The purpose of pretreatment is to remove oil stain, rust and scale on the surface of parts and improve the bonding force between film and substrate. There are many pretreatment methods, such as degreasing with organic solvent or alkaline cleaning agent, shot blasting, vibration grinding, sand blasting and shot blasting. The dacromet pretreatment process is organic solvent (such as dichloromethane) cleaning+ultrasonic cleaning+shot peening, which not only reduces the emission, ensures the centralized collection and treatment of various wastes, but also makes the surface of parts easy to adhere to dacromet treatment solution. Pretreatment should try to avoid acid cleaning to prevent hydrogen embrittlement.
Coating is to spray or impregnate parts with dacromet solution, and then remove excess treatment solution by centrifugal drying, natural vertical flow and air blowing. Generally, the coating thickness of one coating and one drying is 3-4um, and two coating and two drying or three coating and three drying can be carried out according to the product requirements to increase the coating thickness and improve its corrosion resistance.
Baking is the process of converting dacromet treatment solution on metal substrate into film layer, which is usually carried out in a mesh belt circulating hot air oven. The whole drying tunnel is divided into preheating zone, and the temperature is 60- 180 degrees Celsius (treatment time is 10 minute). Parts should be preheated slowly to make the moisture of the coating gradually escape, so as to avoid foaming and porosity of the coating.
I refer to the knowledge of Changzhou Hejun website. Please consult them for detailed questions.