Electric induction furnace lining wear detection system

Abstract

An electric induction furnace for heating and melting electrically conductive materials is provided with a lining wear detection system that can detect replaceable furnace lining wear when the furnace is properly operated and maintained.

Claims

1. An electric induction furnace with a lining wear detection system comprising: a replaceable lining having an inner boundary surface and an outer boundary surface, the inner boundary surface of the replaceable lining forming an interior volume of the electric induction furnace; an induction coil at least partially surrounding an exterior height of the replaceable lining, the induction coil disposed within a coil refractory material; a furnace ground circuit having at a first circuit end at a ground probe protruding into the interior volume of the electric induction furnace and a second circuit end terminating at an electrical ground connection external to the electric induction furnace; at least one electrically conductive mesh embedded in a castable refractory disposed between the outer boundary surface of a wall of the replaceable lining and the coil refractory material, the at least one electrically conductive mesh forming an electrically discontinuous mesh boundary between the castable refractory in which the at least one electrically conductive mesh is embedded and the replaceable lining; and a direct current voltage source having a positive electric potential connected to one of the at least one electrically conductive mesh, and a negative electric potential connected to the electrical ground connection, a wall lining wear detection circuit formed between the positive electric potential connected to the one of the at least one electrically conductive mesh, and the negative electric potential connected to the electrical ground connection, whereby a wall DC leakage current level in the wall lining wear detection circuit changes as the wall of the replaceable lining is consumed; at least one electrically conductive bottom mesh embedded in a bottom castable refractory disposed below a bottom outer boundary surface of a bottom of the replaceable lining, the at least one electrically conductive bottom mesh embedded in the bottom castable refractory forming an electrically discontinuous bottom mesh boundary below the bottom castable refractory in which the at least one electrically conductive bottom mesh is embedded; a bottom lining wear direct current voltage source having a bottom lining wear positive electric potential connected to one of the at least one electrically conductive bottom mesh embedded in the bottom castable refractory, and a bottom lining wear negative electric potential connected to the electrical ground connection, a bottom lining wear detection circuit formed between the bottom lining wear positive electric potential connected to the one of the at least one electrically conductive mesh embedded in the bottom castable refractory, and the bottom lining wear negative electric potential connected to the electrical ground connection, whereby a bottom DC leakage current level in the bottom lining wear detection circuit changes as the bottom of the replaceable lining is consumed; and at least one lining wear detector connected to the wall lining wear detection circuit and the bottom lining wear detection circuit for detecting the wall DC leakage current level and the bottom DC leakage current level.

2. The electric induction furnace with the lining wear detection system of claim 1 wherein the at least one electrically conductive mesh comprises a cylindrically shaped electrically conductive mesh surrounding a height of the replaceable lining, the cylindrically shaped electrically conductive mesh having a vertical gap between opposing vertical ends.

3. The electric induction furnace with the lining wear detection system of claim 1 wherein the at least one electrically conductive mesh comprises a cylindrically shaped electrically conductive mesh surrounding a height of the replaceable lining, the cylindrically shaped electrically conductive mesh having an overlapping opposing vertical ends separated by an electrical insulation.

4. The electric induction furnace with the lining wear detection system of claim 1 wherein the at least one electrically conductive mesh comprises an array of electrically conductive meshes surrounding a height of the replaceable lining, each one of the array of electrically conductive meshes electrically isolated from each other.

5. The electric induction furnace with the lining wear detection system of claim 1 wherein the at least one lining wear detector comprises a single lining wear detector connected to the wall lining wear detection circuit for each one of the at least one electrically conductive mesh and the at least one electrically conductive bottom mesh, the electric induction furnace with the lining wear detection system further comprising a switching device for switchably connecting the single lining wear detector among the wall lining wear detection circuit for each one of the at least one electrically conductive mesh and the bottom lining wear detection circuit for each one of the at least one electrically conductive bottom mesh.

6. The electric induction furnace with the lining wear detection system of claim 1 wherein the at least one lining wear detector comprises a separate wall lining wear detector connected to the wall lining wear detection circuit for each one of the at least one electrically conductive mesh and a separate wall lining wear detector connected to the bottom lining wear detection circuit for each one of the at least one electrically conductive bottom mesh.

7. The electric induction furnace with the lining wear detection system of claim 1 wherein the at least one electrically conductive bottom mesh comprises a circular electrically conductive mesh having a radial gap between opposing radial ends.

8. The electric induction furnace with the lining wear detection system of claim 1 wherein the at least one electrically conductive bottom mesh comprises a circular electrically conductive mesh having an overlapping radial ends separated by a bottom mesh electrical insulation.

9. The electric induction furnace with the lining wear detection system of claim 1 wherein the at least one electrically conductive bottom mesh comprises an array of electrically conductive bottom meshes, each one of the array of electrically conductive bottom meshes electrically isolated from each other.

10. The electric induction furnace with the lining wear detection system of claim 1 wherein the at least one lining wear detector comprises a single bottom lining wear detector for the bottom lining wear detection circuit for each one of the at least one electrically conductive bottom mesh, the electric induction furnace with the lining wear detection system further comprising a switching device for switchably connecting the single bottom lining wear detector among the bottom lining wear detection circuit for each one of the at least one electrically conductive bottom mesh.

11. The electric induction furnace with the lining wear detection system of claim 1 wherein the at least one lining wear detector comprises a separate bottom lining wear detector for each bottom lining wear detection circuit for each one of the at least one electrically conductive bottom mesh.

12. An electric induction furnace with a lining wear detection system comprising: a replaceable lining having an inner boundary surface and an outer boundary surface, the inner boundary surface of the replaceable lining forming an interior volume of the electric induction furnace; an induction coil at least partially surrounding an exterior height of the electric induction furnace in which the replaceable lining is disposed, the induction coil disposed within a coil refractory lining; a furnace ground circuit having at a first circuit end at a ground probe protruding into the interior volume of the electric induction furnace and a second circuit end terminating at an electrical ground connection external to the electric induction furnace; at least one electrically conductive mesh embedded in a castable refractory disposed between the outer boundary surface of a wall of the replaceable lining and the coil refractory lining, the at least one electrically conductive mesh forming an electrically discontinuous mesh boundary between the castable refractory in which the at least one electrically conductive mesh is embedded and the replaceable lining; a direct current voltage source having a positive electric potential connected to one of the at least one the electrically conductive mesh, and a negative electric potential connected to the electrical ground connection, a lining wear detection circuit formed between the positive electric potential connected to the one of the at least one electrically conductive mesh, and the negative electric potential connected to the electrical ground connection, whereby a wall lining level of a wall lining DC leakage current in the lining wear detection circuit changes as the wall of the replaceable lining is consumed; at least one electrically conductive bottom mesh embedded in a bottom castable refractory disposed below a bottom outer boundary surface of a bottom of the replaceable lining, the at least one electrically conductive bottom mesh forming an electrically discontinuous mesh boundary below the bottom cashable refractory in which the at least one electrically conductive bottom mesh is embedded; and a bottom lining wear direct current voltage source having a bottom lining wear positive electric potential connected to one of the at least one electrically conductive bottom mesh and a bottom lining wear negative electric potential connected to the electrical ground connection, a bottom lining wear detection circuit formed between the bottom lining wear positive electric potential connected to the one of the at least one electrically conductive mesh, and the bottom lining wear negative electric potential connected to the electrical ground connection, whereby a bottom lining level of a bottom lining DC leakage current in the bottom lining wear detection circuit changes as the bottom of the replaceable lining is consumed.

13. The electric induction furnace with the lining wear detection system of claim 12 further comprising at least one bottom lining wear detector connected to the bottom lining wear detection circuit for each one of the at least one electrically conductive mesh for detecting a change in the bottom lining level of the bottom lining DC leakage current.

14. The electric induction furnace with the lining wear detection system of claim 12 wherein the at least one electrically conductive bottom mesh comprises a circular electrically conductive mesh having a radial gap between opposing radial ends.

15. The electric induction furnace with the lining wear detection system of claim 12 wherein the at least one electrically conductive bottom mesh comprises a circular electrically conductive mesh, the circular electrically conductive mesh having an overlapping radial ends separated by a bottom mesh electrical insulation.

16. The electric induction furnace with the lining wear detection system of claim 12 further comprising a single bottom lining wear detector for the bottom lining wear detection circuit for each one of the at least one electrically conductive bottom mesh, the electric induction furnace with the lining wear detection system further comprising a switching device for switchably connecting the single bottom lining wear detector among the bottom lining wear detection circuit for each one of the electrically conductive lining mesh.

17. The electric induction furnace with the lining wear detection system of claim 12 further comprising a separate bottom lining wear detector for each bottom lining wear detection circuit for each one of the at least one electrically conductive bottom mesh.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The figures, in conjunction with the specification and claims, illustrate one or more non-limiting modes of practicing the invention. The invention is not limited to the illustrated layout and content of the drawings.

(2) FIG. 1 is a simplified cross sectional diagram of one example of an electric induction furnace.

(3) FIG. 2 is a cross sectional diagram of one example of an electric induction furnace with a lining wear detection system of the present invention.

(4) FIG. 3(a) illustrates in flat planar view one example of an electrically conductive mesh, a lining wear detection circuit, and a control and/or indicating (detector) circuit used in the electric induction furnace shown in FIG. 2

(5) FIG. 3(b) illustrates in top plan view the electrically conductive mesh shown in FIG. 3(a) in the shape as installed around the circumference of the electric induction furnace shown in FIG. 2.

(6) FIG. 4 is a cross sectional diagram of another example of an electric induction furnace with a lining wear detection system of the present invention that includes a bottom electrically conductive mesh.

(7) FIG. 5 illustrates in top plan view a bottom electrically conductive mesh, bottom lining wear detection circuit, and control and/or indicating (detector) circuit used for bottom lining wear detection in one example of the present invention.

(8) FIG. 6(a) through FIG. 6(f) illustrate fabrication of one example of an electric induction furnace with a lining wear detection system of the present invention.

(9) FIG. 6(g) illustrates fabrication of another example of an electric induction furnace with a lining wear detection system of the present invention where standoffs are used to offset a mesh from the inner wall perimeter of cast flowable refractory.

(10) FIG. 7 is a detail of one example of the electrically conductive mesh embedded in a cast flowable refractory used in an electric induction furnace with a lining wear detection system of the present invention.

(11) FIG. 8 is a cross sectional diagram of another example of an electric induction furnace with a lining wear detection system of the present invention.

(12) FIG. 9(a) through FIG. 9(d) illustrate alternative arrangements of electrically conductive mesh, lining wear detection circuits and detectors used in the electric induction furnace with a lining wear detection system of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(13) There is shown in FIG. 2 one example of an electric induction furnace 10 with a lining wear detection system of the present invention. A cast flowable refractory 24 is disposed between coil 16 and replaceable furnace lining 12. In this example of the invention, electrically conductive mesh 26, (for example, a stainless steel mesh) is embedded within the inner boundary of castable refractory 24 that is adjacent to the outer boundary of lining 12. One non-limiting example of a suitable mesh is formed from type 304 stainless steel welded wire cloth with mesh size 44; wire diameter between 0.028-0.032-inch; and opening width of 0.222-0.218-inch. As shown in FIGS. 3(a) and 3(b), for this example of the invention, mesh 26 forms a discontinuous cylindrical mesh boundary between castable refractory 24 and lining 12 from the top (26.sub.TOP) to the bottom (26.sub.BOT) of the outer boundary of the lining wall. One vertical side 26a of mesh 26 is suitably connected to a positive electric potential that can be established by a suitable voltage source, such as direct current (DC) voltage source V.sub.dc that has its other terminal connected to furnace electrical ground (GND). A lining wear detection circuit is formed between the positive electric potential connected to the electrically conductive mesh and the negative electric potential connected to the furnace electrical ground. Vertical discontinuity 26c (along the height of the lining in this example) in mesh 26 is sized to prevent short circuiting between opposing vertical sides 26a and 26b of mesh 26. Alternatively the mesh may be fabricated in a manner so that the mesh is electrically isolated from itself; for example, a layer of electrical insulation can be provided between two overlapping ends (sides 26a and 26b in this example) of the mesh. As shown in FIG. 3(a) the voltage source circuit can be connected to control and/or indicating circuits via suitable circuit elements such as a current transformer. The control and/or indicating circuits are referred to collectively as a detector. As lining 12 is gradually consumed during the service life of the furnace, DC leakage current will rise, which can be sensed in the control/indicating circuits. For a particular furnace design, a leakage current rise level set point can be established for indication of lining replacement when the furnace is properly operated and maintained.

(14) In some examples of the invention, a bottom lining wear detection system may be provided as shown, for example in FIG. 4, in addition to the wall lining wear detection system shown in FIG. 2. In FIG. 4 electrically conductive bottom mesh 30 is disposed within cast flowable refractory 28 with bottom mesh 30 adjacent to the lower boundary of lining 12 at the bottom of the furnace. As shown in FIG. 5 in this example of the invention, bottom mesh 30 forms a discontinuous circular mesh boundary between bottom cast flowable refractory 28 and the bottom of lining 12. One discontinuous radial side 30a of bottom mesh 30 is suitably connected to a positive electric potential established by a suitable voltage source V.sub.dc that has its other terminal connected to furnace electrical ground (GND). A bottom lining wear detection circuit is formed between the positive electric potential connected to the electrically conductive bottom mesh and the negative electric potential connected to the furnace electrical ground. Radial discontinuity 30c in mesh 30 is sized to prevent short circuiting between opposing radial sides 30a and 30b of mesh 30. Alternatively the mesh may be fabricated in a manner so that the mesh is electrically isolated from itself; for example, a layer of electrical insulation can be provided between two overlapping ends (radial sides 30a and 30b in this example) of the mesh. As shown in FIG. 5, the bottom lining wear detection circuit can be connected to a bottom lining wear control and/or indicating circuits, which are collectively referred to as a detector. As the bottom of lining 12 is gradually consumed during the service life of the furnace, DC leakage current will rise, which can be sensed in the bottom lining wear control and/or indicating circuits. For a particular furnace design, a leakage current rise level set point can be established for indication of lining replacement, based on bottom lining wear, when the furnace is properly operated and maintained.

(15) The particular arrangements of the discontinuous side wall and bottom meshes shown in the figures are one example of discontinuous mesh arrangements of the present invention. The purpose for the discontinuity is to prevent eddy current heating of the mesh from inductive coupling with the magnetic flux generated when alternating current is flowing through induction coil 16 when the coil is connected to a suitable alternating current power source during operation of the furnace. Therefore other arrangements of side wall and bottom meshes are within the scope of the invention as long as the mesh arrangement prevents such inductive heating of the mesh. Similarly arrangement of the electrical connection(s) of the mesh to the lining wear detection circuit, and the control and/or indicating circuits can vary depending upon a particular furnace design.

(16) In some examples of the invention refractory embedded wall mesh 26 may extend for the entire vertical height of lining 12, that is, from the bottom (12.sub.BOT) of the furnace lining to the very top (12.sub.TOP) of the furnace lining that is above the nominal design melt line 25 for a particular furnace as shown, for example, in FIG. 8.

(17) In other applications, wall mesh 26 may be provided in one or more selected discrete regions along the vertical height of lining 12. For example in FIG. 9(a) and FIG. 9(b) wall mesh comprises two vertical electrically conductive meshes 36a and 36b that are electrically isolated from each other and connected to separate lining wear detection circuits so that lining wear can be diagnosed as being on either one half side of the furnace lining. In this example there are two electrical discontinuities 38a (formed between vertical sides 37a and 37d) and 38b (formed between vertical sides 37b and 37c) along the vertical height of the two meshes 36a and 36b. Further any multiple of separate, vertically oriented and electrically isolated wall mesh regions may be provided along the vertical height of lining 12 with each separate wall mesh region being connected to a separate lining wear detection circuit so that lining wear could be localized to one of the wall mesh regions. Alternatively as shown in FIG. 9(c) the multiple electrically conductive meshes 46a through 46d can be horizontally oriented with each electrically isolated mesh connected to a separate lining wear detection circuit and control and/or indicating circuits (D) so that lining wear can be localized to one of the isolated mesh regions. Most generally as shown in FIG. 9(d) the multiple electrically conductive meshes 56a through 56p can be arrayed around the height of the replaceable lining wall with each electrically conductive mesh connected to a separate lining wear detection circuit, and control and/or indicating circuits (not shown in the figure) so that lining wear can be localized to one of the isolated mesh regions that can be defined by a two-dimensional X-Y coordinate system around the circumference of the replaceable lining wall with the X coordinate defining a position around the circumference of the lining and the Y coordinate defining a position along the height of the lining.

(18) In similar fashion bottom mesh 30 may cover less than the entire bottom of replaceable lining 12 in some examples of the invention, or comprise a number of electrically isolated bottom meshes with each of the electrically isolated bottom meshes connected to a separate lining wear detection circuit so that lining wear could be localized to one of the bottom mesh regions.

(19) Alternatively to a separate detector (control and/or indicating circuits) used with each lining wear detection circuit in the above examples, a single detector can be switchably connected to the lining wear detection circuits associated with two or more of the electrically isolated meshes in all examples of the invention.

(20) While the figures illustrate separate wall and bottom lining wear detection systems, in some examples of the invention, a combined wall and bottom lining wear detection system may be provided either by (1) providing a continuous side and bottom mesh embedded in an integrally cast flowable refractory with a single lining wear detection circuit and detector or (2) providing separate side and bottom meshes embedded in a cast flowable refractory with a common lining wear detection circuit and detector.

(21) FIG. 6(a) through FIG. 6(f) illustrate one example of fabrication of an electric induction furnace with a lining wear detection system of the present invention. Induction coil 16 can be fabricated (typically wound) and positioned over suitable foundation 18. As shown in FIG. 6(a) trowelable refractory (grout) material 20 can be installed around the coil as in the prior art. One suitable proprietary trowelable refractory material 20 is INDUCTOCOAT 35AF (available from Inductotherm Corp., Rancocas, N.J.). If a bottom lining wear detection system is used, bottom mesh 30 can be fitted at the top of foundation 18 and embedded in cast flowable refractory 28 by pouring the cast flowable refractory around bottom mesh 30 so that the mesh is embedded within the refractory after it sets as shown in FIG. 6(b). Alternatively the bottom mesh can be cast in a cast flowable refractory in a separate mold and then the cast refractory embedded bottom mesh can be installed in the bottom of the furnace after the cast flowable refractory sets.

(22) A suitable temporary cast flowable refractory mold 90 (or molds forming a formwork) for example, in the shape of an open right cylinder, is positioned within the volume formed by coil 16 and refractory material 20 to form a cast flowable refractory annular volume between refractory material 20 and the outer wall perimeter of the mold as shown in FIG. 6(c). Mesh 26 is fitted around the outer perimeter of temporary mold 90 and the cast flowable refractory 24, such as INDUCTOCOAT 35AF-FLOW (available from Inductotherm Corp., Rancocas, N.J.), can be poured into the cast flowable refractory annular volume to set and form hardened castable refractory 24 as shown in FIG. 6(d). Vibrating compactors can be used to release trapped air and excess water from the cast flowable refractory so that the refractory settles firmly in place in the formwork before setting. Mesh 26 will be at least partially embedded in cast flowable refractory 24 when it sets inside of the cast flowable refractory annular volume. In other examples of the invention mesh 26 can be embedded anywhere within the thickness, t, of cast flowable refractory 24. For example as shown in FIG. 7, mesh 26 is offset by distance, t.sub.1, from the inner wall perimeter of cast flowable refractory 24. Offset embedment can be achieved by installing suitable standoffs 94 around the outer perimeter of mold 90 as illustrated in FIG. 6(g) and then fitting mesh 26 around the standoffs before pouring the cast flowable refractory. In the broadest sense as used herein, the terminology mesh embedded in a cast flowable refractory means the mesh is either fixed within the refractory; at a surface boundary of the refractory, or sufficiently, but not completely, embedded at a surface boundary of the refractory so that the mesh is retained in place in the the refractory after the refractory sets.

(23) After cast flowable refractory 24 sets, temporary mold 90 is removed, and a replaceable lining mold 92 that is shaped to conform to the boundary wall and bottom of interior furnace volume 14 can be positioned within the volume formed by set cast flowable refractory 24 (with embedded mesh 26) to form a replaceable lining annular volume between set cast flowable refractory 24 and the outer wall perimeter of the lining mold 92 as shown in FIG. 6(e). A conventional powder refractory can then be fed into the lining volume according to conventional procedures. If lining mold 92 is formed from an electrically conductive mold material, lining mold 92 can be heated and melted in place according to conventional procedures to sinter the lining refractory layer that forms the boundary of furnace volume 14. Alternatively the lining mold may be removed and sintering of the lining refractory layer may be accomplished by direct heat application.

(24) Distinction is made between the replaceable lining refractory, which is typically a powder refractory and the cast flowable refractory in which the electrically conductive mesh is embedded. The cast flowable refractory is used so that the electrically conductive mesh can be embedded in the refractory. The cast flowable refractory is also referred to herein as castable refractory and flowable refractory.

(25) FIG. 6(f) illustrates an electric induction furnace with one example of a lining wear detection system of the present invention with addition of typical furnace ground leak detector system probe wires 22a and electrical ground lead 22b that is connected to a furnace electrical ground (GND)

(26) The fabrication process described above and as shown in FIG. 6(a) through FIG. 6(f) illustrates one example of fabrication steps exemplary to the present invention. Additional conventional fabrication steps may be required to complete furnace construction.

(27) In alternative examples of the invention rather than using a separate trowelable refractory (grout) around coil 16, cast flowable refractory 24 can be extended to, and around coil 16.

(28) The induction furnace of the present invention may be of any type, for example, a bottom pour, top tilt pour, pressure pour, or push-out electric induction furnace, operating at atmosphere or in a controlled environment such as an inert gas or vacuum. While the induction furnace shown in the figures has a circular interior cross section, furnaces with other cross sectional shapes, such as square, may also utilize the present invention. While a single induction coil is shown in the drawing for the electric induction furnace of the present invention, the term induction coil as used herein also includes a plurality of induction coils either with individual electrical connections and/or electrically interconnected induction coils.

(29) Further the lining wear detection system of the present invention may also be utilized in portable refractory lined ladles used to transfer molten metals between locations and stationary refractory lined launders.

(30) The examples of the invention include reference to specific electrical components. One skilled in the art may practice the invention by substituting components that are not necessarily of the same type but will create the desired conditions or accomplish the desired results of the invention. For example, single components may be substituted for multiple components or vice versa.