Introduction to Manufacturing

Chapter 13: Rolling

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Rolling• Process of reducing the thickness or

changing the cross-section area of a long work piece by compressive forces.• accounts for about 90% of all metals

produced by metalworking processes.

forging operations produce discrete parts, where rolling operations produce continuous products.

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Rolling

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Rolling Rolls

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Rolled Texture

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Unrolling and Straightening of Rolls (Maytag)

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Roll Loading

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Rolling Process

• Terminology (raw material)• Bloom: square cross section of at least 6"

on the side. (sheets)

• Billets: square cross section, smaller than bloom. (rod, pipe)

• Slab: rectangular in shape, rolled into plates and sheet. (rails, I-beams)

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Rolling Mills• Two-high

• primary roughing (cogging mills).

• Three-high• primary roughing (reversing mill).

• Four High & Cluster• principal (small diameter) rolls lower the roll

forces and power requirements, but must be supported in order to reduce deflection.

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Rolling Mills

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Rolling Mills

• Tandem Rolling• strip is rolled continuously through a

number of strands (set of rolls with its own separate housing and controls) to smaller gauges with each pass.

• Group of Strands = train

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Roll Deflections

• Rolling forces cause deflection and roll flattening.

• Crown: thicker in the center than the

edges.

• Chamber: thicker in the edges than

center.• Spreading: increase of width after rolled.

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Roll Deflections

• Forces can be reduced by:

• reducing friction.

• reducing contact area.

• smaller reductions per pass.

• rolling at elevated temperatures to reduce

strength of material.

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Roll Materials

• Cast iron

• Cast steel

• Forged steel

• Aluminum Alloys

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Rolling Processes• Flat-rolling

• hot or cold work (slabs, blooms, billets, or sheet metal).

• 3000 °F for refractory alloys.

• 2300 °F for alloy steels.

• 850 °F for aluminum alloys.

• Pack Rolling: two or more layers of metal rolled together (Al foil example)

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Flat-rolling (Cont.)

• Defects (P. 327)

• wavy edges

• zipper cracks

• edge cracks

• alligatoring

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Rolling Processes• Shape Rolling (P. 331)

• structural shapes (I-beam, rails, etc.)• requires specially designed rolls

• Ring Rolling (P. 332)• ring (which is the part) placed between two rolls,

to increase diameter.• large rings for rockets, gearwheel rims, ball

bearing and roller- bearing races, flanges, reinforcing rings for pipes, etc.

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Rolling Processes• Thread rolling (P. 333)

• cold-forming process where threads are formed

on round rods by use of flat reciprocating dies

which pass the part between them.

• no material loss.

• no cutting through grain line flow improves

strength.

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Rolling Processes

• Rotary Tube Piercing (P. 334)• hot working process for making long, thick

walled seamless tubing/pipe.• round bar subjected to radial compressive

forces causing tensile stresses toward the center of the bar.

• cavity forms from cyclic compressive stresses.