KR100208625B1 - Induction heating line - Google Patents

Abstract

An induction heating coil assembly for use in a roller induction heating line of the present invention includes a magnetic shunt for receiving a portion of an electromagnetic field generated along an axis of an induction coil and adjusting a portion thereof along a path parallel to an operating piece passing through a heating line . This flux path allows the swirling current induced in the operating piece to flow practically perpendicularly to the operating piece axis and to generate an arc between the operating piece and the conveyor rolls in which the swirling current moves, Ensure that it does not flow.

Description

Induction heating line

FIG. 1 schematically shows that an operating piece is heated by an induction heating coil according to a conventional technique; FIG.

Figs. 2a and 2b are perspective views showing that the operating piece is heated by the induction heating coil according to the present invention. Fig.

Figure 3 is a perspective view of the induction heating coil assembly according to the present invention showing that the magnetic shunt has been removed to show the induction coil beneath it;

4 is a cross-sectional view taken along line 4-4 of FIG. 2;

5 is a cross-sectional view taken along line 5-5 of FIG. 6;

6 is a longitudinal section along line 6-6 of FIG. 2a.

FIGS. 7 and 8 are another longitudinal sectional view of the line 6-6 of another embodiment of FIG. 2a.

FIG. 9 is a partial cross-sectional view showing in more detail an insulating layer between a magnetic shunt and a coil turn of a coil assembly according to the present invention; FIG.

10 is an enlarged view of an optional magnetic shunt end plate of a coil assembly in accordance with the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS

10: induction heating line 12: operating piece

14, 16: Conveyor roll 18: Induction heating coil

20: ac power supply 22: roller induction heating line

24: coil assembly 26: slab

27,29: Conveyor roll 28: Induction coil

30: magnetic shunt 31: end

34, 38: transverse yoke 42: intermediate yoke

44,46: Spacer

The present invention relates to induction heating lines of continuous cast products such as slabs, billets, bars, and the like.

It is often desirable to heat such cast products while moving a continuous cast product (i.e., slab, billet, or other operating piece) along a path from one location to another. Typically, such products are moved by conveyor rolls, which are supported from underneath the product and driven to impart linear motion to the article of manufacture.

A conventional continuous casting product roller induction heating line 10 according to the prior art is schematically illustrated in FIG. Continuous cast products such as tubular actuating pieces 12 are conveyed from right to left by steel conveyor rolls 14 and 16 as shown in FIG. Conveyor rolls 14 and 16 are journalled rotatably in the support frame and are rotationally driven counterclockwise in a known manner as shown in FIG. The conveyor rolls 14 and 16 provide linear movement from right to left to the tubular operating piece 12, as indicated by the large arrows on top of the first view.

As the tubular operative piece 12 is conveyed by the conveyor rolls 14 and 16, the tubular operative piece passes through the induction heating coil 18. This induction heating coil 18 is a conventional spirally wound coil known in the art. The induction heating coil 18 is also energized by a high frequency ac power source 20, which is known in the prior art, to generate an electromagnetic field that passes through the tubular operative member 12. [ Normally, the operating piece 12 is positioned such that its axis is co-linear with the axis of the coil 12. [ The electromagnetic field generated by the induction coil 18 induces an eddy current in the tubular operative member 12. The electrical resistance of the tubular operating piece 12 relative to the induced eddy current is I ² R which heats the tubular operating piece 12.

However, a problem arises because the induction coil 18 generates a component of the electromagnetic field which is small, but not negligible, perpendicular to the axis of the coil, and therefore along the axial direction of the tubular actuating piece 12. [ The components of this electromagnetic field induce a current flowing along the axis of the tubular operative member 12, as indicated by the small horizontal arrows pointing to the right in FIG. This current, referred to as parasitic current, begins to circulate along the path from the tubular operative member 12 to the conveyor rolls 14 and 16 through a common ground, such as a support frame in which the rolls are journaled. This path is indicated by the curved path shown below the rolls in FIG. 1 (although the figure shows the parasitic current flow in one direction, the parasitic current is understood to be AC because the chill is excited by the ac power supply). This phenomenon induces pitting and other damage to the conveyor rolls by creating an arc between the moving tubular operative piece 12 and the conveyor rolls 14 and 16.

Prior to the present invention, the most common way to prevent the flow of parasitic current was to isolate the conveyor rolls from the ground to disrupt the path of the current. This has resulted in cumbersome and expensive steps. One solution was to manufacture the conveyor rolls with ceramic. Ceramic conveyor rolls are very expensive and can easily crack. Other techniques include constructing conveyor rolls with concentric inner and outer steel tubes insulated from each other by an intermediate insulator such as a ceramic. Such conveyor rolls are very expensive to manufacture and are liable to fail due to different expansion and contraction between the steel and the insulating material when such rolls are subjected to high temperatures that are involved in subsequent heating operations.

In some cases, no attempt has been made to eliminate the parasitic current. The current was allowed to flow and the conveyor rolls were periodically removed from the line and a new surface was attached to remove the fittings. Clearly, none of these solutions were satisfactory.

Accordingly, the present invention provides a method for preventing the flow of parasitic current. The present invention therefore avoids damage to the conveyor caused by parasitic currents and eliminates the need for an insulating sheme and a specific conveyor to prevent the flow of parasitic currents. Therefore, the present invention makes roll induction heating easier and less expensive than the conventional solution.

Summary of the Invention Briefly, the present invention is directed to an induction heating coil assembly for use in a roller induction heating line. The induction heating coil is constituted by conveyor rolls for conveying the actuating piece such as a slab to induction heating along a linear path and an induction heating coil surrounding the path. The induction heating coil assembly has a central axis and includes an induction coil and a magnetic shunt surrounding the coil. The induction coil has a plurality of turns and is configured to define a preselected peripheral length so that the actuating piece is received within its perimeter. The magnetic shunt includes first and second transverse yokes and a plurality of intermediate yokes spaced from each of the first and second transverse yokes at opposite ends of the coil. The intermediate yokes are positioned between the first plurality of yokes and the second plurality of yokes and extend parallel to the axis of the coil. The intermediate yokes extend along a peripheral rim defined by the induction coil. The first and second plurality of yokes are axially separated from each other and are electromagnetically coupled together by a plurality of intermediate yokes.

In operation, the plurality of orcs function as a magnetic flux that is parallel to the axis of the coil, i. E., Along the path parallel to the slab, indicating the direction of the electromagnetic field generated in the induction coil. This flux path induces a swirl current in the operating piece. However, since the yokes are rotated, there is no component perpendicular to the magnetic flux that can be sensed (i.e. there is no component perpendicular to the coil or actuating piece that can be sensed). Thus, The induced eddy current flows perpendicular to the axis of the operating piece. The induced parasitic eddy current does not flow enough to be sensed either below the operating element or along the operating element. Thus, the parasitic current does not damage the circulation through the conveyor rolls.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown by way of example only, On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

Referring now to the drawings, FIG. 2a is a perspective view showing a roller induction heating line 22 and a novel induction heating coil assembly 24 associated therewith. FIG. 3 is a perspective view of a novel induction heating coil assembly 24. For clarity, Figures 2a and 3 are illustrated together. The line 22 carries a continuous cast operative piece such as the slab 26 accordingly. The line 22 may also carry other types of actuation pieces, such as the tubular actuation piece 12 shown in the prior art of FIG. 2a, slab 26 is linearly conveyed by steel conveyor rolls 27 and 29 from right to left. These rolls operate in the same manner as described above with respect to the first prior art technique.

The induction heating coil assembly 24 surrounds the slab 26 so that the slab 26 penetrates the coil assembly 24. The assembly 24 includes a magnetic shunt 30 and an induction heating coil 28 surrounding the distal end 31 and the outer edge P _{0 of the} induction heating coil 28. The induction heating coil 28 is a conventional spirally wound coil shown in FIG. 1 as a conventional technique. The induction heating coil 28 has a central axis A and a length l _c . Thus, the slab 26 passes through an area defined by the inner edge P _i and length l _c of the coil. It is preferable that the coil 26 is located such that the longitudinal axis B of the slab is coaxial with the center axis A of the induction coil with respect to the slab 26. [

The magnetic shunt 30 is shown as having three different parts. The first part consists of each lateral yoke 34 of the first plurality 32 and the second part consists of each lateral yoke 38 of the second plurality 36. And the third part consists of each of the intermediate yokes 42 of the third plurality 40. However, if desired, such lateral yokes and intermediate yokes may be a single unit, or may be joined together to form a single unit. The plurality of transverse yokes 34, 38 are spaced apart from one another in such a way as to be stacked or sandwiched by nonconductive spacers 44 of the same shape. A plurality of intermediate yokes 42 are also spaced apart from each other in a similar stacking manner with nonconductive spacers 46 of the same shape. Suitable as a non-conductive material with respect to the yoke is such yanghyeongtae Mylar ^ⓡ.

More specifically, the plurality of transverse yokes 34, 38 extend completely around all regions of the distal end 31 of the induction coil 28, while the intermediate yokes 42 are arranged in a plurality of groups , Each group being separated by a relatively small air gap. This air gap creates a small discontinuity along the outer edge P _A of the assembly 24.

The particular arrangement of the yokes is an important feature of the present invention. A plurality of first and second respective lateral yokes 34 and 38 are laterally directed with respect to the outer edge P ₀ of the induction coil 28 and located at the opposite end of the coil. Each of the transverse yokes 34, 38 is defined by an inner opposing planar end 48 and an outer opposing planar end 50. The transverse yokes 34 and 38 are positioned at the opposite end 31 of the induction coil 28 and extend axially beyond the inner periphery P _i of the induction coil 28 slightly inward. The nonconductive spacers 44 are oriented in the same way as the transverse yokes 34, 38 (?).

The transverse yokes 34 and 38 and the spacer 44 extend completely around the edge of the edge of the induction coil 28 but do not contact. In the illustrated embodiment, the yokes 34, 38 extend around the rim in a generally flat elliptical shape. The lateral length l _t of the yokes 34 and 38 and the spacers 44 are the same along the whole rim and the opposing planar ends 48 and 50 of the inner and outer sides of the yokes 34 and 38 , And terminate in each common radial plane, as shown in FIG.

In order to accommodate the edges of the elliptical shape, the lateral yokes 34, 38 along the corners and the spacers 44 are in wedge form.

The individual intermediate yokes 42 are positioned between the transverse yokes 34 and 38 and extend parallel to the central axis A of the induction coil 28. [ Thus, the intermediate yoke 42 appears as if it were radial fins extending from the induction coil. Each intermediate yoke 42 has a slightly greater vertical length (l _c) than the length (l _c) of the induction coil (28).

The plurality of intermediate yokes 42 do not closely surround or contact the outer edge P ₀ of the induction coil 28. Each intermediate yoke 42 is defined by an inner facing planar end 52 and an outer opposing planar end 54. The opposing planar ends 54 of the intermediate yokes 42 terminate at an elliptical radial plane such as the planar ends 50 facing the outside of the transverse yokes 34 and 38 . In addition, the nonconductive spacers 46 are oriented in the same direction as the intermediate yokes 42.

The transverse yokes 34 and 38 extend around the entire rim of each end of the induction coil 28 while the intermediate yokes 42 are arranged in spaced apart groups by small air gaps. As best shown in FIG. 5, in the embodiment described herein, there are 16 such groups.

The first and second plurality of transverse yokes 34, 38 are electromagnetically coupled together by respective intermediate yokes 42 located in the same plane or positioned closely adjacent to each other. For example, in the third figure, the lateral yokes 34 ₁ , 38 ₁ are joined together by the intermediate yoke 42 ₁ . This electromagnetic coupling allows the magnetic flux to flow easily along the length of the magnetic shunt 30. [ Due to the air gap 56, not all lateral yokes 34, 38 are electromagnetically coupled in the same plane by the respective intermediate yokes 42. These pairs of transverse yokes 34 and 38 are electromagnetically coupled by an adjacent intermediate yoke 42. [ Since the air gap 56 is relatively small relative to the length of the elliptic flux path, there will be a small but relatively negligible divergence at each end flux path.

2b shows the functional advantages of the induction heating coil assembly 24 during operation of the roller induction heating line 22, When the power source is applied to the induction coil 28 (which is not visible in the visible direction of the diagram), the induction coil 28 has a horizontal path to the center axis A (not shown) And generates an electromagnetic field having a component along one path. The vertical component is very small compared to the horizontal component, but it is large enough to be a problem if it is not removed. The plurality of yokes in the magnetic shunt direct the two electromagnetic field components to a path parallel to the central axis A of the induction coil 28 and thus parallel to the longitudinal axis B of the slab 26. [ The magnetic flux induces a swirl current in the slab 26. The lateral yokes 34 and 38 and the intermediate yoke 42 are in a direction parallel to the longitudinal axis of the slab 26 and virtually all of the magnetic flux is along this path. This path is shown in Figure 2b as a series of solid arrows. There is also almost no component perpendicular to the magnetic flux. In other words, there is no component perpendicular to the longitudinal axis B of the slab 26. Therefore, the eddy current induced in the slab 26 flows in a direction perpendicular to the longitudinal axis B of the slab in principle. This swirl current is shown in dashed lines in the slab 26 in FIG. 2b and is best shown in FIG. 5. The parasitic eddy current induced to be sensed does not flow along the vertical axis B of the slab 26 or below. Therefore, the circulation of the parasitic current through the conveyor rolls 27 and 29 is not damaged.

If the magnetic shunt 30 were not present, the electromagnetic field would be diverging in all directions at the end of the induction coil 28, as shown by the phantom arrows, and would have a non-negligible vertical component. Therefore, the parasitic eddy current which can not be ignored will be induced to flow to the slab 26 along the longitudinal axis B of the slab, which will cause the above-described problem.

FIGS. 4, 5 and 6 are end views according to FIG. 2a and show certain features of the invention more clearly.

FIG. 4 is an end view along line 4-4 of FIG. 2a. This figure shows the arrangement of the non-conductive spacers 44 completely surrounding the ends of each of the transverse yokes 34 and the induction coil 28 of the first plurality 32 of optional features. Since the yoke 34 and the spacer 44 are stacked together or sandwiched together, the induction coil 28 can not be seen in this figure. Also, FIG. 4 clearly shows spacers (i.e., 44 ₂ ) along the edges of the elliptical shape and transverse yokes (i.e., 34 ₂ ) in wedge form. The slab 26 to be heated is located at the inner center of the surrounding lateral yoke 34.

5 is a cross-sectional view taken along line 5-5 of FIG. 6; This represents a space 46 separated by sixteen spaced groups of intermediate yokes 42 and a small air gap 56. Also, one induction coil 28 turn can be seen in this figure. FIG. 5 also shows the eddy current induced as a dotted line arrow in the slab 26. FIG. Of course, the direction of this current alternately changes at the same frequency as the frequency at which the used AC power source excites the induction coil 28. [ What is shown in FIG. 5 is the direction at the given instant.

6 is a longitudinal sectional view taken along the line 6-6 in FIG. This shows two transverse end yokes 34,38 and a connecting intermediate yoke 42 located in the same vertical plane. In this figure, a plurality of induction coil 28 turns can be seen. Sixth turn also, shows that a magnetic shunt (30) is surrounded with an outer rim (P ₀₎ and a terminal of the induction coil. As described above, the yokes of the magnetic shunt 30 provide a magnetic flux path for the electromagnetic field along the central axis A of the induction coil 28. The path through the yokes 34, 42, 38 and the slab 26 is shown by the solid line arrows. It should also be understood that the direction of the path is alternately changed at the same frequency as the frequency at which the used AC power source excites the induction coil 28. Shown in FIG. 6 is the direction at a given instant.

The magnetic shunt 30 may be configured in a variety of different ways, as shown in FIGS. 7 and 8. FIG.

In Figure 7, the transverse end yokes 34, 38 are shorter in length and the intermediate yoke 42 is longer at each end and overlaps with the respective end yokes 34, 38. In Fig. 8, the transverse end yokes 34, 38 and the intermediate yoke 44 are formed as one continuous material. In addition, the nonconductive spacers 44 and 46 are configured in a one-and-a-half arrangement such as the yoke.

As described and illustrated, embodiments of the present invention employ a rod or operating piece in the form of a square, such as a slab. However, the scope of the present invention includes embodiments in the form of other rods, such as tubular or cylindrical actuating pieces. In this alternative embodiment, the coil 28 and the magnetic shunt 30 are generally oval rather than circular in their cross-section.

The coil assembly 24 will be subjected to a very large dynamic force as a result of the magnetic action between the coil 28 and the operating piece. For large installations, this force can reach several tons. That is, in a conventional cylindrical induction coil, this force is equally distributed around the circumference of the coil, so that it is balanced around the coil rim, or becomes radial symmetry. However, in the present situation, that is, in a situation in which the coil is flat oval, the force will not be symmetrical around the coiled stylus and will cause a net force of actual magnitude between the coil and the operating piece. To assist in strengthening the coil assembly 28, the magnetic shunt can be clamped tightly against the coil turn, as shown in FIG.

FIG. 9 shows a plurality of clamps 58 on the intermediate and lateral yokes 38.

Clamp 58 provides a clamping force on the coil turn. In the intermediate yokes, the compression force is radial, as indicated by the arrow F _R , and the compression force at the end yoke 38 is the axial direction, as indicated by the arrow F _A. Clamp 58 may have any shape or structure designed to provide a clamping force to the yokes and coil. To prevent electrical shorts between the coil turns, the yoke is insulated from the coil turns by an insulating spacer (60). The already described shunt arrangement is very effective in indicating the direction of the magnetic flux generated by the coil, but as shown in FIG. 10, the operating characteristic can be further improved by the end plate deflecting the electro-conductive flux. FIG. 10 is an enlarged view of the coil assembly 24 including the end plates at each end plate 62 of the coil assembly 24. The distal plate 62 is generally rectangular in shape and has a volume slightly larger than the entire outer volume of the coil 24. Each end plate 62 has a generally rectangular hole at its center, through which the operating piece is received. The hole 64 is approximately equal in size and shape to the hole through which the operating piece in the coil assembly 24 passes. The terminal plate is preferably a good electrical conductor and is preferably made of copper that deflects the magnetic flux with minimal loss. The end plate 62 is positioned adjacent to and axially positioned external to the distal yokes 34 and 38. Advantageously, said end plate is located at a short distance from said end yokes. It is within the scope of the present invention to place the insulating spacer between the end plate 62 and the end yokes and also to secure the end plate 62 to the clamp Can be fixed. The use of the shunt assemblies already described above makes it possible to reach the rollers 14 and 16 with a magnetic flux scattered from the coil assembly 24, especially when the rollers are very close to the end of the coil assembly. These scattered fluxes can induce parasitic currents to flow to the roller and disable the shunt effect. The end plates 62 can escape from the center hole of the coil assembly 24 to the end yokes 34 and 38 and adjust the direction of any scattered fluxes that can escape from them to the intermediate yoke 42. In addition, the distal plate 62 greatly enhances flux concentration within the coil.

The present invention described above eliminates arcing between the moving operating piece and the conveyor roll by providing a selective approach to preventing effective parasitic currents from flowing along the operating piece. Inductive heating of the rollers is now easier and less expensive than conventional methods, since it is no longer required to employ a specific conveyor roll or insulation mechanism to prevent damage to the conveyor rolls from such currents.

The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof, and accordingly, the scope of the present invention should be defined by the appended claims rather than the foregoing detailed description.

Claims (12)

And an induction heating coil assembly surrounding the path, the induction heating coil having a central axis substantially co-linear with the path and a pre-selected axial length An induction coil having a plurality of turns and configured to receive a motion piece within a rim and to define a pre-selected rim to be traversed along the path, and a first and a second plurality of transverse yokes And a plurality of intermediate yokes spaced apart from each other and extending between the first plurality of transverse yokes and the second plurality of transverse yokes and parallel to the central axis of the coil assembly, The two lateral yokes surround the coil, Wherein the yokes extend around the main portion of the rim defined by the induction coil and the first and second yokes are axially separated from each other and are electromagnetically coupled together by the plurality of intermediate yokes. Heating line. 2. The roller induction heating line of claim 1, wherein the first and second plurality of transverse yokes extend around the entire opposite end of the coil. 3. The roller induction heating line of claim 2, wherein the intermediate yokes are arranged in spaced groups. 2. The roller induction heating line of claim 1, wherein the plurality of intermediate yokes extend radially from the induction coil. The roller induction heating line according to claim 1, wherein the induction coil is spiraled. 2. The roller induction heating line of claim 1, wherein the first and second transverse yokes and adjacent intermediate yokes adjacent to each other are spaced apart by a nonconductive spacer. The roller induction heating line according to claim 1, wherein each of the intermediate yokes is flush with each pair of axially separated lateral yokes. The roller induction heating line according to claim 1, wherein the first and second plurality of transverse yokes and the plurality of intermediate yokes are arranged in a generally elliptical arrangement in cross-section. The roller induction heating line according to claim 1, wherein the first and second plurality of transverse yokes and the plurality of intermediate yokes are formed of one continuous material. 2. The roller induction heating apparatus according to claim 1, further comprising a clamp acting on the transverse yokes and the intermediate yokes to exert axial and radial forces on the induction coil. 11. The roller induction heating line according to claim 10, comprising a non-magnetic insulating material between the yokes and the induction coil. 2. The roller induction heating line of claim 1, further comprising an end plate axially adjacent to the outside of the transverse yokes and biasing the electro-conductive flux.