Definition and functions of chemical pretreatment
Taking advantage of the technique with chemical solution or solvent to have pretreatment towards the aluminum surface can be effectively remove the greasy dirt、pollutants、natural oxide film of the original aluminum product surface to have a wetting 、even、cleaning surface.
1. Common process flow of chemical pretreatment
Common process flow of chemical pretreatment includes many methods such as derosination、alkali washing、ash disposal、rough surface preparation of fluoride and washing. Based on the application、the requirement of surface quality of unsolved aluminum products, we can adopt different process flow of chemical pretreatment.
2. The principles and functions of derosinatiion
Grease will have hydrolysis reaction to generate glycerol and rather higher fatty acid during acidic degreasing solution. With the help of a small amount of wetting agent and emulsifier, grease can be dissolved more easily and to achieve the better greasing effect. Greasing treatment can remove the grease and dust of the aluminum surface, which makes the later alkali washing become comparable even.
3. The principles and functions of alkali washing
Putting aluminum into alkaline solution whose major component is caustic soda to carry on etch reaction helps remove the smudge on the surface. To wipe off the natural oxide film on the aluminum surface thoroughly will appear pure metallic matrix so that follow—up anticathode oxidation can be moving .
4. The principles and functions of removing fluoride
After the alkali washing, the product surface will attach intermetallic compound with a layer of insoluble caustic washing tank solution and its alkali washing product, which are layers of taupe or dark gray dusting. The goal of removing the dusting is that it can prevent the follow—up anticathode oxidation procedure bath solution from polluting.
5. The principles and functions of rough surface preparation of fluoride
The meaning of rough surface preparation of fluoride is a kind of acid etching technique using fluoride ion to make the aluminum product surface produce highly even and high density pitting corrosion, whose purpose is to eliminate the extrusion mark on the product surface and to have a smooth one. However, due to its serious pollution to the environment, it hasn’t been promoted the use any more.