Abstract:
The actuating unit comprises a piston element ( 21 ) slidable in a cylinder element ( 20 ) and connectable to a closure rod ( 16 ) slidable in an injection duct ( 14 ) between an extended position in which it blocks an injection hole ( 15 ) and an injection position in which it is retracted into the injection duct. The piston element ( 21 ) has an engaged seat ( 46, 47 ) which can house a head end portion ( 16   a ) of the rod ( 16 ). The engagement seat is shaped so as to allow the piston element ( 21 ) to be translated transversely relative to the axial direction of movement of the rod ( 16 ) in order to release the piston element ( 21 ) from the rod.

Description:
This is a Nailkona Stage Entry under 37 C.F.R. § 371 of PCT/EP00/04503, with an international filing date of May 18, 2000, the complete disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a unit for actuating the rod of a closure element in a mould for the injection-moulding of plastics material. 
     An injection-moulding mould provided with a conventional actuating unit is shown in partial section in FIG. 1. A heated nozzle  10  is mounted beneath a heated plate  11  in order to receive the molten plastics material from a supply duct  12  and to inject it into a moulding cavity  13  through an injection duct  14  and a lower injection hole  15 . 
     A closure rod  16  slides coaxially inside the injection duct  14 , the axial position of the rod  16  being controlled by an upper actuating unit, generally indicated  17  and housed in a cavity  18  formed in an upper plate  19 . The actuating unit  17 , which is pneumatically operated, comprises a cylinder  20  in which a piston  21 , to which the upper end  16   a  of the rod  16  is connected, can slide vertically. 
     The vertical movement of the piston  21  and of the rod  16  is brought about by sending an operating fluid (air) alternately through an inlet duct  22  and an inlet duct  23  which are formed in the upper plate  19  and communicate with the cavity  18  in upper and lower positions, respectively, in order to admit the operating fluid to the cylinder  20  through a duct  24  or a duct  25 , so as to raise or lower the piston  21 . As is known, in the lowered position (not shown), the lower end  16   b  of the rod  16  blocks the injection hole  15  whereas, in the raised position (as shown in FIG.  1 ), the injection hole is open to allow plastics material which is injected from the duct  14  of the nozzle  10  to pass through to the moulding cavity  13 . 
     To prevent the injected material From reaching the actuating unit  17 , a tempered steel sealing bush  26  is provided and is housed in a cavity  27  in the hot plate  11 ; the sealing bush  26  is fitted on the slidable rod  16 . A reaction ring  28  is interposed between the hot plate  11  and the upper plate  19 . A closure cover  29  is fixed to the upper plate  19  to restrain the actuating unit  17  at the top. 
     A conventional actuating unit of this type requires numerous seals; in addition to two seals  30  and  31  between the piston  21  and the cylinder  20 , there is a seal  32  between the cover  29  and the upper plate  19 , there are two seals  33  and  34  between the upper plate  19  and the stationary cylinder  20 , and there is a further seal  36  mounted on an enlarged element  37  acting as a stop for the rod  16 . 
     Injection moulds provided with actuating units configured as described above have a disadvantage of a practical nature when it is necessary to perform adjustment or maintenance operations on one or more closure rods, for example, when it is necessary to replace a worn rod or to clear an injection duct of accumulations of waste. For example, in order to gain access to an injection nozzle, it is necessary to remove the upper plate  19  and with it all of the closure units of the various injection nozzles of which there may be a considerable number ( 48  or more) in cases in which the mould comprises several nozzles and numerous moulding cavities. During the removal of the upper plate  19 , all of the rods of the various closure units are thus removed. 
     Since an operation of this type is performed hot to enable the rods to be removed, the plastics material tends to rise through the sealing bushes  26  and thus to be deposited on surfaces which should, however, remain clean. Once the maintenance or adjustment operation has been performed on the nozzle or nozzles which required it, it is therefore necessary to clean the surfaces on which plastics material has been deposited during the operation, for all of the nozzles of the mould, before the upper plate with the respective rods and closure units is reassembled. 
     As will be understood, the removal of the upper plate, complete with closure units and rods, is a complex operation but, above all, careful cleaning at many points of the mould as referred to above requires long periods of inactivity of the apparatus and is therefore expensive. 
     SUMMARY OF THE INVENTION 
     Moreover, during the reassembly of the closure units, it is necessary to pay particular attention to the various seals, ensuring that they are positioned correctly before closing the mould again. 
     An object of the invention is to provide an actuating unit in which the piston can be released from its rod easily without requiring the latter to be removed from the nozzle. 
     An object of the present invention is to propose an actuating unit which is easy to install and to maintain, and which can prevent the problems of the prior art discussed above. 
     A further object of the present invention is to provide an actuating unit having an improved and simplified system for adjusting the travel of the closure rods; in particular, the adjustment of the travel and the removal of the rod of a particular actuating unit should be independent operations. 
     This further object is achieved, again according to the invention, by an actuating unit having the characteristics defined in claim  4 . 
     Yet another object of the invention is to mould products which do not bear obvious marks on their surfaces in the regions of the injection points when these points lie on surfaces which are not perpendicular to the closure rod. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further important characteristics are claimed in the other dependent claims. 
     The characteristics and advantages of the invention will become clear from the detailed description of an embodiment thereof, given with reference to the appended drawings, provided by way of non-limiting example, in which: 
     FIG. 1 is a schematic, vertical section through a conventional actuating unit, 
     FIGS. 2 and 3 are schematic views showing, in section, a portion of an actuating unit according to the present invention in two opposite operative positions, 
     FIG. 4 is a view showing the actuating unit of FIGS. 2 and 3, in section and on an enlarged scale, 
     FIG. 5 is a plan view of a key element cooperating with the actuating unit of FIG. 4, and 
     FIGS. 6 and 7 are schematic views showing the detail of two different embodiments of the lower end of a closure rod. 
    
    
     With reference to FIGS. 2,  3  and  4 , and with the use of the same reference numerals as were used to indicate corresponding elements and parts already mentioned with reference to FIG. 1, an actuating unit  17  according to the present invention is mounted in a seat  40  formed in a hot plate  11 . 
     The cylinder  20  is in the shape of an inverted cup with side walls  41  and an upper end  42  which is closed at the top by a top plate  19 . 
     Ducts  22  and  23  are formed in the top plate  19  for providing a flow of operating air, into the cylinder  20  and causing, respectively, the lowering and the raising of the piston  21  which is slidable vertically in the cylinder  20 . An opening  43  is formed in the upper end  42  of the cylinder in a substantially central position corresponding to the position of the inlet duct  22 ; ducts  44  formed in the side walls  41  of the cylinder put the inlet duct  23  into communication with the lower surfaces of the piston  21  in order to raise it. The side wall  41  of the cylinder forms a lower, cylindrical, annular appendix SO which is fitted in the seat  40  and is in close contact with the peripheral wall  45  thereof, and a radial surface  51  which can come into axial abutment with a radial surface  11   b  of the hot plate  11 . 
     DETAILED DESCRIPTION OF THE INVENTION 
     The terms “lateral”, “radial”, and “axial” as used herein should be interpreted with reference to the longitudinal axis x of the rod  16 , unless indicated otherwise. 
     The lower face of the piston  21  has a recess  46  forming, on one side, an undercut  47  of a size such as to house the enlarged head  16 a of the rod  16  with predetermined minimal axial clearance. On the opposite side to the undercut  47 , the recess  46  forms an empty space for allowing the piston to slide transversely relative to the rod when it is necessary to disconnect these two elements, as will be explained further below. 
     The outer and upper lateral portion of the piston  21  bears a seal  48  which performs sealing action against the inner surface of the side wall  41  of the cylinder  20 . The piston  21  has a lower, outer, annular appendix  21   a  which terminates in a radial lower face  49 . The lower end of stroke position of the piston  21 , which corresponds to the position in which the injection hole  15  is blocked, is defined by the abutment of the lower face  49  of the piston against an annular element  52  of calibrated axial thickness, housed in the bottom of the seat  40  in the hot plate  11 . 
     Again according to the invention, as shown more clearly in FIG. 4, a flat face  53 , is formed on an upper portion of the rod  16 , so that the rod is prevented from rotating about its own longitudinal axis, in order to keep the rod in a predetermined angular position. The flat face  53  cooperates with a key element  54 , shown separately in FIG. 5, which is mounted so as to be prevented from rotating relative to the hot plate and bears on the upper face  26   a  of the bush  26 . In the example shown, the key element  54  is fork-shaped and has, on one side, a radial appendix  55  which is locked rotationally by the hot plate, and on the, opposite side, a pair of opposed projections  56  between which an edge  57 ,which can act on the flat face  53  of the rod  16 , is defined. 
     The key element  54  is restrained axially against the upper face  26   a  of the sealing bush  26  by means of an inverted cup-shaped ring nut  58  having a lower cylindrical portion  59  in which a thread  60  is formed for screwing the ring nut onto the hot plate  11 . 
     The unit operates as follows. 
     Plastics material is injected through the supply duct  12  and, at the same time, the piston  21  and the rod  16  are raised by the sending of air through the duct  23 , to reach the configuration of FIG.  3 . As the rod  16  is refracted upwards, it opens the injection hole  15 . Once the moulding cavity  13  has been filled, injection is stopped by the sending of operating air through the duct  22 , which results in lowering of the piston  21  and of the rod  16  the lower end of which closes the injection hole (FIG.  2 ). 
     When it is necessary to operate on a particular actuating unit, the piston  21  is first raised to its upper end of stroke position by the sending of air through the duct  23 ; the upper plate  19  is then removed from the hot plate  11  and it is possible to operate solely on the closure unit or units which require the operation, leaving the other closure units of the mould undisturbed. In order to gain access to the rod  16 , the cylinder  20  is removed vertically from the seat  40  in the hot plate and the piston  21  is translated transversely in the direction indicated by the arrow A in FIG. 4, thus releasing the head of the rod  16 . The ring nut  58  is then unscrewed and the key element  54  can be removed and the rod  16  taken out of the sealing bush  26  and the heated nozzle  10 . 
     In order to adjust the axial travel of the rod  16  once the cylinder  20  and the piston  21  have been removed, the annular element  52  which defines this travel can be removed from the seat  40  and replaced by a similar, thicker or thinner element, or may be replaced in its seat after having been made thinner. As will be noted, when the operation does not require travel adjustment, once the actuating unit has been reassembled, the annular element  52  keeps the original travel of the rod unchanged without the need for any adjustment. 
     It will be appreciated that, in comparison with the prior art discussed in the introductory part of the description, with the present invention, the number of seals is reduced to a minimum; this speeds up reassembly operations which conventionally required particular care with regard to the repositioning of the seals which, if they were not correctly arranged, could in turn be the cause of a further and subsequent maintenance operation. 
     It will also be noted that, in order to remove the annular element  52 , the piston can advantageously be removed without the need necessarily to remove the rod from the nozzle. 
     Above all, it will be appreciated that, by virtue of the present invention, before the unit on which an operation has been performed is reassembled, it is necessary to perform cleaning limited purely to the closure unit or units from which the rods have been removed, resulting in a considerable saving in time and costs. 
     The seat with the undercut which restrains the head of the rod axially on the piston ensures a precise and durable coupling which requires no maintenance and which, unlike the threaded couplings which are used conventionally, ensures perfect verticality of the rod. 
     Finally, the maintenance of a given angular orientation by the above-described key configuration is particularly useful when the surface of the moulding cavity in the region of the injection hole is curved or inclined relative to the plane passing through the hole. To prevent a visible mark remaining on the moulded product at this point, the lower end  16   b  of the rod  16  may have an end surface  16   c  which is shaped so as to be level with the surface of the mould cavity, for example, so as to be inclined as in FIG. 6 or curved as in FIG.  7 . In cases such as these, the key enables the orientation of the rod  16  to be maintained. 
     Naturally, the principle of the invention remaining the same, the forms of embodiment and details of construction may be varied widely with respect to those described and illustrated purely by way of non-limiting example, without departing from the scope of the invention as defined in the appended claims.