WO2000035250A1 - Unite de chauffage par induction, et ensemble comportant ladite unite - Google Patents

Unite de chauffage par induction, et ensemble comportant ladite unite Download PDF

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Publication number
WO2000035250A1
WO2000035250A1 PCT/SE1999/002200 SE9902200W WO0035250A1 WO 2000035250 A1 WO2000035250 A1 WO 2000035250A1 SE 9902200 W SE9902200 W SE 9902200W WO 0035250 A1 WO0035250 A1 WO 0035250A1
Authority
WO
WIPO (PCT)
Prior art keywords
unit
poles
workpiece
base plate
pole
Prior art date
Application number
PCT/SE1999/002200
Other languages
English (en)
Inventor
Göran Langstedt
Tord Cedell
Original Assignee
Linlan Induction Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Linlan Induction Ab filed Critical Linlan Induction Ab
Priority to AU20139/00A priority Critical patent/AU2013900A/en
Publication of WO2000035250A1 publication Critical patent/WO2000035250A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/36—Coil arrangements
    • H05B6/44—Coil arrangements having more than one coil or coil segment
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/10—Induction heating apparatus, other than furnaces, for specific applications
    • H05B6/14—Tools, e.g. nozzles, rollers, calenders
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/36—Coil arrangements
    • H05B6/365—Coil arrangements using supplementary conductive or ferromagnetic pieces

Definitions

  • the present invention relates generally to treatment of materials by electromagnetic heating thereof. More specifically, the invention relates to an induction heating unit and a heating assembly having at least two such units. The invention also relates to a press provided with such heating, use of such a unit or such an assembly, and methods for controlling the same.
  • This device is intended for heating a workpiece in a press and consists of a core of electric sheet steel enclosing the workpiece, a coil arrangement placed round the core and a voltage source.
  • the voltage source is connected to the coil arrangement to generate a magnetic field in and round the core.
  • the core has two poles which between them receive a press tool which encloses the workpiece to be treated.
  • the poles are displaceable relative to each other to apply a press force to and conduct the generated magnetic field into the tool .
  • This device enables rapid heating of the tool/work- piece but still has a number of drawbacks .
  • the core and opposite poles of the device must in terms of size be adjusted to the tool which is being treated. Therefore the construction yields in a fairly poor geometric flex- ibility in that it is difficult to treat tools of different size in one and the same device. It has also been found that there is a risk of local overheating of the tool/workpiece .
  • a further drawback arises when the penetration depth of the magnetic field in the tool/work- piece has to be very small, such as in the treatment of thin tools/workpieces .
  • the penetration depth certainly decreases with an increase of the frequency of the applied voltage, but an increased frequency at the same time causes undesirably great losses in the core, i.e. a low degree of efficiency of the heating device.
  • An object of the present invention is to obviate the above problems, i.e. to provide a more uniform and more controlled heating and an increased geometric flexibility.
  • a further object is to provide induction heating with a high degree of efficiency independently of the thickness of the workpiece/tool . It is also desirable to be able to provide different temperatures in different parts of the tool/workpiece in one and the same process cycle .
  • the invention is applicable to heat treatment of workpieces enclosed in a press tool.
  • a non-limiting example of such workpieces is raw materials which wholly or partially consist of plastic or composite material.
  • the invention is also applicable to direct heat treatment of workpieces, such as components comprising both metallic and polymeric materials, with a view to achieving a separation of these materials.
  • the present invention starts from separate units, or modules, which are designed to be arranged against the tool/workpiece. Since the unit has no core in the usual meaning, i.e. a core enclosing the tool/ workpiece, one or more units can be arranged essentially arbitrarily over the tool . This yields great geometric flexibility since the number of units can be selected and positioned so that heating of desired parts of the tool is achieved.
  • the unit is designed in such manner that two identical, juxtaposed units together have an essentially constant distance between poles nearest or neighbouring each other, both within a unit and between the juxtaposed units, a uniform distribution of the magnetic field over the tool is made possible when several units are combined to a large assembly.
  • the distance between two poles is meant the minimum distance between the outer circumferences of the poles. Since the strength of the generated magnetic field decreases in proportion to the square of the distance from the respective poles, a constant pole distance within such an assembly results in a more uniform heating of the tool/workpiece arranged under the units .
  • the outer contour of the base plate is formed with at least one abut- ment portion which is designed to abut against a corresponding portion of another, identical unit. Consequently, two units can be made to abut against one another and, thus, without any mutual spacing cover a portion of the tool/workpiece.
  • the outer contour of the base plate is completely com- posed of rectilinear abutment portions.
  • many units can be arranged with their base plates edge-to-edge over the tool/workpiece.
  • each unit has at least two poles, which are arranged in a two-dimensional pat- tern over the base plate. This enables a still more uniform distribution of the generated magnetic field over the workpiece/tool and, thus, a more uniform heating of the same. Moreover, when using the inventive unit in a press, the press forces will be more uniformly distri- ubbed over the tool/workpiece.
  • the pattern of poles within a unit is rotationally symmetrical since this results in a uniform distribution of the magnetic field as well as any press forces over the tool .
  • the poles are in cross-section preferably formed without sharp or right-angled edges.
  • the coils are connected to the voltage source in such manner that the currents in the coils of poles neighbouring each other are phase-shifted relative to each other. This means that the magnetic flux will alternatingly be directed away from and to each pole. Seen over a longer period of time, the magnetic flux will be essentially homogeneously dis- tributed over the workpiece/tool, thereby achieving good uniformi-y in heating.
  • the phase difference between the coils of poles neighbouring each other is an integer multiple of 60 degrees. This means that both two-phase and three-phase systems, and also other systems, can be used and that a uniform line load can be ⁇ rovided. Equivalent advantages apply to the inventive heating assembly.
  • the heating assembly units are arranged on each side of the tool/workpiece.
  • the penetration depth of the magnetic field through the tool/workpiece can thus be controlled.
  • the penetration depth is at its maximum when two opposite poles are driven in opposition, i.e. with a phase difference of 180 degrees, and at its minimum when the phase difference is 0 degrees.
  • the penetration depth may vary while maintaining a high degree of efficiency.
  • the assembly can be used to heat a workpiece of uneven thickness since each pair of opposite poles can be controlled individually to generate a magnetic field having a desired penetration depth.
  • the assembly can be used to provide a uniform temperature distribution in the workpiece independently of its form. Alternatively, different temperatures can be provided in different parts of the workpiece in one and the same process cycle.
  • the inventive method comprises at least one of the steps of : a) determining the frequency at which a maximum active power transfer occurs from each unit to the work- piece or tool to be heated; b) tuning a resonance circuit so that a maximum active power transfer occurs to the workpiece/tool; c) locking the phase of the voltage supplied to the respective coils for providing a uniform heating in a plane extending parallel to the poles of the unit; and d) controlling, by pulse width modulation, the duty cycle of the voltage supplied to the respective coils so chat the desired power transfer is obtained.
  • each of the above steps makes ic possible to influence both the power transferred co the cool and the uniformity in heating.
  • each unit is preferably controlled individually for optimum control of the heating, i.e. the temperature in the tool/workpiece.
  • Fig. 1 is a sectional view of a heating assembly comprising a number of inventive units for induction heating of a workpiece.
  • Fig. 2a is an exploded view of an inventive unit
  • Fig. 2b is a top plan view of a heating assembly with corresponding units.
  • Figs 3a-3f are top plan views of different embodiments of inventive units, which are made to abut directly against each other to form a heating assembly. For the sake of clarity, only the poles and base plates of the units are shown.
  • Fig. 4 is a top plan view of three heating units which are arranged side by side and which each have a centrally arranged pole of circular cross-section. For the sake of clarity, only the poles and base plates of the units are shown.
  • Fig. 5a is a diagram of the time variation of the phases in a three-phase system
  • Figs 5b-5c illustrate schematically the magnetic flux between the poles within a unit at two different points of time
  • Fig. 6 is a sectional view of two units which are arranged on each side of a workpiece. Description of Preferred Embodiments
  • Fig. 1 illustrates an assembly for induction heating of a tool .
  • the assembly comprises two separate bodies 1 each composed of a plurality of separate heating units or modules 2.
  • the bodies 1 are arranged on each side of a tool 3 which contains a workpiece 4 to be heated.
  • Each heating unit or module 2 comprises in the shown embodiment a disc-shaped base plate 5, three poles 6 and a coil 7 arranged round each pole 6.
  • the poles 6 are fixedly connected to the base plate 5 and are arranged to abut against the tool 3.
  • Each coil 7 is connected to a voltage source 8 and a control unit 9.
  • the illustrated heating assembly can be mounted in, for example, a press so that opposite press forces are applied to the sides of the bodies 1 facing away from the tool 3.
  • Fig. 2a shows in more detail an inventive module 2.
  • the disc-shaped base plate 5 of the module 2 consists of a bottom part 5' and a top part 5".
  • the bottom part 5' has milled grooves 10, in which a cooling medium can pass while flowing from an inlet tube 11 to an outlet tube 12.
  • the cooling medium is adapted to carry off heat which is pos- sibly conducted into the module 2 in the heating of the tool 3.
  • the cooling medium can be water, air or some other fluid suitable for the purpose.
  • Three poles 6 projecting perpendicularly from the base plate 5 are formed on the top part 5" of the base plate 5.
  • a coil 7 is arranged round each pole 6.
  • the coils 7 are via lines
  • the cross-section of the poles 6 is essentially circular.
  • the cross- section of the poles 6 can alternatively be elliptic or polygonal, e.g. hexagonal.
  • the poles 6 are arranged in a two-dimensional pattern on the base plate 5 of the module 2 to provide as uniform heating as possible of the workpiece 4. For the same reason, the poles 6 are arranged in a constant spaced-apart relationship on the base plate 5.
  • the cross-sectional area of the poles 6 is maximised so that as large a contact surface as possible is provided to conduct the generated magnetic field into the tool.
  • the poles 6 should cover a total of at least about 20% of the surface of the base plate 5.
  • the modules 2 are preferably so designed that two identical, juxtaposed modules 2 have an essentially constant distance between each pole 6 and its neighbouring poles 6 both within a module 2, if each module has at least two poles, and between adjoining modules 2.
  • Fig. 2b shows a body 1 which comprises a plurality of separate, juxtaposed modules 2. For the sake of clarity, the coils of the modules are omitted.
  • the modules 2 are arranged in and mutually fixed by a frame structure 1 ' .
  • the poles 6 of the modules 2 are in the shown example arranged in a two-dimensional pattern at an essentially constant distance to each other. In this case, the maximum geometric flexibility will be achieved when each unit is formed with a single, central pole (not shown) . It will be appreciated that the base plates 5 of the modules 2 may have an essentially arbitrary outer contour.
  • each module 2 it is preferred for the base plate 5 of each module 2 to have such an outer contour that a por- tion of a module 2 can be brought to plane, direct abutment against a corresponding portion of another, identical module 2, so that these modules 2 without any mutual spacing cover a portion of the tool 3.
  • This embodiment allows a simpler design of the heating assembly 1 since the frame structure 1 ' can be omitted or at least simplified.
  • the absence of air gaps between the modules 2 also increases the heating efficiency of the assembly 1. Examples of particularly preferred embodiments are given in the top plan views in Figs 3a-3e.
  • each base plate 5 has an outer contour in the form of a triangle. More specifically, the outer contour of the base plate 5 is equilateral in Fig.
  • the outer contour of the base plate 5 can alter- natively have portions which essentially have the form of an arc tan curve, as illustrated in Fig. 3c.
  • the outer contour consists of two mutually symmetrical arc tan portions and two rectilinear portions, which at right angles connect the two arc tan portions with one another. This construction allows modules to abut against each other without any mutual spacing and also enables both an optimal positioning of the poles and a maximising of the cross-sectional surface of the poles. In fact it is desirable to avoid strong magnetic fields in the joint between two juxtaposed modules 2 since this may cause great losses.
  • each pole 6 should have a maximum distance to the outer contour of the base plate 5 while at the same time the poles 6 should cover as much as possible of the surface of the base plate 5.
  • a good compromise between these contradictory requirements is achieved by means of the module shown in Fig. 3c.
  • the outer contour of the base plate 5 is, however, preferred for the outer contour of the base plate 5 to be made up of rectilinear portions.
  • An example of a "rectilinear" arc tan curve is given in Fig. 3d.
  • Figs 3e and 3f where the outer contour of the base plate 5 has the form of a regular, i.e. equilateral, hexagon or a "honeycomb structure" .
  • FIG. 4 illustrates three such juxtaposed modules 2.
  • Each base plate 5 has the form of a regular hexagon and has only one centrally arranged pole 6 which is circular in cross-section.
  • This outer contour and arrangement of the poles are easy to accomplish and guarantee that each pole 6 has a constant distance to adjoining poles 6 when the modules 2 abut against each other.
  • each module is individually controlled in the preferred embodiment. This enables local control of the magnetic field that is being generated and, thus, heating of different parts of the workpiece or tool to different degrees.
  • each coil 7 is preferably connected to an associated phase of a voltage source 8 with three phases.
  • the poles 6 abut against the tool 3 and thus form a magnetically closed circuit when the coils 7 are supplied with a voltage.
  • the magnetic field which is generated when a current flows through the coils 7 causes different losses in the tool 3, which result in the tool 3 being heated.
  • the loss mechanisms which cause the heating are hysteresis loss, eddy current loss and anomalous loss, also called micro- eddy current loss. Control of the phases makes it possible to affect the magnetic field and, thus, the heat- ing, both along the surface and in depth, as will be described below.
  • Fig. 5a shows how the three phases of the voltage source, which are designated R, S and T, vary over time
  • Figs 5b and 5c illustrate the time variation of the magnetic flux between the poles of a module with three poles, as is illustrated in e.g. Figs 3a-3f, or an assembly of three modules abutting against each other and each having one pole, as shown in e.g. Fig. 4.
  • Each pole 6 is via a coil connected to an associated phase of the voltage source 8.
  • the R phase has its maximum current intensity, and the magnetic flux flows from the R-phase-connected pole R, in equal parts, to the poles S, T that are connected to the S and T phases, respectively, of the voltage source.
  • the module has two poles, one central pole and one concentrically arranged, annular pole.
  • the poles are surrounded by at least one coil each.
  • the coil of the annular pole is supplied with a voltage which is phase- inverted relative to the voltage supplied to the coil of the central pole.
  • the magnetic flux moves back and forth in the radial direction between the two poles so as to provide uniform heating .
  • the poles associated with the respective phases have essentially the same cross-sectional area since this results in uniform load of the voltage source and good uniformity in heating.
  • Fig. 6 shows schematically a first module 2a, which with its poles 6 is arranged on a first side of a workpiece 4, and a second module 2b which is arranged on a second, opposite side of the workpiece 4. Thus the poles are facing each other and aligned in pairs.
  • Each module is individually controllable .
  • the modules are arranged so that the R pole of the first module 2a is positioned in front of the R pole of the second module 2b, that the S pole of the first module 2a is positioned in front of the S pole of the second module 2b, and that the T pole of the first module 2a is posi- tioned in front of the T pole of the second module 2b.
  • the cwo modules 2a, 2b are driven by the same voltage, two opposite magnetic fluxes are generated. This results in the fluxes deflecting before having time to penetrate far into the workpiece 4. Consequently, only surface heating of the workpiece 4 is provided. If instead the voltage supply to the second module 2b is phase-inverted by 180 degrees compared with the first module 2a, the opposite condition is achieved, viz. that the magnetic flux is driven straight through the workpiece 4, which causes uniform heating of the entire workpiece 4, not only its surface. By a variable phase difference existing between the modules 2a, 2b, which is between 0 and 180°, different penetration depth in the workpiece 4 can thus be achieved. This can be performed, for example, by a simple phase locking loop.
  • the heating of the workpiece 4 can also be con- trolled by physically turning the opposed modules 2a,
  • poles opposing each other are R-S, S-T and T-R, respectively.
  • the poles need not necessarily be positioned exactly in front of each other, but can also be partially displaced in the lateral direction relative to each other.
  • the heating is automatically controlled.
  • the tool 3 is equipped with a number of temperature sensors, which are of a type known per se and whose output signals func- tion as input signals of 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 affected on at least one of essentially three levels.
  • the supplied voltage is controlled by a simple type of regulator, for example an on/off regulator or a P/D regulator.
  • the duty cycle of the voltage supply i.e. by pulse width modulation controlling the length of the periods with voltage supply to the module, the heating can be controlled.
  • the energy supplied to the tool in fact depends on, inter alia, the length of the periods with voltage supply to the coils.
  • a resonance circuit which comprises a capacitor having a variable capacitance or alternatively an inductor having a variable inductance .
  • the design of the control unit may be varied to achieve the maximum power transfer to the tool.
  • other pole patterns and base plates than those described above can be provided.
  • each base plate can have more than three poles.
  • neighbouring poles it is preferred for neighbouring poles to be connected to different phases of the voltage source.
  • the poles should be arranged in a rota- tionally symmetrical pattern on the base plate, so that a turning of the module through 120 degrees maximum trans- fers the pole pattern to 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 turning of the module through 60 degrees.
  • a heating assembly may comprise pairs of opposite units, or a body which is arranged on one side of the tool/workpiece and is formed of a plurality of units, or a combination of these. If units are only arranged on one side of the tool/workpiece, a magnetically conductive abutment, however, should be arranged on the opposite side of the tool/workpiece. Without such an abutment, the generated magnetic field will essentially extend directly between the poles of the units, which makes the penetration depth small. With an opposite abutment, the magnetic field is to a greater extent driven through the intermediate tool/workpiece.
  • the poles of the modules are made of a material other than electric sheet steel since it may be difficult and costly to arrange poles in electric sheet steel in a suitable pattern and with a suitable cross- section, i.e. without sharp or right-angled corners.
  • the poles are preferably made by compacting a metal powder, preferably of pure iron or an iron alloy containing silicon or nickel, and a binder, such as epoxy or phenolic resin. This method of production is per se known in other fields, see e.g. US-A-2 , 937 , 964. Before compaction, each metal powder particle is preferably coated with a thin surface layer of an insulating material, such as an oxide. Thus the metal powder particles are isolated from each other.
  • the base plate and the poles are made in one piece of this material.
  • the poles can be manufactured separately and then fixed to the base plate by gluing, bolt joints or some other equivalent technique.
  • the base plate can be made of this material, but also other materials are conceivable, for instance electric sheet steel.
  • the base plate can also be composed of a number of separate parts.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • General Induction Heating (AREA)

Abstract

L'invention concerne une unité (2) de chauffage par induction d'une pièce, comprenant une plaque (5) de base en forme de disque. Un pôle (6) au moins est connecté à la plaque (5) de base, et il est disposé de manière à buter contre un côté de la pièce ou d'un outil contenant ladite pièce. En outre, l'unité (2) comprend une bobine disposée autour de chaque pôle (6), conçue pour être connectée à une source de tension afin de générer un champ magnétique dans et autour de ce pole (6) au moins. L'unité (2) est conçue de manière que deux unités identiques juxtaposées soient séparées d'une distance sensiblement constante entre des pôles, à proximité l'un de l'autre, les deux pôles se trouvant entre les unités, et si l'unité comporte plus d'un pôle (6), à l'intérieur de leur unité respective. Un ensemble de chauffage comprend au moins deux unités (2) de ce type, conçues et disposées côte à côte de manière que chaque pole (6) de l'ensemble de chauffage se trouve à une distance sensiblement constante du/des pole(s) (6) voisin(s).
PCT/SE1999/002200 1998-11-26 1999-11-26 Unite de chauffage par induction, et ensemble comportant ladite unite WO2000035250A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU20139/00A AU2013900A (en) 1998-11-26 1999-11-26 Unit for induction heating and assembly having such a unit

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9804058A SE513132C2 (sv) 1998-11-26 1998-11-26 Enhet för induktiv uppvärmning, uppvärmningsaggregat, press, användning av en enhet samt förfarande för styrning av en enhet
SE9804058-7 1998-11-26

Publications (1)

Publication Number Publication Date
WO2000035250A1 true WO2000035250A1 (fr) 2000-06-15

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ID=20413423

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE1999/002200 WO2000035250A1 (fr) 1998-11-26 1999-11-26 Unite de chauffage par induction, et ensemble comportant ladite unite

Country Status (3)

Country Link
AU (1) AU2013900A (fr)
SE (1) SE513132C2 (fr)
WO (1) WO2000035250A1 (fr)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3980858A (en) * 1973-08-22 1976-09-14 Mitsubishi Denki Kabushiki Kaisha Exciter for induction heating apparatus
EP0776146A2 (fr) * 1990-11-30 1997-05-28 Nordson Corporation Séchoir à induction et séparateur magnétique
WO1997026776A1 (fr) * 1996-01-16 1997-07-24 Linlan Induction Ab Dispositif de chauffage d'un outil de presse, presse equipee de ce dispositif et procede de fabrication

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3980858A (en) * 1973-08-22 1976-09-14 Mitsubishi Denki Kabushiki Kaisha Exciter for induction heating apparatus
EP0776146A2 (fr) * 1990-11-30 1997-05-28 Nordson Corporation Séchoir à induction et séparateur magnétique
WO1997026776A1 (fr) * 1996-01-16 1997-07-24 Linlan Induction Ab Dispositif de chauffage d'un outil de presse, presse equipee de ce dispositif et procede de fabrication

Also Published As

Publication number Publication date
AU2013900A (en) 2000-06-26
SE9804058D0 (sv) 1998-11-26
SE9804058L (sv) 2000-05-27
SE513132C2 (sv) 2000-07-10

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