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By 1991, the U.K. economy had slowed drastically. Demand for bricks dropped. Plants that had only recently increased production capacities now struggled to keep the plants at optimum running speeds. Due to this over-capacity and the reluctance to slow production, producers were forced to lower their selling prices. Between 1989 and 1997, average prices dropped by more than 20%—from 190 pounds (~$307) per thousand brick to just over 140 pounds (~$226) per thousand (see Figure 2). As a result, some of the more marginal plants were forced to sell or close.
The Search for a SolutionThe U.K. housing market is now recovering, but it is difficult to raise brick prices even to past levels. This, combined with the prospect of increased demand for bricks, has led producers to consider radical alternatives to their conventional brick production methods, which rely on large brick packs with an extremely high thermal mass fired slowly in large kiln installations. These big installations are very expensive and are also inflexible with regard to cycling on and off or making adjustments.
In the search for solutions, many producers have begun looking at the way other ceramic manufacturers handle, dry and fire their products. Within the past decade, kiln suppliers have begun reducing the thermal mass on a kiln car by making kilns wider and lower in profile. These new kilns have spread rapidly through the whitewares industry over the last few years, and constant improvements have been made to their operation. Computer-controlled combustion systems have led to improved temperature uniformity, which in turn has led to better yields and more uniform products—even from much faster cycles. The lower setting heights have also allowed drying to take place on the same setting plate as firing, thus removing the need to reset the product for firing. This, in turn, has made plant automation much simpler.
Within the heavy clay industry, improvements have already been made in clay preparation facilities for refining material consistency and properties, and allowing firing soaks to be optimized and reduced. Color stains and their applications have also been improved steadily. As a result, the reliance on long, complicated firing conditions to create specific colors and effects is no longer necessary. Flexible computerized control equipment enables simpler conditions such as flashing to be readily and consistently achieved. This flexibility allows manufacturers to reduce lead times and thus hold significantly reduced finished stocks.
Fast Firing OperationTo test the feasibility of using fast firing systems in the brick industry, a “virtual” plant was designed around a fast firing system* (see sidebar: Fast Firing Plant Design). Robots are programmed to pick up green bricks and place them in the desired configuration on the empty batts (see top and bottom illustrations). During the day shift, these full batts pass directly to the dryer and into both layers of the storage system. When the production shift has finished, the dryer and kiln are fed from the storage system. At the same time the fired product leaving the kiln is stored in the system.
After passing down one length of the dryer, across a transfer and back down the second length of the two-stage dryer, the batts are automatically loaded onto the kiln cars. Loaded cars pass through the kiln in a 6 to 10 hour firing cycle. This rapid firing cycle is only achieved because of the reduced thermal mass of the mini packs and excellent temperature uniformity within the kiln. The kiln firing conditions are constantly monitored and controlled by “state-of-the-art” computer and control systems.
Fired bricks are automatically removed from the kiln cars and conveyed to the robot unloaders. The empty kiln cars are returned quickly to their loading position. This fast kiln car return system reduces the overall number of kiln cars required and allows some of the residual heat to be retained.
The robot unloaders feed the selection and packaging department from both the kiln and the stock of bricks accumulated during the night shift. The fired bricks are directed into the double deck storage system during the night shift. The system fills with fired bricks at the same rate as the green bricks are pulled from stock.
Improved Quality, Optimized PerformanceThe fast firing brick plant was designed to achieve low total manufacturing costs by improving quality and optimizing performance. This design has provided proven benefits in tableware, sanitaryware and advanced ceramics plants. The advanced computer control system leads to flexibility and improved temperature uniformity. Companies using fast firing systems can more easily change their capabilities to react to market demands. Other benefits include reduced labor, energy and land costs; reduced firing cycles; and a reduction in customer lead times and brick stocks.
New plants aren’t the only facilities that can benefit from this technology—the fast firing design can easily be integrated into existing brick plants and used with a company’s current clay preparation, extrusion and packaging equipment. The system operates in conjunction with simple robot loaders and unloaders well within the plant’s accepted limitations. The carrier batt system allows wide variations of setting and product to ensure consistent product quality, and computer monitoring and control allow operator-free running and significant reduction in maintenance.
Firing in the FutureManufacturers in similar industries are already feeling the benefits of these production process improvements, and comparable systems are in production in the U.S. and elsewhere in the world. This technology holds a great deal of potential for the brick industry, and may prove to be the key to boosting production efficiency in the U.K. and in the brick industry worldwide.
For More InformationFor more information about fast firing systems, contact Adam Slater at Drayton Kilns Ltd., (44) 1782 657361, fax (44) 1782 658946, e-mail firstname.lastname@example.org.
SIDEBARFast Firing Plant Design
Overall System Advantages