Wash tub of plastics material for clothes washing machines

A wash tub for a front loading clothes washing machine of domestic type is made in a single body, preferably by injection moulding of plastics material. The tub is provided with a cylindrical band having at least two portions of different diameter. In the area of the region where the band changes in diameter, an annular stiffening rib is provided having seats for locking the suspension members of the tub. The rear portion includes in one piece box-like housings, or at least a bracket, capable of being filled with counterweight material or fixed to added ballast masses, respectively.

BACKGROUND OF THE INVENTION 
The present invention relates to a wash tub of plastics material capable of 
being used in a front loading clothes washing machine of domestic type. 
As is known, a clothes washing machine of this type is provided with a wash 
tub which can contain a rotatable drum and the liquids which are required 
for the washing operations. The drum is supported by a shaft, in turn 
brought by a hub which is provided with bearings and fixed, through 
sealing gaskets, to the rear wall of the wash tub. 
In order to reduce the difficulties and costs for manufacturing and 
servicing of metal tubs, several solutions have been provided for tubs 
made of plastics material. 
For example, French Pat. No. 1362919 relates to an enbloc tub made of 
plastics material and including all the auxiliary members (bearings, 
connectors, etc). However, this tub is of the top loading type, which 
undergoes reduced dynamic stresses as the relevant drum is supported on 
both sides. 
Further patents (e.g. British Pat. No. 1555746 and W. German Utility Model 
No. 7231098) disclose tubs wherein only a few members, those which undergo 
less mechanical and/or thermal stresses, are made of plastics material. 
W. German Pat. No. 1585866 describes a washing machine having a tub which 
is made of plastics material but provided with a metal stiffening band to 
which all the support elements are connected. 
Moreover, French Pat. No. 1513957 discloses a plastic wash tub which is 
sustained by a support frame connected with the drive and support elements 
and ensuring the necessary strength when the tub is in operation. 
Finally, Italian Utility Model No. 162400 relates to a wash tub made of 
thermoplastic material and consisting of two half-shells which are fitted 
to each other by means of bolted flanges. 
Other plastic wash tubs having thick walls are known which, however, do not 
satisfactorily overcome the technical problems arising when replacing 
metal with plastics. Basically, these problems are due to the considerable 
deformations occurring in plastics material when the tub is subjected to 
strong mechanical stresses, particularly when the wash drum is 
spin-drying, and high thermal changes, due to the different washing stages 
of the machine. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide an enbloc 
plastic wash tub, preferably made by injection moulding, which embodies 
also all the auxiliary members such as bearings, connectors, water supply 
and discharge conduits, etc., the tub having a maximum of reliability, 
structural simplicity and strength. 
This object is attained, according to the invention, in a wash tub of 
plastics material, for a front loading clothes washing machine of domestic 
type, made in a single body including a rear wall which embodies a hub 
wherein bearings are located for a shaft capable of supporting the wash 
drum, the body including also a cylindrical band which carries ballast 
masses and is provided with inlet and discharge apertures for the washing 
liquid, as well as with flanges for fixing thereto the drive members of 
the drum and the suspension members for the drum and tub assembly. 
The tub is characterized in that the cylindrical band has at least one 
front and one rear portion of different diameter, that of minor diameter 
being adjacent to the rear wall, the outer surface of the band being 
provided, in the area of the region where the band changes in diameter, 
with an annular rib including transverse stiffening elements and seats for 
locking suspension members. 
Furthermore, the rear wall of the tub is provided with radial ribs which 
are shaped so as to stand the dynamic and thermal stresses occurring 
during the washing operations.

DETAILED DESCRIPTION OF THE INVENTION 
With reference to the drawings, the wash tub according to the invention 
consists of a substantially cylindrical, single body preferably made by 
injection moulding of a proper thermoplastic material and comprising a 
cylindrical band or member 7, which in turn includes two portions 8 and 9 
of different diameter, as well as a rear wall 10 which is integral with 
band 7. The front portion 8 has a diameter which is larger than that of 
the rear portion 9 and is provided with three circular apertures 11, 12, 
13 which can respectively be connected to an inlet conduit and a discharge 
conduit for the washing liquid, as well as to a recirculating conduit 
which is provided for recovering the detergents that are collected at the 
bottom of the tub. The cylindrical portion 8 is provided with a front edge 
14 projecting radially outwardly and capable of co-operating with a flange 
(not shown) which carries, in a way known per se, ballast masses, portion 
8 defining also a front aperture for loading the clothes washing machine. 
The rear portion 9 is adjacent to the rear wall 10 and is provided at the 
top with outer box-like housings 18 communicating with each other through 
passage holes 30 and capable of being filled with a counterweight 
material, e.g. concrete. 
In another embodiment, the box-like housings may be replaced, with the same 
location on the rear portion 9, by at least one bracket 19 integral with 
the band 7 and to which added ballast masses can be fixed. 
In the area of the region where the band changes in diameter, an annual rib 
15 is provided having transverse stiffening tongues 16 and seats 17 for 
locking thereto the suspension and support members of the drum and tub 
assembly. In this way, the annular rib 15 and the relevant transverse 
stiffening tongues 16 can withstand all the dynamic stresses which are 
produced by the rotation of the drum and therefore make it possible to 
obtain a simpler construction of the tub, which further may be made with 
thinner walls. 
The bottom side of the rear portion 9 is integral with a flange 20 
including seats for locking and supporting the electric motor of the 
machine. 
The rear wall 10 of the wash tub has a configuration including generally 
radial ribs 21 which are so arranged and shaped as to form a type of 
circular fret pattern around the perimeter of the wall 10. Thus, as shown 
in the drawings, the wall 10 and ribs 21 define segments which 
alternatively recessed. This feature enables the whole structure of the 
tub to gradually and evenly exchange heat, preventing in this way any 
deformation due to thermal changes during the different washing cycles. 
At the center of the rear wall 10 is fitted a metal hub 22 for the bearings 
of the drum shaft. 
Furthermore, the bottom side of the rear wall 10 is provided with apertures 
25, 26 for inserting thermostatic switches capable of sensing the 
temperature of the washing liquid, and is also provided with a box-like 
housing 28 which is divided into two compartments forming relevant 
air-traps for corresponding pressure-switches (not shown) capable of 
monitoring the liquid level in the wash tub. 
In the same region of the tub an integral housing 27 for the heating 
elements of the washing liquid is also provided, which housing radially 
projects outwards from the band. This projection enables a heating 
resistance (not shown), due also to the fact that the front portion 8 of 
the cylindrical band 7 has a larger diameter, to be located in a well 
defined area and completely submerged even with a minimum water level in 
the tub. This feature results in a reduction of electric energy 
consumption during operation. 
Adjacent to its perimeter, the rear wall 10 of the tub has therein a 
plurality of outwardly projecting metal pins 29 the projecting ends of 
which are threaded and capable of co-operating with locking means for 
fixing the tub to the casing of the machine, during transportation 
thereof, in order to keep the tub steady. 
Around the pins 29, the tub is provided with integral radial stiffening 
tongues or members 23 that, like the transverse tongues 16 of the annular 
rib 15, serve the function of distributing stresses onto surfaces of the 
tub (in the example given, those of the rear wall 10) which are as large 
as possible. 
The main advantages of the wash tub according to the invention may be 
summarized as follows: 
simplified and rationalized manufacture; 
reduction of operations required for assembling the various components onto 
the tub; 
improved strength of the tub against thermal and mechanical stresses.