US3211590A

US3211590A - Method of and apparatus for annealing sheet metal

Info

Publication number: US3211590A
Application number: US217761A
Authority: US
Inventors: Frank D Hazen; Howard H Nichols
Original assignee: Hazen Engineering Co
Current assignee: Hazen Engineering Co
Priority date: 1962-08-17
Filing date: 1962-08-17
Publication date: 1965-10-12
Anticipated expiration: 1982-10-12

Description

Oct. 12, 1965 D. HAZEN EI'AL METHOD OF AND APPARATUS FOR ANNEALING SHEET METAL Filed Aug. 17, 1962 3 Sheets-Sheet 2 IN V EN TOR.

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Oct. 12, 1965 F. D. HAZEN ETAL 3 5 METHOD OF AND APPARATUS FOR ANNEALING SHEET METAL 5 Sheets-Sheet 3 Filed Aug. 17, 1962 INVENTOR.

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United States Patent O 3,211,590 METHOD OF AND APPARATUS FOR ANNEALING SHEET METAL Frank I). Hazen and Howard H. Nichols, Pittsburgh, Pa.,

assigors to Hazen Engineering Company, Pittsburgh,

Pa., a Corporation of Pennsylvania Filed Aug. 17, 1962, Ser. No. 217,761 6 Claims. '(Cl. 148-16) This invention relates to new and useful improvements in methods and apparatus for annealing steel in sheet or strip form which is coiled when heat treated by directing heated and cooled inert gases through the eye of the coils and between and around the coils at average temperatures required for annealing.

Heretofore, coiled strip was heated in so-called box annealing furnaces which consists of a base on which the coils are stacked or supported, the coils being enclosed by an inner cover supported on the base and an outer cover disposed around the inner cover of a size to provide a space between the outer and inner covers. Radiant heaters were disposed in the space between the covers whereby the heat was radiated from the heaters to the inner cover and from the inner cover to an inert gas surrounding the charge within the inner cover closure. To assist in the heat transfer from the heated inner covers circulating fans were employed in the base causing the ases to flow downward through the eye of the coil, where coils were annealed, thence through the fan and upward along the space outside of the inner cover.

By the use of the inner cover, the products of combustion from the radiant tube burners Would not come in contact with the steel enclosed by the inner cover, however, inert gases were employed within the inner cover closure to prevent oxidation of the bright surface of the metal coils or sheets.

Such prior art devices and the method of heating the steel made it difficult to obtain uniform annealing at an average temperature of 1250 F. because the radiant tubes in the space between the outer and inner covers would cause the heat to concentrate at the top and excessively heat the top coils or sheets charged in the enclosure of the inner cover. Also, such non-unifonnity of temperature required the use of an excess amount of fuel and a very long soakng period to let the temperature of the metal equalize after which the outer cover was removed and the charge allowed to cool while retained in the inert gas atmosphere within the closure.

In accordance with the present invention, these difficulties are overcome and the double cover type of box annealing furnace is eliminated. Instead, a single cover is employed to house the sheet metal and provide a hermetically sealed chamber. The radiant heaters employed within the space between the inner and outer covers are also eliminated and the metal is heated by inert gases that are heated outside of the annealing furnace by a special heating device or in any suitable manner to temperatures from 1l00 F. to 1400 F. for steel and are then circulated at a Volume of from 3000 to 7500 c.m.f. in contact with the charge in the single cover chamber. After the charge has been brought to proper annealing temperatures, the inert gases are wthdrawn from the annealing chamber and circulated through a cooling device from which the gases are again circulated through the annealing chamber to effect rapid cooling of the annealed metal while retaining the inert gas atmosphere.

The invention will become more apparent from a con sideration of the accompanying drawing constituting a part hereof in which like reference characters designate like parts and in which:

Patented Oct. 12, 1965 FIGURE 1 is a vertical cross-sectional View partially in elevation, of a box annealing furnace embodying the principles of this invention;

FIGURE 2 is a vertical cross-sectional view of a heater for heating inert gases to uniform annealing temperatures for circulation through the coils in the annealing apparatus of FIGURE l;

FIGURE 3 is a vertical cross-sectional view, partially in elevation, of a cooling device through which the inert gases are circulated from the annealing chamber of FIG- URE 1 to cool the same for recirculation through the annealing chamber; and

FIGURE 4 is a schematic diagram illustrating the steps of the heating and cooling cycles in thhe heat treating process.

With reference to FIGURE 1, the numeral 1 is a base of refractory material, such as refractory brick, on which is mounted a supporting annulus 2 having air flow passages 3 with a base plate 4 for supporting coils of strip or sheet designated by the

numerals

5, 6 and 7, the coils being separated by

convector plates

8 and 9 and crowned by a cover plate 10. The convector plates 9 are provided with circulating Slots 11 with openings 12 for a purpose to be hereinafter explained. When the coils are charged, as shown in FIGURE 1, a cover 13 having lugs 14 for receiving crane hooks in the eyelets 15, is lowered on a seal 16 to hermetically seal the chamber in which the coils are charged. The cover has a sheet metal inner lining 17 and a refractory body portion 18 to retard heat loss by radiaton.

Again with reference to FIGURE 1, the base 1 is provided with an opening 19 in which is disposed a pipe 20 having an injector type nozzle 21 from which inert gases are directed to the interior of the annealing chamber `and recirculated from the bottom of the annular space, as shown by arrows. An exit flow passage 22 leading to a pipe 23 outside of the annealing chamber is provided to rernove the inert gases from the annealing chamber. A pipe 24 having a valve 25 is connected to a purge and atmosphere gas makeup to supply inert gas to the annealing chamber as will be hereinafter explained. A pipe 26 having a valve 2661 communicates with the annealing chamber, as shown, and with a flame detector, generally designated by the numeral 27 having a pilot burner 28 with a valve 29. The pilot light will cause a bleeder flarne designated by the numeral 30 to light when the atmosphere purged from the annealing chamber is combustible, which indicates that the annealing chamber is free from an oxidizing atmosphere.

The inlet gas pipe 20 is connected to a manifold 31 of a gas heating device generally designated by the numeral 32, FIGURE 2. The outlet pipe 23 of the annealing chamber of FIGURE 1 is shown connected to the heater 32 of FIGURE 2. Disposed within the heating unit is a radiant tube heater generally designated by the numeral 33 connected to a source of air supplied through a tube 34 and to a gas line 35 'controlled by valve 36. A pilot burner 37 connected to the fuel line 35 directs the fiame into the combustion chamber 38 of the radiant tube burner and a mixture of gas and air is burned within the combustion chamber which is housed in a tubular housing 39 from which the products of combustion are withdrawn by a pipe 40. A shroud 41 having a flange 42 is supported on a partition 43 below the outlet pipe 23 of the annealing chamber, the shroud 41 having an open end 44 and is open at the top so that gases flowing Any number of radiant heating tubes, as shown in FIG- URE 2, may be employed to heat the inert gases needed for annealing the metal charged in the chamber and the manner of connecting them to inlet and outlet manifolds will be readily understood by those skilled in the art.

The cooling device shown in FIGURE 3 of the drawings, consists of a housing 50 supported by buckstays 51 in which are disposed a series of tubes 52. At the top of the housing 50 a header box 53 is mounted, which header box is provided with an inlet pipe 54 that has valved connection with the outlet pipe 23 of the annealing chamber of FIGURE 1. A manifold 55 is provided with a valve connection to the gas inlet pipe 20 of the annealing chamber of FIGURE 1 so that gases flowing from the annealing chamber of FIGURE 1 through the pipe 23 pass into the chamber 56 of the header box 53 from which they pass through the space between the shroud tubing 52 and a tube 57 which is closed at its bottom end, as shown at 58, and open at the top in communication with a chamber 59 of the header box 53. The chamber 59 is connected to a vent 60 disposed within the tube 57. An inner tube 58a, which is open at the bottom end, opens into a top chamber 61 that is connected by a pipe 62 to a fan or blower for delivering cold air into the chamber 61 which passes downward through the tubes 58 and around the space between the tubes 57 and 58a and thence to the atmosphere through pipe 60. Any desi-red Volume of cold air may thus be blown into the Suspended tubes 58a of the cooling device and the hot gases ente-ring chamber 56 through the inlet 54 pass through the passage between the shroud tube 52 and the tube 57, as shown by arrows, and thence out through the manifold 55 to the annealing chamber of FIGURE 1. In this way, hot gases brought in from the pipe 54 pass down through the cooling tubes and out of gas pipe 20 and nozzle 21 to the annealing chamber.

The heating and cooling cycle of the annealing process in relation to the apparatus for carrying it out will now be described in connection with the several figures of the drawing, including the schematic diagram of FIGURE 4.

The col is placed on the base plate 4 and a convector plate 8 is placed on the top of this col, as shown. The col 6, with another convector plate 9, is then stacked on top of coil 5 and a col 7 with a convector plate is placed on the convector plate 9 of the col 6. So much of the handling of the coils is standard practice with the exception that the top convector plate 10- may have its center closed to function as a cover whereas the

convector plates

8 and 9 have open centers 12 of a dimension corresponding substantially to the center hole or eye of the coils. With the coils and their convector plates stacked in place, as shown i-n FIGURE l, the pressure tight cover or hood 13 is placed over the stack and the inside diameter of the hood will be approximately 4 inches larger than the largest col to be annealed, leaving a space between the hood and the outer surface of the col. The hood structure is mounted on the pressure tight seal 16 and is of a Construction of sufl iciently heavy materials to Withstand from 16 to 18 inches of mercury vacuum.

With the hood in place, the next step is to evacuate the space under the hood and voids in the metal coils to approximately 14 inches of mercury by the use of a vacuum pump designated by the numeral 65, FIGURE 4 of the drawing, which diagrammatically shows four annealing chambers such as the chamber of FIGURE 1, which are designated by the reference character F. Greater vacuums may be used if the cover and seals are of suitable Construction. The evacuation of the annealing chamber 'of FIGURE 1 may be controlled by a timer 66 to close valve 79 and shut ofi the vacuum and open an inlet valve 67 to an atmosphere makeup source of gas which may be designated by the numeral 68. The gas suitable to maintain an inert non-oxidizing atmosphere may be hyd rogen and nitrogen mixtures or a mixture of from 75 to 85% nitrogen and hydrogen with carbon monoxide and carbon dioxide with methane. This gas enters the space beneath the cover and fills the coil voids as well as the space around the coils and when the charge has reached positive pressure, the pressure switch 74 will open the bleeder valve 26a from the line 26, FIGURE l, permitting the inert gases and air to escape. This valve will remain open with the pu rged gas continuing to flow until the atmosphere gas leaving the bleeder will maintain a constant flame 30, FIGURE l, at which time the bleeder valve 26a is partially closed to permit only small quantities of atmosphere gas to bleed and be burned.

Upon completion of the purge, hot inert gases from the heating unit of FIGURE 2, which is designated by the reference numeral 32, FIGURE 4 of the drawing, will be introduced through valves 70 to the nozzle 21, FIG- URES 1 and 4, at the bottom of the stack ofcoils and will pass upward through the eye of the coils between the convector plates into the spaces between the convolutions of the coil and then downward along the space between the cover and the coils and pass out through the pipe 23 back to the heater 32 of FIGURE 2, the exit flow being controlled by valve 70a. The flow of the hot gases is designated by arrows in FIGURE 1 of the drawing. The inert gases are heated in the heaters 32 to suitable annealing temperatures which may be as low as 1000 F. to Stress relieve rather than recrystalize certain specialty steels and they may be as high as 2000 F. on other specialties. The normal range of temperatures for steel will be in the neighborhood of from 1100 to about 1400 F.

It will be noted that the nozzle 21 is an injector type nozzle through which the hot inert gases are delivered under pressure at a rate of appr oximately 3000 cubic feet per minute. As the gases pass through the eye of the coils, they will go through the

convector plates

8, 9 and the cover plate 10 from which they pass outwa rd to the space between the coil and hood 13, as shown by arrows in FIGURE 1. Some of the gases will, of course, pass between the convolutions of the coil, but whether they do or not, the pressure is dissipated so that when the gases pass downward through the annular space between the coil and hood, the pressure is greatly reduced to be slightly above atmospheric pressure as it is returned for recirculation to the injector nozzle 21. This drop in pressure insures minimum loss of the inert gases through the seal 16.

After the coils have been annealed for a predetermined period of time, the inlet and outlet valves 70 and 70a will close and valves 71 and 71:: will open to permit the inert atmosphere to flow from the inside of the box annealing chamber to the cooling device 50 of FIGURE 3, where the gases will be circulated from the cooling unit upward through the eye of the coil and down through the annular space outside of the coil and inside the cover in the same manner as the hot gases were circulated to cause a rapid cooling of the coils to a temperature of about 300 F. after which the hoods may be removed.

From the foregoing description, it is obvious that the steel in the box annealing furnace will be subject to a uniform temperature throughout, thus improving the quality. The Volume of the hot inert gases delivered through the nozzle 21 will be approximately 3000 c.f.m. and as shown by the frusto-conical shape of the ejector nozzle, the inert atmosphere is recirculated so that the total Volume circulated will be as much as 7500 cubic feet per minute. This causes a very rapid heating of the coils and also a very rapid cooling so that the total time of annealing will be a fraction of the time of conventional box annealing furnace annealing. It is estimated that annealing by the method herein disclosed will require approximately 26 hours while the time consumed by present-day practices is approximately 60 hours.

As 'shown in FIGURE 4, a valve 72 is connected in the line leading to the cooling device which is designated by the numeral 50 and a fan 73 is provided to circulate the gases from the annealing chamber through the cooler.

A fan 75 is employed to force cold air through the cooling unit 50 at suflicient Volume velocty to cool the inert gases circulated through the cooler at a high rate.

A fan 76 is provided in the line between the annealing chamber of FIGURE 1 and the heating unit of FIGURE 2 to control the rate of circulation of the inert gases between the annealing chamber and the heating unit. A pushbutton control 78 may be employed and the system can be operated automatically by the use of timers 66 and 77.

In operation, the fan 76 will circulate a constant volume of constant temperature gases into the eye of the coils under pressure and the time required to anneal a given size coil can be predetermned and when the annealing cycle is completed, the cooling system will be connected to circulate the inert gases from the annealing chamber to the cooler 50. The cooling rates will be adjusted to suit metallurgical requirements of the material being annealed, such adjustment being etected through the Valve 72 which will control the quantity of cold gases being circulated to permit the cooling rate to be slower or more rapid as required.

It is evident from the foregoing description of this invention that various modifications may be made in the details of Construction and operation without departing from the principles herein set forth. For example, while there are four box annealing furnaces designated by the character F shown in FIGURE 4 of the drawing, it is evident that the same bleeding, purging, heating and cooling units may be employed on more or less of such furnaces.

We claim:

1. In the method of annealing a coil of sheet metal supported on an annular base having a central opening for alignment with the eye of the coil and a cover constituting a closure for said coil spaced from the side and top of the coil to form an annealing chamber having inlet and outlet connections with a heating and cooling device for a gaseous treating medium, the steps of:

(a) displacing the oxygen laden atmosphere of the annealing chamber by an inert gas until the charge has reached positive pressure,

(b) passing said inert gas through a heater to heat the gas to a desired annealing temperature for the metal being treated,

(c) njecting the heated gas under pressure into the eye of the coil to cause it to flow upward through the center of the coil and around the coil and recirculate with the incoming heated gas until the temperature of the metal in the coil is equalized, and,

(d) replacing the heated gases in the annealing chamber with a cooled inert gas for crculation through the eye of the coil and between the coil and cover to rapidly cool the coil.

2. The method as set forth in claim 1 in which a plurality of coils are stacked in superposed relaton with convector plates therebetween through which the circulating gases pass from the eye of the coils to the space between the coil and cover and between the convolutions of the coil and whereby the pressure of the gases entering the eye of the coils is dissipated.

3. The method of annealing coils as set forth in claim 1 in which the annealing chamber is evacuated before the inert gases are admitted.

4. The method of annealing coils as set forth in claim 1 in which the inert gases are injected into the eye of the coil at a Volume of approximately 3000 c.f.m. and the total Volume circulated, including the recrculated gases, Will be approximately 7500 c.f.m. to cause rapid heating of the coils.

5. The method of annealing coils as set forth in claim 1 in which the inert gases heated will be from 1100 to 1400 F. for steel.

6. Apparatus for annealing strip and sheet metal coils by direct contact of the treating medium with the metal comprising, in combination, a base for supporting the coils having a central opening for the eye of a coil and radial flow passages, a cover supported on said base and spaced from the coils to form an annular flow passage around the coil, an injector nozzle extendng through the base into the eye of the coils, apparatus for heating the gases and for delivering them under pressure to the injector nozzle for circulation through the eye of the coil and around the coil at reduced pressure, the Volume flow of the gases and velocty thereof being such as to recirculate the gases from the outside of the coil to the eye of the coil along with the fresh gases entering the coil until the temperature of the metal of the coils is equalized, said base having an inlet connection for inert gases, a bleeder outlet for determining the characterstcs of the gases circulating in the annealing chamber and an outlet connection for the means for heating the gases and for cooling said gases.

References Cited by the Examiner UNITED STATES PATENTS 1,453,411 5/23 Smail 148-16 1,938,306 12/33 Webb 266-5 2,432,239 12/47 Hoak 266--5 2,479,102 8/49 Dailey 266-5 2,495,561 1/50 Wilson 148-16.7 2,638,426 5/53 Brace 148--16.7 2,809,140 10/57 Smeaton 148 13.1 3,012,591 12/61 McCormack et al. 148-16 3,109,877 11/63 Wilson 148-16 OTHER REFERENCES Metals Handbook (1948 edition), published by the A.S.M., pages 257-8 and 294 relied on.

DAVID L. RECK, Pr'mary Exam'ner.

Claims

1. IN THE METHOD OF ANNEALING A COIL OF SHEET METAL SUPPORTED ON AN ANNULAR BASE HAVING A CENTRAL OPENING FOR ALIGNMENT WITH THE EYE OF THE COIL AND A COVER CONSTITUTING A CLOSURE FOR SAID COIL SPACED FROM THE SIDE AND TOP OF THE COIL TO FORM AN ANNEALING CHAMBER HAVING INLET AND OUTLET CONNECTIONS WITH A HEATING AND COOLING DEVICE FOR A GASEOUS TREATING MEDIUM, THE STEPS OF: (A) DISPLACING THE OXYGEN LADEN ATMOSPHERE OF THE ANNEALING CHAMBER BY AN INERT GAS UNTIL THE CHARGE HAS REACHED POSITIVE PRESSURE, (B) PASSING SAID INERT GAS THROUGH A HEATER TO HEAT THE GAS TO A DESIRED ANNEALING TEMPERATURE FOR THE METAL BEING TREATED, (C) INJECTING THE HEATED GAS UNDER PRESSURE INTO THE EYE OF THE COIL TO CAUSE IT TO FLOW UPWARD THROUGH THE CENTER OF THE COIL AND AROUND THE COIL AND RECIRCULATE WITH THE INCOMING HEATED GAS UNTIL THE TEM-