Note: Descriptions are shown in the official language in which they were submitted.
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ELECTRIC HEATER FOR TUMBLE DRYERS
Field of the invention
The present invention relates to an electric heater used in tumble dryer
devices.
State of the art
Various electric heaters used in tumble dryer devices are known.
Some known electric heaters have at least a coil-shaped wire, for example
helically wound, which is fitted on a support structure.
While such electric heaters with coil-shaped wire are commonly used in the
tumble
dryer devices, they have some disadvantages.
A first disadvantage is that large heaters are needed in order to provide a
sufficient
heating power, e.g. higher than 5 kW.
A second disadvantage is that the air flow passing through the coil-shaped
wires
may cause vibrations in the wires, and therefore an irritating noise during
operation.
A further disadvantage is due to the coil-shaped heating wires tending to
become
curved and capture dust, and their breakage may cause short circuits.
It is therefore felt a need for implementing an electric heater for tumble
dryers
which allows to overcome the aforesaid drawbacks.
Summary of the invention
The primary object of the invention is to implement an electric heater for
tumble
dryers which allows to simply and functionally overcome the aforementioned
drawbacks. Such a heater is provided with a compact structure consisting of at
least one resistive member having a zigzag-bent, "flattened wire" section,
supported by a multilayer structure made of an insulating material.
Another object of the invention is to implement an electric heater which
simplifies
the application to the used apparatus while ensuring a high safety level.
Therefore, the present invention aims at attaining the above-discussed objects
by
implementing an electrical heater for tumble dryer devices which, in
accordance
with claim 1, comprises at least one resistive member, a support structure for
supporting said at least one resistive member, in which said support structure
comprises flat parts which are connected to one another so as to define a
polygonal shape of the structure having at least one open side, and in which
said
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at least one resistive member comprises a flattened filament which is bent so
as to
define a plurality of zigzags, said filament being arranged on a plane which
is
substantially perpendicular to each flat part of the support structure.
Each flat part or strip is formed by three overlaying layers of an insulating
material
and is provided, at one longitudinal edge thereof, with a substantially L-
shaped
support member having a short arm connected to the flat part and a long arm
adapted to be connected to a heater housing, so that the flat parts are
arranged
along plans which are orthogonal to the bottom of said housing.
Each flat part and the respective support member may be integrally secured to
one another or constructed as a single piece. Alternatively, there is provided
a
single support member with flat parts or strips of the support structure
secured
thereto.
The heater object of the present invention does not advantageously require the
large size presently needed to provide high powers. Furthermore, the
particular
shape of the resistive member reduces the vibrations transmitted to the
apparatus
and therefore the noise heard by the user. A further advantage given by the
heater
shape is the lower tendency to dust deposition on the heating member and the
safety against short circuits in case of filament breakage.
A variant of the invention provides for the possibility of inserting more
resistive
members so as to be able to choke the total power with a subsequent energy
saving in case of not full loads of laundry in the dryer.
A further variant provides for the possibility of placing the resistive
members on the
optimal side, e.g. either on the inner side only or on the outer side only or
on both
sides, with respect to the polygonal structure formed by the mica supports of
the
heater, by adjusting the heater itself to the specific requirements of the
apparatus.
A first variant, for example, provides for a single resistive member arranged
outside or inside the support structure. On the other hand, a second variant
provides for a first resistive member arranged outside the support structure
and at
least one a second resistive member arranged inside said support structure. In
a
preferred variant, there are provided two second resistive members arranged
inside the support structure. Alternatively, there may also be provided two
resistive
members arranged outside the support structure and one resistive member
inside.
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Other variants may be obtained by providing for the possibility of varying the
final
geometry of the heater by using a single support structure with the advantage
of
being able to use the same resistor on variously sized apparatuses, thus
avoiding
costs for specific equipment.
The dependent claims describe preferred embodiments of the invention.
Brief description of the drawings
Further features and advantages of the invention will be more apparent in view
of
the detailed description of a preferred not exclusive embodiment of an
electric
heater, illustrated by way of non-limiting example, with the aid of the
accompanying drawings, in which:
Fig. 1 shows a view of an electric heater according to the invention;
Fig. 2 shows a cross-section view of the heater in Fig. 1;
Fig. 3 shows an exploded view of part of the heater in Fig. 1;
Fig. 4 shows a partially exploded view of part of the heater in Fig. 3.
Detailed description of preferred embodiments of the invention
With reference to the Figures, a first preferred embodiment of an electric
heater is
depicted, globally indicated by reference numeral 1, which may be especially
used
in tumble dryer devices.
In this first embodiment, the heater object of the present invention
comprises:
- at least one resistive member, or simply resistor, 8 arranged on an outer
side of
the heater;
- at least two resistive members 9 arranged on an inner side of the heater;
- a support structure 6 for said resistive members 8 and 9 having a polygonal
shape with at least one open side;
- means 3 for connecting resistive members 8 and 9 to the mains for powering
the
resistors.
By passing forced air, e.g. at a rate higher than 5 m/s, through the resistors
having
a design temperature at a steady state of e.g. 400 C, the air rapidly heats
thus
allowing the laundry placed in the household appliance compartment to be
dried.
Support structure 6 advantageously comprises a plurality of strips or flat
parts 6'
made of an insulating material, having high dielectric strength and excellent
chemical stability, preferably mica. Other usable insulating materials may be
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ceramic materials such as steatite or cordierites.
Strips 6' are reciprocally connected at their ends so as to form a polygonal-
shaped
structure with at least one open side. Strips 6' are at least four in number.
Therefore, support structure 6 has two ends 10, 11 spaced apart by an empty
spacing or gap 12. These ends 10, 11 are provided with electric terminals 4
for the
connection to the electric network.
In the preferred embodiment of Fig. 1, strips 6' are seven in number.
Each strip 6' is formed by three layers 13, 14 and 15 of mica or other
suitable
insulating material and is integrally secured, at the longitudinal edge
thereof, to a
substantially L-shaped support member 7, which may be better seen in Fig. 2.
The
short arm of this L-shaped member is secured to strip 6', whereas the long arm
is
secured to the housing 5 of the heater so that strips 6' are arranged along
plans
which are orthogonal to the bottom of housing 5.
In an alternative variant, each strip 6' and the respective L-shaped support
member 7 may be constructed as a single piece.
In a further variant, there is provided a single support member to which all
strips 6'
of the support structure are secured. This single support member is suitable
for
being connected to the housing 5 of the heater so that strips 6' are arranged
along
plans which are orthogonal to the bottom of said housing 5.
With reference to Figures 3 and 4, the outer mica layer 13 of each strip 6' of
support structure 6 is advantageously provided with a first longitudinal
series of
holes 16, substantially arranged along the longitudinal axis of the strip,
within
which a first resistor 8 is passed, the resistor being defined by a zigzag-
shaped,
flattened filament and secured between said outer layer 13 and the
intermediate
mica layer 14.
On the other hand, the inner mica layer 15 of each strip 6' is provided with
two
second longitudinal series of holes 17, 18 arranged along straight lines
parallel to
one another and to the longitudinal axis of the strip, close to said axis. A
respective second resistor 9 is passed within each second series of holes, the
resistor being defined by a zigzag-shaped, flattened filament and secured
between
said inner layer 15 and the intermediate mica layer 14.
Alternatively, in a second preferred embodiment, a single series of holes and
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therefore a single resistor 9 may also be provided on the inner mica layer 15.
The zigzag shape of the resistors or heating filaments 8, 9 has first tips
which are
connected to support structure 6 and second tips which are spaced apart from
said support structure. By securing the first tips of the resistors to the
support
5 structure by means of the holes provided on the inner and outer mica layers
15,
13, short circuits and bending of resistors are avoided even in case of
filament
breakage. The arrangement of the resistors allows a high strength also against
intense air flows, only minimal vibrations being produced.
The three mica layers 13, 14, 15 are held by means of rivets or other suitable
securing means so as to be integral with one another. The mica layers provide
electric insulation and prevent the resistors from coming in contact with one
another or with parts of the household appliance once the heater of the
invention
has been installed.
This configuration of resistors 8 and 9, arranged on planes which are
substantially
perpendicular to strips 6' and substantially parallel to the bottom of housing
5,
advantageously allows to offer the lowest resistance to the air flow, thus
optimising
the thermal yield and the load loss.
Specifically, providing in the first embodiment two resistors 9 on the inner
side of
the heater is advantageous because, even in cases with less ventilation in the
central zone of the apparatus, the surface temperature of the resistive
filament
may be limited by doubling the heat emitting surface.
Resistors 8, 9 are at least 10 mm wide, preferably from 20 and 30 mm wide.
They
are made of materials such as, for example, resistive FeCrAI - FeNiCr alloys.
The distance between the series of holes 17, 18 related to the side having
more
filaments is at least 6 mm, preferably between 7 and 20 mm.
A further advantageous embodiment of the invention provides for a single
resistor
or resistive member or filament, having a "flattened wire", zigzag-bent
section,
placed on the inner or outer side of the heater.
The turn "connecting" two sectors of the mica supports or strips 6' which
define the
support structure 6, is inserted into an appropriate "open" slit so that the
shape of
the turn itself may automatically conform to the configuration produced by the
support structure 6.
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This is effective both on the inner side of the polygon formed by the strips
6' where
there is provided at least a slit 20 open at the ends of the inner mica layers
15, and
on the outer side of said polygon where there is provided at least a slit 19
open at
the ends of the outer mica layers 13. The corresponding open slits in the
inner
and/or outer layers are suitable for defining a passage for a turn of a
resistive
member between two subsequent flat parts or strips 6'.
This peculiarity, along with the possibility of taking different sizes for
anchoring the
heater to the apparatus, allows to make the same resistor also applicable to
apparatuses which are dimensionally different to one another. Indeed, by
varying
the angle defined by the connection between strips 6', the median diameter
taken
by the resistor varies, i.e. the aforesaid diameter increases with the
increase in the
angle, thus allowing to obtain different sizes for anchoring the heater to the
tumble
dryer device.
