US2529155A

US2529155A - Method of and means for removing contamingation from an atmosphere controlled furnace

Info

Publication number: US2529155A
Application number: US661026A
Authority: US
Inventors: Walter C Hasselhorn
Original assignee: Cook Electric Co
Current assignee: Cook Electric Co
Priority date: 1946-04-10
Filing date: 1946-04-10
Publication date: 1950-11-07
Anticipated expiration: 1967-11-07

Description

0v. 1950 W. o. HASSELHQRN METHOD OF AND MEANS FOR REMOVING CONTAMINATION FROM AN ATMOSPHERE CONTROLLED FURNACE Filed April 10, 1945 INVENTOR. M 0

Patented Nov. 7, 1 950 IVEETHQD OF AND MEANS FOR REMOVING CONTAMINA'TIUN FROM AN ATMUSPHERE CONTROLLED FURNACE Walter C. Hasselhorn, Chicago, 111;, assignor to Cook Electric Company, Chicago, 111., a corporation of Illinois Application April 10, 1946, Serial No. 661,026

11 Glaims.

This invention relates to controlled atmosphere furnaces and to means and processes for decontaminating the atmosphere of a controlled atmosphere furnace.

Furnaces for treating articles whether such articles are of a metallic or non-metallic character frequently necessitate the use of an atmosphere other than air within the treating furnace, nitrogen and hydrogen bein common examples of such furnace atmospheres. These furnace atmospheres are subject to contamination by air including water vapor entering from the exterior through seepage as well as through doors which are opened to insert articles into or remove articles from the furnace. The furnace atmospheres are also subject to contamination resulting from the treatment of articles passing through the furnace. Such contamination may include the presence of particles of solid matter resulting from certain brazing operations such as brass brazing, and the presence of deleterious gases such, for example, as the various fluorides and sulphurous gases. Even where the furnace atmosphere is air, it is usually desirable to maintain a certain degree of purity or freedom from the presence of water vapor, solid particles and deleterious gases formed as described for other furnace atmospheres. In treating furnace gases to remove the undesired contamination,- the furnace gases or atmospheres are circulated through a closed system including different components of apparatus to remove the various components of contamination. In order for the work produced by the furnaces to be an acceptable character, it is of prime importance that the various impurities be removed from the furnace atmosphere and further, itis frequentlyneces sary that the contamination be removed at its. source so as to prevent its spreading throughout the furnace.

An example of this situation is the removal of moisture or water vapor from the nitrogen atmosphere of a furnace treating ceramic articles, ceramic articles usually being treated in a cycle including a heating phase followed by acocling Ill) 12 relatively large. One satisfactory method of preventing air from entering is to use a fire curtain at each door whenever that door is opened. That is, a source of fuel, preferably a gaseous fuel such as natural gas is provided adjacent the lower edge of the furnace door. The natural gas may be supplied through a conduit having a large number ofrelatively closely spaced holes. Then, when the furnace door is about to be opened the gas is turned on, flows through the 'at the exit from the cooling end of the furnace Where the furnace temperature is apt to be low enough to effect condensation of the water vapor formed. The presence of water vapor or moisture in the cooling phase of treating ceramic articles results in undesirable qualities, and accordingly, it is a further object of the invention to provide an improved system for removing Water vapor from the furnace atmosph re and for preventing Water vapor from entering'and permeating the furnace chamber.

It is a further object of the invention to provide improved furnace apparatus of the character indicated to remove water vapor from the furnace atmosphere.

It is a further object of the invention to provide improved furnace apparatus of the character indicated to remove fine particles and deleterious gases from the furnace atmosphere.

I It is a further object of the invention to provide an improved system for removing cohtamination from the atmosphere of a controlled atmosphere furnace.

It is a further object of the invention to provide an improved process for removing the contaminatio-n fromthe atmosphere of a controlled and atmosphere furnace.

In carrying out the invention in one form, a conditioning system for conditioning the atmosphere within a furnace is provided comprising an atmosphere conditioning unit, first conduit means leading from the furnace from positions adjacent the points of greatest atmosphere contamination to' the conditioning unit for removing the contaminated atmosphere from the furnace, second conduit means leading from the conditioning unit to the furnace at a position relatively remote from the position of the first conduit means for returning conditioned atmosphere to the furnace, and means for circulating the furnace atmosphere in series through the furnace, the first conduit means, the conditioning unit, and the second conduit means.

For a more complete understanding of the invention reference should now be had to the accompanying drawing in which:

Figure 1 is a, schematic representation of furnace apparatus and a decontaminating system embodying the invention; I

Fig. 2 is a fragmentary view of the apparatus of Fig. 1 in one stage of operation; Fig. 3 is a view taken substantially along lines 3-3 of Fig. 2; and

Fig. 4 is a fragmentary diagrammatic represeng tation of a modification of the invention.

Referring more particularly to the drawing, the invention is shown embodied in furnace,decon taminating, and atmosphere generating apparatus including a furnace I0, an atmosphere generator l l, and decontaminating apparatusincluding the water vapor or moisture remover 52, the solid particle remover or precipitator l3 and the deleterious gas remover or absorber I4 connected in a complete cycle.

The atmosphere generator II is shown schematically and may comprise anywell known generator for forming the desired gaseous atmosphere of substantial purity. In the present application the invention will be described with reference to a gaseous atmosphere of nitrogen which is formed in the generator H, but it will be understood that any other gaseous atmosphere which may be desired may be generated without departing from the spirit and scope of the invention. The nitrogen gas is supplied to the furnace l8 through a conduit I5 extending from the generator H and is also supplied to the water vapor remover l2 through a conduit The furnace atmosphere is removed from the furnace through a conduit l1 and is directed into the water vapor remover along with the nitrogen from conduit [6 through a conduit I8, and after passing through the water vapor remover l2 it passes through a conduit I9 into the precipitator l3, which removes solid particles from the circulating gases after the water vapor has been removed, a pump 2! being arranged between water vapor remover I2 and precipitator l3 in order 4 to effect circulation of the gases. The precipitator i3 is connected to the absorber I4 through a conduit the absorber I4 being adapted to remove unwanted gasesfr-om the circulating furnace atmosphere after the water vapor and the solid particles have been removed, the absorber l4 being connected to the furnace ll) through a conduit 22 for conducting the purified atmosphere back to the furnace. Thus, the atmosphere removed from the furnace is returned ing chamber.

through conduit H. and the nitrogen added through conduit It may be varied as .desired.

The furnace I0 may comprise a heating chamber or a hearth 25 and a cooling chamber 26 positioned. immediately adjoining the heating chamber so that articles to be treated pass through the furnace in the direction of the arrow A, and accordingly, hearth 25 is provided with an entrance door 2! and an exit door 28. The treated articles may pass directly from hearth 25 into cooling chamber 25, which is provided with an exit door 29, the exit door 28 from hearth 25 also serving as an entrance door to the cool- The .doors 21, 28 and 29 may be arranged to open or close in any desired fashion and are disclosed as sliding vertically to the open position, vertical frames 3|, 32 and 33 being provided above the furnace to receive the doors in their open position. While the hearth 25 and the cooling chamber 26 are arranged immediately adjoining each other, this beingthe preferred arrangement, it will be understood that these two chambers may be separated from each other, if so desired. Moreover, hearth 25 and cooling chamber 28 may be constructed in any desired manner, such for example as of refractory material, and the hearth 25 is provided with any suitable heating means, due regard being had for the furnace atmosphere being used. Thus, for example, where an explosive atmosphere such as hydrogen is used, heating means involving open flames or any exposed heating unit would necessarily be avoided. The

doors

27, 28 and 29 in their closed positions seat firmly against their respective openings in order that outward seepage of the furnace atmosphere is reduced to a minimum. i

The nitrogen gas is supplied from generator II to the hearth 25 through conduit l5, conduit l5 being connected to hearth 25 adjacent the entrance door 27 and the nitrogen gas is supplied at a pressure above atmospheric thereby causing the gas to tend to flow outwardly through door 2'! whenever this door is opened. The tendency of air to flow throughfldoor 2? is thereby lessened and articles placed within the furnace are immediately subjected to a clean atmosphere of nitrogen gas. However, even though the nitrogen is supplied adjacent the entrance of hearth 25 and at a pressureabove that of atmosphere, some air wiil tend to flow into chamber 25 along withthe articles being treated. To substantially prevent this from occurring, 2. burner 34 is arranged adjacent entranc door 21 of hearth 25 at the lower edge thereof as shown best in Figs. 1, 2 and 3, the burner comprising a conduit having a series of holes in it, along with -a valve 35 by means of which a gaseous fuel,

I such for example as natural gas, may be supplied.

thereto after decontamination, the circulation 7 taking place virtually through a, closed system,

the nitrogen being added through conduit IE to replace the furnace atmosphere which is lost during the furnace operation, such for example as when the entrance and exit doors are opened. A valve 23 and a valve 24 are arranged respectively in conduits I1 and H5 in order that the relative amounts of furnace atmosphere removed The holes in th conduit are arranged along the lower edge of the entrance to hearth 25, and, when door 21 is about. to be opened, the valve 35 is opened and the gas issuing from the openings in burner 34 is lighted. Sufiicient gas is supplied to burner 3 and sufiicient pressure is exerted on it so that the flames 30 formed by the burning gas completely cover the entrance to the furnace, thereby creating very strong convection current rising upwardly infront of the furnace. Consequently, when the door 21 is opened, the tendency of air to pass into the furplaced within hearth 25 and the door 2'! is closed, the valve 35 is closed to stop flames 30 from issuing from burner 34. If it is not desirable to supply nitrogen gas through conduit I5 to hearth 25, a valve I5 may be provided in conduit I5. At the exit end of cooling chamber 26 there is also a burner 36 arranged in a manner similar to burner 34 and constructed in a manner substantially similar thereto so that whenever the door 29 is about to be opened, gas is supplied to burner 36 and the gas is lighted to form a fire curtain adjacent the door 29 to prevent the entrance of air into chamber 26.

While the fire curtains formed at the door 27 and the door 29 when articles are being placed in or removed from the furnace substantially prevent the entrance of air into the furnace, a portion of the water vapor formed during the combustion of the natural gas is conducted past the fire curtains, and consequently, it forms a source of contamination of the furnace atmosphere. The gaseous fuel consumed by burners 34 and 36, whether natural gas or a manufactured gas, contains substantial amounts of hydrogen, which, during burning, of course forms water and in the relatively intense heat of the flames forms water vapor. The rising currents of air carry most of the water vapor upward and away, but some of it tends to escape into the furnace chambers, particularly adjacent exit door 29 of the cooling chamber where the furnac surfaces are relatively cool and some of the water vapor may condense. During th treatment of articles within the furnace, the water vapor may be harmful and other harmful products may be formed, it being these contaminations which are intended to be removed according to this invention.

In order that the water vapor within the furnace atmosphere does not hinder the operation of the precipitator I3 and the absorber I4, the furnace atmosphere is first supplied to the water vapor remover I2 during the course of treatment. Th water vapor remover I2 includes a pair of substantially similar units arranged in series, the first unit thereof comprising a container 37 which is adapted to receive the furnace atmosphere through conduit I8 and is further provided with an exit conduit 38, the water vapor in the furnace atmosphere being removed by a refrigerating or cooling unit associated with container 31. Disposed inside of container 37 there is a water vapor condensing surface 39 which may comprise the evaporator of a conventional refrigerating unit, the refrigerating fluid being supplied to the evaporator (water vapor condensing surface 39) through one of the conduits 4| and 42 from the remainder of the refrigerating unit illustrated schematically by the box 43. The condensing surface 39 may embody a series of expansible and compressible bellows flanges sealed together at their centers to form a convoluted surface having a large surface area for the volume occu-- pied, sufficient refrigerating fluid being supplied thereto and this fluid being supplied at a temperature such'that the surfac 39 is maintained at a temperature sufficient to condense water vapor coming into contact with it.

The second water vapor removing unit of water vapor remover i2 is serially arranged with the first unit and comprises a container 44 communicating with container3'l through conduit 3-8 and being provided with an exit conduit I9. Thus furnace atmosphere may pass into container 31 through conduit I8, out of container 31, and into container 44 through conduit 38,

and out'ofcontainer 44 through conduit iii, any water vapor remaining in the furnace atmosphere after having passed through the first unit being removedby a refrigerating unit associated with the container 44. Disposed inside of container 44 there is a water vapor condensing surface 46 which may be the evaporator of a conventional refrigerating unit, the refrigerating fluid being supplied to the evaporator (water vapor condensing surface 46) through one of the conduits 41 and 48 from the remainder of the refrigerator equipment indicated schematically by the box 49. Similarly to condensing surface 39, the condensing surface 46 comprises a series of expansible and compressible bellows flanges sealed together at their centers to form a convoluted surface having a large area for the volume occupied. Connecting containers 3'! and 44 at their lowest points is a conduit 53 associated with which there is a container or trap 5| adapted to receive the water vapor condensed into water by the condensing surfaces 39 and 46, a faucet 52 being connected to trap 5| to remove the Water as desired.

After the water vapor has been extracted from the furnace gases, the gases are pumped by means of pump 2| through conduit I9 into the precipitator I3 which may comprise a container 54 includinga grid, 55 arranged adjacent its entrance so that the furnace gases entering the precipitator flow past the grid, and a closely spaced series of plates 56 arranged adjacent its exit end so that the furnace gases passing out of the 'precipitator pass'in close Proximity to the plates. The grid 55 may preferably be a screen of fine wire and the plates 56 may comprise relatively large flat metallic plates electrically con nected' together and to a terminal'conductor 51, which is brought out of the container 54 through an insulator 58. Similarly the grid 55 is conne'cted to a terminal conductor 59 which is brought out of container 54 through an insulator BI. The terminal conductor 59 is connected to the positive side of a direct current voltage source, which for example may approximate 25,000 volts, and the terminal conductor '51 is connected to the negative side thereof. Solid particles resulting from'the treatment of articles in the furnace I I], such for example as flecks of zinc oxide formed during the process-of brass brazing, are removed by the precipitator I3. It is well understood that the positive grid '55 places a charge upon these solid Particles as they pass between the grid wires, and when these charged particles come within the proximity of the negatively charged plates 56,the positively charged particles are attracted thereto and settle upon the plates 56, thereby effectively removing them from the furnace atmosphere. After the plates 56 have become completely coated with particles, they may be removed and the dust particles scraped therefrom, after which the plates may be reinserted. H

After the furnace atmosphere has passed through the precipitator I3 and has had the solid particles removed therefrom, the furnace atmosphere which may still contain gaseous fluorides resulting from the flux used in brazing operations within the furnace and sulphurous gases such as sulphur dioxide, which may be formed during the combustion of the natural gas in the fire curtains, and some of which may be formed in the nitrogen generator II is conducted into absorber I4. The absorber I4 comprises a container 62 communicating with entrance conduit and exit conduit 22., Inside of container 62 a series of supports 63 are disposed, the supports being adapted to hold an absorbing material, such for example as activated charcoal or silica gel. As the furnace gases pass through the container 62, the gases in effect filter through the absorbing material which is relatively loosely. placed upon supports 63, thereby com: ing into intimate contact with the furnace gases and removing the undesirable ones, such as the sulphurous gases and the fluorides. The traces of water vapor and solid particles not removed in the units l2 and [3 may also be removed by absorption within the absorber 14, but in order to prevent the absorbing material in absorber [4 from becoming contaminated with the solid matter and the water vapor, these products are removed before the furnace gases reach the absorber. After the undesirable gases have been removed in absorber [4, the furnace atmosphere is conducted back to the cooling chamber 26 by means of the conduit 22 and the cycle is ready to repeat itself.

The furnace atmosphere is taken from the cooling chamber 26 through two conduits 64 and 65 feeding into respectively the series of bellows flanges 66 and 61, which in turn are joined to feed into the conduit I1. The series of bellows flanges 6-6 and 61 may comprise expansible and compressible members having a relatively large surf-ace area in order to cool the furnace gases a certain amount before these gases pass into the water vapor removing unit. The conduits 64 and 65 are, arranged immediately adjacent the doors 29 and 28, respectively, of the cooling chamber, while the conduit 22 feeding the furnace atmosphere back to the furnace is connected to the cooling chamber 26 between conduits 64 and 65 so as to be relativel remote from each of the removal conduits. In this manner the decontaminated or purified gas coming into chamber26 has a relatively lengthy pathway of travel before it is removed through the conduits 64 and 65.

During the use of any furnace in which a controlled atmosphere otherthan air is used and it is necessary to open and close the doors leading into and out of the furnace, outside air will tend to-enter the furnace and contaminate the furr nace atmosphere, and, 1n order to prevent such placing 'a fire curtain in front of each door whenever that door is open, thereby preventing the entrance of air into the furnace. Howevenas a result of using the fire curtain, water vapor which is'also an undesirable element of a controlled atmosphere furnace may escape into and contaminate the'furnace atmosphere. This, as has already'been explained, results from the formation of the water vapor from burning the hydrogen in the gas consumed to form the fire curtain. Particularly in the case of a-furnace treating ceramic articles, it is of prime importance-that the watervapor be removed from the furnace atmosphere so as not to come into contactwith thearticles treated. Not only is it important to remove the water vapor, but it is important that the water vapor be prevented from coming into contact-with the articles being treated, and hence, it is important that the water vapor be prevented from enteringthe furnace. .During the heating stage, or in the hearth where the temperature is very high, any water vapor present is in a highly super-heated condition and the articles being treated are at a high temperature. Consequently, water vapor present does not have any substantial deleterious effects on the articlesbeing treated. However, in the cooling chamber 26, where the articles being treated are reduced in temperature and the atmosphere therewithin is also at a reduced temperature, the water vapor present has a tendencyto come into contact with the surface of the articles being treated with resultant undesirable discolorations as well as other defects. Consequently, the removal conduit 65 is arranged immediately adjacent the door 28 so that when this door is opened and articles are pushed from chamber 25 into chamber 26, any

furnace atmosphere moving from chamber 25 into chamber 26 is extracted from chamber 25 through conduit 65 without circulating generally throughout chamber 26. Thus the water; vapor contaminated atmosphere is removed at, the source of greatest contamination. The fire curtain formed at the door 29, as already explained, results in the formation of water vapor, some, of which condenses and escapes into the furnace at rnosphere inside of chamber 26. By disposing the removal conduit 64 immediately adjacent the door 26 to extract furnace gases, the furnace atmosphere which is contaminated with water vapor is extracted through conduit 64 at the point of formation of the Water vapor.

The purified furnace atmosphere entering through conduit 22 enters at a pressure above atmospheric so that the atmosphere will flow into and diffuse throughout the chamber 26, and, in doing so, any water vapor and furnace atmosphere tending to enter chamber 26 through doors 28 and 29 are resisted from flowing throughout the chamber 26, and hence, they are easily removed through conduits 64 and 65. Removing the water vapor contaminated furnace atmosphere at the points of greatest contamination and bringing the purified furnace gases into chamber 26 at a point relatively remote from the points of extraction of the contaminated atmosphere so that the purified gases tend to prevent the spread of the water vapor within the furnace chamber results in maintaining the atmosphere within the furnace virtually completely free from the presence of Water vapor. Since the absence of water vapor is of greater importance in the cooling chamber 26 than in the heating chamber 25, the nitrogen atmosphere from conduit [6 is first passed through the water vapor removing unit l2 before entering the chamber 26, whereas the conduit l5 supplying nitrogen from generator II to the hearth 25 does not pass through the'water vapor removing unit I2 initially. However, conducting the nitrogen through conduit l5 to a point adjacent to door 2'! in hearth 25, and conducting the nitrogen at a pressure above atmospheric tends to prevent the escape of water vapor into the hearth 25 through the door 21 when the fire curtain is being used. By inserting valve [5' in conduit l5 and closing it, the gas from entrance conduit 18a and an exit conduit lSa corresponding respectively to conduits I8. and IQ of the water vapor removing unit l2. (Illustrated in Fig. 1.) Thus to connectwater vapor removing unit H into the system illustrated in Fig. 1, the entrance conduit 58a is connected to the same point as conduit i8 and the exit conduit |9a is connected to the same point as conduit I9.

However, the pump 72 for circulating the furnace I atmosphere in the embodiment shown in Fig. 4 precedes the water vapor removing unit rather than succeeding it as does the pump 2! in Fig. l.

The Water vapor removing unit ll also comprises a pair of units connected in a series, but the first one is a pro-cooling unit and reduces the temperature of the hot furnace gases to a lower temperature which may approximate room temperature, for example, but which is still above the water vapor condensation point, and the second unit is associated with a refrigerating system which maintains a sufiiciently low temperature and has sufficient capacity to condense the water vapor carried by the furnace gases. The pro-cooling unit comprises a container 73 having an entrance conduit i l and an exit conduit 15. Arranged inside of container i3 there is a series of compressible and expansible bellows flanges connected together to form a convoluted surface 11 having a large surface area. The furnace gases enter from conduit l8a through pump 12 and conduit 76 into the inside of the pro-cooling surface Ti, and out through conduit 18 into the water vapor removing unit. To 0001 the furnace gases that are flowing inside of the pre-cooling surface ll, cooling water is circulated through the container 73 outside of surface H, the cooling water entering through conduit is and passing out through conduit l5.

The water vapor removing unit comprises a container 19 arranged inside of which there is a water vapor condensing surface 8! comprising a series of expansible and compressible bellows flanges connected together to form a surface having a large surface area for the volume occupied. Also arranged inside of container 19 and surrounding the water vapor removing surface 8!, there is a series of coils 82 constituting the evaporator of a refrigerating system. The space inside of container 19 is filled with heat transfer fluid such for example as ethylene glycol with a small amount of an inhibitor such for example as dibutyl amine phosphate. The furnace atmosphere enters the inside of water vapor removing surface 8| through conduit i8 and passes out through the conduit Isa, the condensed water vapor running down into a trap 83 from which it may be removed at any time by means of a faucet 84. The evaporator 82 cools the fluid inside of container Hi to a sufficiently low value to thereby maintain the water vapor condensing surface 8! at a suniciently low temperature to condense the water vapor from the gases circulating therethrough, the fluid providing stabilization from temperature variations. Thus the furnace gases are first cooled to a relatively low temperature in the cooling surface Ti and thereafter the water vapor is removed by condensation within the surface 8!. After removal of the water vapor, the furnace gases pass through conduit lea and into the precipitator is to continue the purifying cycle as already described.

The evaporator 82 forms part of a refrigerating system including the condenser 85 and the compressor 86. The refrigerating system func tions in the conventional manner by having the refrigerating fluid as a gas compressed by the compressor 85 and pumped through conduit El into the condenser 85 where it is condensed into a liquid. From the condenser it passes through 510 a conduit 88 into the evaporator coils 82, and after evaporation it passes through the conduit 89 to the inlet side of the compressor. The com pressor 88 is provided with a cooling jacket 9! communicating with conduit is from the container 13 so that the cooling water entering through conduit M and pro-cooling the furnace gases inside of the cooling surface 7? passes into the cooling jacket ill and 00015 the compressor after which it is exhausted through a conduit 92. While the cooling fluid entering the cooling jacket 9| from conduit 15 has been heated up by heat transfer from the furnace gases, the flow may be so regulated that it will be at a sufligiiently low temperature to cool the compressor Without further elaboration, the foregoing will so fully explain the gist of my invention that others may, by applying current knowledge, readily adapt the same for use under varying conditions of service, without eliminating certain features, which may properly be said to constitute the essential items of novelty in-- volved, which items are intended to be defined and secured to me by the following claims.

I claim:

1. In furnace apparatus including a heating chamber and cooling chamber, the cooling chamber having an entrance from the heating chamber and an exit to the atmosphere, a conditioning system for conditioning the atmosphere within said cooling chamber comprising a moisture removing unit having a cooling unit and a condensing unit serially arranged, conduit means extending from said cooling chamber from positions closely adjacent said entrance and said exit to said cooling unit, said condensing unit being maintained at a sufliciently low temperature to condense substantially all of the water vapor in the circulating furnace atmosphere, 2. particle precipitating unit adapted to receive the circulating atmosphere from said condensing unit, an impurity absorbing unit adapted to receive the circulating atmosphere from said precipitating unit, and conduit means for conducting the decontaminated atmosphere from said absorbing unit to said cooling chamber at a position relatively remote from said entrance and said exit.

2. In a furnace apparatus including a heating chamber and cooling chamber, the cooling chamber having an entrance from the heating chamber and an exit to the atmosphere, a conditioning system for conditioning the atmosphere within said cooling chamber comprising a moisture removing unit having a pro-cooling unit and a condensing unit serially arranged, said condensing unit comprising a condensing surface and a refrigerating member surrounded by a' heat transfer fluid, conduit means extending from said cooling chamber from positions closely adjacent said entrance and said exit to said cooling unit, said condensing unit being maintained at a sumciently low temperature to condense substantially all of the water vapor in the circulating furnace atmosphere, a particle precipitating unit adapted to receive the circulating atmosphere from said condensing unit, an inn purity absorbing unit adapted to receive the circulating atmosphere from said precipitating unit, and conduit means for conducting the decontaminated atmosphere from said absorbing unit to said cooling chamber at a position relatively remote from said entrance and said exit.

. 3. In furnace apparatus including a heating in the cooling chamber comprising a source of i furnace atmosphere, a moisture removing unit having a cooling unit and a condensing unit serially arranged, means for conducting atmosphere from said source to said heating chamber,

conduit means extending from said cooling chamber from positions closely adjacent said entrance and'said exit to said cooling unit, means for conducting atmosphere from said source to join said conduit means at said cooling unit, said condensing unit being maintained at a sufficiently low temperature to remove substantially all of the Water vapor in the circulating atmosphere, an electro static particle precipitator unit adapted to receive the circulating atmosphere from said condensing unit, a gaseous impurity absorbing unit adapted to receive the circulating atmosphere from said precipitating unit, and conduit means for conducting the decontaminated atmosphere from said absorbing unit to said cooling chamber at a position relatively re mote from said entrance and said exit.

4. In a controlled atmosphere furnace system including a treating chamber, a source of atmosphere, means for conditioning the furnace atmosphere and means for circulating the furnace atmosphere through said conditioning means, means for reducing the amount of contamination in such treating chamber comprising, means for removing the atmosphere from the treating chamber adjacent the point of greatest contamination and supplying it to the conditioning means, and means for supplying the atmosphere from the conditioning means to the treating chamber at a point remote from said removing means.

5. In a controlled atmosphere furnace system including a heating chamber and an adjoining cooling chamber, a source of atmosphere, means for conditioning the furnace atmosphere and means for circulating the furnace atmosphere through said conditioning means, means for reducing the amount of contamination in such cooling chamber comprising, means for removing the furnace atmosphere from the cooling chamber adjacent the point of greatest contamination and supplying it to the conditioning means, and means for supplying the atmosphere from the conditioning means to the cooling chamber at a point remote from said removing means.

6. In a controlled atmosphere furnace system including a treating chamber havingan entrance and an exit, a source of atmosphere, means for conditioning the furnace atmosphere, and means for circulating the furnace atmosphere through said conditioningmeans, means for reducing the amount of contamination in such treating chamber comprising, means closely adjacent such entrance and such exit for removing the atmosphere from such treating chamber and supplying it to the conditioning means, and means for supplying atmosphere from such conditioning means to such treating chamber at a point remote from such entrance and such exit.

7. In a controlled atmosphere furnace system including a heating chamber, an adjoining cooling chamber having an entrance and an exit, means for conditioning the furnace atmosphere, and means for circulating the furnace atmosphere through said conditioning means, means for reducing the amount of contaminationinsuch cooling chamber comprising, means for removing the furnace atmosphere for such cooling chamber closely adjacent such entrance and such exit for removing the atmosphere from such cooling chamber and supplying it to the conditioning means, and means for supplying atmosphere from such conditioning means to such cooling chamber intermediate such entrance and such exit. 1

8. In a process of maintaining a purified atmosphere Within a furnace having a heating and cooling chamber adjoining each other including the steps of generating an atmosphere, conducting a portion of such atmosphere above atmospheric pressure to adecontaminating unit, extracting the furnace atmosphere from the cooling chamber and conducting it into the decontaminating unit along with such portion of such atmosphere, purifying the combined generated atmosphere and furnace atmosphere in the decontaminating unit, and conducting the decontaminated atmosphere to the cooling chamber, the improvement comprising, supplying a portion of the atmosphere from such generating unit above atmospheric pressure to the heating chamber adjacent its entrance, extracting the atmosphere from such cooling chamber adjacent the position of maximum contamination, and conducting such decontaminated atmosphere to such cooling chamber at a position relatively remote from the position of maximum contamination.

9. In a process of maintaining a purified atmosphere Within a furnace having a heating and cooling chamber adjoining each other including the steps of generating an atmosphere, conducting a portion of such atmosphere above atmospheric pressure to a decontaminating unit, extracting the furnace atmosphere from the cooling chamber and conducting it into the decontaminating unit along with such portion of such atmosphere, purifying the combined generated atmosphere and furnace atmosphere in the decontaminating unit, and. conducting the decontaminated atmosphere to the cooling chamber, the improvement comprising, supplying a portion of the atmosphere from such generating unit above atmospheric pressure to the heating chamber adjacent its entrance, extracting the atmosphere from such cooling chamber adjacent the entrance and exit thereof, and conducting such decontaminated atmosphere to such cooling chamber at a point relatively remote from the said exit and entrance.

10. In a process of maintaining a purified atmosphere Within a furnace having a heating and cooling chamber adjoining each other including the steps of generating an atmosphere, conducting a portion of such atmosphere above atmos pheric pressure to a decontaminating unit, extracting the furnace atmosphere from the cooling chamber and conducting it into the decontaminating unit along with such portion of such atmosphere, purifying the combined generated atmosphere and furnace atmosphere in the decontaminating unit, and conducting the decontaminated atmosphere to the cooling chamber, the improvement comprising, supplying a portion of the atmosphere from such generating unit above atmospheric pressure to the heating chamber adjacent its entrance, extracting the atmos phere from such cooling chamber adjacent the entrance and exit thereof, and conducting such decontaminated atmosphere to such cooling 13 chamber at a point intermediate said entrance and exit.

11. In a process of maintaining a purified atmosphere within a furnace having a heating and cooling chamber adjoining each other including the steps of generating an atmosphere, conducting a portion of such atmosphere above atmospheric pressure to a decontaminating unit, extracting the furnace atmosphere from the cooling chamber and conducting it into the decontaminating unit along with such portion of such atmosphere, purifying the combined generated atmosphere and furnace atmosphere in the decontaminating unit, and conducting the decontaminated atmosphere to the cooling chamber, the improvement comprising, supplying a portion '01" the atmosphere from such generating unit above atmospheric pressure to the heating chamber adjacent its entrance, extracting the atmosphere from such cooling chamber at a plurality of points, and conducting such decontaminated atmosphere to such cooling chamber at a point intermediate said plurality of points.

WALTER C. HASSELHORN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Certificate of Correction Patent No. 2,529,155 November 7, 1950 WALTER C. HASSELI-IORN It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 14, list of references cited, under the heading UNITED STATES PATENTS add the following- 2,023,285 0m Dec. 3, 1935 and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Ofiice. Signed and sealed this 6th day of February, A. D. 1951.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.