Description
What is Cold Rolling?
Process by which hot rolled strip or stock is introduced between a set of rotating rollers and then squeezed or compressed to the desired thickness, amount of strain introduced determines the properties of the finished product.
Hot rolled Pickled Coils are reduced to the desired thickness. This is achieved either in Reversing Cold Rolling Mills: Thickness achieved by repeated passes through the same rolling stand back and forth or in Tandem Cold Rolling Mills: Thickness achieved through series of rolling stands in tandem.
Why Cold Rolling?
Appearance of the product is of prime importance.
Surface should have greater corrosion resistence.
The sections required cannot be achieved in hot rolling mills.
The mechanical properties required cannot be achieved in hot rolling mills.
Dimensional tolerances cannot be achieved in hot rolling mills.
Processing Steps in a Cold Mill
Acid Pickling to remove oxide layers.
Cold Rolling Mill to reduce thickness.
Surface cleaning to remove rolling oils and other debris.
Annealing to soften the work hardened steel.
Skin passing to suppress yield point elongation.
Surface inspection
Packaging to prevent transit damage.
What is Annealing?
Heating the cold rolled steel to the recrystallization temperature in an inert or reducing atmosphere.
Soaking at this temperature for sufficient time for homogenization and necessary changes to occur.
Cooling at a predetermined rate.
Why Annealing is needed ?
Steel Coils become hard and brittle after Cold Rolling. The as-rolled sheets are not suitable for for most of the applications except for probably sheeting applications. So ductility (Softness) of the cold rolled steel is recovered by annealing process.
Annealing Ensures
Softening of the cold rolled steel- Relieving the internal stress developed during cold rolling Develop desired mechanical properties suitable for intended applications. Bright Surface Finish.
COLD ROLLING MILL COMPLEX - INDICATIVE PRODUCT CHEMISTRY (WT %)
| Grade | C | Mn | S | P | Si | A1 | N | Ti | Nb |
|---|---|---|---|---|---|---|---|---|---|
| O/D A1-Killed | 0.08 | 0.45 | 0.025 | 0.03 | 0.06 | 0.07 | 0.01 | ||
| DD A1-Killed | 0.05 | 0.18 | 0.02 | 0.025 | 0.05 | 0.07 | 0.009 | ||
| DD A1-Killed | 0.044 | 0.18 | 0.015 | 0.015 | 0.015 | 0.06 | 0.006 | ||
| EDD IF FOR CRCA/GI | 0.005 | 0.2 | 0.015 | 0.015 | 0.02 | 0.003 | 0.055 | ||
| DD/EDD IF FOR GA | 0.005 | 0.2 | 0.015 | 0.015 | 0.02 | 0.003 | 0.055 | ||
| HSS |
COLD ROLLING MILL COMPLEX - INDICATIVE MECHANICAL PROPERTIES OF CRCA PRODUCTS
| Properties Grade | Yield Strength(MPa) | Tensile Strength(MPa) | YS/UTS | Elongation(%) | Average Lankford Value, r | Strain Hardening Index, n |
|---|---|---|---|---|---|---|
| O/D(CQ) | =270 | >=35 | ||||
| DDQ | >=270 | 0.60 | >=40 | >=1.6 | ||
| EDDQ | <=160 | >=290 | 0.55 | >=45 | >=1.9 | 0.20-0.24 |
| Super EDDQ IF grade | <=150 | >=290 | 0.5 | >=50 | >=2.1 | 0.20-0.24 |
Application for Cold Rolled Steel
Automobile components
Panels for White Goods/Appliances
Packaging (Drums ,Barrels and Containers)
Furniture
Electrical Panels
General Engineering.