Cracking – in whatever stage of production – is a major loss issue faced within all types of clay manufacturing and the reduction/elimination is paramount for increased profitability and yields.
In today’s heavy clay market there is becoming a push for more product in faster lead times. This need is putting extra pressure on manufacturers especially to increase throughput times. Although kilns and sometimes driers can be the bottleneck, there is added pressure on the moulding equipment to produce clay products quicker.
Before bricks and tiles can be fired the majority of water used in its moulding needs to be removed from the clay product. Any excess residual water or moisture left in the article as it enters the kiln to be fired will be removed very quickly leading to major problems such as blow out, warpage or in the extreme – as has been seen on numerous occasions – to explode causing serious damage to the kiln and production.
The first process required to begin the production of clay bricks or roof tiles is to make available the raw materials required for the process. The major material used in manufacture are clays and as such brickworks will have been built as close to a clay quarry as possible although some clays are still trucked in to aid in varying colours and technical characteristics.
All brick and tile manufacturers strive for the elusive 100% yields, but in reality, the norm is anywhere from circa 50% upwards depending upon raw materials, products being produced and processes. These losses have been seen to occur in the extruding/moulding of the clay products, during the drying and firing processes and throughout all handling stages of production.
Various amounts of water are added within brick and tile manufacturing depending upon which process route you choose. A stiff extrusion may have water content as low as 10% while a soft mud factory may be as high as 30%. With hand made and water-struck products, this water addition value may even go higher. However, although these levels of water may be advantageous for manufacturing, they still require to be driven out during the drying process to enable the products to be fired.
Although the EU have downgraded Barium Carbonate from "Poisonous" to "Harmful If Swallowed", it is still treated as a toxic material in various countries across the world. However, its position as the most useful additive for the elimination of salt scumming from clay bricks and tiles is unchanged. For those countries where barium is prohibited, or due to increases in price and reduced availability, manufacturers look for alternatives.
In modern brick production, massive investments in infrastructure and machinery dictate the way we make bricks and roof tiles, i.e it will take a lot of effort (not to mention a lot of money) to rearrange a production line or buy new equipment. Still, optimizing production is always a subject of attention. Given a fixed production line, a technical manager soon runs out of options when trying to produce more bricks or tiles. However, leaning on modern chemistry, it is possible to increase the extrusion rate significantly.