US1991374A - Apparatus for heat treating material - Google Patents

Description

F. W. BROOKE APPARATUS FOR HEAT TREATING MATERIAL p AVM HA8 4%.

4 Sheets-Sheet 1 Filed Feb. 10, 1932 i-i- ,n'JF: y!

Feb. 19, 1935.

4 Sheets-Sheet 2 F. W. BROOKE APPARATUS FOR HEAT TREATING MATERIAL Filed' Feb. 10, 1932 .F I k \\\\\\\\\\\\\vm INVENTOR I I I I 4 ;W:LN\

Feb. 19, 1935.

Feb. 19, 1935. F. w. BROOKE APPARATUS FOR HEAT TREATING MATERIAL Filed Feb. 10, 19:52 4 Sheets-Sheet 3 INVENTOR Feb. 19, 1935. p w' BROOKE 1,991,374

APPARATUS FOR HEAT TREATING MATERIAL Filed Feb. 10, 1932 4 Sheets-Sheet 4 I I i I I I l I I I l I 1 '7] g 76-: l l 7&4 i l l I l :44 l. l 1 I I Patented Feb. 19, 1935 UNITED STATES PATENT OFFICE APPARATUS FOR HEAT TREATING MATERIAL Application February 10, 1932, Serial No. 592,971

3 Claims.

from oxidation and improve their physical and chemical properties.

It relates more particularly to a method and apparatus in which the material to be treated is stacked in piles at a plurality of stations and covered with shields to which a non-oxidizing gas is supplied. The heating of the material within the shields is accomplished by lowering a hood type furnace successively over the shields, the furnaces being provided with electrical resistors for heating the material. In this manner, a large proportion of the heat absorbed by the brickwork of the hood is retained and is applied to the heating of the material stacked within the next shield. The hood is provided with suitable sealing means for preventing the inflow of outside air.

The electrical resistors mounted on the inside of the hood which are used for heating the material within the shield are made of strips or rods of an alloy such as an alloy of nickel and chromium. Such alloys are adapted for a safe maximum temperature of about 1850 F. even in the presence of air without substantial oxidation and deterioration thereof. There is, however, at the present time a tendency to employ higher temperatures in order to increase the speed of the heat treatment and to produce certain physical and chemical characteristics in the material being heat treated, the temperature sometimes employed being 2000 F. or more. If such temperatures are employed while the resistors are in an oxidizing atmosphere, such as air, their life is greatly lessened. In accordance with the present invention, nonoxidizing gas, after being supplied to the material within the shield is caused to flow freely from the inside of the shield into the furnace chamber proper and to envelop the resistors so as to protect them from oxidation. The non-oxidizing gas first forces any air which may be present within the chamber proper to the outside and thereafter envelops and surrounds the resistors. In this manner, the non-oxidizing gas not only protects the material which is being heat treated, but also protects the electrical resistors, the life of which would ordinarily be greatly reduced except for the fact that they are protected by the non-oxidizing gas.

In the accompanying drawings, which illustrate several embodiments of my invention,

Figure l is a partial side elevation and partial longitudinal section through the complete apparatus showing the material to be heat treated within a shield and the shield surrounded by a heating hood having electrical resistors;

Figure 2 is a transverse section through the apparatus shown in Figure 1;

Figure 3 is a partial longitudinal section through the shield illustrating the means whereby non-oxidizing gas is fed into and circulated 10 through the shield;

Figure 4 is a horizontal section taken on the line IVIV of Figure 3;

Figure 5 is a view similar to Figure 4 showing a modification;

Figure 6 is a transverse section through a modifled form of shield, within which is a stack of sheets;

Figure '7 is a perspective view on a smaller scale of the sealing means shown in Figures 1 20 and 2 for sealing the interior of the furnace from the outside atmosphere;

Figure 8 is an enlarged detail sectional view of a portion of the furnace shown in Figure 2 illustrating the sealing means;

Figure 9 is a horizontal section through another type of shield made up of two parts, one part telescoping within the other; and

Figure 10 is a vertical section on the line X-X of Figure 9.

Referring more particularly to the accompanying drawings, the material A which is to be heat treated is shown in the form of sheets which are placed one upon another to form a stack resting on a plate 2. The plate 2 rests on 35 a bottom plate 3 which is supported on a refractory base 4. The base is supported by a suitable framework comprising I-beams 5, angle irons 6 and a bottom plate 7.

A shield, indicated generally by the reference 40 numeral 10, is placed over the stack of plates A with its bottom edge resting on the plate 3. The shield is generally rectangular in horizontal section to conform rather closely to the stack of sheets which are to be heat treated, and is pro- 45 vided with side flutes or corrugations 11, and an end flute 12 as shown in Figure 4, and flutes 13 along the top. Each shield may weigh in the neighborhood of a half ton and, although they are made of an alloy adapted to withstand high 50 temperatures, there is a tendency for them to warp as they are subjected to alternate heating and cooling during the heat treatment of each stack. The flutes take care of slight inequalities during expansion and contraction and prevent ll undue distortion of the shield. They also are employed for conducting non-oxidizing gas through the'shield, as will be described later.

Surrounding the shield is an electric furnace of the hood type which is indicated generally by the reference numeral 15. This hood has electrical resistors 16 on its inside surface which are used for heating the material A within the shield. The resistors are mounted on pedestals 17 secured by any suitable means to the inside wall 18 of the hood. The side walls of the hood have a layer 19 of a refractory heat insulating material and outside of that are other layers 20 and 21 of brickwork or masonry construction. The hood has metallic side plates 22 and top plates 23 held in place by vertical and horizontal I- beams 24 and 25 to provide a structure which can be lifted bodily and placed successively over the shields in which the material to be treated is stacked. The hood may be lifted by a crane, not shown, to which is secured a chain 26 which may be connected to a lifting frame 27, as indicated in Figure 2.

Any suitable non-oxidizing gas, for example nitrogen, hydrogen or cracked ammonia, may be used for protecting the sheets and the electrical resistors. The gas is supplied to the inside of the shield through an inlet pipe 30 extending through the base 4, as shown in Figure 3. A conduit 31 is disposed within the end flute '12 and is welded to the shield so as to make it integral therewith. The bottom of the conduit fits over the upper end of the inlet pipe 30 and the top of the conduit is curved toward the center of the shield, as indicated by the reference numeral 32, so as to direct the gas toward the stack of sheets A. The gas envelops the sheets, thereby protecting them from oxidation, and then flows through the top flutes 13 and side flutes 11 to the bottom of the stack of sheets. After reaching the bottom of the stack of sheets, the gas flows outwardly from the shield between the bottom edge thereof and the plate 3. In the embodiment shown in Figures 1, 2 and 3, the bottom edge of the shield 10 simply rests on the plate 3 and the pressureof the gas is sufficient to cause it to flow freely from under the edge of the shield into the furnace chamber proper and surround the electrical resistors. Outlet pipes 35 extend through the walls of the hood and are provided with valves 36. As shown in Figures 1 and 2, four of these outlet pipes are provided, two' adjacent each end of the furnace. As the non-oxidizing gas sweeps out from under the edge ofthe shield 10, it forces the air originally present within the hood.

through the pipes 35 and fills the entire hood chamber. As the non-oxidizing gas is first supplied to the furnace, a mixture of air and gas is discharged through the valves 36. A pilot light 37 is arranged adjacent each of the valves 36, the pilot lights acting as indicators to show when all of the air has been discharged from the furnace. Before the furnace has been supplied with nonoxidizing gas, the indicator or pilot lights 37 have a certain color, but when the air has been expelled from the interior of the furnace and nly non-oxidizing gas is issuing from the valves, the color of the flame changes. In this manner, it can be easily determined when the air has been exhausted from the furnace.

Instead of providing a conduit 31 in the form of a pipe, as illustrated in Figures 3 and 4, for conducting the non-oxidizing gas to the top of the shield, a portion of the end flute 38 into which the pipe 30 extends may be closed off by a plate 39 so as to form a conduit which leads the gas to the top of the shield.

In the embodiment thus far described, the bottom edge of the shield rests upon the plate 3 and the gas escapes at the Joint between the bottom edge of the shield and its supporting plate. This arrangement ordinarily'is suflicient for causing sufficient flow of non-oxidizing gas from the interior of the shield into the furnace chamber proper so as to protect the electrical resistors from oxidation. However, a freer flow of gas from the shield may be provided by an arrangement such as shown in Figure 6. In this embodiment, the stack of sheets 13 rests on a base plate 40 supported on a refractory base 41 in a manner generally similar to that described in connection with the arrangement shown in Figure 2. However, instead of supporting the bottom edge of the shield on the plate 40, the shield is supported from its top 42 which rests on a weight 43 placed on top of the pile of sheets. The base 41 is formed in a step 44 which is spaced from the bottom edge 45 of the shield. The side walls 46 of the shield conform rather closely to the vertical wall 47 of the base, but the side flutes 48 extend outwardly beyond the wall 47, and since they are open at the bottom, provide a free and open passage for the nonoxidizing gas from the interior of the shield into the hood chamber. The non-oxidizing gas is supplied to the shield through inlet pipes 50 and 51 and then flows through the top flutes 52 and side flutes 48 as indicated'by the arrows and escapes freely from the opening at the bottom of the side flutes.

The hood 15 is sealed from the outside atmosphere by a sand seal 55 and a liquid seal 56. A trough is formed by a channel iron 57, an angle iron 58 and the base plate 7, as shown in Figure 8, which trough is adapted to contain oil or other liquid. Extending into the liquid and forming a seal is one leg 59 of an angle iron secured to the bottom of the hood. The nonoxidizing gas which is supplied to the inside of the furnace is lighter than air and, therefore, tends to rise. It is desirable to know when the entire hood chamber is filled with non-oxidizing gas so that the resistors will be amply protected from oxidation. For this purpose. notches 60 are formed in the flange 59 so as to cause escape of the gas through the notches before it escapes at any other points along the liquid seal. Adjacent each of these notches is a pilot light 61. Escape of non-oxidizing gas through the notches is indicated by a change in color in the flame or by other simple tests. It will be seen that the non-oxidizing gas will escape through the notches before it escapes at any other points along the seal, since the head of liquid at the notches is less than at other points and, therefore, offers the least resistance to the flow of gas through the seal. It is only necessary to observe the color of the pilot light 61 in order to determine whether the non-oxidizing gas is under sufficient pressure to entirely fill the furnace chamber, since the notches 60 insure that if there is escape of gas at any point in the seal, it will be at the notches.

In Figures 9 and 10 there is illustrated another type of shield made up of a plurality of parts, one part fitting within another part and being movable relative thereto so as to compensate for contraction and expansion of the shield. The shield has two parts and 71, the part 71 fitting within the part 70. Each of the parts has a top wall 72, side walls '73 and an end wall 74. The bottom of each of the parts is open and the ends of each part opposite the end walls 74 are also open. The end 75 of part 71 is bent outwardly to form a flange 76 which contacts with the inner surface of the top and side walls of the part 70.

The end wall 74 of the part 70 is formed in a flute 7'7 corresponding to the flute 12 in Figures 1 to 4, and disposed within the flute '77 and secured to the walls thereof is a conduit 78 which corresponds to the conduit 31 shown in Figure 4. The conduit 78 is adapted to flt over an inlet pipe, not shown, which extends through the base on which the shield rests, the inlet pipe being connected to a source of non-oxidizing gas.

The non-oxidizing gas supplied to the inside of the shield through the conduit '78 flows through the joints formed by the flange '76 and the inner walls of the part 70 into the furnace chamber proper and envelops the resistors so as to protect them from oxidation. The part 71 is free to slide within the part 70 so as to compensate for contraction and expansion of the shield, thereby preventing undue warpage of the shield. The parts may be telescoped to a greater or lesser extent than shown in the drawings so as to form a shield of a size suitable for the particular material being heat treated. It is desirable to have the shield conform rather closely to the stack of material being heat treated as excessive space between the stack and the shield acts as an insulating medium which cuts down the proportion of heat transmitted to the sheets. A shield of the type described may be adjusted so as to make it conform closely to different length sheets.

A telescoping shield of the type shown in Figures 9 and 10 may be provided with flutes or passages in the side walls, top wall, or both, if desired, so as to cause the non-oxidizing gas supplied to the inside of the shield to flow more freely into the furnace chamber proper. The shield may be supported at its lower edge as shown in Figures 1, 2 and 3, or it may be suspended from its top with its lower edge hanging free and unsupported as shown in Figure 6.

In heat treating sheets or other material in accordance with the present invention, the sheets are stacked in piles at the various heat treating stations and shields are placed over them. The hood type heater is then lowered over the shield at the first station and electric current is supplied to the resistors. Non-oxidizing gas is supplied to the interior of the shield, the gas circulating through the flutes in the shield, displacing the air within the shield and flowing freely into the furnace chamber proper. The gas displaces the air within the heating hood, causing it to flow out of the pipes 35, and the resistors are enveloped by the gas so as to protect them from oxidation. When the color of the flames of the pilot lights 37 and 61 changes, this is an indication that the air within the furnace has been displaced by non-oxidizing gas, and the furnace may be raised to the desired temperature without danger of unduly oxidizing the resistors. The heating is carried out for a time necessary to properly heat treat the material within the shield, after which the electric current to the resistors is cut off and the hood is raised from around the shield and placed over the shield at the next heat treating station.

The material within the shield at the first heat treating station is allowed to cool while it is enveloped in an atmosphere of non-oxidizing gas. As the material cools, the gas within the shield contracts so that it is usually advisable to supply more gas to the inside of the shield in order to prevent inflow of air into the shield. The nonoxidizing gas is lighter than air, so that even though there is a free passage at the bottom edge of the shield, particularly when a shield of the type shown in Figure 6 is employed, the gas tends to remain within the shield and no great amount of gas is lost. After the material has been cooled to a temperature such that it will not oxidize materially in air, the shield is removed and the sheets are separated from each other.

By utilizing the non-oxidizing gas both for preventing oxidation of the material being heated and for enveloping the electrical resistors so as to prevent their oxidation, the heat treatment may be carried out at higher temperatures than if the resistors were subjected to the air originally present in the furnace. The present invention, therefore, enables the use of higher temperatures without substantial oxidation or deterioration of the electrical resistors than could be used according to prior practices.

I have illustrated and described several embodiments of my invention. It is to be understood that the invention may be otherwise embodied or practiced within the scope of the following claims.

I claim:

1. Heat treating apparatus, comprising a base adapted to support the work to be treated, a shield suspended by the work with its bottom edge hanging freely, a hood adapted to be lowered over the shield and seal it from the outside atmosphere, electrical resistors on the inside of the hood, and means for supplying non-oxidizing gas to the inside of the shield.

2. Heat treating apparatus, comprising a base adapted to support the work to be treated, a shield suspended from its top by the work with its bottom edge hanging freely, a hood adapted to be lowered over the shield and seal it from the outside atmosphere, electrical resistors on the inside of the hood, and means for supplying nonoxidizing gas to the inside of the shield.

3. Heat treating apparatus, comprising a base adapted to support the work to be treated, a shield suspended by the work, said shield having flutes forming passages which are open at the bottom, a hood adapted to be lowered over the shield and seal it from the outside atmosphere, electrical resistors on the inside of the hood, and means for supplying non-oxidizing gas to the inside of the shield and flowing it outwardly from the shield so as to surround and protect the electrical resistors.

FRANK W. BROOKE.

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