Arrangement for joining foil material by inductive heating under pressure

Jan. 5, 1960

l. g. wAstberg 2,920,173

ARRANGEMENT FOR JOINING FOIL MATERIAL BY INDUCTIVE HEATING UNDER PRESSURE

Filed June 2, 1958

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INVENTOR

LARS 60TE WASTBER8

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AGENT'

United States Patent Office

2,920,173

Patented Jan. 5, 1960

2,920,173

ARRANGEMENT FOR JOINING FOIL MATERIAL BY INDUCTIVE HEATING UNDER PRESSURE

Lars Gote Wastberg, Bromma, Sweden, assignor to North American Philips Company Inc., New York, N.Y., a corporation of Delaware

Application June 2, 1958, Serial No. 739,025

Claims. (Cl. 219—10.53)

The present invention relates to an an-angement for jointing foil material such as plastic foils, paper, tissue or metal foils covered with plastic or suitable glue by inductive heating. More exactly defined, the present invention relates to an arrangement for jointing the walls of a pipe of such material containing a liquid or another substance which by sealings, obtained by joints of the opposite walls of the pipe in equal distances, is portioned into separate packings.

Arrangements of this kind are previously known, in which a pressing member is provided, having a contact surface intended to contact the foil material and having one or two narrow heating zones consisting of resistance wires or tapes passed by electric current, which wires or tapes for making possible a quick continuous procedure are heated momentarily (pulse heating) and then cooled down. These arrangements have the inconvenience that they are mechanically weak and that the resistance material after having been heated cools down slowly, as the resistance material must be surrounded with insulating material, by which reason the time required for a joint becomes relatively long.

Another disadvantage is the difficulty to feed the resistance material with the energy required for heating it. Since as a rule the pressure member is movable, this must be done by means of sliding contacts or such like, which easily causes varying contact resistances and consequently irregularities in the finished joints:......

These inconveniences are eliminated by the present invention by the pressure member being heated inductively. The contact surface of the pressure member is then at least in its main part metallic, and for the heating of the contact surface an inductor coil passed by a high frequency current is so arranged in relation to the contact surface that one or more, in relation to the dimension of the contact surface, narrow heating zones are formed by the concentration of the induced high-frequency currents to narrow current paths in the contact surface. Thus, it is possible that the heat resulting from the heating process after the heating period is quickly conducted from the heating zone or zones without being restrained by some insulating material, as the case is in the known arrangements. In arrangements according to the invention also the problems in connection with the energy supply of the movable pressure member are eliminated, since the energy required may be supplied to the pressure member inductively.

In the following, the invention is explained more closely with reference to the annexed drawing, where Fig. 1 shows a schematic representation of an arrangement according to the invention, and Figs. 2-4 show cross sections of the' pressure member according to three different embodiments.

In Fig. 1 the pipe containing a liquid and consisting of paper 2 with a thin inside layer of plastic 3, is designated 1. On an endless band 4 or such like a number of pressure members 5 are mounted, which are moved on by the same speed as the pipe 1 and are pressed one after ³⁵ one towards the pipe. Spacer members 10 are illustrated in Fig. 1 as located between the paper 2. On the opposite side of the pipe another endless band 8 or such like structure is mounted having a number of members 9, which each have a contact surface corresponding to the total contact surface of the pressure member and which are moved on in correspondence with the pressure members 5 and are pressed towards the pipe for constituting a counterpart to the pressure members. Each pressure member 5 is provided with an outer coupling coil 6, through which the high-frequency current is conducted as a short pulse from a stationary coupling coil 7 to the inductor coil (not shown), when the coupling coils pass each other. The stationary coupling coil 7 is placed so that the current pulse is transmitted at the same moment as the pressure member presses together the walls of the^:pipe, and the walls are then kept pressed together during a further moment while the joint cools off. Since joints following each other are arranged in planes which are right-angled to each other, there must be provided a further pair of bands with pressure members, not shown on the drawing, for obtaining these joints.

The pressure members 5 may be shaped in different ways within the scope of the invention and in Figs. 2-4 three embodiments are shown. The part of the pressure member having a contact surface 11 is here designated 12, the inductor coil 13 and the foil material 14.

For obtaining a joint, the pressure member presses the foil material 14 against a counterpart 15, which has a surface facing the foil material and corresponding to the total contact surface of the pressure member. When the inductor coil 13 is passed by a high frequency current, high frequency currents are induced in the contact surface 11, which thereby is heated. Here it is of great importance that the part 12 and the contact surface 11 have such a form and consist of such material that the heating and particularly the cooling following thereupon take place quickly. Therefore the pressure member is for instance so shaped, as is shown in Fig. 2, that the currents induced by the inductor coil are concentrated at the edge portions 16 of the contact surface 11, the heating zones, which have a small thickness and-therefore a small heat capacity in relation to the part 12 of the pressure member with the contact surface. Since the contact surface 11 as well as the part 12 consist of good conducting material, the heat accumulated by the heating process is quickly conducted away from the heating zones 16 after the end of the heating period. For joints of opposite walls in a tube-shaped strand containing a liquid or the like, the contact of liquid with the heating zones 16 is avoided by the walls being pressed together even between the inductor coil 13 and the counterpart 15 beyond the heating zones 16.

The arrangement according to the invention may also be embodied in a way shown in Fig. 3, where the inductor coil 13 and the contact surface 11 of the pressure member are arranged on opposite sides of the foil material. The heating zones 16 are then formed substantially along the projection of the inductor coil 13 on the contact surface 11. By arranging the inductor coil 13 a bit within the limit lines of the contact surface 11, nonheated edge portions 17 are formed beyond the heating zones 16, by which the quick carrying off of the heat away from the heating zones is essentially facilitated. Besides it is avoided, similarly as with the preceding embodiment, that the liquid gets into contact with the heating zones.

A corresponding effect is obtained with the embodiment, shown in Fig. 4, where the contact surface consists of a thin metal layer 11, e.g. a thin metal sheet, in which the heating zone 16 is provided. In order to obtain a good energy transmission from the coil 13 to the

2,820,173 sheet 11, the coil is imbedded in a material 18 having good magnetic conductivity as for instance iron powder. In this case a good heat transfer is obtained from the sheet to the coil, which suitably may be water-cooled. The inductor coil 13 is here arranged immediately under the thin metal layer 11, but it may also be arranged in the manner shown in the preceding embodiments.

The shown embodiments are of course only chosen as samples for the application of the invention, and therefore different modifications are possible within the scope of the invention. Thus, for the pressure members shown in Figs. 2 and 3 contact surfaces consisting of thin metal layers with an underlying, considerably thicker layer of metal powder material may be applied, as shown in Fig. 4. Similarly, for the pressure member shown in Fig. 2 the inductor coil 13 may alternatively be arranged within the member 15 on a corresponding place, a portion of insulating material being provided beyond the heafng zones 16. Furthermore the arrangement according to the invention may be provided with, two opposite pressure members, which press together the foil material between them, the respective heating zones of the pressure members possibly being so arranged that they substantially coincide with each other.