The reasons for the shrinkage on the surface of the parts are:
(1) There is oil stain on the surface of the parts after pretreatment. This may be caused by the incomplete degreasing of the parts, or it may be caused by oil stains in the gloves or the transfer box during the suspension and transfer of the parts;
(2) The compressed air contains oil;
(3) The powder-spraying conveyor chain has just been added with lubricating grease recently. During the high-temperature baking in the curing tunnel, the grease volatilizes in the air in the drying tunnel and is adsorbed on the surface of the parts to form shrinkage cavities. There is oil in the drying tunnel. The lubricating grease of the conveyor chain condenses on the wall of the drying tunnel after baking, and if it is not cleaned for a long time, the oil contamination accumulates, volatilizes under high temperature conditions, diffuses in the drying tunnel, and is adsorbed on the surface of the parts to form shrinkage holes;
(4) Mixing powders of the same color from different manufacturers will also cause shrinkage;
(5) Improper ratio or insufficient grade of manufacturing raw materials of powder coating itself will also cause shrinkage cavities
(6) The fluidizing plate in the powder box is polluted by oil, which can also cause shrinkage. However, this problem is ultimately caused by the presence of oil in the compressed air.
