Rolling Report { Production}

Alexandria University - Faculty of EngineeringProduction Engineering Department

ts1 Year Naval Architecture and Marine Engineering DepartmentFirst Semester - Academic Year 2009/2010

Subject NameMaunfucturing Engineering

Report: Metal Rolling

Team Members:

1) Hassan MahmoudAhmed 2) Hesham Atef Mohamed3) Abdelrahman Khamis 4) Riham Taher Ahmed5) Abdelrahman Abdullah Ali 6) Sara Hassan Ali7) MahmoudMahmoud Shawky 8) Hader Mostafa Azat

Presented to: Dr. Ismail A.Abdullah

Due Date: 23/12/2009

Metal Rolling Report1Page

1. Introduction:

ROLLING is the process of reducing the thickness or changing thecross section of a long work-piece by compressive forces appliedthrough a set of opposed rotating rolls (Fig. 1). This PrimaryWorking operation takes a solid piece of metal (generally from acast state, such as an ingot) and breaks it down successively intoshapes such as slabs, plates, and billets. Rolling is a bulkdeformation process. The term bulk deformation is applied to theprocessing of workpieces having a relatively small surface area-to-volume (or surface area-to-thickness) ratio. In all bulk deformationprocessing, the thickness or cross-section of the workpiece changes.Rolling, which accounts for about 90% of all metals produced bymetal working processes, was first developed in the late 1500s.Temperature, size of the workpiece can group rolling processes. Forexample, using temperature as a criterion, the categories would behot rolling and cold rolling. If we are interested in size, it isimportant to note that plates are generally regarded as having athickness greater than 6 mm, whereas sheets are generally less than6 mm thick. And where plates are used for structural application,such as machine structures, ship hulls, bridges and nuclear vessel,we find that sheets are provided to manufacturing facilities as flatpieces or as strip in coils for further processing into variousproducts, such as automobile, aircraft bodies, food and beveragescontainers, and kitchen an office equipments. Flat rolling, striprolling, or simply rolling, is the most basic operation, where therolled products are flat plates and sheets, and the main purpose is toreduce the thickness of the material (Fig.1). This process results inthe production of flat plate, sheet, and foil in long lengths, at highspeeds, and with good surface finish, especially in cold rolling. Itrequires high capital investment and low to moderate labor cost.In addition to flat rolling, various shapes can be produced by shaperolling. Straight and long structural shapes, such as solid bars (withvarious cross-sections), channels, I-beam, and railroad rails, arerolled by passing the stock through a set of specially designed rolls(Fig.1)


Traditionally, the initial material form for rolling is an ingot, but thispractice now is being rapidly replaced by that of continuous castingand rolling, at much efficiency and a lower cost.Rolling is usually first carried out at elevated temperatures (hotrolling); during this phase, the coarse-grained, brittle, and porousstructure of the ingot or the continuously cast material is brokendown into a wrought structure having finer grain size andenhanced properties.

FIGURE 1 Schematic outline of various flat and shape rolling processes


2. Flat Rolling:

A schematic illustration of the flat rolling processes is shown in Fig.2a.A strip of thickness ho enters the roll gap and is reduced to thickness hfby a pair of rotating rolls, each roll being powered through its own shaftby electric motors. The surface speed of the roll is Vr. The velocity of

the strip increases from its entry value, Vo, as it moves through the rollgap, in the same way fluid must flow faster as it moves through aconverging channel.The velocity of the strip is highest at the exit from the roll gap; wedenote it as Vf there. Because the surface speed of the roll is constant,there is relative sliding between the roll and the strip along the arc ofcontact in the roll gap, L.At one point the contact length, called the neutral point or no-slip point,the velocity of the strip is the same as that of the roll. To the left of thispoint, the roll moves faster than the strip; to the right of this point, thestrip moves faster than the roll. Hence, the frictional force, which opposemotion, act on the strip as shown in Fig.2b.

FIGURE 2 (a) Schematic illustration of the flat-rolling process. (b) Friction forces actingon the strip surfaces. (c) The roll forces, f, and the torque acting on the rolls. The width W of thestrip usually increases during rolling, as is shown in Fig. 5.


2.1 Frictional Forces:

The rolls pull the material into the roll gap through a net frictional forceon the material. It can be seen that this net frictional force must be to theright in Fig.2b; consequently, the frictional force to the left of the neutralpoint must be higher than the frictional force to the right.Although frictional is necessary for rolling materials, energy isdissipated in overcoming the friction; thus, increasing friction meansincreasing forces and power requirements. Furthermore, high frictioncould damage the surface of the rolled product. A compromise has to bemade, one which induces low coefficients of friction by using effectivelubricants.

The maximum possible draft, defined as the difference betweenthe initial and final thicknesses, (ho – hf), is a function of the

coefficient of friction, μ, and the roll radius, R:ho – hf = μR

Thus, the higher the friction and the larger the roll radius, thegreater the maximum possible draft (and reduction in thickness)becomes. This situation is similar to the use of large tires (highR) and rough treads (high μ) on farm tractors and on off-road earth-moving equipment, which permit the vehiclesto travel over rough terrain without skidding.

2.2 Roll Force & Power Requirement:

Because the rolls apply pressure on the material in order toreduce its thickness, a force perpendicular to the arc contact(Fig. 2c) is needed. Note, in Fig. 2c, that this roll force, f, isshown as the perpendicular to the plane of the strip rather thanas at an angle. This alignment is used because the arc of contactis generally very small compared to the roll radius, so we canassume the roll force to be perpendicular without causingsignificant error.

The roll force in the flat rolling can be estimated from the


formula f = L W Yavg

Where L is the roll-strip contact length, W is the width of thestrip, and Yavg is the average true stress of the strip in the rollgap. This equation, ideally, is for a frictionless situation.The higher the coefficient of friction is between the rolls and thestrip, the greater becomes the divergence, and the formulapredicts a lower roll force than the actual force.The power required per roll can be estimated by assuming thatthe force f acts in the middle of the arc of contact: In Fig 2.c,

a= L/2 . Torque per roll is the product of f and a. therefore,the power per roll in S.I units is

Power= πf LN/ 60,000 (KW) or

Power= πf LN/ 33,000 (hp)This formula calculates the power for one roll, so to calculatethe total power we multiply it by 2.Reducing Roll Force, Roll forces can cause deflection andflattening of the rolls; such changes will, in turn, adverselyaffect the rolling operation. Also, the roll stand, including thehousing, chocks, and bearing (Fig. 3), may stretch under the rollforces to such an extent that roll gap can open significantly.Consequently, the rolls have to be set closer than was calculated,to compensate for this deflection and to obtain the desired finalthickness. So, Roll force can be reduced by any of the followingmeans:

1. reducing friction;2. using smaller-diameter rolls, to reduce the contact

area;3. taking smaller reductions per pass, to reduce the

contact area; and4. rolling at elevated temperatures, to lower the strength

of the material.


FIGURE 3 Schematic illustration of a four-high rolling-mill stand, showing itsvarious features. The stiffnesses of the housing, the rolls, and the roll bearings are allimportant in controlling and maintaining the thickness of the rolled strip.

2.3 Geometric Considerations:

Because of the forces acting on them, rolls undergo certaingeometric changes. Just as a straight beam deflects under atransverse load, roll forces tend to bend the rolls elasticallyduring rolling (Fig. 4a); the higher the elastic modulus of the rollmaterial, the smaller the roll deflection.As a result of roll bending, the rolled strip tends to be thicker(have a crown) at its center than at its edges. The usual methodof avoiding this problem is to grind the rolls so that theirdiameter at the center is slightly larger than at their edges (givethem camber). Thus, when the roll bends, its contact along thewidth of the strip becomes straight and the strip being rolled hasa constant thickness along its width.For rolling sheet metals, the radius of the maximum camberpoint is generally 0.25 mm greater than that at the edges of theroll. When properly designed, cambered rolls produce flat strips(Fig. 4b). However, a particular camber is correct only for acertain load and a certain strip width. To reduce the effects ofdeflection, the rolls can be subjected to bending, by the


application of moments at their bearings (a similar technique tobending a wooden stick at its ends); this manipulation simulatescamber.

FIGURE 4 (a) Bending of straight cylindrical rolls, caused by the roll force. (b)Bending of rolls ground with camber, producing a strip with uniform thickness.

Because of the heat generated by plastic deformation duringrolling, rolls can become slightly barrel-shaped (thermalcamber). (Unless compensated for by some means, thiscondition can produce strips that thinner at the center than at theedges.) Consequently, the total (or final) camber can becontrolled by varying the location of the coolant on the rollsduring hot rolling.Roll forces also tend to flatten the rolls elastically, producing aneffect much like the flattening of automobile tires. Thisflattening of the rolls is undesirable; it produces, in effect, alarger roll radius and, hence, a larger contact area for the samedraft. The roll force, in turn, increases with increased flattening.

Spreading. In the rolling of plates and sheet having highwidth-to-thickness ratios, the width of material remainseffectively constant during rolling. With smaller ratios,however, such as with a square cross-section, the widthincreases considerably in the roll gap, as a result of the same


effect that occurs in the rolling of dough with a rolling pin. Thisincrease in width is called spreading (Fig. 5).It can be shown that spreading increases with a decrease in thewidth-to-thickness ratio of the entering material (because ofreduction in the width constraint), with an increase in thefriction, and with a decrease in the ratio of the roll's radius to thestrip's thickness (the latter two being due to increasedlongitudinal constraint of the material flow in the roll gap).Spreading can be prevented by the use of vertical rolls in contactwith the edges of the rolled product (as in edger mill).

FIGURE 5 Increase in the width (spreading) of a strip in flat rolling. Similarly,spreading can be observed when dough is rolled with a rolling pin.

2.4 Flat-Rolling Practice:

The initial breaking down of an ingot or of a continuously castslab is done by hot rolling. A cast structure includes coarse andnonuniform grains. This structure is usually brittle and maycontain porosities. Hot rolling converts the cast structure to awrought structure (Fig. 6). This structure has finer grains andenhanced ductility, both resulting from the breaking up of brittlegrain boundaries and the closing up of internal defects,


especially porosity.

FIGURE 6 Changes in the grain structure of cast or of large-grain wroughtmetals during hot rolling. Hot rolling is an effective way to reduce grain size inmetals, for improved strength and ductility. Cast structures of ingots and continuouscastings are converted to a wrought structure by hot working.

Now, almost all traditional methods of casting ingots are beingrapidly replaced by continuous casting. Temperature ranges forhot rolling are typically about 450 °c for aluminum alloys, up to1250 °c for alloy steels, and up to 1650 °c for refractory alloys.The product of the first hot-rolling operation is called a bloomor slab (Fig.1). A bloom usually has a square cross-section, atleast 150 mm on the side; a slab is usually rectangular in cross-section. Blooms are processed further, by shape rolling, intostructural shapes, such as I-beam and railway rail. Slabs arerolled into plates and sheets.Billets are usually square, with a cross-sectional area smallerthan blooms; they are later rolled into various shapes, such asround rods and bars, by the use of shaped rolls. Hot-rolled roundrods are used as the starting material for rod and wire drawing;they are called wire rods.In hot rolling blooms, billets and slabs, the surface of thematerial is usually conditioned (prepared for a subsequentoperation) prior to rolling. Conditioning is done by variousmeans, such as the use of a torch (scarfing) to remove heavyscale or of rough grinding to smoothen surfaces. Prior to coldrolling, the scale developed during hot rolling may be removedby pickling with acids (acid etching) or by such mechanical


means as blasting with water (or grinding, to remove otherdefects as well).Cold rolling is carried out at room temperature and, comparedto hot rolling, produces sheet and strip with much better surfacefinish ( because of lack of scale), dimensional tolerances, andmechanical properties (because of strain hardening).Pack Rolling is a flat-rolling operation in which two or morelayers of metal are rolled together; this process improvesproductivity. Aluminum foil, for example, is pack rolled intwo layers. One side of aluminum foil is matte, the other sideshiny: The foil-to-foil side has a matte and satiny finish, but thefoil-to-foil side is shiny and bright, because it has been incontact with the polished rolls.Mild steel, when stretched during sheer-forming operations,undergoes yield-point elongation, a phenomenon that causessurface irregularities called stretcher strains or Lueder's bands.To correct this situation, the sheet metal is subjected to a finallight pass of 0.5% to 1.5% reduction, known as temper rollingor skin pass.A rolled sheet may not be sufficiently flat as it leaves the rollgap, because of variations in the material or in the processingparameters during rolling. To improve flatness, the rolled strip ispassed through a series of leveling rolls. Several different rollerarrangement are used, one of which is shown in Fig.7. Each rollis usually driven separately, by an individual electric motor. Thestrip is flexed in opposite directions as it passes through the setsof rollers.

FIGURE 7 A method of roller leveling to flatten rolled sheets.


2.5 Defects in Rolled Plates & Sheets:

Defects may be present on the surfaces of rolled plates andsheets, or there may be internal structural defects. Defects areundesirable, not only because they degrade surface appearancebut also because they may adversely affect the strength, theformability, and other manufacturing characteristics.A number of surface defects, such as scale, rust, scratches,gouges, pits and cracks, have been identified for sheet metals.These defects may be caused by inclusions and impurities in theoriginal cast material or by various other conditions related tomaterial preparation and to the rolling operation.Wavy edges on sheets (Fig. 8a) are the result of roll bending.The strip is thinner along its edges than at its center; because theedges elongate more than the center, the buckle, because theyare restrained from expanding freely in the longitudinal (rolling)direction. The cracks shown in Fig.8b and c are usually theresult of the poor material ductility at the rolling temperature.Alligatoring, shown on Fig. 8d, is a complex phenomenon andmay be cause by nonuniform deformation during rolling or bythe presence of defects in the original cast billet. Because thequality of the edges of the sheet is important in sheet-metalforming operations, edges defects in rolled sheets are oftenremoved by shearing and slitting operations.

FIGURE 8 Schematic illustration of typical defects in flat rolling; (a) wavyedges, (b) zipper cracks in the center of the strip, (c) edge cracks, and (d) alligatoring.


FIGURE 9 (a) Residual stresses developed in rolling with small rolls or atsmall reductions in thickness per pass. (b) Residual stresses developed in rolling withlarge rolls or at high reductions per pass. Note the reversal of the residual stresspatterns.

2.6 Other Characteristics:

Residual Stresses. Because of nonuniform deformation of thematerial in the roll gap, residual stresses can develop in rolledplates and sheets, especially during cold rolling. Small-diameterrolls or small reduction per pass tend to deform the metalplastically at its surfaces (Fig.9a). This situation producescompressive residual stresses on the surfaces (which can bebeneficial for improved fatigue life) and tensile stresses in themiddle.On the other hand, large-diameter rolls and high reduction tendto deform the bulk more than the surfaces (Fig.9b); this is due tothe frictional constraint at the surfaces along the arc of contactbetween the roll and the strip. This situation produces residualstresses that are opposite of those in the case of the small-diameter rolls.

Dimensional Tolerances. Thickness tolerances for cold-rolledsheet usually range from ± 0.1mm to 0.35mm. Tolerances aremuch greater for hot-rolled plates. Flatness tolerances areusually within ± 15mm/m for cold rolling and ± 55mm/m for hotrolling.


Gage Number. The thickness of a sheet is usually identified bya gage number; the smaller the number, the thicker the sheet.Several numbering systems are used, depending on the type ofsheet metal being classified. Rolled sheets of copper and ofbrass are also identified by thickness changes during rolling,such as 1/4 hard, 1/2 hard, and so on.

3. Shape-Rolling Operations:

In addition to flat rolling, various shapes can be produced byshape rolling. Straight and long structural shapes, such as solidbars (with various cross-sections), channels, I-beams, andrailroad rails, are rolled by passing the stock through a set ofspecially designed rolls (Fig. 10). Because the material's cross-section is to be produced nonuniformly, the design of a series ofrolls (roll-pass design) requires considerable experience in orderto avoid external and internal defects, to hold dimensionaltolerances, and to reduce roll wear.

FIGURE 10 Stages in the shape rolling of an H-section part. Various otherstructural sections, such as channels and I-beams, are also rolled by this kind ofprocess.


3.1 Ring Rolling:

In the ring-rolling process, a thick ring is expanded into a largediameter ring with a reduced cross-section. The ring is placedbetween two rolls, one of which is driven (Fig. 11a), and itsthickness is produced by bringing the rolls closer together asthey rotate. Since the volume of the ring remains constantduring deformation, the reduction in thickness is compensatedby an increase in the ring's diameter.

FIGURE 11 (a) schematic illustration of a ring-rolling operation. Thicknessreduction results in an increase in the part diameter. (b) Example of cross-sections thatcan be formed by ring rolling.

The ring-shaped blank may be produced by such means as bycutting from a plate, by piercing, or by cutting a thick-walledpipe. Various shapes can be ring rolled by the use of shapedrolls (Fig. 11b). Typical applications of ring rolling are large


rings for rockets and turbines, gearwheel rims, ball-bearing androller-bearing races, flanges, and reinforcing rings for pipes.The ring-rolling process can be carried out at room or atelevated temperature, depending on the size, strength, andductility of the workpiece material. Compared to othermanufacturing processes capable of making the same part, theadvantages of this process are short production times, materialsaving, close dimensional tolerances, and favorable grain flowin the product.

3.2 Thread Rolling:The thread-rolling process is a cold-forming process by whichstraight or taped threads are formed on round rods, by passingthem between dies. Threads are formed on the rod or wire witheach stroke of a pair of flat reciprocating dies (Fig. 12a). Typicalproducts are screws, blots, and similar threaded parts.Depending on die design, the major diameter of a rolled threadmay or may not be larger than a machined thread (Fig. 13a) -this is the same as the blank diameter. In either case, volumeconstancy is maintained, because no material is removed.The process is capable of generating similar shapes, such asgrooves and various gear forms, on other surfaces, and it can beused in the production of almost all threaded fasteners at highproduction rates. In another method, threads are formed withrotary dies (Fig. 12b) at production rates as high as 80 pieces persecond.The thread-rolling process has the advantages of generatingthreads without any loss of material (scrap) and with a goodstrength (due to cold working). The surface finish is verysmooth, and the process induces compressive residual stresseson the workpiece surfaces, thus improving fatigue life.Thread rolling is superior to the other methods of manufacturingthreads, because machining the threads cuts through the grain-flow lines of the material, whereas rolling the threads leaves agrain-flow pattern that improves the strength of the thread(Fig.13b).


Threads are rolled on materials in the soft condition, because ofductility requirements; however, they can subsequently besubjected to heat treatment and, if necessary, to final machiningor to grinding. For metals in the hard condition, threads aremachined and/or ground. Rolled threads are readily available inthe most widely used standard thread forms; uncommon orspecial-purpose threads are usually machined.

FIGURE 12 Thread-rolling processes: (a) and (c) reciprocating flat dies; (b)two-roller dies. Threaded fasteners, such as blots, are made economically by theseprocesses, at high rates of production.

FIGURE 13 (a) features of a machined or rolled thread. (b) Grain flow inmachined and rolled threads. Unlike machining, which cuts through the grains of themetal, the rolling of threads causes improved strength, because of cold working andfavorable grain flow.


Lubrication is important in thread rolling operations in order toobtain good surface finish and surface integrity and to minimizedefects. The manner in which the material deforms duringplastic deformation is important, because internal defects caneasily form. Usually made of hardened steel, dies are expensiveto make because of their complex shape. They usually cannot bereground after they become worn. With proper die materials andpreparation, however, die life may range up to millions ofpieces.

4. Production Of Seamless Pipe & Tubing:

Rotary tube piercing is a hot-working process for making long,thick-walled seamless pipe and tubing (Fig.14). It is based onthe principle that when a round bar is subjected to radialcompressive forces, tensile stresses develop at the center of thebar. When it is subsequently subjected to cyclic compressivestresses (Fig. 14b), a cavity begins to form at the center of thebar. This phenomenon can be demonstrated with a short piece ofround eraser, by rolling it back and forth on a hard flat surface,as shown in Fig. 14b.Rotary tube piercing (or Mannesmann Process) is carried outusing an arrangement of rotating rolls (Fig.14c). The axes of therolls are skewed, in order to pull the round bar through the rollsby the axial component of the rotary motion. An internalmandrel assists the operation, by expanding the hole and sizingthe inside diameter of the tube. The mandrel may be held inplace by a long rod, or it may be a floating mandrel without asupport. Because of the severe deformation that the barundergoes, the material must be high in quality and free fromdefects.The diameter and thickness of tubes and pipes can be reducedby tube rolling, which uses rolls (Fig. 15). Some of thoseoperations can be carried out either with or without an internalmandrel. In the pilger mill, the tube and an internal mandrelundergo a reciprocating motion; the rolls are specially shapedand are rotated continuously. During the gap cycle on the roll,


The tube is advanced and rotated, stating another cycle of tubereduction.

FIGURE 14 Cavity formation in a solid round bar and its utilization in therotary tube piercing process for making seamless pipe and tubing. (The Mannesmannmill was developed in the 1880s.)

FIGURE 15 Schematic illustration of various tube-rolling processes: (a) withfixed mandrel; (b) with moving mandrel; (c) without mandrel; and (d) pilger rollingover a mandrel and a pair of shaped rolls. Tube diameters and thicknesses can also bechanged by other processes, such as drawing, extrusion, and spinning.


5. Rolling Mills:

Several types of rolling mills and equipment are built; they usediverse roll arrangements. Although the equipment for hot andcold rolling is essentially the same, there are differences in theroll materials, process parameters, lubricants, and coolingsystems.The design, construction, and operation of rolling mills requiremajor investments. Highly automated mills produce close-tolerance, high-quality plates and sheet at high production ratesand low cost per unit weight, particularly when integrated withcontinuous casting.The width of rolled products may range up to 5m and be as thinas 0.0025mm. Rolling speeds may range up to 25m/s (about amile a minute) for cold rolling, or even higher in highlyautomated and computer-controlled facilities.Two-high or three-high rolling mills (Fig.16a and b) are usedfor hot rolling in initial breakdown passes (primary roughing orcogging mills) on cast ingots or in continuous casting, with rolldiameters ranging from 0.6m to 1.4m. In the three-high orreversing mill, the direction of material is revered after eachpass; the plate being rolled is repeatedly raised to the upper rollgap, rolled, and then lowered to the lower roll gap by elevatorsand various manipulators.Four-high mills (Fig.16c) and cluster mills (Sendzimir or Zmill; Fig. 16d) are based on the principle that small-diameterrolls lower roll forces and power requirements and reducespreading. Moreover, when worn or broken, small rolls can bereplaced at less cost than can large ones. However, small rollsdefect more under roll forces and have to be supported by otherrolls, as is done in four-high and cluster mills. Although the costof a Sendzimir mill facility can be millions of dollars, it isparticularly suitable for cold rolling thin sheet of high-strengthmetals. Common rolled widths are 0.66m, with a maximum of1.5m.


FIGURE 16 Schematic illustration of various roll arrangements: (a) two-high;(b) three-high; (c) four-high; (d) cluster (Sendzimir) mill.

The Planetary mill (Fig. 17) consists of a pair of heavy backingrolls surrounded by a large number of planetary rolls. Eachplanetary roll gives an almost constant reduction to the slab as itsweeps out a circular path between the backing rolls and theslab. As each pair of planetary rolls ceases to have contact withthe workpiece, another pair of rolls makes contact and repeatthat reduction. So, the overall reduction is the summation of aseries of small reductions by each pair of rolls. Therefore, theplanetary mill can hot reduce a slab directly to strip in one passthrough the mill, as it capable of reducing up to 98% in onesingle pass.

FIGURE 17 Schematic illustration of the planetary mill.


In tandem rolling (Fig. 18) the strip is rolled continuously,through a number of stands, to smaller gages with each pass.Each stand consists of a set of rolls with its own housing andcontrols. A group of stands is called a train. The control of thegage and of the speed at which the sheet travels through eachroll gap is critical. Electronic and computer controls, along withextensive hydraulic controls, are used in tandem rollingoperations.

Rolls. The basic requirements for roll material are strength andresistance to wear. Common roll materials are cast iron, caststeel, and forged steel. Tungsten carbides are also used forsmall-diameter rolls, such as the working roll in a cluster mill.Forged-steel rolls, although more costly, have greater strength,stiffness, and toughness than cast-iron rolls. Rolls for coldrolling are ground to a fine finish; for special applications, theyare polished.Note that the bottom surface of an aluminum beverage canappear to have longitudinal scratches on it. This surface is areplica of the roll surface, which is produced by grinding; in thisway, we can easily determine the rolling direction of the originalaluminum sheet.Rolls made for cold rolling should not be used for hot rolling,because they may crack from thermal cycling (heat checking)and spalling (cracking or flaking of surface layers). Note fromearlier discussion that the elastic modulus of the roll influencesroll deflection and flattening.

Lubricants. Hot rolling of ferrous alloys is usually carried outwithout lubricants, although graphite may be used. Water-basedsolutions are used to cool the rolls and to break up the scale onthe rolled material. Nonferrous alloys are hot rolled with varietyof compounded oils, emulsions, and fatty acids. Cold rolling iscarried out with water-soluble oils or low-viscosity lubricants,such as mineral oils, emulsions, paraffin, and fatty oils.


The heating medium used in heat treating billets and slabs mayalso act as a lubricant. For example, residual salts from molten-salt baths offer effective lubrication during rolling.

FIGURE 18 A tandem rolling operation.

A typical tandem sheet-rolling is shown in Fig.18, whichindicates the thickness and the speed of the sheet after eachreduction in the stands. The 2.25mm-sheet is supplied from apay-off reel. The surface speed of the sheet after the firstreduction (stand 5) is 4.1m/s. Four additional reductions aretaken through the rest of the stands. The final thickness of thesheet is 0.26mm, and the sheet is taken up by the take-up reel ata speed of 30m/s. the total reduction taken is

(2.25 -0.26)/2.25=0.88, or 88%.

Metal Rolling ReportPage 23

6. Summary:

Rolling is the process of reducing the thickness or changing thecross-section of a long workpiece by compressive forces appliedthrough a set of rolls. In addition to flat rolling, shape rolling isused to make products with various cross-sections. Products madeby rolling include: plates, sheet, foil, rod, seamless pipe, andtubing; shape-rolled products, such as I-beam and structuralshapes; and bars of various cross-section. Other rolling operationsinclude ring rolling and thread rolling.

Rolling may be carried out at room temperature (cold rolling) or atelevated temperatures (hot rolling). The process involves severalmaterial and process variables, including roll diameter (relative tomaterial thickness), reduction per pass, speed, lubrication, andtemperature. Spreading, bending, and flatting, are importantconsiderations for controlling the dimensional accuracy of therolled stock.

Rolling mills have a variety of roll configurations, such as two-high, three-high, four-high, cluster (Sendzimir), planetary andtandem. Front and/or back tension may be applied to the material,to improve performance and to reduce roll forces.

Metal Rolling ReportI

Contents

1. Introduction……………………………………………12. Flat Rolling…………………………………………….3

2.1 Frictional Forces…………………………………………....42.2 Roll Force & Power Requirements………………………....42.3 Geometric Considerations………………………………….62.4 Flat-Rolling Practice………………………………………..82.5 Defects in Rolling Plates & Sheets………………………..112.6 Other Characteristics…………………………………..…12

3. Shape-Rolling Operations…………………………….133.1 Ring Rolling……………………………………………….143.2 Thread Rolling…………………………………………….15

4. Production of Seamless Pipe & Tubing………………175. Rolling Mills……………………………………………196. Summary……………………………………………….23

Metal Rolling ReportII

References

1. Manufacturing Engineering Technology,Fourth Edition, By Serope Kalpakjian andSteven R.Schmid.

2. Manufacturing Engineering ReferenceBook, By D.Koshal.

Rolling Report { Production}

Documents

Transcript of Rolling Report { Production}