US 3715566 A
A water heater tank has a sacrificial anode and an electric heating element assembly protected by a zinc coated sheath. The element is mounted on the tank wall with the sheath electrically insulated from the steel of the tank. A zinc block also may be mounted at the wall of the heating element assembly.
Description (OCR text may contain errors)
United States Patent [191 Wasson 1 Feb. 6, 1973 CORROSION GUARD SYSTEM FOR ELECTRIC WATER HEATER Reielences Cited  Inventor: Loerwood- C. Wasson, Milwaukee, UNITED STATES PATENTS 3,176,115 3/!965 Balis ..2l9/3l8  Assignee: A. 0. Smith Corporation, Milwau- 3,414,707 1'2/1968 Aldous ..2l9/322 ke e, Wis. 3 Primary ExaminerC. L. Albritton  Flled 1972 Attorney-Andrus, Sceales, Starke & Sawall  Appl. No.: 219,936
'  ABSTRACT Related U.S. Application Data i v A water heater tank has a sacrificial anode and an  'P of 12512091 March electric heating element assembly protected by a zinc 197Labandoned' coated sheath. The element is mounted on the tank wall with the sheath electrically insulated from the  U.S. Cl ..2l9/322, 219/318 Steel of the tank. A zinc block also may be mounted at [5 113tthe wall of the heating element assembly - Field of Search ..219/300, 312, 316, 318, 320,
219/722, 336, 338 5 Claims, 2 Drawing Figures 7, 1 'l (C: /M l a, l
PATENTED FEB 6 I975 FIG. 2
LOERWOOD C. WASSON J 4 m'vmron.
ATTORNEYS CORROSION GUARD SYSTEM FOR ELECTRIC wATER IIEATER BACKGROUND OF THE INVENTION This application is a continuation-in-part of application Ser. No. 125,209 filed Mar. 17, I971 and now abandoned.
.years portions of the steel may become exposed. Thus,
sacrificial anodes, such as magnesium anodes, are used to provide cathodic protection by way of the electrolytic currents between the anode and the exposed steel.
It has been found that in some installations the anodes can dissipate too rapidly because of electrolytic interaction with the heater element, which is generally constructed with a protective sheath of a metal such as copper or of some other similar material. In some heaters, the copper sheath is itself protected by tin plating. However, over the course of years when the sacrificial anode becomes inoperative either due to depletion of the magnesium or due to the formation of an insolu ble film over the anode, the tin plating causes rapid tank deterioration because of the highly corrosive electrolytic cell which the tinplating creates.
Other metals, such as zinc have been proposed for use as a coating for the heating element shield, as for instance in U.S. Pat. No. 2,l54,26l to Brandt, and in U.S. 'Pat. No. 3,176,115 to Balis. Zinc is anodic to the steel tank and thus does not create the corrosive electrolytic cell. However, these proposals eliminated the usual primary anode or were not for use with a primary anode, and thus would sacrifice the more adequate and long lasting protection which the primary anodes could provide.
" Further, the assemblies proposed in such systems would act as discharge points'or bleeder anodes for current from the primary anodefand theywould themselves pit and dissipate, thus endangering the heating element and shortening theuseful life of the waterheater.
SUMMARY OF THE INVENTION preferably to the tank material in an assembly which is mounted on the tank and electrically insulated from the metal of the tank at the place of mounting. In this arrangement, the anodic coating acts as a bleeder anode for discharge to ground of current resulting from the electrolytic current from the primary anode. This heating element assembly does not form a corrosive electrolytic cell with the tank walls.
In the practice of the invention, the sheath of the heating element is completely covered by a thin coating of high purity zinc which is anodic to the sheath. In some installations when the stored water is more corrosive, a mass or a portion of zinc is mounted on the sheath and its base and is also electrically insulated from the metal of the tank. With the entire sheath so covered, the zinc depletion due to current flow from the coating to the sheath is small and the mass of zinc is sufficient to provide discharge of the current over a long period of years. In some installations where there is less of a problem with corrosive water, the zinc coating on the sheath may be eliminated and only a ring like portion of zinc or mass be employed.
The described constructions minimize the amount of anodic material which is needed and provides a protective sheath for the heater element which is not subject to pitting and thus provides longer lasting protection for the heater element in addition to preventing corrosion of the exposed portion of the metal tank.
DRAWINGS The drawings illustrate the best mode presently contemplated by the inventor for carrying out the practice of the invention. I
In the drawings:
FIG. 1 is a side elevation of a water heater with parts broken away to reveal the invention; and
FIGI'Z is an enlarged view of a portion of FIG. 1 with parts in section.
DESCRIPTION Referring to the drawings, a water heater tank 1 of the electrical immersion type has the conventional steel walls, including an upper head 2, a lower head 3 and cylindrical shell 4. The heads and shell of tank 1 have a glass or ceramic coating 5 on the inside surfaces for protection from corrosion.
The water heater has the conventional water inlet 6 and dip tube 7 through upper head 2 as well as the usual water outlet 8. Also as in a conventional model, a primary anode 9 is fixed to upper head 2 and depends within the tank to near lower head 3. Anode 9 is best constructed of a magnesium material which is anodic to the steel of the tank, and affords corrosion protection for any exposed portions of the steel of tank 1. This is accomplished by the electrolytic currents in the water 10 that normally fills tank 1 in use.
An electrical heating element assembly 11 is mounted through a suitable opening 12 through the bottom portion of wall 4 to provide the electric heating of the water. It is preferred to include a second element assembly 11 similarly mounted near the top for more uniform heating.
Each assembly 11 has a resistance element 13 formed in a loop which projects within the tank and is connected electrically to contact assembly 14 on the shell 4 for connection to leads from a power supply and control, not shown. The resistance element loop is embedded within a sheath 15 constructed of copper or other protective material having good heat conduction characteristics. In accordance with the invention,
sheath 15 is coated completely with a material which is anodic to the sheath l5 and preferably to the tank, which is a thin layer of zinc coating 16 of a high purity zinc for best results.
Further in accordance with the invention, assembly 11 is mounted on shell 4 such that zinc coating 16 is electrically insulated from shell 4. The result of this arrangement is that coating 16 serves as a bleeder anode to discharge the current picked up from electrolytic action between the primary anode 9 and the inner end of the heating element assembly 11. Because coating 16 is anodic to sheath 15, the current picked up will be,
discharged from zinc coating 16 across to the non coated portion of the steel shell 4 which is exposed at opening 12, rather than from sheath 15. The sheath is therefore not dissipated or pitted by discharge of the electrolytic current.
To provide this insulated relation, the base ends of heating element 11 extend through a backing plate 17 mounted in spaced relation along the exterior surface of shell 4 at opening 12. There, the heating element 11 is secured in any suitable fashion within contact assembly 14 which is fixed to the outside surface of-plate 17. A sealing gasket 18 constructed of electrically insulating material is secured between plate 17 and shell 4 around opening 12 to seal the opening and space plate 17 from shell 4.
A fastener plate 19 is welded or otherwise secured to shell 4 around gasket 18 and provides a threaded opening for a screw fastener 20 through an opening 21 in backing plate 17 to fasten heating element assembly 11 to shell 4. An insulator 22 with a tubular portion 23 and a flange 24 fits around the shank of screw 20 and between plate 17 and the head of the screw for purposes of electrically insulating the plate from the shell 4. Thus, assembly 11 is fastened to shell 4 in an arrangement that insulates zinc coating 16 from the steel of the shell.
in the optimum practice of the invention to meet all types of high corrosive water conditions, an additional mass or layer of material which is anodic to the sheath 15 may be disposed at the base of the heating element assembly 11 in contact with sheath 15 and also insulated from thewall 40f the tank. For best results, this mass may be in the form of a zinc block 25 adhered or otherwise fastened to the inside surface of backing plate 17 and having bores 26 through which the base ends of the heating element 11 extend. Zinc block 25 in acting as a bleeder anode will dissipate in discharging theelectrolytic current attracted to the sheath 15 from ,stallations, it may be possible to use only the block 25 or other layer or massof material and eliminate coating 16. The corrosive conditions to which the installation is subjected would govern this usage.
In use, primary anode 9 will slowly dissipate through galvanic or electrolytic currents to the inside ends of eater element assemblies 11 and to any exposed areas of steel on heads 2 and 3 and shell 4 or the joints therebetween. lf primary anode 9 becomes inoperative for some reason, such as through dissipation or the formation of an insoluble film on the anode, the zinc coating 16 and zinc block 25 are also anodic to the steel and will continue the corrosion preventing electrolytic currents, rather than forming a highly corrosive electrolytic cell as would a tin covered sheath. To add years of life to the tank, elements 11 can be easily removed and replaced or the zinc coating 16 or zinc block 25 replaced, instead of replacing the primary anode 9 which is a more difficult operation.
The practice of the invention as in the example described provides better corrosion protection and better protection of the heater element without appreciably increasing the cost of manufacturing electrical immersion water heaters.
Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter that is regarded as the invention.
1. In a water heater tank having metallic walls and a primary anode anodic to the walls, the improved electrical immersion water heater assembly comprising a resistance heating element protruding into the tank, a protective sheath covering said resistance heating element, a layer of material covering the sheath and anodic to said sheath, fastening means securing said resistance heating element to a metallic wall of the tank and electrically insulating the anodic layer and sheath from said tank wall, and a mass of material anodic to the sheath and connected to the heater assembly at the fastening means in electrical contact with the anodic layer on said sheath and in a position electrically insulated from the metallic walls of the tank.
2. In a water heater tank having metallic walls and a primary anode anodic to the tank walls and electrically connected thereto, a resistance heating element protruding into the tank, a protective sheath covering the resistance heating element, a bleeder anode consisting of a layer of material anodic to the sheath disposed in engagement with the sheath of the heating element, fastening means securing the heating element to the wall of the tank, and insulation material disposed between the wall of the tank and the fastening means, protective sheath and bleeder anode to electrically insulate these parts from the tank wall, the bleeder anode discharging to the tank wall through the water stored in the tank any electrolytic current directed to the sheath from the primary anode to thereby protect the sheath against damage by the electrolytic action of said current.
3. The water heater assembly of claim 2, wherein said bleeder anode is of zinc.
4. The water heater assembly of claim 2, wherein said bleeder anode is a coating of zinc over the entire sheath.
5. The water heater assembly of claim 2, wherein the bleeder anode is a block of zinc in contact with the base of the sheath and insulated from the wall ofthe tank.