GB2157326A

GB2157326A - Wash tub

Info

Publication number: GB2157326A
Application number: GB08409615A
Authority: GB
Inventors: Philip Barnish; Dennis Wilfred Shore
Original assignee: Philips Electronic and Associated Industries Ltd
Current assignee: Philips Electronics UK Ltd
Priority date: 1984-04-13
Filing date: 1984-04-13
Publication date: 1985-10-23
Also published as: IT8521358V0; FR2562920A1; DE3512137A1; FR2562920B1

Abstract

A wash tub, for a domestic front-loading washing machine, having a "Greek fan" back plate 4 which is formed separately from the rest of the tub and comprises structural foam. This enables thick wall sections to be used around the hub 3 and maintain adequate rigidity in the region of the hub. The hub may be formed of metal (21, Fig. 4 not shown). <IMAGE>

Description

SPECIFICATION Wash tub This invention relates to a wash tub for a domestic front-loading washing machine, the back plate of which tub is arranged to support a rotatable wash drum within the tub.

It is well known in such washing machines to minimise the clearance between the drum and the tub in order to reduce the quantity of water needed. To achieve this, it is necessary for the back plate to be substantially rigid in order to prevent, as far as possible, any vibration of the drum caused by out-of-balance wash loads. To achieve a substantial degree of rigidity without having to resort to a heavy construction which uses a large amount of material, it is known to construct the back plate in the form of a so-called "Greek fan" or "Greek fret" in which the plate is divided into an even number of segments which, at least at their ends adjacent the rotational axis of the drum, are staggered from each other in alternate axial directions. These segments are joined together by radially-extending ribs to form a continuous back plate.This construction is suitably rigid, assuming an adequate number of segments (usually at least ten), and has been made in the form of an aluminium die-casting which allows fairly thin segments and ribs to be used. This achieves substantial savings in material quantities and, hence, manufacturing costs.

The die-casting process is relatively expensive unless very large manufacturing quantities are involved. In order to reduce costs for smaller quantities, it is known to form the tub from a plastics material by the injectionmoulding process. An example of this is described in European Patent Application No.

0043429 and comprises an en bloc tub produced by a single injection-moulding operation of a thermoplastic material. The tool cost of such a tub is-at least theoretically-less than that for a drum made of two or more separate parts, for example having a separately manufactured end plate. There are, however, some problems which arise from an en bloc construction, particularly during the cooling and shrinking period immediately after the release of the tub from the mould, when stresses are set up in the tub. Another problem is that it is not practical to provide a water-retaining flange on the front end of the tub as is now generally used in the art.

A more serious problem, however, is concerned with the need in such mouldings to avoid thick sections since these tend to distort excessively during the cooling/shrinking phase. Thick sections would, however, be particularly useful in the region of the back plate which surrounds a metal hub for the drum shaft bearings since maximum possible strength is required in that region to carry the load from the bearing. This load has increased, of course, with the steady increase in the maximum spin-drying speeds over the last few years and, to ease the problem, it is customary to provide two roller or ball bearings in the hub, the front bearing having a larger diameter than the rear bearing. This can be seen from the hub 22 in Fig. 2 of the above-mentioned European patent application, which clearly illustrates the disadvantage of not being able to use thick wall sections in mouldings.The problem arises principally because the diameter of the hub 22 is greater at the front than the rear. The front-to-back slope of this hub 22 is opposite to that of the required draw-off angle (typically 5 ) for separating the mould dies and releasing the moulding. Thus the thickness of the wall section in the region of the upper portion of hub 22 as seen in the above-mentioned Fig. 2 should increase quite substantially from left to right. To avoid the problems arising from thick wall sections, however, it has been necessary to provide a double wall and it is to be noted that, as a result, there is no stiffening affect of the upper segment 10 on the hub 22 in this region. Since this applies to each alternate segment around the hub, a substantial amount of the benefit of the Greek fret configuration is lost as far as the rear end of the hub 22 is concerned.

One object of the invention is to eliminate, or at least reduce, this problem.

According to the invention there is provided a wash tub for a domestic front-loading washing maching of the type having a rotatable wash drum within the tub and at least partially supported by the back plate of the tub, characterised in that the back plate comprises a structural foam moulding secured to, but not formed integrally with, the remainder of the tub.

Structural foam mouldings are well known and are formed from a plastics material containing foaming agents to produce a foamed core with substantially solid skins on either side. Due to the foamed core, relatively thick wall sections can be used without giving rise to any problems and so the required thick section can be used around the metal hub to ensure that it is rigidly supported around its whole length. Further, such a construction allows the diameter of the front bearing to be increased relative to that of the rear bearing to allow for higher spin speeds.

Though structural foam mouldings require a longer moulding cycle, the resultant increase in cost is at least partially offset by the fact that less material is used and a further saving may be achieved due to the fact that a structural foam panel is stronger than a solid panel of the same thickness, with the result that the sectional dimensions may be reduced in some regions.

On the other hand, no significant advantage acrues from the use of structural foam for the remainder of the tub but the increased cost is a disadvantage. By manufacturing the back plate separately from the rest of the tub, the latter may be either a solid or a structural foam moulding. A further advantage of separate manufacture is that an integral waterretaining flange can be formed at the front end of the tub.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, of which Figure 1 is a cross section of the upper portion of a wash tub plate according to the invention, Figure 2 is an elevational view of part of the back plate, Figure 3 is a section along A-A in Fig. 2, and, Figure 4 is an alternative hub arrangement.

Fig. 1 shows a vertical section through the portion of a wash tub 1 which extends above the axis 2 of a metal hub 3 arranged to support a wash drum by means of a shaft journalled in a pair of bearings in the hub.

The bearings, shaft, and wash drum are not shown in the drawings.

Hub 3 is an insert moulded into a structural foam backplate 4, formed by an injection moulding process, and is necked to provide two abutment surfaces 5 and 6 against which respective bearings for the drum shaft may be pressed with a forced fit. The hub 3 is held rigidly by a generally cylindrical wall 7 of back plate 4. It is to be noted that relatively large bearing surfaces 5 and 6 are provided by a substantially reduced diameter of hub 3 in the necked portion and that, as a consequence, the surrounding wall 7 is relatively thick in this area. Without the use of a structural foam moulding, the thickness could be too great and an alternative, and less satisfactory, design would have been necessary. In practice, the necked portion of hub 3 is provided on its outer surface with one or more axially extending ribs which serve to prevent any rotation of the hub in the wall 7.

In addition to wall 7, back plate 4 includes a peripheral rim portion 8 having an outwardly-directed lip 9 and an even number of segments extending between the hub 3 and the rim 8. The segments are arranged in the Greek fret configuration with segments 11 extending from the front region of wall 7 to rim 8 and segments 12 extending from the rear of wall 7 to rim 8. The edges of these segments 11 and 12 are joined by radiallyextending ribs 13 to form the known Greek fret configuration.

The remaining portion of the tub 1 comprises an injection moulding having a generally cylindrical portion 14 with a water-retaining flange 15 at one end and an outwardlydirected lip 16 at the other end. The lips 9 and 16 are forced towards each other by an encircling troughed metal band 17 so as to compress a resilient O-ring sealing gasket 18 to form a water-tight seal between the back plate 4 and the cylindrical portion 14. The latter may be a solid moulding or may be of structural form.

It can be seen that the wall 7 has a drawoff slope 19, extending at about 5 downwards from the end of segment 11 and a corresponding slope 20 extending downwards from the end of segment 12. These slopes are required in order to allow the moulding dies to be moved apart and the moulded end plate removed. These slopes result in the central portion of wall 7 being thicker than would otherwise be required. This thick portion presents no problems due to the use of a structural foam moulding.

Referring now to Fig. 4, the metal hub 21, corresponding to hub 3 of Fig. 1, is so shaped as to accomodate a larger bearing on face 22 at the front end than on face 23 at the rear end. As explained above, the larger front bearing allows higher spin speeds to be achieved. In this case the draw-off slope 24 corresponding to slope 20 in Fig. 1 causes a very thick cylindrical wall section at the rear end of the wall. Since the back plate is of structural foam, such a thick section is entirely practical, and there is no need to split the wall into two portions, and hence reduce the rigidity, as is necessary in the wash tub described in the above-mentioned European patent application.

It will be understood by those skilled in this art that many features common to wash tubs, such as water inlets, detergent dispensers, ballast weight fixing arrangements, mounting arrangements, heater and other access apertures, have been omitted from the drawings since these form no part of the invention. It will also be appreciated that the wash drum may additionally be supported at the front end.

Claims

1. A wash tub for a domestic front-loading washing machine of the type having a rotatable wash drum within the tub and at least partially supported by the back plate of the tub, characterised in that the back plate comprises a structural foam moulding secured to, but not formed integrally with, the remainder of the tub.

2. A wash tub as claimed in Claim 1, wherein the back plate includes a metal hub suitable for accommodating two rotary bear ings mounted on a shaft of said drum, which hub is arranged to accommodate a larger bearing at its front end than at its rear end.

3. A wash tub, for a domestic front-load ing washing machine, substantially as herein described with reference to the accompanying drawing.