company news about Process flow Of powder coating

Process flow Of powder coating:
Use electrostatic powder spraying equipment (electrostatic spraying machine) to spray powder coating to the surface of the workpiece, under the action of static electricity, the powder will be uniformly adsorbed on the surface of the workpiece, forming a powder-like coating; The powder coating is cured by high temperature baking and leveling, and becomes the final coating with different effects (different kinds of effects of powder coatings).
Detailed steps:
1. Pre-treatment
Purpose: To remove the oil, dust, rust on the surface of the workpiece, and generate a layer of corrosion resistance and can increase the adhesion of the spray coating "phosphating layer" or "chromium layer". Main process steps: oil removal, rust removal, phosphating (chroming), passivation. Not only is there no oil, rust, and dust on the surface of the workpiece after pre-treatment, but also a uniform and rough gray phosphating film (chromium film) that is not easy to rust is generated on the original silver-white glossy surface, which can both prevent rust and increase the adhesion of the spray layer.
There are three common pre-treatment types: soaking type, spray type and waterfall type. Soaking type requires multiple soaking tanks; Spraying requires a spray line to be set up on the spray line; In the waterfall mode, the solution flows directly down the workpiece from the height.
2, electrostatic spraying
Purpose: The powder coating is evenly sprayed on the surface of the workpiece. Special workpiece (including the position that is prone to electrostatic shielding) should be sprayed with a high-performance electrostatic spray molding machine.
Process steps: Using the principle of electrostatic adsorption, spray a layer of powder coating evenly on the surface of the workpiece; The fallen powder is recovered through a recovery system.
3. Curing
Objective: To solidify the sprayed powder onto the workpiece surface.
Process steps: The sprayed workpiece is placed in a high temperature furnace of about 200 for 20 minutes (the curing temperature and time are determined according to the quality of the selected powder, and the curing temperature of the special low temperature powder is about 160, which is more energy saving), so that the powder is melted, levelled and cured. [3]
Common problems:
1, coating impurities
Common impurities mainly come from particles in the powder spraying environment, as well as impurities caused by various other factors, which are summarized as follows.
1) Solidify impurities in the furnace. The solution is to thoroughly clean the inner wall of the curing furnace with a wet cloth and a vacuum cleaner, focusing on the gap between the suspension chain and the air duct. If it is black large particle impurities, it is necessary to check whether there is damage to the air duct filter, and replace it in time.
2) Impurities in the dusting room. Mainly dust, clothing fibers, equipment abrasive particles and powder system fouling. The solution is to use a compressed air blowing duster system every day before work, and thoroughly clean the duster equipment and duster room with a damp cloth and a vacuum cleaner.
3) Suspension chain impurities. It is mainly the product of the suspension chain oil baffle plate and the primary spinner water plate (made of hot galvanized plate) after being corroded by the pretreatment acid and alkali vapor. The solution is to clean these facilities regularly.
4) Powder impurities. It is mainly caused by excessive powder additives, uneven dispersion of pigments, powder points caused by extrusion. The solution is to improve powder quality and powder storage and transportation.
5) Pretreatment of impurities. It is mainly caused by large particles of impurities caused by phosphating slag and small impurities caused by yellow rust of phosphating film. The solution is to clean up the slag in the phosphating tank and spray pipeline in time, and control the concentration and proportion of the phosphating tank.
6) Water quality impurities. It is mainly caused by impurities caused by excessive sand and salt content in the water used for pre-treatment. The solution is to add water filters and use pure water as the last two stages of cleaning water.
2, coating shrinkage hole
1) Shrinkage hole caused by surfactant residue caused by unclean oil removal before treatment or unclean water washing after oil removal. The solution is to control the concentration and proportion of the pre-degreasing tank and degreasing tank liquid, reduce the amount of oil in the workpiece and strengthen the washing effect.
2) Shrinkage caused by excessive oil content in water quality. The solution is to add water filters to prevent oil leakage from the supply pump.
3) Shrinkage caused by excessive water content of compressed air. The solution is to discharge compressed air condensate in time.
4) Shrinkage hole caused by moisture of powder. The solution is to improve the powder storage and transportation conditions and increase the dehumidifier to ensure the timely use of recycled powder.
5) The shrinkage hole caused by the oil on the suspension chain being blown onto the workpiece by the air conditioner. The solution is to change the position and direction of the air supply outlet of the air conditioner.
6) Shrinkage caused by mixing powder. The solution is to thoroughly clean the dusting system when changing powder.
3, coating color difference
1) Color difference caused by uneven distribution of powder pigments. The solution is to improve the quality of the powder and ensure that the L, a and b of the powder are not different and positive and negative unity.
2) Color difference caused by different curing temperatures. The solution is to control the set temperature and conveying chain speed to maintain the consistency and stability of the workpiece curing temperature and time.
3) Color difference caused by uneven coating thickness. The solution is to adjust the dusting process parameters and ensure that the dusting equipment runs well to ensure uniform coating thickness.
4, the coating adhesion is poor
1) Incomplete pre-treatment washing causes poor adhesion caused by residual degreaser, chromified slag on the workpiece or alkaline contamination of the washing tank. The solution is to strengthen water washing, adjust the parameters of degreasing process and prevent degreasing liquid from entering the washing tank after phosphating.
2) Poor adhesion caused by phosphating film yellowing, blooming or local no phosphating film. The solution is to adjust the concentration and proportion of phosphating tank and increase the phosphating temperature.
3) Poor adhesion caused by unclean drying of moisture at the corners of the workpiece. The solution is to increase the drying temperature.
4) Poor adhesion of large area coating caused by insufficient curing temperature. The solution is to increase the curing temperature.
5) Poor adhesion caused by excessive oil and salt content in deep well water. The solution is to add the inlet filter and use pure water as the last two cleaning water. In short, there are many electrostatic powder spraying technology and its application methods, which need to be flexibly used in practice.
5. Powder-coated orange peel
1) Judge the appearance of powder coating orange peel:
(1) Visual method
In this test, the template is placed under a double-tube fluorescent lamp. The reflective light source of the template can be obtained by placing the template properly. Qualitative analysis of the clarity of the reflected light allows visual assessment of flow and leveling properties. In the case of poor liquidity (orange peel), the two fluorescent tubes look blurred and not clear, while the high liquidity product can obtain a clear reflection.
(2) "Shape Measurement Method"
In this method, the surface shape is recorded by the offset of a highly sensitive probe. This can quickly distinguish rough, orange peel and poor flow caused by shrinkage, pinhole or dirt.
2) Avoid the occurrence of orange peel
The appearance of the coating is becoming more and more important in the manufacture of new equipment. Therefore, one of the main objectives of the coating industry is to achieve the best performance of the coating according to the final requirements of the user, which also includes the satisfaction of the surface appearance. The surface condition affects the visual effect by color, gloss, fog shadow and surface structure. Gloss and image clarity are often used to control the appearance of the coating. However, even if the use of high gloss coating, its surface fluctuation also affects the appearance of the entire coating, and it is believed that gloss measurement can not control the visual effect of fluctuations, this effect is also known as "orange peel". The orange peel or microwave is a corrugated structure with a size between 0.1mm and 10mm. On the surface of the high-gloss coating, one can see wavy, alternating areas of light and dark.
It should be pointed out that sometimes in order to cover the surface defects of the substrate or to obtain a special surface appearance of the coating, a certain fluctuation or ripple structure is purposefully designed.