US3467366A - Furnace construction having atmosphere curtain - Google Patents

Description

P 6, 1969 H. w. WESTEREN ET AL 3,467,366

FURNACE CONSTRUCTION HAVING ATMOSPHERE CURTAIN Filed Oct. 2, 1967 2 Sheets-Sheet l a i a I l Inventors: I Herbert IV. Westeren,

H William Hjfim ball,

' 82 j/zefiv WV T Atgys.

Sept. 16, 1969 w, WESTEREN ET AL 3,467,366

FURNACE CONSTRUCTION HAVING ATMOSPHERE CURTAIN Filed Oct. 2, 1967 2 Sheets-Sheet 2 Inventors: Herbert h. Westeren, William HJfimbaZ/Z, ywa z W A tfyls'.

United States Patent 3,467,366 FURNACE CONSTRUCTION HAVING ATMOSPHERE CURTAIN Herbert W. Westeren, Providence, and William H. Kimball, Barrington, R.I., assignors to C. I. Hayes, Inc., Cranston, R.I., a corporation of Rhode Island Filed Oct. 2, 1967, Ser. No. 672,085

Int. Cl. F27b 9/24, 9/30; F27d 3/12 US. Cl. 263-6 9 Claims ABSTRACT OF THE DISCLOSURE Background of the invention The furnace construction embodied in the present invention is of the type that includes a continuously moving conveyor belt on which articles that are adapted to be heat treated are carried. The conveyor belt transfers the articles to be heat treated in work baskets into the heat treating chamber of the furnace where they are subjected to the required temperature during the heat treating operation. In this type of furnace construction, the heat treating chamber must be properly conditioned with an atmosphere that is introduced therein so that he articles are heat treated under those conditions most favorable for obtaining the required results. Since reducing gases, such as hydrogen and dissociated ammonia are employed as atmospheres in conveyor furnaces, it is an ever increasing problem of preventing mixture of the furnace conditioning atmosphere with atmosphere air both within the furnace and in the room in which the furnace is located. Under certain conditions, mixing of a reducing atmosphere and atmospheric air can result in an explosive mixture and thus the requirement of preventing the mixing of the atmospheres becomes a safety problem. In this connection, furnace operators are becoming increasingly safety conscious and are now requiring that there be absolutely no detectable explosive gas mixture present in a furnace room. Yet, notwithstanding these rigid requirements, the work to be heat treated and the fixtures on which they move must be free to pass into and out of the furnace on the conveyor belt, which necessarily exposes the furnace chamber to the outside atmosphere for a brief period of time.

Some attempts have been made heretofore to protect the furnace chamber interior by establishing a curtain of inert atmosphere at the furnace inlet and exit throats. However, none of these prior known systems have been completely successful, since the work passing through such an atmosphere curtain has caused some air to enter into the furnace therewith. Although high velocity jets were employed to increase the flow of the inert gas,, this only resulted in eddying of the gas curtain which caused cross-leakage to occur.

Summary of the invention The atmosphere curtain as used in the furnace construction of the present invention is obtained by providing a vestibule area at the entrance and exit throats of the furnace and introducing an inert gas into each vestibule area at a very low velocity, thereby producing a dense cloud of the inert gas in the vestibule areas. The dense cloud of inert gas acts to prevent inflow of atmospheric air therethrough, but if any does filter therethrough it is removed by an aspirator or ejector system.

The ejector system includes an exhaust section that is located on the furnace side of and adjacent to the inert gas distributor section in which the dense cloud is introduced. The exhaust section is fitted with two carefully lo cated slots that are disposed in the top and bottom thereof. Each slot includes a gas-tight collection box to which pipe connections are joined. The suction side of a small aspirator or ejector communicates with the lower gas collection box and the motive force for this aspirator is low-pressure nitrogen that is supplied from an external source. Flow to the small aspirator is adjusted to produce a suction in the floor of the vestibule area which pulls mostly inert gas from the gas distributor section. This discharge from this small or lower aspirator is a mixture of nitrogen, plus whatever it has picked up from the floor of the vestibule area. The mixture is then directed to a larger aspirator, the suction of which is attached to the upper collection box through an adjustable valve. Further suction is created to remove the conditioning atmosphere from this area and the entire mixture is directed to a burn-off igniter for disposal.

Accordingly, it is an object of the invention to provide a furnace construction having an atmosphere curtain for preventing the admixture of atmospheric air and a reducing atmosphere used in the heat treatment operation.

Another object is to teach a method of producing an atmosphere curtain in a furnace construction.

Still another object is to provide an atmosphere curtain which includes means for introducing an inert gas into a vestibule area of a furnace with a minimum of velocity to form a cloud that acts as a barrier to inflow of atmospheric air.

Still another object is to use the discharge of an aspirator to drive a larger aspirator which is then employed for removing lighter furnace atmosphere gases.

Other objects, features and advantages of the invention will become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.

Description of the drawings In the drawings which illustrate the best mode presently contemplated for carrying out the present invention:

FIG. 1 is a diagrammatic illustration of a furnace construction and the atmosphere curtain of the present invention as employed therewith;

FIG. 2 is a sectional view of the entrance area of the furnace construction illustrating the details of the atmosphere curtain embodied in the present invention;

FIG. 3 is a sectional view of an aspirator as employed in the atmosphere curtain;

FIG. 4 is a sectional view taken along lines 4-4 in FIG. 2;

FIG. 5 is an enlarged fragmentary view of a portion of the atmosphere curtain shown in FIG. 2 and illustrating one of the barrier curtains employed therein; and

FIG. 6 is an elevational view, with parts shown in section, of the tubular element that is utilized for introducing the inert gas into the vestibule area of the furnace at a low velocity.

Description of the invention Referring now to the drawings and particularly to FIG. 1, the furnace construction embodied in the present invention is generally indicated at 10 andincludes a heat treating chamber 12 through which metallic articles are continuously moved by a conveyor belt 14 during the heat treating cycle. As illustrated, the furnace construction 10 is of the straight-through type; however, it will 3 be understood that the concept of the present invention may also be employed in the so-called hump-back furnace. Both the straight-through furnace as illustrated in FIG. 1 and the hump-back furnace include a conveyor system having a conveyor belt 14, for carrying the articles to be heat treated in baskets through the furnace chamber 12; and although no particular conveyor drive means is illustrated, it is understood that this is a conventional apparatus and does not form a part of the present invention.

Communicating with the heat treating chamber 12 is a cooling chamber 16 through which the heat treated articles are carried after the heat treatment operation. A suitable cooling fluid, such as water in continuously circulated through a cooling jacket surrounding the cooling chamber 16 for effectively reducing the temperature of the heat treated articles as they pass through the cooling chamber.

Also communicating with the furnace chamber 12 is a source of conditioning atmosphere for introduction therein. The conditioning atmosphere such as hydrogen, is directed from a suitable supply into a line 18 and passes through a series of control valves for introduction into the furnace 12 by way of lines 19 and 20. The hydrogen atmosphere may also be introduced into the cooling chamber 16 from the lines 18 and 19 through connecting lines 22 and 24. In order to purge the furnace chamber 12 and the cooling chamber 16, after a heat treatment operation, a purge line 26 is provided that communicates with a source of inert gas, such as nitrogen. As illustrated in FIG. 1 the purge gas is introduced into the cooling chamber 16 and furnace chamber 12 by way of a line 28, appropriate control valves and the lines 22, 24 and line 20, respectively.

Located on the entrance side of the furnace chamber 12 is a vestibule area generally indicated at 30, while a similar vestibule area generally indicated at 32 is located on the exit side of the furnace chamber in communication with the cooling chamber 16. As will be described hereinafter, the vestibule areas 30 and 32 are substantially similar in construction and in operation and are so arranged as to provide in an atmosphere curtain therein for preventing the inflow of atmospheric air into the furnace heating chamber 12 during the heat treating cycle. As shown in FIG. 1, an entrance door 34 of conventional construction provides access to the vestibule area 30, while an exit door 36 is operative to permit discharge of the heat treated articles as they exit from the vestibule area 32 following the heat treatment cycle.

Referring now to FIGS. 2 through 6, the vestibule area 30 is illustrated in detail, together with the constructional details that define the atmosphere curtain embodied in the present invention, and it will be understood that the vestibule area 32 is constructed similarly and operates in substantially the same manner as the vestibule area 30. Interconnected to the furnace chamber 12 is an elongated hollow body portion 38 having flanges 40 and 42 formed on the ends thereof. The flanges 40 and 42 are suitably connected to flanges 44 and 46, respectively, thereby interconnecting the body portion 38 on one side to a connecting portion 46 that is joined to the furnace chamber 12 and that communicates with the interior thereof.

Located within the hollow body portion 38 of the vestibule area 30 are a plurality of curtain assemblies indicated in FIG. 2 at 48, 50, 52 and 54. The curtain assemblies are constructed substantially identical and divide the body portion 38 into segregated sections, which, as will be described, aid in preventing inflow of atmospheric air into the furnace chamber 12. As illustrated in FIGS. 4 and 5, the curtain assembly 52 which is representative of the other curtain assemblies includes individual curtain elements 56, 58, 60, 62 and 64. The curtain sections 5664 vary in vertical dimension, the rearmost section 56 being the longest section and the forwardmost section 64 the shortest. As will be described this permits move- 4 ment of a Work load thereunder wherein only those sections that engage the work are moved as the work passes thereunder. The curtain sections are secured to a common connection at the upper end thereof, and as illustrated, the nut 66, fixes the curtain sections between a plate 67 and the upper wall of the body portion 38. As further illustrated in FIG. 4, each of the curtain sections is formed with a plurality of vertically extending slits, as indicated at 68, that separate each of the curtain sections into individual curtain elements that are freely movable. It is seen that the curtain sections of each curtain assembly provides for movement of work articles through the vestibule area 30 with a minimum of opening of the curtain assemblies due to the staggering of the vertical dimension thereof and the slitting of each of the curtain sections as indicated.

As further illustrated in FIG. 2, the curtain assemblies 48 and 50 define a chamber 69 in the vestibule area, while curtain assemblies 50 and 52 define a chamber 70 and the curtain assemblies 52 and 54 define a vestibule chamber 72. It is seen that the vestibule chambers 69, 70 and 72 are effectively enclosed by the hanging vertical curtain assemblies which act to limit flow of the atmospheres exteriorly of the vestibule area 30.

One of the novel features of the invention is to introduce an inert gas into the vestibule area at very low velocity, thereby forming a plug or cloud of gas that in effect prevents inflow of atmospheric air therethrough. This is accomplished by locating a source of the inert gas immediately [below the chamber 70 in the vestibule area 30 as represented by the box 73. As shown in FIGS. 4 and 6, a tubular element 74 extends into the box 73 and is disposed within the box such that the longitudinal axis thereof is substantially perpendicular or normal to the direction of movement of the conveyor belt 14. Since the inert gas must pass from the tubular element 74 upwardly from the box 73 and into the chamber 70 at low velocity, the tubular element 74 is provided with a plurality of individually formed openings 76, as indicated in FIG. 6, the effect of the openings forming the tubular element 74 in what appears to be a porous mesh member. Since the inert gas will in effect pour out of the openings 76 at low velocity, a cloud will form that will accumulate in the chamber 70 of the vestibule area.

'Referring again to FIG. 1, it will be noted that the inert gas, such as nitrogen, is directed from a source through a line 77 and suitable control valves into a line 78 for introduction into the tubular element 74. A suitable coupling member 80 is secured to the end of the tubular element 74 for locating the tubular element 74 in communication with the line 78. It will be further noted in FIGS. 4 and 6 that the end of the tubular element 74 is blanked as indicated at 82 so that when the inert gas passes into the tubular element 74, it will be discharged through the openings 76 at low velocity to form the dense cloud for accumulation in the chamber 70.

In order to assure that atmospheric air will not enter into the furnace chamber 12, a unique system is provided that cooperates with the apparatus just described to discharge the inert gas cloud to a point exteriorly of the vestibule area 30. Referring again to FIG. 2, a lower box 82 is joined to the cylindrical portion 38 and communicates with the interior chamber 72. Similarly, an upper box 84 is joined to the cylindrical section 38 and also communicates with the chamber 72. As shown in FIG. 1, the lower box 82 which communicates with the interior chamber 72 also communicates with the suction side of an aspirator, generally indicated at 86, through a line 88. The aspirator 86 is a fluid operated ejector, as illustrated in FIG. 3, and is adapted to move a fluid, such as a gas, from one point to another with a minimum of operating pressure. In order to provide a motive force for the aspirator or ejector 86, an inert gas, such as nitrogen, is directed from a source through a line 90 and through a suitable control valve into an inlet end 92 of the aspirator. The inert gas is moved at an increased velocity through a jet section 94 in the aspirator and then through a nozzle section 96 for discharge through an outlet 98. The suction side of the ejector 86 indicated at 100 is connected to the box 82 through the line 88; and upon introduction of the inert gas through the inlet 92, a suction is created at the suction inlet 100 to induce a flow of the gases from the chamber 72 of the vestibule area 30 into the box 82 and then through the ejector 86.

The discharge of the ejector 86 is connected directly through a line 102 to a still-larger ejector generally indicated at 104. The larger ejector 104 is constructed similarly to the ejector 86 and has its suction side connected to the upper box 84 through an adjustable valve 105 and a line 106. The discharge of the ejector 104 is directed through a line 108 to a burn-off indicated at 110. It is seen that the flow to the ejector or aspirator 86 may be adjusted to produce a suction in the chamber 72 that will draw inert gas from the vestibule area, as well as conditioning gas from the furnace chamber 12, which may be discharged from the chamber 12 as the articles to be heat treated are passed therein. The discharge from the small or lower aspirator 86 is then a mixture of motive force nitrogen for the larger aspirator as directed from a source through the line 90, plus whatever is pulled through the box 82 from the floor of the vestibule area 30 and the furnace chamber. The mixture of the gases entering the aspirator 86 through the inlet 92 and suction 100 is now directed to the larger aspirator 104, the suction of which is attached to the upper collection box 84 through the valve 105. The mixture of gases discharging from the aspirator 86 thus defines the motive force for the operation of the aspirator 104. As indicated in FIG. 2 by the arrows in chamber 72, inert gas from the chamber 70 and furnace atmosphere conditioning gas is also drawn from the chamber 72 through the collection box 84 and into the suction side of the aspirator 104.

It is seen that the cloud of inert gas that is introduced into the chamber 70 of the vestibule area effectively prevents inflow of atmospheric air therethrough. The cloud is continually dissipated from the chamber 70 as it is drawn into the chamber 72 by the suction created from the aspirators 86 and 104. In the event that any atmospheric air filters into the vestibule area 30, it is admixed with the cloud of inert gas located in the section 70 and is then withdrawn from the vestibule area through either of the boxes 82 and 84. Mixture of atmospheric air and the conditioning gas is also effectively prevented since any conditioning gas that may escape from the furnace chamber 12 is rapidly withdrawn by the suction of the aspirators through the boxes 82 and 84.

Since there are no doors or valves to control for operation of removal of the gases as indicated, work loads can be continuously introduced into the furnace without the requirement of taking special precautions to prevent the inflow of atmospheric air into the furnace chamber. The combination of directing the low velocity inert gas into the vestibule area and then providing the inert gas as a motive force for the lower aspirator and the discharge of the lower aspirator as a motive force for the upper aspirator results in a system that effectively eliminates all detachable traces of the conditioning gas exteriorly of the furnace unit.

While there is shown and described herein certain specific structure embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described.

What is claimed is:

1. In a furnace construction, a heat treating chamber, means for supplying a conditioning gas to said chamber, means for conveying articles to be heat treated through said chamber, means for cooling said heat treated articles,

and means for preventing mixing of atmospheric air with said conditioning gas, said preventing means including a vestibule area located exteriorly of said chamber, and in communication therewith, means for directing an inert atmosphere at relatively low velocity into said vestibule area, and means communicating with said vestibule area for producing a relatively high velocity jet for withdrawing the inert atmosphere and gases mixing therewith from said vestibule area, said inert atmosphere in said vestibule area and the withdrawal therefrom forming a curtain for preventing the mixing of atmospheric air and said conditioning gas, either interiorly or exteriorly of said heat treatment chamber.

2. In a furnace construction as set forth in claim 1, the section of the vestibule area into which the low velocity inert atmosphere is directed being located more closely adjacent to the exterior end of said vestibule area than the point of withdrawal of the gases by the high velocity jet.

3. In a furnace construction as set forth in claim 2, the velocity of the inert atmosphere that is introduced into said vestibule area being sufliciently low enough to produce a dense inert atmosphere cloud therein, said cloud forming an atmosphere barrier that aids in preventing inflow of atmospheric air into said vestibule area.

4. In a furnace construction as set forth in claim 3, said means for directing the inert atmosphere into said vestibule area including a tubular element in which a plurality of openings are formed, the inert atmosphere being received interiorly of said tubular element and diffusing under low velocity outwardly through the openings therein and into said vestibule area to form said cloud.

5. In a furnace construction as set forth in claim 4, a chamber located under said vestibule area and communicating therewith, said tubular element being positioned in said chamber such that the longitudinal axis thereof is normal to the direction of movement of said conveying means.

6. In a furnace construction as set forth in claim 1, said means for producing the high velocity jet including a first aspirator through which an inert atmosphere is directed, and a second aspirator communicating directly with the discharge end of said first aspirator and using the discharge therefrom as its motive force.

7. In a furnace construction as set forth in claim 6, both of said aspirators having a low pressure inlet that communicates with the vestibule area for withdrawing the atmosphere circulating therein into said aspirators for discharge exteriorly of said vestibule area.

8. In a furnace construction as set forth in claim 7, a plurality of flexible curtains being located in said vestibule area in spaced relation and defining barrier chambers.

9. In a furnace construction as set forth in claim 7, said means for directing the inert atmosphere at low velocity into said vestibule area including a tubular element having a plurality of openings formed therein, the longitudinal axis of said tubular element being disposed in perpendicular relation to the direction of travel of said conveying means.

References Cited UNITED STATES PATENTS 1,725,129 8/1929 Carpenter et al. 26350 2,200,619 5/1940 Fallon 2636 2,253,897 8/1941 Doderer 2636 3,086,764; 4/ 1963* Beck 26 3--8 JOHN J. CAMBY, Primary Examiner U.S. Cl. X.R.

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