It is understood that the right to protection is to be extended to the plant that implements the process of the invention.

Gas assisted technology has been developed in the last decades and it has been identified as the most suitable technology for the forming of parts with thick sections, since it reduces the consumption of molding material and accelerates production cycles.

The said molding technique involves the injection of gas into the mold, after injecting a quantity of molding material that is sufficient to partially fill the cavity, so that the gas can push forward the fluid material to complete the filling process. In this stage the gas hollows a central canal in the fluid material and at the same time stretches the molding material against the internal walls of the cavity.

When the cooling cycle is finished, the gas is vented and the mold opened in order to proceed with the extraction of the part, which internally shows the canal where the gas has passed by.

The gas assisted injection molding technology has the following advantages: reduction of weight for the molded part, reduction of cooling time in the mould, and reduction of duration for each molding cycle.

However, it must be mentioned that this molding technology is not always easy to implement, in view of the many difficulties, both in terms of part design and process implementation.

An intricate problem to solve is the one related to the long cooling time of the internal walls of the part, that is the walls around the hollow part which was cored out by the gas, which has a very high temperature, unlike the external walls of the part, which can dissipate the heat by transferring it to the internal walls of the cavity, which are cooled by a suitable refrigerating system

of the mold.

The high temperature at the interior of the part not only lengthens the molding cycle, but can also lead to unforeseen and intolerable deformation and stress, due to the difference in cooling time between the exterior and the interior of the part.

The aim of the present invention is to solve both the above mentioned problems, with a gas assisted injection process that allows for maintaining the gas temperature below a predefined value in order to reduce the temperature gradients between the interior and exterior of the part until the part is inside the mold.

This result is achieved by the molding process of the invention, which is characterized by the injection of gas mixed with atomized water in the mold.

Due to the high gas injection pressure, the atomized water cannot vaporize, in spite of the high temperature inside the cavity during the injection stage.

Once the fluid mass of molding material has been discharged by the mixture of gas and atomized water, the chamber with the mixture communicates with an atmospheric condition environment, thereby favoring the immediate evaporation the mass of atomized water.

Naturally, the transformation from liquid state to vapor state results from the absorption of the latent heat of evaporation at atmospheric conditions by the atomized water, thus cooling down the internal walls of the part, which is still in the mold and opens only when the gas and water vapor contained in the hollow part caused by the gas inside the fluid mass of the molding material are discharged.

In order to have a better insight of the invention the description continues with reference to the attached figures, which only have an illustrative, not limiting purpose, in which: - Fig. 1 shows the process scheme according to the invention ; - Figs. 1 to 6 show the conditions that are to be found inside the mold during the various phases of the process according to the invention; - Fig. 7 shows a schematic section of the nozzle used to inject the mixture of gas and atomized water in the mold.

With reference to Fig. 1, the molding process of the invention consists of: - One gas compression unit (1) (usually nitrogen) distributed from a vessel (1 a) ; - One water atomizing unit (2) where water and gas from unit (1) are mixed, producing a mixture of pressurized gas and atomized water; - A special nozzle (3) with three canals, which allows for injecting gas and atomized water at the interior of the mold (4) and discharging the mixture of gas and atomized water from the mold to atmospheric conditions; - An ordinary nozzle (5) that is used to inject the molding material into the mold (4).

With, particular reference to Fig. 7, the nozzle (3) has an inlet canal (3a) where the mixture of gas and atomized water comes in, a first outlet canal (3b) through which the said mixture can be injected into the mold and a second outlet canal (3c) through which the said mixture of gas and atomized water can be discharged from the mold (4) to an external environment with atmospheric pressure.

A pin (3d), which goes up and down in the nozzle, determines the opening or closing of the three mentioned canals of the nozzle (3), depending on its position.

The sequence of phases of the injection cycle of the mentioned process is as follows: -Injection of the molding material into the mold (4) through the nozzle (5) till a partial fill of the internal cavity (4a) of the mold (4), as shown in Fig. 2, which also illustrates the nozzle (3), whose canals (3a) and (3c) are both closed ; - Injection of the gas and atomized mixture into the mold (4) through the nozzle (3) till the complete filling of the cavity (4a) of the mold with the molding material, which is distributed onto the internal walls of the cavity, while in the molding material a core (6) is formed, caused by the pressurized mixture of gas and water, as illustrated in Figs. 3 & 4, which show the canals (3a) & (3b) in open position and the canal (3c) in closed position.

- Opening of the second outlet canal (3c) of the nozzle (3) so that the core (6) comes into contact with an environment at atmospheric pressure, causing the immediate evaporation of atomized water, as shown in Fig. 4, which shows the canals (3b) & (3c) in open position and the canal (3a) in closed position; - Venting to the atmosphere, through the nozzle (3), of the gas and vapor contained in the core (6), as illustrated in Fig. 6, which shows the canals (3b) & (3c) in open position and the canal (3a) in closed position.

It is obvious that the next phase is the opening of the mold and extraction of the part.

Although the description makes reference to water, it is understood that the patent also covers those cases in which other atomized fluids are used as refrigerants instead of atomized water, working in the temperature range of 100° C to 300° C with a sudden drop to atmospheric pressure, causing the transformation from liquid to gaseous state.

Moreover, it includes other refrigerating substances, such as powder of a gas in solid state, which will result in sublimation and not evaporation.

In this perspective, for example, atomized alcohol or atomized butylen can be used instead of atomized water, as well as powder of solidified ice (carbon dioxide in solid state), which sublimates as soon as the pressure in the chamber (6) gets down to atmospheric pressure.