INFRARED HEATING METHOD AND APPARATUS FOR CURING REFRACTORIES

Abstract: A method and a device for curing a refractory material are provided. The device includes a mandrel having an opening therein defined by interior surfaces thereof, wherein the mandrel is dimensioned to fit within a vessel and define a gap therebetween corresponding in thickness to a predetermined thickness of a vessel refractory lining. An infrared heater is disposed within the mandrel opening and is oriented to irradiate an interior surface of the mandrel. The method for curing refractory material includes inputting a refractory material into a gap between a mandrel and a tundish, radiating infrared heat energy from a plurality of infrared heating elements toward interior surfaces of the mandrel to heat the mandrel, curing the refractory material within the gap using heat transferred to the refractory material through the mandrel to form a refractory material lining for the tundish.

Description: INFRARED HEATING METHOD AND APPARATUS FOR CURING REFRACTORIES BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates generally to a heating system for use with curing refractory materials and more specifically to an infrared heating system for use with curing refractory materials. DESCRIPTION OF RELATED ART A tundish is a large intermediate holding vessel for molten metal used in casting processes, such as in the continuous casting of steel. The tundish is, in effect, an intermediate process reservoir which receives a large quantity of molten metal from conveying ladles exiting a furnace in which actual melting ofthe ore occurs, and which then transfers the molten metal to a casting mold. A system of inlet and outlet nozzles typically controls the flow of molten metal into and out ofthe tundish. The tundish itself is generally a steel vessel which is lined with several layers of a refractory composition. A permanent lining, generally of refractory brick, serves as an inner lining to protect the vessel. The permanent lining is, in turn, coated with a disposable wear lining, generally of a refractory composition which is applied to the permanent lining by gunning, spraying, trowelling, or dry vibration. Alternatively, the disposable lining can be constructed of a plurality of performed refractory boards designed to fit the specific tundish being lined. Such preformed refractory boards are fitted together and their adjoining edges or joints are carefully sealed to avoid penetration ofthe molten metal between the lining and the metal casing ofthe tundish. The disposable lining is in direct contact with the molten metal in the tundish and protects the permanent lining from exposure to the molten metal, acting as a thermal and chemical barrier against the molten metal. After one or more heats of molten steel are put through the tundish, the disposable liner must be replaced. Refractory materials generally include materials, typically powdered, characterized by a high melting temperature, often in excess of about 1000°C. Refractory materials typically include, but are not limited to, silicon carbide, titanium carbide, boron carbide, silicon nitride, titanium nitride, alumina, alumina silicates, graphite, zorconia, yttria, quartz (silica), mullite, or mixtures thereof. Conventional refractory materials used as a disposable lining material also typically have a high magnesia (MgO) content. Since refractories consisting solely of magnesia-based coatings have a unfavorably high thermal expansion coefficient, which may lead to bulging ofthe disposable lining away from the underlying permanent lining due to differences in rates and degrees of expansion, various additives are added, such as plasticizers and binders, to the refractory composition. Plasticizers increase the refractory's ability to adhere to a surface to which it is applied, while a binder increases the composition's lateral strength characteristics and ability to withstand forces acting perpendicularly against it. Other additives include, but are not limited to, homogenizers, wetting agents, wetting/foaming agents, modifying agents, stiffening agents, volume stabilizers, retarding agents, and secondary binders may also be added in a manner known to those skilled in the art to achieve desired application, curing, or operational characteristics. In general, there are two categories of compositions used as disposable tundish refractory material. The first category includes those refractories which require the addition of a liquid phase, most commonly water, in order to allow the composition to be applied as a tundish lining. Compositions that require a liquid phase are generally applied by trowelling, gunning, or spraying. The spray system involves the spraying ofthe refractory materials typically including a particulate refractory filler material, a sodium silicate binder, a small proportion of fibrous material, sintering aids, a small proportion of a wetting agent and up to about 25% water, over the permanent lining ofthe tundish The second category of refractory materials are applied in a dry phase, often requiring vibration of a mold in order to compact the material upon the surface ofthe permanent liner. The dry vibration system involves the use of a similar particulate refractory filler material with a resin binder and a small proportion of a sintering aid, such as sodium silicate. A former, mold, or mandrel is placed inside the tundish to define a cavity between the mandrel and the tundish walls. The mandrel generally corresponds to the contour ofthe inner dimensions ofthe tundish and, more precisely, define a cavity between the mandrel and the tundish that corresponds to the form ofthe desired expendable lining. The cavity is then filled with the dry lining composition and the mandrel is vibrated to ensure adequate filling ofthe cavity. Heating the mandrel and tundish then sinters the lining composition leaving it adhered to the walls ofthe tundish upon removal ofthe mandrel. This method allows for the even application of a desired thickness of monolithic refractory (dry vibratable) in large or complex vessels. Alternatively, there are dry phase methods which do not requiring a former or mandrel, which involve preheating the vessel from about 1200°F to about 2000T, whereupon the vessel is completely filled with the dry refractory formulation. The refractory is allowed to cure in the vessel for up to about 5 minutes, after which the unclaimed refractory is reclaimed for reuse and the cured layer formed a substantially uniform disposable lining. This method allows the control of application thickness by time allowed for curing and is useful for lining small or uncomplicated vessels. In particular, dry vibratable type refractory compositions applied to a surface utilizing vibration for uniform distribution and compaction typically include various thermally activated binders, inclusive of both organic and/or inorganic binders or mixtures thereof, although inorganic binders are generally preferred. A wide variety of refractory aggregates or refractory filler materials may be utilized including, for example, doloma, calcined dolomite, olivine, silica, alumina (calcined bauxite or corundum, chromite, chamotte, zircon, aluminosilicate, calcia, or other oxides or silicates. Binders are used to hold the refractory compositions together during use. A reactive binder, such as an acid salt, is preferably used, as it can react with the filler or alternately, if a substantially inert filler is used, reactive materials such as MgO or CaO can be added to react with the filler. Multiple binders can also be used, wherein low temperature binders (e.g., phenolic resins) are used to hold an applied composition together, as installed, before activation of high temperature binders, which typically comprise, for example, metal powders, alloys or mixtures, including aluminum, silicon, alloys or mixtures of aluminum and silicon, or alloys of aluminum and magnesium. Traditional dry vibratable bond systems include a low temperature bonding agent, usually an organic resin, and a high temperature bonding agent, usually a silicate. Dry vibratable tundish lining materials have recently found favor in a number of North American steel mills owing to the advantages arising therefrom including longer casting sequences, increased safety lining life, higher quality steel, better thermal efficiency, faster tundish turnaround, improved deskulling rates, constant tundish volume, reduced energy requirements, and lower tap temperatures. Conventional methods for curing refractory materials utilize an inefficient gas dryer, an example of which is depicted in simplified Figure 1A. The hot air blower/gas dryer 10 heats incoming air and forces the heated air through insulated hot air piping 20 into a mandrel 30 cavity (plenum) 40. Alternatively, the hot air blower/gas dryer 10 may be disposed immediately adjacent the mandrel 30 or may be incorporated into or disposed on the cover ofthe mandrel 30. Heat is transferred from the air to the plenum prior and ultimately through the mandrel 30 and into the refractory material 50 lining the tundish 60 prior to exhausting ofthe exhaust gas, as shown in simplified Figure IB. The mandrel 30 exhaust port 70 typically comprises a tubular baffle 80, a thermocouple 90, and a damper 100. The thermocouple 90 is positioned to measure the gas temperature at a point inside the exhaust port 70 adjacent the damper 100 and provides temperature information to the burner controls 110, which regulate the temperature ofthe gas dryer 10. The baffle 80 prevents the hot air from short circuiting directly to the exhaust port 70 by retarding the passage ofthe gas through the mandrel cavity 40. The damper 100 also helps hold back the heated air, giving the gas time to transfer heat into the mandrel 30 shell defining the plenum 40, wherein it is then transferred into the refractory material 50. However, the above method and apparatus is relatively slow and inefficient. The hot air blower 10 runs continuously even when the gas is throttled back, bringing cooler air into the plenum 40 reducing the temperature ofthe gas therein. Also, since the thermocouple 90 is provided at the exhaust port 70 to ensure the exhaust end temperature is maintained at an appropriate curing temperature, the incoming air is maintained at an even higher temperature than the outlet, causing uneven heating and hot spots in the plenum 40. Moreover, the gas method requires significant time to fully cure a working lining and can produce an unevenly cured product wherein some areas have lower cold strengths due to the hot spots. The dry vibratable tundish lining material method possesses various drawbacks, as well. Manual labor is often required to direct a spout to fill an engineered gap between the mandrel and the tundish back-up lining, often taking about 20 to 30 minutes per lining. The filling process also typically requires the tundish area crane to be called upon to hold the hopper or spout bag, thus delaying other operations in the tundish area that require the crane. The may become a severe problem if a number of linings are to be made. Further, once the gap between the mandrel and the tundish is filled, the mandrel must be heated with a gas heater to set the refractory before use. This process generates dust, fumes, and heat in the tundish area and is very time-consuming, generally taking more than two hours. Thus, there is a need for a system for curing refractory materials evenly and efficiently. Particularly, there is a need for a shorter curing time, greater energy efficiency, a more evenly distributed product cold strength, a shorted cooling time, reduced maintenance on exterior mandrel surfaces, reduced mandrel warpage, decreased crane usage and moves, and decreased utilization of shop space, such as for a heater cover. SUMMARY OF THE INVENTION The present invention overcomes the above problems and meets the needs noted above as discussed herein. In one aspect, the invention provides a device for curing a refractory material comprising a mandrel having an opening therein defined by interior surfaces thereof, wherein the mandrel is dimensioned to fit within a vessel and define a gap therebetween corresponding in thickness to a predetermined thickness of a vessel refractory lining. An infrared heater is disposed within the mandrel opening and is oriented to irradiate an interior surface ofthe mandrel. In one aspect thereof, the infrared heater is a stamped foil electric medium wavelength infrared heater. In another aspect, the invention provides a method for curing refractory material comprising the steps of inputting a refractory material into a gap between a first surface and second surface, radiating infrared heat energy from an infrared heater toward the first surface to heat the first surface, and curing the refractory material within the gap using heat transferred to the refractory material through the first surface to form a refractory material lining for the second surface. In still another aspect, the invention provides a method for curing refractory material comprising the steps of inputting a refractory material into a gap between a mandrel and a tundish, radiating infrared heat energy from a plurality of infrared heating elements toward interior surfaces ofthe mandel to heat the mandel, curing the refractory material within the gap using heat transferred to the refractory material through the mandel to form a refractory material lining for the tundish. The foregoing and other features, aspects and advantages ofthe present invention will become more apparent from the following detailed description ofthe present invention when taken in conjunction with the accompanying drawings. Additional aspects of he present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment ofthe present invention is shown and described, simply by way of illustration ofthe best mode contemplated for carrying out the present invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive. BRIEF DESCRIPTION OF THE DRAWINGS The various merits and advantages ofthe present invention will become more clearly appreciated as a description ofthe preferred embodiments and structures associated therewith, are given with reference to the appended drawings wherein: Figs. 1A and IB are illustrations of conventional gas heating methods for refractory tundish linings. Fig. 2 depicts a computer control system usable in accord with the invention. Figs. 3A-3C depict a top view, front view, and side view of one aspect ofthe invention. Figs. 4A and 4C provide a simplified cross-sectional view a mandrel in accord with the invention in relation to a tundish during and following curing, respectively. Fig. 4B provides a simplified isometric view of a mandrel in accord with the invention. Figs. 5A-5C depict various wiring configurations for infrared heater assemblies in accord with an aspect ofthe invention. Fig. 6 illustrates the comparative advantages ofthe electric infrared mandrel heating system in accord with the present invention against conventional gas heating systems. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a method and an apparatus for infrared curing of refractory material(s). In one aspect ofthe invention, the device includes a mandrel dimensioned to fit within a vessel having an interior volume of a predetermined shape and to define a gap therebetween corresponding in thickness to a predeteπnined thickness of a refractory lining. The device also includes a plurality of infrared heaters disposed within the mandrel, the infrared heaters being oriented so that infrared energy radiated therefrom is radiated outwardly toward interior surfaces ofthe mandrel. Energy transfer utilizing conventional gas heat is a function ofthe temperature difference between the materials to the first power. In other words, Q = h x A x dl, wherein Q is the heat transfer rate, h is the heat transfer coefficient that is a function ofthe flow direction and velocity, A is the area being heated, and dT is the temperature difference between the body to be heated and the air flowing past it. In contrast, energy transfer utilizing infrared radiation is a function ofthe temperature difference between the materials to the fourth power. In other words, Q = εσ( - T SUR ) wherein Q is the heat transfer rate, ε is the emissivity ofthe emitter, σ is the Stefan-Boltzmann constant {σ = 5.67x10 "8 W/m 2 • K 4 ), Ts is the absolute temperature (K) ofthe emitter, and T S U R is the temperature ofthe surroundings or a mandrel in the instant case. Additionally, with convection heating, heat must be transferred twice, first from the heat source to the gas and then from the gas to the object to be heated (e.g., a mandrel). Further, with a gas heater, heated air is expelled from the exhaust port ofthe mandrel and only a small percentage ofthe available energy is retained within the system to heat the mandrel. In view of these and other factors, the present invention advantageously utilizes infrared radiation to improve the speed and efficiency of mandrel heating and of refractory lining curing. It is generally preferred to utilize a computer or processor-based control system to implement the method and control the apparatus for infrared curing of refractory material(s) in accord with the invention, although a computer or processor-based control system is not vital to the invention and the method and apparatus ofthe invention may be practiced independently of any such control system. Figure 2 depicts one suitable control system that may be used in accord with the method and apparatus ofthe invention. Such a control system may comprise a video display 210, printer 220, central processing unit (CPU) 230, interfacing electronics 240, electronics cooling modules 250, if necessary, and a keyboard or other data entry means 260. CPU 230 includes a bus 232 or other communication mechanism for communicating information, and one or more processors such as one or more Intel Pentium™ IV processors coupled with bus 232 for processing information. CPU 230 also includes a main memory 236, such as a random access memory (RAM) or other dynamic storage device, coupled to bus 232 for storing information and instructions to be executed by the processor(s). Main memory 236 may also be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor(s). CPU 230 includes a read only memory (ROM) 238 or other static storage device coupled to bus 232 for storing static information and instructions for the processor(s). A storage device 270, such as a magnetic or optical disk, is coupled to bus 232 for storing and providing information and instructions. CPU 230 may be coupled via bus 232 to monitor 210 for displaying information to a computer user. Input device or data entry means 260, including alphanumeric and other keys or a microphone to enable voice activated functions, is coupled to bus 232 for communicating information and command selections to the processor(s). Other types of user input devices may include cursor control, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to the processor(s) and for controlling cursor movement on display 210. Transmission media for data to and from processor(s) and associated devices, including bus 232 may comprise coaxial cables, metal wire or metal layers and fiber optics. Transmission media can also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. CPU 230 also includes a communication interface 280 coupled to bus 232 to provide two-way data communication coupling to a link, such as a network link 282, by sending and receiving electrical, electromagnetic or optical signals that carry digital data streams representing various types of information to an attached network or LAN 290. It will be appreciated that various forms of output devices may be operatively connected to the CPU 230 through the transmission media to be controlled thereby, including but not limited to control of a positioning/lifting crane movement or control ofthe infrared heaters. The computer or CPU 230 may advantageously be used to control the tundish lining curing in accord with the invention. In accord therewith, control ofthe curing may be provided by computer 230 in response to execution by the processor of one or more sequences of instructions contained in main memory 236. Such instructions may be read into main memory 236 from a computer-readable medium, such as storage device 270. Execution ofthe sequences of instructions contained in main memory 236 causes the processor to perform the process steps described herein. In alternative embodiments, hard- wired circuitry may be used in place of or in combination with software instructions and it is to be understood that no specific combination of hardware circuitry and software are required. The instructions may be provided in any number of forms such as source code, assembly code, object code, machine language, compressed or encrypted versions ofthe foregoing, and any and all equivalents thereof. "Computer-readable medium" refers to any medium that participates in providing instructions to the computer 230 for execution and "program product" refers to such a computer-readable medium bearing a computer- executable program. The computer usable medium may be referred to as "bearing" the instructions, which encompass all ways in which instructions are associated with a computer usable medium. Computer-readable mediums include, but are not limited to, non- volatile media, volatile media, and transmission media. Non- volatile media include, for example, optical or magnetic disks, such as storage device 270. Volatile media include dynamic memory, such as main memory 236. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus 232. Transmission media can also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read. With the aid of an appropriately configured or programmed computer controlled curing system, such as illustrated in Figure 2, the control ofthe refractory curing may quickly adapt to changes in process parameters and may even be configured or programmed to control the curing process in accord with any one of a plurality of input refractory material types. The properties of refractory material compositions or recipes are known to vary significantly and attempts are made to identify or engineer recipes for specific applications in consideration of various factors such as but certainly not limited to operational temperature ranges, chemical activity, required preheat stages if preheat is desired prior to exposure to molten metal, and application efficacy. If a plurality of refractory materials are used at once or at different times, the computer may be programmed or reprogrammed, as needed, with separate control parameters to permit automatic control of a plurality of different refractory materials to reduce a burden on the plant staff and to improve efficiency. An infrared heating apparatus configuration in accord with the invention is depicted in Figures 3A-3C, wherein a mandrel 300 corresponding to a specific tundish or vessel is lined with infrared heaters 350 which are engineered for a specific refractory material and a specific tundish lining geometry. As previously noted, the mandrel 300 is configured for placement inside a particular tundish 310 or vessel to define a cavity 320 therebetween into which refractory material 395 is disposed, as shown in Figure 4A. A suitable refractory material may include any refractory material or combinations of materials commonly known to those skilled in the art and conventionally sold as complete recipes or mixtures known under various tradenames known to those skilled in the art. Such refractory recipes are provided, for example, in U.S. Patent No. 5,300,144, issued to Adams; U.S. Patent No. 5,366,944, issued to Rumpeltin, et al.; or U.S. Patent No. 5,602,063, issued to Dody, et al., each reference hereby being incorporated by reference. This cavity 320 corresponds to the form ofthe desired expendable refractory lining. In other words, the size and shape ofthe mandrel 300 and the arrangement and selection of infrared heating elements 350 corresponds to variables including the shape ofthe desired refractory lining, the mix or composition ofthe refractory materials 395, and the interior geometry ofthe tundish 310. Thus, Figures 3A-3C depict merely one example of a mandrel 300 in accord with the invention and are not intended to be limiting in any respect. In a broader sense, the infrared heating apparatus and method ofthe present invention may comprise, for example, a cylindrically arranged infrared heating apparatus configured for insertion within a substantially cylindrical steel vessel or ladle to cure a working or protective lining therein. In the mandrel heating system configuration depicted in Figures 3A-3C, which is merely one example ofthe many forms that the invention may assume, the mandrel 300 upper end possesses a length of 144 7/8", a depth of 29 9/16", and a height from the base of 29". The base or bottom 340 ofthe mandrel 300 has a length of about 111" and a depth of 15 Vz Conventionally, tundishes are trough-shaped and the inner walls 315 ofthe tundish 310 are not perpendicular to the inner base 325 ofthe tundish and, instead, are generally oriented at an some obtuse angle α greater than 90° with respect to the imier tundish base 325. Likewise, mandrel 300 is trough shaped and the side walls 335 ofthe mandrel are arranged at substantially the same obtuse angle α greater than 90° with respect to the mandrel base 345. Figures 4A-4B show a mandrel 300 with a cover 400 attached to a top portion ofthe mandrel in a manner known to those skilled in the art. Trunions 410 and lift rings 420 are provided to by which the cover may be individually lifted or the cover and mandrel, in an attached configuration, may be lifted. A vibrator 430 is provided on the cover to vibrate the mandrel and compact refractory materials 395 disposed in gap or cavity 320 between the mandrel 300 and the tundish 310, as shown in Figure 4B. As previously noted, infrared heaters 350 comprising individual infrared heating elements are provided on an interior of mandrel 300 and are oriented to face the interior surfaces 335 ofthe four walls and the bottom 345 ofthe mandrel. In other words, the infrared heaters 350 face outwardly toward inner surfaces 335, 345 ofthe mandrel 300 to heat these surfaces by irradiation, as generally depicted in Figures 3A-3C and 4A-4B. As shown in Figure 3C, the infrared heaters 350 may be disposed parallel to the mandrel 300 walls, such as the infrared heaters arranged toward the top of mandrel 300, or may be disposed at an angle to irradiate more than one surface (e.g., 334, 345) ofthe mandrel, such as the infrared heaters arranged toward the bottom ofthe mandrel. The heat is conducted through the mandrel walls, inclusive ofthe mandrel bottom, as shown in Figure 4 A, and imparted to the refractory materials 395 to heat and cure the refractory materials 395. Following completion ofthe curing process, which is principally determined by the refractory materials 395 employed, the mandrel 300 is removed from the completed tundish working lining 500, as depicted in Figure 4C. In the embodiment ofthe invention depicted in Figures 3A-3C, thirty-two electric infrared heaters are provided on an interior of mandrel 300. Eight 34"x8" infrared heaters, twelve 27 ^"xδ" infrared heaters, six 24"x8" infrared heaters, two 21"x8" infrared heaters, two 15 W'xS", and two 15 1 /2"x4" infrared heaters are provided, as illustrated. The infrared heaters 350 may be placed between about 1" to 24" from the inner surfaces 335 ofthe mandrel walls and bottom 345 ofthe mandrel. The nominal distance ofthe infrared heaters 350 from the inner surfaces 335 ofthe mandrel walls and bottom 345 is about 3" to 4". An interior ofthe mandrel 300 is fitted with a framework, chassis, or truss (not shown) which supports the infrared heaters 350. Upper ends ofthe framework may be fixedly attached to or embedded within an upper edge ofthe mandrel 300 side wall 335 and a lower end ofthe framework may be attached to a bottom 345 ofthe mandrel between adjacent infrared heaters 350. It is preferred that the framework does not extend above a top surface ofthe mandrel 300 so as not to interfere with the mating surfaces of the mandrel cover 400. It is naturally preferred to provide for expansion and contraction ofthe framework in accord with conventional techniques. To facilitate assembly and routine maintenance, each ofthe electric infrared heaters 350 includes a connection device including but not limited to studs, tabs, screws, or clamping devices, on a side or a back side thereof for mounting ofthe infrared heaters 350 on the mandrel 300 interior framework. The infrared heaters 350 are provided with a plurality of lead wires in flexible metal conduit routed through or around the framework and through the mandrel cover 400. The vibrator 430 may advantageously incorporate all ofthe necessary electrical connections to supply power to the electric infrared heaters 350 and to receive inputs from thermocouples or other sensors disposed within an interior of mandrel 300. The electric infrared heaters 350 depicted in Figures 3A-3C are grouped into three control zones: top 355, bottom 365, and end 375. However, any number of control zones are possible. Additional control zones more precisely isolate and control the heating of smaller portions ofthe mandrel and refractory materials adjacent outer surfaces thereof. This is particularly important in applications where the vessel or tundish geometry is non- uniform. Thus, four, five, six, eight, ten, or twenty or more zones may be advantageous in accord with the present invention. It is preferred that the infrared heaters 350 are medium wavelength electric infrared heaters and, more particularly, stamped foil medium wavelength electric infrared heaters or the equivalent thereof. The stamped foil medium wavelength electric infrared heaters 350 are fast response sinuated foil type heaters that heat up and cool down in about 5 seconds. Because there is no quartz or other material between the emitter and the product being heated, these heaters cost much less to operate than most other heaters in a similar application. Medium wavelength infrared heaters 350 advantageously heat the mandrel 300 uniformly, heat up and cool down very rapidly, can be repaired very easily in the field by plant personal at a low cost, and can be operated in any physical arrangement. Additionally, infrared heaters 350 can be customized to meet the specific shape ofthe mandrel 300 and the medium wavelength infrared heaters require less power to provide the required heat output than some other types of infrared heaters. Medium wavelength infrared heaters 350 produce radiation having wavelengths in the middle infrared range, between about 1.5 and 5.6 microns. Near infrared, comprising energy having wavelengths between about 0.72 microns and 1.5 microns and far infrared, comprising energy having wavelengths between about 5.6 to 1,000 microns, are not as ideally suited for the present application as the medium wavelength infrared energy, although infrared heaters in these wavelengths may also be used. Metal surfaces are typically poor absorbers of short- wavelength radiation, particularly highly reflective surfaces. For this reason, metal surfaces tend to be heated more efficiently by medium- wavelength and long- wavelength infrared radiation. However, the interior surfaces ofthe mandrel may be surface treated to decrease reflectivity and to increase absorption and/or emissivity, such as by oxidation or application of high-temperature resistant materials, such as special paints or finishes. Moreover, materials known to exhibit a high degree of absorptivity and emissivity for a particular range of wavelengths may be selected to permit use of near or far infrared radiation, provided these materials also comport with desired material and chemical characteristics at the expected process temperatures. As configured and as depicted in Figures 3A-3C, the infrared heaters 350 are powered by a connected power load that provides at least 114 kW to 115 kW when operating at 100% capacity (137 Amps @ 480 V, 3-phase supply). Temperature control of the three zones 355, 365, 375 is accomplished by varying the voltage with three 3-phase silicon-controlled rectifier (SCR) power controllers. In the illustrated aspect ofthe invention, a 30-amp, 60-amp, and a 100-amp 3-phase SCR power controller are used and are supplied by Radiant Energy Systems, Inc. of Wayne, New Jersey. Medium wavelength infrared heater 350 assemblies comprising a plurality of individual medium wavelength infrared heating elements (not shown) may utilize, but are not limited to, any ofthe wiring diagrams represented by Figures 5A-5C. Figure 5 A depicts a 240 V 1 -phase connection providing a heater wattage of 9.3 kW @ 240 V, a heater amperage of 39 A, and a Watt density of 63.6 W/in. Figure 5B depicts a 240 V 3- phase connection providing a heater wattage of 9.3 kW @ 240 V, a heater amperage of 22.4 A, and a Watt density of 63.6 W/in. Figure 5C depicts a 480 V 3-phase connection providing a heater wattage of 9.3 kW @ 240 V, a heater amperage of 12 A, and a Watt density of 63.6 W/in. For the 480 V configuration, it is preferred, although not necessary, to voltage limit the SCR to about 455-460 V. Additional SCR controllers, or other conventional controllers, may be used in accord with the number of zones and the energy requirements of each zone. For example, the two zones 365, 355 respectively corresponding to the 60-amp and 100-amp SCR power controllers could be further subdivided into five or six zones utilizing separate 30- amp SCR power controllers. The zones and infrared heaters, and even the individual heating elements may be individual controlled or may be ganged or wired together to energize and de-energize in unison. The zones, infrared heaters, and individual heating elements may be controlled solely in correspondence to selected set-points, or may adaptively be controlled by outputs of computer programs analyzing multiple process variables as inputs to adjust the heat output of one or more zones, heaters, of individual heating elements, in accord with the measured variables and programmed empirical relations between these variables and the desired outcome ofthe process. As depicted in Figures 3A-3C, one thermocouple 385 is provided for each zone 355, 365, 375. The thermocouples are disposed inside a quartz container or tube that is installed in the emitter refractory backing material of one electric infrared heater 350 per zone. Although the quartz introduces a lag time in the temperature measurement, the lag time has been observed to be relatively insignificant for the curing processes contemplated by the method and apparatus ofthe present invention. In effect, the lag time simply increases the amplitude ofthe temperature modulation about the desired set point. It is preferred that the SCR power controllers are controlled by a closed loop system wherein temperature signals are provided by one or more thermocouples disposed in each ofthe designated temperature zones to a CPU 230 which then provides appropriate control signals to the SCR power controllers to regulate the output thereof. For automatic control ofthe infrared heaters 350, the preferred closed loop control system includes a high temperature cut-off switch to prevent damage to any ofthe mandrel 300, infrared heating elements, instrumentation and wiring, refractory materials, or mechanical components or systems. Manual control means for the heating system may be include, for example, calibrated dials and variable potentiometers. The mandrel heating system configuration depicted in Figures 3A-3C and described above, is designed to, from ambient, raise the mandrel 300 temperature to 250°F - 300°F and hold the temperature within this range for approximately 10 minutes at which time the mandrel heating system then raises the mandrel temperature to 625°F - 675°F and holds the temperature within this range for up to about 60 minutes. Figure 6 illustrates the comparative advantages ofthe mandrel heating system configuration depicted in Figures 3A-3C and described above in relation to conventional gas heating/curing systems. Namely, Figure 6 compares temperature (°F) versus time (t) at the interface between steel mandrel 300 and a tundish lining material in the gap 320 between the mandrel and the tundish 310 for the infrared heating system ofthe invention and the conventional gas heating system. Following an initial 10-15 minute warm-up, the electric infrared heating system operates for only about 2 minutes at full power (i.e., about 137 Amps), after which time the power is reduced to about half power for 58 minutes. The electric infrared heaters 350 are then turned off at about t = 75 minutes when the temperature at the mandrel 300 and refractory material 395 interface is approximately 560°F, after which time the mandrel 300 cools and starts to contract and pull away from the cured refractory tundish 310 lining at about t = 90 minutes. The mandrel 300 may then be pulled from the tundish 310 at about t = 120 minutes. In contrast, the gas heating system must be operated until t = 150 minutes to attain the requisite temperature and curing and the mandrel may not be pulled until about t = 165 minutes. The temperature and duration of heating at the mandrel 300 and refractory material 395 interface will vary significantly in accord with the refractory material 395 composition, the thickness ofthe lining, and the configuration ofthe lining, and method of application ofthe refractory materials, to name but a few variables. Refractory materials may only require about 500°F to cure or may require 2000°F or far greater to cure. The curing duration may also vary significantly. The electric infrared heating system ofthe present invention is aptly suited for such variations in refractory material 395 and process variables. To account for such variation in demand, the infrared heating system ofthe invention would require, at a minimum, variation in the power (e.g., 30% or 90% power) output by the heating elements to achieve the desired temperatures or curing effect, or at most, a reconfiguration ofthe infrared heaters 350. Such a reconfiguration could include, for example, an increase in power output ofthe infrared heaters 350, a decrease in the distance between the infrared heaters and the mandrel im er surfaces 335, 345, an increase in the density ofthe individual infrared heating elements, or an increase in the insulation inside the mandrel. Additionally, the compactness ofthe heater design makes available alternative design configurations possible that are presently unattainable in conventional gas heated curing systems. Specifically, it is desirable to physically integrate the mass flow application hopper, mandrel 300, and infrared heaters 350 into a single unit to further reducing the number of required crane moves and to correspondingly increase shop efficiency. This configuration is not feasible when gas is used as a heat source due to the large amount of equipment, such as hot air ducting and control equipment, needed for the gas train and disposed about the mandrel cover. A method for curing refractory material in accord with the invention, in view ofthe above, generally comprises the steps of inputting a refractory material 395 into a gap 325 between a first surface and second surface, radiating infrared heat energy from an infrared heater 350 toward the first surface to heat the first surface, and curing the refractory material within the gap using heat transferred to the refractory material through the first surface to form a refractory material lining 500 for the second surface. It is preferred to also control at least one of a radiated infrared heat energy, a first surface temperature, a second surface temperature, and a refractory material 395 temperature. Following completion of curing, the method also includes the step of withdrawing the first surface from the cured refractory material lining 500. With respect to a mandrel 300, for example, the first surface may comprise an outer wall surface ofthe mandrel. Likewise, with respect to a tundish, the second surface may comprise an inner surface 315 thereof. In accord with the above, one aspect ofthe invention comprises the steps of raising the temperature ofthe first surface from ambient to a first temperature between about 250 to 300° F and maintaining the first surface temperature at the first temperature for approximately 10 minutes, followed by raising the first surface temperature to a second temperature between about 625 - 675° F and maintaining the first surface temperature at the second temperature for approximately 60 minutes. The method and apparatus ofthe present invention also realize a cost savings over conventional gas heat curing systems. In a gas unit, the system consumes 1 ,000 cubic feet/hr of natural gas to output 1,000,000 Btu/hr. At an average price of $2.75 US per 1,000 cubic feet of natural gas with approximately 140 minutes at full consumption or full burn, the cost of natural gas is about $7.00 US per refractory lining curing. Additionally, the electric blower motor, typically a 1 hp, 460 V, 3-phase motor operating at 3600 φm, consumes about $0.75 kW/hr. With a required operation time of about 200 minutes total, the 2.5 kW costs $0.13 cents US assuming a cost of $0.05/kW US for a combined cost of $7.13 US per tundish lining. The electric infrared heating system ofthe present invention, on the other hand, costs $3.10 US per tundish lining (2 minutes at full power at 137 Amps ($0.20 US) + 58 minutes at 50% power ($2.90 US)). This difference results in a net savings, based on energy consumption alone, of approximately $5,166 US per year for an estimated 1282 tundish linings per year. Thus, the present invention permits an extremely energy efficient (i.e., about 90% or more) and fast acting heating and curing system that is able to cure a refractory material more evenly than conventional gas heating applications and producing more consistent cured cold strength ofthe product in shorter curing times than conventional systems. The method and apparatus also yields other advantages including reduction in equipment size and corresponding increase in available storage space, elimination of some crane movements necessary in conventional curing techniques, and reduced generation of dust and fumes in the tundish area. Still further, unlike gas heat curing systems, virtually no heat or fumes are generated during operation ofthe electric infrared curing system and the surface condition ofthe installed linings is superior, having fewer cracks and increased strength. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope ofthe inventive concept, as expressed herein.

Claims: WHAT IS CLAIMED IS: 1. A device for curing a refractory material comprising: a mandrel having an opening therein defined by interior surfaces thereof, said mandrel being dimensioned to fit within a vessel and define a gap therebetween corresponding in thickness to a predetermined thickness of a vessel refractory lining; and an infrared heater disposed within the mandrel opening, said infrared heater being oriented to irradiate an interior surface ofthe mandrel. 2. A device for curing a refractory material according to claim 1, further comprising: a plurality of infrared heaters disposed within the mandrel opening, said infrared heaters being oriented to irradiate at least one interior surface ofthe mandrel. 3. A device for curing a refractory material according to claim 2, wherein said plurality of infrared heaters are distributed within the mandrel opening to define a plurality of temperature control zones, each of said temperature control zones including at least one thermocouple outputting temperature signals. 4. A device for curing a refractory material according to claim 4, wherein each thermocouple outputs temperature signals to a computer-based closed loop control system, and wherein each of said plurality of infrared heaters is linked to and controllable by the computer-based closed loop control system. 5. A device for curing a refractory material according to claim 4, wherein said mandrel is substantially trough-shaped. 6. A device for curing a refractory material according to claim 4, wherein said plurality of infrared heaters are medium wavelength electric infrared heaters. 7. A device for curing a refractory material according to claim 6, wherein said plurality of infrared heaters are stamped foil medium wavelength electric infrared heaters. 8. A device for curing a refractory material according to claim 7, wherein said plurality of infrared heaters are disposed between about 3" to 4" from said at least one interior surface ofthe mandrel. 9. A device for curing a refractory material according to claim 5, further comprising an insulating cover configured to seal the opening of the mandrel. 10. A device for curing a refractory material according to claim 2, wherein said at least one interior surface of said mandrel is finished to increase absorptivity of infrared radiation. 11. A method for curing refractory material comprising the steps of: inputting a refractory material into a gap between a first surface and second surface; radiating infrared heat energy from an infrared heater toward the first surface to heat the first surface; curing the refractory material within the gap using heat transferred to the refractory material through the first surface to form a refractory material lining for the second surface. 12. A method for curing refractory material according to claim 11, further comprising the step of: controlling at least one of a radiated infrared heat energy, a first surface temperature, a second surface temperature, and a refractory material temperature. 13. A method for curing refractory material according to claim 12, further comprising the step of: withdrawing the first surface from the cured refractory material lining. 14. A method for curing refractory material according to claim 12, further comprising the steps of: raising the temperature ofthe first surface from ambient to a first temperature between about 250 to 300° F; maintaining the first surface temperature at the first temperature for approximately 10 minutes; raising the first surface temperature to a second temperature between about 625 - 675° F; maintaining the first surface temperature at the second temperature for approximately 60 minutes. 15. A method for curing refractory material comprising the steps of: inputting a refractory material into a gap between a mandrel and a tundish; radiating infrared heat energy from a plurality of infrared heating elements toward interior surfaces ofthe mandel to heat the mandel; curing the refractory material within the gap using heat transferred to the refractory material through the mandel to form a refractory material lining for the tundish. 16. A method for curing refractory material according to claim 15, further comprising the step of: controlling at least one of a radiated infrared heat energy, a temperature ofthe mandrel, a temperature ofthe tundish, and a refractory material temperature. 17. A method for curing refractory material according to claim 16, further comprising the step of: withdrawing the mandrel from the cured refractory material lining. 18. A method for curing refractory material according to claim 17, further comprising the steps of: raising the temperature ofthe mandrel from ambient to a first temperature between about 250 to 300° F; maintaining the mandrel temperature at the first temperature for approximately 10 minutes; raising the mandrel temperature to a second temperature between about 625 - 675° F; maintaining the mandrel temperature at the second temperature for approximately 60 minutes.

Inventors: KOTYUK MARK D, KOTYUK, MARK, D.
Applicants: SPECIALTY MINERALS MICHIGAN, SPECIALTY MINERALS (MICHIGAN) INC.
Application year: 2001
Main classification: C04B35
IPC codes: B22D11, B22D41, C04B33, C04B35, F27D1, F27D3, F27D19, F27D23