Rolling

Question 1

Process Description of Rolling

Answer 1

A process of reducing the thickness or changing the cross section of a long work piece by compressive forces, applied through a set of rolls.

Question 2

Development of Product stage

Answer 2

Ingot –> Bloom, Slab, Billet –> Rails, Coils,Plates, Sheets, Bars, Rods

Question 3

What is a Bloom? and what products do you get?

Answer 3

Big square cross section–> Rails

Question 4

What is a Billet? and what product do you get?

Answer 4

smaller square cross section than bloom –> Rods, Bars

Question 5

What is a Slab ? and what product do you get?

Answer 5

right angled cross section –> Coils, Plates, Sheets

Question 6

Typical Products made with rolling

Answer 6

ships, bridges, rails, machines

Question 7

material properties

Answer 7

• low yield strength
• high ductility
• area of plastic deformation

Question 8

DIfferent types of Rolling

Answer 8

Cold Rolling - Performed at room temperature or slightly above
Warm Rolling - Above room temperature, below recrystallization temperature
Usually temperatures above 0.3Tm
Hot Rolling - Above the recrystallization temperature (usually above 0.5Tm and less than 0.75Tm)

Question 9

Grain Structure Hot vs. Cold

Answer 9

• Hot: changes grain structure from large to smaller more organized grains –> higher ductility and strength-
• Cold: less organized –> bigger grains –> less ductility and strength

Question 10

Advantages Cold working

Answer 10

• Better accuracy (closer tolerances)
• Better surface finish
• Increased strength and hardness (due to strain hardening)
• No heating required
• ->Lower energy costs
• ->Higher production rates

Question 11

Disadvantages cold working

Answer 11

• Higher forces & power required
• Starting surfaces must be free of dirt & scale
• Strain hardening limits amount of forming that can be accomplished

Question 12

Advantages of Hot Working

Answer 12

-Capable of producing substantial plastic deformation
-Lower forces & power required for deformation
-Metals that would fracture when cold worked can be
hot worked
-No strengthening of part from strain hardening

Question 13

Disadvantages of Hot working

Answer 13

• Lower dimensional accuracy
• Higher total energy required
• Surface oxidizes, leaving a scale on part
• Poorer surface finish
• Shorter tool life

Question 14

Difference Plates vs Sheets vs Foile

Answer 14

Plates thickness: 6-150 mm

Sheets thickness: less than that

Question 15

Multi Roll Mill

Answer 15

The more rolls, the better the pressure control

Question 16

Whats the Yield Strength

Answer 16

Force to permanently change the form of a workpiece, plastic deformation

Question 17

Sendzimir Mill

Answer 17

a lot of rolls, but only two have direct contact to workpiece:

• better pressure control
• work really hard materials
• higher accuracy

Question 18

Different Variations of Rolling

Answer 18

• Flat Rolling (reduces thickness)
• Shape Rolling (stock goes through a series of specially designed rolls)
• Roll Forging (cross section of a round bar is shaped by passing it through grooves)
• Skew Rolling (making ball bearings from rods)
• Ring Rolling (thick ring is expanded into a large diameter, thinner ring)
• Thread Rolling (straight or tapered threads are formed on round rods or wire)
• Pilger Rolling (Reduce of Diameter and Wall Thickness simulatanesously big changes possible)
• Tube Rolling (The diameter and thickness of pipes and tubes are reduced)

Question 19

Advantages of Thread Rolling

Answer 19

• Machining cuts through the grains of the metal. Rolling of threads imparts improved strength because of cold working and favorable grain flow (see figure on next slide).
• Compressive residual stresses improve fatigue strength
• No scrap in the process
• Surface finish is smooth