Metal Rolling Processes Metal Rolling Processes and Equipmentand Equipment

Text Reference: “Manufacturing Text Reference: “Manufacturing Engineering and Technology”, Engineering and Technology”, Kalpakjian & Schmid 6/e 2010Kalpakjian & Schmid 6/e 2010Kalpakjian & Schmid, 6/e, 2010Kalpakjian & Schmid, 6/e, 2010

Chapter 13Chapter 13

RollingRollingRollingRollingThe process of reducing the thickness orThe process of reducing the thickness orThe process of reducing the thickness or The process of reducing the thickness or changing the cross section of a long changing the cross section of a long workpiece by compressive forces appliedworkpiece by compressive forces appliedworkpiece by compressive forces applied workpiece by compressive forces applied through a set of rolls through a set of rolls

FIGURE 13.1 FIGURE 13.1 Schematic outline of various flatSchematic outline of various flat--rolling and shaperolling and shape--rolling processesrolling processes Source:Source: After American Iron and Steel InstituteAfter American Iron and Steel Instituterolling processes. rolling processes. Source: Source: After American Iron and Steel Institute.After American Iron and Steel Institute.

FlatFlat--Rolling ProcessRolling ProcessFlatFlat Rolling ProcessRolling Process

FIGURE 13 2FIGURE 13 2 (a) Schematic illustration of the flat(a) Schematic illustration of the flat rollingrollingFIGURE 13.2 FIGURE 13.2 (a) Schematic illustration of the flat(a) Schematic illustration of the flat--rolling rolling process. (b) Friction forces acting on strip surfaces. (c) Roll process. (b) Friction forces acting on strip surfaces. (c) Roll force, force, FF, and torque, , and torque, TT, acting on the rolls. The width of the , acting on the rolls. The width of the strip w usually increases during rolling as shown later in Figstrip w usually increases during rolling as shown later in Figstrip, w, usually increases during rolling, as shown later in Fig. strip, w, usually increases during rolling, as shown later in Fig. 13.5.13.5.

FIGURE 13.3 FIGURE 13.3 Schematic illustration of various roll arrangements: (a) fourSchematic illustration of various roll arrangements: (a) four--high high rolling mill showing various features. The stiffness of the housing, the rolls, and the rolling mill showing various features. The stiffness of the housing, the rolls, and the g g gg g groll bearings are all important in controlling and maintaining the thickness of the rolled roll bearings are all important in controlling and maintaining the thickness of the rolled strip; (b) twostrip; (b) two--high mill; (c) threehigh mill; (c) three--high mill; and (d) cluster (or high mill; and (d) cluster (or SendzimirSendzimir) mill.) mill.

Strategies to reduce roll forceStrategies to reduce roll forceStrategies to reduce roll forceStrategies to reduce roll force

Reducing friction at the rollReducing friction at the roll--workpiece interfaceworkpiece interfaceReducing friction at the rollReducing friction at the roll workpiece interfaceworkpiece interfaceUsing smaller diameter rolls to reduce the Using smaller diameter rolls to reduce the contact areacontact areaTaking smaller reductions per pass to reduce Taking smaller reductions per pass to reduce the contact areathe contact areaRolling at elevated temperatures to lower the Rolling at elevated temperatures to lower the strength of the materialstrength of the materialApplying front and/or back tensions to the stripApplying front and/or back tensions to the strip

FIGURE 13 4FIGURE 13 4 (a) Bending of straight cylindrical rolls(a) Bending of straight cylindrical rollsFIGURE 13.4 FIGURE 13.4 (a) Bending of straight cylindrical rolls (a) Bending of straight cylindrical rolls caused by roll forces. (b) Bending of rolls ground with caused by roll forces. (b) Bending of rolls ground with camber, producing a strip with uniform thickness through camber, producing a strip with uniform thickness through the strip width. Deflections have been exaggerated for the strip width. Deflections have been exaggerated for p ggp ggclarity.clarity.

FIGURE 13.5 FIGURE 13.5 Spreading in flat rolling. Note that similar spreading can Spreading in flat rolling. Note that similar spreading can be observed when dough is rolled with a rolling pinbe observed when dough is rolled with a rolling pinbe observed when dough is rolled with a rolling pin.be observed when dough is rolled with a rolling pin.

FIGURE 13.6 FIGURE 13.6 Changes in the grain structure of cast or of largeChanges in the grain structure of cast or of large--grain grain wrought metals during hot rolling. Hot rolling is an effective way towrought metals during hot rolling. Hot rolling is an effective way towrought metals during hot rolling. Hot rolling is an effective way to wrought metals during hot rolling. Hot rolling is an effective way to

reduce grain size in metals for improved strength and ductility. Cast reduce grain size in metals for improved strength and ductility. Cast structures of ingots or continuous castings are converted to a wrought structures of ingots or continuous castings are converted to a wrought

structure by hot working.structure by hot working.

Hot and Cold RollingHot and Cold RollingHot and Cold RollingHot and Cold RollingHot Rolling leaves a rough mill scale on surfaceHot Rolling leaves a rough mill scale on surfaceg gg gRemove HR mill scale by:Remove HR mill scale by:

Acid etching (“pickling”)Acid etching (“pickling”)Water blastingWater blastingGrindingGrinding

Cold Rolling produces sheets and strips with:Cold Rolling produces sheets and strips with:Cold Rolling produces sheets and strips with:Cold Rolling produces sheets and strips with:finer surface finish (absence of mill scale)finer surface finish (absence of mill scale)better dimensional tolerancesbetter dimensional tolerancesbetter dimensional tolerancesbetter dimensional tolerancesenhanced mechanical properties (due to strain enhanced mechanical properties (due to strain hardening)hardening)

Pack RollingPack RollingPack RollingPack Rolling

Roll two or more sheets togetherRoll two or more sheets togetherRoll two or more sheets togetherRoll two or more sheets togetherImproved productivityImproved productivity

Aluminum sheets (aluminum foil)Aluminum sheets (aluminum foil)Aluminum sheets (aluminum foil)Aluminum sheets (aluminum foil)Matte, satin side Matte, satin side –– foilfoil--toto--foil contactfoil contactSS ffShiny, bright side Shiny, bright side –– foilfoil--toto--roll contact due to roll contact due to high contact stresses with polished rollshigh contact stresses with polished rolls

FIGURE 13.7 FIGURE 13.7 (a) A method of roller leveling to flatten rolled sheets. (a) A method of roller leveling to flatten rolled sheets. (b) Roller leveling to straighten drawn bars(b) Roller leveling to straighten drawn bars(b) Roller leveling to straighten drawn bars.(b) Roller leveling to straighten drawn bars.

FIGURE 13.8 FIGURE 13.8 Schematic illustration of typical defects in flat rolling: Schematic illustration of typical defects in flat rolling: (a) wavy edges; (b) zipper cracks in the center of the strip; (a) wavy edges; (b) zipper cracks in the center of the strip; ( ) y g ( ) pp p( ) y g ( ) pp p

(c) edge cracks; and (d) alligatoring. (c) edge cracks; and (d) alligatoring.

FIGURE 13.9 FIGURE 13.9 (a) Residual stresses developed in rolling with small(a) Residual stresses developed in rolling with small--diameter diameter rolls or at small reductions in thickness per pass. (b) Residual stresses rolls or at small reductions in thickness per pass. (b) Residual stresses

developed in rolling with largedeveloped in rolling with large diameter rolls or at high reductions per passdiameter rolls or at high reductions per passdeveloped in rolling with largedeveloped in rolling with large--diameter rolls or at high reductions per pass. diameter rolls or at high reductions per pass. Note the reversal of the residual stress patterns.Note the reversal of the residual stress patterns.

Gauge (Gage) NumbersGauge (Gage) NumbersGauge (Gage) NumbersGauge (Gage) Numbers

Thickness of sheet is identified by gaugeThickness of sheet is identified by gaugeThickness of sheet is identified by gauge Thickness of sheet is identified by gauge numbernumberThe smaller the number, the thicker the sheetThe smaller the number, the thicker the sheet,,Several numbering systems are used, Several numbering systems are used, depending on type of sheet metal being depending on type of sheet metal being p g yp gp g yp gclassified (steel, copper, aluminum, etc.)classified (steel, copper, aluminum, etc.)Rolled sheets of nonRolled sheets of non--ferrous material are also ferrous material are also identified by thickness changes during rolling, identified by thickness changes during rolling, such as ¼ hard, ½ hard, etc.such as ¼ hard, ½ hard, etc.

FIGURE 13.10 FIGURE 13.10 View of a rolling mill. View of a rolling mill. Source: Source: Courtesy of Ispat Inland.Courtesy of Ispat Inland.gg y py p

FIGURE 13.11 FIGURE 13.11 An example of a tandemAn example of a tandem--rolling operation.rolling operation.pp g pg p

FIGURE 13.12 FIGURE 13.12 Steps in the shape rolling of an ISteps in the shape rolling of an I--beam part. Various beam part. Various other structural sections, such as channels and rails, also are rolled by other structural sections, such as channels and rails, also are rolled by yy

this kind of process.this kind of process.

FIGURE 13.13 FIGURE 13.13 Two examples of the rollTwo examples of the roll--forging operation, also known forging operation, also known as as crosscross--rolling. rolling. Tapered leaf springs and knives can be made by this Tapered leaf springs and knives can be made by this gg p p g yp p g y

process. process. Source: Source: After J. Holub.After J. Holub.

FIGURE 13.14 FIGURE 13.14 (a) Production of steel balls by the skew(a) Production of steel balls by the skew--rolling rolling process. (b) Production of steel balls by upsetting a cylindrical blank. process. (b) Production of steel balls by upsetting a cylindrical blank.

Note the formation of flash The balls made by these processesNote the formation of flash The balls made by these processesNote the formation of flash. The balls made by these processes Note the formation of flash. The balls made by these processes subsequently are ground and polished for use in ball bearings.subsequently are ground and polished for use in ball bearings.

FIGURE 13.15 FIGURE 13.15 (a) Schematic illustration of a ring(a) Schematic illustration of a ring--rolling operation. rolling operation. Thickness reduction results in an increase in the part diameter. (b) Thickness reduction results in an increase in the part diameter. (b) through (d) Examples of cross sections that can be formed by ringthrough (d) Examples of cross sections that can be formed by ringthrough (d) Examples of cross sections that can be formed by ring through (d) Examples of cross sections that can be formed by ring

rolling.rolling.

FIGURE 13.16 FIGURE 13.16 ThreadThread--rolling processes: (a) and (b) reciprocating flat rolling processes: (a) and (b) reciprocating flat dies; (c) twodies; (c) two--roller dies; (d) A collection of threadroller dies; (d) A collection of thread--rolled parts made rolled parts made economically at high production rateseconomically at high production rates Source:Source: Courtesy of TeskerCourtesy of Teskereconomically at high production rates. economically at high production rates. Source: Source: Courtesy of Tesker Courtesy of Tesker

Manufacturing Corp.Manufacturing Corp.

FIGURE 13.17 FIGURE 13.17 (a) Features of a machined or rolled thread. Grain flow (a) Features of a machined or rolled thread. Grain flow in (b) machined and (c) rolled threads. Unlike machining, which cuts in (b) machined and (c) rolled threads. Unlike machining, which cuts

through the grains of the metal the rolling of threads imparts improvedthrough the grains of the metal the rolling of threads imparts improvedthrough the grains of the metal, the rolling of threads imparts improved through the grains of the metal, the rolling of threads imparts improved strength because of cold working and favorable grain flow.strength because of cold working and favorable grain flow.

FIGURE 13.18 FIGURE 13.18 Cavity formation in a solid, round bar and its utilization Cavity formation in a solid, round bar and its utilization in the rotary tube piercing process for making seamless pipe and in the rotary tube piercing process for making seamless pipe and y p g p g p py p g p g p p

tubing. (See also Fig. 2.9.)tubing. (See also Fig. 2.9.)

FIGURE 13.19 FIGURE 13.19 Schematic illustration of various tubeSchematic illustration of various tube--rolling rolling processes: (a) with a fixed mandrel; (b) with a floating mandrel; (c)processes: (a) with a fixed mandrel; (b) with a floating mandrel; (c)processes: (a) with a fixed mandrel; (b) with a floating mandrel; (c) processes: (a) with a fixed mandrel; (b) with a floating mandrel; (c)

without a mandrel; and (d) pilger rolling over a mandrel and a pair of without a mandrel; and (d) pilger rolling over a mandrel and a pair of shaped rolls. Tube diameters and thicknesses also can be changed by shaped rolls. Tube diameters and thicknesses also can be changed by

other processes, such as drawing, extrusion, and spinning.other processes, such as drawing, extrusion, and spinning.p , g, , p gp , g, , p g

Rolling SummaryRolling SummaryRolling SummaryRolling SummaryProcess of reducing thickness or changing cross Process of reducing thickness or changing cross g g gg g gsection by compressive forces applied through a section by compressive forces applied through a set of rollsset of rollsCR or HRCR or HRCR or HRCR or HRRolling Mills may have a variety of roll Rolling Mills may have a variety of roll configurations; threeconfigurations; three--high, tandem, etc.high, tandem, etc.Continuous casting into semiContinuous casting into semi--finished products finished products has economic benefitshas economic benefitsIntegrated mills are large expensive facilitiesIntegrated mills are large expensive facilitiesIntegrated mills are large, expensive facilities Integrated mills are large, expensive facilities with complete sequence of rolling and forming with complete sequence of rolling and forming activities. Minimills utilize scrap metal.activities. Minimills utilize scrap metal.