CA2108887A1 - Electric heater and method of making a heater - Google Patents
Electric heater and method of making a heaterInfo
- Publication number
- CA2108887A1 CA2108887A1 CA002108887A CA2108887A CA2108887A1 CA 2108887 A1 CA2108887 A1 CA 2108887A1 CA 002108887 A CA002108887 A CA 002108887A CA 2108887 A CA2108887 A CA 2108887A CA 2108887 A1 CA2108887 A1 CA 2108887A1
- Authority
- CA
- Canada
- Prior art keywords
- moulding
- heating element
- heater
- electric heaters
- casing
- 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.)
- Abandoned
Links
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 7
- 238000010438 heat treatment Methods 0.000 claims abstract description 52
- 238000000465 moulding Methods 0.000 claims abstract description 31
- 239000000463 material Substances 0.000 claims abstract description 27
- 239000004033 plastic Substances 0.000 claims abstract description 22
- 229920003023 plastic Polymers 0.000 claims abstract description 22
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 7
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 7
- 239000002245 particle Substances 0.000 claims abstract description 5
- 239000000758 substrate Substances 0.000 claims abstract description 5
- 239000003365 glass fiber Substances 0.000 claims abstract description 3
- 239000012777 electrically insulating material Substances 0.000 claims abstract 2
- 238000000034 method Methods 0.000 claims description 21
- 239000000206 moulding compound Substances 0.000 claims description 13
- 229910052751 metal Inorganic materials 0.000 claims description 11
- 239000002184 metal Substances 0.000 claims description 11
- 238000000748 compression moulding Methods 0.000 claims description 5
- 230000005611 electricity Effects 0.000 claims description 4
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 5
- 229910052802 copper Inorganic materials 0.000 description 5
- 239000010949 copper Substances 0.000 description 5
- 229920000728 polyester Polymers 0.000 description 5
- 229910052782 aluminium Inorganic materials 0.000 description 4
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 4
- 239000003677 Sheet moulding compound Substances 0.000 description 3
- 239000004411 aluminium Substances 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 150000001875 compounds Chemical class 0.000 description 2
- 239000011810 insulating material Substances 0.000 description 2
- 238000009413 insulation Methods 0.000 description 2
- 125000006850 spacer group Chemical group 0.000 description 2
- 229920001187 thermosetting polymer Polymers 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- RNFJDJUURJAICM-UHFFFAOYSA-N 2,2,4,4,6,6-hexaphenoxy-1,3,5-triaza-2$l^{5},4$l^{5},6$l^{5}-triphosphacyclohexa-1,3,5-triene Chemical compound N=1P(OC=2C=CC=CC=2)(OC=2C=CC=CC=2)=NP(OC=2C=CC=CC=2)(OC=2C=CC=CC=2)=NP=1(OC=1C=CC=CC=1)OC1=CC=CC=C1 RNFJDJUURJAICM-UHFFFAOYSA-N 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000003251 chemically resistant material Substances 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000001125 extrusion Methods 0.000 description 1
- 239000003063 flame retardant Substances 0.000 description 1
- 238000009787 hand lay-up Methods 0.000 description 1
- 238000001746 injection moulding Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000000615 nonconductor Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 238000007650 screen-printing Methods 0.000 description 1
- 239000002689 soil Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 229920001169 thermoplastic Polymers 0.000 description 1
- 239000004416 thermosoftening plastic Substances 0.000 description 1
- 238000001721 transfer moulding 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
- H05B3/00—Ohmic-resistance heating
- H05B3/20—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater
- H05B3/22—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible
- H05B3/28—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible heating conductor embedded in insulating material
- H05B3/286—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible heating conductor embedded in insulating material the insulating material being an organic material, e.g. plastic
-
- A—HUMAN NECESSITIES
- A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
- A01K—ANIMAL HUSBANDRY; AVICULTURE; APICULTURE; PISCICULTURE; FISHING; REARING OR BREEDING ANIMALS, NOT OTHERWISE PROVIDED FOR; NEW BREEDS OF ANIMALS
- A01K63/00—Receptacles for live fish, e.g. aquaria; Terraria
- A01K63/06—Arrangements for heating or lighting in, or attached to, receptacles for live fish
- A01K63/065—Heating or cooling devices
-
- 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
- H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
- H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
- H05B3/14—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
- H05B3/146—Conductive polymers, e.g. polyethylene, thermoplastics
-
- 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
- H05B3/20—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater
- H05B3/22—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible
- H05B3/28—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible heating conductor embedded in insulating material
-
- 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
- H05B3/20—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater
- H05B3/22—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible
- H05B3/28—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible heating conductor embedded in insulating material
- H05B3/283—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible heating conductor embedded in insulating material the insulating material being an inorganic material, e.g. ceramic
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Environmental Sciences (AREA)
- Engineering & Computer Science (AREA)
- Biodiversity & Conservation Biology (AREA)
- Animal Husbandry (AREA)
- Chemical & Material Sciences (AREA)
- Marine Sciences & Fisheries (AREA)
- Ceramic Engineering (AREA)
- Inorganic Chemistry (AREA)
- Resistance Heating (AREA)
- Surface Heating Bodies (AREA)
- Central Heating Systems (AREA)
- Air-Conditioning For Vehicles (AREA)
Abstract
An electric heater comprises a heating element (10) encapsulated in a rigid plastics moulding (11). The element may be in the form of a flexible sheet and may comprise a substrate of electrically insulating material such as a woven glass-fibre mat (12), coated with electrically resistive material, such as a plastics material containing carbon particles. A method of making the heater is also disclosed.
Description
~T/IB~ 92 /Oo 68 9 21~8~87 3~ 3u~e 199~
ELECTRIC HEATER AND A HETHOD OF MA~ING A HEATER
This invention relates to an electric heater and a method of making a heater.
According to a first aspect of the lnvention there is provided a method of making an electric heater comprising a heating element encapsulated in a rigid plastics moulding and means for connecting the heating element to a source of electricity externally of the moulding, the method comprising the steps of:-(a) placing the heating element between twosheets of a moulding compound, and (b) subjecting the assembly comprising the heating element and the two sheets of moulding compound to a compression moulding step, wherein (c) part of the connecting means adjacent to, and not disposed between, the two sheets of moulding compound i5 protected from exposure to excessive heat during the moulding step.
Preferably, the part of the connecting means adjacent to, and not disposed between, the two sheets of ~ ~, F ~
. ~ , . ~ ' 3a June ~993 2 ~ ~8~
-2~ 21~;~689 mouldlng compound is contained within a metal retaining device during the moulding step. In this case, the metal retaining device is, preferably, positively located in the mould during the moulding process.
Preferably, the heating element is in the form of a flexible sheet.
Preferably, the heating element comprises an electrically insulating substrate, such as a flexible woven mat, coated with electrically resistive material, such as a plastics (or other) material containing carbon particles. In this latter case, the resistivity of the electrically resistive material can be predetermined by the amount of carbon in the plastics material.
Preferably, the heating element is disposed in the rigid plastics moulding adjacent to a major external surface of the moulding, and typically is spaced not substantially more than about 2mm from said major surface of the moulding.
In many applications it will be desirable to arrange for the heating element to be substantially equi-distantly spaced from each of two opposite major externalsurfaces of the moulding in order to radiate heat from said two surfaces. However, in other applications it may be desirable to arrange for the heating element to be . . . . .. ~
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.
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closer one major surface than the other.
A metal plate may be secured to at least one of the major external surfaces of the rigid plastics moulding to increase the area over which heat is dispersed.
According to a second aspect of the invention there is provided an electric heater made by a method according to the first aspect of the invention.
According to a third aspect of the invention there is provided a heating device comprising a casing, a plurality of electric heaters according to the second aspect of the invention mounted in spaced relationship in the casing, and means for causing air to pass over the electric heaters.
Preferably there are at least three of said electric heaters and the spaces between adjacent pairs of electric heaters are connected together in series.
According to a fourth aspect of the invention, there is provided a heating device comprising a casing, at least three electric heaters mounted in spaced relationship in the casing, and means for causing air to pass over the electric heaters, wherein each electric heater comprises a heating element encapsulated in a rigid plastics moulding and means for connecting the heating ,' 't: ~li F7'.'1t~ V-- 3 ~
` 2~8~7 -3a- -~ J~ 1993 element to a source of electrlcity externally of the moulding and wherein the spaces between adjacent pairs of electric heaters are connected together in series.
The invention will now be more particularly described, by way of example, with reference to the accompanying drawing, in which:
Figure 1 is a partly cutaway perspective view of a heater according to the first aspect of the present invention, Figure 2 is a perspective view illustrating one step in the manufacture of a heating according to the third aspect of the invention, Figure 3 is a side view of part of a compression moulding machine, 1~ SUBSTlTUTa S~T
r~: .i~l Ac~licatlon . ~
.
2 1 ~ 7 ; `
Figures 4 to 6 show alternative embodiments of a heater according to the present invention, Figure 7 is a vertical section taken through part of one embodiment of a heating device according to the second aspect of the invention, and Figure 8 is a sectional view taken along line VIII - VIII of Figure 7.
Referring to Figure 1 of the drawings, the heater shown therein is in the form of a panel and comprises a heating element 10 encapsulated in a rigid plastics moulding 11.
The heating element 10 is in the form of a flexible sheet and comprises a woven glass-fibre mat 12 provided with a resistive coating of plastics material containing carbon particles, and two copper ribbons 13 stitched or otherwise secured to opposite edges of the Z0 mat 12.
The heating element 10 also has wire or cable terminations 14 sheathed in rubber or pvc insulation and soldered as at 15 to respective copper ribbons 13 for connecting the heating element to a source of electricity.
- In some circumstances, it may be desirable to , : ,: - , -- :
, . ' ~ ~` ' . ' , W092/2020~ 8 ~ ~ 7 PCT/GB92/00689 -5~
provide four spaced copper ribbons 13 on the mat 12 to avoid hot spots developing in the heating element 10.
In this case, alternate copper ribbons will be electrically connected together.
The panel is typically about 4mm thick with the heating element 10 substantially equi-~istantly spaced from each major external surface of t~e panel.
It follows that the heating element 10 is within about 2mm of each major external surface of the panel. This is important if heat is to be radiated by both major surfaces as plastics material is a poor conductor of heat. There may however be applications in which it is desirable to radiate heat from only one major surface of the panel or to radiate more heat from one than the other surface. In this case, the heating element is arranged closer to the one surface.
The encapsulating process may be carried out by conventional moulding methods, including compression moulding, transfer moulding, injection moulding, casting, hand lay up G.R.P and extrusion moulding.
Typically, however, the encapsulating process is carried out by compression moulding.
The encapsulating material may be any appropriate heat resistant plastics material, including both thermosetting and thermoplastics materials.
, - ' ' ' .
W O 92/20200 P ~ /GB92/00689 2~8~7 -6-Typically, the encapsulating material is a thermosetting polyester but other plastics materials wili also withstand temperatures of about 200 c without showing signs of degradation. It is desirable that the plastics material should also be impact resistant.
Certain polyester sheet moulding compounds supplied by DSM Compounds UK Limited, of 5 Civ~c Way, Ellesmere Port, South Wirral, have been found to be suitable. In particular, the sheet moulding compound sold under their grade no. 5520 has been found to be suitable when a flame retardant material is required and the sheet moulding compound sold under their grade no.
47-5710 has been found to be suitable when a chemically resistant material is required.
The plastics material of the resistive coating of the heating element 10 is typically a polyester based compound and the resistivity of the coating can be predetermined by the amount of carbon in the plastics material in order to tailor the heating element 10 to give specific watt densities. At given electrical input values, this will determine the maximum attainable temperature of a given heater and theoretically it is possible to produce heating elements which will work on any specific a.c. or d.c. voltage.
The maximum temperature attainable by the W092t20200 2 l ~ 3 8 ~ 7 PCT/GB92/00689 . .
heater is dependent on the watt density of the heating element 10, the power available and the temperature characteristics of the encapsulating material.
A metal plate, typically of aluminium, may be secured to at least one of the major external surfaces of the moulding to increase the area over which heat is dispersed.
One method of making the panel will now be more particularly described with reference to Figures 2 and 3.
Firstly, referring to Figure 2, a sheet 16 of polyester moulding compound is laid on a suitable non-stick surface. The heating element 10 is then laid in position directly on top of the sheet 16 and the cable terminations 14 are located in a groove in the lower half of a two part cable retaining device 17 supported in a jig 18. A further sheet (not shown) of polyester moulding compound is then laid directly over the heating element 11 and pressed flat. The upper half (not shown) of the cable retainlng device 17 is then located on the lower half thereof and the two halves of the cable retaining device are fastened together with sc~ews. The purpose of the cable retaining device 17 is to prevent the insulation on the cable terminations 14 rom becoming damaged by heat during the moulding process.
210 8 ~ 8--The device 17 may, therefore, be made of metal and it is important that it should abut the edges of ~he two sheets of moulding compound.
The assembly comprising the two sheets of moulding compound, the heating element 10 and the cable retaining device 17 is then placed into a compxession moulding machine 20 (see Figure 3) and the mould is closed. Two spigots 21, only one of which is shown, in the lower part of the mould extend into holes 22 in the cable retaining device 17 and a spring loaded plunger 23 in the upper part of the mould bears against the upper surface of the retaining device 17, to positively locate the retaining device 17 and ensure that the mould cavity is closed.
After moulding, the aforesaid assembly is removed from the mould 20 and cooled. The cable retaining plate 17 is removed from the assembly and used, after cooling in cold water, for a subsequent moulding operation.
To ensure even flow of material in the mould, it may prove necessary to provide additional moulding material at appropriate positions on the outer surfaces of sheets of moulding compound. This can be done by laying strips of the moulding compound below the lower sheet 16 and on top of the upper sheet.
~ W092l20200 2 PCT/GB92/00689 :
_g _ The panel need not be flat but could be profiled, such as is shown in Figure 4, to suit a particular application, this being made possible by the flexible nature of the heating element 10.
The panel can be of any desired colour and, if required, can have a decorative finish applied by spraying or silk screen printing The heater is fully insulated and water proof enabling it to be immersed in a liquid or exposed to wet or damp environments. Also, by ensuring that no air is included in the panel, oxidation of the heating element 10 and the connections between the element 10 and the terminations 14 will be prevented, thus ensuring a long element life.
The heater described above can be used in any application requiring a constant source of heat. For example it has application in cabinet heaters (anti-condensation/anti-frost panels), fishpond heaters, under soil heaters, heated brewing pads, under desk heaters, aquarium and vivarium heaters, ceiling heaterg, diesel tank heaters (especially for motor vehicles), incubators, plant and seed propagators, food heaters, railway point heaters, and heated electrical insulators.
: .
., ~1~2~87 -lo-In the case of ceiling heaters, these could look like, and be substituted for, selected ceiling tiles, particularly above work areas.
In the case of railway point heaters, these could include a metal slipper attached to one surface of the heater. The slipper could be coated in PTFE which is chemically etched to the metal.
The heater need not be in the form of a panel. It could be of any other appropriate shape, and may, for example, be in the shape of a vessel, such as is shown in Figure 5, or in the shape of a tube, such as is shown in Figure 6.
Referring now to Figures 7 and 8 of the drawings, the heating device shown therein comprises a casing 30 and a heater unit 31, which comprises a plurality of spaced apart heaters 32 (typically six in number), mounted in the casing 30. The heating device also comprises a fan 33 for drawing air in through an air intake opening 34 at the lower end of one side of the casing 30 and for causing that air to pass serially between adjacent pairs of heaters 32 before exiting through an air outlet 35 at the upper end of the casing 30.
Each heater 32 has a metal plate 36, typically , ~ .
W092/20200 "~ c~Q~ PCT/GB92/00689 of aluminium, secured to each of its two major external surfaces to disperse heat over substantially the entire surface area of the heater. The heaters 32 are assembled into the unit 31 by threaded rods 37 which extend through aligned apertures in the heaters 32, by spacers 38 mounted on the threaded rods 37 between adjacent pairs of heaters 32, and by nuts 39 which co-operate with the ends of the threaded rods 37-to clamp ' the heaters 32 and the spacers 38 together.
Adjacent heaters 32 are staggered vertically with respect to one another, as best shown in Figure 8, and panels 40 of thermally insulating material are fixed to top and bottom of the heater unit 31 so as to extend over all but the foremost heater 32 at the bottom and the rearmost heater 32 at the top so that the spaces between each pair of adjacent heaters are connected together in series. The front, rear and two sides of the heater unit 31 are also preferably covered by panels of thermally insulating material.
The casing 30 is formed of aluminium and comprises an inner lower part 3Oa, which extends below and serves to support the heater unit 31 and to house the fan 33, and an outer part 30_ which houses the heater unit 31 and which extends over and is secured to the lower part 30a, typically by rivets.
.:
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W092~20200 PCT/GB92/00689 2 ~a'~r~ -12-The top of the outer casing part 30_ may be in the form of a h~nged lid 30c which can be pivoted between a position as shown- in Figure 8 in which it defines the air outlet 35 and a closed position when the heating device is not being used.
The heating device also comprises an on/off switch 42, an indicator light 43, a cable clamp 44, and a thermal cut-out device 45.
The heating device described with reference to Figures 7 and 8 is a space heater which will run off a 24 volt supply, typically drawing about 8 amps. It has particular application as a heater for the cab of a heavy goods vehicle which it can heat without difficulty.
The embodiments described above are given by way of example only and various modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined by the appended claims. For example, whilst it is highly desirable for the heating element to be flexible, it need not necessarily comprise a woven mat coated with resistive material. It could instead comprise any other appropriate electrically insulating substrate supporting resistive material or could be a resistive sheet such as :, :
W092/20200 ; ! . . 2 ~ ~ ~ 8 ~ 7 PCT/GB92/00689 1 " ~
a mat formed from a single aluminum strand. Also, the copper ribbons could be replaced by any other appropriate conductlve strips. Also, the heating element could be made up of two or more parts connected electrically in series.
... ...
. .
ELECTRIC HEATER AND A HETHOD OF MA~ING A HEATER
This invention relates to an electric heater and a method of making a heater.
According to a first aspect of the lnvention there is provided a method of making an electric heater comprising a heating element encapsulated in a rigid plastics moulding and means for connecting the heating element to a source of electricity externally of the moulding, the method comprising the steps of:-(a) placing the heating element between twosheets of a moulding compound, and (b) subjecting the assembly comprising the heating element and the two sheets of moulding compound to a compression moulding step, wherein (c) part of the connecting means adjacent to, and not disposed between, the two sheets of moulding compound i5 protected from exposure to excessive heat during the moulding step.
Preferably, the part of the connecting means adjacent to, and not disposed between, the two sheets of ~ ~, F ~
. ~ , . ~ ' 3a June ~993 2 ~ ~8~
-2~ 21~;~689 mouldlng compound is contained within a metal retaining device during the moulding step. In this case, the metal retaining device is, preferably, positively located in the mould during the moulding process.
Preferably, the heating element is in the form of a flexible sheet.
Preferably, the heating element comprises an electrically insulating substrate, such as a flexible woven mat, coated with electrically resistive material, such as a plastics (or other) material containing carbon particles. In this latter case, the resistivity of the electrically resistive material can be predetermined by the amount of carbon in the plastics material.
Preferably, the heating element is disposed in the rigid plastics moulding adjacent to a major external surface of the moulding, and typically is spaced not substantially more than about 2mm from said major surface of the moulding.
In many applications it will be desirable to arrange for the heating element to be substantially equi-distantly spaced from each of two opposite major externalsurfaces of the moulding in order to radiate heat from said two surfaces. However, in other applications it may be desirable to arrange for the heating element to be . . . . .. ~
'tl ~alf~ Of~
- ~ lonal ~ al c, ~- -~.
.
' , ' ~;
2 ~ ~ ~; 8 '~
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closer one major surface than the other.
A metal plate may be secured to at least one of the major external surfaces of the rigid plastics moulding to increase the area over which heat is dispersed.
According to a second aspect of the invention there is provided an electric heater made by a method according to the first aspect of the invention.
According to a third aspect of the invention there is provided a heating device comprising a casing, a plurality of electric heaters according to the second aspect of the invention mounted in spaced relationship in the casing, and means for causing air to pass over the electric heaters.
Preferably there are at least three of said electric heaters and the spaces between adjacent pairs of electric heaters are connected together in series.
According to a fourth aspect of the invention, there is provided a heating device comprising a casing, at least three electric heaters mounted in spaced relationship in the casing, and means for causing air to pass over the electric heaters, wherein each electric heater comprises a heating element encapsulated in a rigid plastics moulding and means for connecting the heating ,' 't: ~li F7'.'1t~ V-- 3 ~
` 2~8~7 -3a- -~ J~ 1993 element to a source of electrlcity externally of the moulding and wherein the spaces between adjacent pairs of electric heaters are connected together in series.
The invention will now be more particularly described, by way of example, with reference to the accompanying drawing, in which:
Figure 1 is a partly cutaway perspective view of a heater according to the first aspect of the present invention, Figure 2 is a perspective view illustrating one step in the manufacture of a heating according to the third aspect of the invention, Figure 3 is a side view of part of a compression moulding machine, 1~ SUBSTlTUTa S~T
r~: .i~l Ac~licatlon . ~
.
2 1 ~ 7 ; `
Figures 4 to 6 show alternative embodiments of a heater according to the present invention, Figure 7 is a vertical section taken through part of one embodiment of a heating device according to the second aspect of the invention, and Figure 8 is a sectional view taken along line VIII - VIII of Figure 7.
Referring to Figure 1 of the drawings, the heater shown therein is in the form of a panel and comprises a heating element 10 encapsulated in a rigid plastics moulding 11.
The heating element 10 is in the form of a flexible sheet and comprises a woven glass-fibre mat 12 provided with a resistive coating of plastics material containing carbon particles, and two copper ribbons 13 stitched or otherwise secured to opposite edges of the Z0 mat 12.
The heating element 10 also has wire or cable terminations 14 sheathed in rubber or pvc insulation and soldered as at 15 to respective copper ribbons 13 for connecting the heating element to a source of electricity.
- In some circumstances, it may be desirable to , : ,: - , -- :
, . ' ~ ~` ' . ' , W092/2020~ 8 ~ ~ 7 PCT/GB92/00689 -5~
provide four spaced copper ribbons 13 on the mat 12 to avoid hot spots developing in the heating element 10.
In this case, alternate copper ribbons will be electrically connected together.
The panel is typically about 4mm thick with the heating element 10 substantially equi-~istantly spaced from each major external surface of t~e panel.
It follows that the heating element 10 is within about 2mm of each major external surface of the panel. This is important if heat is to be radiated by both major surfaces as plastics material is a poor conductor of heat. There may however be applications in which it is desirable to radiate heat from only one major surface of the panel or to radiate more heat from one than the other surface. In this case, the heating element is arranged closer to the one surface.
The encapsulating process may be carried out by conventional moulding methods, including compression moulding, transfer moulding, injection moulding, casting, hand lay up G.R.P and extrusion moulding.
Typically, however, the encapsulating process is carried out by compression moulding.
The encapsulating material may be any appropriate heat resistant plastics material, including both thermosetting and thermoplastics materials.
, - ' ' ' .
W O 92/20200 P ~ /GB92/00689 2~8~7 -6-Typically, the encapsulating material is a thermosetting polyester but other plastics materials wili also withstand temperatures of about 200 c without showing signs of degradation. It is desirable that the plastics material should also be impact resistant.
Certain polyester sheet moulding compounds supplied by DSM Compounds UK Limited, of 5 Civ~c Way, Ellesmere Port, South Wirral, have been found to be suitable. In particular, the sheet moulding compound sold under their grade no. 5520 has been found to be suitable when a flame retardant material is required and the sheet moulding compound sold under their grade no.
47-5710 has been found to be suitable when a chemically resistant material is required.
The plastics material of the resistive coating of the heating element 10 is typically a polyester based compound and the resistivity of the coating can be predetermined by the amount of carbon in the plastics material in order to tailor the heating element 10 to give specific watt densities. At given electrical input values, this will determine the maximum attainable temperature of a given heater and theoretically it is possible to produce heating elements which will work on any specific a.c. or d.c. voltage.
The maximum temperature attainable by the W092t20200 2 l ~ 3 8 ~ 7 PCT/GB92/00689 . .
heater is dependent on the watt density of the heating element 10, the power available and the temperature characteristics of the encapsulating material.
A metal plate, typically of aluminium, may be secured to at least one of the major external surfaces of the moulding to increase the area over which heat is dispersed.
One method of making the panel will now be more particularly described with reference to Figures 2 and 3.
Firstly, referring to Figure 2, a sheet 16 of polyester moulding compound is laid on a suitable non-stick surface. The heating element 10 is then laid in position directly on top of the sheet 16 and the cable terminations 14 are located in a groove in the lower half of a two part cable retaining device 17 supported in a jig 18. A further sheet (not shown) of polyester moulding compound is then laid directly over the heating element 11 and pressed flat. The upper half (not shown) of the cable retainlng device 17 is then located on the lower half thereof and the two halves of the cable retaining device are fastened together with sc~ews. The purpose of the cable retaining device 17 is to prevent the insulation on the cable terminations 14 rom becoming damaged by heat during the moulding process.
210 8 ~ 8--The device 17 may, therefore, be made of metal and it is important that it should abut the edges of ~he two sheets of moulding compound.
The assembly comprising the two sheets of moulding compound, the heating element 10 and the cable retaining device 17 is then placed into a compxession moulding machine 20 (see Figure 3) and the mould is closed. Two spigots 21, only one of which is shown, in the lower part of the mould extend into holes 22 in the cable retaining device 17 and a spring loaded plunger 23 in the upper part of the mould bears against the upper surface of the retaining device 17, to positively locate the retaining device 17 and ensure that the mould cavity is closed.
After moulding, the aforesaid assembly is removed from the mould 20 and cooled. The cable retaining plate 17 is removed from the assembly and used, after cooling in cold water, for a subsequent moulding operation.
To ensure even flow of material in the mould, it may prove necessary to provide additional moulding material at appropriate positions on the outer surfaces of sheets of moulding compound. This can be done by laying strips of the moulding compound below the lower sheet 16 and on top of the upper sheet.
~ W092l20200 2 PCT/GB92/00689 :
_g _ The panel need not be flat but could be profiled, such as is shown in Figure 4, to suit a particular application, this being made possible by the flexible nature of the heating element 10.
The panel can be of any desired colour and, if required, can have a decorative finish applied by spraying or silk screen printing The heater is fully insulated and water proof enabling it to be immersed in a liquid or exposed to wet or damp environments. Also, by ensuring that no air is included in the panel, oxidation of the heating element 10 and the connections between the element 10 and the terminations 14 will be prevented, thus ensuring a long element life.
The heater described above can be used in any application requiring a constant source of heat. For example it has application in cabinet heaters (anti-condensation/anti-frost panels), fishpond heaters, under soil heaters, heated brewing pads, under desk heaters, aquarium and vivarium heaters, ceiling heaterg, diesel tank heaters (especially for motor vehicles), incubators, plant and seed propagators, food heaters, railway point heaters, and heated electrical insulators.
: .
., ~1~2~87 -lo-In the case of ceiling heaters, these could look like, and be substituted for, selected ceiling tiles, particularly above work areas.
In the case of railway point heaters, these could include a metal slipper attached to one surface of the heater. The slipper could be coated in PTFE which is chemically etched to the metal.
The heater need not be in the form of a panel. It could be of any other appropriate shape, and may, for example, be in the shape of a vessel, such as is shown in Figure 5, or in the shape of a tube, such as is shown in Figure 6.
Referring now to Figures 7 and 8 of the drawings, the heating device shown therein comprises a casing 30 and a heater unit 31, which comprises a plurality of spaced apart heaters 32 (typically six in number), mounted in the casing 30. The heating device also comprises a fan 33 for drawing air in through an air intake opening 34 at the lower end of one side of the casing 30 and for causing that air to pass serially between adjacent pairs of heaters 32 before exiting through an air outlet 35 at the upper end of the casing 30.
Each heater 32 has a metal plate 36, typically , ~ .
W092/20200 "~ c~Q~ PCT/GB92/00689 of aluminium, secured to each of its two major external surfaces to disperse heat over substantially the entire surface area of the heater. The heaters 32 are assembled into the unit 31 by threaded rods 37 which extend through aligned apertures in the heaters 32, by spacers 38 mounted on the threaded rods 37 between adjacent pairs of heaters 32, and by nuts 39 which co-operate with the ends of the threaded rods 37-to clamp ' the heaters 32 and the spacers 38 together.
Adjacent heaters 32 are staggered vertically with respect to one another, as best shown in Figure 8, and panels 40 of thermally insulating material are fixed to top and bottom of the heater unit 31 so as to extend over all but the foremost heater 32 at the bottom and the rearmost heater 32 at the top so that the spaces between each pair of adjacent heaters are connected together in series. The front, rear and two sides of the heater unit 31 are also preferably covered by panels of thermally insulating material.
The casing 30 is formed of aluminium and comprises an inner lower part 3Oa, which extends below and serves to support the heater unit 31 and to house the fan 33, and an outer part 30_ which houses the heater unit 31 and which extends over and is secured to the lower part 30a, typically by rivets.
.:
`''',:
' :, , . , , . ~:
W092~20200 PCT/GB92/00689 2 ~a'~r~ -12-The top of the outer casing part 30_ may be in the form of a h~nged lid 30c which can be pivoted between a position as shown- in Figure 8 in which it defines the air outlet 35 and a closed position when the heating device is not being used.
The heating device also comprises an on/off switch 42, an indicator light 43, a cable clamp 44, and a thermal cut-out device 45.
The heating device described with reference to Figures 7 and 8 is a space heater which will run off a 24 volt supply, typically drawing about 8 amps. It has particular application as a heater for the cab of a heavy goods vehicle which it can heat without difficulty.
The embodiments described above are given by way of example only and various modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined by the appended claims. For example, whilst it is highly desirable for the heating element to be flexible, it need not necessarily comprise a woven mat coated with resistive material. It could instead comprise any other appropriate electrically insulating substrate supporting resistive material or could be a resistive sheet such as :, :
W092/20200 ; ! . . 2 ~ ~ ~ 8 ~ 7 PCT/GB92/00689 1 " ~
a mat formed from a single aluminum strand. Also, the copper ribbons could be replaced by any other appropriate conductlve strips. Also, the heating element could be made up of two or more parts connected electrically in series.
... ...
. .
Claims (16)
1. A method of making an electric heater comprising a heating element encapsulated in a rigid plastics moulding and means for connecting the heating element to a source of electricity externally of the moulding, the method comprising the steps of:-(a) placing the heating element between two sheets of a moulding compound, and (b) subjecting the assembly comprising the heating element and the two sheets of moulding compound to a compression moulding step, characterised in that (c) part of the connecting means adjacent to, and not disposed between, the two sheets of moulding compound is protected from exposure to excessive heat during the moulding step.
2. A method as claimed in claim 1, wherein that part of the connecting means adjacent to, and not disposed between, the two sheets of moulding compound is contained within a metal retaining device during the moulding step.
3. A method as claimed in claim 2, wherein the metal retaining device is positively located in the mould during the moulding process.
4. A method as claimed in any one of the preceding claims, wherein the heating element is in the form of a flexible sheet.
5. A method as claimed in any one of the preceding claims, wherein the heating element comprises a substrate of electrically insulating material, coated with electrically resistive material.
6. A method as claimed in claim 5, wherein the substrate is in the form of a woven mat.
7. A method as claimed in claim 6, wherein the mat is of woven glass-fibres.
8. A method as claimed in any one of claims 5 to 7, wherein the electrically resistive material includes carbon particles.
9. A method as claimed in claim 8, wherein the electrically resistive material is a plastics material containing carbon particles.
10. A method as claimed in any one of the preceding claims, wherein the heating element is disposed in the rigid plastics moulding adjacent to a major external surface of the heater.
11. A method as claimed any one of the preceding claims, wherein the encapsulating material is an impact resistant plastics moulding.
12. A method as claimed in any one of the preceding claims, wherein a metal plate is secured to at least one of the major external surfaces of the rigid plastics moulding.
13. An electric heater made by a method according to any one of the preceding claims.
14. A heating device comprising a casing, a plurality of electric heaters according to claim 13 mounted in spaced relationship in the casing, and means for causing air to pass over the electric heaters.
15. A heating device as claimed in claim 14, wherein there are at least three of said electric heaters and the spaces between adjacent pairs of electric heaters are connected together in series.
16. A heating device comprising a casing, at least three electric heaters mounted in spaced relationship in the casing, and means for causing air to pass over the electric heaters, wherein each electric healer comprises a heating element encapsulated in a rigid plastics moulding and means for connecting the heating element to a source of electricity externally of the moulding and wherein the spaces between adjacent pairs of electric heaters are connected together in series.
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9109110-8 | 1991-04-26 | ||
| GB919109110A GB9109110D0 (en) | 1991-04-26 | 1991-04-26 | Electric heater |
| GB9206453-4 | 1992-03-25 | ||
| GB9206453A GB2255262B (en) | 1991-04-26 | 1992-03-25 | Electric heater and method of making same |
| PCT/GB1992/000689 WO1992020200A1 (en) | 1991-04-26 | 1992-04-15 | Electric heater and method of making same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2108887A1 true CA2108887A1 (en) | 1992-10-27 |
Family
ID=26298798
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002108887A Abandoned CA2108887A1 (en) | 1991-04-26 | 1992-04-15 | Electric heater and method of making a heater |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0581796A1 (en) |
| JP (1) | JPH06506790A (en) |
| AU (1) | AU1547192A (en) |
| CA (1) | CA2108887A1 (en) |
| GB (1) | GB2281017B (en) |
| WO (1) | WO1992020200A1 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2266949A (en) * | 1992-05-11 | 1993-11-17 | John Anthony Page | Low energy wall space-heaters |
| FR2725104B1 (en) * | 1994-09-27 | 2000-01-14 | Guerleau Patrick | CARBON HEATING |
| WO1999002014A1 (en) * | 1997-07-02 | 1999-01-14 | Beckers Karl Heinz | Electric radiator |
| EP0919120A1 (en) * | 1997-11-20 | 1999-06-02 | AB7 Industries SA | Intermediate aquarium support sheet combining the functions of heating and of absorbing mechanical stresses |
| CN102625497A (en) * | 2012-03-30 | 2012-08-01 | 常熟市海晟电器有限公司 | Carbon-fiber electric heating device |
| DE102016208587A1 (en) * | 2016-05-19 | 2017-11-23 | Robert Bosch Gmbh | Device for heating a fluid stored in a reservoir, method for producing such a device |
| KR102508218B1 (en) * | 2022-09-20 | 2023-03-09 | 한화시스템(주) | Multilayer detachable cabinet for ship mounting |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE500534C (en) * | 1927-04-09 | 1930-06-21 | Aeg | Process for the production of electric radiators |
| DE1778570A1 (en) * | 1968-05-11 | 1972-03-23 | Kurt Gaiser | Electric surface heating |
| FR2251151A1 (en) * | 1973-11-09 | 1975-06-06 | Triplet Albert | Electrically heater plate for incubation chamber - has resistance wire embedded in plastics sheet |
| GB1498792A (en) * | 1974-12-13 | 1978-01-25 | Hobbs R Ltd | Liquid heating vessels |
-
1992
- 1992-03-25 GB GB9421353A patent/GB2281017B/en not_active Expired - Fee Related
- 1992-04-15 WO PCT/GB1992/000689 patent/WO1992020200A1/en not_active Application Discontinuation
- 1992-04-15 CA CA002108887A patent/CA2108887A1/en not_active Abandoned
- 1992-04-15 AU AU15471/92A patent/AU1547192A/en not_active Abandoned
- 1992-04-15 EP EP19920908296 patent/EP0581796A1/en not_active Withdrawn
- 1992-04-15 JP JP4507737A patent/JPH06506790A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPH06506790A (en) | 1994-07-28 |
| EP0581796A1 (en) | 1994-02-09 |
| GB2281017B (en) | 1995-05-03 |
| GB2281017A (en) | 1995-02-15 |
| AU1547192A (en) | 1992-12-21 |
| GB9421353D0 (en) | 1994-12-07 |
| WO1992020200A1 (en) | 1992-11-12 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |