U.S. patent number 3,627,981 [Application Number 04/874,201] was granted by the patent office on 1971-12-14 for areal heating element.
This patent grant is currently assigned to Kabel-und Metallwerke Gutehoffnungshutte Aktiengesellschaft. Invention is credited to Gerald Kuhn.
United States Patent |
3,627,981 |
Kuhn |
December 14, 1971 |
AREAL HEATING ELEMENT
Abstract
An areal heating element is disclosed in which the resistive
portion is established by a polyester fleece contacting metal tapes
as current lead-ins. The arrangement is lined with insulation
layers, e.g., fiber fleeces or plastic sheets. The latter
arrangement can be clad in a grounded metal foil. The insulating
layers are bonded to the polyester fleece and to the tapes by
adhesive or through heat sealing.
Inventors: |
Kuhn; Gerald (Nurnberg,
DT) |
Assignee: |
Kabel-und Metallwerke
Gutehoffnungshutte Aktiengesellschaft (N/A)
|
Family
ID: |
27181598 |
Appl.
No.: |
04/874,201 |
Filed: |
November 5, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Nov 9, 1968 [DT] |
|
|
P 18 08 022.3 |
Jan 25, 1969 [DT] |
|
|
P 19 03 799.1 |
Mar 20, 1969 [DT] |
|
|
P 19 14 117.4 |
|
Current U.S.
Class: |
219/212; 219/538;
338/210; 219/528; 219/549; 392/435 |
Current CPC
Class: |
H05B
3/146 (20130101); H05B 3/342 (20130101); E21D
11/38 (20130101); F24D 13/02 (20130101); H05B
2203/017 (20130101); H05B 2203/026 (20130101); Y02B
30/00 (20130101); H05B 2203/005 (20130101); H05B
2203/011 (20130101); Y02B 30/26 (20130101); H05B
2203/028 (20130101) |
Current International
Class: |
F24D
13/02 (20060101); E21D 11/38 (20060101); H05B
3/34 (20060101); H05B 3/14 (20060101); H05b
001/00 () |
Field of
Search: |
;219/212,213,345,528,543,549
;338/210,324,212,325,214,328,225,332 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Albritton; C. L.
Claims
I claim:
1. Flexible electric areal heating element comprising:
a thin electrically conductive polyester fleece having two opposed
flat sides and serving as resistive heating element;
at least a pair of electrically conductive tapes each having two
flat sides, one flat side of each tape being in direct flat
surface-to-surface contact with the fleece the tapes having
perforations also in contact with the fleece, the tapes being
disposed on the fleece in spaced apart relationship from each
other;
insulating layers lining the fleece and tapes, on both flat sides
of the fleece; and
adhesive layer means between said fleece and said insulating layers
bonding the insulating layers to the fleece particularly along the
tapes and through the perforations and bonding one of the
insulating layers to the respective other flat sides of the tapes
for position-arresting the tapes to the fleece, for maintaining
contact making engagement between the respective one flat sides of
the tapes and the fleece.
2. Flexible heating element as in claim 1, the insulating layers
are provided as fiber fleeces.
3. Flexible heating element as in claim 1, the metal tapes being
made of bare copper.
4. Flexible heating element as in claim 1, the metal tapes being
perforated.
5. Flexible heating element as in claim 4, the perforations being
excentric to the centerline of the tape, closer to the edge of the
tape facing the other tape across the fleece.
6. Flexible electric areal heating element as in claim 1, the tapes
being flush with long side margins of the fleece.
7. Flexible electric heating element as in claim 1, the tapes
running parallel to each other.
8. Flexible electric heating element as in claim 1, the tapes
having an angle to each other.
9. Flexible electric heating element as in claim 1, there being a
metal foil on the outer side of at least one of the insulating
layers, the metal foil being grounded.
10. Flexible electric heating element as in claim 9, there being a
third metal tape attached to the metal foil in contact therewith to
establish grounding of the foil.
11. Flexible electric heating element as in claim 10, the third
tape being centrally positioned in relation to the two tapes in
contact with the fleece.
12. Flexible electric heating element as in claim 9, the foil being
made of aluminum.
13. Flexible electric heating element as in claim 9, there being a
heat-sealing layer interposed between the foil and the
one-insulating layer.
14. Flexible electric heating element as in claim 1, the insulating
sheets made of plastic and provided with heat-sealing layers for
bonding to the fleece and the tapes. 15. Flexible electric heating
element as in claim 14, the heat plastic sheets being made of
polyester, the heat-sealing
layer comprising polyethylene. 16. Flexible electric heating
element as in claim 14, the plastic sheets being made of polyimid,
the heat-sealing layer comprising a copolymer of
polytetrafluoroethylene-perfluoropropylen.
7. Flexible electric heating element as in claim 1, the tapes
projecting beyond the fleece for connection to connecting wires,
the tapes being
flexible to permit folding over for riveting. 18. Flexible electric
heating element as in claim 1, there being a plurality of tapes on
the
fleece, in excess of two. 19. Flexible electric heating element as
in claim 18, the tapes being asymmetrically arranged relative to
each other so that the distances between the tapes of different
pairs of neighboring tapes differ.
Description
The present invention relates to a flexible, electrical areal
heating element which includes a resistive means for converting
electrical energy to thermal energy and which further includes a
source of electric current for connection to the resistive means by
means of appropriate lead-in for providing electric power to the
resistive portion.
Stationary areal heating systems are known for heating interior
rooms as well as for providing outdoor, open area heating. The
areal heating elements in such systems usually comprise resistance
wires arranged to form mats. Current supplied to the wires is
converted therein to thermal energy. The individual wires are
usually covered with a heat-resistive insulation comprised of
rubber or a suitable plastic. Other known areal heating elements
are clothlike mats comprised of plastic thread or metallic wires
interwoven with bare or insulated heating conductors. Such
cloth-type areal heating elements are usually used for installation
in nonstationary surface heaters.
These two types of partially flexible-partially inflexible heating
mats have a number of deficiencies. First of all, the temperature
distribution is not uniform as there are relatively high
temperatures, locally concentrated in the vicinity of the
conductors and comparatively low temperatures prevail in the region
between adjacent but spaced apart heating conductors. Moreover,
such mats or cloths are rather complicated to make, require manual
labor to a considerable extent and are therefore rather
expensive.
These mats or cloths are usually operated at similar voltages,
namely from the mains, but difficulties arise if it is desired to
provide such cloths or mats so as to furnish different heating
powers per unit area or even to trim and to adjust them
accordingly. This is particularly so because in essence variable
parameters are the distance between the conductors in the mat or
cloth, the length of the conductor, or the construction thereof.
Additionally, of course, the heating conductors must be provided
with lead-in and connecting wires which have to remain cold,
particularly in case provisions are to be made for normal manual
plug-in.
In other types of areal heating heaters which are also known as
wall-heating mats, looped conductors are embedded in a foam
plastic, whereby temperature equalizing metal foils are positioned
inbetween the heating conductors. Again, the manufacturing of such
conductors, and the contacting of the individual looping heating
elements forming the heating surface and which are individually
connected in parallel, is rather complicated, It is a particular
disadvantage or these types of areal heaters that they have
relatively large installation height.
Furthermore, metal foils have become known which are slotted or
provided with indentations or longitudinal recesses so that in
between two longitudinally extending outer strips, loop-shaped
conductors are established which, upon application of voltage, are
heated in the desired manner. Again, the manufacturing of such
areal heaters is rather time consuming and there is the additional
disadvantage that actually there are provided alternating zones of
high and low temperatures. Furthermore, these heating foils have
rather low mechanical strength and, therefore, break easily which
in turn increases the danger of short circuiting. Finally, there is
the difficulty that different heating output per unit area can be
obtained only by changing the cutting or stamping tools.
Still another type of heating element is known in which a cloth is
woven from textile or glass fibers which have been made
electrically conductive by spraying on a thin carbon or graphite
layer. The resulting thin layer conductivity is instrumental to
obtain the desired conversion of electricity in thermal energy.
However, the weaving of such a cloth is very slow and the cost of
making such a heating element is rather high accordingly. Moreover,
the electric contact making with the sprayed-on conductive layer is
complicated to obtain and still not certain and durable,
particularly in case of flexing.
It is a principle object of the invention to provide an areal
heating element obviating the deficiencies outlined above and which
has such layer thickness which is so low that the heating element
can be actually provided underneath wallpaper without being clearly
visible. It is another object of the present invention to provide
an areal heating element which inherently includes broad surface
contact between current lead-in and resistance element. It is a
further object of the present invention to provide an areal heating
element in which flexibility is not the result of trade-off with
certainty of contact making. It is a still further object of the
present invention to provide an areal heating element which does
not require weaving of metalized fibers, wires or the like.
In accordance with present inventions the heating element provided
in accordance with the preferred embodiment employs an electrically
conductive, polyester fleece as resistive heating element. Metal
tapes are placed on the fleece in flat surface contact therewith
and at a distance from each other to serve as lead-in conductors.
Polyester fleece and metallic tape are completely covered by
electrically insulating layers. In the preferred embodiment these
layers are comprised of fiber fleeces (or a single, folded-over
fiber fleece) having an adhesive layer on their sides facing
polyester fleece and tape to provide secure connection between all
the various parts outlined above.
The polyester fleece is to be very thin to be highly flexible, but
still has good mechanical strength, and it retains its shape in
spite of a very small value in thickness. The electric resistivity
of such a fleece is rather constant over a large temperature range.
One can make such a fleece even at large lengths without
difficulties. Firm connection and, therefore, positive contact
making between polyester fleece and metal tapes is primarily
obtained through the fiber fleece adhering to a metal tape as well
as to the polyester fleece at both sides (edges) of the tape thus
urging the latter to the former. The fiber fleece may, for example,
be bonded to the polyester fleece by concurrent application of heat
and mechanical pressure.
In order to improve the contact making between fleece and metal
tape, it may be advisable to provide the construction with the
following particular features. The metal tapes may be provided with
apertures. These apertures may in particular be located somewhat
excentrically, closer to that edge of the tape facing the other
tape across the polyester fleece. The adhesive layer on the fiber
fleece contacts the polyester fleece through the apertures and
provides for additional positioning of metal tape relative to and
in contact with the polyester fleece.
The heating element in accordance with the invention can be
improved further in that at least on one side of the outer
insulating fleece or sheet there is provided a metal foil which, in
turn, in connected to a grounded contact, for example, of the
mains. The advantage of this feature is protection against danger
from severe damage to the heating element; for example, if a nail
pierces the several layers, the nail makes contact with that foil
and is in effect grounded. Particular protection is afforded here
to the person wielding the hammer.
This metal foil may preferably be made of aluminum in accordance
with an additional aspect of the invention, and as it is connected
to the ground terminal of the mains it grounds all contacting,
conductive objects, including a piercing nail. Of course
conventional protective circuit means may be used in addition in
circuit connection with the areal heating element operating
preferably on a selective basis to stop current flow through the
particular damaged element in order to avoid large leakage currents
into that element as extensive damage or even fire may result, for
example, from local excessive heating.
A further improvement of the inventive concept will be as follows.
In lieu of a fiber fleece or fleeces a plastic sheet or foil is
provided carrying on one side a heat-sealing layer prior to
assembly. For example, the plastic, insulating foil could be a
polyester foil having a polyethylene layer to be used for bonding
the insulating foil to the heating element proper. As a
heat-sealing layer one can also use a copolymer of
polytetrafluoroethylene-perfluoropropylene on a polyimid foil as
insulating sheet. Such an arrangement has the advantage that the
plastic or foil as suggested has considerably mechanical strength,
is voltage proofed, for regular AC as well as DC and has a very
low-water vapor permeability. Therefore, such an areal heating
element can be handled roughly during the installation. Also, it
establishes a heating element which can be used for heating highly
humid rooms.
Foil layering of the heating element in accordance with this aspect
of the invention, has the further advantage in that upon mounting
the heating element, for example, to a wall, regular wallpaper glue
can be used even though it contains a rather large amount of water.
Moisture will not penetrate into the electrically conductive
polyester fleece so that damage to the latter does not have to be
expected. The foil structure guarantees in addition that the
element maintains its shape and can be wound on a roll. The quality
and certainty of contact making between metal tapes and polyester
fleece is also improved in view of the high-bonding strength of
heat sealing.
While the specification concludes with claims particularly pointing
out and distinctly claiming the subject matter which is regarded as
the invention, it is believed that the invention, the objects and
features of the invention and further objects, features and
advantages thereof will be better understood from the following
description taken in connection with the accompanying drawings in
which:
FIG. 1 illustrates an elevational view of an areal heating element
in accordance with the preferred embodiment of the present
invention.
FIG. 2 illustrates a cross section along lines 2--2 in FIG. 1,
however, with grossly exaggerated representation of thickness
dimensions to facilitate illustration thereof.
FIG. 2a is a detail of a modified arrangement.
FIGS. 3 and 4 show elevations of further embodiments of heating
elements in accordance with the present invention; and
FIGS. 5 and 6 show cross sections through heating elements in
accordance with two additional embodiments of the present
invention.
Turning now to the detailed description of the drawings, in FIGS. 1
and 2 there is illustrated a polyester fleece 1 to be used as
resistive element for an areal heater and in which conversion of
electrical energy to thermal energy takes place. Along the long
sides of fleece 1 there are provided two metallic tapes 2 and 3.
Edges of fleece 1 and outer edges of tapes 2 and 3, respectively,
are vertically aligned, as can be seen in FIG. 2. Preferably these
metallic tapes are made of copper and have dimensions that on one
hand the thickness of the heating element as a whole is not
noticeably increased and in addition, they are sufficiently thick
so that current flow through them does not cause heating to any
significant degree.
Fleece 1 is covered on both sides with fiber fleeces 4 and 5, fiber
fleece 4 particularly covering also the conducting tapes 2 and 3 on
that particular side. The inner sides of the fiber fleeces 4 and 5
are provided with an adhesive layer permitting direct bonding to
polyester fleece 1 and metal tapes 2 and 3 were in surface contact.
As can be seen in particular in FIG. 2, fiber fleeces 4 and 5 have
overhanging portions along the edges of fleece 1. The adhesive
layers on fleeces 4 and 5 thus bond them together, providing an
all-around enclosure for fleece 1.
FIG. 1 illustrates, furthermore, one end of this elongated areal
heating element, and one can see that tapes 2 and 3 project beyond
that edge of fleece for providing lead-ins for connection to a
suitable conductor through which voltage is applied to and between
conductors 2 and 3. Of course, additional layers could be provided
on top of the fiber fleeces, transparent or opaque foil or layers,
etc. It should also be mentioned that the fiber fleece layers or at
least one thereof may itself be made of transparent or translucent
material which facilitates control and inspection of the quality of
contact making particularly between metallic tapes 2 and 3 and
polyester fleece 1.
FIG. 2a illustrates another feature of the invention, the metal
tape 12 used here as current lead-in for the heating element, has
asymmetrically positioned apertures 13. Aperture 13 is closer to
the edge facing away from the tape edge which is flush with the
edge of fleece 1 along which tape 12 extends.
Generally, it should be mentioned that the metal tapes are
maintained in position by being bonded to fleece 5. Moreover,
fleece 5 is bonded to fleece 1, particularly also along the portion
adjacent the tapes but not covered by them. Additionally, fleece 5
is bonded to fleece 4 along the edge of the tapes, respectively
flush with the edges of fleece 1. Here, the fleece grips somewhat
around the tapes. Additionally, the tapes are position-arrested in
that the fleece grips through the aperture and is bonded to fleece
1 were exposed through the apertures. This gripping-through is not
illustrated in FIG. 2, because of the exaggerated thickness
dimensions. It is emphasized that in reality the apertures in the
tapes 2 and 3 are considerably wider than the tapes are thick.
It is of significance that the areal heating element of the type
illustrated has a very small layer thickness which is instrumental
in obtaining large versatility of employment. Also, the heating
power per unit area or other parameters are readily adjustable. For
a chosen areal heating power, the particular distance between the
conductors 2 and 3 is predetermined. The entire heating element can
now be as long as desired to obtain a particular overall heating
output.
Particular areas of employment are, for example, installation as
ceiling or wall heaters underneath even thin wallpaper, whereby the
transition between, for example, a central wall zone provided with
such elements, and a marginal or corner zone of the wall without
heater underneath, is in fact hardly noticeable. The novel heating
element can also be employed as floor heater and can particularly
be installed under parquet layers or vinyl and other plastic type
of floor covers, or even underneath wall-to-wall carpeting. Heaters
in accordance with the invention are not limited to employment as
large area covers, instead, one can make such areal heating
elements part of small mats; one can even use this type of heating
element in and for hot plates. It should be mentioned finally that
for most areas of employment conventional and commonly used
adhesives can be used to provide the adhesive layer on the fiber
fleeces 4 and 5.
FIG. 3 illustrates another embodiment of the invention. For
example, in certain long polyester fleeces having not too small a
width and having a wider than normal width one can provide more
than two metallic tapes; also more than two metallic tapes may be
required as lead-ins in case two areal elements of different
heating power are to be provided next to each other. FIG. 3
illustrates such an embodiment.
There are shown three metallic tapes, 2, 3 and 6. Tapes 2 and 6 are
arranged essentially as are tapes 2 and 3 in FIG. 1, along the long
edges of fleece 1, but possibly at a larger distance from each
other. Tape 3 is provided here between tapes 2 and 6, dividing the
total heating area into zones A and B. The arrangement is somewhat
asymmetrical, i.e., the distance between tapes 2 and 3 is larger
than between tapes 3 and 6, area A being larger than area B.
TApe 3 is, for example, connected to a return reference or ground
terminal and similar voltages are applied to conductors 2 and 6. As
the distance between tapes 2 and 3 is larger than between the tapes
3 and 6 and if the polyester fleece 1 has uniform thickness, area A
is heated less than area B. One can, therefore, see that in a
rather simple manner, i.e., by providing an asymmetrical tape
conduction arrangement on the areal heating power can readily be
controlled particularly as far as ratio of heating powers of two
different areas is concerned.
FIG. 4 illustrates another special case in which the two metallic
conductor tapes, again denoted here with 2 and 3 on fleece 1 are
not equidistantly spaced, they do not run parallel to each other
but have an acute angle between them. Voltage applied to the two
conductors 2 and 3 is similar along the fleece, but Region D is
heated more on a per unit area basis than Region C with stepless,
gradual increase of heating power from C to D. One can see that a
gradient of developed heat per unit area is obtained and heating
increases continuously from top to bottom in the drawing.
Turning now to the embodiment shown in FIG. 5, there is again
illustrated the polyester fleece 1 with metal tapes 2 and 3 for
providing current to flow through fleece 1. Also, and as in the
embodiments described above, polyester fleece and metallic tapes
are clad by a pair of fiber fleeces 4 and 5 bonded together along
the margin of fleece 1 by means of an adhesive layer. In this
particular embodiment and in accordance with the general principles
outlined in the introduction there are provided additional metallic
foils for lining the sheet arrangement as described thus far. There
is in particular illustrated a lower foil 7 and an upper foil 8.
However, this may actually be one and the same foil folded over at
the end of the heating element. The metal foil or foils are
preferably made of aluminum.
In principle, of course, it may be sufficient to provide such a
metal foil on one side of the arrangement only. However, in this
case it would be critical how to place the heating element, as the
side provided with that metal foil should be the side not facing
the wall, floor, ceiling, or other support element to which the
heating element is to be attached. This selection rule, of course,
can be dispensed with in case both sides of the arrangement are
lined with metal foil as illustrated.
The purpose of the metal foil cover is to provide for flat
grounding of the heating element as a whole. The metal foil or
foils is/are, of course, insulated from thermoconduction 1. In
order to properly ground the foil or foils 7, 8, they make contact
with a metal tape 11, serving as the lead-in for a connection
between foil or foils and ground. Tape 11 is a thin metal tape
preferably of the same type used to supply current to fleece 1.
Generally it is of advantage if tape 11 is positioned approximately
halfway in between the two tapes 2 and 3.
Foils 7 and 8 are bonded to the heating element construction,
particularly to the outer surfaces of insulating layers 4 and 5 by
means of conventional glue or adhesive, or a foil for heat sealing,
for example, a thin polyethylene foil, may be provided between the
grounded metal foil on one hand and the fiber fleeces on the other
hand. The polyethylene foil is caused to melt by application of
external mechanical pressure at an elevated temperature. Upon
melting and resolidification the metal foil(s) are bonded to the
fiber fleeces.
The thickness of the areal heating element as a whole is only
insignificantly increased by the two additional layers of metal
foil and the latter should be very thin so that the flexibility of
the heating element is not impeded. Flexibility is desirable as,
for example, a long sheet of such heating element may be wound on
spools or rolls for facilitating transportation. Therefore, it is
repeated here, that also in FIG. 5 the dimensions representing
thickness of the heating element and other several foils, layers
and fleeces are quite exaggerated.
FIG. 6 illustrates an example of another embodiment of the
invention. Again reference numeral 1 refers to the polyester fleece
and electric current is provided to and across the polyester fleece
by the two metallic tapes 2 and 3. Polyester fleece and metallic
tapes are clad in insulating lining provided here by two plastic
foils 14 and 15 each of which having on one side a heat-sealing
layer. The heat-sealing layers are respectively denoted with
reference numerals 9 and 10. The heat-sealing layers face polyester
fleece 1, but since foils 14 and 15 reach beyond fleece 1 along the
margin thereof, heat-sealing layers 9 and 10 are in direct
engagement along the margin of fleece 1. Metal foils 7 and 8 are
provided above plastic foils 14 and 15, respectively.
The metal tapes 2 and 3 themselves make good contact with the
polyester fleece in all of the embodiments, but due to their
flexibility they are also highly suitable for connecting to other
current supply elements. For this it is merely necessary to bend
over the ends of the metallic tape projecting from the heating
element. The thus resulting loops or eyes receive the connecting
wires or the like. Tapes and connecting wires are secured to each
other, for example, by means of hollow rivets.
The invention is not limited to the embodiment described above but
all changes and modifications thereof not constituting departures
from the spirit and scope of the invention are intended to be
included.
* * * * *