3210 Furnace Fans

Continuous fiber-reinforced ceramic composites can also be made into complex shapes. An example is fan blades. The thermal stability and other properties of CFCCs make them attractive for high-temperature fans such as those used in heat-treating furnaces.

Metals and other materials are heat treated in furnaces to assure uniform and desired properties. This requires uniform heating produced by locating circulation fans to eliminate thermal "dead spots" in the furnace. Historically, these fans were made of superalloy steel. Performance has been limited due to the limited thermal stability of the steel as well as fatigue and creep, which lead to imbalance and failure. Fan imbalance requires lower fan speed, excessive maintenance, downtime, limited furnace loads, and increased operating costs. To preserve metal fans, furnace atmosphere is cooled before the fan and reheated upon exit, adding to the complexity and cost of the furnace.

The use of CFCC fans enables an increase of furnace temperature to 1200°C (2200°F) from the previous <1040°C (<1900°F). The creep resistance of CFCCs permits fan speeds above 1100 rpm, increasing circulation, resulting in faster heat-up rates, reduced load turnaround time, and uniform heat-treated product at a higher yield. CFCC fans reduce fuel consumption by 3%. In addition, CFCC fans are much lighter. They require only one person to install them (Fig. 3.14).

FIGURE 3.14 CFCC furnace fans reduce weight, requiring only one-man installation and consuming less operating energy.

COI Ceramics Corporation, San Diego, California, provides fans to furnace manufacturer Surface Combustion Corporation to place in its heat-treating furnaces. After 6 months use, the CFCC retains 75% of its original strength. Tests indicate that CFCC fans have twice the life of metal ones.

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