Pretreatment process: phosphating and degreasing

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Pretreatment process: phosphating and degreasing

Quality phosphate film can only be formed on the surface of the workpiece where the oil is removed thoroughly. Because, oil residue on the surface of the workpiece, not only will seriously impede the growth of phosphate film, but also affect the adhesion of the coating film, drying properties, decorative properties and corrosion resistance.

    Table 1-5 Effect of degreasing and cathodic electrophoretic coating film corrosion resistance

 

Serial number	Degreasing + (phosphating)	Salt spray test	Remarks
1	Untreated (with oil)/h	240	Coated on cold-rolled steel plate with a coating film thickness of 20μm.
2	Only degreasing/h	480
3	(Degreasing+phosphating)/h	840

       Phosphate film grains are formed on the surface of the workpiece, the more grain reaction points, the finer the film crystallization more dense. Conversely, the fewer the grain points, the smaller the interaction between the grains, the more coarse and sparse the grains of the film layer obtained.

       Strong alkaline degreasing often contains not easy to clean Na2SiO3, NaOH and other ingredients, easy to pollute the phosphate bath, increase phosphate slag, neutralize many grain points on the surface of the workpiece, prolong the phosphate time, the formation of rough, thin and loose, low corrosion resistance phosphate film, and increase the phosphate film weight.

       Organic solvent degreasing, although the phosphating process can be made less hydrogen precipitation. Phosphate speed, dense and uniform film layer, but the toxicity, pollution, heavy, unsafe, low temperature and water washing at room temperature is difficult.

       In view of the above reasons, low-temperature and room temperature phosphating before the degreasing agent, it is best to use low-temperature or room temperature conditions easy to clean the neutral degreaser, weak alkaline degreaser, slightly acidic degreaser. Chengdu Xianghe Phosphate Co., Ltd. XH-15 type metal heavy grease removal powder and XH-14 type metal neutral degreasing powder, is not contain NaOH, OP-10, Na2SiO3 and other components of low-temperature degreasing agent, XH-16 type room temperature oil removal and decontamination King, is also a micro-acid degreaser without the aforementioned components, and can be used at a temperature of 0 ℃ ~ 40 ℃, in the vast majority of China's winter also It can be used at 0℃～40℃, and in most areas of China, it can be used in winter without heating.