1工件厚度决定涂层厚度和固化时间

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 it is solidified, the heat transfer way is "coating to metal". When cooling, the heat transfer way is "metal to coating". When the thickness of the workpiece is larger (greater than 10mm), the heat dissipation of the coating is slow, the workpiece is thicker, the thermal expansion coefficient of the coating and the workpiece is different, the difference between the two expansion ranges is very different, which leads to the larger stress, which makes the bonding force between the two and the film more brittle. In such cases, it is not suitable for rapid cooling after solidification of the workpiece, so it is necessary to slow down the temperature to avoid the occurrence of larger stress. Appropriately increasing the thickness of the coating will also help to reduce the stress generated during cooling. However, after the coating thickness is increased, the heat transfer rate is bound to decrease because of the thermal conductivity of the coating. The heat transfer from the outer surface of the coating to the inner surface of the coating needs a long time. The curing time of the coating is not synchronized, so the curing time should be increased properly.

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 surface of the workpiece can be covered with dry varnish or color paint to improve the decoration of the coating and to repair the defects. However, it should be noted that the powder coating on the surface of solvent based coatings should not be sprayed. This is because (1) the electrostatic spraying requires good electrical conductivity of the work piece, and after spraying solvent type coating, the resistance of the workpiece is very large and the quality of the electrostatic spray is greatly influenced by the non conducting coating of the coating. Second, when the order of the two is reversed, the upper layer plastic coating is easily bubbling and shedding, because the solvent coating is even dry or solid. After the curing temperature is generally lower than the curing temperature of powder coating, there is still a small amount of solvent in the coating. During the heat curing process of the upper layer powder coating, the remaining solvent in the lower coating is resistant to the coating resistance and volatilizes and escapes and causes the coating to fall off. It needs to be paid attention to.