US1721073A - High-frequency induction furnace - Google Patents

Description

July 16, 1929. r w. ESMARCH -1,721,073

HIGH FREQUENCY INDUCTION FURNACE Filed octr 12, 192 2 Sheets-Sheet 1 July 16, 1929. w. ESMARCH HIGH-FREQUENCY INDUCTION FURNACE Filed Oct. 12, 1927 Shets-Sheet '2 Patented July 16, 1929.

UNITED STATES PATENT OFFICE.

'WILHELM ESMARCH, OF BERLIN-HALENSEE, GERMANY, ASSIGNOR TO SIEMENS & HALSKE, AKTIENGESELLSCHAFT, OF SIEMENSSTADT, NEAR BERLIN, GERMANY, A.

CORPORATION OF GERMANY.

HIGH-FREQUENCY INDUCTION FURNACE.

Application filed October 12, 1927, Serial No. 225,620, and in Germany June 10, 1927.

This invention relates to primary windings for high frequency induction furnaces. Such windings have heretofore been mad of watercooled copper'tubes or even of comp. ratively thick copper bands. In windings of this kind however the influence of the skin effect is highly detrimental, the currents on the inside of the conductor becoming crowded together so that the major part of the cross sectional area of the'conductor is not used for carrying the current, and the efliciency factor of the furnace is lowered. In the smelting of metals for example it has not been possible, owing to the conductivity say of the iron to raise such factor above 70%. It would be still ower if instead of a single layer of windings several such layers were employed.

According to the present invention this disadvantage is overcome by dividing the primary winding into two or more bands set up on edge and insulated from each other, the

thickness of the several bands being so proportioned that the influence of the skin effect 1s no longer noticeable and the cross sectional area is completely utilized for conducting the current, and the several windings being so arranged and shaped as to be alike in respect of resistance, impedance and inductive action on the interior of the furnace.

The accompanying drawings illustrate several constructional examples of the subject matter of the invention with bands arranged in a number of layers.

Fi 1 is a vertical section of a crucible with one orm of my improved primary winding coiled around it; Figs. 2, 3 and 4 are diagrammatic views showing in development and on a smaller scale than Fig. 1, three different forms of coils or winding embodying the invention, the coil shown in Fig. 4: corrcsp0nding to that shown in Fig. 1; Fig. 5 is a detail perspective view of a portion of a coil made in accordance with Fig. 2; Fig. 6 is a vertical section of a crucible with another form of my improved coil; and Fig. 7 is a diagrammatic developed view illustrating de- 4 tails of the coil shown in Fig. 6.

Figure 1 shows in vertical section a crucible t, around which a conductor of the novel type is helically coiled. This conductor may, consist of two three or four layers of thin copper strips. Figs. 2, 3 and 4 are diagrammatic plan views or developed views representing coils or windings embodying two, three, and four layers respectively, and showing the conductors or strips composing said coils, in the condition in which they appear before the are formed into coils. The winding or coil shown in Fig. 1 is represented as having four lar furnace. The thickness is proportion a,

to the square root of the frequency so that this latter for a frequency of 10,000 would be only th of the thickness of the conductor for a frequency of 100. For these frequencies of 10,0C0 and 100 the strips would have thicknesses of, say, 0.67 and 6.7 millimetres respectively.

The copper bands or strips a, b or a, b, 0-

or a, b, 0, d forming the conductors are connected 1n parallel, their ends or terminals 2,, 2, being connected to the source of eurrent. Said bands or strips are insulated fromeach other throughout their length as by a coating of enamel for example. By arranging suitable distance pieces between them, air insulation may be provided for. Finally strips of insulating material are placed between the bands or strips.

The bands are crossed at one or more points in such a way that each of them will be similar to the others and will have portions in different positions at different parts of its length. As shown in Figure 2 a crossing point 6, is provided forthe bands (1 and b and each of them lies for one half of its length on the inside and for the other half of its length on the outside As shown in Figure3 conductors a, b, c areprovided which are crossed at two points .9, in such a way that each conductor has one-third of 'its length on the inside, one-third in the middle and one-thirdon the outside of the entire conductor or coil. As shown in Figure 4 four conductors a, b, 0, d are used, which are crossed at three points 8 in such a way that each band assumes a different position at each one-fourth portion of its total length. In this arrangement of crossings all the parts of the several bands are connected in series and the current therefore flows in the same direction at all portions of the total cross sectional area.

In Figure 5 is shown in perspective a con structional example for the crossing 8 shown in Figure 2. The conductor band I) is turned vertically upwards on a line is lying at an angle of degrees. The connection member 0 thus formed is again turned downwards in a curved form and again turned over obliquely so that the conductor portion 12 runs on at the same level with b but in a plane parallel thereto. Between the two portions a and a of the conductor lies the band a, which is connected by a member '0 to a band portion a lying in front of the part b of the conductor. In the constructional example shown in Figures 3 and 4 three or four connecting members respectively are required. After the whole conductor with its crossed portions has been produced and the several bands connected at their ends a coil or winding of the type shown in Figure 1 will be produced, said figure (like Fig. 4) illustrating a winding or coil composed of four bands.

Instead of the minimum number of crossing points indicated in Figures 2 and 4 a greater number thereof may be employed. The number of the various conductor bands may also be increased. Finally it sufiices for many purposes to use even a single band if it be wound in a suitable number of layers like a coil and possesses the cross sectional area indicated, which gives the maximum current utilization with a minimum skin effect.

In Figures 6 and 7 is shown another constructional example in which the several conductors are connected in series, Figure 6 shows a crucible-like hearth '25 around which band-shaped conductors are wound in three turnsor rings I, II, III of three layers e, f, g each. The several turns of the bands are indicated between the supply terminals 2 2 as shown in Figure 6, and are connected in series in suchv a way that the current flows through in the uppermost ring I in the outer conductor e, while in the next ring II the current flows in the middle conductor f and in the third ring III in the inner conductor g. From this latter the current then passes into the inner conductor f and so on until it finally leaves the outer layer 00f the winding in the lower winding III through the terminal .2

In Figure 7 the connections of the individual windings are shown separately on a larger scale. These are produced by doubly bending over the conductor bands which at the cross-over points u consequently pass from one ring to another and also from one plane to another, while only one transfer to another layer of windings takes place at the connecting points '0 at the outer sides of. the uppermost and lowermost rings I and III respectively.

The arrangements shown enable the efliciency factor of the high frequency furnace to be increased to about 90 to 95 per cent. The arrangement can also be adapted with the same efficiency for crucibles which are not exactly cylindncal, provided the ohmic resistance and impedance and also the inductive action on the interior of the furnace be equal all over.

In order to secure a fine equalization of th course of the current in the action on the secondary circuit any desired kind of parallel and series connections of the band shaped conductors may be used, employing if necessary at the same time the arrangements shown in Figures 2 to 4 and Figure 6.

What I claim as my invention and desire to secure by Letters Patent is 1. A high frequency furnace comprising a crucible and a primary coil inductively associated therewith, said coil comprising a plurality of thin bands of conducting material set on edge, insulated from each other and arranged to form a laminated structure, the width and thickness of each band being so proportioned relatively to the strength and frequency, respectively, of the current that objectionable skin effects will be minimized and the full cross sectional area of the conductors of the coil will be substantially completely utilized.

2. A high frequency furnace comprising a crucible and a laminated primary coil inductively associated therewith, each conducting lamination of said coil consisting of a plurality of substantially equal lengths of a plurality of thin bands of conducting material,

set on edge and connected in series with substantially equal lengths of the bands of each of the other lamination of said coil.

3. A high frequency furnace comprising a crucible and a primary coil inductively associated therewith, said .coil consistin of a plurality of thin conducting insulated ands set on edge and arranged to form a laminated coil structure in which each lamination of the coil consists of ,a plurality of substantially equal lengths of each of said bands.

4. A high frequency furnace comprising a crucible and a primary coil inductively associated therewith, said coil consisting of a' plurality of insulated thin bands of conducting material set on edge, connected in parallel and forming a laminated structure, each band consisting of a plurality of serially connected portions, each arranged at a different distance from the axis of the coil than its adjacent portions, and so that each band will have a substanti ally equal length thereof arranged at the same distance from the axis of the coil band will have substantially the same electrical efiect on the interior of the furnace.

5. A high frequency furnace comprising a crucible and a primary coil inductively associated therewith said coil consisting of a plurality 'of insulated thin bands of conducting material set on edge and connected at their ends in parallel, each band consisting of a plurality of portions arranged in step-like formation at difierent radial distances from the axis of the coil, each of such portions of each band being substantially in line with a pair of adjacent portions of adjacent bands, and the adjacent portions of each band being connectedin series by cross over sections to avoid contacting engagement between adjacent bands.

6. A high frequency furnace comprising a crucible and a primary coil inductively associated therewith, said coil consisting of a plurality of continuous thin bands of conducting material set on edge and connected at their ends in parallel and being insulated from each other throughout their length, each bandconsisting of a plurality of portions ar-' ranged in step-like formation at diflI'erent radial distances from the axis of the coil, and

such portions of each band being so arranged relatively to the portions of the other lamlnations that the coil consists of a plurality of laminated helical turns, in which each lamination consists of a plurality of portions of different bands.

In testimony whereof I aflix my si ature. WILHELM ESMA CH.

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