SEVEN STAGES TO THE END-PRODUCT
The path from clay to the finished paving clinker covers seven stages: we provide a detailed insight:
1. Mining the raw materials
At KERAWIL, various clays from our own pits in the area and clays from the Westerwald area are processed for the "caramel" colour. The clays are mined close to the surface with excavators and wheel loaders. At this early stage, attention is given to the ecological aspects, so that the pits can later be re-cultivated as a biotope, for example. The clay is then transported on trucks to the in-plant clay storage facility, where it is kept until needed.
The red-firing clay from the regional pits and the caramel-firing clay from the Westerwald are initially placed in intermediate storage in the KERAWIL clay storage facility. From here, they are then transferred by wheel loader into the charging boxes, which can be imagined as a kind of giant hopper. The function of the charging boxes is to dose the different materials in a certain ratio, so that the right mix is obtained.
3. Forming / Pressing
Heat and moisture are now added to the prepared material to increase its malleability. In the vacuum chamber, the clay mass has the air extracted from it to compact it. An endless screw further compacts the material, and the clay column is pressed under high pressure through the die relief.
The die relief and the discharge slats give the desired external shape to the parcels of clay. The clay column is cut in the clot cutter in clots of around one and a half metres; then the clots are cut again with a precision down to a few millimetres, using a fine wire cutter, to produce the blanks in the required thickness - at a rate of up to 10,000 parts per hour. The blanks are then set on laths and prepared for drying. The number of blanks per lath depends on the thickness of the blank.
4. Drying unit
The moist blanks are driven into the drying chambers on the laths, where the air is heated (mainly using the waste heat from the tunnel kiln). The humidity needed for forming and pressing is now removed from the blanks.
It takes around three to four days before the blanks are completely dried, and thus ready for further processing.
The dried blanks are removed from the drying chambers and taken to the fully-automated stacker. Stacked in an arrangement which varies with the different forms, the blanks are placed in several layers on the tunnel kiln carts.
The stacked kiln carts then pass through the heat retention channel and are driven to the start of the tunnel kiln.
6. Tunnel kiln
The tunnel kiln is the very heart of production at KERAWIL. It is roughly 100 metres long, and is operated from the metering and control station. The kiln is heated exclusively with natural gas.
The journey of the paving clinkers through the kiln takes around 3-4 days. The kiln is always filled throughout its entire length with kiln carts. The KERAWIL tunnel kiln operates continuously: 24 hours a day, 365 days a year.
The paving clinkers are slowly heated by means of a pre-heater and the pilot firing unit to over 1,000 degrees Celsius. At this temperature, sintering (a ceramic process) occurs. This contributes significantly to the hardness of KERAWIL paving clinkers. At such high temperatures, the feed natural gas combusts spontaneously.
After firing, the paving clinkers are cooled down in a controlled process. When they leave the kiln, the bricks are already only hand-warm. The waste heat from the kiln is used to dry out the blanks. Finally, the kiln carts travel to the unloading point.
7. Unloading / Packaging
During unloading, the paving clinkers are subjected to a quality control, so that KERAWIL bricks not only meet the requirements of DIN 18503 and DIN EN 1344, but far exceed them.
Lastly, the bricks are placed on pallets, loaded and transported to their destination.