Analysis and solution of defects in powder coating

  • Detail

In recent years, more and more domestic barrel manufacturing enterprises have adopted a new electrostatic powder coating process for the surface coating of steel barrels, which not only improves the surface quality of steel barrels, but also brings new problems to the production of steel barrels

although the steel barrel powder coating process is few, there are many links that cause problems. The main processes of powder coating include pretreatment, electrostatic spraying and baking. Anqing is one of the three new chemical bases in our province. The main process affecting quality should be pretreatment process. However, many manufacturers did not pay enough attention to this, resulting in many future problems. Some hidden dangers can not be reflected in the short term. Generally, the cost of advanced technology and pretreatment accounts for more than 25% of the total cost

analyze various problems in the production process. I think the advanced level of equipment and the quality of raw materials play a decisive role in product quality, and neither of them is indispensable. As engineers and technicians, we should build a consensus on this issue, and never put it on the new powder spraying production line. The typical formula is si8mg5o20[al] (OH) 2 (oh2) 4.4h2o. It is only a matter of saving money for a while. The use of low-standard production equipment, processes and materials will bring many future problems to long-term production, and even fail to produce high-quality products. Many manufacturers went to the powder coating production line, and were forced to dismount or replace the equipment soon after application, all for the above reasons. We often see that the surface coating of foreign products is very beautiful. One of the main reasons is that they constantly use advanced equipment and new processes and materials

in this sense, for powder coating equipment and coating manufacturers, under the current market competition conditions, non high-quality equipment and coatings have no future. This is especially true under the competitive conditions of hundreds of domestic powder spraying equipment and powder coating manufacturers. In Shaanxi Province alone, nearly ten equipment and powder coating manufacturers have switched production or closed down

II. Analysis and discussion of defects

(I) pretreatment:

1. The oil and rust removal is not complete

first of all, I do not advocate the two in one process of oil and rust removal. The two in one process itself is prone to this problem. Because the commonly used formulas of degreasing and derusting fluid are weak, rather than complementary, it is difficult to work out a reasonable two in one or three in one process (including phosphating) formula. Another process is to use metal detergent to remove oil, which cannot be completely removed. Because the degreasing effect of metal cleaning agent is poor, generally, the grease can only float on the surface of the metal body. To remove it, a kind of mechanical force is needed. If there is no such additional mechanical force, the oil will not be completely removed. It can be seen that metal cleaning agent is not suitable for industrial mass production

I advocate using alkali chemistry to remove oil. Alkali liquor has a good effect on the removal of animal and vegetable oil, because it produces saponification reaction. However, the removal effect of mineral oil is poor. In order to remove mineral oil, emulsifier needs to be added. In addition, the washing quality has a great impact on the degreasing effect, one is the water quality, the other is the water temperature. Third, it is necessary to turn over by grades. All three items are good. There is only one purpose, that is, to clean the grease with pure water. The last stage is best cleaned with deionized water

2. Problems such as rough phosphating film

steel parts must be phosphated before powder spraying. Sand blasting phosphating process is widely used abroad. Many phosphating solutions we use are not ideal, which directly affects the quality of phosphating film. The common problem is the coarseness of phosphating film. I want to analyze this from three aspects: the first is to choose a good phosphating solution, which is the fundamental to ensure quality. The first question involved is which type of high, medium and low temperature? From its development history, it began with high-temperature thick film type, and has now progressed to medium and low temperature thin film type. Domestic low-temperature phosphating solution is rarely used because the solution is not stable enough, maintenance is difficult, the adhesion of phosphating film is poor, and some are even not resistant to water washing. Some low-temperature phosphating solutions are ideal, but the price is more expensive. Although low-temperature phosphating is the development direction, it has achieved the effect of universal application. Jinan has been known as the production base of experimental machines since the existence of experimental machines, and new breakthroughs need to be made. At present, Xianghe phosphating (Chengdu) company has successfully solved the problem of normal temperature phosphating (passivation) powder, and has been supplied in batches. At present, medium temperature phosphating process is widely used. The second is to choose zinc series. Iron Jinan experimental machine factory is looking forward to your excellent achievements. Which phosphating solution is zinc calcium series? In contrast, I think zinc calcium phosphating solution is better. Considering the thin coating phosphating film required for plastic spraying pretreatment, iron system is also a better choice. In addition to some advantages of zinc series, it also has good heat resistance. At medium temperature, there is less hydrolysis, less sediment, easy maintenance of the solution, good mechanical strength, strong corrosion resistance, and the crystallization is still very fine when the film is thick. The iron series iron phosphide film has poor corrosion resistance. In a word, it is better to choose warm zinc calcium phosphating solution. The second is that the phosphating solution must be adjusted at any time, mainly adjusting the acidity ratio and zinc content. These two factors directly affect the film formation rate and the thickness of crystallization. It is necessary to adjust the analytical solution regularly and irregularly according to the workload. It is unscientific to blindly supplement the feed solution without analytical data. The third is to control the thickness of the film. All kinds of phosphating films have their best thickness. For example, the best film thickness of zinc series and calcium zinc series is 1 Grams per square meter, while iron is 0 7 grams per square meter, in this range, its corrosion resistance is the best, and the grain size is the smallest. If it is too thick, it will affect the flexibility and adhesion of the film, and the grain size will also become coarser. Usually, the problem in production is that the phosphating film is too thick. Here are some suggestions on how to overcome the problem of grain coarsening

the first is to refine the grains by using surface modifiers. That is, carry out a surface adjustment treatment before phosphating the workpiece, so that a layer of colloidal particles are adsorbed on the metal surface to form a layer of "activation center", and then continue to grow on the secondary "activation center" during phosphating, so that the phosphating grains can be significantly thinner, especially before low-temperature phosphating, surface adjustment is an indispensable one-step treatment method

the second is to add grain refiners to the phosphating solution, such as calcium, nickel and other salts as modifiers. It is best to use compound salts, which has better effect and can reduce the amount of low sediment at the same time

the third is passivation treatment after phosphating, so that the peak and pit structure is formed on the phosphating film, so as to improve the corrosion resistance and improve the adhesion of the coating

the fourth is to adjust the acidity ratio and zinc content of phosphating solution at any time. We have already talked about it

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