1.What are the principles and steps of chemical cleaning?
Principle: This method utilizes the reaction of acid (hydrochloric acid, sulfuric acid, or phosphoric acid) with iron oxide (FeO, Fe₂O₃, Fe₃O₄) to produce soluble salts and water, thereby stripping away the oxide layer.
Common Acids:
Hydrochloric acid pickling: High efficiency, rapid reaction at room temperature, good surface quality, and relatively easy recovery of waste acid (e.g., using the Luzner process). Currently the most widely used.
Sulfuric acid pickling: Lower cost, but usually requires heating (60-80℃), easily leading to over-pickling and hydrogen embrittlement risks; waste acid recovery is more complex.
Phosphoric acid pickling: Forms a dense phosphate protective film (phosphating film) on the steel surface, providing some rust prevention; often used as a pretreatment before coating. Higher cost.
2.What are the advantages and disadvantages of chemical methods (acid washing)?
Advantages:
Thorough removal, capable of handling complex shapes and the interior of coils.
High surface cleanliness provides a good base for subsequent electroplating or coating.
Suitable for large-scale continuous production (such as pickling and rolling lines).
Disadvantages:
High environmental pressure, requiring the treatment of waste acid and wastewater.
Acid fumes are present, posing a health hazard to workers, requiring good ventilation.
Risk of hydrogen embrittlement (especially for high-strength steel), which may cause the material to become brittle.
Consumes chemicals, resulting in high operating costs.
3.What are the principles and steps of sandblasting/shot blasting cleaning?
Principle: High-pressure air or centrifugal force propels abrasive particles (steel shot, silica sand, steel wire cut shot, etc.) at high speed onto the steel plate surface, removing oxide scale through impact.
Advantages: Thorough cleaning; simultaneously roughens the surface, increasing surface area and improving coating adhesion.
Disadvantages: High equipment investment; dust pollution; high noise levels; may alter the surface roughness or even slightly change the thickness of the sheet material. For thin plates, parameters must be strictly controlled to prevent deformation.
4.What are the principles and steps of mechanical grinding/polishing cleaning?
Principle: The oxide scale is removed by directly rubbing the surface with tools such as grinding wheels, sanding belts, or abrasive brushes.
Applications: Suitable for localized processing, small batches, or thicker sheets. For large areas of roll material, professional grinding units can be used for continuous online processing.
Advantages: Flexible, no chemical pollution.
Disadvantages: Relatively low efficiency, may cause scratches, requires control of grinding depth.
5.What are the principles, advantages, and disadvantages of high-pressure water jet cleaning?
Principle: Utilizing ultra-high pressure water flow (up to 250 MPa or higher) or water flow mixed with fine abrasives to impact the surface and peel off the oxide scale.
Advantages: Very environmentally friendly, dust-free, leaves the treated surface clean and moist, with no secondary pollution. No heat- or chemical impact on the substrate.
Disadvantages: Expensive equipment, high energy consumption, and the treated steel plate needs to be dried immediately for rust prevention.