Hot Rolled (HR) Coils
Hot rolled coils/sheets are primarily used for making pipes and have many direct industrial and manufacturing applications, including the construction of tanks, railway cars, bicycle frames, ships, engineering and military equipment and automobile and truck wheel caps, frames and body parts, pipes, LPG cylinders.
MAKING OF HRAP COILS
Hot rolling involves the following processes:
- Reheating: It involves heating to above recrystallization temperature. The non-uniform initial cast grain structure of metal consists of large dendritic grains. They are usually brittle with weak grain boundaries and may contain defects such as shrinkage cavities, porosity caused by gases, and foreign materials such as metallic oxides. Reheating breaks the dendritic grain structures obtained during casting, giving rise to the formation of new uniform recrystallized grain structures.
- Roughing & Finishing: The reduction is given up to approximately the required coil thickness from the initial slab/bloom thickness using roughing and finishing mill. The finishing mill can be either Steckel (reversible) or a Tandem (continuous) mill.
- Laminar cooling: In some grades, rapid cooling of hot rolled coils is done using water in order to bring down the temperature below 500°C
- Coiling: It is done in order to make the hot rolled sheet convenient for further processing and transportation.
FEATURES
Hot-rolled coils are often used in applications where dimensional tolerances are not very critical, such as railroads and construction materials.
HR Black: The hot rolled coils develop a brownish-black oxide layer on the surface after processing, hence referred to as “HR Black coils.”
HRAP: If a better surface finish is required, then oxide scaling can be removed by shot blasting (mechanically) and pickling (chemically) in order to obtain a No. 1 finish as per ASTM A480/A480M specifications. Hot rolled coils are annealed and pickled in continuous annealing-pickling lines having a scale breaker, shot blasting unit, electrolytic sulphuric acid, and mixed acid bath.
HRAP coils have a cleaner surface and have improved mechanical properties for downstream processing.
AVAILABLE IN COIL/STRIPS (SLIT COIL)/ SHEET FORM.
| THICKNESS | 1.6 MM TO 32 MM |
| WIDTH | 1000 MM TO 1500 MM |
| MAKE | TATA/JSW/AMNS/SAIL/IMPORTED |
| GRADE | E250/E350/IS 2062 |
| SLIT WIDTH | 40 MM TO 1500 MM |