GB2155740A

GB2155740A - Transverse flux induction heaters

Info

Publication number: GB2155740A
Application number: GB08503751A
Authority: GB
Inventors: Robert Charles James Ireson
Original assignee: Davy McKee AG
Current assignee: Davy McKee AG
Priority date: 1984-02-23
Filing date: 1985-02-14
Publication date: 1985-09-25
Also published as: GB8404767D0; GB8503751D0; JPS60216488A

Abstract

A transverse flux induction heater for heating metal strip (1) moving in the direction of its length has an enclosure containing a non-oxidising gaseous atmosphere. The metal strip is moved in the direction of its length through the enclosure between a pair of walls (9, 11) of the enclosure of non-conductive material. A pair of transverse flux induction heater elements (10) are positioned outside the pair of walls and arranged substantially parallel to the strip (1). <IMAGE>

Description

SPECIFICATION Transverse flux induction heaters It is well known to heat metal strip moving in the direction of its length by means of a transverse flux induction heater. This involves passing a metal strip through a space between a pair of transverse flux induction heater elements which are arranged substantially parallel to the path taken by the strip.

In use, flux generated by the elements passes transversely through the moving strip and induces eddy currents which raise the temperature of the strip.

In some applications, however, it is necessary to heat the metal strip while it is surrounded by a protective gaseous atmosphere which prevents oxidation of the heated strip.

It is possible to enclose the entire induction heater in a gas-tight enclosure through which the strip is passed. There are various objections to this, particularly in that, as the strip is heated in the enclosure which also contains the inductor windings, the temperature rise within the enclosure is considerable. Furthermore, if it becomes necessary to change the inductors, then it becomes necessary to open the enclosure with the subsequent loss of the protective atmosphere.

It is an object of the present invention to provide a transverse flux induction heater in which these difficulties are overcome.

According to the present invention, a transverse flux induction heater for heating metal strip moving in the direction of its length comprises an enclosure containing a controlled atmosphere, means providing a path through the enclosure for the metal strip which is moving in the direction of its length, a pair of walls of the enclosure on opposite sides of, and substantially parallel to, a part of said path being of non-conductive material and a pair of transverse flux induction heater elements positioned outside the respective ones of said pair of walls and arranged substantially parallel to said part of the path.

In this way, the heaters can readily be changed or maintenance carried out on them without the necessity of opening the enclosure. The strip is introduced into the enclosure and withdrawn from it through seals which serve to limit the loss of atmosphere from the enclosure.

The walls of the enclosure, which are of nonconductive material, may also serve as heat shields for protecting the inductor elements from the effects of heat developed in the strip.

In order that the invention may be more readily understood, it will now be described, by way of example only with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic side view of an induction heater in accordance with the present invention; Figure 2 is a plan view; and Figure 3 shows a schematic view of a metal strip process line with an induction heater according to the present invention; Figure 4 shows an induction heater in accordance with the present invention incorporated in a metal strip process line of Figure 3; and Figure 5 shows a detail of a roll seal assembly of the strip line of Figure 3.

Referring to Figures 1 and 2, a metal strip 1 is shown moving in the direction of its length. The path taken by the strip leads through an enclosure 3 containing a controlled, non-oxidising gaseous atmosphere. A pair of seals 5 and 7 at opposite ends of the enclosure permit the strip to move through the enclosure and, at the same time, limit the loss of the gas atmosphere from within the enclosure.

Clearly, there will be some gas loss through the seals, so gas is provided through gas inlet 2 for topping up the atmosphere in the enclosure.

A pair of walls 9, 11 of the enclosure, arranged on opposite sides of the path taken by strip 1, are made of a non-conductive material and serve as heat shields against heat generated in the strip as it passes through the enclosure. The heat is generated in the strip by the action of a transverse flux induction heater which includes a pair of transverse flux inductor 10 elements 13 arranged on opposite sides of the path taken through the enclosure by the metal strip and facing the walls 9, 11. These inductor elements are mounted on a rigid frame 15 which has electrical connectors 12 and mounting means whereby it can readily be plugged into, and supported from, a terminal end panel 17 which has corresponding connectors 14. The terminal end panel may have connectors for cooling water for the inductors.The enclosure 3 is also secured to the terminal end panel through mounting 16.

In use, the inductors are energised and the flux passes through the heat shields and induces eddy currents in the strip as it passes through the enclosure.

To change the inductor elements, it is simply a matter of withdrawing the frame 15 and the elements from the panel 17 and replacing them with a replacement unit. The face of each element may have a thin refractory layer on it to act as an additional heat shield.

Although in the embodiment described a nonoxidising gaseous atmosphere e.g. nitrogen is used, it will be understood that the controlled atmosphere could be oxidising or have other properties to produce a surface finish on the strip.

Figure 3 shows a practical application in a strip metal process line where strip 19 passes through seal roll assembly 20 into a first vessel 21 of the line.

The strip then passes about rollers 22 into an enclosure 23 which is of generally U-shape form, through one of the legs 24a of the U-shaped enclosure, along a substantially horizontal bottom portion of the enclosure, and out through the other leg 124b of the enclosure. As the strip passes along the generally horizontal portion of the enclosure, the strip passes between a pair of transverse flux induction elements 25 positioned outside the enclosure. The strip continues through a soak and slow cool stage 26, into a transfer box 27, and then into a second vessel 28. In the second vessel 28 the strip is rapidly cooled before passing out through the exit seal roll assembly 29. The atmosphere in the vessels 22, 28 and U-shaped enclosure 23 is maintained as a non-oxidising gaseous atmosphere by operation of a gas inlet control unit 30.

Referring to Figure 4, which shows a detailed view of the enclosure 23, the transverse flux induction elements 25 are mounted on supports 34 above and below heat shields 31 formed in the wall of enclosure 23. A sensor 32 is located in leg 24a of enclosure 23 to sense the temperature of the incoming strip, and a pyrometer 33 is located at out going leg 24b to sense the raised temperature of the strip. As before, the strip is heated electromagnetically by the elements 25 as it passes along a path which takes it through the enclosure which contains the non-oxidising gaseous atmosphere.

Figure 5 shows a seal roll assembly, in which a pair of rolls 51, 52 are pressed into engagement with the strip to form a seal at the entrance or exit to the line. The support arm assembly of left hand roll 52 has been omitted to show details of the seals behind, but is substantially the same as the right roll support arm assembly now described. The roll 51 is rotatably mounted on one end of a roller arm 53.

The arm 53 is pivotally mounted on an end plate 59 of the seal assembly (20,29). The other end of the arm 53 is pivotally connected to a connector arm 54 which together with a connector arm (shown dotted) of the left hand roll support arm assembly is pivotally connected to a spring mounting block 55. A spring 56 is attached by one end to the mounting block 55 and has its other end attached to a fixing point (not shown). As will be appreciated the spring acts to pull the central ends of the connectors 54 up as shown in Figure 5 which causes the rolls to be urged towards one another, and onto the strip between them. A pneumatic cylinder 57 has a piston connected to the roller arm 53, and actuation of the cylinder will cause the rolls to part.

The rolls 51, 52 are driven, via shafts connected by universal joints to a gear box, by electric motors.

Between each roll 51, 52 and the housing 58 of the exit'entrance to the line is a seal 60 which is in sealing engagement with the housing 58 and one of the rolls 51,52. The seal 60 comprises a general Ushaped seal support 61 which engages the housing 58 through a pivotable seal 62 on one U-arm 61 a. A cast iron seal plate 64 is pivotally mounted on the other U-arm 61 b and is biased by a spring 63 into sealing engagement with the adjacent roll (52).

Claims

1. A transverse flux induction heater for heating metal strip moving in the direction of its length comprising: an enclosure containing a controlled atmosphere, means providing a path through the enclosure for the metal strip which is moving in the direction of its length, a pair of walls of the enclosure on opposite sides of, and substantially parallel to, a part of said path being of nonconductive material, and a pair of transverse flux induction heater elements positioned outside the respective ones of said pair of walls and arranged substantially parallel to said part of the path.

2. A heater as claimed in claim 1 wherein, the strip is introduced into the enclosure and withdrawn from it through seals which serve to limit the loss of atmosphere from the enclosure.

3. A heater as claimed in claim 2 wherein, the seals have rolls biased into sealing engagement with the strip.

4. A heater as claimed in claim 1 or 2 wherein, the walls of the enclosure serve as heat shields for protecting the inductor elements from the effects of heat developed in the strip.

5. A heater as claimed in any one of claims 1 to 4 wherein the atmosphere is non-oxidising.