1.Why is drying a mandatory key step?
Ensuring the Formation and Curing of the Passivation Film:
The passivation solution forms an extremely thin, moisture-containing, gel-like nascent film on the strip surface. Drying (using hot air) removes free water and water of crystallization from this film, transforming it into a dense, stable, and strongly adhesive solid protective film.
An undried wet film has extremely low physical strength and is easily wiped off or damaged during subsequent winding and transportation.
Preventing "Watermark Rust" and "White Rust":
This is the most direct risk. If unevaporated moisture (especially a water film) exists on the strip surface or between coil layers, this moisture cannot evaporate after winding, quickly leading to water stains or even large-area electrochemical corrosion (white rust) on the steel plate.
The purpose of passivation treatment is rust prevention; if rust occurs due to incomplete drying, the original intention of the process is completely defeated.
Avoid disrupting the chemical balance of the passivation solution:
Residual liquid water will continue to dissolve and dilute the passivating agent, potentially leading to uneven composition of the passivation film, failure to form, or excessive reaction, affecting its uniformity and protective performance.
2.What are the drying steps in a typical process flow?
Drying Equipment: Typically employs a high-efficiency hot air drying system (such as a hot air spray box), which rapidly evaporates all moisture from the strip surface by blowing heated air (temperature, airflow, and speed are adjustable).
Control Parameters: Drying temperature and time need to be precisely matched according to the production line speed, passivation solution type, and strip thickness to ensure that the strip surface temperature reaches above the dew point and is completely dry when it leaves the drying chamber.
3.What are the necessary drying steps?
Drying after passivation is not an optional step, but a mandatory process to ensure the effectiveness of the passivation process.
4.What role does drying play?
It ensures the final quality of surface treatment (pickling, rinsing, passivation) and guarantees the stability of the product before storage and transportation.
5.What are the key quality points?
Incomplete drying is one of the most common causes of rust formation on passivated coils in a short period of time. During production inspection, in addition to checking the weight of the passivation film, it is also necessary to check whether the surface is completely dry.