An electric heater, especially for small electric appliances, such
as hair roller heaters, egg boilers, or the like, and a method of
making same utilizes at least one heating element having contact-making
zones on opposite planar parallel surfaces thereof, electrical connection
elements in the form of essentially planar contact plates, a contact
plate being placed on each of the opposite surfaces, and a holding
member having a heat conducting, electrical insulating layer upon
a surface thereof. The holding member is bent into a U-shape so
as to hold the contact plates clamped fast to the heating elements
between legs of the U-shape of the holding member and with the insulating
layer disposed on an inner surface of the U-shape between the plates
and holding member. In accordance with a preferred embodiment, the
insulating layer is of a resilient material having a heat-conductive
additive distributed therethrough and the heating elements are formed
of PTC material.
1. Electric heater, especially for small electric appliances, such
as hair roller heaters, egg boilers, or the lke, comprising:
at least one flat, heating element having contact-making zones
on opposite planar parallel surfaces thereof;
electrical connection elements in the form of essentially planar
contact plates, a contact plate being placed on each of said opposite
and a holding member formed of a flat sheet of material which has
been bent into a U-shape having legs which are mutually spaced in
a manner so as to hold the contact plates clamped fast to said at
least one heating element between the legs of said U-shape of the
holding member by the direct action of a clamping pressure exerted
thereby, said holding member extending over the entire width of
the at least one heating element and the contact plates having a
heat conducting electrical insulating layer upon an inner surface
of said U-shape between said plates and holding member.
2. Heater according to claim 1, characterized in that the insulating
layer is a heat-conductive, electrically insulating coating of the
3. Heater according to claim 1 or 2, characterized in that a space
between the legs of the U-shape is sealed off by an insulating material
at lateral ends of the holding member.
4. Heater according to claim 1 or 2, wherein said at least one
heating element is square.
5. Heater according to claim 1, wherein several heating elements
are provided between the contact plates.
6. Heater according to claim 1, wherein said insulating layer is
a resilient material with a heat-conductive additive distributed
7. Heater according to claim 3 characterized in that the holding
member is sealed-off by insulating material in the region of free
ends of the legs of the U-shaped over the entire length thereof.
8. Heater according to claim 3, wherein said at least one heating
element is square.
9. Heater according to claim 1, characterized in that each of the
contact plates is provided with a contact reed integrally formed
therewith, said contact reeds being extending laterally out of the
10. Heater according to claim 9, characterized in that an insulating
sleeve is placed onto each contact reed over part of the length
11. Heater according to claim 9 or 10, characterized in that the
contact reeds are fashioned as plug-in elements.
12. Heater according to claim 11, wherein the plug-in element of
one contact reed is a flat plug and the plug-in element of the other
contact reed is a flat plug socket.
13. Heater according to claim 1 or 2 or 6, wherein said heating
elements are formed of PTC material.
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to an electric heater, expecially for small
electric appliances, such as hair roller heaters, egg boilers, or
the like, with at least one flat, square heating element with contact-making
zones on opposite surfaces, as well as with electrical connection
elements in the form of essentially planar contact plates placed
on contact-making zones of opposite sides of the heating elements.
In electric warmup or heating appliances, especially small electric
devices such as hair roller heaters or the like, it is desirable
to provide a satisfactory and uniform heat transfer from the heating
elements to the regions to be heated over a relatively large area.
Therefore, flat, elongated heaters are utilized. The heating elements
employed usually are to an increasingly greater extent so-called
PTC elements, i.e. heating elements of PTC material or heat conductors
having a positive temperature gradient. Such PTC elements customarily
exhibit a prismatic shape with two opposed planar-parallel surfaces
and a round or polygonal outline and are contructed, in particular,
as square plates. Such PTC elements ordinarily consist of a ceramic
material, especially on the basis of barium titanate, and have the
property that they are so to speak self-stabilizing with respect
to their rate of electric power input, because the electric resistance
increases greatly within certain temperature ranges so that the
conductivity and the heat transmission of the heating element are
DOS No. 2,845,965 (corresponding to U.S. Pat. No. 4,327,282) discloses
such a heater wherein the contact plates, resting on both sides
on the resistance heating elements, are held together elastically
along the edge zone. This design per se is satisfactory, but cannot
be utilized with equally good effects in every case of application,
for example in those instances where heat transfer to another body
is to be carried out by direct physical contact with the heater.
This is so because the clamping members on the edge side necessitate
a certain spacing between the heated surface of the heater and a
body contacted by the heater, unless the body to be heated up is
fashioned in a suitable manner, which is not always possible.
Therefore, an object of the invention is to solve the problem of
providing a technically simple and thus inexpensive heater exhibiting
flat heat-transfer surfaces which can be placed in a simple and
practical way against a body to be heated.
This problem has been solved according to a preferred embodiment
of the invention in a heater of the type mentioned in the foregoing
by the feature that the heating elements and the contact plates
resting on both sides are clamped fast between the legs of a holding
member bent into a U-shape and provided on the inside with an insulating
layer, this holding member extending over the heating elements and
contact plates along their entire widths. By this construction,
the heating elements and the contact plates are, first of all, reliably
and securely held in place in a simple way. Moreover, the heater
of this invention ensures the presence of a flat and completely
planar contact surface via which the heat generated by the heating
elements can be further transferred uniformly in the entire length
of the heater. The heater of the present invention also exhibits
the advantage that the heat output can be extensively selected arbitrarily
in a suitable way by inserting and retaining a larger or smaller
number of heating elements in the holding member between the contact
The provision is made as a preferred feature that the insulating
layer is a heat-conductive, electrically insulating coating of the
holding member, the coating being resilient in a certain way so
that excessively strong forces during compression of the holding
member into its U-shaped form, wherein it holds the contact plates
and the heating elements together, are not transmitted to the heating
elements. The heat-conductive, electrically insulating coating consists
preferably of silicone rubber rendered heat-conductive by appropriate
additives, such as, for example, magnesium oxide or the like. This
is of advantage, in particular, if the provision is to be made in
a further preferred embodiment that the space between the U-legs
at the ends of the holding member is sealed by an insulating material
and/or that the holding member is sealed off in the area of the
ends of the U-legs over its entire length by insulating material.
If the entire heater is sealed off at the open sides of the U-shaped
holding member, the heater of this invention can also be utilized
in a moist or wet environment, which is not readily possible in
case of the heater according to DOS No. 2,845,965. The latter would
first have to be separately sealed off completely.
A further feature of the preferred embodiment is that provision
is made for the contact plates to be equipped with contact reeds
[tongues] formed integrally therewith, which reeds are laterally
extended from the holding member, the contact reeds being fashioned
especially in the form of plug-in elements. In this case, one plug-in
element can be constructed as a flat plug and the other as a flat
plug socket or receptacle. Preferably, the contact reeds are furthermore
provided with insulating sleeves placed thereon in the zone where
they are extended out of the U-shaped holding member. These insulating
sleeves consist, for example, of shrunk-on film [sheeting] insulating
the contact reeds reliably against each other as well as with respect
to the U-shaped holding member; this is important if the holding
member consists of a conductive material, e.g. aluminum sheet.
These and further objects, features and advantages of the present
invention will become obvious from the following description when
taken in connection with the accompanying drawings which show, for
purposes of illustration only, a single embodiment in accordance
with the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a lateral view of an embodiment of the heater according
to this invention in the direction of arrow I of FIG. 2, with the
FIG. 2 is an illustration of the same embodiment of the heater
according to this invention in the direction of arrow II of FIG.
FIG. 3 is a cross-sectional view taken along line III--III of FIG.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The electric heater 1 illustrated in the drawing consists in its
basic structure of several series-disposed heating elements 3 of
heat-conductive material having a positive temperature coefficient,
or, in short, PTC material. The heating elements 3 have the shape
of flat, square plates (but may be round, rectangular, or other
polygonal shapes) their oppositely disposed, planar-parallel contact
surfaces 5 being provided, in a manner that is conventional per
se, with a metallic contacting (not shown in detail). The resistance
elements are arranged in sandwich style between contact plates 7,
which latter correspond at least in their width to the width of
an individual resistance heating element 3. The two contact plates
7 consist of aluminum sheet material and are equipped with respectively
one contact reed 9,9' fashioned as plug elements, wherein the contact
reed 9 is constructed as a flat plug socket and the contact reed
9' is designed as a flat plug. This creates a simple means for connecting
a cable. Respectively, one insulating sleeve 11, 11' is placed on
the plug elements 9, 9', this sleeve consisting, for example, of
shrunk-on film or the like.
The arrangement described thus far has no inherent cohesion but
rather must be held together by a holding member 13. The holding
member 13 consists of an aluminum sheet material which is provided
on its inner surface with an electrically insulating, but heat-conductive
coating 15. The coating 15 consists, for example, of silicone rubber
with appropriate heat-conductive additives, such as magnesium oxide
or the like. The holding member 13 with coating 15 is then bent
in a U-shape around the above-described arrangement of resistance
elements 3 and contact plates 7 and is compressed in such a way
that it securely retains the contact plates 7 and especially the
heating elements 3. Excessive stress peaks during compression are
absorbed, if necessary, by the resilient coating 15, although the
heater of this invention is nowise impaired in efficiency if the
individual PTC heating elements rupture, as long as the individual
fragments are reliably held by the holding member 13.
The U-shaped profile is sealed off at one end 17 by a plug 19 of
the same material as the coating substance 15. A corresponding closure
may also be provided on the opposite end of the holding member 13
where the connection contacts are extended. Finally, a corresponding
seal 19' could also be arranged between the free ends 21 of the
U-shape 23 of the holding member 13 over the entire length thereof.
A reliable sealing encapsulation of the heater of this invention
is created by such a complete enclosure.
In total, the invention creates a rugged, reliable heater with
an extensively selectable heating output, by being able to insert,
depending on requirements, a larger or smaller number of individual
heating elements 5 in a heater of a predetermined length and to
distribute these heating elements over the length thereof in a suitable
way. In the illustrated embodiment of FIG. 1, three heating elements
5 are provided. In the embodiment shown, approximately six heating
elements of the illustrated dimensions can be inserted in total.
While I have shown and described a single embodiment in accordance
with the present invention, it is understood that the same is not
limited thereto but is susceptible of numerous changes and modifications
as known to those skilled in the art and I therefore do not wish
to be limited to the details shown and described herein but intend
to cover all such changes and modifications as are encompassed by
the scope of the appended claims.