Electric heating – Inductive heating – Specific heating application
Reexamination Certificate
1999-01-25
2001-05-08
Leung, Philip H. (Department: 3742)
Electric heating
Inductive heating
Specific heating application
C219S633000, C219S665000, C219S650000, C219S672000, C219S518000
Reexamination Certificate
active
06229127
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to portable induction heaters.
2. Description of the Related Art
Plastic and rubber membranes are utilised for providing waterproofing to roofing structures, tunnels and tanks. In the roofing industry, the membranes are laid down upon an insulation layer of either rockwool board, plastic resin foam board or even gypsum board, which is itself laid and fixed to the main substructure, which could be concrete, wood or steel sheet. The membranes are fixed either by glue, directly to the insulation boards, as in
FIG. 10
, or glued to numerous small anchor pads that have been screwed to the substructure through the insulation boards, as in FIG.
11
. The glue is usually a solvent based adhesive, which is toxic and unpleasant to apply and can have unacceptably long curing times in cold climate conditions. Alternatively, the membranes are fixed with screws and suitable washers directly through the edge of each sheet of membrane and into the substructure through the insulation boards. This has the disadvantage that additional steps must be taken to prevent leakage through the membrane at the points where the fastenings extends therethrough in that the next sheet of membrane laid must cover the screws and fixings and then be heat welded to the previous sheet, as in FIG.
12
.
In order to overcome the aforementioned problems a rigid plastic anchor disc, as in
FIG. 13
, is fixed to the substructure through a pad of membrane and on through the insulation boards. The membrane pad is substantially larger than the anchor disc and has received a factory coating of heat activated adhesive mixed with a powdered metallic substance on the upper surface of the pad that is clear of the anchor disc. It is also possible that the metallic powder may be incorporated within the substance of the membrane pad at the time of manufacture. The main covering membrane overlays the anchor and membrane pad.
The powdered metallic substance is heated by an induction heater which glues the membrane pad to the overlaying membrane, thereby entrapping the plastic anchor disc and anchoring the membrane. Alternatively a metallic anchor disc can be used as in FIG.
14
.
UK Patent Application No. 9506694.09 (Robertson) describes the use of an induction heater to perform the bonding operation, however it is impossible to locate the induction coil of the induction heater reliably and accurately over the metallic anchor disc or powder that requires heating (within 1 mm), because it cannot be seen underneath the membrane. Failure to guarantee accurate location causes one part of the anchor disc overheat and burn the adhesive whilst the other half is under heated and not properly bonded. Inaccurate placement could cause over-heating damage to both the adhesive and the membrane, whilst under-heating would not provide sufficient bond strength. Either of these conditions could cause the failure of the roof over an extended time scale but particularly during high wind conditions.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome or alleviate the above described drawbacks and to provide for more accurate placement of the induction heater over the metallic substance to be heated.
In accordance with the present invention there is provided an induction heater for heating a hidden metallic substance, the heater having an induction coil for remotely heating a metallic substance, a sensor for detecting the position of said hidden metallic substance and means to facilitate placement of the induction coil directly over the hidden metallic substance based on information provided from said sensor.
The accurate placement of the induction coil over the hidden metallic substance to be heated reduces the incident of operator error and in the case of anchoring roofing membranes to the main roof structure by the use of fixed underlying metallic discs coated with heat activated adhesive, the accuracy of placement of the induction head bears a direct relationship to the strength of the anchor's bond to the membrane, reducing the incidence of the membrane coming away from the roof in high wind conditions and reducing the amount of time needed to secure the membrane to the roof.
Preferably, the means to facilitate the placement of the induction heater comprises a visual display which indicates the direction the heater must be moved to bring the induction coil over the hidden metallic substance. Preferably, the means to facilitate comprises means to provide an audible signal to indicate the progress of the heat cycle.
Preferably the sensor is adjacent the induction coil and insulating means are provided to reduce the flow of heat from the induction coil to the sensor. This reduces damage to the sensor during operation of the induction coil. The insulating means can be an air gap between the sensor and induction coil and/or coiling means provided to cool the induction coil. In a preferred embodiment the induction coil is in the form of a tube which provides a path for flow of a coolant. Preferably said path extends beyond the induction coil and passes through a heat exchanger.
Preferably the induction heater is portable and has a manually directable induction head containing the sensor and the induction coil, which head is connected to a main control box by a flexible cable.
A micro processor controls all the function of the induction heater as well as the continuous monitoring of operating and fault conditions.
A very stable crystal controlled sine wave generator is used to provide the electromagnetic field for the location sensors. This sensor frequency drive is connected to the main induction coil, (or a separate coaxial auxiliary coil if the physical constraints of the size of the metallic substance do not allow use of the induction coil), at all times, except when the heat cycle is in operation. A relay operated by the micro computer disconnects the sensor frequency drive before heating and reconnects it again after heating.
Preferably, the sensor is s four quadrant metal detection device having in a preferred embodiment four, separate, ferrite cored sensing coils placed at opposite ends of two radial orthogonal centre lines about the vertical axis of the induction coil with their sensing poles on the same plane as the lower face of the induction coil. The sensor coils on radially opposite sides of the induction coil are treated as a pair. There are two configurations of the assembly which are as follows: Where it is required to heat a flat metallic object evenly, over its surface, to it's centre, then the sensing coils would be distributed evenly about the external radius of the induction coil, however, if it is required only to heat an external ring of metallic substance then the sensing coils may either be distributed within the internal radius of the induction coil, providing there is sufficient space, or externally as before.
Preferably a high performance induction grade of ferrite is formed into a protective cover over the top surfaces of the induction coil to provide a low impedance magnetic path to protect the sensing coils from being damaged by excessive induction during the induction heating process and to also provide safety screening for EMC and adjacent personnel.
Preferably each of the sensor coils has capacitors added in order to make it resonate at the sensor frequency which is considerably different to, but not a harmonic of, the induction coil frequency.
During location of the metallic substance, the induction coil itself, or a separate auxiliary coil coaxial with the induction coil, is energised at the sensor frequency by a suitable low power signal source which is disconnected automatically prior to the induction cycle to prevent damage. The resonance of the senor coils allows the voltage pick-up sensitivity to be greatly increased, which allows for the detection of a metallic substance over a greater distance.
The sensor coils are mechanically placed to pick up equal voltages when the metallic substance to
Barlow Josephs & Holmes, Ltd.
Leung Philip H.
Valro Manufacturing Limited
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