Counterweights are known, used in household electrical appliances to counter-balance the weight of a door of the appliance which can project (over or dishwasher door when open, dishwasher basket when extracted, etc.) or to attenuate the effect of rotating eccentric masses (rotating washing machine drum).

Known cement counterweights, which are generally preferred to the more costly metal counterweights, generally consist of cast counterweights, pressed counterweights or counterweights enclose in a plastic casing. Cast counterweights are obtained by filling suitable moulds with the cementitious mix in the fluid state.

They have a reasonable surface finish, a satisfactory variability of obtainable shape and a fairly wide range of obtainable maximum density. At the same time they have a mechanical compression strength which depends on the thickness of their resistant cross-section and varies considerably as their maximum density varies, but practically zero tensile strength. Finally they are difficult to handle, particularly during the curing stage, which is very long, they have poor dimensional uniformity, surface flash, high sensitivity to impact, and the ability to release powder and/or to detach small fragments of cementitious material.

Known pressed counterweights are obtained by pressing the cementitious mix in powder form (moist sand) in a mould. They thus require a shorter curing time, with consequently reduced handling problems, and also

have a satisfactory mechanical compression strength which is little conditional on their maximum density, which can be high. Finally they have satisfactory dimensional constancy and have limited surface flash.

However alongside these advantages pressed counterweights also have drawbacks, and in particular a shape depending on the pressing techniques used, a certain sensitivity to impact, poor tensile strength and the ability to release powder and/or to detach small fragments of material.

Cement counterweights enclose in a plastic casing are obtained by filling said casing with a fluid or dry material of suitable density. The resultant product is attractive, has a compact smooth outer surface, and a total absence of powder and small material fragments. However alongside these advantages they have a high production cost, a limited maximum density, a non-constant weight because of the difficulty of filling the plastic casing, poor or no adhesion between the plastic casing and the filling material, and finally mechanical characteristics which depend exclusively on the plastic casing.

An object of the invention is to provide a cement counterweight, particularly for household electrical appliances, which has all the advantages of known cement counterweights, but eliminates those drawbacks which are jointly or separately present.

These and further objects which will be apparent from the ensuing description are attained, according to the invention, by a cement counterweight, particularly for household electrical appliances as described in claim 1.

Two preferred embodiments and one executive variant of the invention are described in detail hereinafter with reference to the accompanying drawings, on which:

Figure 1 is an exploded perspective view of a first embodiment of a counterweight of the invention, Figure 2 shows it in its assemble state, Figure 3 is an exploded perspective view of a second embodiment thereof, Figure 4 is an exploded perspective view of a variant thereof for mounting in a dishwasher, and Figure 5 is a perspective assembled view thereof.

As can be seen from the figures the counterweight of the invention, in the embodiment shown in Figures 1 and 2, comprises a plastic shell 2 of shape substantially corresponding to the shape of the counterweight to be obtained. It is open and is provided with ribs comprising undercuts and/or projections and enlargements the purpose of which is essentially to securely bind the cementitious material to it.

The plastic shell 2 is positioned within a steel mould (not shown) provided with a cavity which perfectly houses said shell. The cementitious mix in powder form (moist sand) is fed into the shell positioned in this manner, and is then pressed to obtain a body 4 which perfectly adheres to the shell 2 to form a product of optimum mechanical characteristics after the cement is cured.

With this embodiment the counterweight of the invention has a completely satisfactory surface finish, a considerably reduction in the formation of powder and/or fragments of cementitious material, no shape limitation, high mechanical compression and tensile characteristics, low or no sensitivity to impact, and constant mechanical characteristics with time, all as a result of just a few operations, together with considerabie dimensional uniformity.

Moreover the plastics material enables a product to be obtained with sharp edges, unobtainable with cement alone, and also enables integral fixing members 6 to be formed for accessories such as pipes 8 and rubber components 10 of the appliance to which the counterweight is to be applied.

In a different embodiment, shown in Figure 3, after its filling with the cementitious material to form the body 4, a plastic counter-shell 12 can be coupled to the plastic shell 2 to completely isolate the cementitious body 4 from the outside. The counter-shell 12 can be fixed to the shell 2 by any traditional means, such as bonding or gluing, or by suitable fixing means applied from the outside or integrated into the shell 2 or into the counter-shell 12 to snap-engage each other.

This embodiment adds to the advantages of the preceding embodiment the further important advantage of total elimination of powder and/or fragments of cementitious material.

This product, in which the cementitious body 4 is completely enclose by the plastics material 2,12 can also be obtained by firstly forming the body 4 with pressed cementitious material and then covering it with plastics material within a suitable mould.

In the variant shown in Figures 4 and 5 the counter-shell 12 is directly formed on that part of the household electrical appliance on which the counterweight is to be mounted. For example in the case of a washing machine that part of the appliance would be a part of the tub 14 which houses the rotary drum. In this case the counter-shell is transformed from a passive member into a member able to perform with said part 14 the active function for which said part is destined. It will be apparent that in this case the counter- shell 12 is obtained practically without any additional operation.