Various processes are adopted for manufacturing hollow o jects of synthetic or natural rubber, such as hot water bottles, for example, utilizing a die composed of three parts, one part which may be called the upper die, anoth opposite it which may be called the lower die and a cent part known as the core.

When the material is placed in the die, in the form of sheets of rubber, one sheet for each of the two halves of the die, by compressing the material in special presses and applying heat to it, a finished product is obtained b the curing process.

To extract the core from the object so produced various measures must be taken; in the case of hot water bottles for example, certain dimensions must be given to the mout so as to allow extraction of the core, but the material i often torn because of the excessive strain put upon it.

Further difficulties arise over application of inserted pieces, such as the threaded ring for the stopper.

According to another process two halves of the body are molded in the two .chambers created between the two halves of the die and the intermediate core.

When molding is finished, the core is removed from the di the edges of the two halves are placed together, fluid un der pressure is injected inside the die after which the elastomer is cured.

During removal of the core, some areas of the two halves of the hollow object tend to be pulled too hard by exit o said core, and become detached from the die especially whe the material is injected through the core. In the process of extracting the core, due to connection between the molded objects and the material remaining in the feed hole, pulling forces are in fact set up tending to detach the half of the object from its half die.

The invention here described avoids the above drawbacks pr viding at the same time considerable advantages as wiil be explained below.

Subject of the invention is a process for molding elasto- mer in dies to form hollow bodies so shaped that, by cut¬ ting them apart on a geometrical plane, the edges of the two halves obtained have outlines substantially suited to complete matching.

This is therefore a process particularly suited to produ tion of hot water bottles.

The complete die is composed of three main parts: an upper half, a lower half and an intermediate core creating one or more pairs of chambers respectively for the two sub¬ stantially complementary halves of each object. The ma- terial Is injected simultaneously into the two chambers for making each object, through a side channel for each chamber, one of said channels being situated between one face of the core and the upper half of the die, and the other between the other face of the core and the lower half of the die.

Said channels, lying parallel, are connected by means of a feed hole passing transversally through the core.

Said hole Is connected,by means of a longitudinal branch¬ ing duct inside the core, with a second transversal hole for influx of the material, opening onto one face of the core, opposite to one of the die halves at a point cor¬ responding to a mouth in said die half, in such a way as to be aligned with the input nozzle for the material.

Each half of the molded object is therefore connected to the material input channel on a lateral edge.

After molding the core is extracted leaving the two halves of the hollow object in the two half dies; the die is then closed once more to align the two edges of said two halves.

Finally, the two edges are welded together during the curing process.

In the area corresponding to each mouth of the core feed hol there are recesses, one in each half die, the outer aper- tures of which are smaller than their internal volume, so that, within said recesses, an appendix of material is formed and is joined to the rest of said material, which on completion of molding, remains in the core feed hole.

Thus, when the die is opened and the core removed, said appendix, reacting to the pulling force on the materialleft inside the core feed hole, causes detachment of said mater¬ ial from the two halves of each hollow object allowing said objects to remain closely fitting to the two half dies to ensure effective curing. The die having been closed following removal of the core, fluid is blown into said die under pressure to assist and maintain close adherence of the two halves of the hollow object to their respective halves of the die while the cu¬ ring process continues. Preferably the die has two pairs of chambers so that two hollow objects cen be produced simultaneously.

The core feed hole lies between the two pairs of chambers.

A channel connects each of the two mouths of said feed hole to the chambers which form the two halves of the hollow object in each half of the die.

The effect of the foregoing is to ensure a more balanced distribution of the material, a higher output from the die, and a superior end product.

In one half die there is a grip slide to support the noz- zles blowing the fluid in under pressure while curing is proceeding, and to permit said nozzles to translate.

Any piece to be inserted, such as the threaded ring for hot water bottles, is preferably associated to the nozzles used for blowing the fluid in under pressure.

The core is supported by a grip slide moving back and forth perpendicularly to the direction in which the die opens and closes.

Characteristics and purposes of the invention will be made even clearer by the following example of its execution Il¬ lustrated by drawings.

Fig. 1 Yiewof the open die, cut through at its central longitudinal axis.

Fig. 2 Detail of the closed die, cut through at its cen- tral longitudinal axis.

Fig. 3 Partial cross section of the die at the position of the core feed hole.

Fig. 4 The cross section of Fig. 3 when Injection molding has been completed. Fig. 5 Front view of the upper half of the die.

Fig. 6 The open die cut -through at the level of an impres¬ sion.

Fig. 7 Ditto as above, closed during molding.

Fig. 8 The die in Fig. 6, closed, during the curing pro- cess.

The die (10) comprises the upper die half (11), the lower die half (12) and the intermediate core (13).

Said die makes possible the simultaneous production oftwo hot water bottles placed side by side. The upper die half (11) shows the female impressions (14) and (16) substantially equal to the impressions (15) and (17) in the lower die half.

The core (13) shows the male shapes (18), (19) and (20), (21), or creating, when the die is closed, the chambers (29), (31) and (30), (32) respectively for the two objects formed by the die, especially two hot water bottles.

The material is injected into the mold through the nozzle

(39) which, at each molding operation, approaches the die (11) penetrating into the housing (40) until it comes in contact with the projecting mouth (41) which, when the die closes, penetrates inside the hole (42) of the die (11). From the mouth (41 ) the fluid material flows, through the vertical hole (22), into the branch duct(23) communicating centrally with the vertical transversal feed hole (24) pas_ sing through the core (13).

The material flows through the upper mouth (25) and lower mouth (26) into the channels (27) and (28) respectively situated in the body of the half die (11) at the top, and of the other half die (12) at the bottom.

Said channels (27) arid (28) connect with the chambers (29) and (30) created by matching the upper die »with the core (13) and, respectively, with the chambers (31) and (32) created by matching up the lower die (12) with the core

(13) ^' .

The body of the upper die (11), in line with the mouth(25) of the transversal feed hole (24) in the core (13), con- tains a recess (33) shaped substantially like a truncated cone the base of which is internal,and similarly, the body of the lower die (12), in line with the mouth (26) of the above hole (24), contains a recess (34) also shaped like a truncated cone the base of which lies internally. After closing the die, elastomer is injected into it.

On completion of the forming process the die is opened to allow the core (13) to be removed.

During the opening stage the material that had previously penetrated inside the recesses (33), (34) creates a force tending to retain ^'' the material present in the channels(27) and (28), breaking connection with the material inside the feed hole (24) opposing those forces that are tending to detach the hollow bodies (35), (36), (37), (38) from the sides of each half die.

Figure 6 shows a longitudinal cross section at the level of the impressions (14) and (15) and of the corresponding male forms (18), (20).

Figure 7 shows the stage corresponding to closure of the die and the beginning of the injection process.

When the core is removed, the two parts of the die are put back together again as seen in Fig. 8 and, after injecting compressed air inside the die, the curing stage begins which welds the outer edges (39) and (40) of the two halves,like (35) and (36) _; of the object that, in the example described, together form a hot water bottle (41).

Curing having been completed all that is required is to open the die and lift out the perfectly shaped hot water bottle. The advantages of the invention are clear.

Avoidance of the drawbacks which injection of the material, made through the core caused because of the tendency for said core to pull the molded bodies away from the dies at the moment of its extraction,leading to spoiled products and their consequent rejection.

Testing of the hollow objects, especially of hot water bot ties,becomes in practice a part of the procedure adopted since the air blown into the die during curing immediately shows up any incomplete or damaged moldings. Using a single machine and a quick and effective injection system, hollow objects in elastomer, especially hot water bottles, are made of excellent quality, speedily and at a low cost. As the applications of the invention have been described as examples only not limited to these, it is understood that every equivalent application of the inventive concepts explained and every product made and/or in operation accor ding to the characteristics of the invention will be co¬ vered by its field of protection.