1 thickness of the workpiece determines the thickness and curing time of the coating

粉末涂料为热的不良导体，固化时，热量传递方式是“涂层→金属”；冷却时，热量传递方式是“金属→涂层”。在工件厚度较大(大于10mm)时，涂层散热慢，而工件较厚，涂层与工件的热膨胀系数相差较大，二者膨胀幅度相差悬殊，导致产生较大应力，使二者间的结合力减小，并且漆膜较脆。此种情况下工件固化后不宜快速冷却，应缓慢降温，避免较大应力的产生。适当增加涂层厚度也有助于减小冷却过程中产生的应力。但是增加涂层厚度后，由于涂料为热的不良导体，热量传递速率必然降低，热量从涂层外表面到达涂层内表面需较长时间，涂层内外表面固化不同步现象严惩，因此固化时间应适当增加。

Powder coating is a poor conductor of heat. When heat is solidified, the heat transfer way is "coating to metal". When cooling, the heat transfer way is "metal to coating". When the workpiece thickness is greater than (10mm), the heat dissipation of the coating is slow and the workpiece is thicker. The thermal expansion coefficient of the coating and workpiece is quite different. The expansion range of the two parts is quite different, resulting in a larger stress, which makes the bonding force between the two decreases, and the paint film is crisp. In this case, the workpiece should not be cooled quickly after curing, and it should be slow down to avoid large stress. Appropriately increasing the thickness of the coating also helps to reduce the stress produced during the cooling process. However, when the coating thickness is increased, the heat transfer rate will inevitably decrease due to the poor thermal conductivity of the coating. It will take a long time for the heat to reach the inner surface of the coating from the outer surface of the coating, and the internal and external surface of the coating is not synchronized. Therefore, the curing time should be increased appropriately.

2复合涂层

2 composite coating

工件表面经喷塑、固化、冷却后，可在其外表面罩自干型清漆或色漆，以提高涂层的装饰性并起到修补缺陷的作用。但需注意，在溶剂型涂料表面不可喷涂粉末涂料。这是因为①静电喷塑要求待喷工件有较好的导电性能，而喷涂溶剂型涂料后，由于涂层不导电，使工件电阻非常大，影响静电喷塑质量；②在二者顺序颠倒的情况下，上层喷塑涂层易起泡脱落，因为溶剂型涂料即使在干燥或固化(固化温度一般低于粉末涂料固化温度)后，涂层中仍含有少量溶剂，在上层粉末涂料受热固化过程中，下涂层中残存的溶剂抵抗上涂层阻力而挥发逸出，使上涂层起泡脱落，需引起注意。

After the surface of the workpiece is sprayed, solidified and cooled, the self drying varnish or paint can be worn on the surface of the workpiece, so as to improve the decorating property of the coating and repair the defect. However, it should be noted that powder coatings can not be sprayed on the surface of solvent based coatings. This is because the electrostatic spray requirement for spray workpiece has good conductivity, and spraying solvent coatings, because the coating is not conductive, the resistance is very large, the effect of electrostatic spray quality; in the two order case, the upper spray coating foaming off, because even in the dry or solvent type coating curing (curing temperature is generally lower than the powder coating curing temperature), a small amount of solvent still contains the coating, powder coating layer in the heat curing process, the residual solvent in the coating coating resistance and volatilizes, make the coating blistering off, must pay attention to.