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Publication numberUS1839801 A
Publication typeGrant
Publication dateJan 5, 1932
Filing dateMar 26, 1930
Priority dateMar 26, 1930
Publication numberUS 1839801 A, US 1839801A, US-A-1839801, US1839801 A, US1839801A
InventorsFitch Northrup Edwin
Original AssigneeAjax Electrothermic Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electric induction furnace
US 1839801 A
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Description  (OCR text may contain errors)

Jan; 5, 1932. E. F; NORTHRUP' 1,339,801

ELECTRIC INDUCTION FURNACE 3 Sheets-Sheet Filed March 26. v19:60 Y

Jan. 5, 1932. I E. NORTHRUP 1,839,801

ELECTRIC INDUCTION FURNACE Filed March 26, 1930 I5 Sheets-Sheet 2 Jan. 5, 1932. E. F. NORTHRU P ELECTRI C INDUCT I ON FURNACE Filed March 26, 1950 a Sheds-Sheet s Patented Jan. 5, 1932 EDWIN FITCH N ORTHRUP, OF PRINCETON, NEW THERM'IC CORPORATION, OF AJAX PARK,


My invention relates to inductor coils. Though applicable in other locations it reaches its highest development in inductor coils of the coreless type, such as reactors and furnace inductors and in various radio uses.

The main purpose of my invention is to reduce the losses within the inductors from stray magnetic flux.

A further purpose is to change the distribution of the dispersed lines of magnetic force so as to cause as large a pro ortion of them as possible to go out throug the end of the coil and thus reduce the interthreading of the sides of the coil by magnetic lines of force.

A further purpose is to vary the ampere turns per axial inch in a coil, increasing the ampere turns at the ends of the coil as compared'with those at the middle of the coil.

A further purpose is to provide a watercooled coil which is flattened with the major axis of the flattened portion parallel to the axis of the coil, (i. e., flat-wound) at the middle of the coil and perpendicular to it at the ends of the coil, (i. e., edge-wound) with permissibly circular or nearly circular cross section in between these points.

Further purposes will appear in the specification and in the claims.

My invention'relates both to the methods or processes involved and'to apparatus by which these methods or processes may be carried out.

' I prefer to illustrate my invention by two varieties only of the same general form among the various forms in which it might appear, selecting coils which are practical, highly eflicient and reliable and which at the same time well illustrate the principles involved.

Figure 1 is a centraLlongitudinal section through a coil embodying my invention.

Figure 2 isa top plan view of the form seen in Figure 1.

Figures 3, 4 and 5 are sections of different portions of the coil seen in Figure 1.

Figures 6 and 7 are side elevations of inductor coils with diagrammatic lines of force therefrom to illustrate my invention.

Figure 8 is a central, longitudinal section of a modification of the form seen in Figure 1, showing connections such as might be used, for example, with either Figure '1 or Figure 8.

In the drawings similar numerals indicate like parts.

In the operation of inductor coils of various characters, whether used as reactors or for the inducing coils of electric furnaces or for other purposes, there is a higher loss through energy dissipated in the coil itself than has been justified by the-normal current losses within the coils. The reason for this seems not previously to have been understood. I have discovered that this relatively excessive loss is due to the fact that electromagnetic lines of force which should pass out through the end of the coil and return in a magnetic circuit completely outside of the inductor coil, in fact short-circuit acrossthe turns of the coil, beginning at points but a short distance apart on opposite sides of the center and extending in greater force to points further fromthe center and nearer to the end of the coil. These short-circuiting lines of force thus pass through the coil ends transversely, causing excessive heating and causing the coil when overheated to overheat at the ends first before overheating in the central sections.

I have discovered" also that this excessive loss of energy in the inductor coils may be avoided and overcome by increasing the electromagnetic effect of those turns of the inductor lying nearest to the ends of the, coil as compared with those lying nearest to the center of the coil.

In Figure 1 I have shown a preferred way of securing this corrective result in a watercooled inductor coil capable of serving as a reactor or as a furnace inductor or for any other allied purpose requiring enough energy to make the saving in the coil advantageous, or in which improper and irregular shortcircuiting leakage of magnetic flux outside of a coil is undesirable in any other way.

In Figure 1 the hollow conductor 10 normally of circular cross-section (Figure 4) is wound to form an inductor 11 comprising turns 10 (Figure 3) wound flat-wise, i. e. parallel to the axis of the coil, and end turns 10 (Figure 5) flattened as in the case of the central turns 10", but otherwise wound. Water connections to and from the coil are made at 12.

As the spacing between the adjoining sides of the respective turns is substantially the same throughout the length of the inductor and the same current passes through all of the turns in series, the ampere turns per unit coil length progressively increase from the center to the ends, giving a higher electromagnetic effect of the turns at and near the ends of the coils than at and near the center.

The result of this variation in electromagnetic effect has been very noticeable and is illustrated as applied to inductor furnace coils in Figures 6 and 7. In these figures inductors are shown having an equal number of turns each and formed of identical copper tubing having the same cross-sectional'area. The tubing was initially exactly alike.

In. Figure 6 the turns are of uniform seetional shape as well as of uniform spacing from center to center of adjoining turns throughout the length of the coil. It will be seen that the magnetic lines of force represented as passing through and returning outside of the coil short-circuit throughout a considerable part of the coil length, beginning at points 13, 13 close to the center and extending at the ends of the coil 14, 14., so that much of the magnetic flux completes its circuit outside of the coil, passing transversely through the coil itself between the center and the coil ends.

In Figure 7' on the other hand, using a coil corresponding to Figure 1, the lines of magnetic flux show but slight short-circuiting and pass almost entirely clear through the coil in an axial direction before they begin their return path.

These two figures are taken from iron filing pictures madefrom these two coils during operation together free from load and in series one with the other to insure the passage of the same current through each.

Tests of the coil losses for these two coils indicated that the energy losses in the coil of Figure 7 approximate 30% less on no load and 12% less on full load than the corre sponding losses in the coil shown in Figure 6.

In order to indicate that my invention is capable of application to coils other than those which are water-cooled and to differences in pitch secured in other ways than by flattening or differently turning the (1011 s themselves, but without attempting to 1nd1- cate all of the differences by which my invention may be carried out Ihave shown in Figure 8 edgewise-wound solid conductors in coil 11 whose turns are spaced to a greater extent at the center 16 than at the ends 17 and 17.

The conductors are located about a furnace crucible 18. The coil is here fed from a source of current 1.) and power factor is corrected by compensative capacity indicated by con denser 20.

It will be obvious that my invention is capable of use to improve inductor leakage conditions in any situation in which such leakage occurs, whether in radio, furnace or other art, but finds its greatest applicability where the amount of leakage is greatest, namely, where there is no interthreading of magnetic material.

In view of my invention, and disclosure variations and modifications to meet individual whim or particular need will doubt less become evident to others skilled in the art, to obtain part or all of the benefits of my invention without copying the structure shown, and I, therefore, claim all such in so far as they fall within the reasonable spirit and scope of my invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is

1. An inductor coil having the axes of the turns of the coil winding closer together at the ends than at the intermediate section of the coil and having the adjoining outer surfaces of the coils approximately uniformly spaced.

2. An inductor coil free from transformer iron having a hollow winding flattened and edgewise wound at the end of the coil and circular in section at an intermediate point in the length of the coil.

3. An inductor coil comprising a tubular winding having the tubular cross section fiatten-ed and edgewise wound at the ends and flattened and flatwise wound at the middle of the coil and having the turns of the edge wise winding axially closer together than the turns of the flat-wise winding.

4. A furnace inductor free from interthreading with transformer'iron having hollow circular cross section between the ends and the middle of the coil and hollow fiattened cross section at'the ends and middle, the flattened section being edgewise wound at the ends and flatwise wound at the middle and. progressively closer together from the middle toward the ends of the coil.

5. A furnace inductor coil having the number of ampere turns per unit axial dimension increased at the extremities of the coil with respect to an intermediate point on the coil of approximate cylindrical inside surface and outwardly flared from the middle upwardly and downwardly.

6. An inductor coil free from transformer iron having a hollow windin flattened and fiatwise wound in a portion 0 its length and round between the flattened portion and the ends of the coils.

7. An inductor coil for a coreless furnace free from interthreading of transformer iron and comprising a metallic conductor having the same cross sectional metal content per unit length with variant width of metal per turn measured along the axial length of the coil.


Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2515211 *Jan 24, 1947Jul 18, 1950Armstrong Cork CoMethod and apparatus for dielectric heating
US2623081 *Dec 13, 1949Dec 23, 1952Schorg Carl ChristianInduction coil mounting
US5090022 *May 21, 1990Feb 18, 1992Inductotherm Corp.Cold crucible induction furnace
US5090112 *Feb 25, 1989Feb 25, 1992Robert Bosch GmbhMethod and apparatus for manufacturing coils
US5446269 *May 27, 1993Aug 29, 1995Inductotherm Corp.Tubing shape, particularly for fabricating an induction coil
US5744784 *May 11, 1995Apr 28, 1998Otto Junker GmbhLow-loss induction coil for heating and/or melting metallic materials
DE3910777A1 *Apr 4, 1989Oct 11, 1990Leybold AgEinrichtung mit einem tiegel, in dem sich ein metall oder eine metall-legierung befindet
DE3910777C2 *Apr 4, 1989Aug 9, 2001Ald Vacuum Techn AgInduktionsofen mit einem metallischen Tiegel
U.S. Classification373/152, 336/206, 336/224, 336/62, 336/223
International ClassificationH05B6/36
Cooperative ClassificationH05B6/367
European ClassificationH05B6/36F