Three Common Methods of Pre-treatment in Painting Production Lines And Their Advantages And Disadvantages

The pre-treatment of the painting production line refers to the stage where the surface of the workpiece has been completely cleaned of air oxidized surface, rust, vegetable oil, dust and other stains, so that the sprayed powder or paint can blend firmly with the metal surface, have strong adhesion, and improve the quality of the workpiece, thereby extending its service life. The process of cleaning the surface of the workpiece by removing various stains (such as lubricating grease, emulsified oil, vegetable oil, sweat scale, etc.) and floating dust before spraying is an indispensable pre-treatment process in the spraying production line. There are three common methods for pre-treatment of spray painting production lines:

1. Full immersion method

A common process of soaking all work-pieces in the tank liquid, waiting for a period of time, and then removing them for oil removal, rust prevention, phosphating treatment, etc. The

 shape of work-pieces varies, and the parts that the liquid can reach can maintain the overall goal. It is a significant advantage of soaking methods, which cannot be compared to automatic spraying and painting. The shortcomings of it are the lack of auxiliary applications for mechanical equipment erosion, resulting in relatively slow response speed and longer solution time, especially when using suspended conveying work-pieces. In addition to the operation time of the workpiece in the tank, there is also uphill and downhill time for the workpiece, which improves the machine equipment, expands the site facilities and project investment. For the phosphating treatment in the pre-treatment of spray coating production lines, the current trend in foreign countries is to use the full immersion method. It is reported that the full immersion phosphating treatment is prone to producing particle crystalline phosphating treatment films with high copper content, which have good compatibility with the principle of negative electrode electrophoresis.

2. Full automatic spraying method

Fill the liquid with a pump and produce mist at a working pressure of 0.1-0.2Mpa, which sprays onto the workpiece to achieve practical results. Due to the erosion of mechanical equipment and liquid upgrading during self spraying, the response speed is accelerated and the time is reduced. The length of the spraying production line has been reduced, which relatively saves space, machinery and equipment. The drawback is that for work-pieces with complex shapes, liquids such as inner walls and corners are not easily accessible, and the actual solution effect is not very good. Therefore, it is only suitable for work-pieces with simple shapes. The self spraying method is not suitable for acid pickling, passivation, and rust prevention treatment. It can cause a series of problems such as machine equipment erosion and rust between process flows. Therefore, when selecting self spraying acid pickling and passivation, great caution should be taken. The key application of the fully automatic spraying method is in powder spraying and electrostatic spraying of electrical products and components.

3. Automatic spray soak fusion type

Automatic spraying+soaking fusion type, usually in a certain process, the workpiece first undergoes self spraying, then enters the tank for soaking, and then self sprays after leaving the tank. All self spraying and soaking are the same tank liquid. This type of fusion method not only preserves the application of self spraying, improves response speed, but also has the entire soaking process, so that all positions of the workpiece can be reasonably solved. Therefore, the combination of self spraying and soaking can solve the process flow in a relatively short period of time, and the occupation of machinery and equipment is relatively small. In addition, satisfactory practical results can be achieved. At present, in various countries around the world, the automotive manufacturing industry with high regulations for pre-treatment of spray painting production lines generally tends to adopt the self spraying soaking fusion method.

The key processing technology for pre-treatment of spray coating production line: degreasing, water washing, (rust removal), surface adjustment, phosphating, water washing, and drying. Pre coating treatment includes three parts: degreasing (oil removal), rust removal, and phosphating. Phosphating treatment is an important process, and oil removal and rust prevention treatment are pre prepared process flows before phosphating treatment. Therefore, in practical life, not only is phosphating treatment a top priority, but also from the perspective of the quality regulations of phosphating treatment, it is important to do a good job in oil removal and rust prevention treatment, especially in paying attention to their mutual influence.

It can be seen from this that it is necessary to have pre-treatment machinery and equipment in order to ensure the successful pre-treatment of the spraying production line. The pre-treatment machinery and equipment for spray painting production lines work in harsh natural environments, constantly exposed to water and steam. Therefore, when solving production equipment problems before design concepts, it is necessary to use corrosion-resistant raw materials (such as high-quality stainless steel plates and products, plastic parts, etc.) and improve the construction of the machinery and equipment.