This article examines the flat-glass manufacturing process and explores several decorating methods that you can use to crack into this large market.
By Wim Zoomer
Handheld, automatic, high-pressure pneumatic systems are available for spray coating. An even movement of the spray system across the horizontally positioned substrate ensures a thin and even deposit. An advantage of spray coating is that it also covers uneven glass surfaces. Furthermore, the technique easily allows more than one color to be applied. Covering the edges before spraying is an effective way of preventing waste and spoiling the outermost areas of the panel. The spray-coating technique results in a wet coating thickness of 20-250 microns.
During curtain coating, a continuous coating liquid flows out of a slit and falls on the horizontally moving flat-glass substrate. The glass substrate is moved by a conveyor. A gutter collects the excess coating material, which is returned to the container for re-use. Curtain coating commonly achieves a wet coating deposit of up to 350 microns. The drawback of curtain coating is the necessity to clean the edges of the substrate after the coating has been applied.
A single roller, or a number of rollers, can be used to apply the coating to flat glass. A conveyor belt transports the glass through the machine. An impression roller, or a transport roller, supports the glass substrate at the bottom and propels the glass substrate through the machine. The coating material between the rubber-covered coating roller and the doctor roller is transferred onto the glass. The thickness of the coating on the substrate is determined by the size of the nip between the doctor roller and the coating roller.
The coating roller allows rotation in the same direction of the moving glass substrate, a process known as direct roller coating. If the coating roller rotates against the direction of the moving glass, the method is then called reverse roller coating. The doctor roller is provided with a squeegee to measure out the quantity of the coating liquid. During reverse coating, the coating roller is oriented slightly off-contact to the substrate. Reverse coating usually results in evenly distributed and smooth depositions.
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