1.What are the mainstream cleaning processes?
Pre-cleaning/Alkaline Spray Wash
Purpose: To remove most of the saponifiable greases (animal and vegetable oils) and some mineral oils, as well as loose particulate matter.
Method: Heated alkaline cleaning solution (typically 50-80℃) is sprayed through nozzles onto the upper and lower surfaces of the steel strip. The alkaline solution reacts with the greases through saponification, causing them to decompose.
Electrolytic Cleaning
Purpose: To deeply remove stubborn mineral oil and tightly adsorbed oil films, a core step in ensuring cleaning quality.
Method: A steel strip, acting as the cathode (or anode), is passed through an alkaline bath while energized. The electrolysis process generates a large amount of hydrogen (or oxygen) gas bubbles.
Mechanical Scrubbing
Purpose: To assist in the removal of oil stains and solid particles (such as iron powder) softened by chemical action, and to renew the surface and improve surface activity through mechanical friction.
Method: Using nylon brush rollers or abrasive brush rollers, the strip steel surface is scrubbed while the cleaning solution is sprayed.
Hot Water/Hot Rinse
Purpose: To thoroughly rinse away residual alkali and detached emulsified oil, preventing secondary contamination and "alkali stains."
Method: Multi-stage countercurrent rinsing (the final stage uses the cleanest desalinated water or hot water). The spray temperature is typically high (60-90℃) to reduce water surface tension, improve rinsing effectiveness, and utilize residual heat for drying.
2.What are some other cleaning processes and methods?
Ultrasonic Cleaning
Primarily used for special steels or precision strips requiring extremely high cleanliness. Ultrasonic waves generate cavitation in the cleaning fluid, creating localized high-pressure shock waves that can remove micron-sized oil and particles. It is relatively expensive and mostly used in segmented cleaning processes.
Organic Solvent Cleaning
Uses halogenated hydrocarbons or hydrocarbon solvents for steam cleaning or spraying. It is highly efficient at removing mineral oils, but poses environmental (VOC emissions), safety (flammable and explosive) and health risks, and its application is decreasing, mainly being replaced by environmentally friendly processes.
High-Pressure Spray Cleaning
Primarily relies on physical impact, using high-pressure water or cleaning fluid jets to impact the surface. Often used as an auxiliary method to remove thick oil stains or in conjunction with other chemical cleaning methods.
3.What are the methods for evaluating effectiveness?
Visual Inspection/Water Film Method: After cleaning, a continuous and complete water film (good hydrophilicity) should form on the surface; any breaks indicate oil residue.
Contact Angle Meter: Cleanliness is quantified by measuring the contact angle of a water droplet on the surface (a smaller contact angle indicates greater cleanliness).
Surface Residue Determination: The steel strip surface is wiped with solvent, and the residual oil content is analyzed using infrared spectroscopy or gravimetric analysis (units are typically mg/m²).
Practical Verification: The adhesion of subsequent plating/coating layers is the final acceptance criterion.
4.What are the key control points?
Cleaning solution management: concentration, temperature, cleanliness (through the filtration system), and replacement cycle.
Process speed matching: Cleaning time (linear speed) must be matched with cleaning intensity.
Water quality: The purity of the rinsing water directly affects the final surface quality.
Equipment condition: Nozzle clogging, brush roller wear, and scale buildup on the electrolytic plate will all severely affect the cleaning effect.
5.What are the characteristics of modern cold-rolled coil cleaning processes?
Combination Approach: Since single methods are insufficient for thorough cleaning, a combined approach of chemical, electrochemical, and physical methods is employed.
Continuous and High-Speed Operation: Integrated with continuous processing lines, adaptable to production speeds of up to hundreds of meters per minute.
Automation and Online Monitoring: Automatic dosing, concentration detection, and temperature control ensure process stability.
Environmentally Friendly: Moving towards the use of biodegradable cleaning agents and incorporating wastewater treatment systems (such as oil-water separation and demulsification) for recycling.