US2832877A

US2832877A - Cross-field furnace having auxiliary poles without coils

Info

Publication number: US2832877A
Application number: US609169A
Authority: US
Inventors: Dreyfus Ludwig
Original assignee: ASEA AB
Current assignee: ABB Norden Holding AB
Priority date: 1956-09-11
Filing date: 1956-09-11
Publication date: 1958-04-29
Anticipated expiration: 1975-04-29
Also published as: CA577104A

Description

L. DREYFUS A ril 29, 1958 CROSS-FIELD FURNACE HAVING AUXILIARY POLESWITHOUT COILS Filed Sept. 11, 1956 INVENTOR. Lucia/{g Prey/ 5 flffarm 6 United States Patent 1 2,832,877 CROSS-FIELD FURNACE HAVING AUXILIARY POLES WITHOUT COILS Ludwig Dreyfus, Vasteras, Sweden, assignor to Allmiinna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a

corporation of Sweden Application September 11, 1956, Serial No. 699,169

4 Claims. (Cl. 219-44167) To the same extent as the induction heating is gaining ground in the manufacturing industry the demand for production capacity and automatic feed is growing.

If the inductive heating of billets is concerned good results have been attained with a conveyer chain according to Letters Patent 2,667,524 but this chain requires a crossfield furnace in which the main direction of the field is vertical when the longitudinal axis of the billet is horizontal, and as shown in Fig. 2a of the mentioned Letters Patent, in the known cross-field furnace the heat from the eddy currents in a billet of rectangular crosssection is produced substantially only along the vertical side surfaces of the billet. The equalization of the differenccs of the temperature across the width of the billet is left to the conduction of heat and will be performed in minor billets where the time constant T is only some seconds. However, the time constant increases quadratically with the width 5 of the billet. Assuming for example that:

Width of the billet 6 15 cm.

watt sec.

Specific heat 0=5-6 Heat transmission coefficient )\=0.3 The time constant will be Obviously it is impossible in practice to wait such a long time for the equalization of the temperature, since the heat losses and the oxidation of the billets would become excessive. a

According to the present invention, a substantially uni form heating along the periphery of the billet is attained in connection with the use of the convcyer chain mentioned above.

The particular feature of the invention is, that in a cross-field furnace in which an alternating field is produced plane-parallelly and at right angles to the longitudinal axis of the billet and symmetrically thereto, and which field is completed through the billet and laminated iron yokes, there are extended from these yokes four distinct poles, of which two co-axial poles having different polarities and working as main poles are provided with windings, while two other auxiliary poles arranged at an angle of 90 with respect to the main poles have no windings, said auxiliary poles causing a weakening of the field within the zones of the billet in front of the said auxiliary poles.

The invention will be described reference being made to the drawing which shows a cross-field furnace through which the articles are fed horizontally. 'T he right-hand half of the figure is a section through the furnace and the left-hand half is a view of the same.

The furnace consists of two laminated yokes ll carrying the main polesZa and 211 from which the alternating field emerges, and of two auxiliary poles 3 turned 90 with respect to the main poles. The winding is divided vertically into two equal parts 4a and 4b each embracing a main pole and having the same current direction on the one yoke and opposite direction on the other yoke. These winding parts arranged at an angle of 45 with respect to the main and auxiliary poles are separated from each "ice other by the auxiliary poles 3 having no windings. The billet is designated by 5. In analogy with what is the case in direct current commutator machines an auxiliary pole without winding weakens the branch of the main field within the billet below the arc of the auxiliary pole in an amount inversely proportional to the width of the air gap between the auxiliary pole and the billet. The field diagram is shown for a quadrant of the furnace and a billet having square cross-section and rounded-off edges. Obviously such a billet has to be positioned with its one diagonal in the direction of the axis of the main poles. he field diagram shows both that it is easy to find a place within the main pole 2b for the supporting elements of the conveyor chain, not shown, and that the field intensity within the loss zone of the billet i. e. the penetration depth indicated by the measure '7 will be largest at the auxiliary pole, despite of its considerable width as shown in the drawing by way of example. If the air gap of the auxiliary pole had been decreased additionally, it had been possible to further weaken there the field somewhat, but the power distribution obtained has been deemed to be sufficiently uniform. To this advantageous result contributes the fact that according to another feature of the invention the current density of the magnet coils decreases in the direction from the main poles toward the auxiliary poles.

This is indicated on the right-hand side of the drawing in that six conductors are shown having heights increasing in the said direction. The arrangement is usable for cylindrical billets having circular or elliptical cross-section. The air gap in the upper main pole is provided for the sake of symmetry. It may be bridged by a yoke piece. The winding is protected against heat radiation from the billet by wedges 8 of refractory material, and against over-temperatures by cooling loops 9 embedded within the auxiliary poles.

I claim as my invention:

1. A cross-field furnace for induction heating of metal lic articles within an alternating field extended planeparallelly and at right angles to the longitudinal axis of the article, and symmetrically to the horizontal as well as to the vertical planes through this axis, and which held is completed through the article and through laminated yokes, said yokes having extended inwardly four distinct poles, two poles of which being arranged coaxially with different polarities and working as main poles provided with windings, while the other two poles Working as auxiliary poles for weakening the field within the Zones of the article facing the auxiliary poles are arranged at an angle of with respect to the said main poles and have no windings.

2. A cross-field furance according to claim 1, wherein the windings of the main poles are arranged so that their axial coil surfaces form 45 angles with the symmetry planes of the main and auxiliary poles.

3. A cross-field furnace according to claim 2, wherein the current density of the windings is decreased from the main poles towards the auxiliary poles for reducing the surface field intensity of the article in the same direction.

4. A cross-field furnace according to claim 1, wherein the windings of the main poles are so arranged that their axial coil surfaces form 45 angles with the symmetry planes of the main and auxiliary poles, and one of the said main poles is provided with a gap for the passage of a convcyer means.

References Cited in the file of this patent UNITED STATES PATENTS 2,176,488 Dreyfus Oct. 17, 1939 2,480,315 Bennett Aug. 30, 1949 2,667,524 Dreyfus et al. Jan. 26, 1954