SE513132C2 - Unit for inductive heating, heater, press, use of a unit and method for controlling a unit - Google Patents

Abstract

A unit (2) for induction heating of a workpiece comprises a disc-shaped base plate (5). At least one pole (6) is connected to the base plate (5) and arranged to abut against one side of the workpiece or a tool containing the workpiece. Moreover the unit (2) comprises a coil arranged round each pole (6) and designed to be connected to a voltage source for generating a magnetic field in and round said at least one pole (6). The unit (2) is designed so that two identical, juxtaposed units have an essentially constant distance between poles neighbouring each other, both between said units and, if the unit has more than one pole (6), within the respective units. A heating assembly comprises at least two such units (2) which are designed and arranged side by side in such manner that each pole (6) of the heating assembly has an essentially constant distance to the neighbouring pole or poles (6).

Description

15 20 25 30 35 513 132 2 piece of bait to be treated. The poles are displaceable relative to each other to apply a pressing force to and guide the generated magnetic field into the tool.

This device enables rapid heating of the tool / workpiece, but still has a number of disadvantages. The core and opposing poles of the device must be sized to fit the tool being treated. The construction therefore gives a rather poor geometric flexibility, in that one and the same device can hardly be used to treat tools of different sizes. It has also been shown that there is a risk of local overheating of the tool / workpiece. A further disadvantage arises when the penetration depth of the magnetic field into the tool / workpiece is to be very small, such as when treating thin tools / workpieces.

Although the penetration depth decreases with an increase in the frequency of the applied voltage, an increased frequency also entails undesirably large losses in the core, ie a low efficiency of the heating device.

The present invention has for its object to overcome the above problems, ie to achieve a smoother and more controlled heating as well as an increased geometric flexibility. A further object is to provide an inductive heating with high efficiency regardless of the thickness of the workpiece / tool. It is also desirable to be able to achieve different temperatures in different parts of the tool / workpiece in one and the same process cycle.

These and other objects, which will appear from the following description, have now been achieved in whole or in part by the invention by means of a heating unit, a heating unit and a press according to the appended claims 1, 25 and 34. Preferred embodiments are stated in the dependent claims. Said object is also achieved in whole or in part by methods according to the following claims 37-38. The invention is applicable to heat treatment of workpieces enclosed in a press tool. A non-limiting example of such workpieces is raw materials that consist wholly or partly of plastic or composite material. The invention is also applicable for direct heat treatment of workpieces, such as components comprising both metallic and polymeric materials, in order to achieve a separation of these materials.

Unlike conventional designs for inductive heating, the present invention is based on separate units, or modules, which are designed for mounting to the tool / workpiece. Since the unit lacks a core in the usual sense, ie a core that encloses the tool / workpiece, one or more units can be placed substantially arbitrarily over the tool. This provides a great deal of geometric flexibility, since the number of units can be selected and deployed so that heating of desired parts of the tool is achieved.

Since the unit is designed so that two identical, side-by-side units together have a substantially constant distance between adjacent poles, both within a unit and between the side-by-side units, an even distribution of the magnetic field across the tool is possible when several units are combined into one larger unit. The distance between two poles refers to the smallest distance between the outer circumference of the poles. Since the strength of the generated magnetic field decreases with the square at the distance from the respective pole, a constant pole distance within such an assembly leads to a more even heating of the tool / workpiece arranged under the units.

According to a preferred embodiment, the outer contour of the bottom plate is provided with at least one abutment portion which is designed for abutment against a corresponding portion of another, identical unit. Thus, two units can be brought into abutment against each other and thus cover a portion of the tool / workpiece without mutual intervals. 10 15 20 25 30 35 513 132 4 According to a particularly preferred embodiment, the outer contour of the bottom plate is completely built up of rectilinear abutment portions. Thus, many units can be applied with their base plates edge to edge over the tool / workpiece.

According to a preferred embodiment, each unit has at least two poles, which are placed in a two-dimensional pattern over the base plate. This enables an even more even distribution of the generated magnetic field over the workpiece / tool, and thus a more even heating of the same. When using the unit according to the invention in a press, a more even distribution of the pressing forces over the tool / workpiece is also obtained.

It is preferred that the pattern of poles within a unit be rotationally symmetrical, as this leads to even distribution of both the magnetic field and any pressing forces across the tool.

To reduce the risk of local overheating, the poles in cross section are preferably designed without sharp or rectangular edges.

According to a preferred embodiment, the coils are so connected to the voltage source that the currents in the coils of adjacent poles are phase-shifted relative to each other. This means that the magnetic flux will alternately be directed from and to each pole.

Seen over a longer period of time, the magnetic flux will be substantially homogeneously distributed over the workpiece / tool, so that a good uniformity in the heating can be achieved.

In a preferred embodiment of the unit, the phase difference between the coils of the nearest poles is an integer multiple of 60 degrees. This means that both two-phase and three-phase systems, as well as other systems, can be used and that an even mains load can be achieved.

In a particularly preferred embodiment of the heating unit, units are mounted on either side of the tool / workpiece. By controlling the phase difference between opposite poles, the penetration of the magnetic field in depth through the tool / workpiece can thus be controlled.

The penetration depth is, for example, greatest when two opposing poles are driven in opposite phase, ie with a phase difference of 180 degrees, and at least when the phase difference is 0 degrees.

Thus, the penetration depth can be varied while maintaining high efficiency. In addition, the unit can be used to heat a workpiece of uneven thickness, since each opposing pole pair can be individually controlled to generate a magnetic field with the desired penetration depth.

The assembly can thus be used to achieve a uniform temperature distribution in the workpiece regardless of its shape. Alternatively, different temperatures can be achieved in different parts of the workpiece in one and the same process cycle.

The method according to the invention comprises at least one of the steps: a) determining the frequency at which maximum active power transfer takes place from each unit to the workpiece or tool to be heated; b) to tune a resonant circuit so that maximum active power transfer takes place to the workpiece / tool; c) locking the phase of the voltage supplied to the respective coil to provide an even heating in a plane extending parallel to the poles of the unit; and d) by controlling by pulse width modulation the duty cycle of the voltage supplied to the respective coil so that the desired power transfer is obtained.

In the preferred embodiment, each of the above steps makes it possible to influence both the power transferred to the tool and the evenness of the heating.

In the heating unit, each unit is preferably controlled individually for optimal control of the heating, ie the temperature in the tool / workpiece.

The above method also enables experimental recording of a suitable time period for current and voltage supply 1313 6 voltage supply to achieve the desired heating in a variety of applications. Thus, a number of different "heating schemes" can be registered, which can then be run regularly.

The invention is described below by way of example with reference to the accompanying drawings, which schematically and by way of example illustrate presently preferred embodiments.

Fig. 1 is a sectional view of a heating unit comprising a number of units according to the invention for inductive heating of a workpiece.

Fig. 2 is an exploded view of a unit according to the invention.

Figs. 3a-3f are plan views of different embodiments of units according to the invention, which are brought into abutment against each other to form a heating unit. For the sake of clarity, only the poles and base plates of the units are shown.

Fig. 4 is a plan view of three heating units which are placed side by side and each of which has a centrally arranged pole with a circular cross-section. For the sake of clarity, only the units' poles and base plates are shown.

Fig. 5a is a diagram of the time variation of the phases in a three-phase system, and Figs. 5b-5c schematically illustrate the magnetic flux between the poles within a unit at two different times.

Fig. 6 is a sectional view of two units placed one side of a workpiece.

Description of Preferred Embodiments Fig. 1 shows an assembly for inductive heating of a tool. The unit comprises two separate frames 1, each of which is built up of a plurality of separate heating units or modules 2. The frames 1 are placed on each side of a tool 3, which contains a workpiece 4 to be heated.

In the embodiment shown, each heating unit or module 2 comprises a disc-shaped base plate 5, three poles 6 and a coil 7 arranged around each pole 6. The poles 6 are fixedly connected to the base plate 5 and are arranged Each coil 7 is connected to a voltage source 8 and a control unit 9. For the sake of clarity, only the connection of two poles to the voltage source 8 and the control unit 9 is shown, which are designed to generate via the coils 7 a magnetic field in and around the respective pole 6. This magnetic field heats the tool 3 and the workpiece 4, as will be described in greater detail below. The illustrated heating unit can, for example, be mounted in a press, so that opposite pressing forces are applied to the sides of the frames 1 away from the tool 3.

Fig. 2 shows in greater detail a module 2 according to the invention included in an assembly according to Fig. 1. For the sake of clarity, the parts of the module 2 are separated from each other.

The disc-shaped bottom plate 5 of the module 2 consists of a lower part 5 'The lower part 5' of the embodiment milled grooves 10, in which a cooling medium can and an upper part 5 "has in the shown pass under its path from an inlet pipe 11 to an outlet pipe 12 The coolant is intended to dissipate heat that may be conducted down into the module 2 during the heating of the tool 3. The coolant can be water, air or any other fluid suitable for the purpose. On the upper part 5 "of the bottom plate 5, three perpendicular to the bottom plate are formed 5 projecting poles 6. A coil 7 is arranged around the respective pole 6. The coils 7 are connected via lines 13 to the voltage source 8 (not shown) and the control unit 9.

In the embodiment shown in Fig. 2, the cross section of the poles 6 is substantially circular. The cross section of the poles 6 can alternatively be elliptical or polygonal, for example hexagonal. However, it is preferred that the cross-sections of the poles 6 have no sharp or right-angled corners, since the generated magnetic field tends to concentrate at such corners and cause local overheating of the underlying portions of the workpiece 4. The poles 6 are placed in a two-dimensional pattern on the module 2 bottom plate 5 for 10 15 20 25 30 35 513 132 8 to give as even heating as possible of the workpiece 4. For the same reason the poles 6 are placed with a constant mutual distance on the bottom plate 5. Furthermore, the cross-sectional area of the poles 6 is maximized, so that as large a contact surface as possible is provided for guiding the generated magnetic field down into the tool. For good controllability of the temperature distribution in the workpiece 4, the poles 6 should in total cover at least about 20% of the surface of the bottom plate 5.

The modules are preferably designed so that two identical, side-by-side modules 2 have a substantially constant distance between each pole 6 and its nearest neighboring poles 6 both within a module 2, if each module has at least two poles, and between adjacent modules 2. It is preferred that the bottom plate 5 of the module 2 has such an outer contour that a portion of a module 2 can be brought into a planar abutment against a corresponding portion of another, identical module 2, so that these modules 2 cover a portion of tool 3. Examples of especially preferred designs are given in the plan views in Figs. 3a-3e. In Figs. 3a and 3b, each bottom plate 5 has an outer contour in the shape of a triangle. More specifically, the outer contour of the bottom plate 5 is equilateral in Fig. 3a and isosceles in Fig. 3b. The outer contour of the bottom plate 5 may alternatively have portions which are substantially in the form of a In this case, the outer contour consists of two mutually symmetrical arctan portions arctan curve, as shown in Fig. 3c. and two rectilinear portions, which at right angles connect the two arctan portions to each other. This construction allows modules to abut each other without mutual spacing and also enables both optimal pole placement and maximization of the poles' cross-sectional area.

Namely, it is desirable to avoid strong magnetic fields at the joint between two side-by-side modules 2, as this can give rise to large losses. Thus, each pole 6 should have a maximum distance to the outer contour of the bottom plate 5, at the same time as the poles 6 should cover as large a part of the surface of the bottom plate 5 as possible. A good compromise between these conflicting conditions is achieved by means of the module shown in Fig. 3c. For manufacturing technical reasons, however, it is preferred that the outer contour of the bottom plate 5 is built up of rectilinear portions. An example of a “rectilinear” arctan curve is given in Fig. 3d. Further examples are given in Figs. 3e and 3f, where the outer contour of the bottom plate 5 has the shape of a regular, ie equilateral, hexagon or a “honeycomb structure”.

A particularly preferred embodiment of the module according to the invention is shown in Fig. 4, which shows three such modules placed side by side 2. Each bottom plate 5 has the shape of a regular hexagon and has only a centrally arranged pole 6 with a circular cross-section . This outer contour and pole placement is easy to achieve and guarantees that each pole 6 has a constant distance to the nearest poles 6 when the modules 2 abut each other. In addition, in this embodiment it is possible to provide both an adequate distance from the pole 6 to the outer contour of the bottom plate 5 and good coverage of the surface of the bottom plate 5.

In the following, the control of a module and an assembly according to the invention is described. First, it is described how the magnetic field changes over time within a module with three poles. Thereafter, the interaction between two such opposing modules will be elucidated. Finally, a way of automatically controlling the heating will be explained.

Each module is controlled individually in the preferred embodiment. This enables a local control of the magnetic field that is generated and thus the possibility of heating different parts of the workpiece or tool to different amounts. In the embodiment according to Fig. 2, each coil 7 is preferably connected to a respective phase of a voltage source 8 with three phases. The poles 6 abut against the tool 3 and thereby form a magnetically closed circuit when the coils 7 are supplied with a voltage. The magnetic field generated when a current flows through the coils 7 gives rise to various losses in the tool 3, which cause the tool 3 to heat up. The loss mechanisms that give rise to the heating are hysteresis losses, eddy current losses and anomalous losses, also called micro-eddy current losses. Control of the phases makes it possible to influence the magnetic field and thus the heating, both in the surface direction and in the depth direction, as described in the following.

Fig. 5a shows how the three phases of the voltage source, which are denoted by R, S and T, 5b-5c, illustrate the temporal variation of it varies over time, and in Fig. The magnetic flux between the poles of a module with three poles, as shown in Figs. 3a-3f, or an assembly of three abutting modules with one pole each, as shown in Fig. 4, for example. Each pole 6 is connected via a coil to a respective phase of the voltage source 8. At time t1 (fig. 5a), the R-phase has maximum current, and the magnetic flux flows from the R-phase-connected pole R, in equal parts, to the poles S, T which are connected to the S-and T-phases of the voltage source, respectively. To facilitate understanding, a vectorial description of the flow is conceivable, where two vectors with the same amount point from the R-pole in the direction of the S-pole and the T-pole, respectively. The resulting vector will then be directed straight downwards in the figure. At a (Fig. 5a) strength, and the magnetic flux flows until the same time tg, the T-phase has minimal current parts from the R- and S-poles of the modules to the T-pole. The resulting vector will at this point instead be directed obliquely downwards to the right in the figure. The resulting flow vector has thus been rotated between the times t1 and t2. This reasoning can be continued in the same way, and leads to the conclusion that the resulting flow vector has rotated a full revolution counterclockwise when an entire oscillation period has elapsed and the R-phase is again maximum. Consequently, over time a very even distribution of the flow between the different poles R, S, T is achieved and thus also a very even heating in surface over the workpiece. In addition, if a number of modules are placed next to each other, to form an assembly, then the synergy effect is created between the poles 6 on different modules 6 and not only within the individual modules, especially when each pole 6 has a constant distance to and is connected to another phase than the nearest poles 6, both within and between the modules.

In another embodiment, not shown, of the invention, the module has two poles, partly a central pole and partly a concentrically arranged, annular pole. The poles are surrounded by at least one coil. In this concentric arrangement, the coil of the annular pole is supplied with a voltage which is phase reversed in relation to the voltage supplied to the coil of the central pole. Thus, the magnetic flux moves back and forth in a radial direction between the two poles, so that an even heating is achieved.

In all the cases described above, the poles belonging to the respective phase have essentially the same cross-sectional area, as this gives an even load on the voltage source and good uniformity in the heating.

By placing modules on each side of the tool / workpiece, you can very accurately control the heating of this, since a magnetic field can be generated and controlled by the tool / workpiece. Fig. 6 schematically shows a first module 2a, which with its poles 6 is mounted against a first side of a workpiece 4, and a second module 2b, which is mounted against a second, opposite side of the workpiece 4. The poles are thus facing and paired with each other. Each module is individually controllable.

Assume first, as indicated in Fig. 6, that the modules are positioned so that the R-pole of the first module 2a is located opposite the R-pole of the second module 2b, that the S-pole of the first module 2a is located opposite the second module 2b S-pole and that the T-pole of the first module 2a is located opposite the T-pole of the second module 2b. If the two modules 2a, 2b are operated with the same voltage, two counter- | C L __: 10 15 20 25 30 35 513 132 12 This causes the currents to deflect before they have penetrated far into the workpiece 4. magnetic currents.

Consequently, only a surface heating of the workpiece 4 is provided. If, instead, the voltage supply to the second module 2b is phase-turned 180 degrees compared to the first module 2a, the opposite relationship is achieved, namely that the magnetic flux is driven straight through the workpiece 4, the entire workpiece 4 and not just its surface.

Because there is a variable phase difference between the modules 2a, 2b, which is between 0 and 180 degrees, different penetration depths in workpiece 4 can thus be achieved. This can be done, for example, with a simple phase locking circuit.

The heating of the workpiece 4 can also be controlled by physically rotating the opposite modules 2a, 2b relative to each other, for example so that the poles which are opposite each other are R-S, S-T and T-R, respectively. The poles do not necessarily have to be located exactly opposite each other, but can also be partially offset laterally in relation to each other.

In the presently preferred embodiment of the invention, an automatic control of the heating takes place. The tool 3 is provided with a number of temperature sensors, which are of a type known per se and whose output signals function as input signals to the control unit 9 which controls the voltage supply to the heating modules.

The control unit 9 can be described as a circuit which can be actuated on substantially three levels. At the extreme level, where the slowest control is achieved, the applied voltage is regulated with a simple type of regulator, for example an on / off regulator or a P / D regulator. By changing the duty cycle of the voltage supply (ie by pulse width modulation, controlling the length of the time periods with voltage supply to the module) depending on the measured temperature, the heating can be regulated. The energy supplied to the tool depends, among other things, on: KJ 10 15 20 25 30 35 513 132 13 other on the length of the time periods with voltage supply to the coils.

At the next underlying level, there are components for regulating the active power transfer to the tool. This provides a faster control than that which can be achieved with the help of the temperature sensors. These components comprise a resonant circuit which comprises a capacitor with a variable capacitance or an inductor with a variable inductance. The active power transfer to the tool is calculated by measuring The current, voltage and phase angle are then regulated. the capacitance of the capacitor, or the inductance of the inductor, until the power factor active power transfer to the tool, is maximized.

Ideally, this means that the drive stage is only loaded by one (cosw), and thus also the resistive load, ie cosç = l.

At the third and lowest level there are components that, if possible, control the frequency until electrical resonance is obtained. coil and that the power factor is maximum.

This means that the capacitor is tuned to This also maximizes the active power transfer to the tool, and the reactive (or "useless") power is minimized.

The heating of the tool is thus maximized. This is the fastest and most basic control.

Only a few possible embodiments of the invention have been described above. Based on the description, the person skilled in the art can provide a number of variants which are suitable for the application in question and which are within the scope of protection of the appended claims. For example, the design of the control unit can be varied to achieve maximum power transfer to the tool. Pole patterns and base plates other than those described here are also possible to achieve. For example, each base plate may have more than three poles. Also in this case, it is preferable that adjacent poles are connected to different phases of the voltage source. The poles should also be arranged in a rotationally symmetrical pattern on the base plate, so that a rotation of the module over a maximum of 120 degrees transmits the pole pattern on itself. In the case of six poles on the base plate and three phases of the voltage source, the pattern should be rotationally symmetrical for a rotation of the module over 60 degrees. Although it is preferred that the units have an outer contour that allows the units to abut directly against each other without mutual spacing, the units may have an arbitrary outer contour. In this case, the units are suitably placed in and mutually fixed by a frame structure for forming said frame.

It should be pointed out that a heating unit according to the invention may comprise units opposite in pairs, or a body attached to one side of the tool / workpiece which is formed by several units, or a combination of these. However, if units are only mounted against one side of the tool / workpiece, a magnetically conductive abutment should be mounted against the opposite side of the tool / workpiece. Without such an abutment, the generated magnetic field will mainly extend directly between the poles of the units, so that the penetration depth will be small. With an opposite abutment, the magnetic field is driven to a greater extent through the intermediate tool / workpiece.

The poles of the modules are preferably made of a material other than electroplate, since it is difficult and expensive to produce poles in electroplate in a suitable pattern and with a suitable cross-sectional shape, ie without sharp or rectangular corners. The poles are preferably made by compressing a metal powder and a binder. This manufacturing technique is known per se in other fields of technology, see for example US-A-2 937 964. More specifically, each metal powder grain is coated with a thin surface layer of a binder before pressing. The metal powder grains are thus electrically insulated from each other. In the preferred embodiment, the binder is phenolic resin. When the powder is compressed under high pressure, a very durable structure is formed which can be machined to the desired shape by cutting machining. In addition to magnetic properties suitable in this context, this material has also been shown to have good strength and be able to absorb large compressive forces. According to a preferred embodiment, the base plate and the poles are made in one piece in this material. Alternatively, the poles can be manufactured separately and then attached to the base plate by gluing, bolted joints or some other equivalent method. The bottom plate can then be made of this material, but also other materials than conceivable, eg electroplate.

Claims (38)

10 15 20 25 30 35 513 132 16 PATENT REQUIREMENTS A unit for inductive heating of a workpiece (4), which unit comprises a disc-shaped base plate (5), at least one pole (6) connected to the base plate (5), which is arranged for mounting against one side of the workpiece (4) containing tools or a workpiece (4) (3), and a voltage source a coil (7) (8) arranged around each pole (6) which is connected to each coil (7) for generating a magnetic fields in and (6), side-by-side units around said at least one pole, the unit being so designed that two identical, have a substantially constant distance between the nearest (6), and between said units. A unit according to claim 1, an outer contour comprising at least one abutment portion as poles located opposite each other both within each unit, the bottom plate (5) being designed for abutment against a corresponding portion of another, identical unit. A unit according to claim 2, wherein at least one abutment portion is rectilinear. An assembly according to claim 2 or 3, wherein at least one abutment portion is substantially in the form of an arctane curve. A unit according to any one of the preceding claims, wherein the bottom plate (5) has an outer contour comprising at least three rectilinear portions. A unit according to any one of the preceding claims, wherein the bottom plate (5) has an outer contour comprising only rectilinear portions. A unit according to any one of the preceding claims, wherein the outer contour of the bottom plate (5) has the shape of a triangle. Unit according to claim 7, gel is equilateral. A device according to claim 7, isosceles. wherein said triane is wherein said triangle is 10 15 20 25 30 35 513 132 17 A unit according to any one of the preceding claims, wherein the bottom plate (5) is preferably a honeycomb structure. outer contour has the shape of a hexagon, 11. ll. Unit according to one of the preceding claims, wherein all poles (6) in total cover at least about 20% of the bottom plate (5) Unit according to one of the preceding claims, surface. each pole (6) in a section along the base plate (5) lacking pointed or right-angled corners. An assembly according to any one of the preceding claims, wherein each pole (6) has a substantially elliptical cross-section. An assembly according to any one of the preceding claims, wherein each pole (6) has a substantially circular cross-section. A unit according to any one of the preceding claims, comprising at least two poles (6), which are placed on the base plate (5) mounting against one side of the workpiece (4) the workpiece (4) An assembly according to claim 15, such that a rotation of the base plate (5) in a two-dimensional pattern for or containing the tool (3). wherein said pattern is over an angle of a maximum of 120 degrees mainly transmits the pattern on itself. A unit according to claim 15 or 16, a pattern having the shape of a regular polygon. wherein said An assembly according to claim 15 or 16, wherein the poles (6) are arranged in a concentric pattern. A unit according to any one of claims 15-18, wherein there is a mutual phase difference between the currents flowing through the coils (7) of adjacent poles (6) on the unit. The unit of claim 19, is an integer multiple of 60 degrees. wherein said phase difference An assembly according to any one of claims 15-20, wherein (7) of adjacent poles (6) are (8). the coils connected to different phases of the voltage source 10 15 20 25 30 35 513 132 18 An assembly according to claim 21, is assigned poles (6) such that the voltage source (8) that the poles (6) for each phase have the same total cross-sectional area. A unit according to any one of the preceding claims, wherein (10) flow-through of a cooling medium. cooling coils are formed in the base plate (5) for An assembly according to any one of the preceding claims, wherein each pole (6) is made by pressing a metal powder and a binder. Heating unit comprising at least one unit according to any one of claims 1-24, wherein at least one unit (2) is mounted against a first side of the workpiece (4) or a workpiece (4) Heating unit comprising at least two tools (3). units according to any one of claims 1-24, wherein the units (2) are arranged side by side against a first side of the workpiece (4) or a workpiece (4) (3). A heater according to claim 26, wherein the piece containing tool the distance between adjacent poles (6) is substantially constant over the entire heater. A heating unit according to any one of claims 25-27, comprising at least one magnetically conductive abutment mounted against a second, opposite side of the workpiece / tool. A heating unit according to any one of claims 25-28, wherein at least one corresponding unit (2) is mounted against a second, opposite side of the workpiece / tool. Heating unit according to claim 29, wherein the opposite poles (6) of the units (2) mounted on either side of the workpiece (4) Heating units according to claim 29 or 30, are arranged opposite each other. comprising a control device (9) designed to electrically control the phase difference between the currents through the coils (7) of said opposite poles (6) in order to vary the penetration depth of the generated magnetic field into the workpiece / tool. 10 15 20 25 30 35 513 132 19 Heating unit according to claim 29 or 30, comprising a control device (9) designed to mechanically effect mutual rotation of said opposing heating units (2) in order to vary the depth of penetration of the generated magnetic field into the workpiece / tool. Heating unit according to claim 31 or 32, comprising a temperature sensor for measuring the temperature in the tool (3), wherein the output signal of the temperature sensor constitutes an input signal to the control device (9). Press for the production of products wholly or partly of plastic or composite material, comprising a unit according to any one of claims 1-24 or an assembly according to any one of claims 25-33. Use of a unit according to any one of claims 1 to 24 or an assembly according to any one of claims 25 to 33 for heat treatment of components comprising both metallic and polymeric materials for the purpose of separating the metallic and polymeric materials from each other. Use of a unit according to any one of claims 1 to 24 or an assembly according to any one of claims 25-33 for heating a press tool mounted in a press for the production of products wholly or partly of plastic or composite material. A method for controlling a unit according to any one of claims 1-24 or an assembly according to any one of claims 25-33, comprising at least one of the steps: a) determining the frequency at which maximum active power transmission takes place from each unit (2) to the workpiece (4); b) to tune a resonant circuit so that the maximum (4): c) to lock the phase of the voltage supplied to active power transmission takes place to the workpiece and coil (7), respectively, to achieve an even heating in a geometric plane which extends parallel to the unit (2) (6); poles and 513 152 d) to control by pulse width modulation the duty-cycle of the voltage supplied to the respective coil (7) so that the desired power transfer is obtained. A method of controlling a unit according to any one of claims 1-24 or an assembly according to any one of claims 25-33, wherein each unit (2) is controlled individually.