US2023285A

US2023285A - Heat treating

Info

Publication number: US2023285A
Application number: US742132A
Authority: US
Inventors: Albert N Otis
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1934-08-30
Filing date: 1934-08-30
Publication date: 1935-12-03
Anticipated expiration: 1952-12-03

Description

Dec. 3, 1935. A 0115 2,023,285

HEAT TREATING Filed Aug. 50, 1954 2 Sheets-Sheet 1 Inventor: Abert N. Otis,

Attorney Dec. 3, 1935. A. N. OTIS 2,023,285

HEAT TREATING Filed Aug. 30, 1954 2 Sheets-Sheet 2 hnven for": AHoert N. Otis,

His Attorneg.

dem all de-i Patented Dec. 3, 1935 UNITED STATES PATENT OFFICE HEAT TREATlN G New York Application August 30,

8 Claims.

My invention relates in general to the art of heat treating and especially to those processes wherein the material being heat treated passes through a heating chamber in a continuous man ner. More particularly it relates to the cooling of the hot material leaving the heating chamber before it is exposed to the outside air, for example the cooling of sheet or strip steel in annealing and normalizing processes.

In the continuous annealing of sheet metal, such as bright sheet steel, if the surface of the sheet is to remain unchanged in the process, the heating and subsequent cooling must be carried out with the sheet surrounded by a protective atmosphere. Before the sheet may be safely exposed to the outside air, its temperature must be reduced from that of the annealing furnace which, for example, may be about 1400 F. to the non-oxidizing temperature of the sheet, which may be about 300 or 350 F. If the cooling of the sheet through such a range is dependent merely upon the heat lost by radiation to the walls of the cooling chamber or by natural convection currents set up in the chamber, a very long cooling chamber, requiring considerable floor space, would be required since the sheet must move at the same rate through the cooling chamber as through the heating chamber.

Whereas in normalizing, the heat treatment is carried'on at a temperature considerably higher than that used in ordinary annealing, for example 1700 F., the cooling range is still greater. In this treatment, moreover, for metallurgical reasons, the rate of cooling of the sheet becomes a very important consideration, for it is well known that the type of grain structure, particularly in the case of sheet steel, is dependent upon the rate of cooling of the steel after it has been raised to the normalizing temperature. For example a very rapid cooling of the steel from a normalizing temperature of approximately 1700 F., results in a very fine grained structure. Such a structure while desirable for some uses may make too hard and too stiff a sheet for other uses. If, however, the sheet is cooled at a less rapid rate, a structure, having a. less fine grain is obtained, which results in a sheet which is less stiff and, for most products has more desirable working properties. By a still slower rate of cooling a still larger grain structure is obtained which, while well adapted for deep drawing operations, may be so coarse that the sheet is unsuitable for use where a highly finished product 'is required, since after setere forming of the sheet, the coarse grain of the structure may give 1934, Serial No. 742,132

a rough appearance to the surface, particularly at sharp bends. The subsequent treatment and the use to which the sheet is to be put, therefore, governs to a. large extent the rate at which the sheet should be cooled upon emerging from the 5 heating chamber.

One object of my invention is the provision of an improved method and means for continuously cooling the hot material passing out of the heating chamber. Another object is the provision of an improved method and means for controlling the rate of cooling of such material in order to obtain desired characteristics thereof.

My invention will be better understood from the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

Referring to the drawings, Fig. 1 is a longitudinal sectional view illustrating one embodiment of my invention; Fig. 2 is a cross sectional view taken on line 2-2 of Fig. 1; Fig. 3 is a cross sectional view taken on line 3-3 of Fig. 1; Fig. 4 is a detail of the cooling means drawn to a larger scale; and Fig. 5 illustrates a modification.

In the drawing l is a furnace which is particularly adapted for annealing or for normalizing metal depending upon the temperature at which the metal is raised therein. The heating portion of the furnace is shown comprising the outer metal casing supported in an elevated position on the structural steel framework 3. Within the casing 2 is a layer of heat insulating material 4 and within that layer is the lining 5 of suitable heat refractory material providing the heating chamber 6. For heating the chamber 6 and the material to be heated therein, I have shown a number of electric heating units 8 arranged adjacent to the roof of the chamber and other electric heating units 9 arranged adjacent to the bottom of the chamber.

In that embodiment of my invention which I have illustrated, the material being annealed or normalized is shown as a continuous strip l0, such as steel, supported in the heating chamber on a plurality of driven rollers H which as best seen in Pig. 2 are supported in bearings l2 arranged outside of the casing 2 thereby better to protect the bearings from the heat of the furnace. The rollers H are each provided with a sprocket l3 which sprockets are engaged by a suitable chain belt drivenin any suitable manner not illustrated.

If desired the material may be carried on a suitable conveyor such as an endless belt of woven wire supported on the rollers or .by other suitable means.

his M a ing chamber to be described later.

The furnace at that end at which the strip I0 enters is provided with a suitable seal represented at I5 but at the outlet end of the chamber the strip merely passes through a small opening in the wall, there being no need of a seal at this end since the strip passes directly into the cool- The heating chamber 8 of the furnace is shown provided with the intake pipe l6 through which a suitable gas, such as hydrogen or burned illuminating gas, may be supplied to provide a protective atmosphere within the furnace. It will be understood that the strip 10 to be annealed or to be normalized in the furnace will be moved therethrough at a uniform speed, the temperature in the heating chamber and the speed of the strip being so regulated that the strip will be brought to the proper temperature while it is passing through.

Adjoining the outlet end of the heating chamher is the cooling chamber 20 through which the strip passes from the heating chamber and in which it is cooled the desired amount and at the desired rate before passing to the outside air. Cooling chamber 20 is shown as comprising a long metal enclosing structure secured at one end to the heating chamber and supported by the structural steel frame-work 2| similar to that sup porting the heating chamber. The strip is supported within the cooling chamber on a plurality of rollers 22 which are similar to rollers H in the heating chamber and which are mounted in bearings supported in lateral extensions 23 on the chamber 20. These rollers also are provided with sprockets 24 arranged to be engaged by a chain drive which may be the'same as that driving the rollers in the heating chamber. At the outlet end of cooling chamber 20 is a seal 25 which may be similar to the seal l5 at the entrance end of the heating chamber.

For the purpose of cooling the strip in the cooling chamber, I have rovided the latter with two series of transverse pzpes, or ducts, the pipes 26 of one series being arranged above and adjacent to the strip and the pipes 21 of the other series being arranged below and adjacent to the strip. If desired, however, one series may be omitted in whole or in part. Each of the p pes 26 and 21 is provided with a suitable opening or nozzle 28, see Fig. 4, on that side of the pipe next to the strip through which a jet or blast of cooling gas is directed toward the strip. The nozzle 28 in each pipe preferably is in the form of,a longitudinal slit cut in the pipe but if desired each pipe may instead be provided with a row of holes extending longitudinally thereof and facing the strip, or otherwise arranged to meet specific requirements.

A protective gas which may be the same gas as that supplied to the heating chamber of the furnace is supplied to the

pipes

26 and 2! through the supply pipes 29 each of which connects witi! the supply header 30 through a separate hand operated regulating valve 3|. The header 30 preferably increases in size in the direction opposite to the flow of gas therethrough for the purpose of compensating for the loss of pressure head therein, due to friction, the header being represented as having three different diameters in the course of its length whereby the cooling chamber may be considered as comprising three corresponding sections. Gas is withdrawn from the cooling chamber by means of the pipes 32 which unite and lead to the cooler 33, shown as provided with the water connections 33, from which the gas is drawn by the blower 34. The

outlet end of the blower connects through pipe 35 with the header 3D. The blower 34 may be driven by any suitable means, such as the electric motor 36, and the cooler may be of any conventional design, such as a stack of tubes. through which water flows, the gas to be cooled being drawn over the external surfaces of and between the tubes.

The valves 3| individually controlling the pipes 26 and 21 may be manipulated to produce various results, namely, the coolzng blasts from the nozzles may be regulated in such a manner that the strip is cooled at a un.form rate from the time that it enters the cooling chamber until it leaves the same, at which time it is sufficiently cool to be safely delivered into the open air without danger of oxidation of its surface; or by a wider opening of the valves controlling the blasts at the entrance end of the cooling chamber the strip may be given a very rapid cooling immediately upon entering the cooling chamber to produce a fine gram structure, the further cooling of the strip through the chamber gradually tapering off to the end thereof. On the other hand. the blasts may be regulated to produce a relatively slow init al cooling of the strip followed by a more rapid or sudden cooling thereof. If desired the entrance end of the cooling chamber may be provided with a lining of heat insulating material such as shown at 20 and the blasts at that end cut off to further retard the initial cooling. From the above it will be seen that by regulating the separate valves 3i, considering the constant rate at which the sheet or strip is being moved through the furnace I am able to effect cooling of the strip at various rates during its passage through the cooling chamber whereby any desired struc ture may be obtained. It will be noted that such structural characteristics of the strip are obtainable with this apparatus without changing the velocity of the strip through the furnace or changing the temperature of the heating chamber.

In the modified form of my invention illustrated by Fig. 5 the nozzles are arranged to be controlled not only by the hand valves 3i bu". also by automatic means, through the tempera ture controlled valves 3'! which are arranged in series with the valves 3! in the pipes 29. As shown in Fig. 5 all of the valves 31 supplied by the last section of the header 30 have their arms 38 pivotally connected to a single bar 39 which bar connects through the lever 40 and the rod M with the worm gear segment 42. Meshing with the latter is the worm gear 43 mounted on the shaft of the reversible motor 44 which by the mechanism to be described below is caused to rotate in a forward or a reverse direction in accordance with the temperature of the strip or of that part of the cooling chamber close to the strip.

The motor 44 is shown having two series field windings 45 and 48 which produce fields of opposite polarity. For connecting one field winding or the other in circuit with the motor armature, I employ a temperature controlled galvanometer contact device including the two fixed contacts 41 and 48 connecting respectively with windings 45 and 46 and the cooperating reciprocating contact 49. The pyrometer 50, which may be a thermo-couple adjacent to the strip to be responsive to the temperature thereof in the cooling chamber. connects with the galvanometer 5i whose needle 52 in deflecting will establish contact between the reciprocating contact 49 and the stationary contact 41 and 48 dedisclosed in the patent to Edgar F. Collins- 1,287,236 dated December 10, 1918 and forms no part of my present invention. Since it is preferable to close the armature circuit of the motor 44 intermittently and for relatively short intervals I have arranged the switch 51 in that circuit with the spring 58 for opening it and the cam 59 on the shaft of the motor 54 for closing it. The

cams

53 and 58 are so arranged on the .motor shaft that simultaneous operation of the contact 49 and switch 51 occurs, the cam 53 preferably being longer than the cam 59. It will be understood that apparatus similar to that shown in Fig. may be employed in each of the other two sections of the cooling chamber, namely, the sections supplied from the two larger portions of the header 30, also that the cooling chamber may be divided into any number of such sections.

I have chosen the particular embodiments described above as illustrative of my invention and it will be apparent that various other modifications and applications to various materials may be made without departing from the spirit and scope of my invention which modifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent in the United States is:

1. The method of cooling sheet material from a heat treating temperature which comprises moving the material continuously in a cooling chamber containing a protective gas atmosphere, withdrawing gas from the chamber at a plurality of points along the path of movement of said material, cooling the gas withdrawn and blowmg the cooled gas against the face of the material at a plurality of points along the path of movement of said material.

2. The method of cooling sheet material from a heat treating temperature which comprises moving the material continuously in a cooling chamber containing a protective gas atmosphere, withdrawing gas from the chamber at a series of points distributed along the path of movement of the material, cooling the gas so withdrawn, blowing the cooled gas against the face of the moving material as a series of transverse jets and regulating the relative flow of gas in the several jets.

3. In apparatus for annealing or normalizing sheet metal, acooling chamber containing a protective gas atmosphere, means for moving the metal continuously through said chamber, and a series of nozzles spaced along the path of movement of said metal and arranged close thereto for directing blasts of gas against the face of the metal, said chamber having means by which gas is withdrawn at points distributed along th path of movement of the metal.

4. In apparatus for annealing or normalizing sheet metal, a cooling chamber containing a protective gas atmosphere, means for moving the metal continuously through said chamber, means for directing a series of cooling blasts against said metal comprising a series of pipes extend- 5 ing transversely of and close to said metal, said pipes having nozzles facing the metal, means for withdrawing the gas from said chamber, means for cooling it, means for supplying the cooled 'gas to said pipes and means for controlling the relative amounts of gas supplied to said pipes.

5. In apparatus for annealing or normalizing sheet metal, a cooling chamber containing a protective gas atmosphere, means for moving the metal continuously through said chamber, means for directing a series of cooling blasts against said metal comprising a series of pipes extending transversely of and parallel with said metal, each of said pipes having a narrow longitudinal slot therein forming a nozzle facing said metal and means for supplying cooling gas to said pipes.

6. In apparatus for annealing or normalizing sheet metal, a cooling chamber containing a protective gas atmosphere, means for moving the metal continuously through said chamber, means for directing a series of cooling blasts against said metal comprising a series of pipes extending transversely of and parallel with said metal, each of said pipes having a narrow longitudinal slot therein forming a nozzle facing said metal, means for withdrawing gas from said chamber at a plurality of points distributed along the path of movement of said metal, means for cooling the gas and means for supplying the cooled gas to said pipes.

'7. In apparatus for annealing or normalizing steel strip, a cooling chamber arranged to receive the hot strip from a heating chamber, means for supporting the strip in and for moving it uniformly through said chambers, a plurality of 40 pipes in the cooling chamber arranged transversely of and adjacent to the strip and having nozzles directed toward the strip, means including a header and a connection therewith to each pipe for supplying a protective gas to said nozzles, a hand valve in each of said connections for regulating the blasts from said nozzles individually, other valve means for controlling said blasts collectively and means responsive to the temperature of the strip in said chamber for controlling 60 said other valvemeans.

8. In apparatus for annealing or normalizing steel strip, a cooling chamber containing a protective gas atmosphere, means for supporting the strip in and for moving it through said chamber, a. plurality of pipes in the chamber arranged transversely of and adjacent to the strip and having nozzles directed toward the strip, a blower connected to withdraw gas from said chamber and to supply it to said pipes, a cooler in said connection, a hand valve arranged to control the gas supplied to each of said pipes, automatic valve means arranged to control the gas supplied to said pipes, and means responsive to the temperature of the strip in said chamber for regulating said valve means.

ALBERT N. OTIS.