Color Management and Application in Powder Coating
1. Use a set of special equipment for each color
The method of using a set of special equipment for each color is to consider using a set of painting equipment for each color. Each set of painting equipment includes powder feeding device, powder spraying chamber and recycling device, and the whole set is replaced whenever the color is changed. The color changing equipment system can be divided into series type and parallel type.
The powder spraying chamber units are arranged in series with one powder spraying chamber for each color, but the powder coatings sprayed in the A powder spraying chamber are easy to be brought into the B and C powder spraying chambers, while the powder coatings sprayed in the B powder spraying chamber are easy to be brought into the C powder spraying chamber to cause interference. In order to minimize the interference between powder coatings of different colors, it is important to consider the order of colors. For example, the powder spraying chamber A is white, the powder spraying chamber B is light yellow, and the powder spraying chamber C is light green. Such color order of powder coatings has less interference on product color. The unit of powder spraying chamber is arranged in parallel, which can switch load white. The conveyor belt sends the coated material into different powder spraying chambers according to the color requirements. Compared with the series type, there is no color interference between the powder spraying chambers, but it needs power and automatic load switching device, and the investment cost of the equipment is higher.
In addition, there are two mobile powder spraying chambers. When changing the color, the recycled powder coating pipeline is unloaded, and the motor automatically switches the powder spraying chamber to spray other powder coating color varieties. At the same time, the unloaded powder spraying chamber is cleaned to prepare for the next use. This kind of powder spraying system can be used for PCM system with less color variety and less capacity of powder spraying chamber, but it is difficult for the painting system with large volume of powder spraying chamber.
2. Coating system with easy cleaning and color change in short time
(1) Automatic multi-color change system
The powder spraying chamber is surrounded by a cleaning device. When the automatic cleaning device moves from the outlet of the powder spraying chamber to the population, the air nozzle sweeps the inner wall of the powder spraying chamber (including the upper and lower left and right walls), and the doors of the inlet and outlet of the powder spraying chamber are closed to prevent the powder coating from escaping. In this step, the cleaning rate of powder coatings is over 90%. When the automatic cleaning device moves from the entrance to the exit, the slightly wetted foam plastics are wiped close to the wall of the powder spraying chamber, and the powder below 10um that can not be blown by the air is swept out, reaching 100% cleaning rate. It's easy to use foam for cleaning. It's removed from the automatic cleaning device. Therefore, the cleaning speed of powder spraying chamber is fast and the color change is convenient.
(2) Filtration and Recovery of Metal Powder Spraying Chamber
Interchangeable banded polyester fiber filter cloth is installed at the bottom of the metal powder spraying chamber, which rotates continuously during the painting process. The exhaust air in the powder spraying chamber is discharged to the powder spraying outdoor through the filter cloth. The fugitive powder coating from the powder spraying chamber is deposited on the conveyor belt and sent to the powder absorber. The powder absorber automatically sucks up the powder coatings, separates them with a small cyclone separator, and separates the recovered powder coatings by a rotary valve and a sifter, which is recycled into the powder trough of the coating system. The advantages of this system are small preparation volume and small floor area, low height at the bottom of the powder spraying chamber, which reduces the height of the equipment, stable air flow in the powder spraying chamber and easy cleaning in the powder spraying chamber due to the frequent recycling of powder coatings on the conveyor belt of filter cloth.
(3)Fast Color Change Powder Coating
There are many forms of rapid color change powder coating system. First, the aforementioned filter element (cartridge) type filter recovery device and coating system are used. The powder spraying chamber of this equipment is made of stainless steel. Its inner wall is smooth and smooth without dead angle. It is easy to clean. Its shape is also designed according to the principle of aerodynamics, and it will not accumulate powder coatings. Because there is no ventilation exhaust pipe in the connection between powder spraying chamber and recycling equipment, it is easier to clean than other equipment systems, and there is a hopper under the powder spraying chamber, so the time of color change is short, and the loss of paint is very small. The powder spraying chamber of this system has high recovery efficiency for powder coatings sprayed with various colors. The biggest problem of this system is that in the large-scale coating system, the number of filter elements is more, the cleaning of filter elements is more troublesome, but the cleaning of pipeline is simple, and there is no cleaning problem of cyclone separator and bag filter. Therefore, compared with other systems, cleaning equipment, color change and coating variety change are relatively simple. PVA (polyvinyl alcohol) conveyor belt type fast color change powder coating equipment port This equipment's powder spraying chamber is made of non-flammable acrylic polymer board. When spraying powder, the powder coating escaped falls on the conveyor belt made by PVA. When it is sent to the outlet of the powder spraying chamber, the air-powder spraying gun installed at the outlet sprays to the coating again. Due to the controlled air flow, the floating powder coating is coated on the surface of the coated material by charging the electrodes on the side of the powder spraying chamber again. The spraying gun supplies the powder coating to the spraying chamber in the form of fog, instead of directly spraying to the surface of the coating. The change of color is installed in the exit [} 1 position of the powder spraying chamber through the grounded aluminum plate. The PVA conveyor belt moves to the aluminum plate, and the remaining powder coating is attached to the aluminum plate. After the conveyor belt runs for 2 to 3 times, the aluminium plate is replaced by the filter assembly, so that the cleaning operation of the powder spraying chamber can be carried out in a short time. The characteristics of the color changing system are: the color changing operation can be completed within 15 - 20 minutes; the equipment is small in size and occupies a small area; there is no need for cyclone separator and bag filter; the exhaust air is circulated through the filter in the room, so no new air is needed.
The different color changing systems mentioned above have their own advantages. Which method should be adopted in construction depends on the type of color used, painting efficiency, allowable degree of mixed pollution of powder coatings, time needed for color changing, equipment cost and arrangement of equipment, etc. If the powder coatings of another color are mixed in one kind of powder coatings, they will not be completely miscible as solvent-based coatings, but become fine particles left behind. After film formation, these small particles appear on the film in the form of spots, which causes the disadvantages of the film. In Table 9-5, the results of visual judgment are listed when white, light green and light yellow powder coatings are mixed with each other. When powder coatings are mixed with 0.1% powder of different colors, obvious pollution will be caused. Therefore, when choosing powder coatings of various colors for powder creeping, the equipment and process of powder coating should be carefully selected so as to ensure the quality of coating film of powder coating products.
(4) Recovery coating system of small multi-cyclone separator
In this system, the recovery of powder coatings adopts a multi-recovery system (MRS) which combines a small multi-cyclone separator with a bag filter. There is also a Wagner ICM complex recovery equipment system which combines a small multi-cyclone separator with a filter core recovery equipment. Their characteristics are that the cyclone separator is miniaturized, which not only reduces the space occupied by the equipment, but also reduces the ghost. It is convenient to clean the interior of the cyclone sharer in color time, especially the connection between the powder spraying chamber and the cyclone sharer does not need a pipeline, which prevents the mixing problem in the pipeline. The equipment system developed by Switzerland is easy to install automatic fire extinguishing devices to prevent dust explosion. As this equipment has many advantages over the previous large cyclone sharers, this powder coating recycling system has been gradually promoted in China, and its application effect is better.
3. The Method of Coordination by Painting Technology
Through the cooperation of different paint varieties, the purpose of multi-color painting can be achieved.
(1)The method of combining powder coating with solvent-based coating is suitable for products requiring various colors. First, the main colors are coated with powder coating, and then other colors are coated with solvent-based coating. In order to make different kinds of powder coatings and solvent-based coatings match better, factors such as coating operation and adhesion between coatings should be considered. If the powder coatings are directly coated with solvent-based coatings without sandpaper polishing or solvent wiping treatment, the adhesion between coatings is often not good. In addition, the compatibility between solvent-based coatings and powder coatings for topcoats should be considered.
(2)The method of mixing powder coatings with water-borne coatings. The coatings used in this kind of coating system are all low-pollution coatings, which are beneficial to environmental protection. One of its characteristics is that it is easy to change the color of waterborne coatings, such as using polyurethane powder coatings as the base, spraying acrylic or amino alkyd waterborne coatings on the coating system. Its coating quality is guaranteed by polyurethane powder coating, and many colors are accomplished by water-borne coatings which are easy to adjust colors.
(3)Dry-wet film one-time baking method This coating method is solvent-based paint after spraying, when most of the solvent volatilizes, then spray transparent powder paint on it, and then bake together. This kind of coating is characterized by good combination of coatings. For example, a solvent-based coating with a thickness of about 15-25um is sprayed on it for 3 minutes, then powder coating is sprayed on it, so that the coating thickness is about 50um, and then baked in a baking oven. The advantages of this method are that the solvent is saved and the color change is easier than that of the pure solvent-based coating system, and the metallic flash powder coating can be prepared.
