Title of Invention

DOUBLE INSULATION SAFE ELECTRICAL WATER HEATER

Abstract

This invention is about a double insulation safe electrical water heater with high efficiency and it belongs to the technical field of household electrical appliances. This electrical water heater consists of the water container in the housing, the curved electrical heating tube in the container, and the control circuit connected with the electrical heating tube; the said electrical heating tube is inserted in the heat conducting insulated sheath with its internal profile basically matching with the outer profile of the electrical heating tube, the said heat conducting insulated sheath is inserted tightly via a metal end cap into the metal support tube with its internal profile matching the outer profile of the heat conducting insulated sheath, the end of the said metal support tube is sealed and welded with the end surface of the metal end cap, and the outer thread of the said end cap is engaged and sealed with the inner thread of the fitting hole on the container. Compared with existing technologies, this invention requires no change to the existing structure of the water heater including the container and features economic cost. It can not only form a double insulation on the exterior of the electrical heating tube, but also a double insulation at the its joint with the container, thereby avoiding a weak link in current leakage prevention.

Full Text

Description Double Insulation Safe Electrical Water Heater Field of invention This invention is about an electrical water heater, especially an electrical water heater with improved insulation structure to ensure safely. It belongs to the technical field of household electrical appliances. Background of Invention Electrical water heaters have become quite popular nowadays as they are convenient in use and have substantially improved the quality of life. A current electrical water heater consists mainly of the control circuit on the housing, the water container in the housing and the electrical heating element inside the container. To facilitate installation and lower the power density of the appliance itself, U-shaped electrical heaters are used mostly for electrical water heaters. To prevent current leakage and ensure safety in use, in addition to such provisions as housing grounding and current-proof diverting pipes, designers have concentrated on different safety provisions of double insulation against the source of current leakage — the electrical heating. However, after in-depth and careful studies, the applicant has discovered some shortcomings in the double insulation structure of current electrical heaters. For example, the Patent No. CN94218994.9 for utility model published a structure with packing between the heating element and housing as additional insulating heat-transfer medium, so that the heater has the double insulation function. Its main shortcoming is loose structure and it takes a large space in the container, moreover, diameter reduction is impossible from the technical point of view, therefore, it is quite difficult to ensure a compact packing. But if air is entrapped in the packing material, pipe wall rupture would likely to occur during use. In the electrical heater with double insulation published in Patent No. CN97224405.0, a continuous and homogenous inorganic glue film is applied on the outer surface of the ordinary metal electrical heating tube, which is then sealed in the metal sheath without gap, to form a double leakage current protection between the living parts and the outer metal sheath. This patent has overcome the shortcoming of the former, but obviously it can only be used for straight tubes and can hardly be realized with a U-shaped electrical heating tube. Furthermore, as the thermal expansion coefficient of inorganic glue film differs grally from that of the metal tube, cracks will likely to occur after use, leading to loss of insulation. The double insulation structures published in China Patent Nos. CN99234598.7 and CN99234808.0 both consist of a metal tube and a glass tube coated with an electrical heating film. They features complicated techniques and can also be hardly realized on curved tubes such as U-shaped electrical heating tubes. Experiments have shown that, due to different shortcomings of their own, the current electrical heating elements with double insulation structure as mentioned above cannot properly meet the standard GB 4706.1 "Safety for electrical appliances for household and similar use" that will soon be published for implementation, especially they cannot be realized on curved electrical heating elements, to keep good heating performance while satisfying the enhanced insulation requirements. In addition, in the above improvements, no substantial improvement has been proposed for the connection between the electrical heating elements and the container, therefore, a weak link of current leakage still exists even if a double insulation structure is adopted. Content of Invention The primary objective of this invention is, with respect to the shortcomings with existing technologies, to propose a double insulation safe Electrical water heater that is suitable for use with curved electrical heating tubes, keeping a good heat conducting performance while enhancing the insulation and is also in compact structure, therefore it can effectively ensure that the safety performance of the electrical water heater satisfies the relevant requirements in the national standard with limited increase of cost. A further objective of this invention is to propose a double insulation safe Electrical water heater with reasonable connection between the electrical heating elements and the container, thereby further ensuring the safety performance of the electrical water heater. To achieve the primary objective as mentioned above, the double insulation safe Electrical water heater of this invention consists of the water container in the housing, the curved electrical heating tube in the container, and the control circuit connected with the electrical heating tube; the said electrical heating tube is inserted in the heat conducting insulated sheath with its internal profile basically matching with the outer profile of the electrical heating tube, and the said heat conducting insulated sheath is made of densely sintered heat conducting insHation ceramic material. The above-mentioned heat conducting insulation ceramic material is one of the alumina, aluminum nitride, silicon nitride, morion, magnesia, silicon carbide, expansion-free ceramics (2LiO+2AL2O3+5SiO2) and similar materials. This sheath structure is quite suitable for U-shaped and other curved electrical heating tubes commonly used in electrical water heaters, and it is in quite compact structure, in about the same volume as the original electrical heating tube with single layer of insulation. The densely sintered heat conducting insulation ceramic material would not be wet by water, so the electrical water heater not only keeps a good heating performance, but also has double guarantee in insulation performance, able to meet the requirements in the national standard. To achieve the further objective of this invention, the said heat conducting insulated sheath is inserted tightly via a metal end cap into the metal support tube with its internal profile matching with the outer profile of the heat conducting insulated sheath, the end of the said metal support tube is sealed and welded with the end surface of the metal end cap, and the outer thread of the said end cap is engaged and sealed with the inner thread of the fitting hole on the container. For fitting, the end cap is screwed into the fitting hole of the container of the water heater. It is not only quite convenient, but also forms an identical double insulation at its joint with the container, therefore avoiding a weak link of current leakage. Experiments have proved that the sheath structure of this invention can overcome the following problems with the existing technologies: 1. It is not likely to be damaged — with the existing double insulation structure of filling insulation and heat conducting medium between the heating element and the housing (such as CN94218994.9), it is difficult to adopt the pipe reduction process, therefore air gap can hardly be avoided in the insulation packing, and it may lead to tube rupture due to expansion of air after heating. With the double insulation structure of coating inorganic glue film on metal tube or applying an electrical heating film on the glass tube (such as CN97224405.0), it may likely be damaged after repeated heating cycles due to large difference in the thermal expansion coefficients between the film and the base materials. The heat conducting insulated sheath in this invention has eliminated the above mentioned technical problems, and therefore will not be damaged even after long-term use; 2. Double assurance — With the double insulation of filling insulation and heat conducting medium, water would permeate into the medium in case of leakage of the outer sheath, gre«dy reducing the insulation performance of the whole electrical heating element; the double insulation structure with coated films will also lose its insulation function when a crack has developed, affecting the overall performance. The double insulation in this invention will not produce inadvertent effect to each other: the outer layer will not be affected when the inner insulation is damaged; when the metal support tube outside is damaged, the insulation performance of the insulated sheath will not reduce, therefore it can provide double insulation effects; 3. Withstanding heating without water — with the existing double insulation structures, in case of abnormal operation of the water heater without water, the heater will be damaged after burning down the metal tube and the resistor wire; with the double insulation structure of this invention, the heat conducting insulated sheath not only has some heat capacity by itself, but also transfer the heat promptly to the external metal support tube, which can further dissipate the heat to the surrounding atmosphere with its large surface area in case of heating without water supply; furthermore, the sealed threaded structure between the end cap and the container can also transfer heat to the container wall, therefore this invention has a good resistance against heating without water. In general, this invention can form a complete double insulation, and overcome die shortcomings of existing technologies in many aspects, therefore has substantial features and has gained outstanding progress. Description of drawings This invention is further described in the following with attached figures. Fig. 1 is the structure schematic of Embodiment 1 of this invention. Fig. 2 is the sectional view of the embodiment of Fig. 1. Figs. 3,4, 5 and 6 are the sectional views of other embodiments. Embodiments Embodiment 1 The double insulation safe Electrical water heater with high efficiency in this embodiment is a preference embodiment. It consists mainly of the control circuit on the housing, the water container in the housing, and the U-shaped electrical heating tube fitted inside the container. EflBept the electrical heating element, all other parts are identical to the existing electrical water heaters, therefore it is highly feasible. The electrical heating element is as shown in Figs. 1 and 2. The basic structure of electrical heating tube 1 is identical to an ordinary electrical heating tube, resistor wire 2 is fitted in outer tube 3, and between the outer tube and resistor wire is filled with insulation powder 4 such as magnesia having been densified by pipe reduction. Different from an ordinary electrical heating tube, the heating section of the U-shaped electrical heating tube 1 of this embodiment has a section as shown in Fig. 2, comprising of two semi-circular electrical heating tubes folded and closed, therefore the closed part of the U-shaped electrical heating tube is in the shape of a cylindrical tube, which can be easily inserted into the cylindrical heat conducting insulated sheath 7 with its cavity closely following its profile. This heat conducting insulated sheath is made of densely sintered alumina heat conducting insulation ceramic material, with the composition of 99.2%, SiO2 The wiring end of the U-shaped electrical heating tube 1 is V-branched, with the sections of branches still keeping the circular shape. The heat conducting insulated sheath 7 at this part is in a horned shape to match this branching. This horn-mouth shaped heat conducting insulated sheath is fitted into the stainless steel end cap 10. The end of the stainless steel support pipe 6 is sealed and welded with the end surface of end cap 10. The external thread of the end cap is sealed and screwed with the inner thread in fitting hole 9 on container 8. The terminals at the wiring end of U-shaped electrical heating tube 1 are provided with insulated sleeve 5. Practice has shown that the improvement design for the heating element in this embodiment is smart and reasonable. The semi-circular closed U-shaped electrical heating tube not only has a compact structure, regular outer sheath profile and good workability, it also facilitates ensuring the close fitting of the outer insulation sheath and support tube, so that the whole electrical heating elements has an ideal heat conducting performance, basically retaining the heating effect of the original heating tube, while greatly improving the insulation and safety performance, able to fully meet the safety standard of the state for category II electrical appliances, without the need to use grounding device for use. It will not develop rupture or crack after long term use, so it can ensure safe operation at all times, to thoroughly avoid current leakage. Following is a comparison through tests to show the insulation and heat conducting performance of the double insulation safe Electrical water heater with high efficiency in this embodiment. (Table Removed) It is shown in the table above that, compared with other existing technologies, the sheath type double insulation electrical water heater can meet various requirements of safety standard for electrical appliances while keeping the heat efficiency basically unchanged, and it also has ideal resistance against heating without water. embodiments In addition to the electrical heating tube with two semi-circular tubes folded and closed together, the electrical heating tube can have varied sections as follows, to form other embodiments, with the basic structure identical to that in Embodiment 1. For example, as shown in Fig. 3, it can consist of two rectangular sectioned electrical heating tubes, so that the closed U-shaped electrical heating tube is in a square section, and is inserted in the heat conducting insulated sheath with its inner profile as a square section. It can also be as in Fig. 4, consisting of two pairs of circular sectioned electric heating tubes, and the closed part of the U-shaped electrical heating tube is inserted in the elliptic sectioned heat conducting insulated sheath with its inner profile following the outer profile of the former. It can also be as in Fig. 5, consisting of two semi-circular sectioned electric heating tubes folded and closed together in reversed direction, and the closed part of the U-shaped electrical heating tube is inserted in the square sectioned heat conducting insulated sheath. It can also take the form as shown in Fig. 6, i.e. two folded and closed square sectioned electrical heating tubes are inserted in the heat conducting insulated sheath with the inner cavity matching with the profile of the former. In all the above embodiments, a stainless steel support tube with the sectional shape matching the outer profile of the heat conducting insulated sheath is closely fitted externally. The stainless steel as mentioned above can also be replaced by ordinary steel tubes with enamel coating or anti-corrosion surface treatment or other anti-corrosion metal materials. In addition to the above embodiments, this invention can also have many other embodiments. For example, the electrical heating tube can be in spiral U-shaped, and W shaped, etc. The heat conducting insulated sheath can also be inserted into the metal support tube with its inner shape matching the profile of the heat conducting insulated sheath via a metal fitting flange, the end of the metal support tube can be connected with the metal flange end surface by fixed connection method such as thread, screw and pressed riveting, and the flange end surface can be in seal-fixed connection with the fitting surface of the container. Also, the V-branching of the wiring end of the electrical heating tube can include close-to-vertical 90 degree branching and U-shaped branching. Any technical plan in the form of identical substitution or equivalent conversion shall fall within the scope of protection required by this invention. What is claimed is: 1. A double insulation safe electrical water heater, consisting of the water container in the housing, the curved electrical heating tube in the container and the control circuit connected with the electrical heating tube, with the features that the said electrical heating tube is inserted in the heat conducting insulated sheath with the inner shape basically matching the profile of the electrical heating tube, and the said heat conducting insulated sheath is made of densely sintered heat conducting insulation ceramic material. 2. The double insulation safe electrical water heater of claim 1, with the features that the said heat conducting insulated sheath is inserted via the metal end cap tightly into the metal support tube with its inner shape following the profile of the heat conducting insulated sheath, the end of the said metal support tube is seal welded with the metal end cap, and the external thread of the end cap is seal screwed with the inner thread of the fitting hole in the container. 3. The double insulation safe electrical water heater of claim 1, with the features that the said heat conducting insulated sheath is inserted via the metal fitting flange tightly into the metal support tube with its inner shape following the profile of the heat conducting insulated sheath, the end of the said metal support tube is in sealed fixed connection with the metal fitting flange, and the end surface of the fitting flange is in sealed fixed connection with the fitting surface of the container. 4. The double insulation safe electrical water heater of claims 2 or 3, with the features that the said heat conducting insulation ceramic material is one of the alumina, aluminum nitride, silicon nitride, morion, magnesia, silicon carbide and expansion-free ceramics. 5. The double insulation safe electrical water heater of claim 4, with the features that the heating section of the said electrical heating tube consists of two semi-circular sectioned electric heating tubes folded and closed together, the said closed section is inserted tightly into cylindrical heat conducting insulated sheath, and the said heat conducting insulated sheath is inserted tightly into the cylindrical metal support tube. 6. The double insulation safe electrical water heater of claim 4, with the features that the heating section of the said electrical heating tube consists of two rectangular sectioned electrical heating tubes folded and closed together, the said closed section is inserted tightly into the square sectioned heat conducting insulated sheath, and the said heat conducting insulated sheath is inserted tightly into the square sectioned metal support tube. double insulation safe Electrical water heater of claim 4, with the features that the heating section of the said electrical heating tube consists of two circular sectioned electrical heating tubes folded and closed together, the said part folded and closed together is inserted tightly into the elliptic sectioned heat conducting insulated sheath, and the said heat conducting insulated sheath is inserted tightly into the elliptic sectioned metal support tube. 8. The double insulation safe Electrical water heater of claim 4, with the features that the heating section of the said electrical heating tube consists of two semi-circular sectioned electric heating tubes folded and closed together in reversed direction, the said part folded and closed together is inserted tightly into the square sectioned heat conducting insulated sheath, and the said heat conducting insulated sheath is inserted tightly into the square sectioned metal support tube. 9. The double insulation safe electrical water heater of claim 5, with the features that the wiring end of the said electrical heating tube is in V-shaped branching, the heat conducting insulated sheath for the said branching section is in the horn-mouth shape in matching with it, and the said horn-mouth shaped heat conducting insulated sheath is wedged into the end cap made of anti-corrosion metal. 10. A double insulation safe electrical water heater, substantially as herein described, particularly with reference to, and as illustrated in the accompanying figures.

Documents:

1781-del-2006-abstract.pdf

1781-del-2006-Claims-(17-01-2013).pdf

1781-del-2006-claims.pdf

1781-del-2006-Correspondence-Others-(17-01-2013).pdf

1781-del-2006-Correspondence-Others-(28-02-2013).pdf

1781-del-2006-correspondence-others-1.pdf

1781-del-2006-correspondence-others.pdf

1781-del-2006-description (complete).pdf

1781-del-2006-drawings.pdf

1781-del-2006-form-1.pdf

1781-del-2006-form-18.pdf

1781-del-2006-form-2.pdf

1781-del-2006-Form-3-(17-01-2013).pdf

1781-del-2006-form-3.pdf

1781-del-2006-form-5.pdf

1781-del-2006-GPA-(28-02-2013).pdf