Mold for injection-compression molding

Abstract

A mold ( 1 ) for injection-compression molding includes a punch ( 2 ) and a matrix ( 3 ) suitable to close on the punch ( 2 ) to delimit with this an injection chamber ( 10 ) to contain the material to be injected. The matrix ( 3 ) and punch ( 2 ) are axially movable between them with respect to an axial direction (Y-Y) of opening/closing of the mold ( 1 ). The mold has a perimetral ring ( 4 ) slidingly associated to the punch ( 2 ) or the matrix ( 3 ), along the axial direction (Y-Y), suitable to define, together with the matrix ( 3 ) and the punch ( 2 ), the profile of the injection chamber ( 10 ). The perimetral ring ( 4 ) includes an interface profile ( 43 ) engaging with the matrix ( 3 ) or with the punch ( 2 ), equipped with a particular geometry generating in the closing phase of the mold ( 1 ), a compression force of the ring ( 4 ) towards the inside of the mold ( 1 ).

1 . A mold for injection-compression molding comprising:
 a punch;   a matrix suitable to close on the punch so as to delimit with the punch an injection chamber to contain material to be injected, said matrix and punch being axially movable relative to one another with respect to an axial direction of opening or closing of the mold,   a perimetral ring slidingly associated with the punch or the matrix, along the axial direction, suitable to define, together with the matrix and the punch, a profile of the injection chamber;   wherein the perimetral ring comprises an interface profile, configured to engage with the matrix or with the punch, equipped with a geometry suitable to generate in the closing phase of the mold, a compression force of the ring towards an inside of the mold.   
     
     
         2 . The mold according to  claim 1 , wherein the interface profile is convex. 
     
     
         3 . The mold according to  claim 1 , wherein the interface profile comprises an upper inclined thrust wall, the upper inclined thrust wall engaged by an inclined plane associated with the matrix, so as to generate a force substantially transverse with respect to the axial direction and with a direction towards the inside of the mold. 
     
     
         4 . The mold according to  claim 1 , wherein, in closing the mold, the perimetral ring is interposed between the matrix and the punch, thereby creating double junction points on the piece. 
     
     
         5 . The mold according to  claim 4 , wherein the perimetral ring defines together with the punch, a double junction point in correspondence of a thickness of the piece. 
     
     
         6 . The mold according to  claim 4 , wherein the perimetral ring defines, together with the matrix, a double junction point in correspondence of an outer edge of the piece. 
     
     
         7 . The mold according to  claim 1 , wherein the perimetral ring defines, together with the matrix and the punch, the profile of the molded piece. 
     
     
         8 . The mold according to  claim 7 , wherein the perimetral ring defines, together with the punch, a thickness of the piece in such a way as to hide junction lines on the piece. 
     
     
         9 . The mold according to  claim 1 , wherein the interface profile is convex polygonal. 
     
     
         10 . Mold, accordance to  claim 1 , comprising an integrated hydraulic circuit for advancement and retraction of the perimetral ring. 
     
     
         11 . The mold according to  claim 10 , wherein the hydraulic circuit comprises hydraulic cylinders activated and/or deactivated by at least one first hydraulic control and at least one non-return valve. 
     
     
         12 . The mold according to  claim 10 , wherein the hydraulic circuit comprises at least one first non-return valve directly controlled by a second hydraulic control and a second non-return valve. 
     
     
         13 . The mold according to  claim 10 , wherein the hydraulic circuit comprises a pressure relief valve allowing setting pressures of the circuit between zero and the pressure of a radial control. 
     
     
         14 . The mold according to  claim 10 , wherein the hydraulic circuit comprises a pressure gauge for controlling the pressure. 
     
     
         15 . A method of closing of a mold according to  claim 10 , comprising the step of:
 opening the mold with the perimetral ring in an advanced position and in thrust:   switching on a first hydraulic control, connected directly to the hydraulic circuit that is put under pressure and determining advancement of the perimetral ring;   switching off the first hydraulic control, in which the pressure is returned to zero, while in the hydraulic circuit, due to the non-return valves, the pressure remains at a value set in the pressure relief valve;   closing the mold with perimetral ring in thrust with a force given by the pressure set with the pressure relief valve;   injecting molten material in the injection chamber;   compressing the material in the injection chamber up to complete closure of the mold;   cooling of the molded piece with the mold closed:   switching on a second hydraulic control, that is put under pressure and, by acting on the non-return valve, determines release of the pressure of the hydraulic circuit, which drops to zero and the perimetral ring stops pushing on the piece;   opening the mold with perimetral ring in a retracted position and rest position.   
     
     
         16 . The method of closing a mold according to  claim 15 , further comprising the step of:
 extracting the piece using an extractor, while the pressure in the hydraulic circuit remains at zero until after extraction.