Compositions: ceramic – Ceramic compositions – Refractory
Reexamination Certificate
1999-06-07
2002-10-01
Marcheschi, Michael (Department: 1755)
Compositions: ceramic
Ceramic compositions
Refractory
C501S096400, C501S096100, C501S097100, C501S097200, C501S097300, C501S098400, C501S092000, C501S098500, C501S102000, C501S106000, C501S107000, C501S108000, C501S109000, C501S119000, C501S120000, C501S122000, C501S118000, C501S123000, C501S124000, C501S125000, C501S127000, C501S128000, C501S129000, C501S130000, C501S126000, C501S096300, C501S098100, C501S111000, C501S087000, C501S088000, C501S089000, C264S030000, C264S031000
Reexamination Certificate
active
06458732
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a dry refractory (i.e., a monolithic refractory installed in dry powder form without the addition of water or liquid chemical binders), particularly a lightweight dry refractory with superior thermal insulation qualities.
Refractories are used as working linings of metal processing and transfer vessels to contain molten metal and slag and the associated heat and gases. These linings typically are consumable materials that are eroded or otherwise damaged by exposure to the conditions within the vessel. When a certain amount of consumption of or damage to the lining has occurred, metal processing must be halted—sometimes for an extended time—in order to repair or replace the refractory lining. The frequency of these interruptions is determined by the rate at which the process consumes the lining. The duration of these interruptions is dependent on the consumption rate and whether it is possible to repair localized damage to the lining without removing the undamaged portions and replacing the entire lining.
Refractories also are used as secondary or backup linings of vessel working linings. Although these secondary linings are not exposed to molten metals or slags under ideal operating conditions, they must be capable of containing molten metals and slags that penetrate the working lining as a result of erosion, crack formation, or other damage.
Refractories also are used to insulate vessels and other structures used in metal processing and other operations carried out at elevated temperatures. These refractories generally are selected for their heat containment capabilities rather than their resistance to molten metals and slags.
Factors important in refractory selection include the operating conditions of the application, speed and ease of installation and repair, insulating value, and cost. The operating conditions include the predicted chemical and thermal environment to which the refractory will be exposed. For molten metal containment applications, the chemical and thermal environment may be affected by (1) the boundary conditions relating to the dimensions of the shell and the desired capacity of the molten metal pool, (2) the identity and physical properties of the metal, and (3) the expected operating environment of the vessel, including its rated capacity and the presence of features such as oxygen injection, plasma torches, and water or air cooling devices.
Refractories typically are available in the form of bricks, blocks, refractory plastics, ramming masses, refractory castables and dry refractories. Installation and repair of brick and block linings are likely to be costly and slow. Bricks and blocks also must be assembled to avoid gaps at the joints, a time-consuming task requiring skilled craftsmen. Even when the bricks and blocks are carefully fitted together, gaps remain which may allow molten metals and slags to penetrate the lining. Refractory bricks and blocks may have a short life (high consumption rate) and may require removal and replacement of the entire lining when only a portion of the lining is eroded or damaged. This increases the cost of repair and greatly increases downtime.
Conventional refractory plastics and ramming mixes also may have a high consumption rate and may require removal and replacement of the entire lining when only a portion of the lining is eroded or damaged. Castable refractories potentially have a longer life (lower consumption rate) and lower operating and maintenance costs when compared to the prior lining materials. These materials offer the potential for longer life and easier, faster, less expensive installation and maintenance when compared to lining materials typically applied. For example, damaged portions of a castable lining generally can be repaired without removal and replacement of the entire lining.
Installation of a castable refractory lining requires onsite mixing with the attendant mixing equipment, water source, skilled labor and supervision costs, and risk of mixing errors. The quality of the castable lining depends, among other things, on the casting water added, the mixing and vibration techniques used, and the skill of the installers. Transporting the mixed wet castables to the job site may be time consuming, awkward and inconvenient. Installation may require forming, which increases installation time and cost. Dryout of a castable lining at elevated temperatures is needed to remove the added moisture before the lining can be cured and placed into service. Heating of the castable refractory during dryout also increases energy costs.
Conventional refractories and castable refractories are prone to crack formation. Some cracks that form can extend completely through the lining from the hot face (molten metal side) to the cold face (steel shell side). When cracks of this nature occur, the possibility of molten metal and/or slag penetrating via these cracks to an outer shell of the vessel exists. When this occurs, the molten materials can burn through the shell, which may result in extensive damage to equipment and/or injury to personnel. A burn-through of this type can cause long, unscheduled delays in the operation to make repairs to the lining, steel shell and structure, and any surrounding equipment.
Dry refractories are unbonded monolithic materials that are capable of forming strong ceramic bonds at a controlled rate in predetermined temperature ranges and do not contain water or liquid chemical binders. They typically are installed by vibrating, compacting or otherwise de-airing the free-flowing material without addition of water or liquid chemical binders. Dry refractories are easy to install and repair because no mixing is required. Installation of dry refractories is faster and less expensive than installation of castable refractories. In addition to the absence of a mixing step, vessel downtime is reduced because dryout of the lining is not required before a new or repaired lining is placed into service.
The chemical and mineralogical composition of dry refractories can be chosen to be resistant to the specific types and temperatures of metals and slags inherent to a metal containment process. In particular, the refractory can be designed to form strong ceramic bonds in predetermined temperature ranges and at controlled rates of formation. Progressive bond formation, which is influenced by time, temperature, and atmosphere, occurs in response to operating conditions in the immediate environment of the composition. Regions exposed to temperatures above the activation temperature of the bonding agent form strong ceramic bonds while regions exposed to lower temperatures form fewer and weaker bonds.
When ceramic bonding of properly selected dry refractories occurs in this manner, the bonded portion of the material becomes dense and hard and is chemically and physically resistant to penetration of both molten metal and slag. Any portion of the dry refractory that remains below the critical temperature for the formation of ceramic bonds remains as an unbonded monolithic material that does not exhibit brittle behavior or cracking tendencies. The presence of a region of unbonded refractory under normal operating conditions provides improved absorption of mechanical stresses, which may extend the operating life of the vessel lining. Progressively bonding dry refractories have excellent resistance to crack propagation because they can form a barrier to any molten metal and slag that penetrates through the bonded region of the refractory and into the unbonded or fluid region.
For example, a dry refractory may be selected so that regions adjacent to the heat source (e.g., a hot face of a process vessel or an intrusion of molten metal and slag into the refractory lining) form strong ceramic bonds and regions furthest from the heat source remain in an unbonded fluid state until the temperature exceeds the critical temperature, with partial bonding in the intermediate regions. The rigid bonded refractory is chemically and physically resistant to penetration of b
Doza Douglas K.
Liu John Y.
Allied Mineral Products, Inc.
Marcheschi Michael
Porter Wright Morris & Arthur LLP
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