Clay Processing Technology

Clay processing begins with the stockpiling of the mined raw clay. Due to the location of the clay mine, open-pit mining operations can only be carried out during dry, precipitation-free weather conditions. It is therefore necessary to ensure that the annual raw clay requirement is extracted and stockpiled during dry periods.

The clay stockpile represents the first technological step in the processing phase, where the mined yellow and grey clay layers are mixed and stored together. Three different technologies are used in clay production.

Clay processing by the wet method

The raw clay stored in the clay stockpile is transported by front-end loader to the beginning of the production line. Using a mini excavator, it is fed onto a conveyor belt.

The conveyor belt discharges the lumpy raw clay into the hopper of a crusher, which reduces it to approximately 10 mm particles to facilitate easier slurrying.

From the crusher, the clay falls into a dissolving mixer, where it is dispersed in water under high-speed mixing. The production of clay slurry is necessary to enable purification by screening.

The clay slurry, with a consistency similar to sour cream, is fed onto a 250-micron vibrating screen, which separates particles larger than 250 microns from the purified clay filtrate. The separated coarse fraction contains unwanted materials such as oversized sand, pebbles formed in marine sediments, shells, and plant residues. The fine fraction is used for further processing. This fine fraction contains the clay minerals as well as the quartz sand required for tempering.

The screened clay slurry is then transferred into a holding mixer, where slow agitation ensures the slurry remains homogeneous and prevents quartz sand particles from settling. The conditioned slurry is pumped by a mass pump at 10 bar pressure into filter presses. During this process, excess water is removed from the slurry through filter cloths. The operation continues until clay cakes of the required firmness are formed inside the filter press. The presses are then opened, and the cakes are removed. At this stage, sufficiently solid, purified clay free from contaminants has been produced.

The next stage is vacuum pugging of the clay cakes. For this purpose, a double-auger pug mill equipped with a vacuum chamber is used. The cakes are placed into the hopper, where two feed rollers draw them into the upper auger section, which forces the clay through a diaphragm. The diaphragm divides the clay into 5 mm strips, which fall into the vacuum chamber. Here, air particles trapped in the clay are removed, eliminating air pockets. The clay strips then fall onto the lower auger rotating at the bottom of the chamber, which further homogenizes and compacts the material. The die at the end of the auger determines the cross-section of the extruded clay. The extruded clay is cut to size and packaged in bags. The packaged 15 kg clay blocks are then assembled onto pallets.

Clay processing using a ball mill

Using a ball mill, ceramic bodies of the desired composition can be produced. This method is used to manufacture our various chamotte-containing (grog) bodies. The ball mill is a horizontally rotating cylindrical drum lined internally with hard porcelain bricks. Hardened porcelain grinding media are used for the milling process.

Through the charging opening of the ball mill, the water and raw materials specified by the formulation are accurately weighed and added. The mill is rotated until the measured raw materials are properly dispersed, form a homogeneous system, and reach the required particle size. In this way, a liquid slip of the desired composition is produced, suitable either for casting ceramic objects or for further processing into a plastic body.

The slip discharged from the ball mill is passed through a vibrating screen of the required mesh size and then further processed.

For the production of a plastic body, the filtered slip is transferred to a holding mixer, where slow agitation ensures its homogeneity.

Using a mass pump, the slip is pumped into a filter press at a pressure of 10 bar, where excess water is removed and filter cakes of suitable strength are formed.

The cakes are then placed into a vacuum pug mill, where an air-free, homogeneous, and compacted plastic body is produced. Bars with a cross-section corresponding to the applied die are formed and cut to the required length. The bars are packaged in bags and assembled onto pallets.

Body production by the dry method

For body production, raw materials with the specified particle size and the amount of water required to achieve plasticity are used.

The raw materials and water, according to the formulation, are fed manually or mechanically into the hopper of the mixer.

The mixer consists of a horizontal trough equipped with two counter-rotating shafts fitted with mixing blades. During operation, the rotating shafts mix and convey the measured materials longitudinally along the trough. By the time the material reaches the end of the trough, it becomes sufficiently homogeneous and plastic.

At the end of the trough, rotating cutting knives mounted on the shaft ends provide additional homogenization and simultaneously remove the body from the trough.

The discharged mass falls into the hopper of the vacuum pug mill located below. A feed roller guides the material into the upper auger. After passing through a diaphragm, clay strips enter the vacuum chamber, where entrapped air is removed. The lower auger then compacts the mass by forcing it through a narrowing barrel section.

Bars with a cross-section corresponding to the applied die are produced and cut manually to size. This method is used for manufacturing the white plastic body.