US3463864A

US3463864A - Coreless chip melting furnaces

Info

Publication number: US3463864A
Application number: US624535A
Authority: US
Inventors: Mario Tama
Original assignee: Ajax Magnethermic Corp
Current assignee: Park Ohio Holdings Inc
Priority date: 1967-03-20
Filing date: 1967-03-20
Publication date: 1969-08-26
Anticipated expiration: 1986-08-26
Also published as: DE1758016A1; DE1758016B2; GB1211103A

Description

Aug. 26, 1969 M. TAMA CORELESS CHIP MELTING FURNACES 2 Sheets-Sheet 2 Filed March 20. 1967 INVENTOR Mar/o Ema I -41 M i g/ H \SZOUGH ATTORNEY United States Patent 3,463,864 CORELESS CHIP MELTING FURNACES Mario Tama, Cortland, Ohio, assignor to Ajax Magnethermic Corporation, Warren, Ohio, a corporation of Ohio Filed Mar. 20, 1967, Ser. No. 624,535 Int. Cl. H05k 5/02, 5/16 US. Cl. 13 -33 9 Claims ABSTRACT OF THE DISCLOSURE Electric furnace method and apparatus for continuous melting of finely divided particles of metal and continuous discharge of the melted metal, by depositing the particles in a turbulent, circulating portion of the =melt and discharging the melted metal from a relatively quiescent portion of the melt. This is achieved in an induction furnace inclined to the vertical in a constant continuous overflow pattern therefrom.

This invention relates to induction heating furnaces and particularly to a core-less induction furnace for melting finely divided particles of metal; such as, aluminum, brass, iron, and the like. The invention is particularly applicable for continuous operation and discharge. I

It is well known that a circulation and turbulence of the melt is effected in conventional induction heating furnaces utilizing substantial power densities. The circulation inherent in a coreless induction furnace can be quite violent at low levels and high power densities, to the point of ejecting the charge from the furnace. The surface circulation is quite intense in such furnaces as long as the molten metal level remains substantially within the vertical heighth of the power coil, and as the level exceeds the top of the power coil, the surface circulation diminishes rapidly. Within a relatively short distance above the coil top, the surface of the melt becomes substantially quiescent, even at relatively high power densities. In the batch melting of finely divided particles, the charge must be sized so that the molten level will stay substantially within the power coil, taking advantage of the strong circulation to stir in the charge. If charging has been much beyond the top of the power coil, the usual result at the end of the heating period is a layer of chips or particles which float on top of the melt and must be puddled or stirred i by hand.

If a conventional vertical coreless furnace is filled to a level high enough to maintain a quiet surface for continuous, controlled overflow discharge therefrom, the melt level in the furnace is substantially above the top of the coil, and virtually no surface turbulence occurs with the result that the charge is not stirred into the melt. Even though a substantial head of finely divided particles is maintained, it will still tend to float on the surface rather than submerge into the melt. Thermal conductivity through such a mass is very low thereby preventing efficient transfer of heat from the molten metal bath to the particles. The heating of such finely divided particles by induction presents special difliculties, including oxidizing atmosphere which greatly reduces the yield. Conventional radiant heating; for example, as found in gas heating furnaces, also tends to oxidize small particles before they liquefy. Various means of mechanical and liquid agitation have been employed by others with attendant high maintenance.

The present invention utilizes the inherent circulation present in a coreless induction furnace in a unique manner in order to obtain rapid submergence and good stirring of the chips or finely divided particles, such rapid submergence melting the charge in a favorable manner which gen- 3,463,864 Patented Aug. 26, 1969 erally eliminates oxidation and increases yield. The furnace of the present invention is also adapted to continuously discharge the melted metal from the furnace, the chips being fed to the surface of the melt in quantities sutficient to maintain a substantially constant overflow level in the furnace.

In the preferred embodiment of this invention, the furnace and power coil are inclined in such manner that the level of the molten metal at the front or discharge side of the furnace is disposed above the upper level of the power coil, and the level at the back or charging side of the furnace is disposed at or near the upper level of said coil. When the power is on, the molten metal which is disposed above the power coil is relatively quiescent as aforesaid, and that portion disposed at or near the upper end of the power coil is relatively turbulent. Finely divided particles of metal are deposited into the turbulent, low level portion of the melt, where the more violent stirring takes place, and the chips or particles are stirred into and completely incorporated within the melt before discharge. At normal, relatively low operating frequencies, the chips or particles are not heated by induction but are liquefied almost immediately by conduction from the heat of the melt. Essentially, therefore, the invention may be stated to be operative with a turbulent, relatively low level i the rear of the furnace at which point stirring of the finely divided particles occurs and a quiescent, high level at the front or discharge side of the furnace where discharge of the melt takes place.

In view of the above, the primary object of the present invention is to provide a method and apparatus for melting finely divided particles of metal in an improved manner.

Another object of the invention is to provide a coreless, electric induction heating furnace which is adapted for continuous melting of finely divided particles of metal and continuous discharge of the melted metal.

Still another object is to provide a furnace having a coaxial induction heating coil wherein the individual turns of the coil may be disposed at substantially right angles to the axis of the coil and wherein the axis of both the coil and the furnace crucible portion are disposed at an angle.

Yet another object of the invention is to provide a coreless induction furnace having the above features and characteristics wherein the level of the melt at the discharge side is disposed a substantial distance above the upper end of the power coil whereas the level of the melt at the back or charging side of the furnace is disposed at or near the upper end of said coil.

A still further object is to provide a method for continuous melting of finely divided particles and continuous discharge of the melt wherein said finely divided particles are introduced into a molten heel of metal at a turbulent surface portion thereof and wherein molten metal is discharged at a quiescent surface portion thereof.

A further object of the invention is to provide a method and apparatus for controlling the meniscus of melted metal whereby to effect a low, turbulent, charging side for receiving and stirring in a finely divided particles and a high, quiescent, discharging side for overflow discharge of the melt.

These and other objects of this invention will become more readily apparent from a purview of the invention as set forth in the appended description and disclosed in the drawings, in which said drawings:

FIGURE 1 is a side elevational View of the coreless furnace positioned according to my invention;

FIGURE 2 is a front elevation showing the discharge side of the furnace;

FIGURE 3 is a transverse sectional view of the furnace of FIGURES 1 and 2 showing the metal level under different operating conditions.

Referring now to the drawings in all of which like parts are designated by like reference characters, a furnace is shown at mounted upon a suitable support surface; such as, a base or floor 11 by means of upright weldments 12 surmounted by bearing support brackets 13. The furnace 10 has an outer frame or housing 14 provided with a radially extending flange 15 adjacent to the upper end thereof which said flange carries a pair of rigidly mounted journal members 16 adjacent to the front or discharge side of said furnace. The journal members 16 are pivotally mounted to the support brackets 13 by means of short, co-axial shafts 17 whereby the furnace can be tilted forwardly about the axis of said shafts for leveling or emptying said furnace. A pair of jack posts 18 are provided at the rear and beneath the furnace 10 for maintaining said furnace at a tilted angle of approximately 30 and for adjusting the tilt of said furnace forwardly or backwardl to the precise, optimum operating angle. Above the flange 15, the furnace 10 is provided with an upper housing portion 19 which is so constructed that the upper open end 20 thereof is disposed at substantially a horizontal level when said furnace is tilted at the aforesaid angle of approximately 30, i.e. between 20 and 40. A pouring spout 21 is carried by said upper housing portion 19 and projects forwardly beyond the upright weldments 12 for pouring the molten metal from said furnace.

Referring now particularly to FIGURE 3 of the drawings the housing 14 and the upper housing portion 19 encase and support a refractory inner furnace liner 25 and induction coil 26. Said coil surrounds said liner and is preferably water cooled and has suitable electrical leads L1, L2 at the upper and lower ends, respectively, which are connected to suitable transformers and other auxiliary electrical equipment (not shown). Immediately above and co-axial with the inductor coil 26 is a hollow auxiliary cooling coil 27, and immediately below said inductor coil is a similar cooling coil 28. Said cooling coils are connected to a suitable source of pressurized fluid in a well-known manner (not herein shown). The refractory liner 25 defines an essentially cylindrical crucible having preferably cylindrical side walls 29 and a bottom wall 30 connected to said side walls by a taper 31. In the form shown, the side walls are relatively thin while the bottom wall of the refractory lining is relatively thick.

The pouring spout 21 is provided with a suitable refractory lining 31 defining a fairly large groove 32 centrally thereof whereby a substantial depth of molten metal may be carried by said spout. Said pouring spout may be electrically heated if desired and is preferably inclined downwardly and forwardly when the furnace is in the tilted position shown. The furnace, it will be noted, is provided with a rearwardly disposed, tapered upper side wall portion 33 adjacent to the upper open end 20; and a means for depositing finely divided particles of metal, schematically indicated as a hopper 34, is preferably positioned above and directs the charge into said furnace adjacent to said side wall portion.

In the furnace herein illustrated, and particularly as detailed in FIGURE 3, a liquid level line 40 indicates the level of the melt which would normally be maintained within the furnace and as it would appear with the power turned off. The line 40 is preferably maintained at the discharge level 41 of the discharge means or pouring spout 21. It will be noted that due to the angle at which the furnace is disposed, the portion of the line 40 adjacent to the pouring spout 21 is substantially further above the top of the power coil 26 than the opposite end of said line disposed at the back or charging side of the furnace. A phantom line 40a illustrates the contour which the upper surface of the melt takes when the power is turned on. It will be noted that the upper surface of the melt defines a convex meniscus which dips sharply in a downward direction at the back of the furnace where the liquid is nearest to the power coil 26 and flattens out in the area of the pouring spout 21. The sharp drop off in the liquid surface at the back of the furnace indicates an area of turbulence and intense circulaion whereas the flatter portion of the surface adjacent to the discharge side of the furnace indicates a relatively quiescent portion of the melt. It will also be noted that the level of the melt at the front of the furnace raises above the discharge level 41 under a power-on condition whereby it is discharged from the pouring spout 21.

In the furnace herein illustrated as an embodiment of the present invention, the power coil 26 is forty-nine inches in diameter and has an axial length of substantially the same dimension. The capital letter P on the drawing designates the point at which the axis of the coil intersects the plane of the top of the coil, said plane being indicated by the dotted line 42. Measuring vertically from the point P, the level 40 is eighteen inches above said point P. The line 40a indicates the shape of the upper surface of the melt at the power level of 1000 kilowatts being applied to the power coil. Expressing the powerotf level 40 in terms of power coil diameters, said level 40 is positioned at P+.37 diameter.

The pouring spout indicated at 21 has a discharge level 41', and a furnace provided with such pouring spout 21' would be provided with a power-off liquid level indicated by the line 40 which intersects and is at the level of the point P. A line 40a illustrates the contour which the upper surface of the liquid level would take under the same power conditions providing a power level of 1000 kilowatts. It will be noted that the convex meniscus of the line 40a dips more sharply toward the back of the furnace thereby indicating more intense turbulence and stirring at this point but that said line 40a levels off toward the front or discharge side of the furnace indicating that the melt is relatively quiescent in this area.

In operating the furnace of this invention, finely divided particles of metal are introduced into the crucible, preferably adjacent to the upper side wall portion 33, by any suitable means; such as, the hopper 34. A baffle 35 may be provided, said baflie extending downwardly into the upper open end 20 of the furnace and extending below the level of the power-off line 40. It will be readily understood that a'baflie may be used in a furnace having a pouring spout such as that shown at 21 in which case the bafile would extend downwardly below the line 40. The finely divided particles of the charge enter the melt in the turbulent, circulating area and are carried toward the back of the furnace where they liquefy almost imnediately and are stirred into the melt. The melted metal 18 simultaneously discharged through the pouring spout 21 or 21' in a continuous stream.

The furnace may be either choke charged or trickle charged; that is, the finely divided particles may either be introduced into the furnace at a rate sufiicient to build up a head above the upper surface of the melt, or it may be introduced at 'a rate which is constant and substantially equal to the melting rate whereby no head accumulates. In either case, the finely divided particles are stir red into and incorporated with the melt in a highly efficient manner and with a resulting high yield.

It has been found that efiicient results are obtained within a range of liquid levels referred to power-off con ditions, between the point P or the level line 40' and P .50 diameter or a liquid level line disposed above the point P a distance equal to substantially one-half the diameter of the power coil 26. Generally, heavier metals such as iron would be most efficiently melted in the lower part of the aforementioned range whereas lighter metals such as aluminum would be more efficiently melted in the upper part of said range. The details of the furnace as herein illustrated and described are given by way of example, and it will be understood that optimum operating conditions vary depending upon the volume of the melt or the furnace geometry, the power density applied, the density of the metal with which the furnace is charged,

and the particular supply frequency employed. It is contemplated that the frequencies used would be relatively low, generally not exceeding 960 Hz.

The operating level of the pouring spout 21 or 21', which is controlled by either the discharge level 41 or 41', can be varied by varying the thickness of the refractory lining within the pouring spout. Major changes in liquid level would, of course, necessitate major changes in furnace design; such as, placing the spout in the position as indicated at 21'; in which case the upper cooling coil 27 may be shortened and suflicient refractory lining provided in such redesigned spout.

It will be understood that many changes in the details of this invention herein described and illustrated may be made without, however, departing from the spirit thereof or the scope of the appended claims.

What is claimed is:

1. The method of continuously melting finely divided particles of metal and continuously discharging molten metal comprising disposing metal within the crucible of an induction furnace having an inductor coil associated therewith, applying power to said inductor coil sufficient tomelt said metal and effect circulation therein, creating relatively quiescent surfaces adjacent the discharge and relatively turbulent surfaces of the melt opposite thereto, feeding finely divided particles of metal into said relatively turbulent portions, rapidly incorporating said particles into the melt, simultaneously discharging said resultant melt from said crucible adjacent said relatively quiescent surfaces.

2. In the method as set forth in claim 1, maintaining said melt, under power-off conditions, substantially at a predetermined level, said predetermined level being located between a first level defined by the intersection of the axis of said coil and the plane of the top of said coil, and a level disposed vertically above the first level a distance equal to one-half of the diameter of the coil.

3. The method of continuously melting finely divided particles of metal by induction heating comprising disposing the metal within the crucible of an induction furnace having an induction coil associated therewith and comprising the application of power to said induction coil relatively closer to certain surface portions of the melt than to other portions thereof, and forming the upper surfaces of the melt in a generally convex meniscus having a high relatively quiescent area and a low relatively turbulent area feeding finely divided particles of metal into the more turbulent area, discharging the melted metal from the quiescent area and the melt being continuously discharged.

4. An induction furnace for the continuous melting of finely divided metal particles and simultaneous continuous discharge of molten metal, consisting of a substantially cylindrical coil comprising a plurality of turns, all of .which are substantially perpendicular to the axis of said coil, a refractory lining inside said coil defining a substantially cylindrical melt container co-axial with said coil and extending upwardly and beyond it, the common axis of said coil and container having a predetermined fixed angle from the vertical during continuous discharge, a discharge opening in said refractory lining disposed in the upwardly extending portion of said lining above the lowest portion of the uppermost turn of the coil at an elevation between a first level defined by the intersection of the axis of said coil and the plane of the top of said coil, and a second level disposed vertically above said first level a distance equal to one-half of the diameter of said coil whereby under power-applied conditions the surface of the molten metal is relatively quiescent in the surface area adjacent the discharge opening and turbulent and depressed in the surface area remote therefrom, and charging means for continuously charging finely divided metal particles into said turbulent and depressed surface areas of said molten metal at a rate compatible with the furnace melting rate, the molten metal being continuously discharged through said discharge opening simultaneously therewith.

5. An induction furnace as set forth in claim 4, characterized by the furnace container being angled from the vertical more than 20 and less than 40.

6. An induction furnace for the continuous melting of finely divided metal particles as set forth in claim 4 wherein the top of the container is disposed at a substantially horizontal level and said furnace is angled to the vertical between 20 and 40.

7. An induction furnace for continuously melting finely divided metal particles as claimed in claim 4 characterized by the positioning of charging means adjacent the rear wall of said container opposite said discharge openmg.

8. An induction furnace for the continuous melting of finely divided metal particles as claimed in claim 4 wherein a container wall opposite the discharge opening in said refractory lining has its upper portion provided with a rearwardly disposed tapered portion, and charge means are disposed above and adjacent said tapered upper side wall portions.

9. A coreless induction furnace for continuous melting of finely divided metal particles and simultaneous continuous discharge of molten metal, said furnace having an induction coil surrounding the same, said coil comprising a plurality of turns, all of which are substantially perpendicular to the axis of the coil, the common axis of said furnace and coil being disposed at a predetermined fixed angle to the vertical during continuous discharge, said furnace having a discharge opening above said coil on the side toward which the furnace is inclined, wherein with furnace power applied the surface of said molten metal extends from said discharge opening above said coil to a point below the top of said coil on the side opposite said discharge opening, the surface of said molten metal being relatively quiescent adjacent said discharge opening and relatively turbulent on the said side opposite thereto, charging means for continuously charging finely divided metal particles into the turbulent surface of said molten metal opposite said discharge opening.

References Cited UNITED STATES PATENTS 2,709,842 6/1955 Findlay 1333 X 2,774,803 12/1956 Dreyfus l326 X 2,940,620 6/1960 Haas 13-33 X 3,004,091 10/1961 Tama et a1. 1327 2,962,377 11/1960 Morrill 26634 X 3,171,877 3/1965 Thring 26611 BERNARD A. GILHEANY, Primary Examiner H. B. GILSON, Assistant Examiner US. Cl. X.R. 1327