Title of Invention

METHOD FOR MANUFACTURING AN ENAMEL COATED HEATING TUBE AND AN ENAMEL COATED HEATING TUBE THEREOF

Abstract This invention is about a heating element for electrical water heaters, as well as the manufacturing method of this heating element, and belongs to the technical field of household electrical appliances. The enamel coated heating tube for electrical water heater in this invention is in bended shape, the tube contains electrical heating wires isolated by insulation terminals from the metal tube sheath, insulation and heat conducting material is filled between the heating wires and metal tube sheath, and the surface of the metal tube sheath is covered with an enamel layer. The key step in the manufacturing method is that the tube is connected to power for heating itself after enamel coating is applied to the outer surface of the metal tube, and the heating temperature and temperature keeping time is controlled as for enamel sintering process. This invention has made a breakthrough to the fixed pattern of thinking and traditional processes in the industry, realized the enamel coated heating tubes for electrical water heaters with a simple, smart and reasonable sintering process, thus opening an economic and practical way to proper solution to the issue of anticorrosion and anti-scaling for electrical water heaters.
Full Text FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003 COMPLETE SPECIFICATION
[See section 10, Rule 13]
ENAMEL COATED HEATING TUBES FOR ELECTRICAL WATER HEATERS AND THEIR MANUFACTURING METHOD;
A. O. SMITH (CHINA) WATER HEATER CO., LTD.,
A CORPORATION ORGANIZED AND EXISTING
UNDER THE LAWS OF CHINA WHOSE
ADDRESS IS 336 YAOXIN AVENUE, NANJING
ECONOMIC AND TECHNOLOGICAL
DEVELOPMENT ZONE, NANJING 210038, CHINA.
THE FOLLOWING SPECIFICATION
PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

Field of Invention
This invention relates to a heating element for use in electrical water heaters, and also includes the manufacturing method of this heating element. It belongs to the technical field of electrical appliances.
Background of Invention
With the continuous improvement of living quality of people, electrical water heaters are being used in many families, as one of the most common household electrical appliances. The heating elements in the water heaters are normally bent electrical heating tubes, which contain insulation terminals and electrical heating wires isolated from the metal tube sheath, with insulation and heat conducting materials such as magnesium oxide and quartz sand filled between the heating wire and metal tube sheath. The electrical water heaters are quite convenient in use, but it is a major technical difficulty to remove scale and prevent corrosion for electrical heating elements.
To solve this problem, people have been seeking new type coating materials suitable for electrical heating tubes. It has been found in our retrieval that an electrical heater with a non-adhesive Teflon coating resisting high temperature on the external surface is made public in the Chinese patent application with the application No. 00227016.1 and the title "A new type electrical water heater"; an electrical heating tube with additional carbon and fluorine polymer ductile coating on the surface is made public in the Chinese patent application with the application No. 01262675.9 and the title "Electrical heating tube resisting to scale deposit and corrosive liquid'; and an electrical heating tube with non-adhesive coating such as Teflon or imported Teflon coating material
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on the external surface is made public in the Chinese patent application with the application No. 01256220.3 and the title "An electrical heating tube resisting to corrosion and adhesion". According to the presentation, these electrical heating elements can reduce the forming of water scale, raise the heat conductivity and are safe in use.
In the long practice, the applicants realized after necessary theoretical analysis and experimental verification that, although electrical heating elements made with traditional electrical plating process or directly using anticorrosion materials (such as stainless steel) are resisting to rust, scaling can hardly be avoided, so the heating efficiency of electrical water heaters will decrease significantly after a period of time of use. Plastic non-adhesive materials such as Teflon can prevent scaling, but the cost is high and they cannot withstand cyclic thermal expansion and contraction and long-time immersion in hot water. It is likely to peel off after a period of time, so the service life is limited.
Only the enamel coating has good anticorrosion and anti-scaling properties, insulating, resisting to high temperature, and economic in application. The only pity is that the conventional process for enamel coating cannot be used for the structure of electrical heating tube. If the enamel is coated after the electrical heating tube has formed, the high temperature in sintering will surely damage the insulation material in the insulation terminals; but if the enamel is coated first before fitting the heating wire and insulation terminals in the tube, the enamel coating will certainly be damaged due to deformation of the tube in the subsequent shrinking and bending process.
Therefore, as far as the applicants know, in over half a century since the birth
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of electrical water heater, despite the continuous emergence of new coating materials, electrical heating tubes coated with enamel has never appeared, and even never been thought of by any person. Because it could not be realized, a set pattern of thinking has gradually formed in the industry — seeking for new coating materials has become the only orientation to achieve anticorrosion and anti-scaling.
Summary of the Invention
The purpose of this invention is to propose an enamel coated heating tube for electrical water heater with definite applicability value, and also give its manufacture method, so that the heating tubes of electrical water heaters will have both good anticorrosion property and ideal anti-scaling performance, and are economic and durable.
To achieve these objectives, the enamel coated heating tubes for electrical water heaters in this invention are in bent shape, containing the electrical heating wires isolated from metal tube sheath by insulation terminals, with insulated heat conducting material filled between the wire and metal tube sheath, and the metal tube sheath surface is coated with a layer of enamel.
The manufacture method of the above-mentioned enamel coated heating tubes for electrical water heaters is as follows:
1) Fit the heating wire into the metal tube, and the insulation and heat conducting material is filled;
2) Insulation terminals are fitted at both ends, to isolate the heating wire from the metal tube sheath;
3) The assembled metal tube is bent to the required shape;
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4) The enamel coating material is applied onto the outer surface of the metal tube;
5) The tube is connected with power for heating, and the heating temperature and temperature keeping time is controlled as for the enamel sintering process, so that the enamel material on the outer surface of the metal tube is sintered into a dense and solid enamel layer.
In this way, enamel coated heating tubes for electrical water heaters completely conforming to application requirements can be made.
To ensure proper filling of insulation and heat conducting material, to avoid any short-circuiting between heating wire and metal tube sheath during bending and forming, step 3)' may be added between the above steps 2) and 3), to stretch the metal tube while reducing its diameter, so that the volume in the tube is decreased, to allow the insulation and heat conducting material to fully fill the space inside the tube.
The step 4) above includes various methods of coating, such as immersing in and spraying on enamel slurry and electrostatic spraying enamel powder.
During the heating by energizing the heating tube, the connection resistance value of the wire at both ends is very low and the temperature is not high, so the insulation terminals will not be damaged. Although no sintered enamel layer can be formed at the ends, they will not heat up in actual service, therefore they are not required to be anti-scaling, so this will not affect the actual performance of the enamel coated heating tube.
It can be seen that this invention has made a breakthrough to the fixed pattern of thinking and traditional processes in the industry, realized the enamel
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coated heating tubes for electrical water heaters with a simple, smart and reasonable sintering process, thus opening an economic and practical way to proper solution to the issue of anticorrosion and anti-scaling for electrical water heaters.
In addition, it is worth mentioning that the method of heating by applying power to the tube itself has not only solved the question of reasonable heating and sintering in a smart manner, it is different from the traditional enamel sintering of heating from surface to the inner layer as the heat source produces the sintering temperature from the center to the surface, so the enamel layer is sintered from the inner layer to the surface gradually. Therefore, inspection has shown that the enamel layer is more compact and is bonded with the metal tube base more firmly, which is more favorable to anticorrosion and anti-scaling and can extend the service life. As the heating surface is coated with insulating enamel, the anode protection current in the water tank can be reduced effectively, so that the consumption of anode bar is reduced and the protection time and life of the water tank can be extended.
Brief Description of attached drawings
This invention is further explained in conjunction with the drawings.
Fig. 1 is the schematic of structure of Embodiment 1 of this invention.
Fig. 2 is the schematic of structure of Embodiment 2 of this invention.
Embodiments
Embodiment 1
In this embodiment, an enamel coated heating tube (also called Jingui) for electrical water heater for a power of 2kW is made in the following steps:
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1) Fit the heating wires into the metal tube, which is filled with quartz sand insulation and heat conducting material;
2) Insulation terminals are fitted at both ends of the metal tube, to isolate the heating wires from the metal tube sheath;
3)' Stretch the metal tube and reduce its diameter;
3) Bend the assembled metal tube to U shape;
4) The metal tube is immersed into enamel paste, to apply a coating on its surface at a thickness controlled at 0.4-0.6mm;
5) Connect the tube to power to heat it, and the heating temperature is controlled at 800~900°C which is kept for 10min (normally it is controlled for 8~12min) as for enamel sintering process, so that the enamel coating on the outer surface of the metal tube is sintered into a layer of dense and hard enamel.
The completed enamel coated heating tube for electrical water heater is as shown in Fig. 1: the insulation terminals 1 are fixed rigidly in U-shaped metal tube sheath 3. Metal tube sheath 3 contains heating wires isolated from it, and quartz sand insulation and heat conducting material is filled between the heating wires and metal tube sheath 3. On the surface of metal tube sheath 3 is coated with a homogeneous layer of enamel 4, the thickness of which is usually controlled at 0.1-0.4mm. Experiments show that this layer has not only ideal high temperature resistance and insulation properties, but also good performance to resist scale deposit and corrosion, therefore it can reduce the consumption speed of anode bar in the inner container of the water heater and maintain the heat efficiency of the electrical water heater.
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Insulation terminals 1 are also fixed rigidly with threaded connectors 2 for mounting purpose, therefore the heating tube can be mounted by turning on the water tank of the electrical water heater, making the assembling and disassembling quite convenient.
Embodiment 2
This embodiment includes an enamel coated heating tube for electrical water heater for a power of 1.5kW, and it is made in basically the same method as for Embodiment 1, with the following differences:
1) The metal tube sheath 3 is bent to L shape, and insulation terminal 1 is in rigid connection with bowel shaped flange 2 for mounting purpose;
2) The enamel coating is applied by spraying onto the surface of L-shaped metal tube sheath 3;
3) Provisions for thermal insulation should be taken during heating with power, as the electric power of the heating tube is comparatively low.
The application effect will be the same as Embodiment 1, and will not be repeated here again.
This invention may also be embodied in other forms in addition to the above. Any technical plan in the form of identical substitution or equivalent conversion shall fall within the scope of protection required by this invention.

WE CLAIM
1. An enamel coated heating tube for electrical water heater, the tube containing electrical heating wires isolated from metal tube sheath by insulation terminals, and insulation and heat conducting material being filled between the said heating wires and the metal tube sheath, wherein the said metal tube sheath is covered with an enamel layer on the surface.
2. An enamel coated heating tube for electrical water heater of Claim 1, wherein the said metal tube sheath is in U shape, and the said insulation terminals and the U-shaped metal tube sheath are in rigid connection with a thread connector for mounting;
3. An enamel coated heating tube for electrical water heater of Claim 1, wherein the said metal tube sheath is in L shape, and the said insulation terminals and the L-shaped metal tube sheath are in rigid connection with a bowel-shaped flange for mounting;
4. A manufacturing method for enamel coated heating tube for electrical water heater, including the following steps :

1) Fit the heating wire into the metal tube, and the insulation and heat conducting material is filled;
2) Insulation terminals are fitted at both ends, to isolate the heating wire from the metal tube sheath;
3) The assembled metal tube is bent to the required shape;
4) The enamel coating material is applied onto the outer surface of the metal tube;
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5) The tube is connected with power to heat itself, and the heating temperature and temperature keeping time is controlled as for the enamel sintering process, so that the enamel material on the outer surface of the metal tube is sintered into a dense and solid enamel layer.
5. The manufacturing method for the enamel coated heating tube for electrical water heater of Claim 4, wherein step 3)' is included between steps 2) and 3), to stretch the metal tube to reduce its diameter.
6. The manufacturing method for the enamel coated heating tube for electrical water heater of Claim 4 or 5, wherein the coating in the said step 4) is one of the following: immersion in enamel slurry, spraying enamel slurry and electrostatic spraying enamel powder.
7. The manufacturing method for the enamel coated heating tube for electrical water heater of Claim 5, wherein the heating temperature with power is 800 ~ 900°C and the temperature is kept for 8-12 min.


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Abstract
This invention is about a heating element for electrical water heaters, as well as the manufacturing method of this heating element, and belongs to the technical field of household electrical appliances. The enamel coated heating tube for electrical water heater in this invention is in bended shape, the tube contains electrical heating wires isolated by insulation terminals from the metal tube sheath, insulation and heat conducting material is filled between the heating wires and metal tube sheath, and the surface of the metal tube sheath is covered with an enamel layer. The key step in the manufacturing method is that the tube is connected to power for heating itself after enamel coating is applied to the outer surface of the metal tube, and the heating temperature and temperature keeping time is controlled as for enamel sintering process. This invention has made a breakthrough to the fixed pattern of thinking and traditional processes in the industry, realized the enamel coated heating tubes for electrical water heaters with a simple, smart and reasonable sintering process, thus opening an economic and practical way to proper solution to the issue of anticorrosion and anti-scaling for electrical water heaters.

Documents:

14-MUM-2006-ABSTRACT(20-10-2009).pdf

14-mum-2006-abstract(granted)-(12-2-2010).pdf

14-mum-2006-abstract.doc

14-mum-2006-abstract.pdf

14-MUM-2006-CANCELLED PAGES(20-10-2009).pdf

14-mum-2006-claims(granted)-(12-2-2010).pdf

14-mum-2006-claims.doc

14-mum-2006-claims.pdf

14-mum-2006-correspondence 1(19-5-2009).pdf

14-mum-2006-correspondence 2(20-10-2009).pdf

14-mum-2006-correspondence(ipo)-(17-2-2010).pdf

14-MUM-2006-CORRESPONDENCE(IPO)-(25-5-2009).pdf

14-mum-2006-correspondence-received-ver-040106.pdf

14-mum-2006-correspondence-received-ver-080306.pdf

14-mum-2006-correspondence-received-ver-200106.pdf

14-mum-2006-correspondence-received-ver-270206.pdf

14-mum-2006-correspondence-received.pdf

14-mum-2006-description (complete).pdf

14-MUM-2006-DESCRIPTION(COMPLETE)-(20-10-2009).pdf

14-mum-2006-description(granted)-(12-2-2010).pdf

14-MUM-2006-DRAWING(20-10-2009).pdf

14-mum-2006-drawing(granted)-(12-2-2010).pdf

14-mum-2006-drawings.pdf

14-MUM-2006-FORM 1(20-10-2009).pdf

14-mum-2006-form 1(27-2-2006).pdf

14-mum-2006-form 1(4-1-2006).pdf

14-mum-2006-form 18(29-6-2007).pdf

14-mum-2006-form 2(20-10-2009).pdf

14-mum-2006-form 2(granted)-(12-2-2010).pdf

14-MUM-2006-FORM 2(TITLE PAGE)-(20-10-2009).pdf

14-mum-2006-form 2(title page)-(granted)-(12-2-2010).pdf

14-MUM-2006-FORM 3(20-10-2009).pdf

14-mum-2006-form-1.pdf

14-mum-2006-form-2.doc

14-mum-2006-form-2.pdf

14-mum-2006-form-26.pdf

14-mum-2006-form-3.pdf

14-mum-2006-form-5.pdf

14-mum-2006-other document(19-5-2009).pdf

14-MUM-2006-OTHER DOCUMENT(20-10-2009).pdf

14-MUM-2006-PETITION UNDER RULE 137(20-10-2009).pdf

14-MUM-2006-REPLY TO EXAMINATION REPORT(20-10-2009).pdf

14-mum-2006-specification(amanded)-(20-10-2009).pdf

abstract1.jpg


Patent Number 238618
Indian Patent Application Number 14/MUM/2006
PG Journal Number 8/2010
Publication Date 19-Feb-2010
Grant Date 12-Feb-2010
Date of Filing 04-Jan-2006
Name of Patentee A.O. SMITH (CHINA) WATER HEATER CO., LTD.
Applicant Address 336 Yaoxin Avenue, Nanjing Economic and Technological Development Zone, Nanjing 210038
Inventors:
# Inventor's Name Inventor's Address
1 DING WEI 336 Yaoxin Avenue, Nanjing Economic and Technological Development Zone, Nanjing 210038
2 QIU BU 336 Yaoxin Avenue, Nanjing Economic and Technological Development Zone, Nanjing 210038, China.
3 WANG JIANBAO 336 Yaoxin Avenue, Nanjing Economic and Technological Development Zone, Nanjing 210038, China.
4 WAN HUAXIN 336 Yaoxin Avenue, Nanjing Economic and Technological Development Zone, Nanjing 210038, China.
5 JU PING 336 Yaoxin Avenue, Nanjing Economic and Technological Development Zone, Nanjing 210038, China.
PCT International Classification Number F24H0/20
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2005/0037670.1 2005-01-11 China