1.Why can alkali clean the oil stains on galvanized coils?
Saponification: Alkali reacts chemically with saponifiable oils, such as animal and vegetable oils, to produce soap and glycerin. These products are soluble in water and can be rinsed away.
Emulsification: For unsaponifiable oils, such as mineral oil, the surfactants in alkaline cleaners reduce the interfacial tension between the oil and water, dispersing the oil into fine droplets and forming an emulsion. This allows the oil to escape from the steel plate surface and become suspended in the water for removal.
Dispersion: This prevents the removed oil particles from reaggregating and redepositing on the galvanized coil surface.
Penetration: The cleaning agent penetrates the interface between the oil and metal, weakening the bond and making it easier to remove.
2.How to adjust the concentration of alkali solution?
Avoid high concentrations: The zinc coating will chemically react with high concentrations of strong alkali, corroding and dissolving it, causing the surface to lose gloss and darken, and even damaging the passivation film.
Recommended: Use a medium-low temperature, medium-low concentration alkaline cleaner. Generally, use a weak alkaline cleaner with a pH between 9-11, rather than a strong alkali with a pH as high as 13-14.
3.What are the effects of temperatures that are too high or too low?
Proper heating (e.g., 40°C to 60°C) can significantly improve cleaning efficiency, as heat reduces the viscosity of grease and accelerates chemical reactions.
However, excessively high temperatures can exacerbate alkali corrosion of the zinc layer.
4.How to clean?
In industry, spraying or immersion are commonly used:
Spraying: Alkaline solution is sprayed onto the steel strip surface through a high-pressure nozzle, using the impact force to assist in stripping away oil stains. This method is highly efficient and suitable for continuous production lines.
Immersing: The galvanized coil is immersed in an alkali bath. This method is suitable for heavily oiled or complex-shaped steel strips.
5.What is the recommended cleaning process?
Pre-cleaning (optional): For heavily greased surfaces, scrape them off physically or pre-treat with a mild detergent.
Alkaline Cleaning: Use a prepared neutral or weakly alkaline metal cleaner at an appropriate temperature and concentration, either by spraying or immersion.
Water Rinse: Thoroughly rinse with multiple washes of clean water (especially deionized water in the final rinse).
Drying: Immediately air dry and then dry in a dryer.
Passivation (optional but recommended): If long-term rust protection is required, a re-passivation treatment can be performed after drying to repair any minor damage to the passivation film.