Fast firing

High-speed burners, for which a preliminary pressure of about 70 mbar is necessary, are used in high-speed kilns for the glost firing of porcelain. The cycle time for this firing process is 3 hours. The burners are installed in the side walls, only above the goods; the firing material is located underneath on a carriage plateau. Such fast firing kilns have a useful width of 0.7 m to 0.8 m and a useful height of 0.35 m, adapted to the maximum pot height.

Fast firing furnaces are equipped with indirect cooling, combustion air preheating and atmosphere control with zirconia probes. These measures, in combination with a light car insulation and a modern process control system, make such plants suitable for the current requirements in terms of energy efficiency.

The cleaning zone

Approximately 1/3 of the temperature rise of a fast firing kiln takes up the so-called cleaning zone. The heating process up to temperatures of 950°C to 1150°C takes place in a strongly oxidizing firing atmosphere with approx. 8% oxygen content. This ensures that organic components are burned out of the body, glaze and embedded carbon particles. In this area, the glaze must not yet be closed, i.e. no melting phase must have formed, so that the aforementioned degassing processes can take place unhindered. This also includes deacidification processes of possibly introduced carbonates.

The reduction zone

Directly after the cleaning zone, the reduction zone begins, which is just below the maximum temperature of the fast firing kiln. In this zone there is a lack of oxygen with an average CO content of 2% and, depending on the fuel used, a corresponding H 2 content (approx. 3%), the iron content (approx. 0.4% -0.8%) in the kaolin and binding clay of Fe 2 O 3 in FeO is reduced, resulting in a bluish-white coloration of the porcelain. If oxidizing firing were used in this area, the porcelain would fog up with bubbles and spots.

The hard firing zone

After the reduction zone, the porcelain is transferred to a slightly oxidizing firing zone in the maximum temperature zone.

This section is still "under construction"