The pretreatment work required before stainless steel passivation is crucial. These works are aimed at ensuring the smooth progress of the passivation process and the excellent performance of stainless steel materials after passivation.
First, the stainless steel surface must be thoroughly cleaned to remove all oil, dust, welding slag and other contaminants. This is the first and most critical step in pretreatment. Cleaning can be done by solvent cleaning or high-pressure water cleaning. Solvent cleaning usually uses organic solvents such as petroleum ether, acetone or alcohol, which can effectively dissolve and remove grease and dirt on the surface. High-pressure water cleaning is suitable for removing dirt from hard surfaces, and the dirt is washed away by high-pressure water flow.
Degreasing is an important step to remove grease and lubricants from the surface of stainless steel. The presence of grease will affect the contact between the passivation liquid and the stainless steel surface, thereby affecting the passivation effect. Common degreasing methods include alkaline cleaning agents and emulsifier cleaning. Alkaline cleaning agents usually contain ingredients such as sodium hydroxide and sodium carbonate, which can chemically react with grease to dissolve and remove it. Emulsifier cleaning disperses grease in water through emulsification to form an emulsion, and then removes the grease from the stainless steel surface by rinsing.
After degreasing, some alkaline substances or other chemicals may remain on the stainless steel surface, which will affect the subsequent passivation effect. Therefore, surface adjustment is required, and dilute acid (such as dilute sulfuric acid or dilute hydrochloric acid) is usually used to neutralize the surface to remove residual alkaline substances. This step helps to ensure that the stainless steel surface is neutral or nearly neutral before passivation, which is conducive to the passivation reaction.
If there is an oxide layer or rust on the stainless steel surface, these substances will hinder the formation of the passivation film, thereby affecting the passivation effect. Therefore, before passivation, an appropriate pickling solution (such as a mixture of hydrochloric acid, sulfuric acid or nitric acid) is needed to remove the oxide layer and rust on the surface. Pickling can be done by immersion or spraying. The specific method depends on the shape and size of the workpiece and the severity of the oxide layer.
After pickling, stainless steel passivation must use a large amount of clean water to thoroughly clean the stainless steel surface to remove residual acid and substances produced by the reaction. After cleaning, drying treatment is also required to ensure that the surface is completely dry and there is no moisture residue. The presence of moisture will affect the passivation effect and may even cause spots or corrosion on the surface.
After the pretreatment work is completed, the stainless steel surface needs to be inspected to ensure that the surface cleanliness meets the requirements and no impurities such as oil, dust, and oxide layer remain. At the same time, it is necessary to prepare the equipment and materials required for passivation, such as passivation tanks, passivation liquids, cleaning tanks, etc., and ensure that these equipment are in good working condition.
During the entire pretreatment and passivation process, operators need to wear appropriate personal protective equipment, such as gloves, glasses, protective clothing, etc. to ensure safety. In addition, it is necessary to ensure that the workplace is well ventilated to avoid the accumulation of harmful gases.
The pretreatment work before stainless steel passivation includes multiple steps such as thorough surface cleaning, degreasing, surface adjustment, removal of oxide layer and rust, thorough cleaning and drying, inspection and preparation, and safety protection. Strict implementation of these steps is the key to ensuring the passivation effect.
