Cold rolling mill has been built for the purpose of producing the final product and the products are sent to the customers.
Pickling line 1 and 2:
This line has been installed to serve the following purposes:
1.Elimination of the surface oxides by passing the sheet through hydrochloric acid baths
2.Side trimming of the sheet in order to achieve the desired width and elimination of the possible defects in the edges of the sheet.
3.Oiling the surface of the sheet using the electrostatic oiling machine.
4.Correcting the shape of the hot-rolled sheet using the stretch-leveler which has the two basic functions:
A.It breaks the oxide scales and improves the performance of the pickling line
B.It corrects the forming defects, so it improves the sheet quality in later stages of the operation. 5.Coil inspection for checking and controlling all basic details of the coil (heat no., plan no., weight, thickness, width, grade of steel, coiling temperature, etc) and detection of any effects due to the previous processes (head and tail out of thickness, side cutting, surface defects, non-metallic impurities, oxide scales, cracks, rusting, etc.)
In the pickling process, the coils enter the acid baths after they have been opened by coil openers. After getting washed and coming out of the bath, the coil is washed in water and passed through hot-air tunnels to dry. After oiling, they are shaped back into coils and stored in the storehouse.
The pickling products fall into the following three categories:
•Coils to be sent to tandem mill
•Coils to be sent to two-stand rolling mill
•Coils to be sent to customers
Tandem mill unit:
The purpose sought by installation of this line is to reduce the thickness of the sheet in the ambient temperature. After opening, the sheet passes though 5 four-rolled vertically positioned stands and reduces minimum 50 percent and maximum 85 percent of the sheet thickness and the sheet finally is coiled in the coiler unit. The product is the sheets 0.3 to 3 millimeters in thickness.
The products of the cold rolling mill re called crude coils and fall into the following three categories:
1.Crude coils for the customer
2.Crude coils for the galvanizing line
3.Crude coils for the annealing unit
Two-stand rolling mill:
This line is responsible for the reduction of the sheet thickness in the ambient temperature. The coil passes through two 4-roll stands in a regressive way after it has been opened and loses its thickness by 60 – 90 percent as a result of 2 – 3 rolling passes and is coiled by the coiler machine.
The products of this line that are called crude coils fall into the following three categories:
• Crude coils for tin-plating line
• Crude coils for hydrogen annealing and continuation of the cold-rolling operations
• Crude coils for galvanizing and color-coating
The two-stand rolling mill is one of the most important steps in the tin-plating chain and is responsible for the following technological functions:
1.Optimal thickness reduction
2.Creating shapes suitable for the working cycle projected for the final product
Electrolyte cleaning unit:
This unit is responsible for the electrolyte cleaning of the rolled sheet surface in order to have its surface contaminations and greases removed in two dipping in the alkaline solution and electrolyte cleaning. The product goes to the hydrogen annealing unit after it has been given a final wash and dried for curing.
In general, the electrolyte cleaning unit is responsible for the cleaning of the sheet and removing all remaining emulsions, iron powder and non-ferric solid impurities created by the cold-rolling operations.
Hydrogen annealing unit:
In the hydrogen annealing unit, the heating and curing of the coils takes place for the purpose of homogenizing the metallurgical structure of the sheet and achieving the desired metallurgical qualities, and the coils are cooled down after the completion of the heat treatment and final cooling down before they are sent to the temper mill.
Considering the fact that crude coils coming from the temper mill and two stand rolling mill are not formable enough, they have to undergo annealing in high temperatures before they can go to the upcoming processes.
Temper mill unit:
The temper mill unit consists of two 4-roll stands (each containing two work rolls and two backup rolls) that are responsible for the hardening of the sheet surface and creating desired mechanical properties after passing through annealing furnaces. In general this unit is responsible for the following goals:
1.Leveling the sheet surface and removing the waves
2.Giving the desired hardness to the sheet
3.Giving the desired coarseness to the sheet in accordance with the customer order and rendering the sheet suitable for the tin-plating operations and desired surface finishes such as shiny surfaces, stone-like surfaces and dull surfaces.
the products of this unit fall into the three following categories:
1.Tempered coils for cutting lines
2.Tempered coils for tin-plating line
3.Thinned down coils for tin-plating line (DCR sheets)
The roll shop is responsible for grinding all rolls and blades in operation in the cold rolling mills and finishing lines of the hot rolling mill.
In this process, the rolls enter the roll shop, have their chokes dismantled, and mounted on the grinding machine for grinding. After the completion of the grinding stage, in case roughing is required, the roll undergoes the grit blast process.
Advanced grinding machines are used for this purpose in this unit. This unit uses EDT technology for roughing the surface of the rolls.
Box annealing unit no. 1 with the protective atmosphere of HNX
1.Softening the steel sheet
2.Improving the machining properties and formability of the sheet
3.Increasing the flexibility of the sheet
4.Removing tensions inside the sheet caused by rolling mill.
5.Eliminating or reducing the inconsistencies in the crystalline structure of the steel sheet in thermal cycles.
6.Improving the properties and structure of the sheet and preparing it for the next operation. 500,000
Skin pass 1
1.skin passing of the annealed sheet with some elongation in order to increase the consistency of the stress – strain in the sheet and improving its mechanical properties and formability
2.improving the smoothness on the sheet surface
3.giving the adequate roughness to the sheet surface for applications involving formability, painting and lamenting
4.creating adequate hardness in the sheet 550,000
Skin pass 2 (Capacity: 650,000 MT)
Sheet correction unit 1
1.cutting the coil in the form of plates with predetermined dimensions and feeding back the coil to the bundles of sheets
2.inspecting the coil surfaces
3.eliminating waves and improving the levelness of the sheet surface
4.side (edge) trimming in order to align the edge within the required tolerance
5.cutting the defective parts
Sheet correction unit 2 (Capacity: 300,000 MT)
Longitudinal shearing Unit
1.longitudinal shearing of the coil and splitting the coil into several narrow coils with the requested widths
2.side (edge) trimming in order to align the edges
3.oiling the sheet surface 50,000
Coil packaging unit
Packaging the coils of the longitudinally sheared coils and sheet correction
Light shearing (for .3-1.5 mm )
1.cutting the coil into plates with predetermined dimensions and cutting the coil into sheet bundles
2.inspecting the sheet surface
3.removing the sheet waves
5.cutting the defective parts
Heavy shearing (for 0.6-3.0 mm) thickness (Capacity: 160,000)
Sheet packaging line Bundling and packaging the plates coming from the light and heavy cutting line and sending them to the customer.