Abstract:
Mould ( 10 ) for a blow-moulding machine, for moulding thermoplastic containers, the mould ( 10 ) comprising several mould parts having centring features ( 36, 38, 50 ) and complementarily-shaped centring features ( 40, 42, 44 ), said centring features ( 36, 38, 50 ) and complementarily-shaped centring lecture ( 40, 42, 44 ) being capable of cooperating with one another, characterized in that at least a portion of at least one of the centring features ( 36, 38, 50 ) and complementarily-shaped centring features ( 40, 42, 44 ) is made or tin anti-friction composite material so as to avoid lubrication thereof.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the field of the molding of containers, notably bottles, made of a thermoplastic such as PET (polyethylene terephthalate), by blow molding or stretch-blow molding heated preforms. 
         [0002]    More specifically, the invention relates to a mold of a machine for blow molding containers and to the method of manufacturing the mold, and to the blow molding machine comprising such a mold. 
       BACKGROUND OF THE INVENTION 
       [0003]    In one configuration, a mold of such a blow molding machine comprises two half molds for forming the shoulder and the main body of the containers, and a mold bottom for forming the bottom of the containers. The two half molds are hinged relative to one another about an axis. They are moved relative to one another between a mold-closed blow-molding position and a mold-open position in which the shaped container is removed. The mold bottom is moved vertically between the mold-closed and mold-open positions. 
         [0004]    Centering and locking components are fixed to the half molds and to the bottom to provide centering and form the molding cavity accurately thus preventing flash at the parting line. 
         [0005]    However, the centering and locking components have to be regularly lubricated. Such maintenance operations require the blow molding installation to be stopped and, more generally, the entire container production line to be shut down. 
         [0006]    These stoppages reduce the production rates and increase the cost of manufacture of the containers. In addition, these maintenance operations are carried out under conditions that are relatively difficult for the operators involved, notably in terms of the ambient temperature obtaining around the machine. 
         [0007]    Furthermore, these lubricating operations sometimes contaminate the molds. 
         [0008]    It is a particular object of the invention to eliminate these maintenance operations. 
       SUMMARY OF THE INVENTION 
       [0009]    To this end, a subject of the invention is a mold for a machine for blowmolding containers made of thermoplastic, the mold comprising a plurality of mold parts comprising a centering relief and a centering relief of complementary shape; said centering relief and centering relief of complementary shape being able to collaborate with one another,
       at least part of at least one of the centering relief and centering relief of complementary shape comprising a composite antifriction material in order to avoid the need to lubricate it.       
 
         [0011]    According to some specific embodiments, the mold has one or more of the following features:
       the mold comprises three mold parts, at least two mold parts of which comprise a centering relief and a centering relief of complementary shape;   the mold comprises three mold parts each equipped with one relief out of a centering relief or a centering relief of complementary shape;   the mold comprises only two mold parts, one of them comprising a centering relief and the other a centering relief of complementary shape;   at least one relief out of the centering relief and the centering relief of complementary shape is fixed to a mold part; said fixed relief being made of composite antifriction material;   the composite antifriction material contains a plastic, and at least one relief out of the centering relief and the centering relief of complementary shape is fixed to a mold part; said fixed relief being produced by plastic injection molding;   the composite antifriction material comprises a framework, known as a reinforcement, which provides mechanical integrity;   the composite antifriction material comprises a protective element called a matrix;   the composite antifriction material is a surface coating;   the composite antifriction material contains polyetherimide;   the composite antifriction material contains lubricating compounds;   the lubricating compounds contain polytetrafluoroethylene; and   the lubricating compounds contain polyphenylene sulfide.       
 
         [0024]    Another subject of the invention is a method of manufacturing a mold intended for a machine for blow molding containers made of thermoplastic; the mold comprising at least two mold parts respectively comprising a centering relief and a centering relief of complementary shape; said centering relief and said centering relief of complementary shape being able to collaborate with one another; said method comprising the following steps:
       machining at least two mold parts, at least one mold part comprising at least one receiving face;   injection molding at least one relief out of a centering relief and a centering relief of complementary shape in a composite antifriction material; and   fixing the molded relief to the receiving face of the or each mold part.       
 
         [0028]    As an alternative, the method of manufacturing a mold intended for a machine for blow molding containers made of thermoplastic, comprises a step of machining at least two mold parts respectively comprising a centering relief and a centering relief of complementary shape; said centering relief and said centering relief of complementary shape being able to collaborate with one another,
       said method comprising a step of applying a composite antifriction coating to at least part of at least one out of the centering relief and the centering relief of complementary shape so as to avoid the need to lubricate the mold.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    Finally, a subject of the invention is a machine for blow molding containers, notably bottles, made of thermoplastic, characterized in that the machine comprises at least one mold as mentioned hereinabove. 
           [0031]    The invention will be better understood from reading the following description which is given solely by way of example and makes reference to the drawings in which: 
           [0032]      FIG. 1  is a partially sectioned view of the mold according to the invention; 
           [0033]      FIG. 2  is a perspective view of a three-part mold comprising two half molds and a bottom; 
           [0034]      FIG. 3  is a perspective view of a two-part mold comprising two half molds; and 
           [0035]      FIG. 4  is a perspective view of a wearing and positioning ring and of a portion of a wearing and centering annulus of the mold according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    In the remainder of the description, the terms “upper” and “lower” are defined with respect to the usual position of a mold in a blow-molding machine. These terms should not be interpreted as limiting the scope of the present invention to any one particular mold orientation. 
         [0037]    As is known, a blow-molding machine comprises a supporting structure supporting a carousel that can be rotated about a central axis. 
         [0038]    The carousel supports a number of molding units. Each molding unit comprises a mount  8 , a mold  10  and one or more actuators to maneuver the various parts of this mold. 
         [0039]    Other blow-molding machines, such as a linear-molding (press system) machine for example, may be used. 
         [0040]    According to another configuration of the invention which has been depicted in  FIGS. 1 and 2 , the mold  10  comprises a first mold half-face  14  and a second mold half-face  16 , these henceforth being known as half molds, in which a cavity  14 A,  16 A has been hollowed to form the shoulder and main body of the containers, and a mold bottom  18  in which a cavity  18 A has been hollowed to form the bottom of the containers. 
         [0041]    In the example illustrated, the two half molds  14 ,  16  are hinged relative to one another about an axis which has not been depicted. This type of mold is generally known as a hinged mold. A first drive unit, not depicted, is able to move the half molds  14 ,  16  between the mold-closed position in which the half molds are touching and a mold-open position in which the half molds are separated from one another to allow the shaped container to be removed. 
         [0042]    The bottom  18  is carried by a support  19  which is able to move vertically with respect to the mount  8 . The bottom  18  and the support  19  are joined together by screws  21 . 
         [0043]    A second drive unit, not depicted, is able to move the support  19  between the closed position of the mold  10 , in which position the bottom  18  collaborates with the half molds  14 ,  16 , and an open position in which the bottom  18  is moved into a position away from the half molds  14 ,  16 . 
         [0044]    Each half mold  14 ,  16  is optionally fitted with two connections  26  so that the temperature of the preforms inside the mold  10  can be regulated. 
         [0045]    With reference to  FIGS. 1 and 2 , each half mold  14 ,  16  has a substantially semicylindrical shape. In particular, each half mold  14 ,  16  comprises a support  20 , a shell holder  22  nesting in and fixed onto the support  20 , and a shell  24  nesting in and fixed into the shell holder  22 . The cavities  14 A and  16 A are hollowed in the internal face of the shells  24 . Together with the cavity  18 A of the bottom they form a molding space  28  when the two half molds  14 ,  16  and said bottom  18  touch. 
         [0046]    The half mold  14  has collaborating or bearing faces  29 ,  30  which, in the mold-closed position, press against the bearing faces  32 ,  34  of the half mold  16 . 
         [0047]    The bearing faces  29 ,  30  of the half mold  14  are equipped with centering reliefs intended to collaborate with centering reliefs of complementary shape formed on the other half mold  16 . The centering reliefs and the complementary centering reliefs may be formed on the supports  20 , on the shell holders  22  or on the shells  24 . 
         [0048]    In the example illustrated, the centering reliefs  36 ,  38  consist of centering pins  36 ,  38  and the centering reliefs of complementary shape are formed of housings  40 ,  42  of a shape and depth corresponding to those of said centering pins. 
         [0049]    The pins  36 ,  38  and the housings  40 ,  42  are able to key and to correctly position one half mold  14  with respect to the other half mold  16 . The pins  36 ,  38  or the housings  40 ,  42  contain a composite antifriction material  43  to avoid the need to lubricate them. 
         [0050]    Thus, no lubrication of the pins  36 ,  38  or of the housings  40 ,  42  is performed after over 10 000 000 blow molding cycles or more, or after two years of production. 
         [0051]    According to a first embodiment of the invention, the composite antifriction material  43  contains a plastic known as a matrix. 
         [0052]    In that case, the pins  36 ,  38  and/or the housings  40 ,  42  are produced by injection molding an insert in the form of a pin or of a socket. These are then force-fitted into holes pierced in the half mold  14  and/or the half mold  16 . 
         [0053]    As an alternative, the pins  36 ,  38  and the housings  40 ,  42  are screwed into tappings in the half molds  14 ,  16 . 
         [0054]    In particular, the composite antifriction material  43  contains polyetherimide (PEI) and preferably polyetherimide filled with lubricating compounds such as polytetrafluoroethylene. 
         [0055]    The polyetherimide is also filled with glass fiber or carbon fiber, for example containing 40% of these fibers, in order to increase its rigidity. 
         [0056]    In particular, the composite antifriction material  43  contains polyphenylene sulfide PPS. 
         [0057]    According to a second embodiment of the invention, the component  43  is coated with an antifriction treatment such as DLC (which stands for “diamond-like carbon”). 
         [0058]    The DLC coating is then applied to the inserts that form the pins  36 ,  38  and/or to the inserts that form the housings  40 ,  42  which are, in this case, machined from steel. 
         [0059]    As an alternative, the DLC coating is applied directly to the housing formed in the half mold  16 . 
         [0060]    This type of coating is notably described in the following documents: U.S. Pat. No. 6,303,226; U.S. Pat. No. 5,250,322 and U.S. Pat. No. 5,470,661. 
         [0061]    As visible in  FIGS. 1 and 4 , a portion or segment  44  of a wearing annulus is fixed to the lower face  48  of each half mold  14 ,  16 . This wearing annulus portion  44  is intended to collaborate with a wearing ring  50  formed around the bottom  18  in order to center and to lock the bottom  18  on the half molds  14 ,  16  during the closing operation of the mold  10 . 
         [0062]    To do this, a groove  58  is formed around the periphery of the bottom  18 . This groove  58  is able to accept the wearing ring  50 . The bottom  18  of the wearing ring  50  are joined together by screws  49 . 
         [0063]    The wearing ring  50  or the wearing annulus portions  44  contain the composite antifriction material  43  in order to avoid the need to lubricate them. 
         [0064]    As described earlier, this composite antifriction material  43  is, according to the first embodiment of the invention, a material containing polyetherimide or, according to the second embodiment of the invention, a DLC coating or some other surface treatment or self-lubricating material. 
         [0065]    As an alternative to the second embodiment of the invention, only part of the wearing ring  50  and part of the wearing annulus portions  44  contain the composite antifriction material  43 . These parts are then those parts of the wearing ring and of the wearing annulus portion that are in mutual contact with one another. 
         [0066]    According to another embodiment of the invention, only the wearing ring  50  or the wearing annulus portions  44  contain the composite antifriction material  43 . The pins  36 ,  38  and the housings  40 ,  42  are then lubricated in the conventional way. In that case, the half mold  14  (or  16 ) and the bottom  18  form a first mold part within the meaning of the invention. The half mold  16  (or  14 ) then, completely on its own, forms the second mold part within the meaning of the invention. The wearing ring  50  constitutes the centering relief of the first mold part  14 ,  18 . The wearing annulus portion  44  constitutes the centering relief of complementary shape of the second part  16  of the mold. 
         [0067]    According to a final embodiment of the invention, only the pins  36 ,  38  and/or the housings  40 ,  42  contain the composite antifriction material  43 . The wearing ring  50  and the wearing annulus portions  44  are then lubricated in the conventional way. In that case, the half mold  14  forms the first mold part within the meaning of the invention. The half mold  16  forms the second mold part within the meaning of the invention. The pins  36 ,  38  constitute the centering reliefs of the first mold part  14 . The housings  40 ,  42  constitute the centering reliefs of complementary shape of the second part  16  of the mold. 
         [0068]    In one possible configuration of the invention which has been depicted in  FIG. 3 , the mold comprises only two half molds each provided with a cavity able to form the whole of the shoulder, of the main body and of the bottom of the containers. 
         [0069]    In this configuration, the bearing faces  29 ,  30  of the half mold  14  are equipped with centering reliefs intended to collaborate with centering reliefs of complementary shape on the other half mold  16 . The centering reliefs and the complementary centering reliefs may be formed on the supports  20 , on the shell holders  22  or on the shells  24 . In that case, the half molds  14 ,  16  have no wearing annulus segment  44 . 
         [0070]    The invention also relates to a method of manufacturing the mold  10  as mentioned hereinabove. The method comprises the following steps:
       machining two mold parts, at least one mold part comprising at least one receiving face;   injection molding at least one relief out of a centering relief  36 ,  38 ,  50  and a centering relief  40 ,  42 ,  44  of complementary shape in a composite antifriction material  43 ; and   fixing the molded relief to the receiving face of the or each mold part.       
 
         [0074]    As an alternative, the method comprises the following steps:
       machining the two half molds  14 ,  16  and the bottom  18 ;   machining at least one out of the pins  36 ,  38 , the housings  40 ,  42 , the wearing ring  50  and the wearing annulus portions  44 ; and   applying a composite antifriction coating  43  to at least part of a relief chosen out of the pins  36 ,  38 , the housings  40 ,  42 , the wearing ring  50  and the wearing annulus portions  44 .