“Method for manufacturing a capsule made of aluminum for small tubes with open hole and product so obtained” Description Technical Field The invention relates to an innovative method for manufacturing capsules made of aluminum suited to seal the usual small tubes made of aluminum thereby ensuring a complete eco- sustainability for the packaging, which can be recycled in its entirety due to its being entirely of aluminum. Background art In the packaging sector, and beyond, packages made of small tubes are becoming more and more widespread. Said packages provide to stow the materials to be sold/commercialized within appropriate small tubes made of aluminum, the latter being closed by means of suitable seals, gaskets and capsules. The packaging of products within small tubes made of aluminum allows the seller to comply with all rules related to hygiene and product preservation, by largely reducing costs due to the purchase of various materials and machines suited to sanitize and to create/apply a manmade protective gas. On the other hand, on the client side, the fact of eating/consuming products preserved inside small tubes implies a reduction of waste and promotes an optimal preservation of the product during transportation, by eliminating infiltrations from the environment. In addition, the aluminum used to manufacture these small tubes is also recyclable and this is an advantage of utmost importance in the packaging sector. However, to date a problem still to be solved is a method for closing said small tubes of aluminum. Actually, plastic-made capsules are used but they cannot be recycled together with the small tube due to the fact that they are made of a different material. Given their shape, these plastic-made capsules are easy to mold but they do not meet the needs of a market which more and more aims at environmental friendliness. Moreover, plastic-made capsules commonly used nowadays have several drawbacks, among others a poor resistance to high temperatures. If the product is to be preserved at temperatures exceeding 100°C, then any kind of plastic- made capsule implies the risk of a dispersion of small particles or fragments which pollute the packaged product. For this reason it will be necessary to prefer cold packaging processes, thereby affecting the market. Among previously filed applications or patents, for instance US 4893718, there do not exist solutions to these problems apart from a technique for separating the package into several parts before their recycling. Therefore, it is an object of the present invention to solve the abovementioned problems by providing a method for manufacturing capsules of aluminum suited to seal the common small tubes with open hole. Description of the Invention According to the present invention there is provided a method for manufacturing a capsule made of aluminum for small tubes with open hole, that reliably solves the abovementioned problems. The present manufacturing method provides a new type of capsules made of aluminum suited to seal small tubes with open hole, simplifying in this way the processes of recycling and waste disposal because the entire package is made of aluminum. The so obtained capsule comprises a cylindrical body that confers rigidity to the capsule. The cylindrical body is obtained by means of a drawing process in which all geometrical dimensions are implemented and specified. In one embodiment, said aluminum capsule demands a thickness some millimeter larger than usual for the nozzle/outlet of the small tube, in order to improve the seal effectiveness/reliability. The present aluminum capsule comprises in its interior a thread suited to form a complementary thread on the outlet/nozzle of the small tube in order to improve the sealing effect. A seal is inserted internally in the cavity of the capsule, which is suited to hermetically seal the package and to avoid any kind of infiltration from the outside environment. Finally, a lower band is installed inferiorly on said aluminum capsule, in order to realize a security/warranty seal for distinguishing new capsules from those already opened and therefore used. The present method involving the manufacture of capsules made of aluminum for small tubes with open hole starts with an initial examination of the physical properties of treated aluminum, through an analysis of its elasticity as well as of its resistance to heat and deformation. Thereafter, an aluminum sheet is stretched/extended and engaged within a die adapted to hold in place the aluminum sheet during pressing. The deformation of the aluminum sheet is performed using a punch adapted to impart a cavity, so as to create said aluminum capsule. In one embodiment, said punch is adapted to impart a round and flat shape to the upper face of the capsule, for the purpose of augmenting adherence of the capsule to the open hole of the small tube. In an illustrative and non-limitative embodiment, a conical shape may be given to said capsule, wherein the walls of its cylindrical body are slightly convergent at the upper end for improving the sealing effectiveness. During the aluminum sheet deformation step required to create the cavity which will give rise to the aluminum capsule, said thread is further impressed/engraved in the interior of the capsule. This step is deemed essential in order to form later on, by impression, a thread on the nozzle/outlet of the small tube when the capsule is screwed in order to seal the package. Quality control is carried out randomly on one of the capsules after their manufacture. The insertion of a food grade membrane seal that adheres to the inner upper part of the capsule is adapted to isolate the packaged product within the small tube from the outside environment. Said seal, even if made of non-metal material, is suited for recycling together with the entire small aluminum tube since it constitutes less than 0.4% of the entire package. According to one embodiment, said seal is made of food grade (that is, food contact) silicone material, for the purpose of not altering the properties of the materials contained inside the package. Finally, a lower band is installed which is adapted to represent a security seal, so as to distinguish new small tubes from those already opened. The advantages offered by the present invention are obvious in the light of the foregoing description and they will be even clearer when reference is made to the accompanying figures and to the detailed description. Description of Drawings The invention will be described in at least one preferred embodiment, for illustrative and non- limitative purposes, with reference to the annexed Figures, in which: FIGURE 1 shows the details of a small tube 15 with open hole 22 sealed by a capsule 10 made of aluminum. This capsule 10 comprises a cylindrical body made of aluminum, suited to facilitate the recycling of the entire package after use of the product. This small tube 15 comprises a nozzle or outlet 14 on which a plurality of threads 23 are indicated, which are engraved/etched by the capsule 10 during the first screwing operation. FIGURE 2 shows in greater detail the configuration of the capsule 10 made of aluminum, suited to seal a common small tube of aluminum 15 with open hole 22. This capsule 15 includes in its interior a seal 20, that is a membrane for food products, suited to seal with greater effectiveness/reliability the content of the small tube 15. A thread 17 is imparted during the drawing steps in which a punch forms the capsule 10 starting from a common aluminum sheet. A band 21 is mounted inferiorly on said capsule 10 in order to distinguish a new capsule 10 from one which has been already opened, thereby representing the security seal of the package. FIGURE 3 shows the flowchart embodying the method of the present invention which is linked to the product obtained therefrom. Detailed Description of the Invention The present invention will now be described only for illustrative, but non-limitative or binding purposes, with reference to the accompanying drawings which show some embodiments of the present inventive concept. Turning attention to FIG. 1 it shows a schematical representation of a typical use of a capsule 10 made of aluminum. The capsule 10 is used to seal small tubes 15 which have an open hole 22 on their nozzle/outlet 14. The cylindrical body 12 of the capsule 10 is suited to impart/engrave a thread 23 on this outlet 14 during the first screwing operation. Due to the fact that the capsule 10 is entirely made of aluminum, the whole package assembly is eco-sustainable since it is easily recyclable. Aluminum is in fact one among the most recyclable materials due to its physical properties. Referring to FIG. 2, it shows an internal view of the aluminum capsule 10. The thread 17 is suited to engrave/impart the first thread 23 on the nozzle or outlet 14 of the small tube 15. A seal 20, preferably made of a food grade membrane, is inserted within the capsule 10 in order to increase its sealing properties with regard to the product packaged in the small tube 15. Said seal 20, even if non-metallic, can be recycled together with the whole of the small aluminum tube 15 because it amounts to less than 0.4 % of the entire package. On its lower side, the capsule 10 has a visible lower band 21 which functions as a warranty seal to identify a new capsule 10 and distinguish it from an opened one upon unscrewing. FIG.3 is a representation of a flowchart of the method allowing to obtain said capsule 10 made of aluminum, for small tubes 15 with open hole 22, which includes the following steps: - study 100 of the physical properties of treated aluminum, by means of analysis of elasticity and heat and deformation resistance; - extending 200 an aluminum sheet, engaged within a die adapted to maintain said aluminum sheet in position during pressing; - deformation 300 of the aluminum sheet by means of a punch, adapted to impart a cavity, creating said aluminum capsule 10; - quality control 400 carried out randomly on one of the manufactured capsules 10; - insertion 500 of a food membrane seal 20, which is adherent with the upper internal part of the capsule 10, adapted to isolate the packaged product within the small tube 15 from the outside environment; said seal 20, even if made of non-metal material, is adapted to be recycled together with the entire small aluminum tube 15 since it constitutes less than 0.4% of the entire package; - installation 600 of a lower band 21, adapted to represent the security seal, so as to identify the small tubes 15 that are still new and those already opened. Lastly, it is clear that changes may be made to the invention, as described so far, and even additions or variants obvious for a skilled person are possible, without in this way departing from its scope as defined in the appended claims.