GB2103431A - Heater assemblies for vessels for heating liquids - Google Patents

Abstract

A switch assembly, in a heater assembly of a vessel for heating liquids, has a body 21 defining recesses 23 which accommodate conical connecting portions 12 of flexible metal conductors 11 secured to the body 21 at a portion 10. Each portion 12 has a flange 14 which abuts the body 21 as a cold tail pin 31 of a heater 32 to 35 of the heater assembly is pushed into the portion 12 during assembly of the vessel. In use, the conductors flex to reduce the stresses applied to the element seals 35 due to differential thermal expansion and contraction of various parts of the assemblies, whilst the pins are gripped by the portions 12 to provide good electrical contact therebetween. <IMAGE>

Description

SPECIFICATION Heater assemblies for vessels for heating liquids This invention concerns improvements relating to heater assemblies for vessels for heating liquids.

There are known heater assemblies which comprise an electrical immersion heater element assembly and a switch assembly, wherein the latter is secured to a head of the element assembly and includes thermally responsive means arranged to actuate a switch of the switch assembly to interrupt a supply of electricity to the element assembly in the event of a hot spot on the head exceeding a predetermined temperature; and wherein the element assembly comprises a metal sheathed mineral insulated heating element which terminates at pins (known as "cold tails") which project from the head and are electrically connected to the switch assembly. Such heater assemblies are hereinafter referred to as being "of the kind described" for the sake of brevity.

In several known forms of heater assemblies of the kind described, the cold tail pins are soldered to fixed rigid conductors in the switch assemblies. In order to avoid soidered connections, fasteners were developed to effect electrically conductive mechanical connections (such as those described in British Patent Specification No: 1290596). However such fasteners require the cold tail pins, rigid conductors and fasteners themselves to be made to close tolerances, are expensive to fit and are difficult to remove for repairing the switch or element.

in other forms of heater assemblies of the kind described, the switch assemblies are provided with resilient spring blade conductors which abut and thrust against the tips of the cold tail pins, for as example as shown in Figure 5 in British Patent Specification No. 892685, to effect electrical connections. Whilst such spring connections obviate the need for mechanical fasteners, the tips have to be accurately formed from or coated with a corrosion resistant material such as silver solder at considerable expense, and the springs apply a considerable mechanical load to the cold tail pins, which load has to be resisted by the pin to sheath sealing material at the ends of the element.

What is needed is a method and means for effecting electrical connections between the cold tail pins and the switch conductors so as to obviate the need for soldering, fasteners or expensive preparation of the tips of the cold tail pins, and reduce the load applied to the sealing material at the ends of the element.

According to the present invention there is provided a switch assembly of a heater assembly of the kind described, comprising a neutral conductor and a live conductor, wherein each of said conductors comprises a first portion mounted on a body of the switch assembly, a connector portion, and, between the latter and the first portion, an intermediate portion of flexible strip form; wherein each connector portion is of hollow substantially frusto-conical form so as to provide a socket for a cold tail pin, which socket tapers convergentlyfrom a mouth; wherein a flange is provided on the connector portion at or adjacent the mouth, which flange is joined to the -intermediate portion; and wherein the body pro vides at least one shoulder or abutment for support ing the flange.

The connector portion may be interrupted lon gitudinally by a slit so as to have a C-shaped cross section, and the flange may be similarly interrupted.

The or each conductor may have a further resi liently flexible portion which carries a switch contact.

The conductors are preferably of a beryllium cop per alloy or like material.

The invention includes a heater assembly ofthe kind described wherein the cold tail pins are held in connector portions of the switch assembly of the invention.

The invention will be described further, by way of example, with reference to the accompanying diag rammatic drawings, wherein: Figures 1 and 2 show, in plan and side elevation, a neutral conductor of a switch assembly of the invention; and Figure 3 is a sectional diagram showing the con ductorin situ in a heater assembly which incorpo rates the switch assembly.

Referring to Figures 1 and 2, the neutral conductor is formed from flexible metal sheet or strip material so as to comprise a first portion 10, an intermediate portion 11 of flexible blade form, and a connector portion 12. The connector portion 12 is of hoilow substantially frusto-conical form so as to provide an internal socket which tapers convergently from a mouth 13. A brim flange 14 extends substantially around the mouth and joins the connector portion 12 to the portion 11.

A slit 15 extends longitudinally of the connector portion 12 and interrupts the flange 14.

A fixing aperture 16 is provided in the first portion 10.

As shown in Figure 3, the neutral conductor is located between two parts 20 and 21 of a body of a switch assembly which is secured to a head 22 of an element assembly.

The parts 20 and 21 serve respectively as the thermal insulating member and carrier member of the switch assembly which is either of nonautomatic form as described in our published co pending Great Britain Application No: 2042857A or of automatic form as described in our published co-pending Application No. 2056777A, both of which applications describe the general arrangement of the switch and element assemblies, and reference should be made to these co-pending Applications.

In the heater assembly of the present invention the carrier member 21 is provided with an elongate recess 23 which accommodates the connector portion 12; and is shaped to cooperate with the thermal insulating member 20 to leave a narrow space 24 therebetween to accommodate the flange 14 and intermediate portion 11. The narrow space 24 is preferably sufficiently wide to provide a slight clearance between switch body 20, 21 and the flange 14 and portion 11 so that the portion 11 can bend to allow connector portion 12 to move slightly along the recess 23 before the flange 14 abuts either of the parts 20 and 21 to halt said movement.

The first portion 10 is secured to the carrier member 21 by a neutral terminal pin 25, for connection to a mains connector.

The switch assembly includes a live conductor (not shown) which is similar to the neutral conductor hereinbefore described in that it includes an intermediate portion 11, connector portion 12 and flange 14, but has a first portion which is secured to the part 21 by a peg (not shown) and has, remote from the portion 12, a spring blade portion which carries one of a pair of switch contacts as described in our aforesaid co-pending published Applications, (e.g.

see Figures 8 to 11 in No. 2042847 parts referenced 45 and 62). The switch body provides a further narrow space 24 and recess 23 for the live conductor.

The thermal insulating member 20 provides two tapered stepped passages 30 for cold tail pins 31 of an element 32 which has a metal sheath 33 secured to the head 22. Mineral insulation 34 is provided between the element and the sheath, and the ends of the sheath, around the pins 31 are sealed by seals 35 of a sealing compound, in known manner. The pins 31 extend through the passages 30 into the sockets so as to be gripped by the connector portions 12.

The live and neutral conductors and the switch assemblyofthe invention off several advantages.

For example, the switch assembly can be simply pushed towards the head so as to insert the cold tail pins into the connector portions, whilst the brim flanges abut and are supported by the body, whereby to obviate the need for fasteners, the labour involved in fitting the fasteners and the sockets in the switch body for the fasteners. The outer ends 26 of the recesses 23 in the body may be closed to prevent ingress of dirt and water into the recesses.

Furthermore, the use of fasteners or solder requires the cold tail pins to be held rigidly to the body so that the seals 35 are stressed during the heating cycles as the components of the heater assembly expand and contract, whereas in the present switch assembly the connector portions can move with the cold tail pins to a degree sufficient to relieve the seals of most of the stresses which would otherwise exist during the heating cycles thus reducing the risk of fatigue failure of the seals and the resultant short circuiting of the element.

In comparison with the known spring connections, the switch assembly of the invention obviates the need to prepare the tips of the cold tail pins and relieves the seals of the continuous spring loads which can cause damage if the adhesion of the seals is reduced by radial expansion and contraction of the sheaths and pins during the heating cycles.

Also, the switch assembly is readily removable from the element assembly, e.g. for repair of either assembly, and it is immaterial if the pins become slightly damaged or dirty because the peripheral surface of the pins will be wiped or scraped during reassembly by the connector portions; whereas if the tips of the pins which abut the known spring contacts become damaged or dirty to give faulty contacts, overheating will arise in the switch assembly.

The invention is not confined to the precise details of the foregoing example, and many variations and modifications are possible within the scope of the invention.

For example, the slit 15 may be widened, e.g. up to about 100" of arc, whilst retaining the ability of the connector portion to embrace the pin, or the slit may be omitted, but the provision of a slit is preferred as it permits the tolerances on the diameter of the pins to be relaxed. The brim flange may be reduced to an arcuately short flange or flanges, but a flange extending substantially around the mouth is preferred to stiffen the connector portion against radial expansion and to provide good support during insertion of the pins, whereby to enable the conductor to be made from relatively thin flexible material.

The taper of the connector portion may be selected to suit the diameter and tolerances of the pins, the length of the connector portion and the thickness ofthe material employed, but it is preferred to have the median diameter of the internal socket substantially equal to the nominai pin diameter.

Claims (8)

1. A switch assembly, for a heater assembly of the kind described, comprising a neutral conductor and a live conductor, wherein each of said conductors comprises a first portion mounted on a body of the switch assembly, a connector portion, and, between the latter and the first portion, an intermediate portion of flexible strip form; wherein each connector portion is of hollow substantially frusto-conical form so as to provide a socket for a cold tail pin, which socket tapers convergentlyfrom a mouth; wherein a flange is provided on the connector portion at or adjacent the mouth, which flange is joined to the intermediate portion; and wherein the body provides at least one shoulder or abutment for supporting the flange.

2. A switch assembly as claimed in claim 1 wherein the connector portion is interrupted longitudinally by a slit.

3. A switch assembly as claimed in claim 2 wherein the flange is interrupted by said slit.

4. A switch assembly as claimed in claim 1,2 or 3 wherein the or each conductor has a further resi lientlyflexible portion which carries a switch contact.

5. A switch assembly substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

6. A heater assembly of the kind described comprising a switch assembly as claimed in any one of claims 1 to 4, wherein the cold tail pins are held in the connector portions.

7. A heater assembly as claimed in claim 6 wherein the tapes of the connector portion is selected so that the median diameter of the internal socket, prior to insertion of the cold tail pin, is equal to the nominal diameter of the cold tail pin.

8. A heater assembly substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.