Mixing device

1. A mixing device suitable to mix substances or liquid or semi-liquid mixtures to increase the volume thereof, comprising a hub which develops along a central axis and two mixing spokes connected to the hub, wherein each of said spokes comprises an external lateral fin and two upper and lower connection segments, which connect respective upper and lower ends of said lateral fin to said hub, and wherein said lateral fins and said upper and lower connection segments have respective longitudinal axes of development inclined with respect to each other and/or with respect to said central axis, wherein said spokes are disposed angled with respect to each other by an angle of 180° with respect to said central axis and develop with respect to said central axis in a truncated cone-shaped volume, and in that said fins have respective external edges lying on a common truncated cone-shaped surface, having a flared shape between said lower connection segment and said upper connection segment, and the lateral fin of at least one spoke lies on a vertical lying plane inclined with respect to said central axis by an angle of vertical inclination comprised between 2° and 10°.

2. The mixing device as in claim 1 , wherein said external edges have a flaring angle comprised between 1° and 15° with respect to the central axis.

3. The mixing device as in claim 1 , wherein said external edges have a flaring angle comprised between 5° and 10° with respect to said central axis.

4. The mixing device as in claim 1 , wherein each of said two spokes has a through aperture delimited by said connection segments, by said lateral fin and by said hub suitable to allow, during use, the passage of the substances or the mixture.

5. The mixing device as in claim 1 , wherein the lateral fin of at least one spoke lies on a vertical lying plane inclined with respect to said central axis by an angle of vertical inclination comprised between 4° and 8°.

6. The mixing device as in claim 1 , wherein said upper and lower connection segments of at least one spoke are angled with respect to each other by an angle of horizontal inclination comprised between about 15° and about 25°.

7. The mixing device as in claim 5 , wherein said upper and lower connection segments of at least one spoke are angled with respect to each other by an angle of horizontal inclination comprised between about 18° and about 22°.

8. The mixing device as in claim 1 , wherein at least one spoke is provided with grooves and/or extensions made in an external edge of the respective lateral fin, defining passage channels configured to promote the generation of small bubbles suitable to increase the volume of the substances and of the mixture to mix.

9. The mixing device as in claim 8 , wherein at least one spoke is provided with other grooves made in an internal edge of the lateral fin so as to define extensions, said other grooves being disposed alternate with respect to the grooves and cooperating with them in order to increase the volume of the substances more effectively.

10. The mixing device as in claim 8 or 9 , wherein said passage channels and said grooves have respective squared corners.

11. The mixing device as in claim 1 , wherein said upper and lower connection segments are angled with respect to the respective lateral fin, defining between them respective included angles, comprised between 155° and 175°.

12. The mixing device as in claim 1 , wherein at least one of either said upper or lower connection segments has a shape tapered from said hub toward said fin.

13. A machine to prepare ice-cream comprising a truncated cone-shaped container in which the ingredients are disposed, a cooling circuit to cool the container, a motor member and a mixing device as in claim 1 disposed in said container, wherein the hub is connected to a drive shaft of the motor member in order to be made to rotate around said central axis, and said lateral fins are each located at least partly in contact with the internal side walls of the container.

14. A machine as in claim 13 , wherein said central axis of rotation is inclined by an angle not greater than 20° with respect to a horizontal plane.