WO2011056960A1

WO2011056960A1 - Louvered hot zone for a vacuum heat treating furnace

Info

Publication number: WO2011056960A1
Application number: PCT/US2010/055431
Authority: WO
Inventors: Craig Moller; Werner Hendrik Grobler; Jake Hamid
Original assignee: Ipsen, Inc.
Priority date: 2009-11-04
Filing date: 2010-11-04
Publication date: 2011-05-12

Abstract

A hot zone enclosure for a heat treating furnace, preferably a vacuum heat treating furnace, is disclosed. The hot zone enclosure includes a support frame constructed and arranged for surrounding a workload placed in the heat treating furnace. A plurality of louvers are mounted around the periphery of said support frame. The louvers are constructed and arranged to move from a closed position to an open position. The hot zone enclosure also includes an operating mechanism connected to the louvers for moving the louvers between the closed position and the open position. Motive means is operatively connected to the operating mechanism for moving the operating mechanism to effect opening or closing of the louvers.

Description

TITLE OF THE INVENTION:

LOUVERED HOT ZONE FOR A VACUUM HEAT TREATING FURNACE

BACKGROUND OF THE INVENTION:

Field of the Invention:

This invention relates generally to a furnace for heat treating metal parts and in particular to a hot zone structure for use in such a furnace.

Description of the Related Art:

The heat treating of metal parts includes the steps of heating a work load of such parts up to an elevated temperature at which a desired metallurgical effect occurs. While the heating rate can have an effect on the desired property or properties for the metal parts, the cooling rate can also have a significant effect on properties for some metals. Here and throughout this application the term "metal" or "metals" includes pure metals and alloys. For some metals, it is desired to provide rapid cooling rates. In vacuum heat treating furnaces, rapid cooling rates are provided by injecting a cooling gas into the hot zone where the heated workload is situated. In many types of vacuum heat treating furnaces, a blower or fan is provided in the furnace vessel. The blower is driven by an electric motor and circulates a cooling gas around the workload. The cooling gas absorbs heat from the work load. The cooling gas is circulated over a heat transfer device such as coils containing a cooling fluid. The heat absorbed by the gas is transferred to the cooling fluid which is circulated outside the vacuum furnace to an external heat sink. Although such forced gas cooling systems can be designed to provide rapid cooling rates, there are limits to the rate of cooling that they can provide.

One way of increasing the cooling rate for a forced gas cooling vacuum heat treating furnace is to provide greater exposure of the workload to the outer wall of the furnace pressure vessel. The outer wall of a vacuum furnace is typically cooled with a fluid so that the outside surface of the furnace is relatively cool to the touch, even during a heating cycle. However, the known techniques for increasing the exposure of a heated workload to the furnace's much cooler pressure vessel wall leave something to be desired. U.S. Patent No. 5,524,020 describes a vacuum furnace with a movable hot zone. This design requires a vacuum vessel that is approximately twice as long as the hot zone enclosure resulting in more floor space for the furnace and higher backfill gas usage. Moving the upper section of the hot zone enclosure as described in the Ό20 patent means the heating elements must also move with this section. The power connections to the heating elements have to be disconnected before the movement takes place and then reconnected after the hot zone enclosure is repositioned. Alternatively, long flexible cables would have to be connected between the stationary heating elements and those in the movable section of the hot zone enclosure. In either arrangement, the design is quite complicated and would likely require higher than normal maintenance on the furnace.

U.S. Patent No. 4,610,435 describes a vacuum heat treating furnace that has two bungs formed in the hot zone enclosure, one above the hot zone and one below it. The bungs are configured to open during cooling, primarily to increase wind flow into and out of the hot zone. The bung openings also allow for some heat radiation toward the colder surface of the pressure vessel wall. Directly above and below the bung openings, outside the hot zone, there are wind guiding baffles which somewhat shield the direct radiation from getting to the cold wall of the furnace. However, the baffles may also absorb some of the heat escaping from the hot zone. The bung openings are only about as large as the surface of the load they are above and below, which means that the sides of the load do not "see" the cold areas of the chamber when cooling takes place. Further, heat radiation from the workload is significantly restricted because there are no openings in the sides of the hot zone enclosure.

SUMMARY OF THE INVENTION:

The hot zone enclosure according to this invention is designed to be used inside of a vacuum furnace chamber and to have the ability to open up to expose the heated work load to the cold outer wall of the vacuum vessel. The hot zone enclosure according to this invention allows direct radiation of heat from the work pieces and hot zone to the pressure vessel wall for improved heat transfer compared to forced gas cooling alone. The concept for the louvered hot zone provides for the insulated walls (refractory lining) of the hot zone to be openable, thereby permitting exposure of the inside of the hot zone, as well as the heated work load, to the colder walls of the vacuum vessel. Exposing the hot zone and work load, which are typically at temperatures of 1600F to 2200F right after a heating cycle, to the cold vessel wall will produce a significant radiation heat transfer effect many times more powerful than gas cooling alone. The percentage of louver opening is important and is preferably greater than about 50%. Forced gas cooling can also take place when the louvers are open.

In accordance with the present invention there is provided a hot zone enclosure for a heat treating furnace, preferably a vacuum heat treating furnace. The hot zone enclosure includes a support frame constructed and arranged for surrounding a workload placed in the heat treating furnace. A plurality of louvers are mounted around the periphery of said support frame. The louvers are constructed and arranged to move from a closed position to an open position. The hot zone enclosure also includes an operating mechanism connected to the louvers for moving the louvers between the closed position and the open position. Motive means is operatively connected to the operating mechanism for moving the operating mechanism to effect the opening or closing of the louvers.

BRIEF DESCRIPTION OF THE DRAWINGS:

Figure 1 is a front perspective view of a hot zone enclosure in accordance with the present invention in the closed condition.

Figure 2 is a right side rear perspective view of the hot zone enclosure of Figure 1.

Figure 3 is front perspective view of a hot zone enclosure in accordance with the present invention in the open condition.

Figure 4 is a right side rear perspective view of the hot zone enclosure of Figure 3.

Figure 5 is a front elevation view of the hot zone enclosure of Figures 3 and 4.

Figure 6 is an enlarged view of the louver operating mechanism for a hot zone enclosure according to the present invention with louvers in the closed position. Figure 7 is an enlarged view of the louver operating mechanism for the hot zone enclosure of Figure 6 with the louvers in a partially open position.

Figure 8 is an enlarged view of the louver operating mechanism for the hot zone enclosure of Figure 6 with the louvers in a fully open position.

Figure 9 is a detailed view of the louver operating linkage for the hot zone enclosure of Figure 6.

Figure 10 is a detailed view of the louver operating linkage for the hot zone enclosure of Figure 7.

Figure 11 is a detailed view of the louver operating linkage for the hot zone enclosure of Figure 8.

Figure 12 is a front right perspective view of a second embodiment of a hot zone enclosure according to the present invention.

Figure 13 is a perspective sectional view of the hot zone enclosure of Figure 12 as viewed along line 13-13 therein.

Figure 14 is a left front perspective view of the hot zone enclosure of Figure 12.

Figure 15 is front elevation view of the hot zone enclosure.

Figure 16 is a side elevation sectional view of the hot zone enclosure as viewed along line 16-16 of Figure 15.

Figure 17 is side elevation view of the hot zone enclosure as viewed along line 17-17 of Figure 15.

Figure 18 is a rear elevation view of the hot zone enclosure.

Figure 19 is detail view of a louver drive mechanism as shown in area "B" of Figure 12.

Figure 20 is a detail view of the connector for the louver actuator as shown in area "C" of Figure 14. DETAILED DESCRIPTION:

Referring now to the drawings wherein like reference numerals refer to the same or similar parts, and in particular to Figures 1 to 5, there is shown a first embodiment of a hot zone enclosure 10 for a vacuum heat treating furnace. The hot zone enclosure 10 has a generally cylindrical support structure or frame 12 that is preferably formed of a stainless steel such as AISI Type 304. For some applications straight carbon steel may be suitable. The interior of the support structure 12 includes side heat shielding material 14 around the sidewall of the enclosure and back heat shielding material 16 on the back wall of the enclosure. The heat shielding material can be any of the heat resistant materials suitable for such use in an industrial heat treating furnace.

A plurality of heating elements 20 are disposed within the enclosure 10 and supported from the support structure 12 by electrically insulating stand-offs. A pair of workload supports 22a and 22b are located at the bottom of the enclosure 10 in a known manner. The workload supports are supported from the outer wall of the vacuum furnace vessel (not shown). The support structure 12 also includes a plurality of ducts 30 that extend from the back wall of the support structure 12 to the front of the hot zone enclosure 10. The ducts 30 provide channels for a cooling gas to be injected into the hot zone area to cool a work load after a heat treating cycle. The ducts 30 also serve as reinforcing members for the hot zone enclosure frame 12. A plurality of gas injection nozzles (not shown) are mounted in the interior of the hot zone enclosure 10 and are in communication with the ducts 30 to provide paths for the cooling gas to enter the hot zone from the ducts 30 during a cooling cycle. As an alternative to the gas injection nozzles, two or more slots can be formed in the enclosure sidewall to coincide with the ducts 30 to provide a path for the cooling gas to enter the hot zone. Gas flow control valves (not shown) can also be located in or ahead of the entrances to the cooling gas ducts 30. The flow control valves can be opened or closed depending on the cooling gas flow pattern desired in the hot zone during a cooling cycle. Such an arrangement is shown and described in U.S. Patent No. 6,903,306, issued June 7, 2005, the entirety of which is incorporated herein by reference.

A plurality of louvers 18 are disposed in the sidewall of the enclosure 10. The louvers 18 are spaced at regular or irregular distances from each other around the enclosure sidewall. The louvers 18 are positioned within ports in the enclosure sidewall and are supported for movement within or relative to their respective ports between a first position wherein the port is closed and a second position wherein the port is open. The louvers 18 can be modulated (partially opened) so that the percent opening is changed when a reduction of cooling effect is required. Each of the louvers 18 is mounted on a support shaft (not shown). The ends of the louver support shafts are mounted in high temperature support bearings that are located in recesses in the enclosure side wall adjacent to the respective port so that each louver 18 can be rotated within its respective port. Each louver is sized to substantially close off the port when the louver is in a closed position. The louvers 18 form part of the heat shield of the enclosure and so are made from heat resistant materials including graphite and other carbon-based materials, metals such as molybdenum and high temperature, heat resistant alloys. Preferably, a refractory type insulation material is applied to the louvers to provide additional shielding from the intense heat present during a heat treating cycle. As shown in Figures 1-5, the louvers are configured as a single piece. However, it is contemplated that the louvers can be configured with a two-piece arrangement as described below in connection with Figures 6-11. The support shafts and bearings are preferably made of graphite or other carbon-based material. The ports in which the louvers 18 are situated serve as cooling gas exit openings in the hot zone enclosure 10.

The louvers 18 are linked together such that they can be operated in unison. In this regard, a drive ring 26 is rotatably mounted to the support structure 12 at the front end of the enclosure 10. The drive ring 26 has a circumference that is large enough to avoid obstructing the open end of the hot zone enclosure 10. The drive ring 26 is operatively connected to the louvers 18 such that when the drive ring 26 is rotated in one direction, the louvers 18 move from their closed position to their open position. The drive ring 26 is mounted for reversible movement so that it can be rotated in both clockwise and counterclockwise directions. Thus, the drive ring 26 can be rotated in an opposite direction to move the louvers 18 from their open position to the closed position.

The drive ring 26 is coupled to the louver support shafts in any suitable manner to provide rotation of the shafts, and hence the louvers themselves. In a preferred coupling arrangement, a cam arm (not shown) is coupled between the drive ring 26 and a louver support shaft. In another preferred arrangement, a pinion gear is mounted on the end of each louver support shaft and the drive ring 26 has a plurality of gear teeth formed thereon for engagement with the pinion gears on the louver support shafts. Regardless of the coupling arrangement used, the arrangement is preferably configured so that all of the louvers 18 move in unison between the open and the closed positions.

An actuator 24 is provided to rotate the drive ring 26. In the embodiment shown, the actuator 24 includes a drive arm or rod 28 that is coupled to the drive ring 26 in any known manner. The actuator can be any suitable type of motive device including electric, pneumatic, hydraulic, or a combination of such devices. Although the actuator 24 shown in the drawings provides linear displacement of the drive rod 28, it is contemplated that the actuator could also be a rotary motion device and that the rotary motion device would be coupled to the drive ring 26 by a suitable rotary-type linkage such as drive gear or a friction wheel. When a rotary drive gear is used, the drive ring 26 would incorporate a plurality of gear teeth to engage with the drive gear. Similarly, when a friction drive wheel is used, the drive ring 26 would include a friction surface to engage with the friction wheel.

Referring now to Figures 6 to 11, additional features of the louver operating linkage and a second embodiment of the louver rotation drive linkage is described. In the embodiment shown in Figures 6-1 1, the louvers 18 are configured in two pieces. Each piece is supported at one end by a support shaft. The support shafts are rotatably supported in high temperature bearings mounted in recesses in the support structure 12 adjacent the ports which the louvers 18 cover. The drive ring 26 is supported on a support rail 32 that is mounted to the enclosure support structure 12 by any suitable means. The drive ring 26 has a plurality of wheels 34 that are attached to the drive ring 26 on support pins 36 such that the wheels 34 are free to rotate and travel along support rail 32. The wheels 34 are located at spaced intervals around the drive ring 26 and generally in the vicinity of a louver support shaft. A plurality of drive links 38 are also supported on the drive ring 26 by the support pins. Each drive link 38 has a first end that is adapted to be connected to the drive ring 26 by means of the support pin 36. Each drive link 38 has a second end that is adapted to be connected to a louver support shaft. The drive link 38 is fixedly attached to the louver support shaft such that angular motion of a drive link 38 causes rotation of the louver support shaft to which it is attached. The first end of drive link 38 is movably coupled to the support pin 36 so that the drive link can rotate about the support pin 36 when the drive ring 26 is rotated. As shown in Figures 6-11, the louver support shaft of one piece of a louver 18 is located adjacent to the support shaft of the second piece of the next adjacent louver 18. With this arrangement of the two pieces of adjacent louvers, only a single drive link 38 is needed for the two adjacent louver pieces. In this regard, a pinion gear 40 is affixed to the end of the support shaft for the second louver piece and the second end of drive link 38 has gear teeth (not shown) formed thereon which engage with the teeth on the pinion gear 40. In this manner, the two louver pieces 40 can be rotated between their opened and closed positions by a single drive link 38. A plurality of stops 42 are provided between adjacent, neighboring louver pieces so that the louver pieces cannot be rotated beyond an angle where the louver pieces could hit each other and be damaged.

Referring now to Figures 12 to 20, there is shown a second embodiment of a hot zone enclosure for a vacuum heat treating furnace according to the present invention. The hot zone enclosure 50 includes a support frame 52 which has a front portion 54, a rear portion 56, and a plurality of spacers 58. The spacers 58 are preferable in the form of rods or bars which interconnect the front portion 54 and the rear portion 56 and maintain them in spaced relation to form the support frame 52. The support frame 52 is dimensioned to accommodate a workload 57 of metal parts which would be heat treated in a vacuum furnace of which the hot zone enclosure is a part. The front and rear portions of the support structure are formed of heat resistant metal rings and layers of heat insulating material. The spacers are preferably formed of heat resistant metal such as a high temperature stainless steel.

A plurality of louvers 60 are disposed in the side spaces of the hot zone enclosure 50. The louvers 60 are spaced at regular or irregular distances from each other around the enclosure sidewall, preferably between the spacers 58. The louvers 60 are positioned are supported for rotational movement between a closed position wherein the sides of the hot zone enclosure are closed and an open position wherein the sides of the hot zone enclosure are open. The louvers 60 can be modulated (partially opened) so that the percent opening is changed when a reduction of cooling effect is required. Each of the louvers 60 is mounted on a support shaft (not shown). The ends of the louver support shafts are mounted in high temperature support bearings that are located in recesses in the front and rear portions of the support frame 52 so that each louver can be rotated between the first and second positions. The louvers 60 are dimensioned such that when they are all in the first position the hot zone enclosure they form a wall around the periphery of the support frame. The louvers 60 form part the heat shield of the hot zone enclosure and so are made from heat resistant materials including graphite and other carbon- based materials, metals such as molybdenum and high temperature, heat resistant alloys. In this embodiment, the louvers are preferably formed of a board or slat of heat insulating material such as graphite sandwiched between two outer layers of graphite material. The support shafts and bearings are preferably made of graphite or other carbon-based material.

The louvers 60 are linked together such that they can be operated in unison. In this regard, a drive ring 72 is rotatably mounted to the front portion 54 of the support frame 52. The drive ring 72 has an inside diameter that is large enough to avoid obstructing the opening in the front end of the hot zone enclosure 50. The drive ring 72 is operatively connected to the louvers 60 such that when the drive ring 26 is rotated in one direction, the louvers 60 move from their closed position to their open position. The drive ring 72 is mounted for reversible movement so that it can be rotated in both clockwise and counterclockwise directions. Thus, the drive ring 72 can be rotated in an opposite direction to move the louvers 60 from their open position to the closed position.

The drive ring 72 is coupled to the louver support shafts in any suitable manner to provide rotation of the shafts, and hence the louvers themselves. In a preferred coupling arrangement as shown in Figures 19 and 20, cam arms or links 74 are coupled between the drive ring 72 and an end 64 of a louver support shaft. The drive ring 72 has a plurality of wheels or rollers 76 that are attached to the drive ring 72 such that the wheels 76 are free to rotate and travel along the outer surface of the front portion 54 of the support frame 52. The wheels 76 are located at spaced intervals around the drive ring 72. The drive ring 72 also has a plurality of pins 75 extending therefrom and a first end of each link 74 is connected to one of the pins. The links 74 each have a receptacle 73 for receiving a louver shaft end. Locking means such as a set screw, key, or the like is provided in each receptacle 73 to secure the shaft end in the receptacle and prevent relative motion between the receptacle and the shaft end. The arrangement of the drive ring 72, the links 74, and the louver shafts is preferably configured so that all of the louvers 18 move in unison between the open and the closed positions.

An actuator 78 is provided to rotate the drive ring 72. In the embodiment shown, the actuator 78 includes a drive arm or rod 80 that is coupled to the drive ring 72. Preferably, a connector 82 is attached to the end of the rod 80 and is adapted to be connected to one of the support wheels 76. The actuator can be any suitable type of motive device including electric, pneumatic, hydraulic, or a combination of such devices. Although the actuator 78 shown in the drawings provides linear displacement of the drive rod 82, it is contemplated that the actuator could also be a rotary motion device and that the rotary motion device would be coupled to the drive ring 72 by a suitable rotary-type linkage such as drive gear or a friction wheel. When a rotary drive gear is used, the drive ring 72 would incorporate a plurality of gear teeth to engage with the drive gear. Similarly, when a friction drive wheel is used, the drive ring 72 would include a friction surface to engage with the friction wheel.

As shown in Figures 13, 15, and 18, the hot zone enclosure 50 includes gas exit ports 84a, 84b, 84c, and 84d formed in the wall of the rear portion 56 of the support frame. The gas exit ports include an exit port panel or flap 88a, 88b, 88c, and 88d disposed in the exit port openings 86a, 86b, 86c, and 86d, respectively. Each of the exit port flaps is pivotally supported within its respective exit port opening by a pin or rod (not shown) which is held within the end wall of rear portion 56. The exit port flaps are dimensioned and positioned so as to close the exit port opening when the flap is in a first position thereby preventing or at least substantially limiting the transfer of heat out of the hot zone enclosure during the heating portion of a heat treatment cycle. In the closed position, the flaps prevent the unforced introduction of cooler gas into the interior of the hot zone enclosure during a heat treating cycle. In a second position, each flap rotated outwardly to an open position to thereby permit the forced flow of cooling gas out of the hot zone enclosure through the gas exit ports during a cooling or quenching cycle. For simplicity, each exit port flap is maintained in the first or closed position by the force of gravity. In such an arrangement each exit port flap is preferably oriented such that it will be normally closed. Each exit port flap is preferably formed from a refractory material such as molybdenum, graphite, or CFC and may be lined with a thermally insulating material. Alternatively, the exit port flaps may be formed of a ceramic material if desired. The shapes of the exit port opening 63 and exit port flap are not critical. The exit port openings and exit port flaps are preferably square or rectangular for ease of fabrication. Although the embodiment shown in Figures 15 and 18 has four gas exit ports, it is contemplated more or fewer ports can be used depending on the size and performance requirements for a given vacuum furnace. The above-described embodiments of the present invention are constructed and arranged for operation of the louvers in unison. However, it is also contemplated that the hot zone can be constructed and arranged so that the louvers operate in groups. In such an embodiment, the structure and arrangement of the louvers in the hot zone frame would be essentially as described above. However, in this "grouped operation" embodiment, each group would have a separate operating mechanism including separate actuators and separate linkages between the respective actuators and the respective groups of louvers. This arrangement could be realized by, for example, having the drive ring formed in sectors with each sector operatively connected to an actuator. Other arrangements can be readily designed by those skilled in the art. The use of groups of louvers permits options for cooling a work load in addition to having all of the louvers open and close in unison. For example, it would be possible to open only top and/or bottom groups of louvers while leaving the side louvers closed. Alternatively, only the side louvers could be opened while leaving the top and/or bottom louvers closed. For certain asymmetric workloads, it might be advantageous to open only top and side louvers or only bottom and side louvers.

The operation of a vacuum furnace having a hot zone enclosure as described above would include at least the following steps. The workload is moved into the furnace chamber and positioned within the hot zone enclosure. The furnace door is closed and sealed and the furnace chamber is then evacuated to begin the heating cycle. In this heating step the louvers are maintained in the closed position to retain as much heat as possible in the hot zone. The temperature of the furnace is then increased to heat the load to the desired heat treating temperature. When the heating cycle is completed, the louvers are moved to their open position. At the same time the cooling fan motor is started and the furnace is backfilled with an inert gas to a preselected pressure. The cooling fan circulates the cooling gas until the hot zone and parts are cooled to a desired temperature. In the embodiment shown in Figures 1-5, the cooling gas is blown into the hot zone through the gas injection nozzles on the ducts 30. In the embodiment shown in Figures 12-20, the cooling gas is blown through the open louvers from an external means and exits through the gas exit ports 84a-84d. During the cooling cycle, the louvers can be partially closed to reduce the cooling rate by restricting the volume flow of the cooling gas through the hot zone and the amount of radiation cooling. When the workload has cooled to the desired temperature, the fan is stopped, the gas pressure is relieved, and the furnace vessel door can be opened.

It will be recognized by those skilled in the art that changes or modifications may be made to the above described embodiments without departing from the broad, inventive concepts of the invention. It is understood, therefore, that the invention is not limited to the particular embodiment(s) disclosed, but is intended to cover all modifications and changes which are within the scope and spirit of the invention as defined in the appended claims.

Claims

CLAIMS:

1. A hot zone enclosure for a heat treating furnace comprising:

a support frame constructed and arranged for surrounding a workload placed in a heat treating furnace;

a plurality of louvers mounted around the periphery of said support frame, said louvers being constructed and arranged to move from a closed position to an open position;

an operating mechanism connected to said louvers for moving the louvers between the closed position and the open position; and

motive means operatively connected to said operating mechanism for moving said operating mechanism to effect opening or closing of the louvers.

2. A hot zone enclosure as claimed in Claim 1 wherein said support frame comprises a front portion, a rear portion, and a plurality of spacer members connecting the front portion and the rear portion, said spacer members being dimensioned to maintain the front portion and the rear portion in a spaced relationship.

3. A hot zone enclosure as claimed in Claim 2 wherein said louvers extend longitudinally between the front and rear portions of the support frame and are arrayed between said spacer members.

4. A hot zone enclosure as claimed in Claim 3 wherein each of said louvers is formed of a single slat.

5. A hot zone enclosure as claimed in Claim 3 wherein each of said louvers is formed of two slats.

6. A hot zone enclosure as claimed in Claim 2 wherein the rear portion of said support frame comprises a wall having a closable gas exit port.

7. A hot zone enclosure as claimed in Claim 6 wherein the gas exit port comprises an opening formed in said wall and a panel pivotally mounted in the opening.

8. A hot zone enclosure as claimed in Claim 2 wherein the rear portion of said support frame comprises a wall having two closable gas exit ports.

9. A hot zone enclosure as claimed in Claim 8 wherein each of the gas exit ports comprises an opening formed in said wall and a panel pivotally mounted in the opening.

10. A hot zone enclosure as claimed in Claim 2 wherein said operating mechanism is located on the front portion of the support frame.

11. A hot zone enclosure as claimed in Claim 1 wherein said support frame comprises a front portion, a rear portion, and a wall extending around the periphery of said support frame between said front and rear portions and said wall comprises a plurality of ports in which said louvers are disposed.

12. A hot zone enclosure as claimed in Claim 11 wherein said louvers extend longitudinally between the front and rear portions of the support frame and are arrayed between said spacer members.

13. A hot zone enclosure as claimed in Claim 11 wherein each of said louvers is formed of a single slat.

14. A hot zone enclosure as claimed in Claim 11 wherein each of said louvers is formed of two slats.

15. A hot zone enclosure as claimed in Claim 2 wherein the rear portion of said support frame comprises a wall having a closable gas exit port.

16. A hot zone enclosure as claimed in Claim 15 wherein the gas exit port comprises an opening formed in said wall and a panel pivotally mounted in the opening.

17. A hot zone enclosure as claimed in Claim 11 wherein the rear portion of said support frame comprises a wall having two closable gas exit ports.

18. A hot zone enclosure as claimed in Claim 17 wherein each of the gas exit ports comprises an opening formed in said wall and a panel pivotally mounted in the opening.

19. A hot zone enclosure as claimed in Claim 11 wherein said operating mechanism is located on the front portion of the support frame.