Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
  • F24H9/00—Details
  • F24H9/40—Arrangements for preventing corrosion
  • F24H9/45—Arrangements for preventing corrosion for preventing galvanic corrosion, e.g. cathodic or electrolytic means
  • F24H9/455—Arrangements for preventing corrosion for preventing galvanic corrosion, e.g. cathodic or electrolytic means for water heaters
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
  • F24H1/00—Water heaters, e.g. boilers, continuous-flow heaters or water-storage heaters
  • F24H1/18—Water-storage heaters
  • F24H1/181—Construction of the tank
  • F24H1/183—Inner linings
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
  • F24H9/00—Details
  • F24H9/40—Arrangements for preventing corrosion
  • F24H9/45—Arrangements for preventing corrosion for preventing galvanic corrosion, e.g. cathodic or electrolytic means

Definitions

• the burner In a gas fired water heater, the burner is mounted beneath the lower head of the water storage tank and the waste gases of combustion are discharged through a flue that extends centrally through the tank.
• the hot waste gases passing upwardly through the flue increase the rate of heat transfer to the water contained within the tank.
• the inner surfaces of the tank including the cylindrical shell, the upper and lower heads and the flue, are » normally glass coated.
• other types of corrosion resistant materials ' such as zinc, aluminum and magnesium can be applied to the inner surfaces of the tank.
• Such coating procedures are for example described in U.S. Letters Patent Nos. 2,490,978 and 2,566,138. Methods of application have included hot dipping, spraying and painting.
• the prior art describes tanks which have been provided with non-corrosive liners such as aluminum as described in U.S. Letters Patent No. 2,993,617.
• a sacrificial anode is normally suspended in the upper head of the heater and projects downwardly into the tank.
• the anode is composed of a metal anodic to steel, such as magnesium, aluminum or zinc, and acts to cathodically protect any areas of the steel tank which may be exposed through defects in the glass coating or at the tank fittings.
• the most conventional practice currently in fabricating a water heater is to initially weld the upper head to the upper end of the shell, with the inner surfaces of the preassembled shell and upper head then being coated with glass.
• the flue is welded within an opening in the lower head and the outer surface of the flue as well as the upper surface of the lower head are similarly coated with glass.
• the glass coating Prior to firing the glass at an elevated temperature, the glass coating is brushed away from the inner surface of the annular flange bordering the opening in the upper head, as well as from the upper end of the flue so that when the flue is subsequently assembled within the opening in the upper head, a weld can be made directly from the steel upper head to the steel flue. Similarly, prior to firing, the glass coating along the lower edge of the shell and along the peripheral edge of the lower head is brushed away so that a weld can be made directly between the shell and the lower head.
• the upper heads of water heaters typically have a downwardly depending peripheral flange- which is press fitted for assembly purposes within the upper end of the shell. In effecting such assembly, the upper head is forced through a sizing ring and disposed within the upper end of the shell so that the press fit is provided therebetween.
• the free end of the upper head flange flares inwardly slightly .so that a crevice is created between the outer surface of the upper head flange at its lower extremity and the side wall of the shell.
• Such crevices can be on the order of .015 inches or 15 mils at their opening.
• U. S. Letters Patent 4,113,600 discloses a method of minimizing the exposed steel at the joint between the flue and the flange on the upper head.
• an anodic metal is sprayed in the form of a small strip onto the exposed steel at the upper end of the flue which overlaps the glass coating on the flue.
• the anodic metal coating is press fitted into engagement with the upper head to seal off exposed steel at the joint between the flue and the upper head.
• the core wire is exposed at the lower end of the anode and the exposed end of the steel core wire will result in increased consumption of the lower end of the anode, causing the lower end of the anode to assume a bullet-like shape.
• Another object of the invention is to provide a metallic coating on the interior of the water heater surfaces which will function as a barrier coating in a corrosion sense, as a galvanic sacrificial surface in a cathodic protection sense whereby conventional separate cathodes can be eliminated, and as a hydraulic seal to protect the various joint welds of the heater from the contained water.
• a further object of the present invention is to avoid the drawbacks associated with using glass as a corrosion protective coating wherein glass has more of a tendency to crack than does metal.
• Another object of the invention is to effectively provide a barrier coating, cathodic surface and hydraulic seal across the typical crevice which exists between the upper head flange and interior wall of the heater shell by providing a metallic fillet with sufficient elasticity and thickness to bridge and seal the exposed edge of the flange and associated crevice.
• Yet another object of the invention is to provide cathodic protection to the interior of the water heater in a more effective manner by maximizing the geometrical relationships between the cathodic surfaces (metal coated flue for example) and the heater tank surfaces being protected.
• the invention in a preferred embodiment, is directed to a cathodically protected, gas fired water heater which eliminates the nee of the conventional anode.
• the flue, the upper surface of the lower head and the lower surface and flanged opening of the upper head and the shell are coated with a metal, such as aluminum, or alloys thereof, which is anodic to steel.
• the inner surface of the cylindrical shell as well as the lower surface of the upper head may also be coated with glass or other corrosion resistant coatings, such as organic resin coatings or inorganic silicate coatings.
• the glass coating, or metal coating as the case may be extends to the lower edge of the shell as well as extending to the upper edge of the flange which borders the central opening in the upper head.
• the flue On assembly of the lower head and flue with the shell and upper head, the flue is inserted through the opening in the upper head and the anodic metal coating projects upwardly beyond the upper head. The upper edge of the flange bordering the opening is then welded through the anodic metal coating directly to the flue. Similarly, the lower edge of the shell is welded through the anodic metal coating into the lower head.
• the metal coating such as aluminum, flows around the weld and effectively coats or seals the same with respect to the interior of the heater. In this manner, a barrier coating is provided with respect to the weld as well as a protective anodic surface with the weld being hydraulically sealed off from the tank interior.
• the present invention is also directed to the welded joint between the upper head and the interior surface of the shell.
• a crevice exists between the outer surface of the upper head flange and the inner surface of the shell with the bottom of the crevice being defined by a press fit between the upper head and the shell.
• the opening of the crevice can be on the order of 15 mils or .015 inches.
• the lower edge of the upper head flange is bounded by sharp substantially right angle corners.
• the present invention comprehends the spraying of an aluminum coating about the corners of the lower edge of the flange and into the crevice opening.
• the metal coating on the straight side wall of the shell, flue and heads may be on the order of 8 mils thick but in the area of the crevice between the upper head flange and shell, the metal coating thickness is intentionally increased which typically could be on the order of 15 mils nominal thickness.
• the increased thickness of the coating at the crevice can be imparted for example by a reduced rate of spray head movement or by use of a dwell when utilizing automatic spraying equipment. In this manner, the weld adjacent the base of the crevice is hydraulically sealed off while being provided with a barrier coating and protective cathodic surface.
• the present invention is also directed to the welded joint between the lower portion of the flue and the lower head.
• the lower head and lower flue are first welded together as a subassembly which in turn is sprayed with an aluminum coating.
• the coating fully protects the weld in the same manner that it protects the adjoining surfaces of the flue and lower head.
• the anodic metal coating on the flue replaces the conventional anode rod and is located centrally of the tank so that all surfaces of the cylindrical shell are equidistant from trie anodic coating to provide more effective cathodic protection.
• the metal coating be applied through use of a thermal spraying operation which provides a textured surface that substantially increases the overall contact area of the anodic metal.
• the invention may be utilized to eliminate the need of applying any glass coating and firing the glass coating, thereby providing a cost advantage over conventional methods.
• Fig. 1 is a vertical section of a water heater fabricated in accordance with the invention as including a metal coating anodic to steel sprayed onto all of the interior surfaces of the heater including the flue;
• Fig. 2 is an enlarged vertical section of the welded attachment of the flue to the upper head illustrated in Fig. 1;
• Fig. 3 is an enlarged vertical section showing the welded attachment of the lower head to the shell of the water heater illustrated in Fig. 1;
• Fig. 4 is an enlarged vertical section of the welded attachment of the flue to the lower head of the water heater illustrated in Fig. 1;
• Fig. 5 is an enlarged vertical section of the welded attachment of the upper head to the shell of the water heater illustrated in Fig. 1;
• Fig. 6 is a vertical section of an electric water heater (no central flue) fabricated in accordance with the invention as including a sprayed metallic coating anodic to steel on all of its interior surfaces;
• Fig. 7 is an enlarged vertical section of the welded attachment between the lower head and shell of the water heater illustrated in Fig. 6;
• Fig. 8 is a vertical section of a gas fired water heater fabricated in accordance with the invention as including a glass coating on the interior of the upper head and shell and a metallic coating anodic to steel on the flue and interior surface of the lower head;
• Fig. 9 is an enlarged vertical section showing the attachment of the flue to the upper head of the water heater illustrated in Fig. 8;
• Fig. 10 is an enlarged vertical section of the welded attachment of the lower head and shell of the water heater illustrated in Fig. 8;
• Fig. 11 is a vertical section of an electric water heater fabricated in accordance with the invention as including a glass coating on the upper head and shell and a metal coating anodic * to steel on the interior surface of the lower head;
• Fig. 12 is an enlarged vertical section of the welded attachment between the lower head and shell of the water heater illustrated in Fig. 11.
• Fig. 1 shows a water heater tank 1 (similar components in the water heaters illustrated in Figs. 6, 8 and 11 include the same numerical designation) composed of a generally cylindrical steel shell 2 having its ends enclosed by upper and lower steel heads 3 and 4.
• An annular supporting skirt 5 extends downwardly from the lower end of shell 2 and defines a compartment which houses a standard gas fired burner 6.
• the waste gases of combustion generated by burner 6 are conducted upwardly through shell 2 in a flue 7 which is mounted centrally of or coaxially with shell 2.
• an outer casing not shown, is spaced outwardly of shell 2 and a layer of insulating material is located between the shell and the casing.
• Water to be heated is introduced into tank 1 through a dip tube 8 which is mounted within an opening in upper head 3 and heated water is withdrawn from the tank through an outlet 9 which is also mounted within an opening in upper head 3.
• a coating 12 of a metal anodic to steel such as aluminum, magnesium, zinc or alloys thereof, is applied to the outer surface of .flue 7 and to * the upper surface of lower head 4 after subassembly of those components.
• a further coating 12 of an anodic metal is applied to the inner surface of the upper head 3 and shell 2 after subassembly of those components.
• the subassembled lower head/flue is then assembled with the subassembled upper head/shell to assume the configuration shown in Fig. 1.
• the skirt 5 is welded to the lower edge of shell 2 concurrently with the welding of shell 2 through coating 12 on the lower head 4 into head 4 as will be more specifically described with respect to Fig. 3.
• flue 7 extends beyond the top of the upper head flange 14 as does the anodic metal coating 12.
• the anodic metal coating such as aluminum.
• the sprayed aluminum has the advantage of providing a textured surface which increases the surface area in a cathodic protection sense, and to the extent it is consumed the surface has a corresponding sacrificial characteristic.
• the flange opening and flue are sized taking into account their respective coatings so that preferably a press fit exists between the flue and the flange.
• a weld 15 is then made at the top edge of flange 14 in such a manner as to flow through the coatings 12 into the base material of flue 7.
• the welding process causes the adjoining coatings 12 to flow about the weld 15 and to effectively coat and seal the weld from the interior of the tank.
• the resulting flow of anodic metal about the weld hydraulically seals the same off from the tank interior and provides a corrosion barrier and anodic surface for the weld and associated structural components with respect to contained water.
• Fig. 3 illustrates the weldment of the coated lower head to the shell in which the aluminum coating for example is caused to flow about weld 16 to hydraulically seal off the weld and provide a corrosion barrier as well as an anodic surface to contained water.
• the skirted housing 5 is concurrently welded to the bottom edge of shell 2, with the housing 5 enclosing the gas fired burner means 6.
• the lower head 4 is subassembled with flue 7.
• the subassembly is effected by means 15 of weld 18 with the coating 12 imparted to the subassembly of the head 4 and flue 7.
• An uninterrupted protective anodic surface is provided while isolating weld 18 from contact with the contained water.
• the upper head 3 is shown assembled within the upper end of shell 2.
• the upper head 3 is forced through a sizing ring when being placed within shell 2 which results in an expansion press fit against shell 2.
• This in combination with any distortion which results from the placement of weld 20 on the top edge of shell 2 to the flange of head 3 causes a crevice 22 to be formed between the outer surface of the depending flange of head 3 and the inner surface of shell 2.
• the opening of crevice 22 at its mouth can be on the order of 15 mils.
• the thickness of the coating needed to effectively bridge and seal the crevice 22 varies with the degree of crevice opening. As mentioned, it has been found that crevice openings range upwards of 15 mils, and in that case it has been found that a metal coating thickness (such as aluminum) on the order of 15 mils will dependably bridge and seal the crevice. It is to be noted that the straight wall surfaces on the shell for example can be thinner, on the order of 8 mils for example, depending on the expected service life anticipated for the unit.
• Fig. 6 illustrates a water heater similar to that illustrated in Fig. 1 except for the fact that it is energized electrically. Accordingly, heating elements 24 are provided for water heating purposes.
• the weld 20 between the head and shell is provided in the same manner and for the same reasons as described with respect to Fig. 5. Of course, there are no center flue considerations in the electric heater embodiment.
• an anodic metal such as aluminum is spray coated to the upper surface or interior surface at 12 with respect the lower head 4a. That aluminum coating abuts the aluminum coating 12 on the side wall of shell 2 which flow together about weld 26.
• Weld 26 joins shell 2 to the lower head 4a.
• the hydraulic sealing and resulting corrosion barrier and cathodic protection described with respect to the shell/lower head joint in Fig. 3 is similarly provided to the joint illustrated in Fig. 7 for an electric hot water heater.
• Figs. 8-12 deal with an alternative embodiment of the present invention which includes a glass coating on the inner surfaces of the shell and upper head and an anodic metallic coating such as aluminum on the outer surface of the flue and inner surface of the upper head exposed to contained water.
• the peripheral flange of upper head 3 is again initially welded to the upper end of shell 2.
• the glass coatings 10 and 11 are then applied to the inner surface of the shell as well as to the lower surface of upper head 3, respectively, and the glass coating is then fired at an elevated temperature to provide a fused protective coating on the inner surfaces of the shell and upper head.
• the glass coating 10 extends downwardly to the lower end of shell 2, and similarly the glass coating 11 on upper head 3 extends to the upper edge of the flange 14 bordering the central opening in the upper head and to the lower edge of the peripheral flange surrounding upper head 3.
• the lower end of flue 7 is welded within an opening in lower head 3 and the outer surface of flue 7 as well as the upper surface of lower head 4 are then sprayed with the anodic metal to provide the coatings 12.
• the metal coating 12 extends continuously from the edge of the lower head to the upper end of the flue.
• the subassembled lower head 4 and flue 7 are then assembled with the subassembled shell 2 and upper head 3, with the upper end of the flue being inserted through the opening bordered by flange 14.
• the metal coating 12 extends upwardly to a location above the upper edge of the flange 14.
• flange 14 is then welded, as indicated by 15, through the metal coating 12 directly to flue 7.
• Weld 16 connects the abutting ends of shell 2 and skirt 5 to the peripheral flange of lower head 4, as best seen in Figure 10.
• the glass coating and the anodic metal coating extend Titanium dioxide, as well continuously through the joint between the lower head 4 and the shell 2, thereby eliminating any exposed steel at these joint areas. By eliminating exposed steel at these joints, the consumption of the anodic coating 12 is substantially reduced.
• Figs. 11-12 are similar to Figs. 8-10 in terms of illustrating a water heater having interior surfaces coated with both glass and anodic metal.
• Fig. 11 illustrates an electric water heater which, as in Fig. 6, includes electric heating elements 24.
• the subassembly of the upper head and shell and the glass coatings 10 and 11 thereon are similar to the Fig. 8 construction.
• the lower head 4a is coated with an anodic metal 12 such as aluminum. Accordingly, the aluminum coating 12 abuts the glass coating 10 on shell 2 with weld 26a being provided to structurally join the lower head to the shell. Weld 26a is in turn protected by the flow of the coating 12 material about the weld.
• the conventional anode rod is eliminated, and as the anodic metal 12 is located on the central flue in the gas fired heater, it is equidistant from the inner surface of shell 2 to provide optimum protection for defects in the glass coating or metal coating as the case may be. Of course, in an electric heater, there is no flue.
• thermal spraying to apply the anodic metal coatings to the water heater components, for the sprayed coating is textured which provides an increased surface area.
• FIG. 1 illustrates a gas fired water heater having a single central flue
• a heater can have a plurality of flues that extend between the tank heads.
• the invention can be used with water heaters in which the burner is located within a submerged chamber in the tank as opposed to being located beneath the lower head, as illustrated.

Landscapes

• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Details Of Fluid Heaters (AREA)
• Prevention Of Electric Corrosion (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=25474823

Family Applications (1)

Country Status (3)

Families Citing this family (1)

Family Cites Families (1)

• 1987
  • 1987-12-11 EP EP88900429A patent/EP0334891A1/de not_active Withdrawn
  • 1987-12-11 CA CA000554156A patent/CA1308973C/en not_active Expired - Lifetime
  • 1987-12-11 WO PCT/US1987/003234 patent/WO1988004392A1/en not_active Application Discontinuation

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events