EP1006757A2 - Système magnétique de chauffage - Google Patents

Système magnétique de chauffage Download PDF

Info

Publication number: EP1006757A2
Authority: EP; European Patent Office
Prior art keywords: heating system; magnetic heating; coil; power supply; temperature
Prior art date: 1998-12-01
Legal status (The legal status 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 status listed.): Granted

Application number

EP99309647A

Other languages

German (de)

English (en)

Other versions

EP1006757B1 (fr

EP1006757A3 (fr

Inventor

Philip Anthony Browning

Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)

Mitsubishi International GmbH

Original Assignee

Mitsubishi International GmbH

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.)

1998-12-01

Filing date

1999-12-01

Publication date

2000-06-07

1999-12-01 Application filed by Mitsubishi International GmbH filed Critical Mitsubishi International GmbH

2000-06-07 Publication of EP1006757A2 publication Critical patent/EP1006757A2/fr

2001-11-21 Publication of EP1006757A3 publication Critical patent/EP1006757A3/fr

2004-02-04 Application granted granted Critical

2004-02-04 Publication of EP1006757B1 publication Critical patent/EP1006757B1/fr

2019-12-01 Anticipated expiration legal-status Critical

Status Expired - Lifetime legal-status Critical Current

Links

Images

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
- H05B6/06—Control, e.g. of temperature, of power
- 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
- H05B6/04—Sources of current

Definitions

This invention relates to a magnetic heating system, for example for use in heat treatment of metal components.
a difficulty with conventional systems is in achieving a sufficiently accurate control of heating.
the plastic temperature of aluminium being close to the melting point, a relatively small variation in the power applied can result in molten aluminium flowing out of the heating device rather than a billet ready for working.
a magnetic heating system comprising a core of a magnetic material having a coil wound around at least a part thereof, and a power supply connected to the coil for supplying a low frequency alternating current thereto, wherein the power supply comprises means for varying the frequency of the alternating current in the coil.
the means for varying the frequency comprises an inverter, being a device supplied with an alternating current supply at a first frequency and arranged to output a selectively variable frequency current.
Means may also be provided in the power supply for regulating the voltage applied to the coil as well as the frequency.
While single phase power supplies may be used for relatively low power applications, it is desirable to use three-phase supplies for higher power requirements.
a transformer connected to the three-phase supply to provide a single-phase output to the coil.
the use of a transformer may be dispensed with if an inverter is used, with two of the output phases from the three-phase inverter being connected to the coil. No connection is then made to the third phase.
two separate heating coils, on opposed pole pieces forming part of a C-shaped core are used, the coils being connected in parallel or in series.
the or each coil used in the heating system of the invention is preferably wound so as to provide a single layer winding, as this has been found to be of greater heating efficiency than multi-layer windings.
the system comprises means for measuring the temperature of the article being heated and for signalling the temperature to control means for the power supply, the control means being programmed to control the frequency and the voltage applied to the coil or coils in accordance with the temperature signalled thereto. It has been found convenient to effect coarse control of the temperature by varying the voltage applied to the coils, and fine control by varying the frequency. It will be appreciated that increasing the frequency increases the reactance of the coils, thereby reducing the current in them.
the system employs an inverter 1 having a three-phase alternating current input (L1, L2, L3) at the standard mains supply frequency (50 or 60 Hz) and providing a three phase output of selectively variable frequency and voltage.
an inverter is the Hitachi J300 type, available in a range of power ratings. Inverters of this type will typically be provided with interface means permitting control by an external device of the voltage and/or frequency of the supply to the external load, and providing for monitoring of the current applied. Conventionally, such inverters are used in the control of electric motors.
two coils 2 and 3 connected in parallel are driven by two phases from the inverter. This is done by omitting the connection to the centre phase.
the coils may alternatively be connected in series, or a single coil could be connected in place of the two coils.
the inverter monitors its output current only on the two outer phases, using Hall effect transducers. The omission of any load on the centre phase of the inverter is therefore irrelevant to the inverter control circuit. It will be appreciated that the invention is also applicable to arrangements in which all three phases output by the inverter are employed, supplied to three different coils, or pairs of coils, causing heating through three separate cores, for example in the manner set out in our published International Patent Application WO98/52385.
FIG. 2 shows diagrammatically a practical application of this arrangement.
the inverter 1 is connected to the two coils 2 and 3, which are wound on the same C-shaped core 4, on opposed pole pieces 5 and 6, the upper pole piece 5 being slidable vertically relative to the lower pole piece 6 so as to accommodate different sizes of article 7 to be heated.
thermocouple 8 is attached to the article 7 to monitor its temperature.
the thermocouple 8 connected to a controller 9 operatively linked to the inverter 1 so as to be able to vary the voltage and frequency of the supply to the coils 2 and 3 to control the power supplied to the coils and therefore the heating effect achieved.
the controller may be any programmable device, for example a programmable logic controller (PLC) or a computer.
PLC programmable logic controller
the controller 9 also monitors the current supplied to the coils.
the controller 9 may be linked to the inverter by any suitable means, for example by way of RS-485 standard interface.
the controller can also serve to control other functions of the heating device, for example the pneumatic controls moving the slidable arm of the core and controlling the positioning of the workpiece.
the power may be controlled to heat the article to the desired temperature with sufficient precision to ensure that, for example in the case of an aluminium billet, the plastic temperature is maintained without risk of melting.
thermocouple may be employed to monitor the temperature of the article 7 than applying a thermocouple to the article.
the heat radiated by the article may be detected remotely by an infra-red detector.
Figure 3 illustrates the programming of the controller 9.
heating is carried out rapidly with an optimum coil current, which may be a maximum current available.
the temperature of the article is detected and compared with an offset temperature which is a predetermined amount below the desired temperature, for example 5 to 10°C below.
the offset temperature is reached, the voltage gain on the inverter is reduced to a predetermined lower level and the temperature continues to be monitored. If the desired temperature, the set point, is not reached, the voltage gain is increased by a small increment and the temperature again measured. This is repeated until the set point is reached, as a result of which the voltage gain is reduced to a low level, below the predetermined lower level hereinbefore mentioned. After a delay, the effect on the temperature is again checked.
the frequency of the supply to the coils is increased by a predetermined amount, and the temperature checked after the delay. This is repeated until the temperature begins to decrease. If the temperature drops below the set point, the voltage gain is then increased, and the effect monitored as described hereinbefore. If the temperature does not drop below the set point, the temperature continues to be monitored without the need for corrective action. In this way, the temperature of the article being heated can be controlled very precisely.

Landscapes

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

EP99309647A 1998-12-01 1999-12-01 Système magnétique de chauffage Expired - Lifetime EP1006757B1 (fr)

Applications Claiming Priority (2)

Application Number	Priority Date	Filing Date	Title
GBGB9826232.2A GB9826232D0 (en)	1998-12-01	1998-12-01	Magnetic heating system
GB9826232		1998-12-01

Publications (3)

Publication Number	Publication Date
EP1006757A2 true EP1006757A2 (fr)	2000-06-07
EP1006757A3 EP1006757A3 (fr)	2001-11-21
EP1006757B1 EP1006757B1 (fr)	2004-02-04

Family

ID=10843329

Family Applications (1)

Application Number	Title	Priority Date	Filing Date
EP99309647A Expired - Lifetime EP1006757B1 (fr)	1998-12-01	1999-12-01	Système magnétique de chauffage

Country Status (4)

Country	Link
EP (1)	EP1006757B1 (fr)
AT (1)	ATE259137T1 (fr)
DE (1)	DE69914573T2 (fr)
GB (1)	GB9826232D0 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number	Priority date	Publication date	Assignee	Title
US6717118B2 (en)	2001-06-26	2004-04-06	Husky Injection Molding Systems, Ltd	Apparatus for inductive and resistive heating of an object
US6781100B2 (en)	2001-06-26	2004-08-24	Husky Injection Molding Systems, Ltd.	Method for inductive and resistive heating of an object

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number	Priority date	Publication date	Assignee	Title
US3816690A (en) *	1972-09-18	1974-06-11	Illinois Tool Works	Induction heating apparatus
US5272720A (en) *	1990-01-31	1993-12-21	Inductotherm Corp.	Induction heating apparatus and method
JPH05299161A (ja) *	1992-04-24	1993-11-12	Fuji Electric Co Ltd	誘導炉給電方法
JP3398172B2 (ja) *	1993-04-09	2003-04-21	電気興業株式会社	高周波誘導加熱における加熱温度制御方法及び高周波誘導加熱温度制御装置

1998
- 1998-12-01 GB GBGB9826232.2A patent/GB9826232D0/en not_active Ceased
1999
- 1999-12-01 DE DE69914573T patent/DE69914573T2/de not_active Expired - Lifetime
- 1999-12-01 EP EP99309647A patent/EP1006757B1/fr not_active Expired - Lifetime
- 1999-12-01 AT AT99309647T patent/ATE259137T1/de not_active IP Right Cessation

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number	Priority date	Publication date	Assignee	Title
US6717118B2 (en)	2001-06-26	2004-04-06	Husky Injection Molding Systems, Ltd	Apparatus for inductive and resistive heating of an object
US6781100B2 (en)	2001-06-26	2004-08-24	Husky Injection Molding Systems, Ltd.	Method for inductive and resistive heating of an object
US7041944B2 (en)	2001-06-26	2006-05-09	Husky Injection Molding Systems, Ltd.	Apparatus for inductive and resistive heating of an object

Also Published As

Publication number	Publication date
EP1006757B1 (fr)	2004-02-04
DE69914573T2 (de)	2004-12-16
EP1006757A3 (fr)	2001-11-21
ATE259137T1 (de)	2004-02-15
GB9826232D0 (en)	1999-01-20
DE69914573D1 (de)	2004-03-11

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