APPARATUS FOR INDUCTIVE HEATING

Abstract: Assembly for heating the edge portions of a flat product, such as a billet, strip or sheet-metal, on its way from one location to another, for example coming from a continuous casting machine or a hot-rolling mill or pair, including one or more inductive edge heaters arranged to surround the outer parts of the edges of the product. Accord­ ing to the invention the inductive heater(s) comprise(s) one or more flat spiral coil(s) (1) bent around a side edge of the product and also comprise(s) at least one vertically placed, flat coil (4), located substantially parallel with the side edge (5) of the product.

Description: The invention relates to an assembly for heating the edge portions of a flat product according to the precharacterising part of Claim 1. Such an assembly is known from the EP-A-0 183 209. A similar assembly is described in the EP-A-85 11 4886, the heater(s) constituting one or more bent, flat spiral coil(s), arranged so that the outermost parts of the edges will pass a greater portion of the coil than parts located further from the edges, the outer edge thus being heated more than the inner parts of the product. This results in keeping the outer edges at a temperature corresponding approximately to that of the rest of the product, for example a billet, sheet, or strip. The inductive heaters are arranged to surround the flat product, such as a billet on its way to a rolling mill, on three sides and are suitably arranged to be supplied with a single-phase current of mains frequency or high frequency in the range of 1000-3000 Hz. In processes where flat products are to be kept hot along the production line, the products cool more quickly at the edges than in their remaining sections. Often the heating assembly described above is sufficient. However, as is also apparent from a study of temperatures from calculated temperature distribution for slabs or other flat products, sometimes a more complete compensation for the loss of heat at the edges is required. The invention aims at an assembly for heating the edge portions of a flat product of the above-mentioned kind which allows to keep the flat product across its entire cross-section at approximately the same temperature. To achieve this aim the invention suggests an assembly according to the introductory part of Claim 1, which is characterized by the features of the characterizing part of Claim 1. Further developments of the invention are characterized by the features of the additional claims. In a assembly according to the invention a substantially complete temperature and heat-loss compensation will be obtained along the edges of the flat billets to be further worked. The invention will now be described in greater detail with reference to the accompanying drawings showing - by way of example - in Figure 1 the typical temperature conditions in a flat product prior to the application of an assembly according to the invention, Figure 2 a heater in an assembly according to the invention with combined coils, Figure 3 a side view of the inductive heater in Figure 2 with a side edge of the product, Figure 1 shows typical temperature conditions prior to edge heating. x is the distance from the outer edge of the product and b is the width of the product. Delta T is the difference between the mean temperature at various distances x from the edge and the mean temperature at the centre of the billet. x is smaller than b/2. The assembly according to the invention is intended to reduce the temperature differences revealed in Figure 1. After transport of a product through the assembly, the energy supplied to the billet will be typically distributed as delta T. Figure 2 shows a triangular coil 1 designed to surround a side edge of a flat product on three sides. The coil 1 is supplied via its terminals 2 with a current of single phase mains frequency or high frequency in the range 1000-3000 Hz. Figure 3 shows one side edge of a flat billet, such as a slab or the like, which is surrounded in the afore-said manner by the coil 1. The turns of the coil 1 are wound triangularly so that the outermost parts of the side edge 3 pass more turns of the coil than the sections located more distant from the edge (see the above-mentioned EP-A-85114886). One or more vertical flat coils 4 are arranged in series with or parallel to the coil 1, parallel to the side edge, and this or these coil(s) can be arranged, together with the coils 1, within the same roll gap. The combination of a triangular coil 1 with a vertical flat coil 4 at the edge sides 5 enables the temperature of the edge and corners to be increased even further. The combination according to Figure 2 is thus effected so that the triangular coil is placed in the gap between two consecutive rolls of a conveyor belt and that the flat coil 4 is placed in the same gap. The space requirement for the inductive heater in longitudinal direction is thus limited. The supply sources for the various coils 1,4 may be separate, thus enabling individual variation of the field strength and/or frequency. The assembly according to the above can be varied in many ways within the scope of the following claims.

Claims: Assembly for heating a side edge portion of a travelling flat product, such as a billet, and comprising a first induction coil, in the form of a flat spiral coil (1) bent into a U-shaped form having horizontal sides which are triangular in shape, spaced apart and positioned to overlie the mutually opposite sides of said flat product, travelling between said horizontal sides of the said first induction coil, characterized in that the assembly also includes a second induction coil (4) which is flat in shape and positioned in a vertical plane parallel to the billet's side edge (5), the second coil (4) having a height less than the spacing between the horizontal sides of the first coil and that the second coil is positioned between the horizontal sides of the first coil (1) such as to cooperate with the first coil. Assembly according to claim 1, characterized in that the bent, flat spiral coil(s) (1) and the vertical flat coil(s) (4) are combined to form a coil unit located within the same roll-gap (7). Assembly according to claims 2 or 3, characterized in that the bent, flat spiral coil(s) (1) and the vertical flat coil(s) are supplied from different power sources, to permit individual variation of the field strength and/or the frequency, for instance. Assembly according to any of the preceding claims, characterized in that the bent, flat spiral coil(s) (1) are so shaped that the outermost part of the edges will pass a greater portion of the coil than portions located further from the edges, and that the coils surround the edges on three sides.

Inventors: ANDERSSON, LARS, KLIMT, ZDENEK
Applicants: ASEA AB
Application year: 1987
Main classification: H05B6
IPC codes: C21D9, H05B6