US2810815A - Electric heaters - Google Patents

Description

Oct- 22, 1957 H. c. DlcoME 2,8l0,85

ELECTRIC HEATERS Filed Feb. 19, 1954 J N VEN TOR.

Unite States Patent ELECTRIC HEATERS Herman C. Dicome, Pittsburgh, Pa., assignor to Edwin L. Wiegand Company, Pittsburgh, Pa., a corporation of Pennsylvania Application February 19, 1954, Serial No. 411,437

11 Claims. (Cl. 219-38) My invention relates to electric immersion heaters, more particularly to an improved construction and mounting for protecting an electric immersion heater against corrosive galvanic action, and the principal object of my invention is to provide new and improved means of the character described.

`It has been customary, in water heater construction, to immerse a protective magnesium rod in the Water within the water tank to protect the interior wall of the tank against corrosion in the event the protective lining of the interior tank wall proves to be faulty. The magnesium rod accomplishes its purpose by setting up galvanic currents between itself and any unprotected portion of the tank wall and such currents cause magnesium from the rod to become deposited upon the unprotected n portion of the tank Wall.

In using magnesium rods in Water heaters having conventional electric immersion heating elements, it was found that the magnesium rod was rapidly being consumed because of galvanic action set up between the rod and the heating element.

`ln order to protect the magnesium rod from rapid dissipation and to break up the galvanic action between the rod and the heating element, it was proposed to electrically insulate the heating element from the wall of the water tank; but this was found to be unsatisfactory because a certain amount of galvanic current ilow still occurred between the magnesium rod and the heating element, the current completing the circuit between the heating element and adjacent parts of the tank wall by passing through the water in the tank. This resulted in serious corrosion of the sheath of the heating element and consequent early Vfailure of the element when the corrosion penetrated the sheath.

Thereafter, it was proposed to Vprovide a controlled amount of galvanic current flow between the sheath of the heating element and the wall of the .water tank to prevent ygalvanic current from passing from the element through Vthe water tothe wall of the tank. However, because of size yand space limitations, the prior constructions Awere unable to accurately Vlimit such galvanic current flow and as a result the ilow was either too large with consequent rapid dissipation'of the magnesium rod or the current ow was too small to protect the heating element sheath against corrosion.

My invention provides an electric immersion heater assembly which is economical Vto produce and easy to assemble `and which Aprovides for accurate control of galvanic current iiow kbetween the sheath of the heating elementand the wall ofthe water tank. These and other advantages will become apparent from a study of the following description andkof the drawing appended thereto.

I n ,the drawing accompanying .this specification and forming a part of this application, there is shown, for purpose of illustration, an embodiment which my inventionrnay assume, andin this drawing:

Figure 1 ,is `a fragmentary sectional view showing my rice improved electric immersion heating element assembled with a Water tank,

Figure 2 is a plan view of the element, removed from the tank,

Figure 3 is a fragmentary, separated perspective view of the heating element, and

Figure 4 is a fragmentary sectional view corresponding generally to the line 4-4 of Figure 2.

Referring particularly to Figure l of the drawing, the heating element therein disclosed is of the hairpin-type comprising a metal tubular 'sheath 10 which is of U- shape longitudinally and provides a heating portion 11 adapted to be immersed in the liquid contained in the tank 12 and terminal portions 14 which extend through an opening 15 in the wall of the tank and extend beyond the outer surface of the tank wall. The usual magnesium rod 16 is fragmentarily shown as supported from the top wall of the tank, and it will be appreciated that the tank will have the usual water inlet and outlet openings.

Although the electric heater is herein shown of the hairpin-type, it will be appreciated that it may be made in the form of a single blade or, if desired and depending upon heating requirements, a plurality of blades may be used. The sheath 10 is preferably formed of a metal which will oppose deleterious action of the liquid contained in the tank and as an example copper has been successfully used. Of course, other metal may be used which has been suitably coated for the purpose.

An electrical resistor 17 is disposed within but insulated frorn the sheath it), and in usual construction the resistor comprises a helical coil of resistance wire ernbedded Within suitable granular refractory material contained within the sheath. In the presently disclosed embodiment, terminal pins 18 are secured to respective ends of the resistor 17 and such pins extend outwardly of the respective ends of the sheath 10, any suitable means being used to seal the sheath ends.

A gasket flange 19 extends crosswise of the terminal portions 14 of the herein disclosed heater and such flange is also preferably formed of a metal, such as copper, which will oppose the deleterious action of the liquid contained within the tank 12. As best seen in Figure 3, the flange 19 herein disclosed is substantially rectangular in plan and of relatively thin cross section, and in production such flange may be readily stamped from sheet metal. flheopening 15 in the tank 12 is usually round and the rectangular size of the flange 19 is such that the ange will overlie the opening and form a closure for the same.

For use with a hairpin-type heater, the flange is formed, at its central portion, with a pair of apertures 20, each for passing a respective terminal portion 14 of the sheath 10. The terminal portions pass through the ilange in huid-tight relation and to effect this relation adjoining portions of the terminal portions and the ange may be silver-soldered, or otherwise suitably connected. As shown in Figure l, the ilange may have depressed portions rnargining the apertures 20 to efect a good structure for silver-solder connection.

A rigid backing or mounting plate 21 is provided to impart strength to the closure effected by the gasket plate 19 and in the present construction the backing plate 21 is preferably of the same rectangular size as the gasket plate 19 and is made of steel, or other suitable metal, of the required thickness. The backing plate is also formed with a pair of apertures 22 aligned with, but preferably of greater diameter than, the apertures 20 in the gasket plate 19 and the terminal portions 14 of the heater extend through respective apertures 22.

As seen in Figure l, the backing plate 21 and the gasket plate vi9 are in juxtaposed relation and have facing surfaces, and a strip 23 of thin dielectric material is disposed between such facing surfaces, the strip preferably being of the same rectangular size as the plates 19 and 21, and formed with apertures to pass the terminal portions 14 of the heater. Dielectric bushings'24 are disposed over each of the terminal portions 14 and positioned to lit within the apertures 22 in the backing plate. In the construction thus far described, it will be appreciated that the dielectric strip 23 and the dielectric bushings 24 electrically isulate the backing plate from the gasket plate 19 and from the sheath 10 of the heater.

A sealing gasket 2S of suitable dielectric material, and preferably of the same rectangular size as the plates 19 and 21, is adapted to be disposed between the gasket plate 19 and the exterior wall of the tank 12, and the exterior wall at this place is usually formed flat to suitably engage with the gasket 25 in fluid-sealing relation.

The four corners of the backing plate 21, gasket plate 19, dielectric strip 23 and gasket 25 are formed with aligned apertures, such aligned apertures passing the shanks 26 of bolts, the head 27 of each bolt bearing against the outer face of the backing plate 21 (or against an interposed washer) and the terminal end of the shank of each boit being threaded into a corresponding threaded opening in the tank wall. Thus, the entire assembly may be drawn up tightly against the exterior wall surface of the tank 12.

The construction thus far described provides an electric immersion heater which is fully insulated from the water tank 12. Referring to Figure l, the dotted lines 30 represent galvanic current flow between the magnesium rod 16 and the sheath 10 of the heater and, in the case of a fully insulated heater, it has been found that current will pass from the sheath through the water at the short gap between the sheath and the tank opening (see dotted lines 31') and to the tank, and it is this passage of current which has caused destructive corrosion of the sheath.

lt has been proposed to provide a regulated amount of current flow between the backing plate 21 and the gasket plate 19 to prevent this damaging ow of current across the gap at 31 but heretofore, because of size and space limitations, construction was expensive and results unreliable.

In the embodiment of the invention herein disclosed, I have formed a transverse opening 32 in the backing plate 21 between the openings 22 and I have also formed an opening 33 in the dielectric strip 23. This construction enables the use of a commercially available current resistor 34 which is here shown to be cylindrical in form and of a length slightly greater than the thickness of the backing plate 21. It will be appreciated, however, that a commercially available resistor of other shape or length may be used, provided it meets requirements of the construction of the invention.

Each end of the current resistor 34, as currently available, is provided with an extending wire terminal, and the end portions of such terminals are attened. The terminals are then bent to the form shown in Figure 3.

The assembly of the heater mounting is a relatively simple matter and may be accomplished by first placing the dielectric strip 23 over the ange plate 19, with terminal portions 14 of the heater extending through the apertures 2t) in the strip. Bushings 24 are then slipped over'respective terminal portions 14 to engagement with the dielectric strip 23. The t between portions 14 and bushings 24 need not be extremely tight so that bushings are easily moved to position.

Thereafter, one terminal of resistor 34 is slipped through opening 33 in dielectric strip 23 and positioned flatwise between adjoining faces of strip 23 and gasket plate 19, and the body of the resistor will thereby be held in position generally transverse to the adjacent outer surface of strip 23, with the other terminal extending downwardly from the upper part of the resistor and disposed to overlie the outer surface of thestrip 23.

The backing plate 21 may then be positioned over the strip 23, the body of theresistor 34 freely extending through the plate opening 32 and the bushings 24 freely extending through the openings 22 in the backing plate. it will be appreciated that the apertures 21)--20 in the dielectric strip 23 and the apertures 22-22 in the backing plate 21 will predetermine the lateral disposition of the strip and plate during assembly, and since, in the embodiment disclosed, both sides of the strip 23 and plate 21 are the same, it would make no difference which side is disposed toward its respective adjoining assembled part. In some cases the outer side of the backing plate may carry indicia providing information and of course in such cases the indicia would identify the outer side.

With the parts assembled as shown in Figure 1, it is preferable to provide against ready disassembly so that the completed unit may be shipped and handled without fear of disarrangement or loss of parts. In the present invention, the terminal portions 14 of the heateer and adjoining parts of the backing plate may be secured in tightly wedged relation peripherally of the backing plate aperture. Y

As herein shown, it is presently preferred to provide the wedging action by a staking operation which displaces metal of backing plate 21 inwardly of the outer surface and peripherally at spaced-apart places 35', as seen in Figures 2 and 4. Such staking is easily accomplished and produces sutHcient wedging action to hold the parts assembled for all practical purposes.

In assembling an immersion heater with a water tank, the dielectric sealing gasket 25 is disposed over the sheath of the heater and positioned against the exposed surface of the gasket llange 19. The Shanks 26 of the four bolts are passed through aligned openings at the corners of the various parts and the bolts are threaded into the tank apertures. It will be appreciated that the bolts will draw up the backing plate 21, the dielectric strip 23, the gasket plate 19, the sealing gasket 25 and the outer surface of the tank in tight relation and such drawing force of the bolts will firmly clamp one terminal of the resistor 34 between surfaces of the backing plate and the strip 23 and clamp the other terminal of the resistor between the surfaces of the strip 23 and the gasket plate 19. Therefore, the greater the clamping pressure of the bolts, the more secure will be the electrical engagement between the terminals of the resistor and their respectively engaged surfaces. t

The resistor 34 may be chosen to provide sufficient current flow between the backing plate 21 and the gasket plate 19 and thereby prevent galvanic current leakage at the gap 31. In the present embodiment, the resistor has a xed electrical resistance value of approximately 700 ohms, but it will be apparent that resistors of other values may be used as dictated by operating conditions.

Any suitable cap, preferably of dielectric material, may be dlsposed over the extending terminals 18 to protect such terminals, the resistor 34, and the exposed ends of sheath terminal portions 14, and such cap may provide for electrical connection of the terminals 18 to a source of electrical current suitable for effecting energization of the heater resistor 17.

In View of the foregoing it will be apparent to those skilled in the art that I have accomplished at least the principal object of my invention and it will also be apparent to those skilled in the art that the embodiment herein described may be variously changed and modified, without departing' from the spirit of the invention, and that the invention'is capable of uses and has advantages not herein specifically described, hence it will be appreciated that the herein disclosed embodiment is illustrative only, and that my invention is not limited thereto. I claim: f s

l. An electric heating element assembly for application to a container for heating the contents thereof, comprising a heating element having a metallic sheath including an outer terminal portion for extending through an opening in a wall of said container, a metallic gasket plate having an aperture for receiving therethrough said terminal sheath portion, means for securing said sheath portion to said gasket plate in uid tight relation with respect to said plate aperture, a rigid backing plate in juxtaposed relation to said gasket plate and having an aperture aligned with said gasket plate aperture for receiving therethrough said terminal sheath portion of said heating element, electrical insulation insulating said backing plate from said gasket plate and from said terminal portion, assembly means for forcing said backing plate toward said gasket plate and for forcing the latter toward the wall of the container surrounding the container opening, and a current resistor having terminals respectively clamped against said gasket plate and said backing plate by the force applied by said assembly means, said resistor being adapted to pass a selected amount of electrolytic current between said gasket plate and said backing plate.

2. An electric heating element assembly for application to a container for heating the contents thereof, comprising a heating element having a metallic sheath including an outer terminal portion for extending through an opening in a wall of said container, a metallic gasket plate having an aperture for receiving therethrough said terminal sheath portion, means for securing said sheath portion to said gasket plate in iluid tight relation with respect to said plate aperture, a rigid backing plate in juxtaposed relation to said gasket plate and having an aperture aligned with said gasket plate aperture for receiving therethrough said terminal sheath portion of said heating element, a at body of electrical insulation disposed between facing surfaces of said gasket plate and said backing plate and an electrical insulation bushing between adjoining surfaces of said terminal sheath portion and the wall of said backing plate aperture, whereby said backing plate is electrically insulated from said gasket plate and said terminal sheath portion, assembly means for clamping said facing surfaces against said flat body and for holding the heating element assembly in position on the container wall, and a current resistor having a terminal between said tlat body and said facing surface of said backing plate and another terminal between said fiat body and said facing surface of said gasket plate, said terminals being clamped in position by the clamping action of said assembly means.

3. An electric heating element assembly for application to a container for heating the contents thereof, comprising a heating element having a metallic sheath including an outer terminal portion for extending through an opening in a Wall of said container, a metallic gasket plate having an aperture for receiving therethrough said terminal sheath portion, means for securing said sheath portion to said gasket plate in fluid tight relation with respect to said plate aperture, a rigid backing plate in juxtaposed relation to said gasket plate and having an aperture aligned with said gasket plate aperture for receiving therethrough said terminal sheath portion of said heating element, a flat body of electrical insulation disposed between facing surfaces of said gasket plate and said backing plate and an electrical insulation bushing between adjoining surfaces of said terminal sheath portion and the wall of said backing plate aperture, whereby said backing plate is electrically insulated from said gasket plate and said terminal sheath portion, said backing plate and said flat body and said gasket plate having aligned apertures for passing bolt means threadable into a threaded aperture in the wall of said container to draw said facing surfaces tightly against said at body and to hold the heating element assembly in position on the container wall, and a current resistor comprising a resistor body extending transversely of and through an opening in said backing plate and having a terminal between said at body and said facing surface of said backing plate and another terminal between said flat body and said facing surface of said gasket plate, said terminals being clamped in position by the drawing action of said bolt means to provide for secure electrical connection between said terminals and said backing plate and gasket plate.

4. An electric heating element assembly for application to a container for heating the contents thereof, comprising a heating element having a metallic sheath including an outer terminal portion for extending through an opening in a wall of said container, a metallic gasket plate having an aperture for receiving therethrough said terminal sheath portion, means for securing said sheath portion to said gasket plate in uid tight relation with respect to said plate aperture, a rigid backing plate in juxtaposed relation to said gasket plate and having an aperture aligned with said gasket plate aperture for receiving therethrough said terminal sheath portion of said heating element, and means for frictionally securing said terminal sheath portion to said backing plate in tightly wedged relationship peripherally of said backing plate to constitute therewith and with said gasket plate a unitary assembly, said securing means comprising staking indentations in said backing plate and extending peripherally about the aperture therein.

5. In an electric immersion heater mounting assembly, in combination, a heater for insertion through an opening in a receptacle, said heater including a gasket plate for overlying said opening, an electrically insulating gasket for insertion between the inner surfaceof said gasket plate and the outer surface of said receptacle contiguous to said opening, a rigid backing plate for urging said gasket plate toward said receptacle wall, means adjacent said backing plate for electrically insulating said backing plate from said heater, a current resistor having a terminal engaging said gasket plate and a terminal engaging said backing plate, and mounting means for pressing said backing plate in a direction toward said gasket plate and for compressing said insulating gasket between the receptacle surface and said gasket plate, said terminals being located to receive pressing force of said mounting means whereby good electrical engagement of respective said current resistor terminals with said gasket plate and said backing plate is maintained.

6. For use with a receptacle having an opening in its wall, an electric immersion heater mounting assembly comprising a sheathed electric immersion heater having a metallic closure member for overlying the receptacle opening, a gasket formed of electrically insulating material adapted to be positioned between said closure member and the wall surface of said receptacle adjoining said opening, a rigid metallic backing plate for securing said 'heater in position on said receptacle, means for electrically insulating said backing plate from said closure member and said heater, including an electrically insulating strip member positioned between said backing plate and said closure member, and headed bolt means having the head portion thereof adapted to bear against said backing plate and the shank portion thereof passinfy through aligned apertures in said backing plate, said strip member and said closure member and receivable in threaded aperture means in the wall adjoining said receptacle opening whereby said bolt means is adapted to tightly draw up the assembly against said receptacle wall surface, and current resistor means disposed in a transverse opening in said backing plate and having a terminal between said backing plate and said strip member and another terminal between said strip member and said closure member, said terminals being pressed to good electrical engagement with their engaged parts when said bolt means is drawn up to hold the assembly to the wall of said receptacle.

7. The combination with an electric heater for immersion in a liquid containing tank, of means including a mounting plate and bolt means engaging said mounting plate and threaded into aperture means in the wall of said tank for drawing up said mounting plate against said wall and sealably attaching said heater to said tank,

"7 and means for limiting-,110W of galvanic current between said tank and said heater to a selected amount and comprising electrical connection means which are held fast by the drawing-up action of said bolt means.

8. An electric heating element assembly for application to a container for heating the contents thereof, comprising a heating element having a metallic sheath including an outer terminal portion for extending through an opening in a wall of said container, a metallic gasket plate secured to said terminal sheath portion in iluid tight relation, a rigid backing plate in juxtaposed relation to said gasket plate and having an aperture through which said terminal sheath portion passes and said aperture being suiciently larger than said terminal sheath portion to provide a gap therebetween, electrical insulation insulating said backing plate from said gasket plate, and a current resistor having wire-like terminal connectors respectively engaging said gasket plate and said backing plate to pass a selected amount of electrolytic current therebetween.

9. An immersion heater for heating liquid in a metallic vessel, comprising an electric heating element of the metallic sheathed type adapted to at least in part extend within said vessel in contact with the liquid therein, means for mounting said heating element to a wall of said vessel, said heater having insulating means normally preventing establishment of galvanic circuits between said vessel and said heater, and a radio type current resistor of fixed ohmic properties providing for a controlled galvanic current flow between said vessel and said heater, said resistor having spaced lead wires, one lead wire being electrically connected to said mounting means and the other being electrically connected to the sheath of said heating element.

10. An electric heating element assembly for application to a metallic container for heating the contents thereof, comprising a heatingelement having a metallic sheath including an outer terminal portion adapted to extend through an opening in a wall of said container, a metallic gasket plate having an aperture for receiving therethrough said terminal sheath portion in fluid tight relation, a rigid metallic backing plate in juxtaposed relation to said gasket plate and having an aperture for receiving therethrough said terminal sheath portion of saidv heating element, means electrically insulating said backing plate from said gasket plate and said metallicv sheath, and a radio type current resistor having spaced lead wires providing opposite terminals, one lead wire being electrically connected to said backing plateV and the other-being electrically connected to the metallic sheath of saidheating element to provide controlled current ow between said mounting plate and said sheath.

1l. An electric heating element assembly for application to a container for heating the contents thereof, comprising a heating element having a metallic sheath including an outer terminal portionl for extensionthrough an opening in a Wall of said container, a metallic gasket plate having an aperture for receiving'therethrough said terminal sheath portion in iiuid tight relation, a rigid backing plate in juxtaposed relation toV said gasket plate and having a plurality of transversely extending apertures, one of which is aligned with said gasket plate aperture for receiving therethrough said terminal sheath portion of said heating element, insulating means, including a at body of electrical insulation disposed between facingk surfaces of saidV gasket plate and said backing plate tol electrically insulate said backing plate from said gasket plate, ar radio-type current resistor having a body portion disposed within another of the apertures extending transversely of said backingV plate and having wire-like leads extending from opposite ends of said body portion, one of said leads being bent at an angle to said body portion and disposedl between said flat body of insulationV and the facing surface of sa'id gasket plate and the other lead being bent back along said body portion and thereafter angled for disposition between said flat body of insulation and the facing surface of said backing plate.

References Cited in the le of this patent UNTED STATES PATENTS 2,403,670. Martin July 9, 1946 2,649,532 VWoodman Aug. 18, 1,953 2,670,529 Thomas Mar. 2, 1954 2,723,340 Boggs et al Nov. 8,A 1955

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