Background Art Currently, light-alloy wheels are low-pressure die-cast by means of a shell-type mold in which the filling material is fed from the center of the mold, at the center of the impression that forms the wheel shape.

The mold is fixed on a hydraulic press for the opening and closing actions.

Below the surface on which the mold rests there is a pressurized furnace that contains the alloy in the liquid state; the alloy is introduced at low pressure in the center of the mold through a riser tube, while a PLC (electronic controller) electronically controls all the steps of its filling.

The machine cycle varies between five and six minutes and comprises in succession the steps of filling, feeding, cooling, setting, mold extraction and preparation of the mold for the next wheel.

After the setting step, the furnace below the mold is depressurized, causing the descent of the column of molten filling material into the riser tube from the level of the mold to the level of the material contained in the furnace.

Feeding from the center of the wheel provides a uniform distribution of the material, causes no turbulence problems and provides a good feed when the wheel is small and has a very simple shape.

However, when the wheel has a particularly complicated shape in terms of contour and thickness, undesirable porosities, detectable by X-rays, can be generated.

Most of the times, these porosities form due to insufficient feeding, as a consequence of turbulent motions of the alloy and overheating.

PCT/EP02/07844 filed on July 15,2002 by the same Applicant,

discloses a mold in which the filling points of the impression that forms the shape of the wheel, generated between the lower mold part and the upper mold part, are arranged at the openings of the shape of the wheel, where the upper and lower mold parts are in contact when the mold is in the closed configuration.

This mold solves the problems noted above, improving considerably the quality of the wheel obtained from the casting process, although, in some cases in which wheels having a particularly complicated shape are cast, it has revealed some drawbacks, most of all related to an uneven distribution of the heat of the mold and to a less than optimum feeding step, which cause porosities and mechanical characteristics of the wheel that are not entirely satisfactory.

Disclosure of the Invention The aim of the present invention is to provide a mold that solves or substantially reduces the problems of conventional molds for forming wheels having both particularly complicated and simple shapes.

Within this aim, an object is to provide a mold by virtue of which there is a uniform distribution of the heat in the mold.

Another object is to provide a mold by means of which the feed step is improved.

Another object is to provide a mold that allows to produce wheels that have few porosity defects.

Another object is to provide a mold that allows to obtain a uniform distribution of the alloy in the impression.

Another object is to provide a mold that allows to produce a wheel that has improved mechanical characteristics.

Another object is to provide a mold by means of which the production cycle time is reduced.

Another object is to provide a mold that has a simple structure and can be manufactured with known kinds of equipment and technology.

This aim and these and other objects that will become better apparent hereinafter are achieved by a mold particularly for road vehicle wheels, of the type comprising a lower mold part, an upper mold part and perimetric mold parts that form an impression to be filled with molten material, characterized in that it comprises a distribution unit that is arranged below said lower mold part and is designed to be connected to at least one riser tube, which is shaped so as to form one or more slots shaped like a circular arc for injecting the molten material into said impression, said slots being arranged, when the mold is closed, at the outer front edge'of said impression, said one or more slots being distributed circumferentially so as to allow a balanced injection with respect to the center of the impression.

Brief description of the Drawings Further characteristics and advantages of the invention will become better apparent from the description of a preferred but not exclusive embodiment thereof, illustrated only by way of non-limitative example in the accompanying drawings, wherein: Figure 1 is a transverse sectional view of a mold particularly for forming wheels of road vehicles, having the structure according to the invention; Figure 2 is a transverse sectional view of a part of the mold of Figure 1; Figures 3 and 4 are plan views of two components that constitute the part of the mold shown in Figure 2.

Ways of carrying out the Invention With particular reference to Figure 1, a mold particularly for road vehicle wheels, having the structure according to the invention, is generally designated by the reference numeral 10.

The mold 10 comprises a lower mold part (bottom) 11, to be arranged above a pressurized furnace, generally designated by the reference numeral 12, an upper mold part (male plug) 13, and perimetric mold parts 14 forming as a whole an annular shape; in the closed configuration, said mold parts

form an impression 15 into which the molten alloy is to be injected in order to form a wheel.

The upper mold part 13, which comprises a central body 13 a to be fixed to an annular body 13b, is shaped in a downward region so as to form the rear shape of the wheel.

The lower mold part 11, which is instead constituted by a single body, is shaped in an upward region so as to form the front shape of the wheel.

The mold 10 comprises a distribution unit 16, which is arranged below the lower mold part 11 and is meant to be connected to a riser tube 17, which in turn is connected to the furnace 12 that contains the molten material, for example aluminum.

The distribution unit 16 is substantially a hollow body constituted by two shaped elements that are superimposed, the upper shaped element 16a being in contact with the lower mold part 11, the lower shaped element 16b making contact with the riser tube 17.

The upper and lower elements 16a and 16b are shaped so as to form a central connecting channel 18, which is substantially vertical and is designed to be connected to the riser tube 17 and from which angularly equidistant transverse channels 19 extend radially.

The transverse channels 19 lead into an annular reservoir 20 formed by an internal tubular cavity of the distribution unit 16.

At least one slot 21 is provided in an upward region with respect to the reservoir 20 for injecting the molten material into the impression 15; such slot runs continuously and circumferentially over 360 sexagesimal degrees at the outer front edge of the impression 15 when the mold is closed.

Perimetric lips 22 for connecting to the impression 15 protrude from the edges that form the opening 21.

The connecting channel 18 is shaped, in an upward region, so as to form a redirection element 23 for distributing the molten material that arrives from the riser tube 17 toward the corresponding transverse channels 19.

The distribution unit 16 is further provided with seats 24 for temperature and/or level measurement devices 25 for the molten material that it contains.

The upper and lower elements 16a and 16b that constitute the distribution unit 16 are fixed to each other reversibly by means of first screws 26 and are fixed to the lower mold part 11 by means of second screws 27.

As regards operation, the distribution unit 16 divides the flow of the molten material, for example aluminum, into a plurality of transverse channels 19, conveying it into the reservoir 20, which by means of the slot 21 forms an open injection point that covers 360 sexagesimal degrees at the front outer edge of the impression 15.

As an alternative, the distribution unit 16 can be provided with a plurality of separate slots shaped like a circular arc, which are angularly equidistant, are arranged at the outer front edge of the impression, and are connected in a downward region to corresponding reservoirs that have the same shape and are in turn connected to one or more riser tubes by means of corresponding transverse channels.

In practice it has been found that the present invention has achieved the intended aim and objects.

The distribution of the heat in the mold is more uniform.

The material is distributed very uniformly, avoiding turbulence problems and obtaining a good distribution and feeding of said material, with consequent few X-ray porosity defects, uniformity of the alloy and good mechanical characteristics of the finished product.

Moreover, the machine cycle times and the mold preparation times are reduced considerably.

The present invention is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

The technical details may be replaced with other technically equivalent elements.

The materials, so long as they are compatible with the contingent use, as well as the dimensions, may be any according to requirements.

The disclosures in Italian Patent Application No ; PD2001A000265 from which this application claims priority are incorporated herein by reference.