Group 8 – Chapters 13 and 14

1. Group 8 – Chapters 13 and 14 Jason Becker Andrew Nawrocki Ryan Niehaus Jonathan Ogaldez Stephen Wakeland

2. Chapter 13 Rolling of Metals

3. Introduction Movie

4. Introduction Rolling The process of reducing the thickness or changing the cross-section of a long workpiece by compressive forces applied through a set of rolls Not just for metal Used to enhance plastics, powder metals, ceramic slurry, and hot glass

5. Introduction

6. Introduction First step Generally an ingot or continuous cast metal is "hot" rolled at elevated temperatures Enhances material hardness and strength "Cold" rolling The material can be rolled at room temperature Enhances strength, hardness, and surface finish Requires more energy

7. Introduction Plates Thickness of >6mm Structural applications Ship hulls, boilers, bridges, machinery, and nuclear vessels Sheets Thickness of <6mm Typically provided as coils or flat sheets Large variety of applications

8. Flat-Rolling Process Roll gap, L Where reduction occurs Relative sliding To the right of the no-slip point, material moves faster than the roll To the left of the no-slip point, material moves slower than the roll

9. Flat-Rolling Process Draft Difference between the initial and final strip thicknesses (ho – hf) Frictional Forces Required to move workpiece Must be overcome, increasing rolling forces and power requirements

10. Flat-Rolling Process Roll force Lateral force required to compress the workpiece Perpendicular to the plane of the strip

11. Flat-Rolling Process Reducing roll force Reducing friction Using smaller-diameter rolls Taking smaller reductions-per-pass Rolling at elevated temperatures Applying tensions to the strip

12. Flat-Rolling Process Tension (Longitudinal Force) Back tension Force applied to the strip at the entry zone Apply a braking action to the reel supplying the sheet into the roll gap (pay-off reel) Front tension Force applied to the strip at the exit zone Applied by increasing the rotational speed of the reel receiving the sheet from the roll gap (take-up reel)

13. Flat-Rolling Process Geometric considerations Due to roll forces, rolls may bend (deflection) Causes the rolled strip to be thicker at its center than at its edges (crown) Corrected for by making the rolls larger diameter at their center (camber) To counteract deflection, the rolls can also be externally bent at their bearings

14. Flat-Rolling Process

15. Flat-Rolling Process Spreading Strips with a more square cross-section will cause its width to increase significantly during rolling Increases with: A decrease of width-to-thickness ratio Increase of friction Decrease of ratio of the roll radius to the strip thickness

16. Flat-Rolling Process Vibration and chatter Have significant effects on product quality and productivity of metalworking operations Chatter Self-excited vibration Can occur in rolling, extrusion, drawing, machining and grinding Leads to periodic variations in the thickness of the sheet and its surface finish Rolling speed and lubrication are the two most important parameters

17. Flat-Rolling Practice Initial Hot Rolling Cast structure includes coarse and non-uniform grains Hot rolling converts this to a wrought structure with finer grains and enhanced ductility

18. Flat-Rolling Practice

19. Flat-Rolling Practice First hot-rolling product Slab Large rectangular cross-section Bloom Large square cross-section Billet Square cross-section smaller than a bloom

20. Flat-Rolling Practice

21. Flat-Rolling Practice Conditioning Surface of the slab, bloom, or billet must be prepared for subsequent rolling Torch (scarfing) to remove heavy scale Rough grinding to smoothen surfaces Prior to cold rolling "Pickling" with acid (acid etching) Blasting with water Grinding

22. Flat-Rolling Practice Cold rolling Carried out at room temperature Produces sheets and strips with: Better surface finishes (lack of scale) Better dimensional tolerances Better mechanical properties Pack rolling Two or more layers of metal are rolled together to improve productivity Aluminum Foil

23. Flat-Rolling Practice Defects Adversely affect strength, formability, and other manufacturing characteristics Wavy edges (a) Result from roll bending and is thinner along its edges than at its center Cracks (b & c) Usually result from poor material ductility Alligatoring (d) Typically caused by defects in the original cast material

24. Flat-Rolling Practice

25. Flat-Rolling Practice Other characteristics Residual stresses Small-diameter rolls tend to deform the metal more at its surface than in its bulk Large-diameter rolls tend to deform the metal more in its bulk than at its surface

26. Flat-Rolling Practice Other characteristics (cont'd) Dimensional tolerances Thickness tolerances for cold-rolled sheets are more stringent than for hot-rolled sheets Due to thermal effects, the final thickness of hot-rolled sheets is more difficult to predict Surface roughness Hot-rolled sheets are likely to require finishing operations, while cold-rolled sheets likely are not Gage numbers Smaller number = thicker sheet

27. Section 13.4 Rolling Mills Hot Rolling Cold Rolling Types of Mills Materials Lubricants

28. Types of Mills Two-High Rolling Mills Three-High Rolling Mills Four High Rolling Mills Cluster Mills Tandem Rolling

29. Two-High Mills Used for hot rolling in the initial passes Used on cast ingots Used in continuous casting Roll diameters .06m-1.4m Aka reversing mills Plate or material being rolled will be raised and lowered throughout the machine from upper to lower roll gaps. Three-High Mills

30. Four-High Mills Same principles as cluster mills, Sendzimir mills or Z mills Utilize smaller rolls for lower roll forces Also lower power requirements and reduce spreading Rolls are cheaper to replace Small rolls deflect more so they must be supported by smaller rolls Very adept for cold rolling thin sheets high-strength materials

31. Four-High Rolling Mill

32. Cluster, Sendzimir or Z mill

33. Tandem Rolling Strip of Material continuously rolled through several stands Gauges of stands get smaller progressively Each stand (train) has its own rolls Requires highly automated systems to control thickness and speed

34. Tandem Rolling Mill

35. Rolls Rolls must be made of materials with high strength and resistance to wear Common materials include cast iron, cast steel and forged steel Forged steel has higher strength, stiffness and toughness but costs more Tungsten carbides can be used for smaller diameter rolls Rolls are polished for cold-working and special applications Rolls are heat specific-misuse results in heat checking and spalling

36. Lubricants Hot Rolling Ferrous alloys-None or Graphite Hot Rolling Non-Ferrous Alloys-Oils, emulsions and fatty acids Cold Rolling-Oils, emulsions, paraffin and fatty oils

37. 13.5 Various Rolling Processes and Mills Shape Rolling Roll Forging Skew Rolling Ring Rolling Thread rolling Rotary Tube Piercing Tube Rolling

38. Shape Rolling Used for straight and long structural shapes I-beams, rails, channels Structures usually formed at higher temperatures Requires a series of rolls (material deformed non-uniformly)

39. Shape Rolling

40. Roll Forging Skew Rolling Aka cross rolling Cross section of a round bar is shaped by passing it through rolls with varied groves Used to produce leaf springs, knives and hand tools Similar to roll forging Used for making ball bearings Wire/rod is fed into the roll gap to form spherical blanks

41. Ring Rolling Used to create large rings for rockets and turbines, jet engine cases, flanges and reinforcing rings for pipes Involves using two rollers to expand a thick small ring into a thin large ring Utilizes a series of rollers, driven and stationary The rings thickness is reduce while its diameter is increased (volume of material stays the same. Pieces can be as big as 3m in diameter Advantages: short production time, close tolerances, material savings, increased strength (favorable grain flow)

42. Thread Rolling Thread s are formed on round rods or wire by passing between dies Cold forming process Two reciprocating dies or rotary dies Used to create threads on screws, bolts etc. Production rates of up to 80 pieces per second Generates treads with good strength (cold working) Compressive residual stresses improve fatigue life Gears can also be produce in a similar manner Lubrication is especially important in thread rolling for finish surface and integrity

43. Rotary Tube Piercing Aka Mannesmann Process Used to make long, thick-walled seamless pipe and tubing Hot working process Developed in the 1880’s Rolled bar under cyclical compression develops a cavity that grows down the tube Cavity is then expanded/pierced by a floating mandrel

44. Tube Rolling Process used to reduce the diameter and thickness of pipes/tubes With or without mandrels Process can be stepped

45. 13.5.1 Integration Mills Large facilities that integrate the entire production of a part Includes: production of metals, casting rolling and the finished product MiniMills Recycles scrap metals, usually from local sources to reduce cost, and casts and rolls the metals Usually only produce one kind of product (rod, bar, angle iron)

46. Forging of metals Forging is the basic process which the material is shaped by compressive forces that is applied through various tools and dies. Forging operations create discrete parts Forged parts have good strength and toughness because the grain of the metal can be controlled, thus making ideal for highly stressed applications, such as large rotors for turbines, gears, bolts and rivets, railroads, aircraft, and a variety of other transportation equipment.

47. Open-Die forging Simplest type of forging Dies are inexpensive Wide range of part sizes, ranging from 30-1000lbs Good strength qualities Generally good for small quantities Limited to simple shapes Difficult to hold close tolerances Needs to be machined to final shape Low production rate Poor utilization of materials Highly skilled operation 1100 Ton Hydraulic Forging Press and 20 Ton Capacity Manipulator

48. Open-Die forging

49. Impression Die Forging Better properties of Open Die Forgings Dies can be made of several pieces and inserts to create more advanced parts Presses can go up to 50,000 ton capacities Good dimensional accuracy High production rates Good reproducibility High die cost Machining is often necessary Economical for large quantities, but not for small quantities Completed part before removal of the flash

50. Impression Die Forging operation This form of forging is used to make more complicated parts from Blank bar stock. The Blanks are compressed between two or more dies to shape the part. Once the part is shaped, the flash is removed by either grinding it, trimming, or machining.