Heating of bearing and the like

Abstract: An induction heater for ring-like articles such as bearings includes a hinged clamp-like magnetically inductive core of ferrite which can be opened to receive and closed to accommodate the article to be heated and which has a primary winding and a source of high frequency current derived from a switch mode power supply; and having temperature sensors and safety circuits adapted to prevent damage due to too high temperatures and to ensure proper operation for articles of differing sizes.

Description: FIELD OF THE INVENTION This invention relates to induction heaters for heating ring-like articles such as bearings and the like 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 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. 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 ring-like articles includes a clamp-like magnetically permeable core having a hinged portion moveable between an open and a closed position, the core permitting mounting of an article to be heated around a portion of the core when the core is in the open position; a winding surrounding the core for energising it, the winding forming the primary of a transformer system with the article forming the secondary of the transformer system; and a power supply connected to the primary winding surrounding the core, the induction heater being characterised in that the power supply is a switched mode high frequency 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 demagnetising the article after it has been inductively heated. In a preferred form the core comprises a ferrite material. One 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 magnetisation takes place and a demagnetisation step is avoided. PRIOR ART STATEMENT British Patent GB-A-1 454 783 discloses induction heating equipment for heating metallic rings such as bearings, the equipment comprising a C-shaped core which constitutes a primary coil with a flat surface of the body portion of the equipment. The flat surface receives a bearing and when current is passed through the body and cores a magnetic flux part is created through the bearing. This induced magnetism must, after the heating and subsequent step, be removed and it is an object of the present invention to provide equipment which avoids the necessity for the removal of magnetism in the bearing, which can be a problem. 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 articles according to the invention; Figure 2 is a diagrammatic, partially cutaway view of a heater for small bearings or ring like articles according to the invention; Figure 3 is a diagrammatic view of a temperature sensor for use in the invention; Figure 4 is a diagrammatic view of the housing of the high frequency supply for use in the invention; and Figure 5 is a block diagram of a switch mode power supply for the heater. Referring to Figures 1 and 2, a primary coil 10 is provided on ferrite cores 12, which are hinged at 14 to enable a bearing or other ring-like article 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 temperature sensitive I.C.'s 18, are mounted on a spring clamp 20; one measures the temperature of the bearing, 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 embodiment of the invention, in an aluminium case 24. The primary coil 10 is connected via socket 26 and the temperature sensors 18 are 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 at 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 a load 50, that is to say a bearing or other ring-like article, 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 i Figure 1. These were wound with 15 turns of 2 x 1mm copper wire. An auxiliary circuit is included to cause the main circuit 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 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 losses in them. Variable temperature settings are obtainable by means of 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 is 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.

Claims: An induction heater for ring-like articles including a clamp-like magnetically permeable core (12) having a hinged portion (14) moveable between an open and a closed position, the core permitting mounting of an article to be heated around a portion of the core when the core is in the open position; a winding (10) surrounding the core for energising it, the winding forming the primary of a transformer system with the article forming the secondary of the transformer system; and a power supply (40) connected to the primary winding (10) surrounding the core, the induction heater being characterised in that the power supply is a switched mode high frequency 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 demagnetising the article after it has been inductively heated. An induction heater according to Claim 1 characterised in that the core comprises a ferrite material. An induction heater according to Claim 1 characterised in that it further comprises a housing (13) formed of heat resistant and non-electrically conductive material, and wherein the housing encloses the core (12) and winding (10). An induction heater according to any of the preceding Claims characterised in that the switched mode power supply (40) includes a phase-locked loop.

Inventors: TYLER GEORGE WILLIAM, TYLER, GEORGE WILLIAM
Applicants: FEENEY CHARLES, FEENEY, CHARLES
Application year: 1990
Main classification: H05B6
IPC codes: H05B6