GB2253035A

GB2253035A - Silenced tumble dryer

Info

Publication number: GB2253035A
Application number: GB9202445A
Authority: GB
Inventors: Dino Baggio; Maurizio Saccia; Eleonora Gellner
Original assignee: Zanussi Elettrodomestici SpA
Current assignee: Electrolux Zanussi Elettrodomestici SpA
Priority date: 1991-02-18
Filing date: 1992-02-05
Publication date: 1992-08-26
Anticipated expiration: 2012-02-05
Also published as: FR2672907A1; IT225634Y1; ITPN910003V0; GB2253035B; DE9201623U1; ITPN910003U1; FR2672907B3; GB9202445D0

Abstract

A laundry drying machine comprising a rotating drum (4) for containing the laundry to be dried, and through which passes a flow of air which is drawn in from the exterior and heated by at least one heater, said air being circulated by at least one fan (13) and being expelled by means of a conduit (10) after having absorbed moisture from the laundry to be dried, said conduit or parts thereof being sound-insulated. The conduit is preferably produced by providing a plurality of holes in its surface, the conduit is also wrapped with sound-absorbing material (17) and closed by a preferably rigid cover (18). In particular only the terminal part (15) of said conduit (10) is sound-insulated. <IMAGE>

Description

LAUNDRY DRYING MACHINE WITH SILENCER The invention concerns a laundry drying machine provided with a rotating drum for containing the laundry to be dried and into which is blown a continuous flow of hot air for removing moisture from the laundry.

As is known, in order to provide for drying of the laundry which is introduced into the drum of conventional laundry drying machines, in a satisfactory manner, a continuous flow of air under pressure is circulated through the drum containing the laundry, the air having been heated beforehand by an air heating element, preferably a resistive heating element, which is disposed upstream of the point of entry of the air into the drum, the air being blown by a suitable fan. The air is normally drawn in from the exterior by means of suitable conduits and, after having been circulated within the drum where it absorbs the moisture from the laundry, it is expelled to the exterior by way of other suitable conduits which terminate with an opening for discharge to the exterior.In the great majority of cases, at least for laundry driers for domestic use, that opening is disposed at a position corresponding to the back of the appliance, preferably at the bottom, for readily understandable reasons of aesthetics, space and functionality.

In that way the discharge air is expelled in the most effective manner.

Those hot air laundry driers however suffer from a serious disadvantage from the user point of view.

In fact they suffer from substantial noise generation due predominantly to the turbulence of the flow of air in the conduits and to a lesser degree to the fact that the motor of the fan and the fan itself produce vibrations at an acoustic frequency, in spite of every attempt to reduce that phenomenon.

All the noise which is generated in that way in the conduits is propagated with the air to the outlet and finally issues to the outside of the machine from the opening for discharge of the discharge air.

As a consequence of that, normal laundry drying machines, during continuous operations, are found to be machines which are frequently seriously noisy, as is demonstrated by user complaints.

The aim of the present invention is to eliminate the above-described disadvantages by means of a laundry drying machine which is provided with a particular arrangement using simple structural techniques.

According to the invention there is provided a laundry drying machine comprising a rotating drum capable of containing the laundry to be dried and traversed by a flow of air which is drawn in from the exterior and heated by at least one heater, said air being circulated by at least one fan and being expelled by means of a conduit after having absorbed moisture from the laundry to be dried, wherein at least a part of said conduit is sound-insulated.

The invention will be better appreciated from the following description given by way of non-limiting example and with reference to the accompanying drawings in which: Figure 1 is a view in cross-section of a drier machine according to the invention; Figure 2 is a view in cross-section of an improvement in the terminal part of the discharge conduit; and Figure 3 is a view in longitudinal section of an improvement in the terminal part of the discharge conduit.

Referring to the drawings, the machine comprises an external casing 3 enclosing a rotary drum 4 which is capable of containing the wet laundry to be dried and which is driven in rotation by means of a per se known motor (not shown).

The rear flange 7 of the drum 4 is provided with through openings 9 communicating with an aperture 31 for the intake of the air, which is provided in the rear wall 5 of the casing 3. A conduit 10 communicates on the one hand with the intake opening 11 for the discharge air from the interior of the drum, which is provided in the front flange 6 of the drum, and on the other hand with an air discharge opening 32 provided in the rear wall of the machine.

Disposed in the conduit 10 are a fan 13 which is actuated by a motor (not shown), and at least one final conduit 15 which carries the discharge air directly to the exterior, opening at a suitable hole 16 provided at a suitable position in the rear wall 5.

Experiments carried out in a laboratory situation have shown that the main source of noise, which as stated above is identified as being in the ventilation circuit, diffuses primarily from the terminal part 15 on the conduit 10 and also at a position corresponding to the wall 5 since provided therein is the hole 16 into which is connected the terminal part 15 of the discharge conduit.

In the present description reference is made to the example where the wall 5 is the back of the appliance, but it will be apparent that what is described herein is applicable in identical terms to any wall or surface at which the conduit 10 opens.

In order to eliminate or reduce that disadvantage, a feature of the invention lies in sound-proofing the terminal conduit 15 by providing in its external surface holes of suitable diameter, which are calibrated on the basis of the frequencies to be absorbed.

A certain thickness of sound-absorbent material 17 is wrapped around the discharge conduit 15 of the aboveindicated structure and finally the assembly is closed with a rigid cover 18, preferably of plastics material, to provide a rigid handleable arrangement.

The dimensioning of the cover 18, the volume and the type of sound-absorbent material 17 and the arrangement and diameter of the holes are based on the frequencies and the intensity thereof to be absorbed, and that operation is within the capability of any man skilled in the art.

Furthermore laboratory tests have made it possible to show that the propagated noise is predominantly concentrated around a limited number of acoustic frequencies, typically two or three frequencies. In order thus to optimise the sound-proofing action in respect of said frequencies, it has been found that a substantial improvement in the silencing effect is achieved if the terminal part 15 is of the configuration shown in Figure 2.

The terminal part 15 has a surface region 20 of the conduit, which is protected by a layer of sound-absorbent material 17A of limited thickness, which is particularly suitable for attenuating higher frequencies, and a remaining region 21 which is protected by a layer of sound-absorbent material 17B of greater thickness, which is particularly suitable for attenuating lower frequencies.

It has further been discovered that another improvement in the silencing effect can be achieved with a configuration as shown by way of example in Figure 3.

With reference to Figure 3, it is observed that the layer 17D of insulating material of greater thickness is separated by a divider 22 which delimits a further insulating layer 17C. The two layers 17D and 17C differ insofar as the holes 23 corresponding to the layer 17D present a concentration or mutual distance 33 which is different from the mutual distance 34 of the holes 24 provided at positions corresponding to the layer 17C.

In particular the mutual distance of the second group of holes is less than the distance between the holes in the preceding group.

It has in fact been verified that, with that arrangement, the layers 17D and 17C attenuate the noise in a particularly effective manner around two specific frequencies which depend on the various technical parameters involved (thickness of the layers, length of the layers, diameter and mutual spacing of the holes corresponding to each of said layers).

More generally, it has been found that, by suitably providing the insulating layers, in different thicknesses, lengths, diameter in respect of the holes and mutual spacing thereof, it is possible to minimise the noise at given frequencies and thus attenuate the noise emitted at that frequency in a particularly effective fashion.

A further improvement is achieved if acoustic insulation is also provided between the external edge 18 of the conduit 15 and the exterior wall of teh casing, in this case the rear wall 5 in their common junction region.

In fact it has been verified that a sound source also occurs at direct contact between the discharge conduit 15 and the rear wall 5, since the vibrations at acoustic frequency are transmitted directly and without any attenuation effect from the first of the above-indicated elements to the second thereof.

For that reason, with reference to the detail shown on an enlarged scale at A in Figure 1, the insertion of an acoustically insulating element 19, preferably of annular shape, between the conduit 15 and the wall 5, mechanically separates those elements and thus eliminates the possibility that vibration is transmitted directly, and therewith the associated noise.

It will be appreciated that the present invention may be carried into effect in many different variants and embodiments without however thereby departing from the scope of the appended claims.

Claims

1. A laundry drying machine comprising a rotating drum capable of containing the laundry to be dried and traversed by a flow of air which is drawn in from the exterior and heated by at least one heater, said air being circulated by at least one fan and being expelled by means of a conduit after having absorbed moisture from the laundry to be dried, wherein at least a part of said conduit is sound-insulated.

2. A laundry drying machine according to claim 1 wherein only the downstream part of said conduit for emission to the exterior is formed by a sound-insulated conduit.

3. A laundry drying machine according to claim 1 or claim 2 wherein the sound-insulation is produced by providing a plurality of holes in the conduits, said conduits also being wrapped with sound-absorbent material and being closed by a cover.

4. A landry drying machine according to claim 3 wherein the cover is rigid.

5. A laundry drying machine according to claim 3 or 4 wherein said sound-absorbent material is wrapped into layers of a multiplicity of mutually different thicknesses, each thereof being of a substantially constant thickness in the longitudinal direction.

6. A laundry drying machine according to claim 3, 4 or 5 wherein said sound-absorbent material is composed of a plurality of longitudinal segments which are separated by corresponding transverse separating baffles wherein the distance between the holes in the surface of said conduit relative to a longitudinal segment is different from the distance between the holes which relate to a different longitudinal segment.

7. A laundry drying machine according to any one of the preceding claims characterised in that an acoustically insulating packing element is interposed between the discharge opening of said conduit and the portion of the wall of the machine adjacent the discharge opening.

8. A laundry drying machine constructed and arranged to operated substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.