STATE OF ART GALVANISING PLANT WITH FOLLOWING FEATURES:
-Highest Line speed.
-Produces widest (1200mm) and thickest (0.40mm) sheets.
-Operates a Non – Oxidation Furnace.
-Most sophisticated galvanizing technology in the industry.
-Best quality finished products for the end user.
CHROMIC COATER COOLING PENDENTS
HYDROGEN AND NITROGEN SUPPLYREVERSE OSMOSIS PLANT
SHOP FLOOR FINISHED GOODS STORAGE
- Consists of Pay of Reel which supplies the sheet continuously to the process.
- Welding Unit to join the tail end and head of each the fresh coil.
- Pinch rolls to thread the sheet forward while welding or jogging.
- Bridle rolls to keep the sheet in tension for smooth operation
- Most importantly, the Loopier, also referred as Accumulator, to maintain the continuity in line processing.
- Steering rolls to maintain the sheet in centre line.
- Degreasing unit to clean the oils and coolant from the sheet prior to coating
Degreasing consists of 3 sections:
- Alkali tank
- Hot rinsing tank
- Dryer unit.
• Alkali tank used to clean the oil and greases by alkali wash
• KOH mainly used as alkali.
• Pairs of brush rolls scrub the sheet properly for cleaning.
• Hot rinsing done to clean through hot water.
• Dryer to dry the sheet completely of moisture. 2 PROCESS STAGE
•Entry sheet into the Process Stage
•Process Stage starts with the Non – Oxidation Furnace. (This is the key equipment in the process stage)
The Non Oxidation Furnace is comprised of the following Zones:
– PHF (Pre Heat Furnace)
– RTF (Radiant Tube Furnace)
– SF (Soaking Furnace)
– JCZ (Jet Cooler Zone)
– CALM ZONE
– HBR (Hot Briddle Roll Zone) ANNEALING SECTION IMPORTANT NOTE The first step towards preparing steel for use is to anneal it.
Annealing is a process by which the properties of steel are enhanced to meet machinability requirements. Annealing is a process of heating the steel slightly above the critical temperature of steel (723 degrees Centigrade) and allowing it to cool down very slowly.
The following are some of the advantages of annealing.
1. Softens the steel.
2. Enhances and improves the machinability of steel.
3. Increases the ductility of steel.
4. Enhances the toughness of steel.
5. Improves the homogeneity in steel.
6. The grain size of the steel is refined a lot by annealing .
7. Prepares the steel for further heat treatment.
However, some of the alloys contained in steel, such as manganese, silicon, aluminium, and chromium may result in a thin layer of oxides on the steel surface during the annealing operation preceding the dipping in the Zinc Pot.
The presence of these layer of oxides harms the zinc "wettability" and thus the quality of the coating and ultimately the quality of galvanising. It is well known fact that oxidation (presence of oxygen) causes metals to rust
These phenomena of oxidization are due to diffusion processes of the highly oxidisable alloy components towards the steel strip surface where they can oxidize in the ordinary furnaces.
OUR NON OXIDATION FURNACE PROFFERS A SOLUTION TO THIS PROBLEM
BY SUBJECTING THE STEEL STRIPS SURFACE TO TEMPERATURES AND
ATMOSPHERE CONDITIONS FIT FOR QUICKLY AND DEEPLY OXIDISING THE
ALLOY COMPONENTS IN THE DIRECT FIRED PRE HEAT FURNACE. (PHF)
– Here heating is done by direct burner firing flame on the sheet
– Gas with calculated amount of oxygen supplied for complete combustion as extra oxygen can spoil the quality of coating.
– Used to further clean the sheet from oil and coolants.
– Elevate the temperature of the sheet to annealing or re crystallization temperature of steel.
• SOAKING ZONE
– Here, the sheet is held at a constant temperature for some time
– Soaking is done at a constant temperature for refining of the grain structure.
– Shown in graph.
• JET COOLING SECTION
– Cooling starts from here.
– Provided with fans and heat exchanger to cool the sheet
– Use the fume of inside furnace and circulate through the heat exchanger unit.
– Fan force the cooled gas to the sheet to carry the cooling action.
• CALM ZONE
– Here the sheet is passed undisturbed by any turbulence
– This is very important for the quality of sheet.
– Protective gases N2H2 supplied through this zone. These protective gases provide the environment to avoid oxidation of the sheet and excellent quality of coating
• HBR SECTION
– This is termed as exit section of furnace.
– Provision of two rolls called Hot Bridle Rolls.
– Deflects the sheet into the Pot for coating after heat treatment from the furnace.
ZINC POT SECTION
– Coating kettle is loaded with the molten zinc to carry out the hot dip coating process.
– Consists of dipped roll called Sinker roll to deflect the sheet out after coating.
– Has jet wiper unit from both sides to control the coating.
– Jet wiper wipes extra coating off the sheet by utilizing jet of the air.
– Coating can be controlled by the amount and pressure of air.
COOLING HOOD SECTION
– Cooling is done after coating.
– This section provides towers with several cooling ducts to assist in bringing down the sheet temperature.
QUENCH TANK SECTION
– It is desirable to have sheet temperature at room temperature.
– Further cooling to room temperature is therefore done by a special kind of water
i.e. De-mineralized water (Dm).
– This helps in improving surface luster also.
SKIN PASS MILL & LEVELLER SECTION
– Skin Pass Mill and Leveller sections provide shape control.
– Both work together in giving perfect shape to the sheet by removing buckling, waviness and dents.
3 EXIT STAGE
Passivation is an important activity that takes place in chromating section. Passivation is designed to further prolong the life of galvanized sheets by creating a barrier between the finished sheets and the environment.
Passivation includes the following processes:
– Chemical coating
– Acrylic base application
• Drying is a must after passivation.
• For optimum treatment the temperature of sheet is raised to 100°c - 110°c.
• After passivation, sheet passes through steering gear into the exit accumulator.
• Exit accumulator helps in maintaining the continuity of the production process at the time of coil cutting.
• It adjusts its position to provide enough time to start fresh coiling.
• The processed coil is taken out by coil car and can be sent for further processing as desired, for example, into colour coated sheets and for corrugation etc.