US2175922A - Structure for heat treating metals - Google Patents

Description

Oct. l0, 1939. H. scoTT STRUCTURE FOR HEAT TREATING METALS Filed June 26, 1957 I WITNESSES:

INVENTOR /onfara/Sco/ Patented Oct. l0, 1939 STRUCTURE FOB HEAT TBEATING METALS Howard Scott, Forest Hills, Pa., assignor to Westinghoule Electric Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvaula Application June ze, 1937, serai No. 150,440

4 om (CL zes- 5) This invention relates to a structure for heat treating metals.

In constructing the structures for heat treating metals and particularly for annealing or normalizing metals, a large amount of brick work is employed within the air-tight metal wall which separates the furnace atmosphere of protective gas from the ambient air, The brick work is permeable to gases, being quite porous. This has heretofore been considered a serious disadvantage since the porous brick work contained or retained oxidizing gases and other impurities which contaminate the gases employed in the furnace to protect the metals during the heat treatment.

Experience has proved that in order to make c gas-tight inner lining of the annealing or normalizing chamber, it is necessary to employ metal.; of high temperature strength or impervious ceramic material. The metals having the necessary high temperature strength are, howeverl too expensive for commercial use, whereas the impervious ceramic materials are not satisfactory because they crack on repeated heating and cooling.

An object of this invention is to provide a structure for heat treating metals.

Another object of this invention is to provide a structure in which metals may be heat treated in a high purity protective atmosphere without contaminating the protective atmosphere enveloping the metals.

Other objects will become apparent from the following description. when taken in conjunction with the accompanying drawing, in which- Figure l is a view in section of an annealing furnace embodying the teachings of this invention, and

Fig. 2 is a view in section taken along the line II-II of Fig. 1.

Referring to the drawing, this invention is illustrated with reference to an annealing furnace I having an annealing chamber I2 for receiving a charge of metal, not shown, for heat treatment. The walls Il of the annealing chamber I2 may be constructed of any suitable refractory brick or, as illustrated in the drawing, of a plurality of layers of material permeable to gas in different degrees superimposed upon one another.

Since it is desired to prevent seepage of the gases normally found in the fire brick into the annealing chamber, the inner layers of brick of the wall I4 may be of material less permeable to gases than the outer layer of brick. Thus, the innermost layer of brick may be a heavy ire brick and the outer layer may be of a Suitable lightweight insulating brick which is more permeable to gases.

In a particular embodiment as illustrated in the drawing, the walls of the annealing chamber for use at high annealing temperatures may be constructed of a layer I6 of heavy re brick superimposed upon a layer IB of lightweight insulating brick of facing grade with a coating 20 of about one-eighth to one-half inch deep of a suitable glazing or high density or refractory cement that is less permeable to gas than the brick as an inner liner on the layer I6 of brick. The layer 20 of glazing or high density cement being less permeable to gases than the layers oi brick tends to prevent the gases normally retained in the brick from seeping into the annealing chamber.

In practice, the walls oi the annealing chamber are disposed in spaced relation as by means of I beams 22 or other suitable means in an outer metallic shell 24 which is substantially impervious to gases. A space 26, the purpose of which will be described hereinafter, is thus provided between the walls of the annealing chamber and the airtight metal shell or wall separating the furnace atmosphere from the atmosphere of ambient air.

In order to admit the protective gas into the annealing chamber I2 without danger of its being contaminated, an inlet 28 is so disposed as to admit the gas directly into the annealing chamber. As illustrated, the inlet 28 has a closed wall so extending through the space 26 between the walls of the annealing chamber and the metallic shell 2l that the gas cannot escape from the inlet to the space or to the brick work of the furnace. The extension of the inlet 28 inside the metallic wall 24 may be either a metallic element or, as illustrated, an extension of the glazing or high density cement of the inner layer of the annealing chamber.

In a furnace of the type employed for the continuous heat treatment of metals, as illustrated, an inlet 30 and an outlet 32 may be provided at opposite ends ofthe annealing chamber I2, to facilitate the admission and removal of a charge of metal to and from the chamber. As illustrated in Figs. 1 and 2 of the drawing, the inlet and outlet 30 and 32, respectively, may be of any suitable shape and size for accommodating the charge of metals to be heat treated. In order to limit the ilow of the protective gas out of the inlet 30 and outlet 32, or the flow of ambient air into the furnace, suitable hinged ilaps 3| and 33 may be disposed to cover the free end of inlet 30 and outlet 32, respectively. The inlet and outlet 30 and l2, respectively, may be of any suitable tubing disposed about openings in the metallic shell 24 in alignment with inlet and outlet openings 34 and 36, respectively, disposed through the walls of the annealing chamber. The inlet and outlet 30 and 32 are not sealed to the inlet and outlet 34 and 36, respectively, of the annealing chamber, but instead are in spaced relation thereto, the end of inlet 34 and outlet 36 projecting outwardly from the walls oi the annealing chamber providing a slight space between the ends of the inlets and the ends of outlets smaller than the space 24. This permits the escape of a small amount of the gas from the annealing chamber l2 through the inlet 34 and outlet 36 into the space 26 between the walls of the annealing chamber and the outer metallic shell 24, as will be explained more fully hereinafter.

In order to heat the annealing chamber to maintain a charge of metal at a predetermined temperature, any suitable means may be ernployed. As illustrated, a metallic ribbon 38 of suitable material, such as Nichrome or other material suitable for use as electrical heating elements may be disposed along the side walls of the annealing chamber and connected to a suitable source of power, not shown. rI'he heating elements may be either embedded in the walls or' the annealing chamber or exposed to the protective gases employed during the heat treatment of the metals.

In order to withdraw the gases containing the impurities normally picked up in the furnace from the furnace, a number of exhaust outlets 4i) opening into the space 26 between the walls of the annealing chamber and the outer metallic shell 2d may be suitably disposed in spaced relation about the metallic shell. These exhaust outlets may be connected through a suitable exhaust pump, not shown, to any suitable recircu lating system when it is desired to conserve and repurify the protective gases employed during the heat treatment.

In operation, the inlet 2S of the furnace structure may be connected to any suitable source oi supply of protective gas such as hydrogen, which it is desired to employ in heat treating the charge of metals. The protective gas is admitted directly into the annealing chamber l2 under a pressure slightly greater than atmospheric pressure. At the same time, the outlets 40 may be connected to a suitable recirculating system in which a pump is employed to withdraw the gases from the space between the walls of the annealing chamber and the outer metallic shell 24.

By withdrawing the gases from the space 26, the pressure in the space is reduced to a pressure lower than the pressure in the annealing chamber although preferably maintained above atmospheric pressure. Since the material of the walls of the annealing chamber is permeable to gases, the protective gas under pressure in the annealing chamber will filter through the permeable material of the walls of the annealing chamber to the space 26 of lower pressure, removing any oxidizing gases or other impurities from the porous structure of the walls of the annealing chamber. This is because the glare or inner coating on the brick of the walls of the annealing chamber contains cracks through which the gas may flow. Since the area of the cracks in the glaze or cement is small relative to the total inner wall area, the gas velocity from the chamber through the cracks to the space between the walls is high and therefore prevents the diffusion or iiltering of the impurities from l the bricks into the chamber.

At the same time, the protective gas in the annealing chamber l2 will also flow outwardly from the annealing chamber through the inlet and outlet 34 and 38, respectively, to the spaces between the 'inlets 3l and 34 and outlets 32 and 38 where it tends to ow into the space 23 of lower pressure. This ilow oi.' the protective gas through the inlet and outlet 34 and 33, respectively, to the space 26 provides a blanket of the protective gas in the inlet and outlet to prevent contamination of the protective gas in the annealing chamber by the ambient air, which otherwise may tend to seep around ilaps 3l and 33 and enter through the charge admitting and removing inlet and outlet 30 and 32, respectively.

The gases in the space 26 containing the impurities removed from the permeable material of the walls of the annealing chamber and some of the ambient air admitted through the inlet and outlet, 30 and 32, may be continuously withdrawn from the space 2B and delivered to a suitable purifier, such as a heated metal which is easily oxidized, for removing the oxygen therefrom and over heated copper for removing the sulphur. After the gases have thus been puried they may be continuously readmitted under pressure through the inlet 28 to the annealing chamber.

In annealing the metals, the flow of gases through the annealing chamber may be initiated and the chamber heated to a predetermined temperature before the charge of metals is admitted to the annealing chamber. This insures the removal of the oxidizing impurities from the brick work of the annealing chamber before the metals to be treated are placed in the annealing chamber. After the charge of metal has been subjectedfto the heat for a predetermined length of time, the charge may be cooled at any predetermined rate in the protective gases. Where desired, a cooling zone may be provided between the heated zone and the outlet from which the charge is withdrawn.

Although this invention has been described with reference to a speciilc annealing furnace, it may also be employed in normalizing metals or in the cooling structures or other structures emo ployed in heat treating metals where it is desired to envelope the metals in the protective gas during the heat treatment thereof. This invention is, therefore, not tov be restricted except insofar as is necessitated by the prior art and the scope or the appended claims.

I claim as my invention:

1. A structure for heat treating metals comprising, a charge receiving chamber having walls of material permeable to gases for receiving a charge of metal, an outer enclosing wall of material impermeable to gases disposed in spaced relation to the permeable walls of the chamber, means for admitting a protective gas directly into the chamber without contamination, means for admitting and removing a charge of metal to and from the chamber, said means comprising wall deiining members for providing a passage through the outer enclosing wall into the charge receiving chamber and having an opening therein within the confines of the outer enclosing wall for providing a direct passage of the gas from the chamber to the space between the permeable and the outer walls thereby insuring a blanket of the protective gas in the charge admitting and removing means to prevent contamination of the gas in the chamber, and means for withdrawing the gases from the space between the walls.

2. A structure for heat treating metals comprising, a charge receiving chamber having walls of refractory material permeable to gases for receiving a charge of metal, an outer enclosing wall of material impermeable to gases disposed in spaced relation to the permeable walls of the chamber, means for admitting a protective gas directly into the chamber without contamination, means for reducing the pressure in the space between the walls to insure a filtering of the gas from the chamber through the walls o! permeable material to the space between the walls, the gas iiltering through the permeable material removing impurities therefrom, each of said walls having an opening therein aligned with each other for admitting a charge of metal to the chamber, a tubular member disposed in the opening in the wall of the charge receiving chamber and projecting outwardly therefrom to a point closely adjacent but spaced from the opening in the outer wall to provide a passage between the outer wall and the chamber while providing for the direct flow of the gas from the chamber to the space having the reduced pressure between the walls thereby insuring a blanket of the protective gas in the charge admitting passage to prevent contamination of the gas in the chamber.

3. A structure for heat treating metals comprising, a chamber having walls of material permeable to gases for receiving a charge of metal, an outer wall of material impermeable to gases disposed in spaced relation to the permeable walls oi' the chamber, means for admitting a protective gas directly into the chamber without contamination, means for heating the chamber to a predetermined temperature, means for reducing the pressure in the space between the walls to insure a filtering of the gas from the chamber through the walls of permeable material to the space between the walls, the gas iiltering through the permeable material removing impurities therefrom, each of said walls having an opening therein aligned with each other for admitting a charge of metal to the chamber, means comprising a flap pivotally disposed for movement external of the outer wall to cover the opening therein to limit the flow of ambient air through the opening, a tubular member disposed in the opening in the wall of the chamber and projecting outwardly therefrom to a point closely adjacent but spaced from the opening in the outer wall to provide a passage between the outer wall and the chamber while providing for a direct flow of the gas from the chamber to the space having the reduced pressure between the walls thereby insuring a blanket of the protective gas in the charge admitting passage to prevent contamination of the gas in the chamber, the means for reducing thepressure in the space between the walls also functioning to withdraw the gases therefrom.

4. A structure for heat treating metals comprising a charge receiving chamber having walls of refractory material permeable to gases, the.

walls consisting oi a plurality of layers of refractory material comprising at least one layer of refractory brick and an inner layer of a refractory coating cement, the inner layer oi' cement being less permeable to gases than the layer of refractory brick, an outer enclosing wall of material impermeable to gases disposed in spaced relation to the permeable walls of the chamber, means for admitting a protective gas directly into the chamber without contamination, means for admitting and removing a charge of metal to and from the chamber, said means comprising wall deiining members for providing a passage through the outer enclosing wall into the charge receiving chamber and having an opening therein within the confines of the outer enclosing wall for providing a direct passage ci' the gas from the chamber to the space between the permeable and the outer walls thereby insuring a blanket of the protective gas in the charge admitting and removing means to prevent contamination ot the gas in the chamber, and means for withdrawing the gases from the space between the walls.

HOWARD SCOTT.

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