Abstract:
The present invention relates to a machine for injection molding of rubber products, comprising a plurality of molding units to be operated separately for carrying out a molding cycle. The molding units are mounted on a common support and each unit receives the rubber blend to be used in molding through a duct branched off from a channel fed by a common injection unit. The branched-off feeding ducts of the units are intercepted by a dispensing element moved step by step to sequentially open a predetermined number of the branched-off ducts, so that the corresponding molding units are driven to receive the rubber to be introduced into the mold for execution of molding.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a machine for injection moulding of rubber products. In particular, it relates to a multi-station machine of high productivity.  
           [0002]    In a machine for injection moulding of rubber, the mould receiving the material is always required to remain closed and under pressure over the whole time necessary for vulcanisation of the material itself.  
           [0003]    Therefore, due to its own nature, the moulding unit has a production cycle that goes on for a period of time during which it is at a standstill, comprised between the moment of injection of the material into the mould and the moment of opening of the mould to withdraw the moulded article, which mould is then closed again to be brought back to the cycle starting conditions.  
           [0004]    In order to increase productivity of a moulding machine it is possible to use a single feeding and injection unit which is brought to feed each of a number of moulds in succession. The solution appears to be particularly useful when a relatively long vulcanisation time is required, so as to avoid a correspondingly long time of inactivity of the machine.  
           [0005]    Generally, these multi-station machines with a moving injector are complicated and bulky.  
           [0006]    It is an aim of the present invention to provide a machine of high productivity with reduced bulkiness, adapted for production of rubber articles by injection.  
         SUMMARY OF THE INVENTION  
         [0007]    In accordance with the invention, a machine for injection moulding of rubber products comprises a plurality of moulding units to be operated separately for carrying out a moulding cycle, in which the moulding units are mounted on a common support and each unit receives the rubber blend to be used in moulding through a duct branched off from a channel fed by a common injection unit, the branched-off feeding ducts being intercepted by a dispensing element moved step by step to sequentially open a predetermined number of the branched-off ducts corresponding to the moulding units that are driven to receive the rubber to be introduced into the mould for execution of moulding. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    For better explaining the features and advantages of the machine in accordance with the invention, an embodiment of same will be described hereinafter, by way of example, and illustrated in the accompanying drawings, in which:  
         [0009]    [0009]FIG. 1 is an overall perspective view of the machine;  
         [0010]    [0010]FIG. 2 is a longitudinal section of the machine portion comprising the moulding units;  
         [0011]    [0011]FIG. 3 is a particular view in longitudinal section of one of the moulding units included in the machine.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    Mounted on a base identified by  10  are rubber feeding and injection units, each unit, taken as a whole, being generally denoted at  12  and  13  and not described in detail because it is known by itself and of non-critical structure and configuration to the aims of the invention.  
         [0013]    Advantageously, the feeding units  12  and  13  are of a known type and contemplate a piston-acting plasticization screw i.e. a screw provided with a rotatory thrust movement like an Archimedes&#39; screw combined with the possibility of an axial piston-thrust movement.  
         [0014]    The machine portion comprising the moulding unit, to which more specifically the invention relates, is generally identified by  11 .  
         [0015]    Provision is made for a stationary core  20  around which an annular support element  21  carrying a plurality of moulding units  22  is fastened.  
         [0016]    Mounted between the core  20  and support  21  is a cylindrical movable dispensing body  23  carried by a shaft  24  connected to a power unit  25  to operate a step-by-step rotation controlled by the dispenser  23 .  
         [0017]    In more detail, through a general channel  26 , core  20  is reached by the rubber to be moulded, coming from injectors  12  and  13  which ensure a constant injection pressure in time, i.e. a continuous pressurised feeding.  
         [0018]    This channel  26  branches off into radial ducts  27 . Advantageously, in the embodiment shown, the radial ducts are distributed in three ranks disposed in offset transverse planes of the core  20 , and denoted at  27 ,  27 ′ and  27 ″ respectively, in order to avoid the useful solid core section being too much reduced due to the presence of a too great number of coplanar radial ducts, each terminating at a moulding unit  22 .  
         [0019]    By distributing ducts  27  in different planes offset from each other, and correspondingly distributing the moulding units in different planes, the number of radial ducts  27  lying in the same transverse plane of core  20  is shared out so that the residual solid section is still sufficient to withstand the stresses resulting from the pressures in the ducts, as well as the external loads to which the core is submitted.  
         [0020]    Disposed around the core  20  is the rotating dispensing element  23  carrying passageways  28  each of which is adapted to be arranged, for a predetermined angular portion of the dispenser, in alignment with a duct  27  formed in the core so as to dispose it in communication with a duct  29  constituting the extension thereof and feeding the rubber blend to a moulding unit  22 .  
         [0021]    Obviously, in the dispenser a passageway  28  is provided for each offset rank on which ducts  27  and ducts  29  aligned therewith can be disposed.  
         [0022]    One of the moulding units  22  is shown in more detail in FIG. 3.  
         [0023]    Each moulding unit comprises a mould half  30  carried by the rod of a piston  31  moving in chamber  32  under the effect of a hydraulic fluid under pressure.  
         [0024]    For movement of the double-acting piston  31  fittings  33  and  34  are provided for connection with a hydraulic drive circuit not shown.  
         [0025]    The mould half  30  can be brought by piston  31  close to the mould half  35  to form the moulding cavity into which the blend can be introduced through an injection nozzle  36 . The blend is fed to the nozzle from a chamber  37  in which an injection metering piston  38  moves, which piston is operated to execute a stroke of an amount controlled by a piston  40 . Piston  40  is provided with an adjustable mechanical stop in order to define the stroke and consequently the displacement in chamber  37 .  
         [0026]    As known, the moulding operation involves the steps of moving the mould halves close to each other, creating the vacuum to a predetermined value in the mould with the mould halves close to each other and the vacuum seal in a closed condition, injecting a metered blend amount, waiting for completion of the rubber vulcanisation, opening the mould, withdrawing the formed piece therefrom.  
         [0027]    The whole operation takes a relatively long period of time and only during a small fraction of this time the blend-feeding duct  29  is required to be maintained in communication with the blend feeders  12  and  13  and substantially with the feeding channel  26 .  
         [0028]    Theoretically, duration of this communication is exclusively required during the retraction step of piston  38  for carrying out a driven stroke in order to cause admission to chamber  37  of a metered blend amount.  
         [0029]    Only during this feeding step the dispenser is required to be in such a position that ducts  27  and  29  related to the injection unit are brought into communication with each other, i.e. with a passageway  28  in alignment with them.  
         [0030]    As a result, the moulding process of each unit can mostly take place during a period in which the dispenser element is disposed in such a manner that it can connect other moulding units with the blend feeding unit, to enable admission thereto of the metered blend amount required for a moulding operation.  
         [0031]    A central control unit for the whole machine, herein not shown, which may consist of a computer-based control group, controls the different steps of the moulding operation of each unit and the step-by-step advancing means of the dispenser suitably in an appropriate phase so as to enable the dispenser to bring duct  29  related to each unit into communication with the respective duct  27  when admission of blend to the moulding unit is required.  
         [0032]    Therefore, by controlling the moulding operations carried out by each unit according to a suitable sequential phase displacement, it is possible for a plurality of units, and possibly all units, to be simultaneously operational, so that the machine productivity is really a multiple of the productivity of each unit.  
         [0033]    In the embodiment shown (FIG. 2) it is illustrated how the dispenser  22  brings two diametrically-opposite moulding units into communication with the feeding unit, considering as available for completion of the moulding operation of each unit the time imposed to the dispenser for rotating through 180°, in a sequence of 14 steps, so that the step of sequentially feeding with blend all the 28 moulding units radially mounted on support  21  should be carried out. Additional ducts are formed in core  20  and support  21  of the moulding unit  22  for circulation of a fluid for thermal conditioning of the parts concerned with the blend circulation, according to known technological requirements; therefore the related circuit will not be herein described in detail.  
         [0034]    Due to the particular structure of the machine in accordance with the invention, the ducts holding the thermal-conditioning fluid can follow a path extending in core  20  and advantageously going on in a direct way into support  21  and then into the body of units  22 .  
         [0035]    Accomplishment of the above described machine is to be considered by way of example only and many modifications can be done without departing from the scope of the invention.  
         [0036]    In particular, the dispensing element can take a great number of shapes.  
         [0037]    Arrangement of the different moulding units in axially spaced apart ranks enables also ducts  27  to be disposed in spaced apart ranks in the core, so that transverse core sections too much impoverished in material do not exist therein.  
         [0038]    However, other construction solutions can be adopted to this aim. For example, channel  26  can feed a single annular duct within core  20  and close to the periphery thereof, so as to minimise the length of ducts  27  and the consequent absence of material at the section in which they are formed. In this way, arrangement of all ducts  27  in a single plane transverse to the core could be provided and, as a result, the circumferential alignment of all moulding units.  
         [0039]    Generally, the dispensing device may have any configuration provided it fulfils the function of selectively connecting the predetermined number of moulding units to the blend feeding unit for each of the positions that the dispensing device is driven to take step by step.