlled roll adjustment and roll calibration,which decreases set-up times and guarantees an operator-independ-ent setup. This is an immense improvement because the manualadjustment of the linkage of axes has proven to be the main sourceof error with regard to wear, breakage of rolls, and finned wires.


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Fig. 18. Change of dimensions with a universal profile rollingmachine.

Fig. 17. Schematic sketch of the universal profile rollingmachine.


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Special Rolling Machine DesignsOther machine designs have been developed to serve special

applications, and these designs are mainly variations of the standardprofile rolling machine. One example is the three-roll profile rollingmachine, which is used for round wire production or ribbing of rein-forcement steel wires (see Fig. 21).

Another example is the six-roll profile rolling machine for hexag-onally shaped wires (see Fig. 22).

Components for Rolling MillsMany other components are needed to create a complete rolling

mill. This chapter provides only an overview of equipment necessaryto complete the production line.

PayoffsThe payoff machinery marks the start of a rolling mill line. It

presents the interface to the preliminary production units such as hotrolling or drawing lines. The function of the payoff is to accommo-date the inlet wire in whatever way it is provided.

Payoffs can be classified into two groups: static and dynamicdesigns, in which the wire bunch is either static or rotational during

Fig. 19. State-of-the-art universalprofile rolling machine withdriven top and bottom roll and undriven side rolls.


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line operation. One advantage of static payoffs is that they are gener-ally easier to operate than the dynamic payoffs and they cost less.

Another advantage is that the static wire bunch allows the weld-ing of single lots during line operation, which is not possible withdynamic payoffs. The grade of efficiency of lines equipped with stat-ic payoffs is higher compared with dynamic payoff lines.

When wire straightness is a main requisite, dynamic payoffs arepreferred. The helix created in the wire during static take off leads toirregular and alternating curvature of the paid off wire and finally tostraightness problems in the final wire.

Fig. 20. Modern design universalprofile rolling machine witheight adjustment motors forcomputerized roll adjustment.


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For both static and the dynamic payoff applications many differ-ent machine designs exist that have been adapted to the way the wireis packaged and handled. The main difference in packaging iswhether the wire comes layer wound or as loose coils. Layer windingis advantageous because it allows for the application to and controlof pulling forces on the wire without the risk of wire tangling due tocoil contraction.

Fig. 22. Six-roll profiling machinefor hexagonal wires.

Fig. 21. Three-roll profile rollingmachine for wire ribbing.


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Some examples of dynamic payoffs are:

• Spool payoffs, in cantilever (see Fig. 23) or sleeve design for wire, that are layer wound on spools. For layer-wound,coreless coils these payoffs are equipped with expandablemandrels. This payoff type is available with or without adrive and in either case the package rotates.

• Dynamic horizontal coil payoff (see Fig. 24). This type ismostly used for wire rod with diameters greater than 12mm, and it is the only type that can handle wires biggerthan 20 mm. A drive and a simple straightener are usuallyintegrated to simplify coil handling.

• Dynamic vertical coil payoffs (see Fig. 25). This type isdesigned for wires up to 20 mm diameter provided as loose wound coils or coils on carriers. Below speeds of 100 m/min. a drive is not required and a straightener is not integrated.

Examples of static payoffs include:

• Flyer arms for small wires up to 2 mm on spools or spooledas coreless coils (see Fig. 26). Flyer arms are not driven.They incorporate a brake to adjust wire tension. Sometimesa straightener is integrated.

Fig. 23. Spool payoff.


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• Over-head coil payoffs (see Fig. 27) for wire coils up to 12 mm diameter provided coreless wound, on pallets, oncarriers, or in barrels. The wire is pulled upward out of thepackage; it is pre-straightened; and tangles are removed onthe way up by the weight of the wire.

Usually two coils are put underneath the deflection roll. Theend of the wire coil that is in operation can be welded tothe start of the next coil. This operation method allows forcontinuous production.

• Static horizontal coil payoffs mainly used for hot rolled wire rod, coils up to 12 mm wire diameter. They are easy to load, because coil transport is usually made in thehorizontal position and no tilting is required during loading.

The risk of wire tangling is higher in static horizontalpayoffs compared to over-head coil payoffs because there isno equivalent to the gravity that pre-straightens the wire.Modern designs feature flyer arms or other mechanisms tokeep the entire coil from being pulled from the payoff inthe event of wire tangle. These models also allow loadingand welding functions for continuous operation.

Fig. 24. Horizontal coil payoff.


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StraightenersRaw wires are usually paid off in a wound state necessitating a

straightening process to receive straight wires after passing the mill’srolling machines. Unlike wire processing machines, such as springcoiling or bending machines, the rolling process is not too sensitiveto curved inlet wires. The rolling process itself improves the wire’sstraightness provided that rolling is done with adequate wire guidingand tension.

Fig. 26. Flyer arm fixed the boreof a spool.

Fig. 25. Vertical coil payoff.


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Nevertheless suitable roller straighteners arranged in two planes(horizontal and vertical) with five (see Fig. 28) or seven rolls eachshould be used between the payoff and the first rolling machine.

Fig. 28. Five-roll horizontalstraightener.

Fig. 27. Vertical coil payoff.


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Especially when asymmetric shapes (e.g., trapezoidal, half-roundor triangular form) are rolled, it may be difficult to control straight-ness just by means of guiding and tension. In these cases 9-, 11-, or13-roller straighteners are used before winding the wire. Thisstraightening operation requires extreme care because the wire isalready finish rolled at this point of the mill and further roll contactcan change the shape’s form and dimensions or scratch the wire’s sur-face. To reduce this risk, the straightening rolls are usually adapted tothe wire shape by profiling the grooves on the rolls.

Straightening at this stage, compared to straightening the inletwire, requires much more effort and is only done if other measuresdo not meet the straightness requirements.

Cleaning SystemsIn rolling mills wire cleaning is typically applied to the inlet wire

before rolling and to the finished wire before winding.Inlet Wire Cleaning. Cleaning of the inlet wire is done for different

reasons:

• The degree of forming ability increases when residualdrawing lubricants are removed because the increasedfriction coefficient allows bigger reduction without slippage.

• Cleaned inlet wire will show smaller dimensional variationsafter rolling because the variations of the cleaned wire’sfriction coefficient are smaller than those of a polluted wire,and these variations cause dimensional variations as theyaffect the degree of spread.

• The surface quality of the rolled wire is improved.• The lifetime of the coolant in the rolling machine is extended

because the lubricant does not have to absorb the impuritiesthat are released during rolling.

• Surface impurities, such as scale, cause extensive machineand tool wear.

The cleaning method is selected with regard to the impurities thatmust be removed:

• Hot-rolled wire rod is covered with scale. Since batch descalingby pickling has become environmentally unpopular andbecause the final liming also is a contaminate that influences


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the rolling process, the methods of inline descaling havebecome more important. Best results are reached by shotblasting (see Fig. 29), but this process requires a relativelyhigh investment and maintenance. The method of crackingthe scale by bending the wire with rolls and subsequentbrushing is an alternative. The cleanliness after inlinedescaling depends on the line speed. Higher line speedsrequire more effort in descaling technology and the inlinedescaling unit may bottleneck the line with regard to speed.

• The drawing process for steel wires uses dry or wet lubricantsthat usually are not removed after drawing. Residual lubricantscan be removed by washing (preferably with the heated and high pressured rolling process lubricant), brushing, orultrasonic cleaning. As each of these methods has its prosand cons, the selection is made according to investment andmaintenance costs, required line speed, and cleanliness.

Finished Wire Cleaning. Cleaning of the finished wire is necessary to:

• keep the rolling machine lubricant inside the machineinstead of carrying it out.

• meet the cleanliness requirements for finished wire.

Fig. 29. Descaling by shot blasting.


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Common cleaning methods include:

• Wiping the wire surface to remove rolling lubricant. Themost effective material for wiping (e.g., sponge rubber, felt,leather, wood) is often found by a trial-and-error method,since no material is univerally applicable.

As the wiper picks up the dirt, its cleaning performancedegrades. Therefore, required maintenance is important.

Air wiping is one method to clean finished wire. It involves blow-ing off the lubricant used for rolling with compressed air applied withspecially designed nozzles developed according to the wire’s shape.This method is almost maintenance free since there is no wear of thenozzle (see Fig. 30).

Air wiping is expensive due to the high production costs of com-pressed air. Therefore, it is usually used in combination with mechan-ical wipers. First the lubricant is wiped off and then residual film isblown off.

Ultrasonic Cleaning. This process achieves better results than wip-ing, blowing, or their combination, but it means another level ofinvestment and maintenance since an ultrasonic cleaning unit is acomplex system. The system comes with a sound transmitting fluidthat picks up the removed dirt and, therefore, needs replacement orcleaning. Furthermore the required space for an ultrasonic cleaning

Fig. 30. Air wiper by MGS Hall.


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unit is considerable, at least when high production speeds aredemanded.

Calibration UnitsEach wire that is produced by rolling requires an inlet wire with

a specific section area—usually a specific round wire. The degree ofspread, which determines the inlet wire dimension, is influenced bya combination of parameters and the ideal inlet wire dimensions maydiffer from one day to another.

Ferrous wires with low tensile strength provide influence inspread by tension adjustment between rolling stands or by the mod-ification of the rolling sequence. In contrast high tensile wires showalmost no reaction to these measures.

To adjust dimensions of the inlet wire to the actual demand of theprocess and to minimize the inventory of inlet wires to be kept instock, an inline calibration of the inlet wires is advantagous. Since adie calibration—at least for steel wires—requires a special wire prepa-ration, the calibration by rolling is beneficial (see Fig. 31). Therefore,a single drum capstan and an undriven rolling machine (typically asimple cassette style with two pairs of rolls for round-oval-roundreduction) is the most suitable equipment for calibration.

Guiding SystemsWire guiding is often underrated. At the positions where the wire

enters and exits the roll gap, guides help to:

• fill the caliber that is built by the shaped rolls in theintended way. Trapezoidal shapes, for example, will showdifferent corner radii because of lateral forces during rollingif no inlet guide is used and they will be curved because ofdifferent elongation along the long and short sides of theshape if no outlet guide is used.

• force the incoming wire to enter the caliber slightly besideits center to create a trapezoidal shape with four identicalradii. Outlet guides can obviate wire bending when exitingthe caliber. Guide straightening can eliminate the need forstraightening rolls.

• minimize dimensional variations because wire vibrations aredamped.


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Guiding can be affected by shaped guide rolls, nozzles, or guiderails. Rolls are advantageous because of their smooth contact with thewire. However, due to the size of the guide rolls their distance to theroll gap is rather great and guiding performance is low.

Nozzles are ideal for round wires as their round bore is easy tomake. In contrast manufacturing costs and their disability of adjust-ment inhibit the use of nozzles for shaped wire.

Due to the above reasons guide rails in many cases are the bestsolution with regard to effectiveness and cost. Usually two rails areapplied across from each other. Each rail is adjustable. Either thecomplete rails are shaped to adapt the wire’s profile or the rails areequipped with shaped mouthpieces.

Depending on the application, guides are made of hardenedsteel, tungsten carbide, ceramic, or plastic.

Synchronization UnitsRolling mills incorporate numerous electrically driven units that

are involved in transporting the wire, such as payoffs, rollingmachines, capstans, and spoolers. Due to wire elongation duringrolling or drawing the material’s speed increases when it passes themill. The inlet wire is moving slower than the outlet wire.

Fig. 31. Inlet wire calibration (round→→oval→→round)with undriven rolling machines.


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Moreover the drives of payoffs and spoolers have to adapt to the actual coil diameters for unwinding and winding the wire withproper tension.

In a multi-stand rolling machine, usually the last driven rollingmachine or the last capstan is the speed master for the line. Thespeed of the other driven machines—also referred to a slaves—is syn-chronized to this speed master by means of dancers or tension con-trol units.

Dancer Control. Dancers (see Fig. 32) are able to accumulate a cer-tain volume of wire by means of one or more moveable deflectionrolls if the speed of the slave is too slow or too fast. The term“dancer” is used for these systems because of the motions of themoveable roll. By preloading the deflection rolls by weight, spring,or a pneumatic cylinder, the wire is always tied. Moreover the wiretension can be adjusted by changing the preload.

If the slave’s speed is too slow or too fast, this will increase ordecrease the amount of wire stored in the dancer and the moveabledancer roll will indicate this asynchrony between the speed of themaster and slave by leaving its neutral position. By means of a sen-sor, which forwards the position of the moveable roll to the electricaldrive control, the speed difference is detected and compensated bythe control system until the moveable roll has returned to its neutralposition.

Fig. 32. Dancer integrated in cooling basin.


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Due to the increased dynamics of today’s control systems thesemovements are almost invisible in state-of-the-art rolling machines.

Tension Control. A tension control system also uses a deflectionroll. Unlike in a dancer it cannot move, but it incorporates a load cellinstead. The load cell’s signal is proportional to the wire tension.

The main difference compared to dancer control systems is thattension control systems do not accumulate wire. Any speed asyn-chrony immediately changes wire tension. By adjusting the speed ofthe slave with regard to the load cell signal, tension is kept constant.

The operation of dancer-controlled lines is easier, since thedancer’s ability to accumulate wire reduces the risk of breakage orslippage due to excessive tension, especially during line set-up andwire threading. However the intense wire bending in dancers limitsits use to wire thicknesses below 8 mm. Larger sizes require the useof tension control or torque control.

Torque Control. Unlike dancer or tension control units a torquecontrol system is a speed control technique integrated into the elec-trical control system. The premise is to limit the torque of the slavemotor to just below the torque needed to drive the rolls. The wirepasses the slaves before it enters the master. Because the torque of thespeed master is unlimited, the master pulls all slaves and the wire isalways tensioned.

The difficulty with this system is adjusting to the slaves’ torquelimitation. If torque is too low, the wire might break or slip. If torqueis too high, wire loops will show up between rolling machines. Unlikedancer and tension control systems there are no feedback signals toindicate the wire tension or to enable an automatic adjustment. Eachchange of machine load, which is affected by roll adjustment,changes torque requirements and forces the operator to adjust thetorque limitation.

The main advantage of torque control is that wire deflection isnot needed, minimizing the distance between stands.

Inline Measuring Systems and Automatic Gauge ControlUp to line speeds of 40 m/min. skilled operators are able to check

wire dimensions with a micrometer screw without reducing linespeed. However, safety regulations do not allow this form of meas-urement because in most countries line operation at speeds above 15m/min. requires closed machines that restrict the operator’s access tothe wire.


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It is possible to check wire dimensions when the line is stoppedor in the creep speed range below 15 m/min. where safety coversmay be opened. However, as mentioned before, wire dimensions athigh speeds differ from those at low speed or standstill because of rollexpansion due to heat, machine distortion due to heat, and speeddependency of wire spread.

To determine the actual dimensions at high speeds without theability of measuring during operation, the line must be stopped andthe finished coiled wire must be unwound to be able to check dimen-sions of a portion that was rolled at high speed. This method may beacceptable for a spot check to determine process accuracy, but it isunreasonable for modern quality management.

For the above mentioned reasons modern rolling mills incorpo-rate inline measuring systems. The available units can be dividedinto two groups: contact and non-contact measuring systems.

Contact Measuring Systems. These systems contact the wire withsensors (or displacement transducers). Usually each measuring pointuses two pairs of these sensors to touch the wire on opposite points.The wire dimension is calculated as an average of both signals tocompensate for wire movement or vibration.

Standard contact measuring systems today use digital sensors(displacement transducers) and come with two pairs of sensors in twoplanes displaced by 90 degrees to measure, e.g., thickness and widthof a flat wire or width and greatest thickness of a trapezoidal shape.Also special designs adapted to certain types of wire shapes are available.

Wire guides with rolls to prevent vibrations and wire twist (whichwould falsify the measured values) should be arranged in front of andbehind the measuring unit. However, measurement errors due towire twist is less critical in contact measurement systems as it is innon-contact systems.

Contact measurement units reach accuracies in the range of +/-0.001 mm.

Non-contact Measuring Systems. The most common type of a non-contact measuring system is the laser gauge, which is based on theshadow measuring system. Parallel laser light is emitted by a trans-mitter toward a receiver, and the wire is put between the transmitterand receiver. The size of the receiver’s shadow zone is determined,which corresponds to the size of the wire.


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Just like contact measuring systems, laser gauges usually checktwo dimensions by integrating two transmitter-receiver units with 90degree displacement in a collective housing.

Laser gauges are very sensitive against wire twist. Thicknessmeasurement of a wide flat wire is critical because a slight wire twistwill increase the shadow immensely. Width measurement of thesame flat wire is much less critical. Therefore, sometimes for flat wiremeasurement combinations of a contact measurement system forthickness and a laser gauge for width are found because they are lessexpensive (see Fig. 33).

Since laser gauges do not contact the wire, they cannot distin-guish between wire material and adherent residual coolant or dirt,thus making wire cleaning before measuring critical.

Wire gauges are very precise. They reach accuracy in a rangebelow +/-0.001 mm.

A different approach to non-contact shape measuring is the lightsection method, which uses lasers and cameras to determine wiredimensions like thickness and width. These criteria are displayed ona computer monitor where they can be compared to maximum andminimum shape tolerances.

The accuracy of the systems currently available is in a range of+/- 0.005 mm, which is not acceptable for many of today’s applications.

Once the actual dimensions of the wire are available, these val-ues can be processed in the machine’s control system called

Fig. 33. Contact measuring for thickness combinedwith laser gauge measuring for width.


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Automatic Gauge Control (AGC). Reports can be printed; statisticalevaluations can be provided; and the actual dimensions can be usedto automatically adjust the machine to the nominal wire dimensions.

Then, when the actual and the nominal dimensions are subtracted,the difference is fed into the roll adjustment of the roll that creates theaccordant dimension. For example, in a standard flattening line thethickness control adjusts the final two-high stand and the width con-trol affects the last edger.

State-of-the-art rolling mills do not restrict the AGC to the lastrolling machines for each axis. They allow a free combination of lineroll adjustments and measuring points. For example, all roll adjust-ments of two-high units in a flattening mill could be controlled by thethickness—AGC. This results in a smoother behavior of the entire linesince heat compensation is dispersed to all two-highs units.

Pulling DevicesUndriven rolling machines and drawing dies require a means to

drive the wire. In wire rolling machines the following pulling devicesare used for this task.

Caterpillar Pull-offs. Two driven belts made of steel cord rein-forced rubber are pressed toward each other and form a commonstraight channel into which wire is fed. The advantage of a caterpil-lar pull-off is its friendly operation to the wire surface. Nevertheless,due to the frictional contact between belts and wire the maximumtraction force is limited. Caterpillars are often found in electric cablemachinery and only seldom in wire processing machines.

Single-Drum Capstans. Capstans equipped with a single conicaldrum are typically used in single- or multistand drawing lines forround wire. In rolling machines single drum capstans are used forinline round wire calibration with drawing dies or friction-drivenrolling machines. The wire is wrapped around the drum betweenthree and eight times.

The drum is conical and it is limited by a flange at the greaterdiameter of the cone. The incoming wire squeezes in the gapbetween the flange and first winding, and this forces the windings toslide on the drum away from the flange. The drum’s conical formallows the wire to release tension with each turn. If the cone angle istoo great, the capstan’s pulling ability is limited due to fast tensionrelease and related slip. Cone angles that are too small inhibit the


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axial wire sliding because of tension-related high-contact forces. Thewire will build up at the flange.

Water-cooled drums are sometimes used to cool the wire. In thiscase capstan designs with vertical axes are preferred. Horizontal axesare used sometimes also.

The major disadvantage of single drum capstans is the wire sur-face damage caused by the sliding movement between wire, drum,and flange; the wire-to-wire contact creates scratches.

Double-Drum Capstans. To avoid wire surface defects the doubledrum capstan was introduced to the wire processing industry (seeFig. 34). The axial displacement winding by winding is realized byslightly tilting one of the drums, which eliminates surface defects thatwould have been caused by flange and inter-wire contact. The drumsare cylindrically shaped or are minimally conical.

Because of the mechanical features of the double-drum design itis often used for shaped wires that would be damaged on conicaldrums. For final, favorable skin passes a combination of undrivenprofile rolling machines and a double-drum capstan is used. Unlikedriven rolling machines there is no risk of slippage when undrivenrolling machines are used for skin passes. Moreover the capstan actsas isolation for vibrations between the rolling and the coiling sectionof a mill. Any vibration created by the coiling process (e.g., layerwinding) cannot pass through to the rolling machines. As a result, thedimensional accuracy of the rolling process is enhanced.

Fig. 34. Double-drum capstan.


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Actual double-drum capstan designs come with two driven rolls,a motorized tilting system, tungsten carbide drum coatings, andwater-cooled drums.

Take-upsThe take-up unit represents the end of a rolling machine. Take-

ups are the interface to the shipment packaging or to downstreamprocessing machines, functioning to prepare the wire product inwhatever way it is required.

Take-ups can be classified in two basic groups: static and dynam-ic designs that bunch the wire statically or through rotation duringline operation. One advantage of static take-ups is that in most casesthey are simpler than dynamic take-ups, which makes investmentand operation costs lower.

In lines where wire straightness is a main issue, dynamic take-upsare preferred. The helix created in the wire by static take-ups leadsto straightness problems in downstream wire processing.

Unlike round wiredrawing machines, shaped wire rollingmachines very seldom use static take-ups. One example is the deadblock coiler, which can be used for small wire dimensions. The wire iscoiled onto carriers or into barrels.

Many dynamic take-up designs exist that can be adapted to therequired packaging. The main difference in packaging is whether thewire is layer-wound or if loose coils are produced. Layer-winding isadvantageous because it offers easier unwinding in the subsequentwire processing machines and surface defects are minimized.

Examples of dynamic take-ups include the following.Oscillation-spoolers. Oscillation-spoolers exist in cantilever or

sleeve design (see Fig. 35) for wire that is layer-wound on spools. Tocreate layer-wound coreless coils these spoolers are equipped withexpandable mandrels.

To lay the wire precisely layer by layer, it is advantageous to tra-verse the spool so that the wire maintains its straight direction out ofthe rolling machine. Although more expensive, this system com-pared with the alternative—traversing wire and non-mobile spool—results in fewer injuries and better wire straightness after uncoiling.

Today the traversing systems are usually computer-controlledand provide some special features to generate faultless spools.

Dynamic Horizontal Coilers. This type of coiler is used mostly forlarge shaped rod with dimensions greater than 100 mm2 and it is the


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only type that can handle wires greater than 400 mm2. As the wire iscoreless wound, plastic bending is required, and this is created by aset of adjustable bending rolls. Some types come with oscillatingbending rolls to create more compact coils (see Fig. 36).

Dynamic Vertical Coilers. The basic concept is identical to thedynamic horizontal coiler. The design is simpler and the conceptallows for the use of two carriers to minimize downtime. Few take-ups of this design are found as most wire shapes do not allow thebending of the rolled wire around its vertical axis.

Due to the weight of the wire windings that hang on the bendingrolls this coiler type tends to create wire torsion especially when largesections are processed. Therefore the application of this type of take-up is limited to sections below 200 mm2.

Shears and SawsMany wire products are based on cut-to-length bars. Instead of

coiling the wire after rolling and subsequently de-coiling, straighten-ing and cutting, it is alternatively possible to integrate the cut-to-length process in the rolling machine.

Cutting refers to the different ways of dividing the wire into sec-tions. In practice different methods such as shearing and sawing arecommonly used, and laser and jet-cutting are also possible.

As the cutting and subsequent bar handling processes are notcontinuous processes during rolling, they usually limit the line speed.

Fig. 35. Horizontal spooler insleeve design.


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Rolling machines with integrated cutting equipment are primarilyfound where large wire sections are processed, because their linespeeds usually are lower, and straightening and cutting on separatelines is more intricate for large sections than for small.

Cutting-to-length processes differ in systems that stop the wire forcutting (static systems) and others that accelerate the cutting systemto wire speed before cutting (dynamic or also called flying systems).

Static systems require an accumulator in front to collect the wireduring the cutting process and a clamping system to stop the wiremovement during cutting. Because the accumulator grows in sizewith the wire section, static cutting systems are limited to wire sec-tions below 100 mm2. The cutting is done with hydraulic shears, cut-off grinders, or bandsaws.

For larger sections the cutting system is mounted on a drivenplatform that accelerates to wire speed, cuts, and moves back to itsstarting position. These flying shears or flying saws (see Fig. 37) areequipped with powerful drives. The cycle time for acceleration, cut-ting, deceleration, and return movement limits the line speed to amaximum 100 m/min. For bar lengths below 2 m the maximum linespeeds are even slower.

Fig. 36. Horizontal coiler.


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Lubricating and Cooling SystemIn rolling machines the coolant serves two purposes: wear protec-

tion and cooling.Wear Protection. With regard to wear reduction, the function of the

coolant is to separate metallic surfaces by building a lubricating filmbetween them. This film has to withstand the rolling force and highlocal temperatures.

The quality of the lubrication film also affects the quality (degreeof roughness) of the wire surface.

Cooling. Without cooling, especially in multi-stand lines, the wiretemperature would rise stand by stand. The result would be a loss ofquality with regard to dimensional accuracy, because:

• As the friction coefficient between wire and roll changeswire spread differs.

• As the yield strength of the wire decreases, wire spreaddiffers. This leads to lower separating forces followed bydimensional variations because of the elasticity of the rolling machine.

Insufficient cooling can create other problems when wires arelayer-wound on spools. The wound package shrinks during coolingand this damages either the spools or the wire.

Fig. 37. Flying shear.


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Two types of coolants are used in cold rolling processes: pure oilsand emulsions made of soluble oils and water.

The higher the lubricant viscosity is, the smoother the wire sur-face will be. Therefore, thick oils are preferred over emulsions whensurface quality is the main concern. On the other hand the coolingefficiency of emulsion is approximately twice as high compared topure oils.

To minimize wear and to cool the rolls, the coolant is sprayedinto the contact zones between wires and rolls. For efficient wirecooling between stands modern rolling machines come with coolingzones such as flooded dancer control basins (see Fig. 32).

The lubricant is contained in a tank for each rolling machine ora central tank to serve multiple lines. The tank is connected with pip-ing, and the flow pump and return pump control the coolant cycle(see Fig. 38).

As the energy needed for the rolling process heats up the wireand the wire adds heat to the coolant, the temperature in the tankrises during machine operation. To keep the coolant temperaturewithin an ideal range, the tank is usually equipped with a re-coolingsystem such as a water-cooled heat exchanger.

For high precision wire rolling even-heating systems are used tomaintain proper coolant temperature during standstill times such asmachine setup or weekends.

Another important lubricant issue is its cleaning. Sedimentationis the most effective cleaning process, but because it is extremelyslow it is not applicable. Therefore, filtration is needed. Dependingpurity requirements the filtration either is handled in the mainstreamof the return pump or in a separate cycle that houses its own pump.

The purity of the coolant is important with regard to the lifetimeof the coolant (especially when emulsion is used), machine cleanli-ness, and wire surface quality.

Electric ControlIn the beginning 17th century of the industrialization era in

Europe, man built the first machines to produce round wires. Insteadof pulling the wires manually through iron dies, the first capstanswere used to draw small batches of wire in a single-pass process.These capstans were usually driven by steam engines and transmit-tance belts. The first driven rolling machines—simple two-high designswith manual adjustment—were driven by the same power source.


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When the electric motor was developed around 1870, it displacedthe steam engines. The single-stand rolling machine design was notreplaced, however, until around 1950 when speed control of D.C.motors by converters was introduced into the machine-makingindustry. From then on it was possible to build multistand machineswith independent speed-controlled drives that enabled wire elonga-tion during rolling and spooling with constant tension independentof the actual spool diameter.

Control signals were originally analog. For example, a motor rev-olution between 0 and 1500 rpm was controlled by a speed-propor-tional signal of 0 to 10 V set by a potentiometer or by the position ofa dancer arm. The motor’s tachometer fed back an analog voltagethat was proportional to the actual speed of the motor.

In addition to speed and tension control, these analog drives werealso used for the first automatic gauge controls. The electric controlautomated roll adjustment and increased dimensional accuracy.

In the late 1980s the first programmable logic controls (PLCs)were introduced into rolling machines (see Fig. 39). Instead of wiringbetween sensors (e.g., push buttons, limit switches, etc.) and actors(e.g., motors, valves, etc.) the sensors and actors are connected to theinput and output of the PLC hardware. The linkage between inputand output is made by a software program. Machine functionality ismuch more flexible and versatile. Software modifications are madein minutes. If necessary the service is done via remote access bymodem or Internet.

In the mid 1990s the electronic speed and torque control of A.C.motors was improved. From then on the A.C.-technique was pre-

Fig. 38. Coolant tank with pumps, filter, heatexchanger and piping.


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ferred because of the low maintenance requirements of the A.C.motor and its ability to operate even in dirty or wet environments.

Today A.C. motors represent the industrial standard. Servo- orstep motors are used only in situations that demand the highestspeed, accuracy, or dynamics. In high-dynamic applications such ashigh-speed oscillating spoolers even linear drives are found.

The control is generally done by a PLC. Instead of one PLC inthe machine’s central cabinet, decentralized PLCs are used in cabinetsof line components such as payoffs, rolling machines, and spoolers.The PLCs are connected via a bus system. The cabling is simplifiedand due to short cable lengths connectivity problems are reduced.

Machine operation is done on PC-like touch panels instead ofusing push buttons. Machine setups are stored in and loaded fromrecipes. The control is connected to the Internet to provide world-wide remote service.

The precision of today’s electric controls has increased the accu-racy of the rolled wires. At least 50% of a mill’s quality is reached bysoftware engineering.

Fig. 39. Movable operator panel.


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Some Typical Rolling Mills for Ferrous WiresThe previously described components are used to design com-

plete rolling mills. Typical examples include:

Reduction Rolling MillsUnlike the drawing process the rolling process does not require

any wire preparation such as coating to improve the efficiency of thelubricant. Therefore, the surface quality of the final wire after rollingis better than after drawing. For this reason rolling competes withdrawing, and rolling machines are becoming more and more popu-lar for round wire reduction (see Fig. 40).

Flattening MillsIn flattening mills the wire is rolled alternately vertically with

two-high rolling machines and horizontally with edgers (see Figs. 41and 42). When dimensions are changed, only the profiled edger rollsneed to be changed. Depending on wire dimensions line speedsbetween 80 and 800 m/min. and dimensional accuracies between +/-0.003 mm and +/- 0.020 mm are reached.

Shaping MillsIn shaping mills the wire is rolled with profile rolling machines

(see Figs. 43 and 44). Very often a two-high machine is found as thefirst stand to create spread. Depending on wire dimensions linespeeds between 40 and 500 m/min. and dimensional accuraciesbetween +/- 0.003 mm and +/- 0.020 mm are reached.

Fig. 40. Reduction rolling mill with round→→hexagon→→roundsystem.


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Fig. 43. Two-stand shaping mill.

Fig. 42. High-speed flattening mill.

Fig. 41. Two-stand flattening mill.


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Fig. 44. Modern five-stand shaping mill with housing.


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ROLLING FLAT AND SHAPED WIRE...FERROUS WIRE HANDBOOK 814 Ferrous2_Ch1.qxp 3/14/2008 9:16 AM Page 814 elongation. The simplest example is the flat rolling of round wire (see Fig. 5),