Enamel Coating Process
Enamel manufacturing process mainly include enamel frit manufacturing, metal body casting, enamel coating, drying, firing and testing. For art enamel, cookware, sanitary and architecture etc…It will need decorating and packaging for its good appearance and daily use; For industrial enamel, it will need to be tested then assemble.
First, coat a ground coat on a metal body which is already casted or stamping to the specific shape. After firing and cooling, then coat a cover coat(one time or many times). This is the traditional enamel coating. Ground coat is a transition layer for combination with metal body. It need strong adherence. Cover coat is coated on ground coat, which can cover the ground coat and give it a smooth and beautiful surface and stable physicochemical property. Cover coat can be divided into opacifying cover coat(white and colored) and transparent cover coat. It’s coated on the outermost layer to increase its glossiness or improve its property. Nowadays, there is a new enamel coating process, which is called direct on one time coating. It has only one coat, can be both ground coat and cover coat, only need one time to coat, and one time firing, then the products can be done.
Enamel frit is glassy state silicate or borosilicate coated on metal body. Enamel frit has seven parts, every parts have different functions. Its basic are mainly silicate, boric oxide, aluminium oxide and alkali metal oxide. Its composition can be confirmed by the metal material and end product’s requirements. It need to be accurately weighted, fully mixed, fused to specific average extent in tank, pot or rotary furnace, and after water quenching, air cooling or hot-pressing to flake(0.6-1.5mm). Then milling it(by ball or airflow milling machine) to dry enamel powder or add water to make it enamel slurry.
Coat enamel powder or slurry evenly on the metal body, after firing, coat cover coat on ground coat. Coating ways can be dipping, pouring, spraying and bepowdering. Bepowdering is to sprinkle cover coat enamel powder to red hot ground coat, which makes coating and firing one process. It’s a must for making cast iron products in large size(bathtub, reactor…). Moreover, there’s electrostatic powder spray and electrophoresis coating.
Put the coated metal body to oven, rotary or tunnel furnace and fire. Firing temperature of ground coat with borosilicate is about 820-880℃. In order to form a iron oxide layer on the metal surface which can improve the adherence between enamel layer and metal body. Firing temperature of cover coat is little lower, Antimony cover coat can be fired in 830-850℃, Titanium cover coat can be fired in 800-850℃. In order to make cover coat good opacifying and bright color, and close integration with ground coat, strict control of firing time and condition is a must. Antimony and Titanium cover coat is especially strict on firing condition.
Hunan Noli Enamel Co,. Ltd focus on enamel coating for almost 30 years, which makes us quite professional on enamel coating and very familiar with enamel coating process. We can completely control every process of enamel fritmanufacturing and have strong technical supporting team, which makes our quality very close with Ferro and Pemco corporation. And our cost can be lower.