CA1178319A - Electrical heating element - Google Patents
Electrical heating elementInfo
- Publication number
- CA1178319A CA1178319A CA000389394A CA389394A CA1178319A CA 1178319 A CA1178319 A CA 1178319A CA 000389394 A CA000389394 A CA 000389394A CA 389394 A CA389394 A CA 389394A CA 1178319 A CA1178319 A CA 1178319A
- Authority
- CA
- Canada
- Prior art keywords
- heating element
- fuse
- lead
- resistance
- layer
- 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.)
- Expired
Links
Abstract
H.A.Bergersen et al 4-1 (Revision) Abstract of the Disclosure Electrical resistance heating element including a number of metal strips arranged in a meander-like pattern.
In the resistance metal strips, which are made from a non-expensive base sheet material like lead, there is incorporated at least one fuse which will operate if the heat transfer from a randomly placed area of critical size (a critical area) is substantially blocked. The fuse or fuses are preferably constituted by a lead/tin alloy rolled into intimate contact with the lead base material.
In the resistance metal strips, which are made from a non-expensive base sheet material like lead, there is incorporated at least one fuse which will operate if the heat transfer from a randomly placed area of critical size (a critical area) is substantially blocked. The fuse or fuses are preferably constituted by a lead/tin alloy rolled into intimate contact with the lead base material.
Description
H. A. Bergersen et al 4-1 . (Revision) 1~7~3319 ELECTRICAL RESI5TANCE ~EATING ELEMENT
- Background of the Invention ~ he present invention relates to electrical resistance he~ting elements and in partic.ular to elements having a flat S configuration and consisting of a number of metal strips - arranged in a meander like pattern.embedded in or laminated withi~.an-insulation ~ody.
- ---Such heating elements are well known from U.S. Patents Nos. 3,263,307 and 3,336,557 ~both to O.G. Lund et al) as wèll as from U.S. Patents Nos. 4,~25,893 and ~,092,626 (both to H.A. Bergersen), a main feature of these inventions being that-the resistance metal strips are mads of a material having a-melt-ing point lower than 200C. When such elements are used às electrical heating of apartments and houses and the install~tion necessitates close contact with combustible~
mat-erial such as wood and wallpaper, i~ is essential that the temperature rise of the heating element surroundings at no place exceeds 150~C. This requirement can be achieved by using as a resistance strip a metal alloy consisting of 61.5~ tin, 37.7~ lead and 0.8% antimony, which has a melt-ing point at 183C.
A heating element, where low melting resistance strips are welded between two layers of insulating material, acts as one large thermal fuse if it is operated under abnormal conditions, for example, when it is unduly covered by heat insulating materials. When the temperature in such cases approaches the melting point of the alloy (170C+), the mechanical properties of the foil strips become very poor, and in this state, the foil may fracture at any time before the melting point is reached. At the moment the strip H.A. Bergersen et al 4-1 (Revision) ~7833~9 fracture starts, the cross-section of the strip is reduced~
and it melts instantly, causing the current-path to be broken.
The heating element must thereafter be replaced with a new one.
There are, however, also known resistance heating elements having only one fuse. Such elements are for instance described in U.S. Patent No. 3,417,229 (G.J. Shomphe et al), in which there is inserted a thermal fuse ~or each individual heater unit. Such units will only be guarded against over-heating if the fuse itself is overheated. Such overheating will occur either-if the fuse itself is'excessively thermally insulated or if ~he heater unit draws excessive current. The fuse-will melt at a desired temperature when overheated and ~ cut the current so that the heater unit itself probably need~not be replaced. If, however, a hea-ter unit area some-what-displaced from the fuse is overheated, the wallpaper and: surroundings may catch fire before the fuse cuts the current-path.
- The-safest type of resistance heating el~ments is ' therefore considered to be that previously described. Experi-i~ 20 ments have shown, however, that it is not necessary for each and every square centimeter of the resistance element to be capable of fusing at 'the desired low temperature.
- - ' Summary o~ the Invention ~he'main objec~ of the present invention is the'provision 25- of a new'and improved heating element which maintains the excellent hea~Lng and installation properties of existing ele~ents.' `
'` A feature of the invention is the provision of an electrical resistance heating element in which at least one fuse portion is incorporated in a resistance metal strip.
By using a heating element in accordance with the present inv~ntion thermal overheating will cause breakdown of the current path at defined places, improving the safety and reducing the risk of overheating The thermal fuses must be distributed in such a way that if the resistance element, in addition to the usual installa-tion covering, i5 partly covered by various items, such as - boarding, furniture, carpets, etc., the surface temperature - ~
H.A. Bergersen et al 4-1 ~L7~3~L~3 ( Revi s ion ) on the covered area must a~ no place exceed a critical value.
The degree of unauthorized covering may vary with type and size of material or article, and the worst case will occur if ;heat transfer from a certain area is effectively blocked.
By experiments it will be possible to de~exmine the maximum size of a randomly placed area of the heating element which may be effec~ively thermally insulated without causing rise of the ~urface temperature to ~he critical value at any place within the covered area. This area is called the critical area. The thermal fuses will there~ore have to be distributed - in ~such a way that at least one such ~use will operate if an area-larger than the critical area is covered sufficiently to ~lock the heat transfer.
In many instances, ~hermal insulation of a certain area of a hea~ing element is not effective. In experiments done in=order to de~ine--the critical area, a lO0 mm thick mineral wool mat was used às excess covering on the outside of the regu~ax sur~ace material.
~ In order to simulate a heating element ceiling installa-tion, the following arrangement was used. A heating element, 500 x 1200-mm in size~ constructed from meander formed lead ~antimony strips laminated between plastic sheets, was installed between a~200 mm thick mineral wool mat in horizontal position and a 12 mm thick chip board, the board facing downward. At -stabiIized condi~ions, the heating element was operatingat 210 W/m with a maximum temperature on the chip board o~ 78~C.
In order to simulate harmful covering of the ceiling, pieces of 100 mm thick mineral wool mats were placed against the lower side of the chip board. The critical temperature was chosen to be 175C, and the critical area turned out to be in the order of 400 cm2. The size of the critical area -will decrease with decreased chip board thickness. It will also decrease if the chip board is exchanged with materials having lower sideways heat conduction. The preferred shape for the critical area is a circle, but a square will give a close approximation.
~ - ~, 7~3~9 The well-known process of making heating elements of the described type is to start from a block of a desired alloy and roll this block into a metal sheet of 5-25 ,u thickness.
The sheet is thereafter cut to produce a des;red resistance strip web, e.g. a meander pattern, while laminating the resis-tance strip with insulation material on one or both sides.
When making a suitable resistance element of the pre-sent invention, it is essential that the main metal component is inexpensive, and lead is still considered to be the most suitable material. However, in order to make the lead sheet less brittle, it should be alloyed with about 1% antimony.
The distributed discrete thermal fuses are obtained by locally introducing a layer of metal that alloys to lead giving a composition having a melting point lower than 200C.
A suitable material is a metal selected from the group consis-ting of tin, lead/tin/antimony alloy and lead/bisrnuth alloy.
In summary, according to a first broad aspect of the present invention, there is provided a method for making an electrical heating element comprising: forming a sheet of electrical resistance material; arranging a layer of fuse material in a predetermined pattern on the resistance material;
pressing the fuse material and the resistance material together to form a layer of uniform thickness, and cutting the pressed layer in a meander pattern.
According to a second broad aspect of the present invention, there is provided an electrical heating element comprising: a layer of an electrical resistance material having a predetermined melting temperature; and a fuse material having a melting temperature below said predetermined melting temper-ature arranged in a predetermined pattern incorporated in saidresistance material, saidfuse material having been pressed 33~9 into said resistance material to form a layer havin~ a uniform thickness.
Brief Description of the Drawing The above mentioned and other objects and features of the present invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:
Figure 1 illustrates various ways of thermal fuse arrangements, Figure 2 schematically shows fuse material placed on a base material sheet, Figure 3 illustrates alternative fuse material arrange-ments on a heating element, and Figure 4 shows examples of discrete thermal fuses on the resistance strips.
Description of the Preferred Embodiment ... ... _ .
There are, as illustrated in Figure 1, several ways of introducing thermal fuses in the resistance strip. In Figure la the base material 1 is provided with an insert 2 of fuse material. In Figure lb the fuse material 2 is embedded between two base material layers. In Figure lc the base -4a-3~
- H.A. Bergersen et al 4-1 (Revision) material sheet or strip is broken by a full cross-section of fuse material 2. While a cross-section as illustrated in Fig. la and lb can be obtained by a rolling process, the Fig. lc version will also include a soldering process before rolling. Fig. 2 schematically illustrates various ways of arranging fuse material strips 2 on an uncut base material sheet 1.
When the materials 1 and 2 illustrated in Figs 1 and 2 are lead and tin respectively (preferably the fuse material
- Background of the Invention ~ he present invention relates to electrical resistance he~ting elements and in partic.ular to elements having a flat S configuration and consisting of a number of metal strips - arranged in a meander like pattern.embedded in or laminated withi~.an-insulation ~ody.
- ---Such heating elements are well known from U.S. Patents Nos. 3,263,307 and 3,336,557 ~both to O.G. Lund et al) as wèll as from U.S. Patents Nos. 4,~25,893 and ~,092,626 (both to H.A. Bergersen), a main feature of these inventions being that-the resistance metal strips are mads of a material having a-melt-ing point lower than 200C. When such elements are used às electrical heating of apartments and houses and the install~tion necessitates close contact with combustible~
mat-erial such as wood and wallpaper, i~ is essential that the temperature rise of the heating element surroundings at no place exceeds 150~C. This requirement can be achieved by using as a resistance strip a metal alloy consisting of 61.5~ tin, 37.7~ lead and 0.8% antimony, which has a melt-ing point at 183C.
A heating element, where low melting resistance strips are welded between two layers of insulating material, acts as one large thermal fuse if it is operated under abnormal conditions, for example, when it is unduly covered by heat insulating materials. When the temperature in such cases approaches the melting point of the alloy (170C+), the mechanical properties of the foil strips become very poor, and in this state, the foil may fracture at any time before the melting point is reached. At the moment the strip H.A. Bergersen et al 4-1 (Revision) ~7833~9 fracture starts, the cross-section of the strip is reduced~
and it melts instantly, causing the current-path to be broken.
The heating element must thereafter be replaced with a new one.
There are, however, also known resistance heating elements having only one fuse. Such elements are for instance described in U.S. Patent No. 3,417,229 (G.J. Shomphe et al), in which there is inserted a thermal fuse ~or each individual heater unit. Such units will only be guarded against over-heating if the fuse itself is overheated. Such overheating will occur either-if the fuse itself is'excessively thermally insulated or if ~he heater unit draws excessive current. The fuse-will melt at a desired temperature when overheated and ~ cut the current so that the heater unit itself probably need~not be replaced. If, however, a hea-ter unit area some-what-displaced from the fuse is overheated, the wallpaper and: surroundings may catch fire before the fuse cuts the current-path.
- The-safest type of resistance heating el~ments is ' therefore considered to be that previously described. Experi-i~ 20 ments have shown, however, that it is not necessary for each and every square centimeter of the resistance element to be capable of fusing at 'the desired low temperature.
- - ' Summary o~ the Invention ~he'main objec~ of the present invention is the'provision 25- of a new'and improved heating element which maintains the excellent hea~Lng and installation properties of existing ele~ents.' `
'` A feature of the invention is the provision of an electrical resistance heating element in which at least one fuse portion is incorporated in a resistance metal strip.
By using a heating element in accordance with the present inv~ntion thermal overheating will cause breakdown of the current path at defined places, improving the safety and reducing the risk of overheating The thermal fuses must be distributed in such a way that if the resistance element, in addition to the usual installa-tion covering, i5 partly covered by various items, such as - boarding, furniture, carpets, etc., the surface temperature - ~
H.A. Bergersen et al 4-1 ~L7~3~L~3 ( Revi s ion ) on the covered area must a~ no place exceed a critical value.
The degree of unauthorized covering may vary with type and size of material or article, and the worst case will occur if ;heat transfer from a certain area is effectively blocked.
By experiments it will be possible to de~exmine the maximum size of a randomly placed area of the heating element which may be effec~ively thermally insulated without causing rise of the ~urface temperature to ~he critical value at any place within the covered area. This area is called the critical area. The thermal fuses will there~ore have to be distributed - in ~such a way that at least one such ~use will operate if an area-larger than the critical area is covered sufficiently to ~lock the heat transfer.
In many instances, ~hermal insulation of a certain area of a hea~ing element is not effective. In experiments done in=order to de~ine--the critical area, a lO0 mm thick mineral wool mat was used às excess covering on the outside of the regu~ax sur~ace material.
~ In order to simulate a heating element ceiling installa-tion, the following arrangement was used. A heating element, 500 x 1200-mm in size~ constructed from meander formed lead ~antimony strips laminated between plastic sheets, was installed between a~200 mm thick mineral wool mat in horizontal position and a 12 mm thick chip board, the board facing downward. At -stabiIized condi~ions, the heating element was operatingat 210 W/m with a maximum temperature on the chip board o~ 78~C.
In order to simulate harmful covering of the ceiling, pieces of 100 mm thick mineral wool mats were placed against the lower side of the chip board. The critical temperature was chosen to be 175C, and the critical area turned out to be in the order of 400 cm2. The size of the critical area -will decrease with decreased chip board thickness. It will also decrease if the chip board is exchanged with materials having lower sideways heat conduction. The preferred shape for the critical area is a circle, but a square will give a close approximation.
~ - ~, 7~3~9 The well-known process of making heating elements of the described type is to start from a block of a desired alloy and roll this block into a metal sheet of 5-25 ,u thickness.
The sheet is thereafter cut to produce a des;red resistance strip web, e.g. a meander pattern, while laminating the resis-tance strip with insulation material on one or both sides.
When making a suitable resistance element of the pre-sent invention, it is essential that the main metal component is inexpensive, and lead is still considered to be the most suitable material. However, in order to make the lead sheet less brittle, it should be alloyed with about 1% antimony.
The distributed discrete thermal fuses are obtained by locally introducing a layer of metal that alloys to lead giving a composition having a melting point lower than 200C.
A suitable material is a metal selected from the group consis-ting of tin, lead/tin/antimony alloy and lead/bisrnuth alloy.
In summary, according to a first broad aspect of the present invention, there is provided a method for making an electrical heating element comprising: forming a sheet of electrical resistance material; arranging a layer of fuse material in a predetermined pattern on the resistance material;
pressing the fuse material and the resistance material together to form a layer of uniform thickness, and cutting the pressed layer in a meander pattern.
According to a second broad aspect of the present invention, there is provided an electrical heating element comprising: a layer of an electrical resistance material having a predetermined melting temperature; and a fuse material having a melting temperature below said predetermined melting temper-ature arranged in a predetermined pattern incorporated in saidresistance material, saidfuse material having been pressed 33~9 into said resistance material to form a layer havin~ a uniform thickness.
Brief Description of the Drawing The above mentioned and other objects and features of the present invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:
Figure 1 illustrates various ways of thermal fuse arrangements, Figure 2 schematically shows fuse material placed on a base material sheet, Figure 3 illustrates alternative fuse material arrange-ments on a heating element, and Figure 4 shows examples of discrete thermal fuses on the resistance strips.
Description of the Preferred Embodiment ... ... _ .
There are, as illustrated in Figure 1, several ways of introducing thermal fuses in the resistance strip. In Figure la the base material 1 is provided with an insert 2 of fuse material. In Figure lb the fuse material 2 is embedded between two base material layers. In Figure lc the base -4a-3~
- H.A. Bergersen et al 4-1 (Revision) material sheet or strip is broken by a full cross-section of fuse material 2. While a cross-section as illustrated in Fig. la and lb can be obtained by a rolling process, the Fig. lc version will also include a soldering process before rolling. Fig. 2 schematically illustrates various ways of arranging fuse material strips 2 on an uncut base material sheet 1.
When the materials 1 and 2 illustrated in Figs 1 and 2 are lead and tin respectively (preferably the fuse material
2 should be a lead/tin alloy), it is assumed that the heat resulting from normal operation of the heating element will cause the materials in the contacting area to alloy so that the small portion of the alloyed material will have a desired melting point of about 180~C. It may, however, be 'more desirable to ensure during the manu~acturing process and_before placing the heating element into normal operation tha~'the base~f~se'contact area is alloyed to have the desired melting point.
~hen a heating element is manufactured according to the above or other methods, an element is obtained wherein any one of--the distributed discrete thermal fuses will alloy in a ratio of-approxLmately 60% tin and 40% lead, melt and break the cùrrent path if a randomly placed area of a certain size tcritical areaj o the heating element including the thermal fuse is covered in an unauthorized manner.
~ While thè material of the resistance metal strips has bee~'indicated as lead and tin as well as lead and bismuth, othe~ materials may be used, for examplet steel as base material and silver/copper as fuse material, or chromium/
nickel as base material and brass as fuse material, etc.
Fig. 3 illustrates three alternative ways of arranging fuse material strips 7 on a heating element 5. The electrical resistance strips 6 are for convenience indicated to form a meander pattern, but it should be obvious that the resistance strip or strips can be arranged in any convenient manner.
While the fuse material strips are shown as full drawn lines, it will be understood that the fuse strips will not form a current path along these lines. This statement is at least
~hen a heating element is manufactured according to the above or other methods, an element is obtained wherein any one of--the distributed discrete thermal fuses will alloy in a ratio of-approxLmately 60% tin and 40% lead, melt and break the cùrrent path if a randomly placed area of a certain size tcritical areaj o the heating element including the thermal fuse is covered in an unauthorized manner.
~ While thè material of the resistance metal strips has bee~'indicated as lead and tin as well as lead and bismuth, othe~ materials may be used, for examplet steel as base material and silver/copper as fuse material, or chromium/
nickel as base material and brass as fuse material, etc.
Fig. 3 illustrates three alternative ways of arranging fuse material strips 7 on a heating element 5. The electrical resistance strips 6 are for convenience indicated to form a meander pattern, but it should be obvious that the resistance strip or strips can be arranged in any convenient manner.
While the fuse material strips are shown as full drawn lines, it will be understood that the fuse strips will not form a current path along these lines. This statement is at least
3~9 H.A. Bergersen et al 4-1 (Revision) true for the illustrations of Figs. 3a and 3c, where the final product will look somewhat like the partial view of the heating element shown in Fig. 4a. In Fig. 3b, however, where the fuse strips are placed so as to be parallel with the longitudinal parts of the meander resistance strip pattern, the fuse strip will carry current along a sub-stantial part of its length.
A discrete thermal fuse'is obtained at all crossings or over~appings between a fuse strip 7 and a resistance strip 6 in Figs. 3a, 3b and 3c. In accordance with the present invention the discrete thermal fuses should be distributed so tha~ at least one fuse will be covered wholly or partly by a critical area 8, which. is randomly placed on the heating . element 5. As described, the relevant fuse will operate, i.e. melt, when it is covered so that as its temperature reaches-the cri~ical value, a break will occur in the current'path.'~
Figs.~4a and 4b schematically illustrate an expanded .view` of a part.of the heating element 5 of Figs. 3a and 3b incLuding resistance strips 6 which'are provided with a number of discrete thermal fuses 7' and 7" respectively.
~ The fuse material strips should preferably be placed on the resistance material base foil at some stage prior to cutting.of the base foil into the desired pattern of resistance strips (Fig. 2). In this way it is ensured that - the fuse material strips are also cut to provide the desired number of discrete thermal fuses on the resistance strips.
:- Another possible method is to'arrange the discrete fuses on the resistance strips after the base sheet has been cut into the desired pattern, but such a method will be rather complicated,.and difficulty will also be 'experienced in obtaining the proper contact between the two materials-.
In all embodiments of th.e present invention proper contact or alloyed connec~ion between the two materials wilL be facilitated if the material surfaces are clèan and free from corrosion and oxide films before the contacting operation.
3~9 H.A. Bergersen et al 4-1 (Revision~
.
- While we~have described above the principles o~ our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying-claims.
TNT:MM
August 24, 1981 . .
- -:
.
- -, ' '~ .
-` ;-~ . .
.
, ~
.. - ~
.
A discrete thermal fuse'is obtained at all crossings or over~appings between a fuse strip 7 and a resistance strip 6 in Figs. 3a, 3b and 3c. In accordance with the present invention the discrete thermal fuses should be distributed so tha~ at least one fuse will be covered wholly or partly by a critical area 8, which. is randomly placed on the heating . element 5. As described, the relevant fuse will operate, i.e. melt, when it is covered so that as its temperature reaches-the cri~ical value, a break will occur in the current'path.'~
Figs.~4a and 4b schematically illustrate an expanded .view` of a part.of the heating element 5 of Figs. 3a and 3b incLuding resistance strips 6 which'are provided with a number of discrete thermal fuses 7' and 7" respectively.
~ The fuse material strips should preferably be placed on the resistance material base foil at some stage prior to cutting.of the base foil into the desired pattern of resistance strips (Fig. 2). In this way it is ensured that - the fuse material strips are also cut to provide the desired number of discrete thermal fuses on the resistance strips.
:- Another possible method is to'arrange the discrete fuses on the resistance strips after the base sheet has been cut into the desired pattern, but such a method will be rather complicated,.and difficulty will also be 'experienced in obtaining the proper contact between the two materials-.
In all embodiments of th.e present invention proper contact or alloyed connec~ion between the two materials wilL be facilitated if the material surfaces are clèan and free from corrosion and oxide films before the contacting operation.
3~9 H.A. Bergersen et al 4-1 (Revision~
.
- While we~have described above the principles o~ our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying-claims.
TNT:MM
August 24, 1981 . .
- -:
.
- -, ' '~ .
-` ;-~ . .
.
, ~
.. - ~
.
Claims (10)
1. A method for making an electrical heating element comprising:
forming a sheet of electrical resistance material;
arranging a layer of fuse material in a pre-determined pattern on the resistance material;
pressing the fuse material and the resistance material together to form a layer of uniform thickness; and cutting the pressed layer in a meander pattern.
forming a sheet of electrical resistance material;
arranging a layer of fuse material in a pre-determined pattern on the resistance material;
pressing the fuse material and the resistance material together to form a layer of uniform thickness; and cutting the pressed layer in a meander pattern.
2. The method as claimed in claim 1 further comprising:
laminating the cut pressed layer with an insulating material.
laminating the cut pressed layer with an insulating material.
3. The method as claimed in claim 1 wherein the pressing step includes a rolling process.
4. An electrical heating element comprising:
a layer of an electrical resistance material having a predetermined melting temperature; and a fuse material having a melting temperature below said predetermined melting temperature arranged in a predetermined pattern incorporated in said resistance material, said fuse material having been pressed into said resistance material to form a layer having a uniform thickness.
a layer of an electrical resistance material having a predetermined melting temperature; and a fuse material having a melting temperature below said predetermined melting temperature arranged in a predetermined pattern incorporated in said resistance material, said fuse material having been pressed into said resistance material to form a layer having a uniform thickness.
5. The heating element as claimed in claim 4 wherein said resistance material is lead.
6. The heating element as claimed in claim 5 wherein said fuse material is a metal that alloys with lead and has a melting point lower than 200°C.
7. The heating element as claimed in claim 6 wherein said metal is selected from the group consisting of tin, lead/tin/antimony alloy and lead/bismuth alloy.
8. The heating element as claimed in claim 4 wherein said fuse material is located on said resistance material such that if heat transfer from a critical area of the element is blocked at least a part of said fuse material will melt.
H.A.Bergersen et al 4-1
H.A.Bergersen et al 4-1
9. The heating element as claimed in claim 4 wherein said fuse material is located on said resistance material such that if any location on the element exceeds a critical temperature at least a portion of said fuse material will melt.
10. The heating element as claimed in claim 9 wherein said critical temperature is approximately 180°C.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000389394A CA1178319A (en) | 1981-11-04 | 1981-11-04 | Electrical heating element |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000389394A CA1178319A (en) | 1981-11-04 | 1981-11-04 | Electrical heating element |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1178319A true CA1178319A (en) | 1984-11-20 |
Family
ID=4121335
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000389394A Expired CA1178319A (en) | 1981-11-04 | 1981-11-04 | Electrical heating element |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1178319A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4990744A (en) * | 1988-11-15 | 1991-02-05 | Nuheat Inc. | Under floor covering heating systems |
-
1981
- 1981-11-04 CA CA000389394A patent/CA1178319A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4990744A (en) * | 1988-11-15 | 1991-02-05 | Nuheat Inc. | Under floor covering heating systems |
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| Date | Code | Title | Description |
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