The present invention relates to a method of constructing an inner glass-lined steel tank for a hot water heater and wherein the glass lining has a substantially constant density throughout the inner surface of the tank to prevent corrosion thereof.
An inner tank of a domestic hot water heater is usually formed by a cylindrical steel container having a circumferential side wall, a top dome shell and a bottom wall shell which are welded together. The container is provided with holes to receive fittings which are welded or screwed thereto. These fittings are required to secure piping to the tank, electric heating elements if the hot water heater is to be heated by electricity, a sacrificial anode and other devise such as temperature sensors, etc. The sacrificial anode, or sacrificial rod, is a metallic anode used in cathodic protection where it is intended to be dissolved to protect other metallic components inside the tank. The more active metal is more easily oxidized than the protected metal and corrodes first, hence the term “sacrificial”, and it generally oxidizes nearly completely before the less active metal will corrode, thus acting as a barrier against corrosion for the protected metal. Therefor, the more metal that is exposed inside the tank wall the faster the sacrificial anode will deteriorate and any exposed metal surface will start oxidizing.
Oxidization of exposed metals in hot water heater has been found problematic in the past and attempts have been made to construct the inner casing of the hot water heater of non-corrosive materials. U.S. Pat. No. 5,379,507 describes such a method of manufacture wherein an inner shell of non-corrosive material is cast inside the outer shell while heat is applied to the outer shell. The leak-tight liner is a polymer material such as polyethylene, polyprolyn or nylon. An objective of this design was to substantially reduce the amount of steel required to fabricate the tank as well as preventing corrosion. This would also eliminate the need of a sacrificial anode thereby resulting in a further cost reduction. However, such tanks have not proven efficient due to other problems that it created.
We have found that the life expectancy of the inner steel tanks of hot water heaters can be improved greatly if defects in the glass lining on the inner wall can be eliminated or substantially reduced. One of the major problems which cause corrosion is due to sharp transition areas inside the tank wall and which are caused by weld couplings, element couplings and primarily the joint formed inside the tank wall by the top dome shell and the cylindrical steel shell.
It is therefore a feature of the present invention to substantially reduce abrupt transition areas on the inner sidewall of the hot water tank to thereby produce a glass lining of substantially constant density throughout on the inner surface of the tank to thereby greatly reduce the formation of oxidation.
According to the above feature, from a broad aspect, the present invention provides a method of constructing an inner glass-lined steel tank. The method comprises forming an open-ended cylindrical steel shell from a rolled sheet of steel which is welded longitudinally at opposed longitudinal side edges of the sheet when bent to form a cylinder whereby a longitudinal weld is formed free of burrs on an inner surface of the longitudinal steel shell. A bottom wall shell and a top dome shell are formed, with the top dome shell having a flat circumferential edge between an outer and inner surface of the top dome shell. The flat circumferential edge is machined to create a smooth angulated surface in an abrupt transition edge between the flat circumferential edge and the inner surface of the top dome shell. The top dome shell is press-fitted inside a top end portion of the cylindrical steel shell with the marginal section of the outer surface of the top dome shell in tight frictional contact with an inner surface of the top end of the cylindrical steel shell. The smooth angulated surface merges into the inner surface of the cylindrical steel shell. The top dome shell is welded to the cylindrical steel shell all about an outer surface of the cylindrical shell. The inner surface of the press-fitted top dome shell and the inner surface of the cylindrical steel shell is then sand-blasted and a porcelain enamel is sprayed on the sand-blasted inner surfaces. The porcelain enamel is heated to fuse same on the inner surface of the press-fitted top dome shell and the cylindrical steel shell. The inner surface of the bottom steel support shell is also sand-blasted and a porcelain enamel is applied and heated to fuse the porcelain enamel to the inner surface thereof. The bottom steel support shell is press-fitted in a lower open end of the cylindrical shell and welded all about the outer surface of the cylindrical shell.
A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which:
Referring now to the drawings, and more particularly to
A bottom wall shell 14 and a top dome shell 15 are also formed from a sheet of steel. The top dome shell 15 has a flat circumferential edge 16 extending between the outer surface 15′ and the inner surface 15″ of the top dome shell 15. As hereinshown, this flat circumferential edge 16 creates two abrupt transition zones one defined in the joint area 17 between the inner surface 13 of the cylindrical steel shell 11 and the flat circumferential edge 16, and the other joint area 18 formed between the inner surface 15″ of the top dome shell 15 and the flat circumferential edge 16. These abrupt transition zones in the joint areas 17 and 18 make it difficult for the porcelain enamel to adhere thereto and often bare spots or even exposed surface portions will appear in the joint areas 17 and 18 after the porcelain enamel has been baked or after a few years only of use of the hot water heater due to thin glass-lined areas.
The present invention overcomes this problem by machining the flat circumferential edge 16 as illustrated in
After the top dome shell 15 is press-fitted inside the top end portion 22 of the cylindrical steel shell 11 with a marginal section of the outer shell of the top dome shell in tight frictional contact with the inner surface of the top end of the cylindrical steel shell, a weld 23 is formed all about the outer surface of the top dome shell and the top edge 24 of the cylindrical steel shell 11.
After the top dome shell 15 and the cylindrical steel shell 11 have been press-fitted together, the entire inner surface of the top dome shell and the cylindrical steel shell is shot-blasted prior to applying a porcelain enamel on the sand-blasted inner surfaces. The porcelain enamel can be sprayed wet or powder coated or slushed. This assembly is then heated in an appropriate oven whereby to fuse the porcelain enamel on the inner surface of the assembled components. The bottom wall shell 14 is also sand-blasted on an inner surface 14′ thereof and a porcelain enamel is also sprayed thereon and it is cured in the same fashion as the cylindrical steel shell 11 and the top dome shell 15. It is press-fitted in the bottom open end of the cylindrical steel shell 11 and a weld 25 is formed outwardly between the cylindrical steel shell bottom edge 26 and a lower portion of the side wall 27 of the bottom steel support shell 14.
As shown in
As shown in
As can be seen from the present invention, sharp transition zones have been eliminated on the inner surface of the hot water tank particularly in the transition area between the top dome shell and the cylindrical steel shell thereby eliminating or substantially reducing the risk of early oxidation in this transition area. The result is that the life expectancy of the hot water heater has been greatly increased and the life expectancy of the sacrificial anode has also been increased. Because these hot water heaters have term warranties, the cost of writing reports to insurance companies as well as labour costs involved in dismantling a water heater and replacing it and discarding the water heater in an environmental friendly manner, is reduced.
It is within the ambit present of the invention to cover any obvious modifications of the preferred embodiment described herein provided such modifications follow within the scope of the appended claims. It is pointed out that although the preferred embodiment relates to a cylindrical steel shell for a domestic water heater, the invention should not be restricted thereto as it can apply to storage tanks for storing hot or cold water or other liquids which need to be isolated from steel.
Number | Name | Date | Kind |
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4796344 | Nunlist | Jan 1989 | A |
4889105 | Vago et al. | Dec 1989 | A |
5088192 | Dempsey | Feb 1992 | A |
5379507 | Lindahl | Jan 1995 | A |
5722149 | Lesage et al. | Mar 1998 | A |
20080135565 | Zeiler | Jun 2008 | A1 |
Number | Date | Country | |
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20130022428 A1 | Jan 2013 | US |