In Shahriar Tabriz steel Co., the galvanised sheet is produced by hot dip galvanised process. Cost effective procedure, possibility of producing controlled and desired thickness along with strength and adhesion of galvanised coating can be mentioned as the advantages of hot dip galvanised process over other processes.
The inlet steel coil passes through the following steps to form a galvanised coil. At the beginning of the line, the rolls loaded from the stockroom are unrolled by unrolling machines. After shearing, the edges of the beginning and end edges of the sheets are welded and inserted into production line as a continuous strip. At the primary phase of hot dip coating process steel cleaning is performed by using alkaline liquid combined with degreasing, rinsing and brushing the metal surface. The steel is maintained under pickling phase in order to remove any oxide that might be on steel surface. Passing the flux tank, the steel is inserted into the annealing furnace in order to get prepared for dipping in molten zinc bath. In the bath the steel product is sent around a submerged roll and a thin layer of coating is created on the steel surface.
Once the product is removed from the bath, the high-pressure air is blown to remove any excess molten zinc and creates closely controlled coating thickness. At the cooling phase, before inserting the sheets into water tank and reducing warmth to ambient temperature, air blowers reduce the sheet’s temperature and cools them down by immersing into softened water. Finally, warm airflow completely dries the sheets.
The thickness of zinc coating on sheet’s surface is controlled by thickness gage. Once the sheets get dried, chromate chemical treatment is done in order to passivize the zinc surface. The thin layer of chromate passivation inhibits the formation of wet storage stain and zinc oxides.
Necessary inspections carry out at the end of the line and a steel coil cutting machine cuts the coils in accordance with customer’s order. After packing and labelling, the coils are sent to the market. The quality control department regularly evaluate the sheets and empirical tests are performed in laboratory during the production process and also after completion.