Technical development history of zinc-chromium coating

Dacromet is the Chinese transliteration of DACROMETR, also known as zinc-chromium film, Dacromet, Dacromet, etc. It is called “Zinc/Chromate Coatings” (Zinc/Chromate Coatings) in the upcoming Chinese standards on Dacromet. ), which is defined as: “the water-based zinc-chromium paint is dipped, brushed or sprayed on the surface of steel parts or components, and the scaly zinc and zinc chromate formed by baking are inorganic anti-corrosion coatings as the main components “Dacromet’s technology was invented by the Americans. It is a metal coating treatment technology similar to electro-galvanization. The appearance of the Dacromet coating is uniform silver-gray. The coating contains 80% thin zinc flakes and Aluminum flakes, the rest are chromate, have excellent properties, such as strong corrosion resistance; 7-10 times higher than electro-galvanized; no hydrogen embrittlement; especially suitable for high-strength stress parts, such as those used in subway engineering High-strength bolts; high heat resistance; heat-resistant temperature 300℃. In addition, it has the advantages of high permeability, high adhesion, high friction reduction, high weather resistance, high chemical resistance stability and no environmental pollution. Dacromet coating treatment process is roughly divided into: degreasing and degreasing, shot blasting and rust removal, dacromet coating, curing in the furnace, cooling out of the furnace, quality inspection, post-processing, packaging, according to the size, shape, material and For performance requirements, dacromet coating can be performed in the following ways:
(1) For standard parts such as bolts, nuts, washers, etc., you can first put the workpiece into a screen frame or basket, soak it in a Dacromet bath, and then transfer it to a spinner, and use centrifugal force to remove the surface of the workpiece The remaining liquid is thrown off, so that the thickness of the coating on the surface of the workpiece is uniform, and there is no accumulation of liquid in the groove, generally two coatings and two baking.

(2) For those workpieces with higher requirements on appearance quality, the workpiece can be placed on the hanger and then coated by electrostatic spraying, generally one coating and one baking.

(3) For those large-scale workpieces, hoist the workpiece into the coating liquid tank to soak, and then use air to blow to remove the excess paint on the surface of the workpiece to make the coating uniform, generally one coating and one baking.

(4) Some workpieces can be coated by brushing, such as high-strength bolts used in subway applications, and a special brushing machine can be used for coating.

Dacromet coating adopts a closed-circuit working method during the entire operation. Compared with electroplating, it eliminates the production of waste acid, waste salt, and sewage containing zinc, chromium and other metal ions during the production process. In the process of coating curing to form Dacromet film, the volatilized substances are almost