Coating protection technology for enamel tableware

The coating protection technology of enamel tableware mainly lies in the coating materials, preparation processes, and the combination of the coating and the substrate, etc. The following is a detailed introduction:

Coating material

Enamel coating is a composite material in which inorganic glassy materials are melted and solidified onto the base metal and firmly bonded to it. Its raw materials mainly include three categories:

Mineral raw materials: They are the main components of porcelain glazes and account for a large proportion. They mainly include quartz (the main component is silicon dioxide -SiO₂), feldspar (silicates of alkali metals or alkaline earth metals, commonly potassium feldspar -K₂O·Al₂O₃·6SiO₂), clay (hydrated aluminum-silicon salt minerals, mainly Al₂O₃·6SiO₂ and crystalline water), etc.

Chemical raw materials It is an auxiliary component of the porcelain glaze. It mainly includes borax (Na₂B₄O₇·10H₂O), sodium nitrate (NaNO₃), soda ash (Na₂CO₃), lithium carbonate (Li₂CO₃), calcium carbonate (CaCO₃), magnesium oxide (MgO), zinc oxide (ZnO), titanium dioxide (TiO₂), antimony oxide (Sb₂O₃), zirconium dioxide (ZrO₂), and oxide Cobalt (CoO), nickel oxide (NiO), manganese dioxide (MnO₂), iron oxide (Fe₂O₃), etc.

Pigment raw materials: They are used to decorate the color of porcelain glazes and are divided into various colors such as black, blue, brown, gray, green, pink, white, and yellow.

Preparation process

The preparation process of enamel coating mainly includes the following steps:

Glaze preparation: After mixing mineral raw materials, chemical raw materials and pigment raw materials in a certain proportion, they are first melted into glass liquid and then quenched into broken pieces or thin sheets, which are called glass fuses. Then, the glass frit is added to the ball mill, followed by the addition of ball milling additives such as bentonite, clay, electrolyte and coloring oxide. Finally, water is added. After thorough ball milling, the glaze slurry is obtained.

Surface pretreatment: Clean, degrease, rust removal and other treatments are carried out on the surface of the metal blank to ensure it is clean and smooth, so as to enhance the adhesion between the coating and the substrate.

Coating: The coating methods of glaze slurry include manual coating, gas spray coating, automatic immersion coating or spray coating, electrophoretic coating, wet or dry powder electrostatic spray coating, and many others. For a specific type of workpiece, the coating method should be reasonably selected based on the quantity of the products, quality requirements, raw material sources, production efficiency and economic costs, etc.

Firing: Enamel firing is carried out in fuel oil, natural gas, propane or electric heating furnaces. Furnaces come in continuous, intermittent and periodic types, among which muffle furnaces or semi-muffle furnaces are more commonly used. Firing involves the flow of viscous liquids, solidification, and the escape of gases during the formation of coatings. Appropriate temperatures and times should be selected for different products.

The combination of the coating and the substrate

To ensure the firm bond between the coating and the substrate and enhance the protective effect of the coating, the following measures need to be taken:

Select the appropriate base material: The main metal materials used for enamel include steel, cast iron, aluminum, copper and stainless steel, etc. Different base materials have different chemical compositions, internal microstructure structures, surface conditions and mechanical properties, which play an important role in the quality of enamel.

Adding bonding agents: Adding some excellent bonding agents, such as cobalt oxide, nickel oxide, copper oxide, etc., to the composition of the porcelain glaze is conducive to the combination of the porcelain glaze and the metal.

Control the firing process: The firing temperature and time have a significant impact on the adhesion between the coating and the substrate. It is necessary to strictly control the firing process parameters to ensure that sufficient physical and chemical reactions occur between the coating and the substrate, forming a firm bond.