GB2261770A - An electrical heating element - Google Patents
An electrical heating element Download PDFInfo
- Publication number
- GB2261770A GB2261770A GB9223775A GB9223775A GB2261770A GB 2261770 A GB2261770 A GB 2261770A GB 9223775 A GB9223775 A GB 9223775A GB 9223775 A GB9223775 A GB 9223775A GB 2261770 A GB2261770 A GB 2261770A
- Authority
- GB
- United Kingdom
- Prior art keywords
- rod
- switch
- sheath
- tubular sheath
- extension
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 238000010438 heat treatment Methods 0.000 title claims abstract description 15
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims abstract description 7
- 239000010949 copper Substances 0.000 claims abstract description 7
- 229910052802 copper Inorganic materials 0.000 claims abstract description 7
- 239000011819 refractory material Substances 0.000 claims abstract description 4
- 239000000463 material Substances 0.000 claims description 5
- 229910001030 Iron–nickel alloy Inorganic materials 0.000 claims description 3
- 229910001220 stainless steel Inorganic materials 0.000 claims description 3
- 239000010935 stainless steel Substances 0.000 claims description 2
- 239000011810 insulating material Substances 0.000 abstract description 4
- UGKDIUIOSMUOAW-UHFFFAOYSA-N iron nickel Chemical compound [Fe].[Ni] UGKDIUIOSMUOAW-UHFFFAOYSA-N 0.000 abstract description 4
- 238000010276 construction Methods 0.000 abstract 1
- 238000007654 immersion Methods 0.000 description 4
- 239000012530 fluid Substances 0.000 description 3
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 2
- 239000000395 magnesium oxide Substances 0.000 description 2
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910001369 Brass Inorganic materials 0.000 description 1
- 229910000640 Fe alloy Inorganic materials 0.000 description 1
- 239000010951 brass Substances 0.000 description 1
- 238000005219 brazing Methods 0.000 description 1
- 238000005485 electric heating Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B1/00—Details of electric heating devices
- H05B1/02—Automatic switching arrangements specially adapted to apparatus ; Control of heating devices
- H05B1/0202—Switches
- H05B1/0216—Switches actuated by the expansion of a solid element, e.g. wire or rod
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D23/00—Control of temperature
- G05D23/19—Control of temperature characterised by the use of electric means
- G05D23/275—Control of temperature characterised by the use of electric means with sensing element expanding, contracting, or fusing in response to changes of temperature
- G05D23/27535—Details of the sensing element
- G05D23/27541—Details of the sensing element using expansible solid
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/78—Heating arrangements specially adapted for immersion heating
- H05B3/82—Fixedly-mounted immersion heaters
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Automation & Control Theory (AREA)
- Resistance Heating (AREA)
- Thermally Actuated Switches (AREA)
Abstract
An electrical heating element having a tubular sheath 12, eg copper, enclosing a helical coil of electrical resistance wire 16 and insulating refractory material 14 is provided at one end with a thermal switch 26. An extension rod 18, eg nickel-iron, extends through a seal 20 and a length of sheath 12 which does not contain insulating material. The sheath 12 terminates with a guide bush 24 through which the rod 18 is freely slideable. The end of the rod 18 which projects outside the tube carries a snap-action switch 26 and an adjusting screw to adjust the position of the switch on the rod 18. The different coefficients of linear expansion of the sheath 12 and rod 18 lead to differential expansion of the rod 18 and tube 12 when heated until the tube actuates the switch 26, thereby controlling power to the coil 16. The rod 18 also serves as the electrical connector to the coil 16 thereby simplifying construction of the element and its terminal connection. <IMAGE>
Description
THERMOSTATIC CONTROL DEVICE
This invention relates to a thermostatic control device for electric heaters for the heating of liquids and/or gases.
At present it is the practice for electric immersion type heaters to be controlled by stem thermostats which sense the temperature of the fluid media being heated and adjusts the power inputs to the heater to hold the temperature of the fluid media within the predetermined limits. The thermostat and heater are provided as two separate units which are either mounted separately or within a common housing.
The normal domestic water immersion heater comprises an electric heating element which is brazed to a boss screwed into a flange on the cistern. The boss also carries a pocket consisting of a copper tube sealed at the end remote from the boss, which pocket houses the stem of a thermostat. The heater and the thermostat are however separate units and can be used and/or replaced if required.
One known type of stem thermostat utilises the differential expansion of a nickel-iron rod and a brass tube.
The rod is inserted in the tube and fastened at one end so as to actuate a snap action switch which controls the heater load. Some means of adjustment is usually provided to enable the thermostat to be set to operate within a desired range of temperatures.
It is common practice for heating elements used for immersion in a fluid medium to be heated, for example, water, to consist of a metallic outer tubular sheath inside which is arranged a helix of nickel-chrome wire through which the electric current is passed. The wire is insulated electrically from the sheath by a highly compacted refractory material such as magnesium oxide. A suitable terminal is welded or fastened in a similar manner, to the wire helix at each end of the sheath tube and protrudes from the respective end to receive the necessary electrical connections.
It would be advantageous to provide a unitary heating element and thermostat.
An aspect of the invention provides a heating element comprising a tubular sheath containing a helical coil of electrical resistance wire and a refractory material, the element being adapted at each end for connection to an electrical power source, characterised in that one end of the element is provided with an extension forming part of a temperature sensitive switch.
In a preferred embodiment the extension is a rod formed of a material having a relatively low thermal expansion coefficient and is at least partially enclosed by the tubular sheath which is formed of material having a relatively high thermal expansion coefficient.
Advantageously a guide bush is provided at one end of the tubular sheath, through which the extension projects and which is freely slideable therethrough.
In the preferred embodiment there is preferably provided adjusting means to adjust the position of the switch on the extension and in relation to the tubular sheath. The extension or rod is preferably of a nickel-iron alloy and the tubular sheath is advantageously of copper or stainless steel.
It will be understood that the heating element thus provided incorporates a unitary thermostatic control device which simplifies the switching mechanism and terminal connections.
A preferred embodiment of the invention will now-be described, by way of example, with reference to the accompanying drawing in which the single figure is a sectional side view of a unitary heating element and thermostat.
The heating element according to the invention is referred to generally by the reference numeral 10 and comprises a copper sheath tube 12. The tube 12 is for most of its length, filled with a highly compacted packing 14 or insulating material such as magnesium oxide and a helix 16 of nickel-chrome resistance wire. The resistance wire 16 is connected directly to a terminal (not shown) for connection to an external electric power source (not shown) at one end. At the other end the wire 16 is connected to a nickel-iron rod 18, which extends through a seal 20 and through a length of the sheath 12 which is not packed with insulating material 14.
Instead, there is provided an annular sectioned space 22 between the sheath and rod. The space 22 may be filled with insulating material or may be left empty. This part of the tube 12 extends over several inches and terminates in a guide bush 24 through which the rod 18 is freely slidable, and extends beyond the end of the sheath 12. The part of the rod 18 extending beyond the sheath 12 carries a snap action switch 26 and an adjustment screw 28 for adjusting the position of the switch 26 on the rod 18.
The heating element 10 is brazed into a mounting boss 30 which is carried on the sheath 12 near this end of the element.
The part of the element 10 containing the rod 18 with an annular clearance 22 within the sheath constitutes a stem type thermostat which is made as one unit with the element 10 it controls.
The thermostat works on known principles, i.e. the coefficient of linear thermal expansion of copper is greater than that of the nickel-iron rod 18, so that on heating differential expansion takes place and the rod 18 is apparently "sucked into" the tube 12 until at a predetermined maximum the tube 12 actuates the switch 26.
The rod 18 also serves as a connector to the heating part of the element 10 as well as functioning as part of the thermostat.
With this heating element 10, it is possible to avoid the expenses due to the provision of a pocket normally required for the thermostat, the brazing of the pocket into the head of the heater unit and a simplification of the switch mechanism and its terminals since the rod providing the mechanical actuation is now one of the terminals of the switch mechanism.
Sheath materials commonly used for immersion heaters such as copper, nickel-chrome iron alloy, or stainless steels all have a sufficiently high expansion coefficient relative to nickel-iron alloy to be usable in this invention.
Claims (9)
1. A heating element comprising a tubular sheath containing a helical coil of electrical resistance wire and a refractory material, the element being adapted at each end for connection to an electrical power source characterised in that one end of the element is provided with an extension forming part of a temperature sensitive switch.
2. An element as claimed in claim 1 in which the extension is a rod formed of a material having a relatively low thermal expansion coefficient and is at least partially enclosed by the tubular sheath which is formed of material having a relatively high thermal expansion coefficient.
3. An element as claimed in claim 2 in which a guide bush is provided at one end of the tubular sheath, through which the extension projects and which is freely slideable therethrough.
4. An element as claimed in claim 3 in which a switch is attached to one end of the extension, which switch is arranged to operate on contact with the tubular sheath.
5. An element as claimed in claim 4 in which adjusting means are provided to adjust the position of the switch on the extension and in relation to the tubular sheath.
6. An element as claimed in any preceding claim in which the rod is of a nickel-iron alloy.
7. An element as claimed in any preceding claim in which the tubular sheath is of copper.
8. An element as claimed in any of claims 1 to 6 in which the tubular sheath is of stainless steel.
9. A heating element substantially as hereinbefore described with reference to an as illustrated in the accompanying drawing.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB919124965A GB9124965D0 (en) | 1991-11-25 | 1991-11-25 | Thermostatic control device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9223775D0 GB9223775D0 (en) | 1993-01-06 |
| GB2261770A true GB2261770A (en) | 1993-05-26 |
Family
ID=10705163
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB919124965A Pending GB9124965D0 (en) | 1991-11-25 | 1991-11-25 | Thermostatic control device |
| GB9223775A Withdrawn GB2261770A (en) | 1991-11-25 | 1992-11-13 | An electrical heating element |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB919124965A Pending GB9124965D0 (en) | 1991-11-25 | 1991-11-25 | Thermostatic control device |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB9124965D0 (en) |
Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1052637A (en) * | ||||
| GB663490A (en) * | 1949-06-20 | 1951-12-19 | Genristo Ltd | Improvements in or relating to thermostatically controlled electric heating devices |
| GB864967A (en) * | 1958-06-10 | 1961-04-12 | Contactor Proprietary Ltd | Improved over-temperature heater element safety switch |
| GB940499A (en) * | 1959-09-18 | 1963-10-30 | Merlin Mouldings Ltd | Improvements in or relating to electric heating elements |
| GB1280420A (en) * | 1969-10-24 | 1972-07-05 | Emerson Electric Co | Electric heating element |
| GB2098436A (en) * | 1981-05-07 | 1982-11-17 | Ti Russell Hobbs Ltd | Electrical heating element |
| WO1990009672A1 (en) * | 1989-02-14 | 1990-08-23 | Strix Limited | Immersion heaters |
| WO1992008331A1 (en) * | 1990-10-25 | 1992-05-14 | Backer Elektro-Värme Ab | Electric tubular heating element and temperature controller therefor |
| GB2257341A (en) * | 1991-06-24 | 1993-01-06 | Sheathed Heating Elements Ltd | Heat transfer from resistance element to thermal switch. |
-
1991
- 1991-11-25 GB GB919124965A patent/GB9124965D0/en active Pending
-
1992
- 1992-11-13 GB GB9223775A patent/GB2261770A/en not_active Withdrawn
Patent Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1052637A (en) * | ||||
| GB663490A (en) * | 1949-06-20 | 1951-12-19 | Genristo Ltd | Improvements in or relating to thermostatically controlled electric heating devices |
| GB864967A (en) * | 1958-06-10 | 1961-04-12 | Contactor Proprietary Ltd | Improved over-temperature heater element safety switch |
| GB940499A (en) * | 1959-09-18 | 1963-10-30 | Merlin Mouldings Ltd | Improvements in or relating to electric heating elements |
| GB1280420A (en) * | 1969-10-24 | 1972-07-05 | Emerson Electric Co | Electric heating element |
| GB2098436A (en) * | 1981-05-07 | 1982-11-17 | Ti Russell Hobbs Ltd | Electrical heating element |
| WO1990009672A1 (en) * | 1989-02-14 | 1990-08-23 | Strix Limited | Immersion heaters |
| WO1992008331A1 (en) * | 1990-10-25 | 1992-05-14 | Backer Elektro-Värme Ab | Electric tubular heating element and temperature controller therefor |
| GB2257341A (en) * | 1991-06-24 | 1993-01-06 | Sheathed Heating Elements Ltd | Heat transfer from resistance element to thermal switch. |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9124965D0 (en) | 1992-01-22 |
| GB9223775D0 (en) | 1993-01-06 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |