2025 Rolling GPT o3

The angle of contact ϕ represents the arc length over which the metal is in contact with the roll, affecting the deformation zone during rolling.

μ ≥ tg ϕ

Long products are formed by grooved rolls

Flat products are formed by flat rolls

1. Heating

2. roughing

3. finishing

4. cooling

5. cold rolling

6. annealing

1. Flat Products: Sheets, strips, and plates.

2. Long Products: Bars, rods, rails, and structural shapes.

1. Cluster Mill: Employs multiple backup rolls for rolling very thin strips.

2. Planetary Mill: Features smaller rolls that rotate around a large central roll, allowing for very high reductions.

Hot rolling is performed at high temperatures (typically 1200–1250°C for steels) and is used for large reductions and the initial shaping of ingots into semi-finished products.

Ingot blooming is the initial reduction of large ingots into slabs or billets using two- or three-high reversing mills. Key parameters include:

• Strain per pass: 0.1–0.4

• Strain rate: 1–30 s^-1

During the roughing stage, the metal is initially rolled at 1200–1250°C using one or two stands, with water jet descaling. This stage reduces the strip to a final roughing thickness of about 25 mm.

The finishing stage uses five to ten four-high stands. The exit temperature is maintained at 840–900°C. The coiling temperature (hot >660°C or cold <660°C) affects the precipitation behavior of microalloyed particles.

It involves a roughing stage to reduce billet size followed by a finishing stage to achieve final dimensions. For example, producing round bars (5.5 mm diameter) may require:

• 7–8 roughing stands

• 6–10 intermediate stands

• 10 finishing stands Controlled cooling via water jets and fans is essential.

Cold rolling is carried out at room temperature and involves smaller reductions per pass compared to hot rolling. It typically requires additional processes such as pickling, annealing, and skin passing to achieve the desired properties.

1. Pickling: Acid bath (using H₂SO₄ or HCl) to remove surface oxides.

2. Cold Reduction: Reduces thickness by 50–90%.

3. Annealing (if needed): Restores ductility after deformation.

4. Skin Passing (Temper Rolling): A low reduction (<3%) step to remove the yield-point phenomenon.

Example: A continuous cold-rolling mill with 4–6 four-high stands produces strips at delivery speeds of 25–30 m/s with critical lubrication. Annealing can be:

• Discontinuous Annealing: Conducted in bell furnaces at ~700°C for around 10 hours.

• Continuous Annealing: A faster process that includes cleaning, heating, and cooling.

1. Hot Rolling: May induce dynamic recrystallization (DRX) at high strain rates.

2. Controlled Rolling: Lowers rolling loads and improves final properties; intercritical rolling is used for high-strength steels.

3. Cold Rolling: Leads to significant strain accumulation, often necessitating annealing, and can produce a pancake microstructure (notably in Al‑killed steels).

1. Oxides: Caused by poor descaling or excessive oxidation.

2. Cracks: Can occur in both hot and cold rolling.

3. Edge Cracks: Especially common in high-Si steels and Cu-containing steels.

Internal defects such as lateral spread and barrelling occur due to friction variations between the center and edges of the metal. Mitigation measures include improved lubrication and using edge heaters to better control cooling rates.

1. Thermo-mechanical fatigue: Leading to “firecracks.”

2. Sliding wear: Resulting in “banding” marks on the roll surfaces.

1. In hot rolling, friction decreases with increasing temperature. Roberts' Equation approximates this: μ=0.00049 T−0.071

2. In cold rolling, mixed lubrication (both boundary and hydrodynamic) is used, and ester-based additives can improve lubrication performance.