Localized Heating With Current Concentrated By Externally Applied Magnetic Field

Abstract

Heating of a solid conductor is caused by passing DC or low-frequency AC current through the conductor and restricting the current flow path by an externally applied magnetic field.

Description

This invention relates to the heating of solid conductors by passing relatively high concentrations of electrical current therethrough. More specifically, this invention relates to the restriction of current flow paths in conductors through the application of externally applied magnetic fields.

Heating of conductors has heretofore been accomplished typically by applying alternating high-frequency currents to conductors. Restriction of the current flow paths of these alternating high-frequency currents within conductors has been shown to follow a narrow current flow path defined by the variables of conductor geometry, process of current application and the frequency of the current applied. More specifically, it has not been possible to obtain deep current penetration into conductors of alternating current because of the "skin effect" phenomenon which restricts alternating currents to a flow path at or near the surface of the conductor. Moreover, alternating currents generate their own magnetic fields, which in turn tend to further delimit and define the flow path of such alternating currents.

One of the most common processes of generating heating current within a conductor is the induction heating process. In this process a current is induced within the conductor by an externally applied and fluctuating magnetic field. This field serves to both generate the desired current and simultaneously position the current within the conductor for producing a desired heating effect.

Induction heating has serious disadvantages. Frequently, the magnetic field required to produce a desired current flow will produce a current flow path which has either undesired location or concentrations. Conversely, the magnetic field capable of providing a desirable current flow path will produce a current flow which is either too large or too small to produce the desired heating effect. Either of these induction heating phenomena will result in undesired changes occuring in the properties of the conductor such as immediately adjacent hot and cold areas, burnt conductor edges, and unpredictable heat generation within the conductor.

It is an object of this invention to disclose a method and apparatus for producing a current flow within a conductor to be heated which can be conveniently controlled both as to current flow intensity and current flow path. Accordingly, a source of current, either alternating current or direct current, is applied to the conductor. Independent of this applied current, a magnetic field is positioned about the conductor. By the expedient of either varying the current flow or alternately the independent magnetic field, the location and intensity of heat-generating current flow within the conductor can be controlled within wide limits.

An advantage of this invention is that the shallow current paths commonly associated with alternating high-frequency currents are avoided; current flow paths can be controlled in conductors at virtually any preselected depth.

A further advantage of this invention is that direct current can be used to produce localized heating of the conductor. The generation of dynamic and fluctuating magnetic fields by the heat-inducing alternating current can be completely avoided. Moreover, the skin effect phenomenon, common with high-frequency alternating current, is minimized.

A further advantage of this invention is that current can be concentrated in small current flow areas than their own ambient magnetic fields will permit. This enables more heating to occur with less current flow.

A still further advantage of this invention is that heating of the conductor at areas other than the desired current flow path, common in induction heating techniques, can be avoided.

A still further advantage of this invention is that lower voltage heating currents can be utilized. The likelihood of arcing and dielectric breakdown is reduced.

A still further advantage of this invention is that conventional DC or low-frequency AC power supplies can be used. The expense of building specially adapted high-frequency power supplies, commonly necessary in induction heating techniques, is avoided.

Other objects, features and advantages of this invention will be more apparent after referring to the following specification and attached drawing in which:

FIG. 1 is a side elevation schematic illustrating the use of the technique of this invention for the induction welding of two continuously advanced metallic conductors to form a welded beam of conventional T-shaped cross section;

FIG. 2 is an end elevation section along lines 2--2 of FIG. 1 illustrating schematically both the conductor positioning and magnet configuration for producing the desired localized current flow in the vertically disposed conductor;

FIG. 3 is an end elevation section similar to FIG. 2 illustrating both the conductor positioning and magnet configuration for producing the desired current flow in the horizontally disposed conductor;

FIG. 4 is an end elevation section of the welded T-shaped beam; and

FIG. 5 is a perspective schematic of the technique of this invention used to heat a stationary conductor with alternating current.

With specific reference to FIG. 1, two continuously advancing steel strips A and B are illustrated moving to a point of convergence at squeeze rollers C. Current is applied to strips A and B at contacts D upstream of the point of convergence. Magnets E positioned between the current source D and point of strip convergence cause current flow through each of the strips A and B to be positioned within the advancing strips. In the application here shown, the current flow and the independent externally applied magnetic fields are adjusted to produce heating sufficient for welding strips A and B into the T-section beam illustrated in FIG. 4.

Strips A and B physically are solid conductors. For the practice of this invention, virtually any conductor can be utilized. Such conductors can include both metallic and nonmetallic solids in which heating is desired.

Advancing strip A is here illustrated as a vertically disposed steel strip. This strip has an upper edge 14, which is maintained at a relatively cool state during the welding operation, and a lower edge 16 which is heated for welding under pressure.

Advancing strip B is also of steel but horizontally disposed with respect to strip A. Strip B includes two edges 17 and 19 which are maintained in a relatively cool state during the welding process and a central medial section 20 which is heated for welding under pressure at squeeze rollers C.

Squeeze rollers C may be of any desired configuration for producing conjoinder of the advancing strips A and B under pressure sufficient to produce a weld. As illustrated, strip A is horizontally positioned by paired rollers 22 on either side of strip A. Similarly, strip B is positioned upstream of its point of contact with strip A by paired rollers 24 and downstream of its point of contact with strip A by paired rollers 26, these rollers contacting the edges 17 and 19 of advancing strips B.

In order to produce the desired pressure weld, rollers 28 and 30 are utilized to press strips A and B towards one another. Roller 28 pushes strip B at medial portion 20 into contact with the lower edge 16 of strip A. As is common in the art of pressure welding of metals, the pressure of roller 28 towards roller 30 is adjusted by apparatus (not shown) to produce the desired pressure weld at the temperature of the advancing strips.

Current is here shown applied to the advancing strips A and B by contacts D. As illustrated in FIG. 1, a DC current is applied at contact 32 to edge 16 of advancing strip A upstream of the point of strip convergence, the current applied being of positive polarity. Likewise, current is applied to advancing strip B at contact 34 upstream of its point of seam convergence with strip A, the current applied here being illustrated of negative polarity.

Contacts 32 and 34 produce a current flow. Typically, the current flow (described in conventional direct current flow terminology) flows from contact 32 through strip A to the point of strip convergence at rollers C. From the point of strip convergence at rollers C, the current flows along strip B to contact 34.

Current flow within advancing strips A and B is positioned by magnets E. These magnets are illustrated in section in FIGS. 2 and 3.

The current flow in strip A is positioned by magnet 40. Magnet 40 has a U-sectioned magnetic field conducting core which spans over edge 14 of strip A at the bottom central portion of the U and has two field conducting sides extending parallel along either side of strip A.

Magnet 40 is provided with a field winding 44. This winding is here illustrated as having direct current applied thereto. As can be seen, the winding is positioned to produce a north-south magnetic field which repels current flow from edge 14 and concentrates the current flow at edge 16. This repulsion of the current flow from edge 14 towards edge 16 produces the desired current flow concentration.

It should be apparent, that by varying the intensity of the field produced at magnet 40, the current flow path can be controlled. Where the magnetic field is of high intensity, the current flow cross-sectional area at edge 16 will be reduced. Conversely, where the magnetic field is of low intensity, the current flow cross-sectional area at edge 16 will be of relatively large area.

Referring to FIG. 3 two magnets 42 and 43 are positioned on either side of strip B. Magnet 42 has a U-sectioned magnet field conducting core having the bottom central portion of the U overlying edge 17 of advancing strip B. The two vertically extending side members of the U-sectioned core extend on either side of strip B towards central portion 20 of the strip. A winding 46 about the U-sectioned core of magnet 42 produces a north-south magnetic field as illustrated.

Similar to magnet 42, magnet 43 has a U-sectioned magnetic field conducting core having the bottom central portion of the U overlying edge 19 of advancing strip B. The two vertically extending side members of the U-sectioned core extend on either side of strip B towards the central portion 20 of the strip.

Magnets 42 and 43 each have their respective field windings 46 and 48. These windings are here illustrated as having direct current applied thereto. As can be seen, the windings are positioned to produce a north-south magnetic field which repels current from the edge of the strip adjacent the bottom portion of the U-section and concentrates the current away from each of the strip edges 17 and 19 to medial portion 20 of the strip intermediate its edges. This repulsion of the current flow from edges 17 and 19 towards the central portion 20 of the strip produces the desired current flow concentration.

It should be apparent that by varying the intensity of the fields produced at magnets 42 and 43, the current flow path within central portion 20 of web B can be controlled. Where the high magnetic fields are of high intensity, the current flow cross-sectional area at central portion 20 will be of small cross section. Conversely, where the magnetic fields are of low intensity, the current flow cross-sectional area at central portion 20 will be relatively large.

Thus far, the applied current at contacts D and the field generating current within the magnets E has been illustrated utilizing direct current. It should be apparent that alternating currents can be used for both heating the strips A and B and for producing the desired magnetic fields through magnets E. Moreover, the use of alternating current enables the current flow path to be controlled through the adjustment of either phase or amplitude or both between the respective currents in the magnetic field winding on one hand, and the heat-inducing current in the conductor on the other hand.

As a practical limitation, the heat-inducing current within the conductor should be below those frequencies where the "skin effect" phenomenon causes undue restriction of the current to the conductor surface and prevents the current penetration necessary to provide desired uniform heating. Frequencies above this limit will result in restriction of the current flow path to the surface of the conductor and consequently give undesired localized surface heating.

It should be apparent to the reader that this invention can be used in many additional applications other than that of the illustrated example of welding two continuously advancing metallic strips. For example, a static steel plate can be heat treated along a preselected portion by applied electrical current. Such an example is illustrated in FIG. 5.

Referring to FIG. 5, steel plate F is positioned interior of a C-sectioned electromagnet G. Current is applied to plate F by contacts 51 and 52. These contacts are positioned to flow current through the interior of the C-sectioned core of magnet G and are supplied with alternating current.

Magnet G has its C-sectioned core wound with a winding 54. This core is provided with a magnetic field generated in winding 54 through alternating current supplied from a standard alternating current power source.

The current flow path between contacts 51 and 52 will be a function of the phase relation between the alternating current source connected to contacts 51 and 52 on one hand and the alternating current source connected to winding 54 on the other hand. Consequently, both power sources are here schematically illustrated interconnected by a phase control. By adjustment of the phase of current between contacts 51 and 52 relative to the phase of current in winding 54, the path of current within plate F can be restricted. In the example illustrated here, the current is being restricted to edge 56, adjacent winding 54 on the C-sectioned core.

It should be understood that the path of current flow, in addition to being phase controlled, can be amplitude controlled, either by variations of current, voltage or both. Moreover, different shapes and locations of magnets, conductors, and current applying contacts can be used. Likewise, other modifications of my invention may be practiced, it being understood that the form of my invention as described above is to be taken as a preferred example of the same. Such description has been by way of illustration and example for purposes of clarity and understanding. Changes and modifications may be made without departing from the spirit of my invention.

Claims

What is claimed is:

1. A process of heating a solid conductor along a preselected concentrated path within said conductor comprising the steps of applying a heat-inducing electrical current to said conductor between two points on said conductor at either end of said path said current having a frequency less than that which would produce a skin effect current concentration on said conductor surface; providing a magnetic field about said conductor independent of the magnetic field of said heat-inducing electrical current and between said points to concentrate current flow within said conductor.

2. The process of claim 1 and wherein said heat-inducing current is direct current and said magnetic field is static.

3. The process of claim 1 and wherein said heat-inducing current is alternating current and said magnetic field is a fluctuating magnetic field and including the further step of controlling the phase relation between said fluctuating magnetic field and said heat inducing alternating current to concentrate said current flow path.

4. The process of claim 1 and including the additional step of moving said conductor relative to said applied current and provided magnetic field.

5. Apparatus for heating a solid conductor comprising: first and second electrical contacts in electrical communication with said conductor at spaced-apart points on said conductor; first means for supplying said contacts with electrical current to provide an electrical current flow through said conductor said current having a frequency less than that which would produce a skin effect current concentration on said conductor surface; an electromagnet positioned adjacent said conductor between said spaced-apart points; and, second means for supplying said electromagnet with current to concentrate the current flow path between said points within said conductor.

6. The apparatus of claim 5 and wherein said first and second supplying means are alternating current sources and including means for varying the phase relation between said first and second supplying means.

7. The process of claim 5 and wherein said electrical current from said first means for supplying said contacts with electrical current is a direct current.

8. A process of pressure welding two conductive strips comprising the steps of: continuously advancing said strips from upstream positions where said strips are separate and apart from one another to a downstream position where said strips are in contact with one another; applying a heat-inducing electrical current to said strips between a first point on one said strip upstream of said position of contact and a second point on the other of said strips upstream of said position of contact, said applied current having a frequency less than that which would produce a skin effect current concentration on said conductive strips; providing a magnetic field about at least one of said strips between said point of current application and said position of contact to restrict current in said strip to a point of current flow adjacent the point of contact of one strip with said other strip, said magnetic field independent of the magnetic field of said applied current; applying pressure to said strips sufficient to weld said strip at said position of contact.

9. The process of claim 8 and wherein said applied current is direct current.