Introduction to Manufacturing Chapter 13 Rolling Engr 241

Introduction to Manufacturing Chapter 13: Rolling Engr 241

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. Ú forging operations produce discrete parts, where rolling operations produce continuous products. Engr 241 1

Rolling Engr 241 2

Rolling Rolls Engr 241 3

Rolled Texture Engr 241 4

Unrolling and Straightening of Rolls (Maytag) Engr 241 5

Roll Loading Engr 241 6

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) Engr 241 7

Rolling Mills • Two-high • • Three-high • • primary roughing (cogging mills). 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. Engr 241 8

Rolling Mills Engr 241 9

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 Engr 241 10

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. Engr 241 11

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. Engr 241 12

Roll Materials • Cast iron • Cast steel • Forged steel • Aluminum Alloys Engr 241 13

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) Engr 241 14

Flat-rolling (Cont. ) • Defects (P. 327) • wavy edges • zipper cracks • edge cracks • alligatoring Engr 241 15

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. Engr 241 16

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. Engr 241 17

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. Engr 241 18