Controlling the spray drying of ceramics
15 Jan 2000
Working in partnership with the Spanish Ceramics Institute, Infrared Engineering has developed a new technique for on-line measurement of moisture in ceramic powders used for tile manufacture, in the range 3-7% moisture content.
The challenge was to develop a filter set and algorithm which would deliver a stable moisture measurement in the face of the large variations in particle size, clay colour and depth of product on the conveyor which are common both within and between batches, and also significant variations in ambient temperature, humidity and light. The measurement is used to provide direct, stable control of the spray dryer.
Moisture content is critical in tile manufacture. If the ceramic powder is too wet, tiles will not have the required strength, or may not form at all. If it is too dry, the tiles will crumble. Moisture content also affects the bulk density of the clay and therefore the size of the final product as well as the glaze. In the past, crude laboratory methods for measuring moisture could only provide historical checks, leaving the possibility that large batch volumes of ceramic powder would have to be reworked at significant expense to the manufacturer.
The new on-line NIR measurement technique is the first to offer the industry a method of reliable, automatic control of the spray drying process.
The optical filter set and measurement algorithm were selected, then refined and optimised using extensive laboratory and site experiments. Reference measurements outside the NIR absorption bands of moisture and clay are used to cancel out the effects of ambient conditions such as relative humidity, temperature or changing light conditions.
The result is a robust, repeatable measurement which is now used routinely by tile manufacturers throughout Spain.
