Abstract: In order to ensure the quality of pre-painting treatment, the materials and chemical properties of alkaline cleaning were studied. The selection criteria and detailed cleaning procedures, testing methods and process maintenance contents related to alkaline cleaning agents are introduced. The development trend and progress of cleaning fluids are explained.
1. Alkaline cleaners <br> <br> metal surface oil may be removed by mechanical and chemical methods, chemical methods including solvent cleaning, emulsion cleaning and alkaline cleaning. Alkaline cleaning is the most commonly used chemical degreasing method in automotive pre-treatment. Alkaline cleaning uses synthetic detergents and surfactants with long life cycle, stable performance, easy control and handling, and a wide range of applications. Typical compositions of alkaline cleaners include alkaline materials, surfactants, antifoaming agents, corrosion inhibitors, chelating agents, and hard water resistant agents. Usually one-component or two-component. Generally, the single component is in the form of a powder, and the two components are in a liquid-liquid form, and also in a powder-liquid form.
The amount of alkaline cleaning agent is generally 2% - 10%. Cleaning methods include spraying, soaking, and spraying. The immersion cleaning efficiency is lower than the spray cleaning efficiency, but the solution is easier to reach the inner cavity of the workpiece during immersion, so the complex workpiece cleaning is preferably treated by spraying and immersion. The spraying time is 60-90s, and the soaking time is 3-5 minutes. The temperature of the degreasing solution is generally 45-65 °C. The specific time, temperature, and concentration vary depending on the type of cleaning agent and the substrate.
2. Alkaline cleaning agent selection
The basic requirements of alkaline cleaners are better degreasing ability, no odor, meet specific environmental requirements, easy to wash, chemically stable, chemically unchanged under normal storage conditions, and have little effect on the substrate. The type of grease to be removed (grey, wax, oil, crystalline salt, etc.), conversion film type, workpiece size, type and material should be considered. Before cleaning the phosphating agent, in addition to investigating solubility, degreasing, emulsifying and defoaming properties, it is important to examine whether the interaction between the cleaning agent and the substrate will affect the formation of the subsequent conversion film, that is, the cleaning agent will not It will change the surface state of the workpiece (erosion, ash, etc.), as well as the effect of complex workpieces being brought into the phosphating tank due to incomplete washing. Cleaning as an integral part of the pretreatment has an important effect on the quality of the conversion film.
Treatment costs are an important factor in the selection of cleaning agents, including:
Chemical consumption;
Extra manual, cleaning;
Overflowing
Rework and scrap of the workpiece;
Slotting, cleaning the tank and the possible impact on work efficiency;
Operation management and equipment operation;
Waste liquid treatment, etc.
These factors should be considered together to ensure lower processing costs. At the same time, we must fully consider the product's quality assurance capabilities, technical service timeliness and problem-solving capabilities.
3. Process maintenance
Good pre-treatment products require proper use and maintenance to achieve the best results. The cleaning agent removes the oil from the surface of the workpiece into the solution by physicochemical action, and the grease accumulates in the bath. When the circulation pump is turned on, solid particles are deposited on the bottom of the tank, and grease and organic impurities float on the surface of the solution. Eliminating surface grease and periodically removing bottom sludge can extend the life of the entire tank and reduce the impact on subsequent processes.
Next page
Nickel based Alloys,High Quality Nickel based Alloys,Nickel based Alloys Details, M.M. METALS
JianDa Pipes&Fittings Group Co.,Ltd , http://www.chinasteelpipefittings.com