US3311695A

US3311695A - Coil assembly for an induction melting furnace and method of making same

Info

Publication number: US3311695A
Application number: US402850A
Authority: US
Inventors: Robert J Kasper
Original assignee: Ohio Crankshaft Co
Current assignee: Ohio Crankshaft Co
Priority date: 1964-10-09
Filing date: 1964-10-09
Publication date: 1967-03-28
Anticipated expiration: 1984-03-28

Description

R. J. KAsPx-:R 3,311,695 COIL ASSEMBLY FOR AN INDUCTION MELTING FURNACE arch 28, 1967 AND METHOD OF MAKING SAME Filed Oct. 9, 1964 2 Sheets-Sheet l ATTORNEYS ATTORNEYS 2 6 mm. @l 6, m 4 2 MW o 1 G o VK f 3 l2 m QWE e F f IU A M m N S 4 mdf- R Dn U 2 A m \./m my E G O 3 8 g 2 v0 m1 4 ll/ R TL Y Lm B ES M Elm //Alf// f PTA .mM 7 D Km C lwNw H .AH RRmnm NM H Ym L BA m y w f 5y A L H G` wm u ,L C 9 w .V l l n, 9 O 8 2 .W 7/ h O 1 n d H H e F 4 f 3,311,695 Patented Mar. 28, 19167 United States vPatent Office COIL ASSEMBLY FOR AN INDUCTION MELT- INGEIITURNACE AND VMETHOD OF'MAKING SAM Robert J. Kasper, Seven Hills, Cuyahoga, Ohio, assignor to The Ohio Crankshaft Company, Cleveland, Ohio, a corporation of Ohio Filed Oct. 9, 1964, Ser. No. 402,850 13 Claims. (Cl. 13-27) The present invention pertains to the art ofinduction melting furnaces and more particularly to V"aY coil assembly for an induction melting furnace and a method of making same.l

The. invention is particularly applicable for use within an induction melting furnace of the -tiltable type and it will be described -with particular reference thereto; however, it will be appreciated that the invention has much broader applications and may be used in the construction of other types of induction melting furnaces.

melting metal, such as steel, it has become somewhat common practice to place the steel Within'a refractory melting pot or crucible surrounded by a multiturn'induction heating coil. When the heating coil is energized by a source of alternating current, alternating flux elds are created within the crucible or melting pot. These flux fields induce voltage differentials within the steel,` Consequently, current flow is created within the steel and the steel is heated bythe IZRheating principle.

In the past, an induction melting furnace of the general type defined above included a complicated frameworklfor supporting the heating coil Awith respect to the refractory melting pot or crucible. v Since the refractory melting pot was very weak, especially when subjected to tensile stresses, the framework had to hold the coil rigidly so that motive forces created bythe current flow through the turns ofthe coil did notcause movement of the coil turns against the melting pot. InV order to reinforce the coil to the extent necessary to prevent damage to the refractory melting pot, the framework included a complex metal and refractory structure surrounding the coil and secured to the coil at various points. Such a framework structure was quite expensive to produce. In addition, when the heating coil became defective, the supporting framework and coil had to beremoved from around the refractory melting pot before the Vco-il could be repaired or replaced. Thus, a spare frameworkvand coil assembly had to be provided for use While the framework and coil assembly was removed for repair or replacement of a defective coil. This added to the capital inventory of the melting installation and required extra storage space for the spare framework and coil assembly.

These and other disadvantages have been completely overcome by the present invention which is directed toward a self-supporting or free-standing coil assembly Vfor an induction melting furnace which assembly need not be supported by a complicated and rigid frame to prevent damage to a refractory melting pot positioned within the assembly. y

In accordance with the present invention there is provvided an improvement in an induction melting furnace comprising an induction heating coil assembly having a multi-turn heating coil with input leads, adapted to be connected to -a source of alternating current, and a frame for supporting the coil assembly. The improvement of the induction melting furnace comprises constructing the heating coil assembly to include a hardened refractory material cast as a self-supporting body around -the induction heating coil to iixedly support the coil within the cast body with the input leads of the coil extending outwardly from the body, the body having an inner chamber coaxial with the coil for receiving a rammed refractory melting pot and an outer lateral surface, and a non-conductive band wrapped around the lateral surface of the cast body for reinforcing the body. v

By this construction, the inductionmelting furnace ncludes a self-supporting coil assembly having an inner induction heating coil supported within a cast refractory body. A melting pot, which is preferably formedfrom a rammed refractory material in a manner to be hereinafter described in detail, can be placed within a central chamber of the coil assembly and the coil assembly can be supported by a relatively simple frame. Consequently, should the heating coil become defective, the self-support ing coil assemblymay be easily removed and another coil assembly can be substituted therefor. In this manner, the cost of the furnace is reduced and a user of the furnace need only stock a relatively inexpensive coil assembly instead of a coil and a complicated framework.

By constructing the coil assembly in accordance with the invention, the cast refractory body rigidly supports the heating coil so that the motive forces established by current ow through the coil turns do not cause the coil turns to move against, and exert forces on, the refractory melting pot within the coil assembly. The supporting framel of this coil assembly does not have to perform this function.

In accordance with another aspect of the present invention therev is provided a method of making a self-supporting induction heating coil assembly for an induction melting furnace, the method includes the steps of providing an induction heating coil with input leads, casting a hardenable refractory material in a generally `cylindrical shape around the coil to form a self-supporting cylindrical body with an inner chamber coaxial with the coil and with the input leads of the coil extending outwardly from the body, and helically winding `a non-conductive band under tension around the cylindrical body along a major portion of the bodys axial length to reinforce the ody.

By constructing the coil assembly in accordance with the method dened above, the helical band places the cast refractory body under a slight A'amount of compression which enhances its physical characteristics. Consequently, any tendency of the coil to move within the ttast body ,is restrained by the pre-compression of the ody.

The primary object of the present invention is the provision of an induction melting furnace which is economical to produce, durable in use and inexpensive to repair.

Another object of the present invention is the provision of an induction melting furnace including a self-supporting coil -assembly which assembly requires a minimum of supporting structure.

Still another object of the present invention is the prolvision of an induction melting furnace whichV can be easily repaired should the heating coil become defective.

Another object of the present invention is the provision of an induction melting furnace including a self-supporting coil assembly which may be replaced without requiring a prolonged down time of the furnace.

Yet `another object of the present invention is the provision of a melting furnace including a self-supporting coil assembly formed from -an induction heating coil cast within a refractory material with the refractory material being placed under compression.

These and other objectsV and advantages will become apparent from the following description used to illustrate the preferred embodiment of the present invention as read in connection with the accompanying drawings in which:

FIGURE 1 is a pictorial view illustrating a preferred embodiment of the present invention;

FIGURE 2 is an enlarged cross-sectional view taken generally along' line 2--2` of FIGURE 1;

FIGURE 3 is an enlarged, partial cross-sectional View taken generally along line 3-3 of FIGURE 1;

FIGURE 4 is a cross-sectional view taken generally along line 4-4 of FIGURE 2;

FIGURE 5 is a somewhat schematic pictorial view illustrating in cross-section a certain aspect of the present invention; and

FIGURE l6 is a pictorial, somewhat schematic, view illustrating another aspect of the present invention.

Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only `and not for the purpose of limiting same, FIGURES 1, 2 and 4 show an induction melting furnace A of the type used for melting metal, such as steel, which furnace includes, Ias essential elements, a frame or supporting structure 10 and a novel coil assembly 12. The coil assembly 12, which will be hereinafter described in detail, comprises a self-supporting element which rests on frame 10 and it can be easily removed therefrom when it becomes defective for any reason.

By constructing the coil assembly 12, in accordance with the invention, the frame 10 may be a relatively simple construction to support the free-standing or self-supporting coil assembly 12. In accordance with the illustrated embodiment of the invention, the frame 10 includes horizontally extending

angle struts

20, 22 having lower flanges 24, and terminating in a handle 26. Supportedon flanges 24 is a bottom plate 30 formed from an insulating and refractory material such as, without limitation, an asbestos-cement `board commonly called Transite.` Adjacent the front end of the furnace A there is provided a front plate 32 constructed of similar material as plate and adapted to support the furnace A as it is tipped to empty metal therefrom. A partition 34, spaced from plate 3,2 forms a cavity above the bottom plate 30 which cavity is filled by a castable refractory material y which, in practice, is Alundum, a tabular alumina sold by Norton Company.

Front plate 32 is supported by a pair of spaced vertically extending

angle struts

42, 44 to which-plate 32 is secured by a plurality of bolts 46. A pair of

support struts

50, 52 extend from the

vertical struts

42, 44 to support plates 54, S6 welded onto the upper flanges of the

horizontal struts

20, 22. Consequently, as so far described, the frame or support structure 10 includes a bottom portion for supporting the coil assembly 12 and -a front portion for bracing the coil assembly as the frame 10 is tilted, in a manner to be hereinafter described.

- To tilt the furnace A for emptying metal therefrom, there is provided, in accordance with the illustrated embodiment of the present invention,v a pouring stand having horizontally extending based legs 6-2, 64 adapted ,to support

trunnion arms

66, 68 on opposite sides of the support -struts 50,' 52. To increase the rigidity of

arms

66, 68 there -is provided perpendicularly secured braces .70. Theupper portion of the arms are provided With trunnion recesses 72. These trunnion recesses receive trunnions 74 fixedly secured at the upper ends of

slport struts

50, 52, as is best shown in FIGURE 4. Furnace A may be emptied by grasping handle 26 and tilting frame 10, and thus coil assembly 12, about trunnions 74.

The upper portion of furnace A includes a top plate 80, formed from an insulating material having characteristics similar to the

plates

30, 32. Between the upper end of the coil assembly 12 land the lower surface of top plate there is provided an insulation and sealing sheet 82, which in practice is formed froma thin sheet of asbestos cloth. The top plate 80 is secured'onto bottom plate 30 by a plurality of non-magnetic,'steel tie rods 84 which tie rods, in accordance with the preferred embodiment of the invention, compress the coil assembly 12 between the top land bottom plates so that a compressive force is exerted on'the coil assembly 12 while it is being used. At the front side of the top plate 80, adjacent plate 32, there is provided a non-magnetic pouring spout frame including a front plate 92 with pouring recess 94 and top plates 96 adapted to support side walls 98 so that a refractory material may be molded within the pouring spout frame, in a manner to be hereinafter described, to form a pouring spout for the furnace A.

The essence of the invention is the construction of the coil assembly 12 which includes a multi-turn, rectangular cross-sectioned induction heating coil 100 having outwardly extending

input leads

102, 104 extending through an insulation plate 106 secured onto coil assembly 12. In order to energize coil 100 there is provided

blocks

120, 122 which are connected by lines 1-24, 126 to a source of alternating current, schematically represented as generator 128, see FIGURE 2. As is common practice, the coil 100 is provided with an internal coolant passage 130 having a coolant inlet 132 and a pair of spaced

coolant outlets

134, 136. Coolant, such as water, flows into passage at inlet 132 and the coolant moves upwardly and downwardly through the coil until it exits through

outlets

134, 136.

In accordance with the invention, the induction heating coil 100 is encapsulated by a cast refractory material forming a body completely surrounding the c'oil 100. The body 140 is generally cylindrical in shape and rests on the cast refractory material 40 as i-s best shown in FIGURE 2. Various cast refractory materials could be utilized for encapsulating coil y100; however, in accordance with the invention, Alundum refractory material, a tabular alumina sold by Norton Company, is utilized for encasing the coil. This material has been found to have good heat insulation and heat resistant qualities as well as excellent physical strength in the cast form. It is believed that I am the first 4person to ever use tabular alumina for encapsulating the coil of a melting furnace.

The cast refractory body 140 includes an inner chamber 142, an outer latera surface 144 which may have a variety of cross-sectional shapes and an inner surface 146. In accordance with the illustrated embodiment of the invention, the outer lateral surface 144 is octagonal in shape with one flat surface at the front of the furnace A lying against the front plate 32 and another 4flat surface spaced from the front of the furnace supporting the insulation plate 106., Surrounding the lateral surface 144, in accordance with the invention, there is provided a non-conductive band 150, which in practice is formed from a glass fiber material. This band is helically wrapped in overlapping relationship around the surface 144 and under tension so that the band exerts `an inward force on the body 140. This inward force pre-compresses the body 140 to add rigidity to the coil assembly 12. The band 150 is best shown in FIGURE 3. To hold securely the band 150 onto the lateral surface 144 without releasing the tension in the band, there is provided a coating 152 of hardened material, such as polyester resins. This hardened material unitizes lthe band 150 as a substantially integral portion of the body 140.

Referring now to FIGURES 5 and 6, the method of forming the cast refractory body 140 is schematically illustrated. Spaced inner and

outer forms

160, 162, respectively, are mounted onto a base plate ,163 to form therebetween an annular pass-age into which refractory material may be poured to form cast body 140. One portion of form 1162 includes-the insulation. plate 106 as shown in FIGURE 4. After the material forming body 140 has been allowed to harden, the

forms

160, 162 and the insulation plate 106 are removed as Ishown in FIGURE 6.

Thereafter the band 150 is wrapped under tension around the octagonal lateral surface 144 of the cast body 140. The band is easily maneuvered around the

leads

102, 104 and the inlet 132 during the -wrapping operation. Thereafter, the hardenable coating 152, as shown in FIG- URE 3, is applied to thev wrapped band. In accordance with the schematically illustrated embodiment of the invention, the coating 152 is applied by a nozzle 170 which directs polyester res-in 172 against the outer wrapped su-r- 4face of cast body 140. It is appreciated that the coating 152 could be applied onto the surface by dipping, brushing or by other appropriate means. After the coating .152 is applied onto the outer surface of the cast body, the coating may be hardened by baking the body 140 or by any other appropriate curing operations. After this has been done, the plate 106 is again positioned over the leads 102, 4 and inlet 132 as shown in "FIGURE 4.

After making the coil assembly 12 as a free-standing or self-supporting unit, the coil assembly is positioned within frame 10 and the top plate `80 is secured over the top of the coil assembly. This is a relatively simple operation and may be completed in a matter of a few minutes.V The coil assembly may be positioned with the plate 106 at the left, right or rear by merely rotating the assembly. v

Thereafter, a rammed refractory melting pot 180 is constructed within the inner chamber 142 of coil assemblyk 12 so that the melting pot has a metal receiving chamber 182 and a pouring spout 1'84. To form the chamber ..182 there is provided a metal former 186 yaround .which refractory material is rammed to form the melting pot. Generally, the former 186 remains in the pouring pot. When metal is melted within the pot ,the former 186 melts and the heat of the molten metal frits the inner surface of chamber 1282 to form a hard inner surface on the rammed pouring pot. During use, any cracks which develop in this hard inner surface of pot 1180 allows metal to go into the rammed material forming the melting pot. This molten metal Within the cracks refrits the rammed refractory material in the cracks and prevents or inhibits further progression of the cracks outwardly. The rammed melting pot may be, in some cases, formed from the same cast 'refractory material forming coil assembly 12. l

By constructing the coil assembly in accordancewith the invention, whenever the coil assembly becomes defective, the tie rods 84 are loosened and the top plate 80 is removed. lThe

lines

124, 126, the inlet 132 and the

outlets

134, 136 are disconnected and the coil assembly 112 is removed from frame 10. Thereafter, another coil assembly may be positioned on the frame `10 and assembled in place with a new rammed refractory melting pot. This operation takes a relatively -short time and does not require a complete disasembling of a complicated frame structure and attaching heating coil.

An important aspect of the present invention is the band 150 helically wrapped around the lateral surface 144 of the cast refractory body 140. This band is wrapped under tension so that an inward force is exerted on the surface '144. This inward force creates a pre-compression in the body 140 so that the body is more rigid. Without such a band, the motive forces created by the current ow through the coil 100 cause movement of the coil which tends to spall the refractory material forming the body 140. This spaling can cause a more rapid deterioration of the body 140 and the melting pot positioned therein. This invention is a substantial advance over any known constructions of induction melting furnaces and allows practical use of a free-standing, self-supporting coil assembly for such a furnace'.

Metal wires 190 extending from stud y192 are cast beneath the rammed refractory pot 180. They form e-lectrodes of a ground detector system so that any cracks in the surface of the rammed refractory melting pot will cause an actuation of an electrical device connected onto stud 192. In this manner, defects in the surface of the melting pot can be effectively detected before substantial damage is done to the furnace A. In addition, when molten metal forms large cracks in 'the melting .pot 180, the metal within the pot moves radially outward into close proximity with coi-l 100. This radial movement of the metal can be detected by instruments connected `onto the heating coil since the electrical characteristics of the load change as the spacing between the load and the coil changes. When the electrical characteristics of the load change to a substantial degree indicating that the load is relatively close to the coi-1, an operator will know that a defect is present within the side walls of the furnace and the furnace may be shut down for repairs before the molten metal actually reaches the coil 100. When any defect is noted,the free-standing or self-support-ing coil assembly is replaced in the manner previously described.

The present invention has been described in connection with one preferred embodiment; however, it is appreciated th-at various structural changes may be made in the embodiment without departing from the intended spinit and scope of the present invention `as defined in the yappended claims.

Having thus described my invention, I claim:

1. In an induction melting furnace comprising: an induction heating coil assembly having a multi-turn heating coil with input leads adapted to be connected to a source lof alternating current, and a frame for supporting said coil assembly, the improvement comprising; said coil assembly including a hardened refractory material cast 'as a self-supporting body around said induction heating coil to fixedly support said Icoil within said castv body with said input leads extending outwardlyfrom said body, said body having `an inner chamber coaxial withsaid coil for receiving a rammed refractory melt-ing pot and an outer lateral surface, and a non-conductive band wrapped around said lateral surface for reinforcing said body.

2. The improvement as defined in claim 1 wherein said yband is placed under tension to exert an inward compressive force against said lateral surface. i

3. The improvement as defined in claim 1 wherein said Y band is helically wrapped around said body.

4. The improvement as defined in claim 1 wherein said band is formed from glass fibers.

45. The improvement as defined in c-laim 1 including a hardened, non-magnetic, non-conductive coating over said band for holding said band against said lateral surface of said cast body.

`6. The improvement as defined in claim 1 wherein said hardened refractory material is tabular alum-ina.

7. An induction melting furnace comprising: an induction heating coil assembly having a multi-turn heating coil with input leads adapted to be connected to a source of alternating current; Va frame having a bottom, generally horizontal plate, a refractory base on said plate, said coil assembly being supported on said base; said coil assembly including a hardened refractory material cast as a self-supporting body around said induction heating coil to xedly support said coil within said cast body with said input leads extending outwardly from said body, said body having an inner chamber coaxial with said coil and an outer lateral surface, and a non-conductive band wrapped around said lateral surface for reinforcing said body; a top plate having an opening communicated with said inner chamber and positioned over said body; and, means for drawing said top and bottom plates together to compress said cast body therebetween.

8. An induction melting furnace as defined in claim 7 wherein said top plate includes a radially extending pouring spout frame adapted to receive a refractory material to define a pouring spout for said furnace, said furnace including a non-conductive support plate extendingalong the outer lateral surface of said cast body between said top and bottom plates and in the vicinity of said pouring spout. Y

9. An induction melting furnace as defined in claim 8 including a pair of trunnions, one on each side of said pouring spout, for pivotally mounting said frame to allo-w emptying of said furnace.

10. An induction melting furnace as defined in claim 7 wherein said hardened refractory material is tabular alumma.

11. A method of making a self-supporting induction heating coil assembly for an induction melting furnace, said method including the steps of provi-ding an induction heating coil with input leads, casting a hardenable refractory material in a generally cylindrical shape around sra-id coil to form a self supporting cylindrical body with an inner chamber coaxial` with said coil and with said leads extending outwardly from said body, andvhelically wrapping a non-magnetic band under tension around said cylindrical `body along a major portion of its axial length to reinforce said body.

12. A method of making a self-supporting induction `heating coil assembly for an induction melting furnace, said method including the steps of providing an induction 'heating coil with input leads, casting a ha-rdenable refnactory mate-rial in a generally cylindrical shape around said coil to form a self-supporting cylindrical body with an inner chamber coaxial lwith said coil and with said leads extending outwardly from sai-d lbody, helically wrapping a non-magnetic band under tension around said cylindrical `body along a major portion of its axial length to reinforce said body, and impregnating said band with a hardenable plastic material to hold said band onto said body.

13. A method of making a self-supporting in-duction heating coil assembly for an induction melting furnace,

said method including the steps of providing an inducto har-den into a self-supporting cast body with an outer lateral surf-ace and an inner chamber generally coaxial with said coil, removing said body from said casting form, helically wrapping a non-magnetic band around said lateral surface and covering a major portion of the axial length of said lateral surface and, then, impregnating said band with a hardenable plastic material to secure said 'band onto said cast body.

References Cited by the Examiner UNITED STATES PATENTS Y 3,162,710 12/1964 Anderson 13-27 3,165,572 l/l965 Burtenshaw et al. 13-27 RICHARD M. WOOD, Primary Examiner. L. H. BENDER, Assistant Examiner.

Claims

1. IN AN INDUCTION MELTING FURNACE COMPRISING: AN INDUCTION HEATING COIL ASSEMBLY HAVING A MULTI-TURN HEATING COIL WITH INPUT LEADS ADAPTED TO BE CONNECTED TO A SOURCE OF ALTERNATING CURRENT, AND A FRAME FOR SUPPORTING SAID COIL ASSEMBLY, THE IMPROVEMENT COMPRISING; SAID COIL ASSEMBLY INCLUDING A HARDENED REFRACTORY MATERIAL CAST AS A SELF-SUPPORTING BODY AROUND SAID INDUCTION HEATING COIL TO FIXEDLY SUPPORT SAID COIL WITHIN SAID CAST BODY WITH SAID INPUT LEADS EXTENDING OUTWARDLY FROM SAID BODY, SAID BODY HAVING AN INNER CHAMBER COAXIAL WITH SAID COIL FOR RECEIVING A RAMMED REFRACTORY MELTING POT AND AN OUTER LATERAL SURFACE, AND A NON-CONDUCTIVE BAND WRAPPED AROUND SAID LATERAL SURFACE FOR REINFORCING SAID BODY.