Note: Descriptions are shown in the official language in which they were submitted.
FIELD OF THE INVENTION 2 0 2 9 6 0 0
This invention relates to the induction heating of bearings and other
ring-like articles which are required to be located over shafts, pipes
and the like.
BACKGROUND OF THE INVENTION
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 demagnetized during or after the heating operation.
~ ' .
2029600
-
In an example of the prior art, U.S. Patent No. 2,836,694 (Emerson)
discloses an induction heating method by saturating a magnetic
workpiece with maximum magnetic flux density to effect the heating
process. The DC power source is used so as not to overload the RF
generator at temperatures below the Curie point of the workpiece. The
present invention seeks to utilize low flux density and is concerned
with conductive workpieces. Whereas Emerson relies on magnetization
of the workpiece, the present invention seeks to minimize or eliminate
the magnetization of the workpiece.
In another example of the prior art U.S. Patent No. 3 187 155
(Beckert) recognizes the necessity for a separate demagnetization step
but he achieves this with a bulky and expensive arrangement of a motor
and variable voltage transformer to remove the magnetism created by
the application of a low frequency (60 Hz) current in the initial
heating step. By a careful choice of parameters the present invention
achieves the heating step without having to resort to an additional
demagnetizing step which is not only expensive and time consuming but
also involves the use of bulky non-portable equipment.
U.S. Patent No. 4 311 896 (Junya) uses a 60Hz current to excite a coil
2 surrounding core 4 by a connection 10. Junya also fails to
recognize the advantages of the present invention which uses certain
parameters and items such as a switched mode power supply at high
frequency in a controlled manner.
~ "
2029600
Japanese patent 53-43646 uses eddy currents to heat objects in order
to weld them together; whereas the present invention uses the
workpiece as a secondary to produce circulatory currents in the
workpiece. The Toyota invention is not applicable to the heating of
bearings - in fact, if it was used to heat bearings, the heating
effect would only be obtained in the zone including the gap with the
result,that a bearing would merely be welded together in such a zone.
It is an object of the present invention to heat a bearing so that it
can be fitted to a shaft - it does not seek to weld a few bearing
balls to the bearing bed.
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 magnetize a bearing or ring unduly,
thereby avoiding the necessity for providing a demagnetization step
and apparatus therefor. It will be appreciated that a bearing must
remain free of magnetism to prevent attraction of metallic particles
which could cause considerable damage.
THE INVENTION
According to the invention an induction heater for a ring-like article
comprises
a clamp-like magnetically permeable core, of a ferrite
material having hinged portion movable between an open and closed
position, the core permitting the mounting of the ring-like article
.. .. .
.~ ' ~ .
2029600
around a portion of the core when the core is in its open position;
a winding surrounding the core for energizing it, the wlnding
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
produçed in the core and the article to avoid the need for
demagnetizing the article after it has been inductively heated;
phase locked loop frequency control means to detect the current
load imposed by the article and so to control the supply frequency
depending on the detected load so that the core and article are in
resonance; and
temperature sensing means 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
temperature reaches a predetermined value.
The important advantage of the present invention is that due to the
use of high frequency by means of a switched mode power supply, a low
magnetic flux is produced which effectively prevents the article
becoming magnetized, and this is guaranteed by means of the control
means which ensures that the core and the supply frequency are in
resonance.
, .
The result of the control of frequency results in the oscillations in
the article and the clamp dying away. The selection of the integers
~,. ~ "
~ ,~
202g6ao
of the apparatus of the invention allows a very small and compact
unit to be produced which is easily transportable.
One of the advantages of operating at a resonant frequency is that a
reduction in EMI (Electromagnetic Mechanical Interference) and RFI
(Radio Frequency Interference) is released. The reason being that the
output power transistors switching transitions occur near or at zero
voltage or current.
EMBODIMENT OF T~E 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;
Figure 4 is a diagrammatic viéw 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.
~ .
-- 5
A ~ ~
2029600
Referring to Figures 1 and 2, a primary coil 10 is provided on theferrite cores 12, which are hinged at 14 -to enable the bearing or
ring-like form to be fitted over either point A or point . 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, aremounted 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, inthis form of the invention, in a aluminium case 24. The primary~coil
is connected via socket 26 and the temperature sensors 18 are
connected via socket 28. The mains supply is connected through switch
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.
20 29 600
Referring to Figure 5, a domestic mains supply 40 is first filtered at41 and then rectified to direct current by rectifier 42.
Capacitors 43 serve to smooth the current. When the current is first
switched on and the push button switch 36 pressed, the line from the
on/off control 45 goes HIGH, thereby closing the circuit across the
bearing 46 between the contact 47 and the metal housing of the
temperature sensor 48. The temperature being sensed is set at a value
belowtthat required by the potentiometer 34.
Once the line is HIGH, the signals from the frequency control unit 49can pass through the AND gate 50. As can be seen from the diagram, Ql
and Q4 are turned on simultaneously, at that same time Q2 and Q3 are
turned off. Thus when Q2 and Q3 are on, Ql and Q4 are off. Therefore
nodes A and B are alternately switched between the 320V and O V at a
frequency which is around 20KHz, the frequency is very quickly
adjusted by means of a phase locked loop system inside the frequency
control unit 49 using information fed back from the current sensor
52. Since the inductance of the primary coil 53 will vary according
to the size of the bearing 46 the frequency is adjusted so that the
inductive load and output capacitor 54 are in resonance.
Once the predetermined temperature is sensed or if the contact acrossthe bearing is removed the enable line goes LOW thus instantly
terminating the output to the clamp. Once this has happened the
machine defaults to a standby state and further bearings can be heated
subject to the conditions above.
-
2029600
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
F~gure 1. These were wound with 166 turns of 2 x lmm copper wire.
A phase locked loop system is included to cause the main current to
run at a frequency that produces a power factor of 1 in the primary
coil 53. This is to ensure that maximum power is always delivered to
the load 46. (Under variable load conditions the power factor could
change causing reduced power in the baring 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 51 at
the set temperature point and automatic switch off of the switched
mode power supply 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 workp~ece, a safety circuit will disable the switched
mode power supply thereby inhibiting activation of said supply.
2029600
The invention allows high inductive heating with lower 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.
.~ ,
