AU5427101A - Heater element - Google Patents

Description

-1- Regulation 3.2

AUSTRALIA

PATENTS ACT, 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: Actual Inventor: Address for service in Australia: Invention Title: SOUTHCORP NZ LIMITED Roger Thomas Horlick and Peter Vickers A J PARK, Level 11, 60 Marcus Clarke Street, Canberra ACT 2601 Heater Element The following statement is a full description of this invention, including the best method of performing it known to me/us -2- BACKGROUND TO THE INVENTION Field of the Invention This invention relates to heater elements and in particular to heater element assemblies for electric water heaters.

Summary of the Prior Art Amongst existing prior art water heater element assemblies are those that fall within two forms for fitting to their respective water heater containers.

In one form to which the present invention relates, the heater element assembly has ooooo a threaded forged brass boss brazed onto the conductive shielding of a sheathed heater S. element. The electrodes of the heater element pass through insulated openings through the forged brass boss. In use the threaded boss is screwed into the complementary fitting in the opening of the water heater container, the house wiring live and neutral wires are connected to respective of the heater element terminals and the house wiring earth is connected to the brass boss. There is thus continuity of connection between the conductive shielding of the element and the house wiring earth through the conductivity of the brass boss and of the brazing of the copper shielding to the brass boss.

In the other form to which the present invention relates the element assembly includes a metal plate which in use is bolted to the water heater container. In this form, which is usually for use in domestic and commercial hot water heating systems where sacrificial anode may be employed, the sheath of the heater element is insulated from the mounting plate. A bridging resistor is often fitted between the element sheath and the flange to regulate the leakage current flowing to the flange (which is normally earthed).

In such assemblies the sheathed heating element is mounted through a convex copper -3mounting flange. The convex copper mounting flange is fixed to the heater assembly flange by suitable fixing means such as insulated nuts and washers. An insulating gasket is interposed between the heater element mounting flange and the heater assembly flange.

Further insulating sleeves insulate between the sheath at each end of the heater element where the respective ends pass through openings in the heater assembly mounting plate.

The bridging resistor connects between the convex copper flange and the heater assembly mounting plate. The heater assembly mounting plate in use is bolted to cover the opening of the hot water heater container with the sheathed heating element extending into the ooooo container. The convex copper mounting flange forms a watertight connection with the Sheater assembly mounting plate (together with the gasket) and with the sheathed heater element where the sheathed heater element passes therethrough, and for example may be brazed to the sheathed heater element.

A further form of this second type of heater element is shown in Australian patent i" 626359. That publication describes a water heater element assembly in which the insulating gasket between the heater element mounting flange and the heater assembly plate incorporates the sleeves for insulating between the heating element sheath and the heater assembly plate. A bridging resistor, located in a slot in the insulating gasket is clamped against the insulating gasket on one terminal by the heater element mounting flange and on the other terminal by the heater assembly plate.

A further variation is described in Australian patent 662463. This publication describes, with respect to the embodiment of Figure 1 thereof, the interposition of an elastomeric gasket between the copper mounting flange and the insulating gasket in the heater assembly described with reference to Australian patent 626359. In a further -4embodiment described with reference to Figure 2 thereof the combination of the heater assembly plate and the insulating gasket is modified by increasing the thickness of the plastic insulating gasket and reducing the thickness of the heater assembly plate.

In all of the above described prior art embodiments a watertight brazed connection is required between the heater element sheath and some part of the mounting assembly.

In the former embodiment it is between the heater element sheath and the forged brass boss. In the latter type it is between the heater element sheath and the heater element mounting flange. The inclusion of the brazed joint involves significant manufacturing ooooo cost. Each brazed joint must be tested or carefully inspected, carefully cleaned and the assembly then tin or nickel plated if required. Plating is not required if the element sheath is inherently corrosion restistant (eg stainless steel).

SUMMARY OF THE INVENTION oo It is an object of the present invention to provide a heater element assembly which "will at least go some way towards overcoming the above disadvantages or which will at ooo* least provide the public with a useful choice.

In a first aspect the invention consists in a heater element assembly comprising: a heater element enclosed in a conductive sheath formed such that two ends thereof terminate in close proximity, a conducting earthing yoke connecting with the conductive heater element sheath, an insulative plastic mounting block moulded over the said ends of said sheathed heater element and encapsulating said conductive earthing yoke, with terminal connections of said ends of said heater element extending from an exterior face of said mounting block, earthing means to providing a connection with said conductive earthing yoke from said exterior face of said mounting block, and mounting means adapted to enable watertight securement of said mounting block to a water heater container.

In a further aspect the invention consists in a method of forming a heater element assembly comprising the steps of: bending a sheathed heater element such that two ends thereof are in close proximity, ooooo fitting a metal plate earthing yoke over said ends of said heater element, such that S- said ends pass through respective openings in said earthing yoke, crimping said earthing yoke to said sheath of each said end to form a conductive connection therebetween, moulding a plastic mounting block over said ends of said sheathed heater element, mounting block encapsulating said crimped on earthing plate, and fitting electrical fittings to said heater element ends extending from said sheath ends.

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

BRIEF DESCRIPTION OF THE DRAWINGS -6- Figure 1A is a cross section on a first plane (AA in Figure 1B) through the mounting region of a heater element assembly according to a first embodiment of the present invention.

Figure 1B is a plan elevation of the outside face of the plastic mounting block of the assembly of Figure 1, including hidden detail of the earth yoke in broken line.

Figure 1C is a cross section through a second plane (BB in Figure 1B) of the assembly of Figure 1.

Figure 2A is a plan view of the exterior face of the plastic mounting block ooooo according to a second embodiment of the present invention.

-Figure 2B is a cross sectional elevation through a first plane (CC in figure 2A), including showing the mounted ends of the sheathed heater element.

Figure 2C is a plan elevation of a mounting plate for the heater element assembly including the mounting block embodiment of Figure 2A.

~Figure 2D is a side elevation of the heater element assembly taken through a second plane (DD in Figure 2A) including the heater element fixed in position and the mounting plate fixed in position to the mounting block.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring then to the Figures the present invention is described first with reference to a heating element assembly having a threaded body adapted for screwing into a complementary threaded receiving boss in a water heater container. This embodiment is depicted in Figures 1A to 1C. It is then described with reference to a further embodiment wherein a mounting plate of the heater assembly is bolted to a receiving plate on the water heater. This embodiment is depicted and described with reference to Figures 2A to 2D.

-7- The two embodiments both incorporate the present invention at least in its broadest form. In both embodiments the ends of the heating element are secured within a plastic insulative mounting block which is moulded over the ends of the element. An earthing yoke is connected to the conductive sheath of the heater element adjacent each end thereof.

The earthing yoke may be in the form of a sheet metal earthing plate with a pair of openings therethrough. The ends of the heater element pass through these openings, and the plate surrounding the openings is crimped onto the outer surface of the sheath to form .oeooi an electric conductive joint therewith. The conductiveness of this joint may be enhanced by braising or soldering. The plastic mounting block is moulded over the earthing yoke o o after the earthing yoke has beenjoined to the heating element. The plastic mounting block encapsulates the earthing yoke.

The plastic mounting block forms a seal around the sheath of the heating element !'"•"where the heating element exits the plastic mounting block. The heater element need only be tin or nickel plated (if required) over the length thereof which is not encapsulated by the plastic mounting block. Accordingly the joint between the earthing yoke and the heating element need not be tin or nickel plated and no preparation of that joint for plating is required because the exposed length of heating element is unaffected by the metal electrical processes such as brazing or welding, it may prove that the step of tin or nickel plating can be eliminated entirely.

Therefore in manufacturing the two embodiments share the common steps of: 1. bending a heating element to a useable shape with both ends adjacent; -8- 2. sealing each of the ends of the heater element, between the electrically conductive sheath thereof and the resistive element thereof to enclose the heat conductive insulative material where the conductive sheath ends; 3. fitting a metal plate earthing yoke over the ends of the heating element such that the ends pass through holes in the metal plate earthing yoke; 4. crimping the metal plate earthing yoke in the regions of the openings ooooo to form a clamped on electrically conductive connection with the p.

conductive sheath of the heating element, or otherwise forming an o *o electrically conductive connection between the metal plate earthing yoke and the conductive sheath; moulding a plastic mounting block over the heater element ends, encapsulating the earthing yoke; and 6. fitting any necessary electrical connectors such as connection terminals, to the resistive heater elements ends.

The embodiments of the heater element assembly differ in the manner in which the element assembly is to be mounted to the water heater, and therefore differ in the mounting arrangements provided. They also differ in the manner in which a link is made available between the earthing yoke and the exterior face of the plastic mounting block.

For any given product the selection of an appropriate mounting option and earthing option will depend on the prevalent or intended water heater type (and the mounting that it has) and any electrical code regulatory regime respectively.

First Embodiment Figure 1A to 1C In Figures 1A to 1C the mounting end of the heater element assembly according to the first embodiment of the present invention is shown.

A sheathed heater element 101 has the ends 102 mounted in an insulative plastic mounting block 106. The heater element 101 has a conductive outer sheath 104, a resistive heater element core 103 and a heat conductive but electrically insulative barrier material 105 such as magnesium oxide therebetween. A sealant 117 such as epoxy resin is provided between the sheath 104 and the resistive element 103 where the sheath 104 ooooo ends to enclose the barrier material 105. The sheathed heater element thus described is of conventional and well known form.

An earthing yoke 107 is conductively connected to the conductive sheath 104 of the sheathed element 101. The earthing yoke 107 preferably comprises a conductive sheet metal pressing having a pair of openings 108 therethrough. The ends 102 of the sheathed element 101 pass through the openings 108. The immediate regions 109 of the earthing yoke 107 are deformed or crimped to engage against the conductive sheath 104. This crimped engagement is preferably sufficient to provide a reliable conductive connection.

However the conductive joint may be enhanced by braising the joint.

The conductive yoke 107 is depicted having a hole 118 therethrough (Figure 1 B) to improve the plastic moulding process and the strength of the plastic block 106 by improving contiguity of the plastic block 106.

An earth connection terminal 111 having a threaded bore for receiving a clamping screw, is provided at least partly outside the plastic block 106 and is connected to the sheet metal earthing yoke 107, for example by rivet 112. To provide for the form of the plastic block 106 the earthing yoke 107 has a step 110 therein between the region 109 clamping to the sheathed element 101 and the earth connector 111.

The plastic mounting block 106 has a forward portion 119 and a rearward portion 113. The forward portion has a thread (represented by 115 but not drawn in detail) formed on the outer surface thereof which in use will engage with the thread of a threaded boss of the water heater to which the heating element will be fitted. The thread for example might be a 1 /4 "BSP thread. A short forwardly extending sleeve 116 surrounds the heater element where each end thereof exits the inside face of the mounting block. The sleeve 116 provides extra surface contact between the plaster block of the element improving sealing between the plastic block 106 and the sheathed heater element 101. The rearward portion 113 has a plurality of outwardly facing flats 120 formed therearound, for example 6 flats forming a hexagon. The flats are for engagement by a hand tool for assisting rotation of the heater element when fitting to a water heater. Such hand tool is most :"•'commonly a pipe wrench of appropriate size. A rebate 114 is provided in the exterior face of the rearward portion 113. The rebate 114 accommodates a portion of the heater element terminals. The ends of the resistive heater elements extend from the plastic block 106 into the space provided by rebate 114. Appropriate connectors are fitted to these ends. The earth terminal 111 of the earthing yoke 107 also protrudes into the space provided by rebate 114.

The block is preferably formed by injection moulding over the other components.

It may be of any suitable plastic material. Certain polyphthalamide poly-phenylene sulphide and polyamide materials have been found to meet the necessary requirements.

One such material is available from BP Amoco Polymers Inc under the trade name -11-

AMODEL.

Second Embodiment Figure 2A to 2D In Figures 2A to 2D the mounting end of the heater element assembly according to the second embodiment of the present invention is shown.

A sheathed heater element 201 has the ends 202 mounted in an insulative plastic mounting block 206. The heater element 201 has a conductive outer sheath 204, a resistive heater element core 203 and a heat conductive but electrically insulative barrier *oo 205 such as magnesium oxide therebetween. A sealant 217 such as epoxy resin is 0* provided between the sheath 204 and the resistive element 203 where the sheath 204 ends to enclose the barrier material 205. The sheathed heater element thus described is of conventional and well known form.

An earthing yoke 207 is conductively connected to the conductive sheath 204 of •the sheathed element 202. The earthing yoke 207 preferably comprises a conductive sheet metal pressing having a pair of openings 208 therethrough. The ends 202 of the sheathed element 201 pass through the openings 208. The immediate regions 209 of the earthing yoke 207 are deformed or crimped to engage against the conductive sheath 204. This crimped engagement is preferably sufficient to provide a reliable conductive connection.

However the conductive joint may be enhanced by bracing the joint.

The conductive yoke 207 spans between the ends 202 of the sheathed element 201.

A small area 211 of the yoke 207 is exposed to access from the exterior side of the plastic block 206 via a cavity 212 in the exterior face of the plastic block 206.

The plastic mounting block 206 has a forward portion 233 and a rearward portion -12- 232. The forward portion 233 is sized to fit within the circular opening of the hot water heater to which it is intended to be installed. The rearward portion 232 forms a flange having a greater outward extension than the forward portion 233. This flange has an annular front face 234 which in use will sealingly bear against the sealing face of the water heater opening. The rearward portion 232 of the plastic block 206 also has a pair ofrearwardly extending plastic sleeves 230 formed integrally therewith. The sleeves 230 encase the sheathed heater element ends 202 for a short length rearward from the rearward face of the plastic block 206. A pair of holes 231 are provided in the plastic block 206 for oSooo* screws or other fasteners to engage within as will be discussed below.

*o A conductive mounting plate 235 is secured to the rearward face of the plastic o oo block 206. The mounting plate 235 comprises a substantially square metal plate 239. The metal plate 239 has a number, for example four, of holes 236 at the periphery thereof. In use bolts passing through these holes and secured in threaded holes of the water heater •°mounting face will draw the heater assembly against the water heater mounting face such that the annular front face 234 will bear against that mounting surface.

Holes 237 are provided in the metal plate 239 to align with the holes 231 extending into the plastic block from the exterior face thereof. Fasteners 240 passing through the holes 237 of the metal plate 239 engage and are tightened within the holes 231 of the plastic block. Tightening of the fasteners 240 draws the plastic block 206 and metal plate 239 together.

Further holes 238 are provided in the metal plate 239. The holes 238 are sized and located such that the sleeves 230 extending rearwardly from the exterior face of the plastic block 206 pass therethrough. The sleeves thereby insulate the conductive sheath 204 of -13the heater element 201 from the conductive metal mounting plate 239.

Where necessary, for effecting the earthing connection between the earthing yoke 207 and the conductive metal mounting plate 239 a bridging resistor 241 is fitted within the aforementioned cavity 212 in the plastic block 206. One leg 242 of the resistor 241 is clamped between the metal mounting plate 239 and the exterior face of the plastic block 206 and the other leg thereof is pressed against the exposed surface of plate 207 within cavity 206. The resister 214 is mounted within a plastic carrier 250 such that the second leg 243 thereof passes outside the housing 250. The housing 250 is sized to fit snugly 0..

within the cavity 212. When the mounting plate 239 is engaged against the plastic block 233 the mounting plate 239 presses against the plastic housing 250 causing the rearface of the plastic housing 250 to press a second leg 243 of the resistor 241 against the exposed surface of earthing yoke 207.

WE CLAIM: 1. A heater element assembly comprising: a heater element enclosed in a conductive sheath formed such that two ends thereof terminate in close proximity,

Claims (14)

1. A heater element assembly comprising: a heater element enclosed in a conductive sheath formed such that two ends thereof terminate in close proximity, -14- a conducting earthing yoke connecting with the conductive heater element sheath, an insulative plastic mounting block moulded over the said ends of said sheathed heater element and encapsulating said conductive earthing yoke, with terminal connections of said ends of said heater element extending from an exterior face of said mounting block, earthing means providing a connection with said conductive earthing yoke from said exterior face of said mounting block, and mounting means adapted to enable watertight securement of said mounting *see*: block to a water heater container. S0•

2. A heater element as claimed in claim 1 wherein said conducting earthing yoke 0:00 :00% connects with the conductive heat element sheath adjacent each of the ends of said heater element. *00

3 A heater element as claimed in either claim 1 or claim 2 wherein said conducting earthing yoke comprises a metal plate having a pair of openings therethrough, said V metal plate at said openings crimped onto said conductive sheath of said ends of said heating element which pass through said openings such as to provide 0* V conductive connection therewith.

4. A heater element as claimed in any one of claims 1 to 3 wherein said earthing means comprises a threaded terminal connected to said earthing yoke and extending from said exterior face of said mounting block.

A heater element as claimed in any one of claims 1 to 3 including a metal mounting flange secured to said exterior face of said insulative mounting block and wherein said earthing means comprise a bridging resistor extending beyond said exterior face of said insulative mounting block and connecting with said metal mounting flange.

6. A heater element as claimed in any one of claims 1 to 4 wherein said heater assembly mounting means comprise a threaded forward portion of said mounting block for threading engagement in a threaded opening of a water heater container and tool engagement means on a rearward portion of said mounting block for engagement by a tool for assisting rotation of said mounting block and threading of the forward portion of said mounting block into a threaded opening. o

7. A heater element as claimed in any one of claims 1 to 3 and 5 wherein said heater p. assembly mounting means comprise a metal plate fixable to said exterior face of e:g. *000 o eg 6said mounting block such that terminals of said heater element extend therethrough, said plate having a plurality of mounting holes by which said plate can be secured by fasteners to a water heater container, and fastening means secure said mounting plate to said mounting block. 00. 0.00

8. A heater element as claimed in any one of claims 1 to 7 wherein said insulative mounting block is formed from moulded plastic material.

9. A heater element as claimed in claim 8 wherein said plastic material is selected from a polyphthalamide, a polyphenylene sulphide, or a polyamide.

A method of forming a heater element assembly comprising the steps of: bending a sheathed heater element such that two ends thereof are in close proximity, fitting a metal plate earthing yoke over said ends of said heater element, such that said ends pass through respective openings in said earthing yoke, crimping said earthing yoke to said sheath of each said end to form a conductive -16- connection therebetween, moulding a plastic mounting block over said ends of said sheathed heater element, said mounting block encapsulating said crimped on earthing plate, and fitting electrical fittings to said heater element ends extending from said sheath ends.

11. A method as claimed in claim 10 including the further step of applying a sealant at each of the ends of said heater element between the open ends of the sheath thereof and the heater element extending therefrom.

12. A heater element assembly substantially as herein described with reference to and ease s •as illustrated by figures 1 A to 1 C of the accompanying drawings.

13. A heater element assembly substantially as herein described with reference to and o. oas illustrated by Figures 2A to 2D of the accompanying drawings. 0 6

14. A method of forming a heater element, said method substantially as °herein described with reference to the drawings. *000 000 *005 0@ 0