Metal surface phosphating cleaning process
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Metal surface phosphating cleaning process The purpose of phosphating provides protection to the base metal, to prevent the metal from being corroded to a certain extent; used for primering before painting, improving the adhesion and corrosion resistance of the paint layer; in the metal cold working process In the middle to reduce friction and lubrication.
Phosphating treatment of metal surface is a common pretreatment technology. In principle, it should be treated by chemical conversion membrane, which is mainly used for phosphating of metal surface. Phosphorification can also be applied to non-ferrous metals (such as aluminum and zinc).
Metal surface phosphating is a chemical and electrochemical reaction to form a phosphate chemical conversion film. The phosphate conversion film formed is called a phosphate film.
Metal surface phosphating is a simple, reliable, low-cost, and easy-to-use process for greatly improving the corrosion resistance of metal surfaces. Therefore, it is widely used in actual production.
The modern phosphating process is generally degreasing → washing → descaling → surface adjustment → phosphating → washing → drying.
This article mainly explains the second process in the metal surface phosphating process, the cleaning process.
The cleaning methods are as follows:
(1) Scrub.
(2) Mechanical stirring. Mechanical agitation is carried out in the liquid to thin the liquid film on the solid surface. The stronger the agitation, the thinner the liquid film, but the effect is limited.
(3) Steam cleaning. It is washed with a solvent vapor, and the solvent condenses into a liquid on the surface of the metal, and the liquid flows down to carry the dirt.
(4) Electrolytic cleaning. The gas is generated by electrochemical reaction of the metal surface.
(5) Warming and cleaning to increase heat movement.
(6) Spray washing. Spray with high pressure.
(7) Ultrasonic assisted cleaning. The ultrasonic vibration is used to cause the solid surface to be shocked and vibrated, causing the dirt to leave the metal surface.
Cleaning material
There are several types of materials for metal surface phosphating cleaning: petroleum solvents, alkaline chemical aqueous solutions, emulsions, and the like. Simply put, it is solvent cleaning and lye cleaning.
1) Alkaline water-based cleaning
An aqueous solution mainly composed of an alkaline detergent, which is made into a water-soluble soap by saponification of animal and vegetable oils.
The soap is a surfactant which emulsifies a non-polar mineral oil to "solubilize" the alkaline cleaning agent in the aqueous phase.
The aqueous solution also dissolves inorganic contaminants such as sweat. Adding a cleaning solution for synthetic detergents is more effective in cleaning oils and fats. Generally, the alkaline aqueous solution is not as fast as the organic solvent, and it needs to be heated, but also mechanically stirred, and attention should be paid to the corrosion of metals such as copper, aluminum and zinc in the high pH group. An alkaline chemical aqueous solution can clean all kinds of contaminants and is particularly suitable when a hydrophilic surface is required in the next step.
2) Common organic solvents are:
The petroleum solvent includes solvent gasoline, kerosene, n-hexane, etc.; the aromatic solvent includes toluene, xylene, etc.; and the chlorine solvent includes trichloroethane, dichloromethane, and the like. Organic solvents are characterized by high degreasing efficiency and are suitable for a wide range of metals, parts and sizes. In order to remove the oil, at least two times more than the organic solvent should be used. After using for a period of time, when the oil content in the solvent increases to a certain level, it should be replaced in time. In addition to liquid phase organic solvent degreasing, there is also a gas phase organic solvent degreasing.
The solubility of trichloroethylene is four times greater than that of gasoline. Therefore, it is commonly used for gas phase degreasing. The grease on the part is dissolved in the liquefied organic solvent and is separated from the part. This process continues until the temperature of the part surface. The temperatures of the solvents are equal.
Due to the poor working conditions of oil removal by organic solvents, gas phase degreasing must have good closed degreasing equipment and general equipment. Most organic solvents have strict fireproofing requirements and high degreasing costs. Now there are high-efficiency gambling water-based cleaning agents. Appeared, and now generally no organic solvent is used to remove oil.
[Article source: Hefei Xianghe Phosphate Coating Co., Ltd. http:// 】