The modern process of ‘hot rolling mill’, owes its conception and invention to Henry Cort of Fareham, England, in 1783. Its main function in a steel factory is to reheat intermediate, semi-finished steel slabs, called billets, to temperatures that are close to melting, or re-crystallization. These semi-melted steel billets undergo additional processing in the form of thinner TMT rods using pressurized rolls. The quality and the development of the martensitic and austenitic layers of a rolling mill’s core are negatively impacted by the precision of its metrics and standards. Most of the defects in a steel rod, originating from poor rolling, irregular thickness, surface defects, improper heating, etc can be avoided with the proper usage of a hot rolling mill.
Here is a quick explanation of how hot rolling mills in steel plants operate and need to be maintained:
1. Construction
The hot rolling mill consists of individual units that serve their respective physical processes of shaping, molding, compressing, heating, etc. It comprises de-scaling (cooling) sprays, re-heating units, edging (compressing) molds, roughing mill rolls, croppers (cutters), and finishing units. Together, these devices interact with the semi-molten steel to create the desired-sized rods. The semi-molten steel is cut into bars by an oxygen gas torch in the rolling mill, which primarily consists of three high rolls with a diameter of 24 to 32 inches. These rolls have a network of coilers, motors, gears, and process control systems in addition to a cooling and backup system.
2. Operation
The beam is reheated in the walking beam furnace, where the combustion air temperature rises to above 1000° F. The steel is then cooled by the hot metal entering the enclosures of descaling units, which spray cold water under 1500 psi pressure. This eliminates the iron oxide that has developed on its outside. In order to further reduce the thickness of the slab, heavy rolls are added here using a scale breaker. This eliminates the iron oxide that has developed on its outside. In order to further reduce the thickness of the slab, heavy rolls are added here using a scale breaker. They are subsequently put through vertical rolling platforms, which keep the product homogeneous and further roughen the edges. The final bars are formed by casting the molten metal into molds. They are further surface-treated for finishing and are further processed for packaging.
3. Function
The rolling mill converts the re-heated billets into uniform-formed TMT steel bars. These heat-treated, cold-quenched, hot-rolled bars and rods have an improved lattice composition. In order to further improve the ductility, strength, and durability of steel, these thermo-mechanical procedures are guaranteed. The rolling mill acts as a transitional step between the final rod casting and the furnace that melts the steel.
The Benefits of Hot-Rolled Steel
Opting for hot-rolled steel has a lot of advantages. Benefits include:
- Quality Performance
The hot-rolling method can eliminate inclusions and other flaws while also fine-tuning the grain structure. This improves the material’s ductility. Hot-rolled steel often has better strength and hardness as a result. Applications requiring excellent mechanical performance benefit from these enhanced qualities.
- Better Workability
Hot-rolled steel has improved workability. The steel becomes more malleable and simpler to mold and shape as a result of the high temperatures used in the hot-rolling process.
- Minimal Internal Stress
Internal conflicts are reduced during production when hot-rolled steel is cooled gradually. The substance becomes more consistent and stable as a result. The final product’s performance and durability may be enhanced by this increased stability and homogeneity.
- Economical
Due to the metal’s decreased resistance to deformation at high temperatures, the hot-rolling process uses less energy. This can result in lower production costs.
How Hot Rolling is Done?
The steps involved in the hot rolling process are:
Step 1: Heating
Raise the steel billets or ingots to a temperature of at least 1,700 degrees Fahrenheit, which is greater than their recrystallization temperature.
Step 2: Rolling Mill Machine
Pass the heated steel through a rolling mill machine. It is shaped into the required shape and its thickness is decreased by the machine. Surface flaws are decreased and dimensional accuracy is raised as a result of this technique.
Step 3: Compression
A sequence of rollers compresses the material after it has been shaped in the rolling mill equipment. By applying pressure, the rollers decrease the cross-sectional area of the steel. As a result, the material becomes longer and thinner.
Step 4: Cooling
After being hot-rolled, the steel is cooled using either water or air. This helps prevent deformation and reduce its hardness.
FAQs
What is a hot rolling mill, and how does it work?
A hot rolling mill is a device that refines and reshapes steel by processing it at high temperatures, usually above 1,000°C. After being heated to its recrystallization temperature, the steel becomes pliable and simpler to shape into the sheets, bars, and beams that are needed. The mill uses rollers to compress and elongate the material into its final form.
Why are hot rolling mills essential in steel plants?
Hot rolling mills produce a wide range of steel products, including:
- Sheets and plates used in shipbuilding and the automobile industry.
- Rods and bars for engineering and building.
- Channels and beams for infrastructural initiatives.
How does hot rolling improve the quality of steel?
Hot rolling eliminates defects like cracks and porosity in the steel. By aligning the internal grain structure of the steel, it increases its ductility and toughness. Additionally, it reduces inconsistencies in thickness and enhances surface quality.
How is hot rolling different from cold rolling?
Steel is processed at high temperatures during the hot rolling process, which facilitates shaping but reduces dimensional accuracy. In contrast, cold rolling, which is carried out at room temperature, produces better mechanical qualities, tighter tolerances, and smoother surfaces.
How does automation enhance the efficiency of hot-rolling mills?
Automation improves efficiency by:
- Reducing downtime with predictive maintenance.
- Enhancing safety by minimizing manual intervention.
- Boosting output by processing information more quickly and precisely.
- Maintaining constant quality by carefully managing the parameters.