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Many kiln designs were submitted by UK and European kiln manufacturers, and a variety of refractory linings were considered. The plant decided on three new batch kilns of the following types and sizes:
- A 12-cubic-meter two-car batch kiln
- A 4.5-cubic-meter fixed-hearth swing-door kiln
- A 1-cubic-meter elevator kiln
These kilns are used to fire an extensive range of alumina, mullite, magnesia and zirconia composition refractory components, including crucibles, tubes, saggars, and a variety of special shapes. All three kilns are gas-fired, with the two large kilns exhausted through the loading deck. These fast-fire units operate with 60 to 85 cycles per year and have soak temperatures in the range of 2550 to 2900°F.
In selecting the kiln linings, major consideration was given to energy efficiency (TC UK wanted a low-mass kiln to reduce heat-up energy and cold-to-cold cycle times), low maintenance costs (especially the ability to withstand the stresses of quicker cooling), kiln temperature uniformity over the firing cycle to help minimize rejects from the firing process, and a lightweight lining to simplify the structure of the kiln metal work and thus help minimize the equipment cost.
The Bubble Alumina SolutionDense brick linings, similar to those used in the old kilns at TC UK, were rejected for many reasons, including their poor energy efficiency and high weight. Lightweight fiber systems capable of handling the 2912°F kiln cycles were next examined, but they are limited to high alumina fiber products, which provide little upper temperature limit safety margin and were perceived to be very expensive.
A mullite-bonded bubble alumina brick* (77% Al2O3) was eventually chosen for the hot face kiln linings. The brick has a 3250°F maximum service use limit, which gave an exceptional safety margin and the possibility of using the kilns to higher temperatures in the future. This medium-
density brick, which is designed to provide excellent high temperature strength and good thermal shock resistance, features insulation thermal conductivity and heat storage values less than half those of conventional dense alumina firebrick.
*Insalcor® brick, supplied by Thermal Ceramics.
More than 21,000 straight, arch and tongue-and-groove bubble alumina bricks were used in the construction of the three kiln hot face linings and flues. The bricks are tied back to the structure with high alumina anchor bricks** and stainless steel anchors. The lining construction was simple, lightweight and factory space efficient. This has allowed the 12-cubic-meter batch kiln to be integrated into the department layout. The low-mass bubble alumina brick was also used on the kiln cars, which enabled the company to use a common car handling system for the adjacent lower temperature fiber- and brick-lined kilns.
**Cerox®, supplied by Thermal Ceramics.
Maintenance and Energy SavingsThe three high-temperature batch kilns lined with the bubble alumina brick have been operating successfully for three years with more than 200 cycles each on average. No significant maintenance has been undertaken on the bubble alumina brick linings in any of the fast-fire kilns, and all of the wall and roof linings are still in excellent condition. The bubble alumina brick has performed better than the dense brick construction of the previous kilns, which usually required extensive rebuilding of the structure every two years. A lower temperature conventional brick kiln of similar construction installed at the same time has recently required brickwork repair of damaged wall and door sections.
For more information about bubble alumina firebrick, contact Thermal Ceramics, P.O. Box 923, Dept. 167, Augusta, GA; (706) 796-4200;