Periodic kilns

Sihca brick and large fireclay shapes are fired in circular downdraft kilns. These kilns vary in diameter and can accommodate up to 150,000 23-cm bricks or their equivalent in other si2es. The complete burning cycle for a typical periodic kiln ranges from 21 to 27 days as compared with four to seven days for a tunnel kiln. 

Air Drying Equipment. Tunnel kiln dryers (70) are long furnaces comprised of several zones of different temperature, humidity, and air flow through which the ware travels on a moving car or belt. These kilns afford continuous processing. Periodic kiln cross-circulation dryers (70) are box furnaces in which ware is stacked on permanent racks or on a car that can be shuttled in and out of the furnace. Fans or jets are used to circulate heat uniformly through the ware. The process is not continuous, but production rates can be enhanced by shuttling multiple cars. 

Conventional Sintering Equipment. Like drying furnaces, sintering furnaces (29,76,85) can be periodic or continuous in nature. Periodic kilns offer greater flexibiHty continuous tunnel kilns are more economical. Advanced ceramics are typically siatered in high purity, controUed atmosphere furnaces by electric resistance heating. Ceramic furnaces used to fire traditional ceramic ware are generally heated with inexpensive natural gas, oil, wood, or coal. 

Silica bricks are manufactured from crushed ganister rock containing about 97 to 98 percent silica. A bond consisting of 2 percent lime is used, and the bricks are fired in periodic kilns at temperatures of 1,500 to 1,540°C (2,700 to 2,800°F) for several days until a stable volume is obtained. They are especially valuable when good strength is required at high temperatures. Superduty silica bricks are finding some use in the steel industry. They have a lowered alumina content and often a lowered porosity. 

As a fuel-saving and more productive design, the continuous multi-chamber kiln was developed it comprised a series of periodic kilns (chambers) joined side by side and fired in succession. This allowed the exhaust gases from the chamber being fired to be drawn through the adjacent chambers, thus preheating the charge. The combustion... 

Various types of kilns evolved during the history of ceramic production fired brick walls were constructed for field kilns in contrast to periodic kilns, serving only for a limited production campaign round or tunnel kilns provide different features concerning the duration of the firing cycle or the temperature uniformity. A kiln with an oxygen-deficient atmosphere produces harder ceramics (and a different colour) than a kiln with an oxidising atmosphere. 

Batch-type furnaces and kilns, termed in-and-out furnaces or periodic kilns (figs. 1.1 and 1.2), have one temperature setpoint, but via three zones of control—to maintain uniform temperature throughout, because of a need for more heat at a door or the ends. They may be loaded manually or by a manipulator or a robot. 

Hydrite Process. In this process bricks are fired at 775°C in the presence of water. Gas fuel is burnt in steel tubes on the sides of periodic kilns, in which low quality clays may be fired more rapidly without fluorine emission. 

Periodic Kiln. See intermittent kiln. Peripheral Speed. The rate of movement of a point on the edge of a rotating disk or cylinder it is the product of the circumference and the rate of revolution. The peripheral speed is of importance, for example, in the operation of abrasive wheels and ball mills. 

Sweep-fire System. In this system for bring stoneware pipes in periodic kilns, burners are arranged in opjxised pairs, and the power to opposite burners is varied rhythmically. The system was developed by Paul Schneider Co, and licensed to Bickley Co., in USA and W.Germany (see Z/. Int. 40, (12) 629 1987). 

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