you’re going to build a day tank, I strongly recommend the AZS liner. If you order a liner, the designation that accommodates soda/lime glass would be CS-3. Within the named designation are a series of different types and mixtures of fused cast products with specific applications. Ask the sales person for other AZS block designations that might fit your needs.
Using fused cast refractories as a furnace liner has many advantages. They last longer than all the other types of liners, do not break down under high heat, are not attacked as readily by corrosive glasses, can be heavily insulated, and can be purchased in monolithic shapes, thus avoiding “seams” or joints. Glass block seams are more readily attacked by molten glass.
Look in a one-year-old day tank constructed from alumina block, and you will see corroded seams. As stated earlier, the only downside to AZS refractories is their high initial cost and their sensitivity to thermal shock. You can’t change the cost, but you can guard against thermal shock.
If you wish to receive further information or order, you can e-mail Bud Davis at bud.davis@us.vesuvius. com or Stephen Graham at steve.graham@US.vesuvius. com. One last note: there is usually a delay of 10 to 12 weeks for delivery when placing an order.
In the furnace building section you can find an AZS designed furnace (pg. 147) that might help you in construction. My design is not the beginning and end all of day tank design and construction but is one that has worked for me in the past. As of this writing, Fred Metz has a great web site depicting the construction of an AZS day tank (www.spiralarts.com).
The Poor Man's AZS
Other companies manufacture a type of fused cast block that are less prone to thermal shock. These products are not solid AZS block but are manufactured by grinding fused cast material into a course “gravel” and pressing it into a block. They are also expensive and to my knowledge are not superior or equal to straight AZS. As I said, they do not thermal shock as readily as straight AZS. The AZS composite block is called “Vision” and the other is called “Vista.” To get information on where to purchase these products as well as information sheets in .pdf format, go to ANH Refractories Company (www.hwr.com). Their Website is filled with information.
Castables
Castable refractory materials come in many forms, and each product serves a specific purpose. All castables fall into one of three categories: light-duty, medium-duty, and heavy-duty. It should be noted that within each duty range there are levels of insulating value. Some castables have higher insulating value than others. As the castable density increases, insulating
remember, the hotter you get your furnace the shorter the life span of your block if it’s alumina. This is not such an issue for AZS. So why use alumina block as a glass liner? The only reason is that they are relatively inexpensive and fairly easy to build with.
AZS Block
AZS stands for Alumina Zirconia Silicate. These blocks are also referred to as “fused cast refractories.” AZS is the ultimate in tank liners. If treated properly they will last many years under the harsh conditions of glass melting. The caveat is “if treated properly,” but more about that later.
A great deal has happened to the companies that manufactured AZS block in the last few years. At one time it was possible to purchase this block from two mainline manufacturers, Carborundum and Corhart. Over the last few years both of these companies have been absorbed by other companies. Corhart has been absorbed by St. Gobain/Sefpro, and Carborundum is now part of the Cookson Group/Vesuvius. It is difficult to obtain block from St. Gobain, but as of this writing one can purchase block from Vesuvius/Monofrax.
AZS block is produced by melting pure alumina, zirconia, and silica in a giant, water-cooled electric arc crucible and pouring the mixture into graphite molds. The AZS block is then annealed for weeks. The resulting block has the highest density of any existing glass tank liner block. Don’t try to pick up one of these blocks if you have a bad back. When I say these beauties are dense, I mean dense.
After they are annealed, they are diamond cut to size and then the sides diamond ground to ensure a perfect fit for construction. The high refractory nature of the materials, plus the density of the block, make them ideal for direct glass contact. Since the cost of manufacture is high, the retail price is also high; however, AZS block will last longer than any other type of glass liner you will use and are very cost effective in the long run. AZS works best at elevated temperatures. The downside to AZS is that it is very prone to thermal shock. They need to be maintained at temperatures above 1800° F (982° C). If they fall below that temperature, they have a strong tendency to crack. One must take that into account when charging, as cold cullet or batch can drop the temperature quite suddenly and possibly crack the line. Small charges can help mitigate thermal problems. Regardless of how carefully you maintain the proper temperature, your AZS liner will eventually crack.
When lighting up, it is imperative that you raise the temperature very—and I mean very—slowly to above 1800° F. It is not unheard of to take at least one week to bring them up to operating temperature. I’ve constructed four AZS furnaces and have never had anyone of those furnaces last less than 7 years. If
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