Cover coat

Functional carrier of the external properties of the enamel coat with regard to chemical, mechanical, thermal, visual and decorative aspects. Compared to ground coats, cover coats have a lower coefficient of thermal expansion, surface tension and viscosity (otherwise mixing). The dilatometric softening point must be approx. 20 K lower than that of ground coats.

Direct-on enamels

The use of specific recipes allows ground coats to be manufactured chemically resistant. In this case, they are called direct-on enamels. Direct-on enamels must ensure adherence and, at the same time, exterior properties and meet both functional and decorative requirements.

Enamel

According to RAL 529 A (1940), enamel is a mass that is produced by melting or fritting; an inorganic and essentially oxidic composition fused onto metallic components in one or more layers, partly with additives.

Enamel frits

Depending on the quenching process of the smelt, granules or flake-shape substances (so-called flakes) are produced when quenched with water or during the roller cooling. Granules and flakes are called enamel frits.

Enamelling (process)

Enamelling is the manufacturing process of coating an object with enamel.

Enamelling (product)

A vitreous, inorganic coating applied, fused and bonded to the substrate.

Enamel slip

Enamel slips are produced from ready-to-use suspensions using wet milling of enamel frits and additives such as quartz, clay, zirconium silicate, electrolytes and colour oxides. Their rheological behaviour adapts to the application process. Powders for electrostatic application or for application to hot cast parts are manufactured using dry milling of enamel frits.

Engobes

Engobes are clay slip coatings applied to roof tiles. They are mixed with minerals or metal oxides to achieve colour effects. Engobes are open to diffusion after firing and their capillary structure is similar to that of the ceramic body. They impart a matt to satin finish to surfaces and allow all opaque colours.

ESTA (electrostatic wet spraying)

During electrostatic wet spraying, slip droplets are transported in the electric field and capillary forces allow them to adhere to the substrate. The Corona effect causes the electric charge; the applied voltage or pressure range lies between 60 and 120 kV or 0.17 and 0.25 MPa. Unlike PUESTA and ETE, ESTA allows multi-layer applications using intermediate firings. The ESTA method can be highly automated and is economic and environmentally friendly because it enables the recovery of enamel that is sprayed past the workpiece.

ETE (electrophoretic enamel application)

The ETE method is an electrophoretic enamel application. Electrically charged and suspended enamel particles move under the influence of an applied electric field. Unlike electrolyses, considerably larger solid particles (not ions) are moved. The enamel particles are negatively charged in the surrounding water molecules. In addition to electrophoretic and electrolytic processes, electro-osmosis occurs in ETE coating which has two positive effects: dewatering and mechanical hardening of the applied coat and, at the same time, constant density of the enamel suspension caused by water accumulation at the cathode. The ETA application can be used with 1 coat or 2 coat / 1 fire processes.

Glazes

Glazes consist mainly of frits, clay and setting agents. A dense, glassy coating is fired onto the surface of the ceramic body, allowing high-gloss to matt surfaces and all transparent and opaque colours.

Ground coat

Provides adherence of the enamel coat applied to the metal surface (adherence oxides) and absorbs gases that develop from the metal during fire-on processes (pore structure).

PUESTA (electrostatic dry powder enamel application)

Electrostatic powder application with specially prepared enamel powders offers significant advantages when manufacturing large batches. An electrostatic charge of 60 to 90 kV is applied between the spray guns and the grounded workpiece. The enamel particles move preferably along the electric lines of force of the workpiece. Electrostatic interactions cause the powder to adhere to the substrate during the production processes.

Pyrolysis

Chemical reaction also known as degassing. Pyrolysis is the thermal decomposition of carbon-containing compounds or waste in the absence of oxygen at temperatures of approx. 500°C (low-temperature pyrolysis) or 700 to 900°C (high-temperature pyrolysis), e.g. self-cleaning of an oven.

RTU & RTM

RTU
Ready-to-use

RTM
Ready-to-mill

Wet milling

The grinding of enamel frits (flakes or granules) in a ball mill with mill additions such as clay, quartz, setting agents, colour oxides or substances that affect the subsequent dry film forms the enamel slip in accordance with a preset recipe (mill formula).