DE3919165A1 - Impulse heating to weld or cut plastics - by pressing between cooled contoured tools positioned opposite induction coils which are inside backing plate and connected to HF source - Google Patents

Abstract

A tool for use with plastics, and particularly for welding and/or cutting, is impulse-heated by induction, as induction coil being inside the backing tool. Coating the tools used with PTFE is generally not necessary. ADVANTAGE - The process enables non-linear tools to be used i.e. to make e.g. curved welds or cuts. In an example, a top plate and its adjacent welding tools are both bored for coolant and are hence made of metal. The bottom edge of the tools acts on the films to be welded along their suitable contour (or e.g. can be cutting edges). The top plate is thus moved down to press the films against a plastic backing plate. Beneath the edges of the tools this lower plate contains an induction coil which, in this case, is flattened on its top face and is also bored for coolant. The coils are connected to the h/f generator. The tools are induction-heated under pressure which is maintained until the surface of the tools is below the m.pt. of the film. This produces clean welds (or cuts).

Description

The pulse heating of a tool for processing thermoplastic Plastics are used when the impact of Solidify the plastic surface that has become molten again should, as long as the pressing pressure of the tool continues. You prevent thereby deforming the molten plastic surface for example by sticking to the tool surface or by shrinking tion or by reconnecting the cut edges. The Heating of the active surface of the tool is stopped as soon as the desired effect on the workpiece has been achieved. The heat then flows from the active part of the tool forming the active surface cooler cross-sections behind it, reducing the temperature to a value below the melting temperature of the workpiece. The arrangement is a prerequisite for the application of this method a resistance heating conductor in the immediate and always constant, defined proximity to the active surface, which was previously only possible if the heating conductor is stretched in its longitudinal direction. It follows, that heat pulse tools should only be elongated in a straight line can. Curved welding or separating seams can be drive will not be manufactured. For machining a workpiece along curved lines, for example for executing curved ones Welding or separating seams, one is therefore on high-frequency heating of the Workpiece or relies on permanently heated tools. However, let important thermoplastic materials, such as polypropylene,  do not heat in a high-frequency electrical field. For these materials therefore, only processing by means of permanently heated tools remains but have considerable disadvantages in that the separation of the work stuff from the workpiece at above the melting temperature Tool temperature must take place, what from the above In many cases this leads to unacceptable workpiece quality.

Of greatest interest is therefore a process that uses pulse heating a tool without limitation to straight extension of the Effective area.

The invention provides such a method in that the tool is heated inductively.

To carry out this method, a tool with a counter the workpiece can be pressed and the surface acting on the workpiece che forming, heatable active part according to the invention further formed that a device for inductive heating of the active part is provided.

The principles of induction heating are from other areas of the world Technology (e.g. surface hardening of steel) well known and apply here analogously. They require that the active part as a whole or at least partially conductive to through the eddy currents to be able to be heated in the electrical alternating field of the Inductor are generated. They also require that the inductor in is arranged so close to the active part that the electrical Alternating field is present in the area of the active part. Tool parts that are in the Area of effect of the alternating electrical field are not heated should be made of electrically non-conductive material will.

The inductor can be in the same tool part as the active part and in its immediate vicinity can be arranged. This presupposes that the Tool parts made of non-conductive material surrounding the inductor consist. Since this is often with regard to the dissipation of heat from the Active part is undesirable, it may be appropriate to the inductor in the  the tool part opposite to arrange where he after a further feature of the invention the opposite of the active part Counter jaw can form if it is an editing tool (Welding, embossing, cutting) of plastic films.

With this arrangement, a particular advantage of induction heating can be mung be used, which is that only due to the skin effect a more or less thin surface layer of the ge inductor opposite metal part is heated, the thickness of this layer depends on the frequency and by setting a suitable fre sequence can be controlled for the respective case.

If thick foils are to be processed, it may be expedient to apply heat not only from the inductively heated active part, but also from the Feed counter jaw here, the temperature of the counter jaw up a value that can be controlled compared to the ambient temperature is, however, usually below the melting temperature of the processing material should lie. The heating energy for this tempera Lifting can be provided by the losses of the inductor According to another feature, it is tubular and connected to a circle run for a temperature control medium can be connected. The Temperierme dium can be designed both for supplying heat and for dissipating heat be. This depends on the heat requirement and the ver generated at the inductor heat from.

To quickly drop the temperature of the active part after the pulse heating To be able to lower the melting temperature of the workpiece, it is known to connect the active part in a heat-conducting manner with a heat absorption part. This is also applicable in the context of the invention. Active part and warmth Recording part can be different areas of one and the same work be part of the tool, the area acting on the workpiece Surface is heated in a thin layer due to the skin effect, which forms the active part, while the cross section behind it Partly serves as a heat absorption part. However, different ones can Parts for the formation of the active part and the heat absorption part be drawn, for example, by their permeability and their Distinguish thermal conductivity. For example, the electrical  Conductivity of the heat absorption part in the direction of the induction chip gradient be reduced. For example, it can be comb-like slit or, as with transformer cores, from across the length stretching of the active part extending sheets with insulating intermediate layer be built up in packages.

The heat absorption part of the tool, in particular a tool holder meplatte, on which a web forming the active part is arranged, with be provided with further cooling devices, for example with cooling water channels.

Since the active part does not contain a resistance heating element, the straight ge must be stretched, it can have any shape. The invention appropriate method or tool therefore enables the production ge curved welding, embossing and separating seams with high quality also in such materials that elude HF heating. this is a leaps and bounds of technology. It is known induction apply heating to plastic welding; but there is the metal part to be heated inductively is part of the workpiece (EP-A 01 90 810; EP-A 01 77 147; DE-A 31 08 221).

The invention is described in more detail below with reference to the drawing tion explained, which is an advantageous embodiment of a tool illustrated in a schematic cross-sectional representation.

The tool contains an upper mounting plate 1 with cooling channels 3 , to which welding jaws 2 , which may also contain cooling channels 3 and which consist, for example, of iron or one or more other metals, are attached. The lowest cross-sectional part 4 is to be seen as the cross-sectional part referred to in the above explanation as the active part, which forms the surface interacting with the foils 5 to be welded as a workpiece, which can be designed as desired in a conventional manner. In the case shown, it is shown as a flat, rectangularly delimited welding surface. It can have a different cross-sectional shape and, for example, have a lateral separating edge. The receiving plate 1 is vertically movable with the parts arranged thereon in relation to the plastic counter plate 7 , into which an inductor 6 is cast or incorporated under each active part 4 , which is flattened in the example shown to form a counter jaw and as a tube for Management of a cooling medium is formed. It is connected to a high-frequency generator 8 for energy supply. In the ductors can also have a different shape, for example a flat cross section. You can then be attached to the surface of the plastic plate 7 .

The tool is used like known heat pulse tools, ie the active part 4 is inductively heated in press contact with the workpiece 5 until the desired machining effect is achieved. The pressing pressure is maintained until the surface of the active part has dropped to a temperature below the melting temperature of the workpiece. In this way, clean seam quality is achieved. This also applies in particular to welds for separating seams. Coating the tools with PTFE is usually not necessary.

Claims (8)

1. A method for pulse heating a tool part for processing, in particular welding and / or cutting plastic, characterized in that the tool part is heated inductively. 2. Tool for heat pulse processing, in particular welding and / or cutting plastic with a pressable against the workpiece and the surface acting on the workpiece form the heatable active part ( 4 ), characterized in that a device ( 6 ) for inductive heating of the active part ( 4 ) is provided. 3. Tool according to claim 2, characterized in that the inductor ( 6 ) in the active part ( 4 ) opposite tool part ( 7 ) is arranged. 4. Tool according to claim 3, characterized in that in a tool for processing films ( 5 ), the inductor ( 6 ) forms the counterpart jaw opposite the active part ( 4 ). 5. Tool according to claim 4, characterized in that the tempe temperature of the counter jaw to one compared to the ambient temperature raised value is taxable. 6. Tool according to claim 5, characterized in that the inductor ( 6 ) is tubular and connected to a circuit for a temperature control medium. 7. Tool according to one of claims 2 to 6, characterized in that the heat absorption part is equipped with devices ( 3 ) for heat dissipation. 8. Tool according to one of claims 2 to 7, characterized in that the electrical conductivity of the heat absorbing part in the direction of the induction voltage gradient is reduced.