NZ236123A

NZ236123A - Induction heater for annular articles has hinged ferrite core and

Info

Publication number: NZ236123A
Application number: NZ236123A
Authority: NZ
Inventors: George William Tyler
Original assignee: Feeney Charles
Priority date: 1989-12-18
Filing date: 1990-11-19
Publication date: 1994-02-25
Also published as: NO905463D0; AU622056B2; CA2029600A1; NO178520B; AR247324A1; ATE111292T1; NO905463L; EP0434204B1; PT96225A; BR9006377A; JPH03194881A; PT96225B; DE69012298D1; CA2029600C; EP0434204A1; TW215140B; KR0171051B1; NO178520C; KR910013978A; DE69012298T2

Description

<div class="application article clearfix" id="description"> Patform.#5 Priority Cate(&): . Complete Specification Filad: ft*? Class: tt.Q5Cte.0p. ;Publication Dote: !???. P.O. Journal, No: '.TJ ;NEW ZEALAND PATENT OFFICE t ;I ;19N0VI9W ! ;L ;RECEIVED ;NEW ZEALAND PATENTS ACT 1953 ;COMPLETE SPECIFICATION ;HEATING OF BEARINGS AND THE LIKE ;I, CHARLES FEENEY, a British subject of Buhlem Farm, Ezulwini, Swaziland do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: ;- 1 - ;4656comp/jw ;23 ;FIELD OF THE INVENTION ;This invention relates to the heating of bearings and other ring-like articles which are required to be located over shafts, pipes and the like. ;BACKGROUND ;Induction heating is well known in the art and has conventionally been achieved by means of apparatus which constitutes a primary winding of a transformer with the bearing ring forming the secondary winding. This is accomplished by providing a horseshoe construction for the primary winding and having a connecting piece to complete the circuit, the connecting piece being adapted to receive the bearing in inductive contact. ;Many types of induction heaters are presently in use. Their use, however, is limited by several disadvantages derived from the fact that induction heating presently involves passing a high-power current, often of several kilowatts, through an inducting coil to effect high heat in the conducting metal; and the primary winding is generally of normal supply frequency and is generally of substantial size which makes it difficult to transport. Another disadvantage associated with prior art arrangements is that the bearing requires to be demagnetised during or after the heating operation. ;-2- ;aw ;It is an object of the present invention to obviate some of the disadvantages of the prior art and to provide apparatus which is easily portable and which does not magnetise a bearing or ring unduly. ;THE INVENTION ;According to the invention, an induction heater for a ringlike article comprises: ;a magnetically permeable core of a ferrite material having a hinged portion movable between an open and closed position, the core permitting the mounting of the ring-like article around a portion of the core when the core is in its open position; ;a winding surrounding the core for energizing it, the winding forming the primary of a transformer system with the article forming the secondary of the transformer system; ;a switched mode high frequency power supply connected to the primary winding, the switched mode power supply operating at a sufficiently high frequency so that low magnetic flux density is produced in the core and the article to avoid the need for demagnetizing the article after it has been inductively heated; ;frequency control means to detect the power factor in the primary coil during use and so to control the supply frequency depending on the detected load so that the core and article are in resonance; and temperature sensing and switching means., -t-o sense the temperature of the inductively heated artgk&3=& and to ;/* /'V l-\ Q "7 R 1 ^ J £ o v> i ^ immediately terminate the current supply to the primary winding when the sensed temperature reaches a predetermined value. In a preferred form of the invention the core is of ferrite. The important advantage of the present invention is that due to the novel use of high frequency which may be generated by a compact high frequency generator, it can be made as a very small unit which is easily transportable. The high frequency current used, which involves low flux density in the core and bearing and in which the oscillations die gradually due to the resonant mode of operation, means that little or no magnetization takes place and a demagnetization step is avoided. t f 13 OCT 199351 -3a- ■ 093UV 236 1 PRIOR ART STATEMENT An EPO search revealed the following prior patents: GB-A-1454783 EP-A-027306 US-A-4311896 US-A-3895295 US-A-3187155 EP—A-143091 none of which describe the present invention and rather tend to accentuate the inventive step since none of the prior art mentions the use of high frequency to obviate magnetisation. EMBODIMENT OF THE INVENTION An embodiment of the invention is described below with reference to the accompanying drawings, wherein; Figure 1 is a diagrammatic, partially cutaway view of a heater for large bearings or ring-like forms according to the invention; Figure 2 is a diagrammatic, partially cutaway view of a heater for small bearings or ring like forms according to the invention; Figure 3 is a diagrammatic view of a temperature sensor for use in the invention; -4- 236123 Figure 4 is a diagrammatic view of the housing of the high frequency supply for use in the invention; Figure 5 is a block diagram of a switch mode power supply for the heater. Referring to Figure 1 and 2, a primary coil 10 is provided on the ferrite cores 12, which are hinged at 14 to enable the bearing or ring-like form to be fitted over either point A or point B. The primary coil 10 is associated with a switch mode power supply 40, and is connected to this by means of connector 16. A diagrammatic view of the housing for the switch mode power supply 40, is shown in Figure 4 and a block diagram of the circuit is shown in Figure 5. The ferrite cores 12 are enclosed in a heat resistant and non-electrically conductive housing 13. Referring to Figure 3, two temperatures sensitive I.C.'s 18, are mounted on a spring clamp 20; one measures the temperature of the bearing or ring-like form, the other measures the ambient or reference temperature. The two I.C.'s 18 are associated with the switch mode power supply 40 and are connected to it by means of connector 22. Referring to Figure 4, the switch mode power supply 40, is housed, in this form of the invention, in a aluminium case 24. The primary coil 10 is connected via socket 26 and the temperature sensors 18 are -5- connected via socket 28. The mains supply is connected through switch 30 and fuse 32. Temperature control of the sensors 18 is effected by means of a potentiometer 34^ The switch mode power supply 40 is activated by push button 36 and an indication of the active state is made by the LED 38. Referring to Figure 5, the mains current to the circuit of the switched mode power supply 40, is rectified 42 and smoothed using electrolytic capacitors 44 to produce a smooth DC current. This supply is then used to power a self-oscillating inverter circuit 46, the exact frequency of which is regulated by a control circuit 48, (the inclusion of such a circuit will be obvious to those skilled in the art), the resulting high voltage and high frequency current is then supplied to the primary coil 10, which then heats up any bearing or ring-like form 50, which is in inductive contact. In one example of the invention, a ferrite core was selected which was suitable for use at frequencies of 20KHZ. Type Philips A320 KP 9012 was used of size 94mm in length, 27mm in width and 16mm in thickness and several were assembled together to form the heater as shown in Figure 1. These were wound with 15 turns of 2 x 1mm copper wire. An auxiliary circuit is included to cause the main circuit 40 to run at a frequency that produces a power factor of 1 in the primary coil 10. This is to ensure that maximum power is always delivered to the load 50. (Under variable load conditions the power factor could -6- 236 1 change causing reduced power in the bearing or ring). This circuit also has the function of causing the transistors to switch at zero current, thus reducing the losses in them. Variable temperature settings are obtainable with the control 34 and at the set temperature point automatic switch off of the switch mode power supply 40 is effected together with an audible buzzer. Measurement of the temperature rise can be shown using a liquid crystal display. If, while setting up a workpiece to be heated, the circuit across the temperature sensor is incomplete or the temperature sensor was not fitted to the workpiece, a safety circuit will disable the switch mode power supply thereby inhibiting activation of said supply. The invention allows high inductive heating with low power input. The above embodiment herein discussed is not meant to limit the scope of the invention and its underlying theory. Other embodiments will be obvious to those skilled in the art. </div>

Claims

<div class="application article clearfix printTableText" id="claims"> -8- *,23;WHAT I CLAIM IS:;1. An induction heater for a ring-like article comprising:;a magnetically permeable core of a ferrite material having a hinged portion movable between an open and closed position, the core permitting the mounting of the ring-like article around a portion of the core when the core is in its open position;;a winding surrounding the core for energizing it, the winding forming the primary of a transformer system with the article forming the secondary of the transformer system;;a switched mode high frequency power supply connected to the primary winding, the switched mode power supply operating at a sufficiently high frequency so that low magnetic flux density is produced in the core and the article to avoid the need for demagnetizing the article after it has been inductively heated;;frequency control means to detect the power factor in the primary coil during use and so to control the supply frequency depending on the detected load so that the core and article are in resonance; and temperature sensing and switching means to sense the temperature of the inductively heated article and to immediately terminate the current supply to the primary winding when the sensed temperatru-r-e- reaches a predetermined value. .;c"';I "v;, i J* ^ ; \\ 13 OCT 1993. -9-
2. The induction heating means according to claim 1 in which the switched mode power supply comprises a transistor switching circuit.
3. An induction heating means substantially as described with reference to the Attorneys for the Applicant CHARLES FEENEY n r o>, A\ Wi oy« )»!' IIn j9 fi .. «DMUv </div>