Improvement in plastic tubs for washing machines

Abstract: Clothes washing machine or clothes washing and drying combination, in particular for home use, equipped with a plastic tub (1) accomodating a drum (2) in which the clothes to be washed are loaded, said tub being substantially constituted by a cylindrical mantle (3), which is integral with the rear portion (4), a front flange-like portion (5) moulded separately and applied on to the front opening of the tub, a plurality of counterweights (6, 7) contained in respective plastic shells (8, 9) attached to said tub, wherein at least one of said shells (8, 9) is provided with an appropriate plastic projection (10, 11) fitting together with a corresponding plastic projection (12, 13) located on the outer structure of said tub, whereas said pairs of projections (10, 12; 11, 13) are firmly fastened together through fusion-welding of the pIastics which the respective projections are made of.

Description: This invention relates to a clothes washing machine or a combined clothes washing and drying machine, in particular of the household type, which is equipped with an improved type of plastic moulded washing tub in view of its ability to retain and hold the ballast means in place. Plastic moulded washing tubs for clothes washing machines are known in the art to substantially comprise a rigid structure forming the cylindrical peripheral wrapping and the circular bottom wall of the tub, and a circularly shaped front wall which is sometimes separated and is capable of being joined to said rigid structure with per sè known fastening means. Appropriate heavy elements, acting as counterweights, are usually associated to said tubs in order to counterbalance the tub, ie. to increase its inertia and, as a consequence, limit the oscillations that are generated on the tub during spin-extraction phases, ie. when the drum holding the washload is driven to rotate at its highest revolution speed, ie. a speed that is considerably higher than the one at which the same drum typically rotates during washing and rinsing phases. These oscillations are induced by conditions arising from an uneven distribution of the washload along the cylindrical wall of the rotating drum. If no measure is taken to dampen such oscillations, these would give rise to a number of drawbacks and problems. Counterpoising means for clothes washing machines of the afore specified kind are known to be formed by one or more blocks of concrete or similar masses of material of various kinds with a high specific weight which are prepared separately in advance. These counterpoising blocks or masses are first formed to an adequate shape and are then attached in a suitable arrangement to the washing tub of the respective washing machine by means of any of a number of removable fastening means such as screws, bolts, nuts and the like. However, these types of counterweights have a drawback in that they require a relatively long time for the concrete to be prepared and duly hardened. They furthermore carry with them the risk of the concrete blocks coming or breaking off the seats provided for their attachment to the tub, owing to vibrations that are generated by the operation of the machine and can sometimes cause said blocks to actually collapse and fall to pieces. Further types of counterweights for clothes washing machines are also known, for instance from the Italian utility model no. 34081/B/89 (= FR-A-2 654 443), to be formed by concrete blocks that are prepared separately in advance, onto which a plastic material is then applied by an overinjection moulding technique so as to form in this way an appropriately shaped, enclosed wrapping capable of both preventing said blocks from becoming unduly displaced or undesirably breaking off and being applied in a traditional manner against the tub of the washing machines. This document forms the preamble of independent claim 1. Even in this case, however, there is the drawback of relatively long times required by said concrete blocks for their preparation and hardening, which therefore imply clear disadvantages from an economic point of view. Furthermore, the solution is such as to make its manufacturing rather complicated as an industrial process due to said overinjection of the plastic envelope. Among the various solutions suggested or proposed in this connection, a particularly interesting one is disclosed in the EP-A-0 551 067 (Published 14.07.93) filed under the title "Improvement in the ballast arrangement for clothes washing machines". Said patent application discloses at least a container which is associated to a plastic washing tub and is capable of being filled with some appropriate ballasting means, preferably water, when the machine is installed. The advantage of such a solution resides in the fact that clothes washing machines produced according to this concept are much lighter in weight and, therefore, more convenient to handle during transportation and installation. They of course are also less expensive owing to both the reduction in transportation costs and the saving achieved through avoidance of the costs of a traditional ballast in heavy-weight material such as cast-iron or concrete. Even this solution, however, has a drawback in that it fails to identify in a sufficiently clear and complete way the most adequate technique to be used to manufacture the washing tub in plastic material and the ballast containing arrangement associated therewith, and this of course makes the practical implementation of the same solution rather problematic. It is therefore a purpose of the present invention to get over all these drawbacks by providing both a plastic tub for clothes washing machines and the associated counterweight, made of the high specific-weight material that will be described further on and enclosed in a protective shell of plastic material, said shell being capable of being attached to the plastic tub in such a way as to make it possible to easily and quickly install said shell against the structure of said tub. The invention will be further described by way of non-limiting example with reference to the accompanying drawings in which: Figure 1 is a schematic view of a complete tub assembly of a clothes washing machine according to the present invention; Figure 2 is a view of a portion of the tub illustrated in Figure 1; Figure 3 is a view of the tub and the rotating drum, with the front ballsting means separated therefrom. Referring now to the Figures, it can be noticed that they illustrate a washing tub 1 made of plastic material, and adapted to be applied in a per sè known manner in clothes washing machines, said tub accomodating a per sè known type of perforated drum 2, and consisting essentially of a rigid structure formed by a cylindrical peripheral wrapping 3 and a couple of walls, ie. a rear or bottom wall 4 and a front wall 5. Said tub is ballasted on both its front and rear sides by means of masses of inert material 6 and 7, respectively, which are correspondingly contained in enclosed plastic shells 8 and 9. The front-side shell 8 is provided with an appropriate plastic projection 10 adapted to fittingly come into coupling with a corresponding plastic projection 12 that is provided on the edge of the front opening 14 of said tub. In a similar way, the rear-side shell 9 is provided with an appropriate projection 11 adapted to fittingly come into coupling with a corresponding plastic projection 13. Said front and rear shells, therefore, are applied against the front opening 14 and the rear wall 4 of the tub, respectively, by means of the respective projections adapted to fittingly come into mutual coupling with each other in the above described way. After having in this way been applied on the tub, the shells are then fastened in position by melting the matching projections together. This fusion-welding process can be carried out by means of any of the fusion-welding techniques used to join plastic parts, such as for instance ultrasonic welding or the so-called "mirror-like" welding technique, thereby achieving a firm fastening of the ballast masses. Finally, in view of obtaining at this point a complete tub assembly, it is also necessary that the front opening be appropriately closed with an annular diaphragm that is capable of snugly adapting itself to both the opening of the drum 2 and the bellows-like gasket (not shown), the outer edge of which gets closed against the loading door of the machine. To this aim, an effective improvement lies in forming integrally with said front-side shell 8 a plastic annular diaphragm 5 having the required wall thickness and overall shape. It can now be appreciated that other heavy-weight materials than concrete can also be used to make up the ballast, whereas the flange can also be formed to other shapes than those described above by way of non-limiting example, provided that said other materials are in any case contained within the cavities of the same flange, using traditional processing methods suiting the particular application. In a most advantageous way, said inert material 6, 7 can be formed by calcium carbonate. As a matter of fact, said material is a compound that can be added as a filler to plastics in view of reaching desired properties of the final plastic material or part. As a consequence, when the washing machine is eventually to be consigned to scrap and all its reusable materials have to be recovered for recycling, said shells 8, 9 can be readily detached without any difficulty and sent immediately to regrinding, since the inert material contained therein, ie. calcium carbonate, does no longer need to be first separated from the other plastic parts to be recycled. It will be further appreciated that each tub 1 may also be made to any other shape than the above illustrated one as may be considered to be appropriate without departing from the scope of the present invention.

Claims: Clothes washing machine or combined clothes washing and drying machine, in particular of the household type, comprising a plastic washing tub (1) and accomodating a rotating drum (2) into which the washload is loaded, said washing tub consisting substantially of a cylindrical peripheral wrapping (3), which is integral with the rear portion (4), and a front flange-like portion (5) , which is moulded separately for subsequent application on to the front opening of the tub, a plurality of counterweights (6, 7) contained in respective plastic shells (8, 9) attached to said tub, characterized in that at least one of said shells (8, 9) is provided with an appropriate plastic projecting element (10, 11) that is arranged to fit together with a corresponding matching plastic projecting element (12, 13) arranged on the outer structure of said tub, said pairs of matching projecting elements (10, 12 and 11, 13) being firmly fastenend together by fusion-welding of the plastic material which the respective projecting elements are made of. Clothes washing machine according to claim 1, characterized in that at least one of said plastic shells (8) is applied on to said tub in correspondence of said front opening thereof, its respective projecting element (10) being arranged to fittingly match against the corresponding projecting element (12) provided on the edge of said front opening of the tub. Clothes washing machine according to claim 2, characterized in that said front shell (8), its projecting element (10) and the corresponding projecting element (12) provided on said front opening of the tub are essentially annular in their shape. Clothes washing machine according to any of the preceding claims, characterized in that at least one of said plastic shells (9) is applied on to said tub in correspondence of said rear portion (4) thereof, its respective projecting element (11) being arranged to snugly fit against the corresponding projecting element (13) which is substantially provided on the outer circular edge of said rear portion of the tub. Clothes washing machine according to any of the preceding claims, characterized in that said front-side flange (5) is formed integrally with said front-side annular shell (8). Clothes washing machine according to any of the preceding claims, characterized in that said counterweights (6, 7) are made of calcium carbonate.

Inventors: DURAZZANI PIERO, DURAZZANI, PIERO
Applicants: ELECTROLUX ZANUSSI ELETTRODOME, ELECTROLUX ZANUSSI ELETTRODOMESTICI S.P.A.
Application year: 1993
Main classification: D06F37
IPC codes: D06F37, D06F25