Abstract:
A method and apparatus for accelerated cooling of a furnace such as a furnace containing a susceptor. Cooling gases are split whereby a first percentage are provided to cool the furnace while a second percentage are provided to assist in cooling the heated cooling gases after cooling the furnace, whereby the percentages are changed throughout the process. The system further provides for unique cooling flow arrangement in the furnace which promotes maximum heat transfer through swirling.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to furnaces and the cooling thereof. More particularly, this invention relates to an accelerated gas cooling system for a furnace or like heating system. Specifically, the invention is a method and apparatus for accelerated cooling of a heating system such as a susceptor heating system. 
     2. Background Information 
     It is well known that furnaces or other heating systems are used to heat materials and parts to very high temperatures for a variety of reasons such as heat treating, annealing, curing, baking on coatings, masking, tempering, purification, application of graphite, or hardening. Typically, materials or parts are placed in the furnace that is sealed from the atmosphere or under positive vacuum and thereafter heated to hundreds or thousands of degrees. Once the process is complete, the furnace must cool prior to opening and removing the treated materials and parts. This cooling process is often very time consuming and in many cases may takes hours, days or weeks. 
     Certain types of newer induction furnaces or susceptor systems provide gas cooling systems in various forms for use with induction systems including vacuum chambers and/or steel walled vessels. In these systems, the heat exchange medium is gas that is either re-circulated across an inner water cooled wall surface or forced outside the chamber through a heat exchanger. 
     However, many induction heated susceptor systems are designed without vacuum chambers and/or steel walled vessels. These systems are still in use and continue to be supplied as new and operate where they provide desirable processing of parts; however its users desire to reduce the time required for cool down to a temperature where the furnace may be disassembled or otherwise opened so that unloading and handling of the finished materials and parts may occur. As noted above, often this cooling time is hours or days, and in some cases may take a week or longer. An accelerated or more rapid cooling is desired but must be accomplished without opening the system to the atmospheric air as such opening prior to proper and complete cooling to the oxidation temperature or below may cause metallurgical, chemical or oxidation of the product or susceptor. 
     The alternatives of using a “once through” inert gas flow takes excessively long and results in significant capture costs where done properly to be environmentally safe. In most instances, venting of the inert gas is illegal so this is not an option. 
     It is thus very desirable to discover a method of accelerated cooling for use with the many induction heated susceptor systems that were designed without vacuum chambers and/or steel walled vessels. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a method and apparatus for accelerated cooling of a heating system such as a susceptor heating system. 
     Specifically, the invention includes a heat chamber, a cooling gas circulator fluidly connected to the heat chamber for providing a first portion of cooling gas thereto, a bypass whereby a second portion of the cooling gas bypasses the heat chamber and is merged back in with the first portion of the cooling gas that was provided to the heat chamber after the first portion has exited the heat chamber, and a heat exchanger for removing heat from the cooling gas after the first portion has exited the heat chamber and prior to re-circulating of the cooling gas into the cooling gas circulator. 
     The present invention is also a method for accelerated cooling of a furnace, the method including the steps of circulating a first portion of cooling gas to a heat chamber after heating of the heat chamber has been completed, bypassing a second portion of the cooling gas around the heat chamber, merging the first portion of the cooling gas that was provided to the heat chamber with the second portion of cooling gas that bypassed the heat chamber, and removing heat from the cooling gas after merging the first portion that has exited the heat chamber with the second portion that bypassed the heat chamber. 
    
    
     The foregoing advantages, construction and operation of the present invention will become more readily apparent from the following description and the accompanying drawings. 
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     Preferred embodiments of the invention, illustrative of the best modes in which the applicant has contemplated applying the principles, are set forth in the following description and are shown in the drawings and are particularly and distinctly pointed out and set forth in the appended claims. 
     FIG. 1 is a front elevational view of a first embodiment of a susceptor heating system that provides for accelerated cooling; 
     FIG. 2 is a sectional view of the susceptor portion of the heating system; 
     FIG. 3 is the same sectional view as FIG. 2 except FIG. 3 shows cooling gas flow through the susceptor; 
     FIG. 4 is a sectional view of the base plate of the susceptor taken along lines  4 — 4  in FIG. 2; 
     FIG. 5 is a detailed angular sectional view taken along line  5 — 5  in FIG. 4; 
     FIG. 6 is a sectional view of the inner chamber of the susceptor taken along line  6 — 6  in FIG. 3; 
     FIG. 7 is a detailed sectional view of the inner wall of the inner chamber of the susceptor taken from FIG. 2; and 
     FIG. 8 is a partial sectional view similar to FIG. 2 except that the susceptor lid is being removed. 
    
    
     Similar numerals refer to similar parts throughout the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention as is shown in FIG. 1 is an improved heating system  10 , and method of use thereof, for accelerated cooling of the system and chambers therein. The system  10  includes a heating body  12  with a susceptor body or carrier  14  selectively insertable therein for carrying items  200  to be heated, a cooling gas supply  16 , a gas circulator  18 , a particulate separator  20 , a heat exchanger  22 , and various fluid piping, connectors and valves as described in more detail below. 
     Heating body  12  as best shown in FIGS. 1-2 in one embodiment includes a generally cylindrical outer shell  30  with an open top end  32 , a cover  36  selectively covering the top end  32 , and a bottom end  38 , whereby the combination of which define a main chamber  40  having an inner surface and an outer surface. The shell  30 , cover  36  and end  38  are designed as is well known in the art. Shell  30  in the embodiment shown is a multiple wall design with an inner wall  42  defining the inner surface, an outer wall  44  defining the outer surface, and with an insulating chamber  46  therebetween whereby elongated ribs extend from the outer wall for structural support. Cover  36  is any cover capable of selectively sealing the top end while also being removable to allow for access to the chamber  40 , whereby the cover typically includes hooks or other mechanisms to assist in the lifting of the lid from the shell, and seals or other arrangements for sealing the cover onto the shell as is needed during heating. Various vents, pressure relief valves and/or other devices as are well known in the art are also often present. 
     The shell  30  and/or end  38  may includes an induction heating coil and insulating materials to thermally protect the coil from the hot susceptor where required. In the embodiment shown, the coil is positioned within space  46  that is positioned within the shell while the base  38  includes fluid passages  34  with insulation  35  therearound. 
     The cover  36  includes a lip around its perimeter which serves as a flame deflector. The cover also has a seal for sealing it to the shell; in the preferred embodiment, the cover and seal are designed such that extreme pressure is relieved by the cover lifting slightly, allowing pressure relief, and then re-seating in a sealed manner. 
     The susceptor body  14  is best shown in FIGS. 1-2 to include a main body  50  having an open top area  52  and an open bottom area  54 , a lid  56  for selectively closing the top area, and a bottom plate or bottom  58  for closing off the bottom area, whereby the combination of which defines a susceptor chamber  60  which in the preferred embodiment has a rough or serrated surface as best shown by FIG. 7 to provide for gas turbulence in the chamber. Within the susceptor body  14  is a diffuser plate  64  proximate the top area  52 , and a base plate  66  proximate the bottom end  54  where the base plate includes a plurality of feet  68 , where each of the diffuser and base plates extends completely across the susceptor chamber  60 . The diffuser plate  64  includes top face  72  and a bottom face  74 , and is generally arranged within the chamber  60  such that it is parallel with the lid  56 , the base plate  66  and the bottom plate  58 . The area between the diffuser plate  64  and the base plate  66  is the carrier chamber  65  where the items  200  to be heated are positioned. 
     The diffuser plate also includes a plurality of diffuser holes  76  as best shown in FIGS. 2-5 where in one embodiment each of these holes is angular from the top face  72  to the bottom face  74 , that is diagonal and not perpendicular to the top or bottom faces  72  and  74 , respectively. This diagonal pattern is best shown in the cross sectional view of FIG.  5 . In addition in a preferred embodiment, the plurality of diffuser holes  76  are arranged about a center hole  78  therein, the arrangement as best shown in FIG. 4 being of a multiple row design where each row is annular about the center hole  78 . The base plate  66  also includes a plurality of holes  80  whereby these holes may be perpendicular through the base plate  66 , or alternatively may be angular as described above on diffuser plate  64 . These holes are placed to best collect gases from chamber and direct them to exit therefrom. 
     In one design, the main body  50  is more than one piece as shown in FIG. 2 where it is three pieces, namely an upper wall section  50 A, a middle wall section  50 B and a lower wall section  50 C. Feet  82  support the main body  50  on the base  38 . 
     Also within the susceptor body  14  is a temperature tube  84  that extends from inside to outside of the susceptor body via temperature tube hole  78  in the diffuser plate.  64  and a second temperature tube hole  86  in the lid  56 , whereby in one embodiment the holes are axially aligned with a central axis in the generally cylindrical susceptor body  14 . This temperature sight tube bay be at an angle to the vertical. 
     The lid  56  further includes an offset aperture  88  in which an entrance deflector  90  and entrance tube  92  are seated. The entrance tube  92  provides cooling gas entry into the susceptor chamber  60  from the main chamber  40  which is fed the cooling gas via an entry valve, inlet port or other like device  94 . The entrance deflector  92  receives the entrance tube  90  with its internal passage  96  and branches or “Y”s into a pair of angled entrance passages  98 A and  98 B. The passages  98 A and  98 B empty into an upper plenum area  100  defined as the space between the lid  56  and the diffuser plate  64 . The angled passages  98 A and  98 B eliminate a direct radiation path to the cover. The angle may also assist in swirl effect of fluid as described below. 
     The bottom plate  58  includes a centered bottom aperture  106  in which an exit deflector  108  is seated within an exit seat  110 . The exit deflector is aligned with and in fluid communication with exit tube  112  which seats within exit tube sleeve  114 . The exit deflector  108  provides multiple exit passages, for example as shown as  116 A and  116 B that merge together to align with an internal passage  118  within the exit tube  112  such that fluid within the lower plenum area  120 , defined as the space between the base plate  66  and the bottom plate  58 , fluidly connects to the passages  116 A and  116 B, the internal passage  118  and a mixing tube  124 . The angled exit passages assist in decelerating fluid flow and eliminate direct path of radiation to base. 
     Cool gas tube  126  also fluidly connects to the mixing tube  124 . Typically cool gas tube  126  and internal passage  118  are of a smaller diameter than mixing tube  124 . 
     In addition to the heating body  12  with susceptor body  14  selectively insertable therein, the system  10  includes the cooling gas supply  16  which is any form of a tank or other supply device for supplying fluid for cooling the susceptor body. In one embodiment, the cooling gas supply is a nitrogen supply or tank as is shown in FIG.  1 . 
     The gas supply  16  is connected via a conduit, pipe, or other passage  140 , with a shut off valve  142  therein, to a main section  146  of a main fluid loop  144 . Within main fluid loop  144  are the following components: the gas circulator  18  which is typically some form of a blower or gas/fluid accelerator, a blower-splitter conduit section  148 ,at least one valve  150  within the section  148  where the valve may be a shut off, one way or pressure relief type, a “Y” conduit section  152 , a cooling conduit section  154  connecting the “Y” to valve  94 , a bypass conduit section  156  connecting the “Y” to the cool gas tube  126 , at least one valve  158  and  160  in each of the sections  154  and  156 , respectively, where each valve may be a shut off, one way or pressure relief type, the cool gas tube  126 , the mixing tube  124 , the particulate separator  20 , a separator exchanger conduit section  162 , at least one valve  164  within the section  158  where the valve may be a shut off, one way or pressure relief type, and the heat exchanger  22 . 
     The heat exchanger  22  provides for convective or conductive heat exchange from the main fluid loop  144  to a secondary fluid loop  170 . This loop removes heat via conduction or convection within the heat exchanger from the main fluid loop  144  and removes or disposes of it. Typically, the loop  170  has an intake valve  174  and an outtake valve  176 , as well as a bypass  178 . Typically, within the heat exchanger, the cooling gas passes by coils  180  which are part of the secondary fluid loop  170 . 
     The system further includes the following features. A high temperature heat shield  190  on the cover  36  above the tube  92  to protect the cover from heat escaping from the tube. 
     The entire system is under a slight positive pressure such that any leaks result in an outward flow. This protects the system from contamination by oxygen which causes oxidation of parts in process. 
     The process or method of using this system  10  is described as follows. As is well known in the art, items  200  to be heated for any of a variety of reasons such as heat treating, annealing, curing, baking on coatings, masking, tempering, or hardening are placed within the chamber  60 , typically on racks or other storage devices. This is within the susceptor. The cover  36  is sealed onto the heating body  12 . The system is heated via the induction-heating coil to hundreds or thousands of degrees. In accordance with the invention, once the heating process is complete, the exhaust valves are closed. Also, any purge gas or sweep gas are turned off. Temperature monitoring occurs until the temperature is below a preselected limit, such as 3200 degrees Fahrenheit, whereby the chamber inlet valve  158 , the chamber outlet valve  164 A, and the bypass valve  160  are opened. Thereafter, the blower  18  is turned on and slowly ramps up to full velocity. During the ramping up, a sensor adjacent to the valve  158  monitors the inlet flow rate of cooling gas to make sure the flow does not exceed a preset limit such as 500 CFM whereby if the flow rate does the valve  158  may be closed proportionally to lower the flow. Simultaneous with this flow, cooling fluid is bypassing the susceptor via conduit  156 . 
     The ratio of cooling gas passing through the conduit  156  into the susceptor and the cooling gas bypassing the susceptor via conduit  154  is preferably varied throughout the cooling process. Initially, a majority of the cooling gas bypasses the susceptor, but then merges with the cooling gas that has cooled the susceptor by taking on heat, whereby the significantly higher bypassed cooling fluid better assists in cooling the heated cooling gas exiting from the susceptor. As the system cools, the ratio is adjusted until in the end, a majority of the cooling gas passes through the susceptor to cool the susceptor, but then merges with the cooling gas that has bypassed the susceptor, as very little additional cooling is needed prior to the heat exchanger due to the significant temperature drop that will have occurred by this time in the process. 
     In more detail, the system  10  has an induction-heating coil that is used to heat the susceptor and its contents. Insulating materials protect the coil from the hot susceptor. The susceptor is typically made of graphite, but need not be as it may be made of any electrically conductive material. The coil sets on a base assembly designed to allow the flow of gases out of the chamber  60  of the susceptor and the chamber  40  the susceptor sets in. This area is often referred to as the hot zone. When cooling is desired as described above, the cooling gas are propelled by the blower  18  through an inlet port  94  where the gases are directed into the furnace hot zone via the special passages, plenums, ports, etc. This is best shown in FIG. 3 where the gas is provided at the inlet port  94  as cooling gas A whereby it passes into the furnace as shown at B. The insulating material is shown as dotted shading in chamber  40 . Due to the presence thereof, the cooling gas is directed into the internal passage  96  in entrance tube  92  as shown by arrow C and then directed angularly into the upper plenum area  100  by the pair of angled entrance passages  98 A and  98 B as shown by arrows D. The cooling gas travels through the plenum  100  as shown by arrows E. The cooling gas is the directed through the diffuser plate  64  via the plurality of diffuser holes  76  which are angled thus resulting in the cooling gas traveling as shown by arrows F and G in FIG.  5 . This angular path causes the cooling gas to swirl as it enters the chamber  60  and passes the contents  200  therein. This swirling action is shown by the plurality of arrows H and it assists in creating maximum turbulence. The cooling gases are heated by convection, radiation and conduction with the susceptor and contents thereby cooling the susceptor and its contents, and thus creating heated cooling gas. The walls of the susceptor are typically graphite and preferably include imperfections or a roughened surface to assist in the creation of turbulence of the cooling gas whereby the turbulence maximizes heat transfer from the susceptor walls to the cooling gas. The strategically placed plurality of base plate holes  80  allow the swirling cooling gas to exit the chamber  60  and enter lower plenum  120  as shown by arrows  1 . The cooling gas then is directed into the pair of angled exit passages  116 A and  116 B in exit deflector  108  as seated in exit seat  110  as shown by arrows J, and the fluidly connected internal passage  118  in exit tube  112  seated in exit tube sleeve  114  as shown by arrows K. This conveys the heated cooling gases out of the heating body  12  and susceptor  14  therein. It is conveyed from the exit tube  118  into the mixing tube  124  as shown by arrow L whereby non-heated cooling gas, typically traveling at a higher velocity, is provided by the cooling gas tube  126  as shown as arrow M to assist in rapid cooling of the heated cooling gas from the susceptor. The combined non-heated cooling gas from the cooling tube  126  and the heated cooling gas from the exit tube  118  are mixed so as to begin cooling by diluting the heated cooling gas, and conveyed to the optional particulate separator  20  and then the heat exchanger  22  where complete cooling of the cooling gas occurs. The particulate separator  20  is an optional step and device where any particles that are flowing with the cooling gas are collected and removed to eliminate any particulate erosion of the furnace/heating body, susceptor, contents being heated, etc. The cooling gas is then conveyed into the heat exchanger  22  whose exchange medium may be air, water or other medium that is typically preferably environmentally friendly versus the cooling gas medium with is often an inert gas such as argon or nitrogen. The exchange medium removes heat from the cooling gas such that the cooling gas may be propelled by the blower  18  so as to be re-circulated again through the system  10  for purposes of cooling the susceptor and its contents whereby this is continued until the susceptor is cooled to the desirable temperature where the susceptor and/or its contents may be safely removed from the furnace. As the re-circulation continues the ratio of cooling gas used to cool the susceptor versus bypassing the susceptor to dilute the heated cooling gas changes from a very low ratio, such as 5% or 10%, to a very high ratio, such as 90% or 95%. This assures that the cooling gas efficiently cools the susceptor and its contents while at the same time the heated cooling gas post-susceptor is also partially cooled prior to entrance into the particulate separator  20  and heat exchanger  22  to assure no damage is done to either due to excessive heat and to assure better efficiency of the heat exchanger in returning the cooling gas to its original cooling temperature prior to recirculation. 
     It is noted that the direction of the gas flow may be reversed with suitable re-orientation of the components of the system. 
     The cover is of a suitable design to contain the gases under high temperature and pressure with a suitable lift off feature to safely expel the gases should the pressure exceed safe limits while thereafter re-sealing upon re-seating of the cover. The cover also contains a special hot expulsion gas lift and rotate valve  300  which is motor actuated or pressure actuated at a preset pressure limit to avoid over-pressure within the furnace. 
     Accordingly, the improved system of the above embodiments is simplified, provides an effective, safe, inexpensive, and efficient device which achieves all the enumerated objectives, provides for eliminating difficulties encountered with prior devices, and solves problems and obtains new results in the art. 
     In the foregoing description, certain terms have been used for brevity, clearness and understanding; but no unnecessary limitations are to be implied therefrom beyond the requirement of the prior art, because such terms are used for descriptive purposes and are intended to be broadly construed. 
     Moreover, the description and illustration of the invention is by way of example, and the scope of the invention is not limited to the exact details shown or described. 
     Having now described the features, discoveries and principles of the invention, the manner in which the improved system is constructed and used, the characteristics of the construction, and the advantageous, new and useful results obtained; the new and useful structures, devices, elements, arrangements, parts and combinations, are set forth in the appended claims.