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(11) | EP 0 320 966 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Air flow heater unit, particularly for tumbler clothes driers |
| (57) An air flow heater unit particularly for tumbler clothes driers, comprising at least
one electrical resistance element which heats a flow of drying air, said electrical
resistance element (9) being completely embedded in a body (5,16,20) of die-cast aluminium
alloy. |
[0002] Known tumbler clothes driers comprise an external structure for containing the laundry to be dried, against which a hot air jet is fed. This jet is obtained by passing an air stream through a conveying duct which houses a resistance heater element.
[0003] Generally this conveying duct is formed from two half-shells of die-cast aluminium joined together with a silicone gasket therebetween. An armoured resistance element is fixed to one of the two half-shells by a conventional flange so that it is grazed by the air to be heated, the unit formed from the two half-shells being covered externally with a layer of insulating material, generally glass wool, to prevent excessive heating of the parts external to the heater unit, ie the structure of the clothes drier and its operating and control members.
[0004] These known heater units, which are used mainly in combined washing and drying machines and which are applied to the upper part of the washing tub, suffer however from a series of drawbacks which the present invention obviates.
[0005] One of these drawbacks is that as the surface area of the electrical resistance element grazed by the air to be heated is generally very small and the air quantity to be circulated must be high, the operating temperature must be considerable (about 500-600 °C) to obtain a satisfactory heating effect. This results in:
- high resistance element cost on account of the thermal stresses to which it is subjected;
- high temperature of the tubular duct to which the resistance element is fitted, with its need for external insulation to prevent excessive heating of the structure of the combined washing and drying machine and of its operating and control members;
- the danger of igniting, by simple contact, the fabric threads which are inevitably present in the air flow, and of returning them to the circuit with considerable fire risk;
- the impossibility of constructing combined washing and drying machines with a plastics tub.
[0006] Furthermore, during the washing phase, the resistance is sprinkled by water which in the following drying phase, that is when the resistance operates in air, oxidizes and rusts thus making dirty the clothes.
[0007] It has also been proposed to use particular materials to cover the armature of the resistance, but neither in this case the solution, even considerably expensive, has been shown complete.
[0008] A further drawback is that the drying effect is essentially due to the thermal irradiation and therefore concerns only the clothes placed on the peripheral zone, and not those placed in the center of the tub.
[0009] A further drawback is that the need to mount the resistance element inside the aluminium duct means that this element must be provided with a flange and that a certain complication arises in assembly.
[0010] These drawbacks are obviated according to the invention by an air flow heater unit particularly for tumbler clothes driers, comprising at least one electrical resistance element which heats a flow of drying air, characterised in that said electrical resistance element is completely embedded in a body of die-cast aluminium alloy.
[0011] The present invention is described in detail hereinafter with reference to the accompanying drawings in which:
Figure 1 is a partly fragmented perspective view of a first embodiment of a heater unit according to the invention;
Figure 2 is a plan view thereof;
Figure 3 is a longitudinal partial section therethrough on the line III-III of Figure 2;
Figure 4 is a cross-section therethrough on the line IV-IV of Figure 2;
Figure 5 is a diagrammatically longitudinally view of a washing and drying machine provided with the heater unit according to the invention;
Figure 6 is a perspective view of a second embodiment of a heater unit;
Figure 7 is a diagrammatically transverse view of a washing and drying machine provided with this heater unit;
Figure 8 is the same view as figure 6 of a third embodiment of a heater unit; and
Figure 9 is a diagrammatically transverse view of a washing and drying machine provided with this heater unit.
[0012] As can be seen from the figures the heater unit according to the invention consists, in the embodiment shown in Figures 1 to 5, of a tubular duct indicated overall by 1 and connectable in conventional manner to two external air circulation pipes 2 and 3.
[0013] The tubular duct 1 is constructed of die-cast aluminium alloy and comprises an outer cylindrical casing 4 and an inner cylindrical body 5 which is coaxial to said cylindrical casing 4 and connected to it by three longitudinal ribs 6,7, and comprises a plurality of longitudinal radiant fins 8.
[0014] Two spiral-armoured resistance elements 9 are embedded in the material of this body and have their terminal portions emerging from the cylindrical casing 4. Those portions of the resistance element 9 which pass through the interspace between the casing 4 and body 5 are embedded in the longitudinal ribs 7.
[0015] A safety thermostat 10 is applied to a plate 11 positioned in the casing 4 between the two ribs 7, and a control thermostat 12, preferably of the two-control type (normal laundry and delicate laundry) is provided at the exit of the heater unit, again in the casing 4.
[0016] The described heater unit according to the invention is connected to an external air conveying circuit comprising a fan 13, the inlet pipe 2, for example of plastics material, and the outlet pipe 3, for example of rubber. During operation, the resistance elements 9 are powered to heat the body 5, which then heats the air grazing its walls and allows that, around the pipe 3, the air enters into the tub 14, in the central zone of the rotary drum 15. When the set operating temperature is reached, the control thermostat 12 maintains it at this value by continuously opening and closing the power circuit of the resistance elements 9.
[0017] If the air flow, which helps to ensure thermal equilibrium of the system, should suffer interruption the safety thermostat 10 acts to prevent the heater unit exceeding the preset maximum allowable temperature.
[0018] From the aforegoing it is apparent that the heater unit according to the invention offers the important advantage of a large heat transfer surface between the tubular element 5 and the air to be heated, so allowing the working temperature of the resistance element 9 to be kept substantially low (about 300°C) with the result that it can be constructed at lower cost, is subjected to only low stress, has high operational reliability and need not necessarily require the heater unit to be externally insulated.
[0019] A further important advantage obtainable with the heater unit according to the invention is that it is constructed by a single die-casting procedure, and thus pratically without assembly costs and with the possibility of delivering from the factory a product which can be directly installed in the clothes drier.
[0020] In the embodiment shown diagrammatically in Figures 6 and 7 the heater unit according to the invention consists substantially of a die-cast aluminium alloy plate 16 in which the resistance elements 9 are incorporated in its material and have their terminals emerging from one edge of said plate 16. The plate 16, also incorporating the control and safety thermostats, is fixed to two aluminium cover plates 18 by pins 17 suitably clinched at their ends.
[0021] In order to be installed the heater element is fixed through one plate 18, for example by screws, to a movable portion 19 of the tub 14, which portion substantially forms a swelling of the cylindric wall of the same tub and which is fixed to the tub by screws. With this swelling the inlet pipe 2 comunicates introducing air which, blown by the fan 13, grazes the plate 16, heats and is forced to graze the external wall of the rotary drum 15 and to heat in such a way the laundry placed inside this near the peripheral wall.
[0022] This embodiment has all the advantages of the preceding unit including the possibility of constructing the heater unit in one die-casting procedure, and also has the important advantage of being very flat and therefore installable in already existing washing-drying machines in which there would not be space for a tubular heater unit.
[0023] In the embodiment shown diagrammatically in Figures 8 and 9 the heater unit substantially comprises a die-cast aluminium thin portion 20, slightly curved according to the curvature of the tub 14 of the clothes washing-drier, and a tubular duct 21 provided outside to said portion 20 and extending in a portion 22 centripetally directed.
[0024] Similarly to the previous embodiment, the heater is fixed with its portion 20, for example by screws, to the movable portion 19 of the tub 14, in such a way as the air which enters into the swelling of the cylindrical wall of the same tub, partly grazes said plate heats, goes and passes through the drilled wall of the rotating drum, partly enters into the duct 21 to graze a plurality of fins 23, and goes out through the curved portion 22 to enter into the drum around its front opening.
1. An air flow heater unit particularly for tumbler clothes driers, comprising at
least one electrical resistance element which heats a flow of drying air, characterised
in that said electrical resistance element (9) is completely embedded in a body (5,16,20)
of die-cast aluminium alloy.
2. A heater unit as claimed in claim 1, characterised in that said body (5) is of
tubular shape.
3. A heater unit as claimed in claim 2, characterised in that that surface of the
tubular body (5) which is grazed by the air to be heated comprises a plurality of
radiant fins (8).
4. A heater unit as claimed in claim 2, characterised in that that surface of the
tubular body (5) which is grazed by the air to be heated comprises a plurality of
longitudinal radiant ribs (6,7).
5. A heater unit as claimed in claim 1, characterised in that the tubular body comprises
an outer casing (4) and an inner conduit (5) in which the armoured resistance element
(9) is embedded.
6. A heater unit as claimed in claim 5, characterised in that the outer casing (4)
and the inner conduit (5) are connected together by at least one rib (6,7).
7. A heater unit as claimed in claim 2, characterised in that the armoured resistance
element (9) is spiral-wound.
8. A heater unit as claimed in claim 1, characterised in that said body (16) consists
of a plate-shaped element.
9. A heater unit as claimed in claim 8, characterised in that a plate (18) is provided
on at least one side of the plate-shaped element (16) but spaced apart therefrom.
10. A heater unit as claimed in claim 1, characterised in that at least one control
thermostat (10) and/or one safety thermostat (12) are embedded in the body (5,16,20).
11. A heater unit as claimed in claim 1 characterised in that the body (20) comprises
a curved plate forming a portion of the cilinder surface of the tub of the drier and
a duct (21) having its axis directed according to the generatrices of this curved
plate and its exit end curved toward the central zone of said tub.
12. A heater unit as claimed in claim 11 characterised in that the duct (21) is inside
provided with a plurality of fins (23).
13. A heater unit as claimed in claim 11 characterised in that the fins (23) are directed
parallely to the direction of the air to be heated.