Patent Application
20110220638
1. Field of the Invention
The present invention relates to a heater, and in particular to a finned ceramic heater.
2. Description of Prior Art
When a positive temperature coefficient (PTC) ceramic is supplied with electricity, its resistance will increase rapidly with the temperature in a certain range of temperature, so that the PTC ceramics can be widely used in thermostat heaters, household appliances, automobile heating and protection lines or the like. The PTC ceramics are made by adding rare earth elements into barium carbonate or titanium dioxide and sintering the above mixture at high temperature. The resistance of the PTC ceramic can be maintained low in a wide range of temperature. When the temperature of the PTC ceramic exceeds the Curie temperature, the resistance of the PTC ceramic will increase to a larger extent rapidly.
A conventional heater has a positive temperature coefficient (PTC) ceramic resistor, both surfaces of which are adhered with an electrical-conductive metallic piece. The electrical-conductive metallic piece has an electrical-conductive terminal electrically connected to an external power source thus to obtain electricity. The electric current flows through the two electrical-conductive metallic pieces and the PTC ceramic resistor, so that the PTC ceramic resistor will generate heat. The amount of heat generated equals to the product of the electric current and the square of the resistance of the PTC ceramic resistor. Since the contact area between a thermal-conducting area and the outside is not large enough, the amount of heat that can be dissipated is insufficient. Thus, one side of the electrical-conductive metallic piece is provided with fins for conducting the heat generated by the PTC ceramic resistor and for electrically insulating from the outside for better safety. An insulating plate is sandwiched between the fins and the electrical-conductive metallic piece for obstructing an electric current of the electrical-conductive metallic piece from flowing to the fins. However, since the flatness of the fins, the electrical-conductive metallic piece, and the insulating plate are different, the stress on the insulating plate may be distributed unevenly, which makes the insulating plate to generate cracks so as to reduce the insulating property of the insulating plate.
In view of the above problems, the present inventor proposes a reasonable and novel structure based on his expert experience and delicate researches.
The present invention is to provide a finned ceramic heater, which is capable of enhancing the insulating property of the heater.
The present invention is to provide a finned ceramic heater, which includes a ceramic heating assembly, a pair of electrode plates, a plurality of insulating plates, an insulating adhesive, and a pair of fins. The pair of electrode plates is adhered to both side surfaces of the ceramic heating assembly respectively. The insulating pieces are connected in series and adhered to outer surfaces of the pair of electrode plates. A seam is formed between two adjacent insulating pieces. The width of the insulating piece is larger than that of the electrode plate. The insulating adhesive is filled in the seam. The pair of fins is disposed on the insulating pieces and the insulating adhesive.
The present invention has advantageous features as follows. The insulating pieces are connected in series and sandwiched tightly between the electrode plates and the fins, thereby generating a larger tolerance in the thickness of the insulating pieces and preventing the insulating pieces from cracking due to their inconsistent flatness.
The characteristics and technical contents of the present invention will be described with reference to the accompanying drawings. However, the drawings are illustrative only, but not used to limit the present invention.
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The ceramic heating assembly 100 comprises a plurality of PTC ceramic heating pieces 110 connected in series. The top surface and the bottom surface of each PTC ceramic heating piece 110 are coated with an electrode layer 120. The electrode layer 120 is made of electrical-conductive materials such as aluminum (but not limited thereto). Since the resistance of the PTC ceramic heating piece 110 is very large, an electric current cannot flow through the PTC ceramic heating piece 110. The electrode layer 120 can slightly reduce the resistance of the PTC ceramic heating piece 110 to allow the electric current to flow there through. In this way, the PTC ceramic heating piece 110 can generate heat. An insulating gel 130 is filled between two adjacent PTC ceramic heating pieces 110 for obstructing the electrode layers 120 respectively coated on the top surface and the bottom surface of each PTC ceramic heating piece 110 from generating an electric-arc short circuit. In case of a short circuit, the PTC ceramic heating piece 110 cannot generate heat. The ceramic heating assembly 100 further comprises an insulating block 140 adhered to the distal end of the outmost PTC ceramic heating piece 110, or sandwiched between two adjacent PTC ceramic heating pieces 110 (not exclusively) for enhancing the electrical insulation. The insulating block 140 is made of insulating materials such as aluminum oxide, silicon nitride, aluminum nitride or the like (but not limited thereto). The comparative tracking index (CTI) of the insulating block 140 is not less than 600. The CTI is used to measure the electrical breakdown (tracking) properties of an insulating material, and its value is equal to the voltage caused by the leakage of electricity.
The pair of electrode plates 200 is adhered to the top surface and the bottom surface of the ceramic heating assembly 100 respectively. That is, the PTC ceramic heating pieces 110 are sandwiched between the pair of electrode plates 200. The electrode plate 200 is made of electrical-conductive materials such as aluminum (but not limited thereto). The pair of electrode plates 200 is electrically connected to the electrode layers 120 respectively, so that the electric current can flow through the electrode plate 200 and the PTC ceramic heating pieces 110 more easily. Further, since the electrode layer 120 and the electrode plate 200 are made of the same electrical-conductive material such as aluminum. Displacement of atoms or migration of electrons may not happen between the electrode layer 120 and the electrode plate 200. The pair of electrode plates 200 has an electrical-conductive terminal 210 respectively. The pair of electrical-conductive terminals 210 is electrically connected to a positive pole and a negative pole of an external power source respectively. The electrical-conductive terminals 210 extend in opposite directions, so that the pair of the electrical-conductive terminals 210 can be prevented from getting too close to generate a short circuit when the terminals are electrically connected to the external power source. Since the ceramic heating assembly 100 has a plurality of PTC ceramic heating pieces 110 connected in series and tightly sandwiched between the pair of electrode plates 200, such an arrangement can generate a larger tolerance in the thickness of the PTC ceramic heating pieces 110, so that the PTC ceramic heating pieces 110 may not crack due to inconsistent flatness.
The insulating pieces 300 are connected in series and adhered to outer surfaces of the pair of electrode plates 200. The width of each insulating piece 300 is larger than that of the electrode plate 200 (
The insulating adhesive 400 is filled in the seam 310, thereby tightly binding two adjacent insulating pieces 300 and enhancing the insulating property among the insulating pieces 300 after combination. Further, when the heater is in operation, the insulating pieces 300 will expand when it's hot and contract when it's cold. Since the insulating pieces 300 are tightly bound to each other by the insulating adhesive 400, the deformation caused by the thermal expansion or contraction can be reduced.
The pair of fins 500 is disposed on the outer surfaces of the insulating pieces 300 and the insulating adhesive 400. That is, the fins 500 and the electrode plates 200 sandwich the insulating pieces 300 and the insulating adhesive 400. Further, the width of the insulating piece 300 is larger than the width of the fins 500 (
In use, the electric current enters the heater from one of the electrical-conductive terminals 210, and then sequentially flows through the electrode plate 200 and the electrode layer 120 on the same side, the PTC ceramic heating pieces 110, the electrode layer 120 and the electrode plate 200 on the other side, and finally exits the heater through the other electrical-conductive terminal 210. Since the electric current flows through the PTC ceramic heating pieces 110, the amount of heat generated by the PTC ceramic heating pieces 110 equals to the product of the electrical current and the square of the resistance of the PTC ceramic heating pieces 110. The heat generated by the PTC ceramic heating pieces 110 is conducted through the electrode layers 120, the electrode plates 200, the insulating pieces 300, and the fins 500 on both sides. Finally, the heat is conducted to the outside by means of the high thermal conductivity of the fins 500.
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On the other hand, in order to enhance the insulating property and the structural strength of the heater, as shown in
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Although the present invention has been described with reference to the foregoing preferred embodiments, it will be understood that the invention is not limited to the details thereof. Various equivalent variations and modifications can still occur to those skilled in this art in view of the teachings of the present invention. Thus, all such variations and equivalent modifications are also embraced within the scope of the invention as defined in the appended claims.
