US2843712A

US2843712A - Induction heating furnace and method of heating

Info

Publication number: US2843712A
Application number: US613721A
Authority: US
Inventors: August W Lillienberg; George V Harris
Original assignee: Lindberg Engineering Co
Current assignee: Lindberg Engineering Co
Priority date: 1956-10-03
Filing date: 1956-10-03
Publication date: 1958-07-15
Anticipated expiration: 1975-07-15
Also published as: GB812206A; DE1062848B

Description

A. w. LILLIENBERG ETAL 2,843,712

INDUCTION HEATING FURNACE AND METHOD OF HEATING Filed Oct. 3. 1956 Q 2 Sheets-Sheet l INVEN TORS A TTOR/VEKS.

y 15, 1958 A. w.- LILLIENBERG ETAL 2,843,712

INDUCTION HEATING FURNACE AND METHOD OF" HEATING Filed 001;. a, 1956 r 2 Sheets-Sheet 2 ATTORNEYS.

United States Patent O INDUCTION HEATING FURNACE AND METHOD OF HEATING August W. Lillienberg, Chicago, Ill., and George V. Harris, Racine, Wis., assignors to Lindberg Engineering Company, Chicago, 111., a corporation of Illinois Application October 3, 1956, Serial No. 613,721

12 Claims. (Cl. 21910.41)

of furnace comprises a hollow heating chamber into which a charge of the work materials to be heated is placed for a desired period of time after which the treated materials are removed and another charge of work materials is placed in the furnace for treatment.

Another conventional type of furnace comprises an elongated hollow heating chamber through which the work materials are conveyed by automatic or manual conveyor means. In this type of furnace the work materials may be passed continuously through the furnace for heatmg.

The first type of furnace above mentioned has the disadvantage of being capable of handling only relatively small charges of work material as it does not function continuously. The second type of furnace mentioned above, while adapted for continuous heating operation, has the disadvantage of requiring relatively long heating chambers and, therefore, such furnaces are expensive both from the viewpoint of construction costs and from the amount of floor space required.

In addition to the above, such prior art types of heating furnaces frequently require generally complex control means for maintaining a desired atmosphere within the furnace since this problem is aggravated by the relatively large inherent leakage therein. Since atmospheric gas is rather expensive, this serves to add to the cost of operation of such furnaces.

Accordingly, it is a general object of this invention to provide an improved electric heating furnace and method of heating work materials.

It is another object of this invention to provide an improved electric heating furnace of relatively compact construction having a capacity equivalent to the capacity of conventional furnaces of substantially greater size.

It is still another object of this invention to provide a continuously operating electric heating furnace in which the need for a complex and expensive separate conveyor means for the work materials is eliminated.

It is a further object of this invention to provide an improved electric heating furnace in which the work materials are advanced through the furnace by the cyclical movement of the heating chamber.

It is a still further object of this invention to provide an improved electric heating furnace in which the heating chamber is physically and electrically isolated from the source of electrical energy.

According to one feature of the invention both the heating chamber and the work therein are heated by induced electric current.

It is a still further object of this invention to provide .an improved electric heating furnace which is character- Patented July 15,1958

. 2 ized by its compact construction, its efiiciency and its economy of operation.

In accordance with the features of a specific illustrative embodiment of this invention the improved electric heating furnace comprises a ring-shaped hollow outer shell which preferably is formed of a non-magnetic material, such as aluminum or the like. A smaller ring-shaped hollow member defining an annular heating chamber is positioned within the outer shell and advantageously is thermally insulated therefrom.

This istattained by lining the lower interior portion of the outer shell with a heat resistant refractory, such as brickwork or ceramic, upon which the annular heating chamber is supported. The remaining space between the outer shell interior and the annular heating chamber is filled with a heat insulating material and the heating chamber is afixed to the refractory, as by bolts and the like, to maintain the heating chamber securely in position.

The heating chamber is provided with a loading channel, such as a tubular member which extends through the outer shell and is connected with an opening in the heating chamber for enabling work materials to be inserted in the latter. The heating chamber also is provided with a discharge channel, which may be a tubular member extending from an opening in the lower portion of the heating chamber through the outer shell, to enable the treated Work material to be discharged into a quenching bath or other receivingmeans.

In accordance with a primary feature of this invention, the ring-shaped heating structure which comprises the outer shell and heating chamber is mounted upon bearings to the end that the heating structure may be cyclically oscillated about its vertical axis in a relatively easy manner upon the bearings. This may be attained by any suitable actuating mechanism linked to the outer shell, which mechanism may take the form of a hydraulic cylinder, an air cylinder or any suitable electrical or mechanical device capable of reciprocating the heating structure back and forth at a controllable rate. Thus, it will be appreciated that the work materials inserted into the heating chamber through the loading channel are caused to advance through the chamber towards the discharge channel as the result of the jogging motion provided by the reciprocation of the heating structure, the rate of advance and, hence the heating cycle of the work materials, being controlled by the rate of reciprocation.

Heating of the work material is attained by means of a transformer core and primary winding which is operatively associated with the outer shell. In accordance with one embodiment of this invention, the transformer core completely encloses a portion of the outer shell and the primary coil is wound upon one leg thereof so as to be inductively coupled with the heating chamber within the outer shell when electrical energy is supplied thereto. Thus, the heating chamber serves as the secondary winding of the transformer and when electrical energy is supplied to the transformer the heating chamber is heated to heat the work material as it is advanced through the heating chamber during reciprocation in the manner explained above.

It will be appreciated from the viewpoint of efficient operation that it is desirable to heat only the heating chamber within the outer shell. To this end the outer shell is separated at a portion thereof and the ends are joined by means of an electrical insulating material such that there is no complete electrical path around the outer shell.

In the operation of the heating furnace, Work material is continuously supplied to the heating chamber through the loading channel and is advanced around the chamber towards thedischarge channel as aresult of the reciprocation of the heating structure. The diameter of the ring-shaped heating chamber is chosen so the work material is heated for a desired period of time before it is discharged through the discharge channel and in accordance with available floor space. It will be understood that a heating area equivalent to that of a relatively lengthy heating furnace of the prior art elongated type may be attained with a comparatively small diameter ring-shaped heating chamber. Thus, savings in both floor space and in construction costs are effected by a heating furnace constructed in accordance with the invention.

'In another preferred embodiment of the invention, the heating area of the heating chamber may be increased without any corresponding increase in the horizontal dimensions of the heating furnace by providing a spiral type of heating chamber within the outer shell. Thus, the heating chamber may comprise not one but a plurality of turns within the outer shell. A loading channel is provided at the uppermost turn and a discharge channel is provided at the lowermost turn to the end that the work materials are advanced from the top to the bottom of the spiral during reciprocation. As it is necessary that the heating chamber comprise a completely closed electrical path in order to serve as the secondary coil of the transformer, the loading and discharge ends of the heating chamber are electrically connected as by means of a strap or the like.

It will be appreciated that since the heating chamber is substantially completely enclosed in either of the abovedescribed embodiments, confinement of atmospheric gases therein is greatly facilitated. Thus, an atmospheric inlet channel, such as a tubular member, may be provided in communication with the heating chamber and extending through the outer shell to enable the atmospheric gases to be supplied to the heating chamber. This also serves to provide increased economy of operation of the heating furnace.

It further will be appreciated that the heating chamber may be formed with a variable resistance throughout its length to provide control of heat release therein. Thus, the cross section of the heating chamber may be smaller at the points where increased heat is required, such as at the loading and discharge ends, and the cross section may be reduced throughout the remainder of the heating chamber to decrease the heating temperature thereat. Additionally, control of heat release around the 360 of the heating chamber may be provided by means of the electrical on-off control associated with the transformer primary winding.

The above and other features of novelty which characterize the invention are pointed out with particularity in the claims appended to and forming a part of this specification. For a better understanding of this invention, however, its advantages and the specific objects attained by its use, reference is had to the accompanying drawing and descriptive material in which is shown and described several illustrative embodiments of the invention.

In the drawings:

Figure 1 is a perspective view of an electric heating furnace embodying the invention;

Figure 2 is a top plan view of the furnace;

Figure 3 is a partial section on the line 33 of Fig ure 2;

Figure 4 is a vertical section on the line 44 of Figure 2;

Figure 5 is a section similar to Figure 4 of an alternative construction embodying the invention; and

Figure 6 is a perspective view of the heating chamber of the furnace shown in Figure 5.

The furnace, as shown in Figures 1 to 4, comprises a generally annular or ring-shaped body, indicated generally at 10, through which the material to be heated is passed. The ring-shaped body 10 is movably supported on a supporting framework including legs 11 carrying hearingelements, such as, rollers 12, which support the body 10. The frame may be suitably mounted on a floor or the like and the legs are insulated from each other as by an insulating supporting plate 13 which holds the legs in proper spaced relationship.

The annular ring-shaped body 10, as best seen in Figures 3 and 4, is formed by an outer metallic shell 14 formed of any suitable metal, such as light gauge steel, aluminum, or the like. To prevent induced currents in the shell 14 it is electrically interrupted by insulating strips 15, as best seen in Figures 2 and 3, so that no current can fiow around the shell.

An annular ring-shaped heating chamber 16, which may be formed of a heat resistant electrically conductive material such as steel, is mounted within the shell 14 and is heat insulated therefrom. For this purpose, as shown, the chamber 16 may rest upon refractory material 17, such as brickwork or the like, and the space at the sides of and above the heating chamber may be filled with a heat insulating material 18 of any desired type. The insulating material 18 may take the form of a poured or cast refractory or may be loose refractory insulating material as desired.

Work to be heated is fed into the heating chamber 16 through an inlet conduit 19, as best seen in Figure 3, which extends through the outer shell 14 and the insulating material 18 into the annular heating chamber 16. As shown, the conduit 19 is fitted through an enlarged opening in the outer shell 14 and is spaced from the walls of the opening to be electrically insulated from the shell. The work is discharged from the heating chamber 16 through a similar conduit 21 extending downwardly from the heating chamber 16 through the heat insulating material and the outer shell. In operation, work is fed into the inlet conduit 19 and travels around the heating chamber to be discharged after heating through the conduit 21 into a suitable quenching tank or the like.

To heat the work an electrical primary unit is provided to induce the flow of heating current in the heating chamber 16 and the work therein. As shown, the primary unit comprises a rectangular core 22 looped around the annular body 10 and carrying a primary winding 23 which, preferably, lies within the body 10. The core 22 is supported by plates 24 attached to the insulating disc 13. When the winding 23 is energized by alternating current and, preferably, by high frequency current a secondary heating current will be induced in the annular heating chamber 16 to heat the chamber and by conduction to heat the work therein. As the work in the chamber passes through the magnetic field created by the winding 23, secondary current will also be induced directly in the work itself to augment the heating effect. In this way the work is heated to the desired temperature as it passes through the heating chamber, the desired degree of heating being achieved by regulating the frequency and voltage of the primary current and the time of retention of the work in the heating chamber.

In many instances it may be desirable to vary the heating effect on the work as it travels through the heating chamber. For this purpose, it is contemplated that the cross-sectional area of the heating chamber walls may be varied to produce a greater intensity of current at points where the cross-sectional area of the walls is reduced so that the heat distribution may be effectively regulated. For example, it may be desirable to provide a high temperature adjacent the inlet opening to bring the work up to treating temperature rapidly.

The work is advanced through the heating chamber according to the present invention by reciprocating or oscillating the heating chamber to advance the work therethrough. Any desired type of reciprocating or oscillating means may be employed such as, for example, a fluid motor, as shown in Figure 2. In this construction a cylinder 25 is pivoted at one end to the supporting plates 24, or if preferred directly to the core 22 itself, and contains a piston whose piston rod 26 is pivotally connected to a bracket 27 on the annular body 10. Fluid may be supplied alternately to opposite ends of the cylinder through suitable automatic valve means (not shown) to cause the body to oscillate on the supporting rollers 12. It will be understood that the body 10 may advance relatively slowly in the direction of travel of the work from the inlet to the discharge conduit so that the work will be carried around in the heating chamber and may be returned rapidly in the opposite direction so that the work will not return with it. The rate of travel of the work through the heating chamber may be adjusted by adjusting the rate of oscillation of the body to provide the required retention time of the work in the chamber.

The furnace of the present invention adapts itself readily to treatment of the work in an atmosphere gas. For this purpose a conduit 28 may extend through the shell and insulating material into the heating chamber and may be connected through a flexible hose to a gas generator. Since the chamber is closed except for the inlet and outlet conduits, there will be a relatively small consumption of atmosphere gas and the chamber may be maintained properly filled at all times. The temperature of the chamber may be indicated by means of a thermocouple 29 or the like extending through the shell into contact with the chamber and carrying a suitable indicating instrument at its upper end or connected. through flexible leads to a remote indicating instrument.

In operation of the furnace as shown in Figures 1 to 4, the primary winding 23 may be energized and the annular body 10 may be oscillated at the desired rate. Work pieces to be treated are introduced into the chamber 16 through the inlet conduit 19 and are caused to travel around in the heating chamber in a counterclockwise direction, as seen in Figure 2, to the outlet conduit. During their passage through the heating chamber, the work pieces are heated by conduction from the Walls of the heating chamber and also by induced secondary current directly in the work pieces themselves. Thus, the work pieces may be heated to any desired temperature and maintained at the desired temperature for the required length of time to effect the desired heat treatment.

Since the heating chamber is annular, it provides a relatively long path of travel for the work in a highly confined compact space. Furthermore, the annular construction of the heating chamber provides an effective secondary loop for conduction of secondary heating current to effect heating.

Where still greater retention time is desired, or greater compactness is required, the construction shown in Figures 5 and 6 may be employed. The furnace shown in these figures comprises an annular body, indicated generally at 30, which is similar to the annular body 10 but may be deeper. This body includes a shell 31 formed of metal and interrupted at at least one point in its periphery so that current cannot flow therethrough. A spiral heating chamber 32 is mounted within the shell 31 and is spaced therefrom by heat insulating material 33 to support the spiral chamber and to insulate it from the shell.

The chamber 32 may be formed with any desired number of turns in the form of a helix, as shown, or if preferred as a flat spiral. As illustrated in Figure 6, the heating chamber comprises two complete turns With one end extending upwardly to define an inlet conduit 34 to project through the shell 31 and the opposite end turned downwardly to define an outlet conduit 35 also projecting through the shell 31. In order that the spiral chamber may define a complete closed secondary loop, a conducting strap 36 is connected directly between the inlet and outlet portions of the body so that current can flow through the complete body.

Secondary current is induced in the spiral body and in the work therein by means of a primary unit including a core 37 looped around the body 30, as shown in 6 Figure 5, and carrying a primary winding 38, preferably within the body.

This construction functions in exactly the same manner as the construction of Figures 1 to 4. In operation, the body is oscillated or reciprocated in the same manner as the body 10 of Figures 1 to 4 to cause the work pieces to travel around the spiral from the inlet to the discharge end. During the travel, the work pieces are heated by conduction from the body itself due to induced secondary current therein and by induced currents directly in the work pieces themselves. With the construction of Figure 5 an extremely great length of chamber can be provided in a very compact space so that long retention time and a high degree of heating can be achieved.

While two embodiments of the invention have been shown and described in detail, it will be understood that these are illustrative only and are not to be taken as a definition of the scope of the invention, reference being had for this purpose to the appended claims.

We claim:

1. An electric heating furnace comprising a movable heating structure including a substantially ring-shaped hollow outer shell, a smaller ring-shaped hollow heating chamber enclosed within said outer shell and thermally insulated therefrom, a loading channel extending through said outer shell and communicating with the interior of said heating chamber for enabling work material to be placed within the latter, a discharge channel extending through said outer shell and communicating with the interior of said chamber to enable heated work material to be discharged from the latter, bearing means supporting said movable heating structure, actuating means linked to said movable heating structure for causing the latter to be reciprocated in said bearing means to advance the work material in said chamber from the loading channel towards the discharge channel, and a stationary core having a transformer primary Winding wound thereon in operative association with said heating structure and adapted when energized to cause the work material within said heating chamber to be heated.

2. An electric heating furnace in accordance with claim l further comprising an atmosphere inlet channel extending through said outer shell and communicating with the interior of said heating chamber for supplying atmospheric gases thereto.

3. An electric heating furnace in accordance with claim 1 wherein said ring-shaped outer shell is formed with an insulating segment at one portion thereof to provide a discontinuity in the electric circuit around said outer shell.

4. An electric heating furnace comprising a movable hollow member defining a heat treating chamber, a loading channel communicating with the interior of said chamber for enabling work material to be placed within the latter, a discharge channel communicating with the interior of said channel to enable treated work material to be discharged from the latter, bearing means supporting said heating chamber, actuating means including an energizable cylinder having a piston connected to said movable hollow member for causing the latter to be reciprocated in said bearing means for advancing the work material in said chamber from the loading channel towards the discharge channel, and a stationary core having a transformer primary coil wound thereon inductively coupled to said heating chamber and adapted when energized to cause said heating chamber and the work material therein to be heated.

5. An electric heating furnace comprising a hollow outer shell, a heating chamber positioned within said outer shell and thermally insulated therefrom, means for enabling work material to be loaded into and discharged from said heating chamber, actuating means linked to said outer shell for causing said heating chamber to be reciprocated for advancing the work material therein, and transformer primary means inductively coupled -to 7 said heating chamber and adapted when energized to cause said chamber and the work material therein to be heated. Y

6. An electric hollow heating furnace comprising a heating chamber having inlet and outlet ends for Work material to be heated, means for supporting said heating chamber so as to enable movement thereof, actuating means operatively associated with said heating chamber for cyclically moving the same for causing said work material to be advanced in discrete steps from said inlet to said outlet end, and transformer primary means including a core and an electrical conductor wound thereon inductively coupled to said heating chamber for causing the work material to be heated as it is advancedthrough said heating chamber during said movement.

7. An electric heating furnace in-accordance with claim 6 further comprising an inlet channel extending through a wall of said hollow chamber and communicating with the interior thereof for controlling the atmosphere therein.

8. An electric heating furnace comprising a hollow body defining a housing, bearing means supporting said body, actuating means linked to said body for causing the latter to be cyclically actuated in said bearing means, a hollow coiled member adapted for the passage of work material to be heated therethrough positioned within said hollow body, said coiled member comprising a plurality of turns and having a loading inlet at the upper portion of said housing and a discharge outlet at the lower portion of said housing, means electrically connecting said coiled member at its inlet and outlet ends to form a closed electrical path whereby said coiled member is adapted to serve as a transformer secondary, and a transformer primary operatively associated with said housing, said transformer primary including a stationary core and a primary coil inductively coupled to said coiled member for heating the coiled member and the work material during cyclical actuation of said body, whereby the work material is advanced from said loading inlet towards said discharge outlet during heating.

9. An electric heating furnace comprising a hollow body defining a housing, actuating means linked to said body for causing the latter to be reciprocated about a vertical axis, a hollow coiled member comprising a plurality of turns and adapted for the passage of work material to be heated therethrough positioned within said hollow body, means electrically connecting turns of said coiled member to form a closed electrical path for enabling said coiled member to serve .as a transformer secondary, and a transformer primary operatively associated with said body, said transformer primary including a stationary core and a primary coil inductively coupled to said coiled member for heating the coiled member and the work material during reciprocation of said body.

10. An electric heating furnace in accordance with claim 9 wherein said hollow coiled member is substantially closed and further comprising an atmosphere inlet member communicating with the interior of said coiled member for enabling control of the atmosphere therein.

11. The method of heating work material in an electric furnace which comprises the steps of providing in the furnace a closed heating chamber having loading and discharge openings for the passage of work material to be heated therethrough, reciprocating said heating chamber to cause said work material to be advanced from the loading opening of the chamber to the discharge opening of the chamber, and inducing electric heating current in said chamber and the work material therein during reciprocation of the chamber.

12. The method of heating work material in an electric furnace which comprises the steps of providing in the furnace a plural-turn hollow coiled heating chamber having loading and discharge openings at its upper and lower ends, respectively, for the passage of work material to be heated therethrough, reciprocating said heating chamber to cause said work material to be advanced from the loading end of the heating chamber to the discharge end of the heating chamber, electrically connecting the ends of the heating chamber, and inducting electric heating current in the heating chamber.

References Cited in the file of this patent UNITED STATES PATENTS 1,821,530 Spire Sept. 1, 1931 2,555,450 Lee June 5, 1951 2,616,022 Arnaud Oct. 28, 1952 2,729,731 Kleinpeter Jan. 3, 1956