The long-held goal of eliminating water from the glazing process is now a lot closer to being a realistic proposition for manufacturers in several important new sectors. For some time now, Thuringia Netzsch, Cerdec (dmc2) and Gema St Gallen have been undertaking some intensive work related to the process of electrostatic (dry) glazing and decoration of both ceramic and glassware.
A prototype unit was completed in time for Ceramitec, on which different ceramic and glass articles can be coated electrostatically with glaze or decoration powders. The intention at the exhibition was to familiarise customers with this system; a pilot plant is set up in Thuringia Netzsch’s laboratory in Selb so that follow-up visits can be organised.
Electrostatic technology in this part of the process has a range of interesting applications in the industry:
• Glazing of porcelain, bone china and vitreous china.
• Decoration of glazed ceramic pieces with coloured glaze.
• Glazing of roof tiles.
• Application of functional surfaces on technical ceramics.
On the prototype, the variable cycle speed of the table and infinitely adjustable spindle speed allow the optimum adaptation of the system to requirements in respect of quality and quantity. The glaze is pulverised in a tank; the resultant powder is sucked away through injectors, transported via hoses and then blown out through a gun.
Charging is effected according to the corona principle around the electrode in the mouthpiece of the gun. The glaze powder sticks to the earthed ceramic or glass surface. Overspray is collected and recycled to the fresh powder. The total glaze loss is put at <3%. As the glaze powder can be immediately used after it is supplied to the system, a rapid change of glazes during production is made possible.
Several important advantages of this technique are emphasised by the company:
• A positive contribution to environmental protection due to it being a water and solvent free process with no disposal problems and one leading to a reduction in specific energy consumption.
• Reduction in glaze losses due to the recycling of overspray.
• Elimination of the soaking and drying problems caused by water.
• Good reproducibility of ware coating quality.
• Just-in-time (JIT) production due to the storage of ready to process glaze powder.