1.What is the purpose of uncoiling and welding?
Uncoiling: The coiled cold-rolled or hot-rolled steel plate (base plate) is unwound via an uncoiler for subsequent continuous processing.
Welding: When a coil of steel plate is nearing completion, the tail end is connected to the head of the next coil using welding equipment (usually resistance welding or laser welding) to ensure production continuity and avoid line interruptions due to coil changes.
2.What is the purpose and process of degreasing cleaning?
Purpose: Remove impurities such as oil, dust, and rolling oil from the steel plate surface to prevent them from interfering with the subsequent zinc coating.
Process:
First, spray or soak the steel plate with hot water or an alkaline solution (such as sodium hydroxide) to chemically break down the grease.
Then rinse with clean water to thoroughly remove any residual alkaline solution and impurities, ensuring a clean steel plate surface.
3.What is the purpose and process of pickling?
Purpose: Removes scale (iron oxide) and rust from the steel surface, exposing a clean metal base and creating favorable conditions for the zinc layer to bond to the substrate.
Process: Immerse the steel in a hydrochloric acid or sulfuric acid solution to dissolve the scale through a chemical reaction (for example, iron oxide reacts with hydrochloric acid to produce soluble ferric chloride and water). After pickling, rinse again with clean water to prevent residual acid from corroding the steel.
4.What is the purpose and process of annealing?
Purpose: To eliminate internal stress generated during steel plate rolling, improve its mechanical properties (such as ductility and toughness), and facilitate subsequent processing.
The steel plate surface is further purified in a reducing atmosphere (such as a mixture of nitrogen and hydrogen), removing residual oxide films and impurities, creating an active surface, and enhancing the adhesion of the zinc layer.
Process: The steel plate is fed into a continuous annealing furnace, heated to a specific temperature (usually approximately 700-900°C, determined by the steel material), held for a period of time, and then slowly cooled.
5.What is the purpose and process of galvanizing?
Purpose: To provide a uniform coating of zinc on the surface of the steel sheet.
Process: The annealed steel sheet is then immersed in molten zinc (typically with a purity of 99.5% or higher) at approximately 450°C. The zinc reacts with the steel sheet, forming a zinc-iron alloy layer and an outer layer of pure zinc.