US2801321A

US2801321A - Electric water heater having a wraparound heating element and a glasscoated exterior surface

Info

Publication number: US2801321A
Application number: US590640A
Authority: US
Inventors: Frank D Prindle
Original assignee: AO Smith Corp
Current assignee: AO Smith Corp
Priority date: 1956-06-11
Filing date: 1956-06-11
Publication date: 1957-07-30
Anticipated expiration: 1974-07-30

Description

y 1957 F. D. PRINDLE 2,801,321

ELECTRIC WATER HEATER mvmc A WRAP-AROUND HEATING ELEMENT AND A cuss-comma EXTERIOR SURFACE Filed June 11, 1956 1N VEN TOR. FM 11 PRINDLE :xffornegs United States Patent 01 ELECTRIC WATER HEATER HAVING A WRAP- AROUND HEATING ELEMENT AND A GLASS- COATED EXTERIOR SURFACE Frank D. Prindle, Kankakee, 11]., assignor to A. O. Smith Corporation, Milwaukee, Wis., a corporation of New York Application June 11, 1956, Serial No. 590,640

3 Claims. (Cl. 219-38) This invention relates to an electric water heater construction having a wrap-around heating element.

Recently, the trend in electric water heaters has been to employ a wrap-around heating element which is secured to the outer surface of the tank in place of the immersion type heating element which is located in contact with the water in the tank. The wrap-around heating element has definite advantages over the immersion element in that the wrap-around element can be more conveniently removed, replaced and positioned on the tank surface and also the use of the wrap-around element reduces the number of openings in the tank wall and decreases the amount of exposed metal area within the tank to be protected from corrosion.

As the wrap-around element is alternately heated and cooled, the ends of the element are generally connected by a resilient member such as a spring for expansion and contraction of the element during heating and cooling and to maintain the element in tight contacting relation with the outer wall of the tank at all times.

During operation high temperatures are developed in the wrap-around element and it is essential that the heat be transferred rapidly and uniformly to the tank wall in order to prevent overheating of the element. In commercial practice, the outer surface of the tank wall is often in a somewhat roughened condition due to the cleaning treatments applied to the steel, and thus, in some cases, the heating element is not able to freely move or adjust itself on the tank wall during expansion and contraction of the element due to the frictional resistance of the tank wall. If this expansion and contraction of the element is restricted, a portion of the element may belly outwardly, out of contact with the tank wall and a hot spot will develop in this portion due to the inadequate heat transfer from this portion of the element to the tank wall.

The present invention is directed to an electric water heater having a wrap-around heating element in which the element can freely move on the tank wall during expansion and contraction to thereby eliminate the possibility of overheating the element.

According to the invention, a circumferential strip or band on the outer surface of the tank is coated with a glass or ceramic material and the glass is fused to the tank wall. The wrap-around heating element is disposed over the glass strip and secured around the tank by attaching the ends of the element together by a spring connection.

The use of the glass coating, because of its insulating nature, would normally be expected to restrict the transfer of heat from the element to the tank wall and therefore increase the temperature of the heating element. However, in practice the opposite result was found; nameiy, that the smooth glass coating permits the element to move freely during expansion and contraction of the element. As the element can freely adjust itself on the tank no hot spots" in the element occur and the overall Patented July 30, 1957 "ice operating temperature of the element is lower than without the glass coating on the tank.

Other obiects and advantages of the invention will appear in the course of-the following description:

In the drawing:

Figure l is a side elevation of a water heater employing the present invention;

Fig. 2 is a fragmentary enlarged side elevation of the water heater showing the attachment of the heating element; and

Fig. 3 is a view taken along line 3-3 in Fig. 2.

The drawing illustrates a water heater which includes a tank 1 formed of a generally cylindrical shell which is enclosed at the ends by suitable heads.

Cold water to be heated is introduced into tank 1 through an inlet 2 and heated water is withdrawn through the tank through outlet 3.

The tank 1 is housed within a generally cylindrical casing 4 whch is spaced outwardly from the tank and a suitable insulating material 5 is disposed in the clearance between the tank 1 and casing 4.

The water within tank 1 is heated by a flexible, metal, wrap-around heating element 6 which is disposed around the outer surface of tank 1 and is in heat conductive relation with the tank.

The ends of the heating element 6 are connected together by a spring connection which includes a plurality of spring clips 7. Two of the clips 7 are secured to each end of the heating element 6. The corresponding spring clips 7 are secured together by bolts 8 and by threaded adiustrnent of the bolts, the tension of the heating element around the tank can be varied. The threaded position of the bolts 8 in spring clips 7 is maintained by means of nuts 9 which are threaded on the ends of the bolts. The resilient connection between the ends of the heating element 6 permits the element to freely expand and contract during heating and cooling and tends to maintain the element in tight bearing relation with the tank at all times.

Each end of the heating element 6 is provided with an electrical contact 10 and leads 11 connect the contacts to the thermostat 12 which is secured to the tank 1 at a position located above the heating element 6.

The heating element 6 is housed within a generally channel-shaped casing 13. The open side of the channel-shaped casing 13 faces the tank and the flanges of the casing bear against the tank wall on opposite sides of the heating element 6. The casing 13 not only serves to house and protect the heating element in service but also functions as a guide track through which the heating element is inserted around the tank.

The ends of the casing 13 are connected together by a pair of coil springs 14 which serve to urge the easing into tight bearing engagement with the tank wall.

In the commercial manufacture of water heaters, the steel of which the tank 1 is fabricated is initially cleaned of mill scale and other impurities by sandblasting or the like. This cleaning treatment tends to leave the outer surface of the tank in a somewhat roughened condition and due to the roughened condition, the heating element 6 is not always able to move freely on the tank wall during expansion and contraction.

According to the invention, a strip or band of glass or vitreous enamel is applied to a circumferential portion of the outer surface of the tank wall and the heating element 6 is positioned over this glass strip 15. While the glass coating is in itself an insulating material it provides a smooth surface and enables the heating element to freely adjust itself during expansion and contraction and thereby eliminates the possibility of hot spots being formed on the heating element. In effect, the glass coating 15 increases the heat transfer from the 3 heating element to the tank 1 due to the fact that the heating element can move freely on the tank wall.

In addition to the glass strip 15, the entire inner surface of the tank 1 may be coated with a glass or vitreous coating 16 and the

coatings

15 and 16 can be fired and fused to the tank during the same firing operation.

In assembly of the water heater of the invention the upper head of the tank is welded to the cylindrical shell and the inner surface of the shell and head are coated with a glass slip. At this time a band or strip on the outside of the tank is also coated with the glass slip by dipping, spraying, brushing or the like.

The coated shell and upper head are then fired at an elevated temperature of 1600" to 1800 F. to fuse the glass coatings to the tank wall. A glass coated lower head is then assembled in the lower end of the shell to complete the tank assembly.

The casing 13 is then secured around the tank at a position over the glass coating 15 by means of the springs 14. One end of the heating element 6 is then inserted within the passage defined by the casing and the tank wall and passed through the casing. The ends of the heating element are then connected together by means of the spring clips 7 and bolts 8.

The present invention provides a simple and effective means of producing a more eflicient transfer of heat from a flexible wrap-around heating element to the tank wall and eliminates the possibility of hot spots being formed on the heating element due to the inability of the heating element to adjust its position on the tank wall during expansion and contraction of the element.

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 which is regarded as the invention.

I claim:

1. A water heating apparatus comprising, a tank to contain water to be heated and having a cold water inlet and a hot water outlet therein, a coating of glass fused to the outer surface of the tank and extending continuously around the tank, a flexible metallic wrap-around heating element disposed on said glass coating and extending substantially around the tank, a resilient connection connecting the ends of the element together and serving to bias the element around the tank, and means for introducing an electrical current to said heating element to heat the same and thereby heat the water within the tank, said glass coating providing a smooth surface to thereby permit the heating element to freely move thereon during expansion and contraction of the element due to alternate heating and cooling of the same.

2. A water heating apparatus comprising, a tank to contain water to be heated and having a cold water inlet and a hot water outlet therein, a band of glass fused to the outer surface of the tank and extending continuously around the tank, a flexible metallic wrap-around heating element disposed on the glass band and extending substantially around the tank, spring means connecting the ends of the element together to serving to bias the element around the tank, and means for introducing an electrical current to said heating element to heat the same and thereby heat the water Within the tank, said glass band providing a smooth surface to thereby permit the heating element to freely move thereon during expansion and contraction of the element due to alternate heating and cooling of the same.

3. A water heating apparatus comprising, a tank to contain water to be heated and having a cold water inlet and a hot water outlet therein, a glass coating fused to the inner surface of the tank, a band of glass fused to the outer surface of the tank and extending continuously around the tank, a flexible metallic wrap-around heating element disposed on the glass band and extending substantially around the tank, spring means connecting the ends of the element together and serving to bias the element around the tank, an annular casing spaced outwardly of the element and extending substantially around the tank, said casing having a channel-shaped cross section with the open end of the casing facing toward the tank and the flanges of the casing bearing against said band of glass on opposite sides of said element, means for attaching the ends of the casing together to hold said casing in position on said tank, and means for introducing an electrical current to said heating element to heat the same and thereby heat the water within the tank, said glass band providing a smooth surface to thereby permit the heating element to freely move thereon during expansion and contraction of the element due to alternate heating and cooling of the same.

References Cited in the file of this patent UNITED STATES PATENTS 2,484,893 Kuenne Oct. 18, 1949