Abstract:
According to the present invention a coding plate is interspersed between first and second respective inlet and outlet cross over nozzle parts. The cooling plate engages ends of the cross over nozzles during mould filling and provides a melt transfer passage therebetween. Once the mould is filled, the cooling plate acts to dissipate heat from the melt transfer passage thereby promoting solidification of melt therein. Accordingly melt solidification in the sprue is assured with more certainty than prior art designs enabling relatively fax mould cycling with minimal risk of drool.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to mould distribution arrangements for injection moulding apparatus. More particularly, this invention relates to cross over nozzle arrangements for multi-level stack moulds. Even more particularly, this invention relates to such cross over nozzle arrangements of a sprue gated design. 
     BACKGROUND OF THE INVENTION 
     In injection moulding apparatus utilizing a stack mould design, a melt transfer system is required which transfers melt across mould levels yet which is separable to enable mould separation. The component of the melt transfer system which effects separation is referred to as a “cross over nozzle”. 
     In order to be effective, a cross over nozzle is provided with some means for blocking melt flow upon separation. Prior art systems include a valve gated design such as described in U.S. Pat. No. 4,212,626, a hot probe design such as described in U.S. Pat. No. 4,891,001 and a valveless melt transfer system such as described in U.S. Pat. No. 5,458,843. Each such system has particular benefits for certain types of application. Each however typically drools or leaks in one way or another. 
     The valve gated design utilizes a pair of nozzles which are pressed up one against the other when the mould is closed with respective nozzle orifices in registry. Each nozzle orifice has a pin which can be advanced to block its respective orifice or retracted to unblock the orifice and permit melt flow. A disadvantage with this arrangement is that it is mechanically complex. A positive driving force is required for the pin, which can be mechanical, pneumatic or hydraulic. The driving mechanisms typically require a considerable amount of space and accordingly such an arrangement may not be useable in some applications due to space constraints. There is also typically some stringing at the gate with such an arrangement. As the two pins open and close in a hot resin environment, hot resin may be trapped between the two pins causing a string to form when the mould is opened. 
     The valveless melt transfer design includes an expansive chamber which captures melt during mould opening. This is an effective system which requires minimal shut height yet still causes some angel hair stringing. 
     The hot probe design basically utilizes a heated nozzle tip to selectively allow the resin to solidify and block the nozzle or melt to free the nozzle. As it lacks a valve pin it has a tendency to drool heavily yet has the advantage of being compact and accordingly suited to an arrangement where space is limited. The hot probe design has better control at its “front” where its cooling is better controllable. The hot probe and valveless designs are referred to as being “sprue gated” as opposed to “valve gated” in view of having a sprue but no valve. 
     It is an object of the present invention to provide a sprue gated design without the disadvantages of being prone to heavy drooling. 
     SUMMARY OF THE INVENTION 
     According to the present invention a cooling plate is interspersed between melt delivering and melt receiving cross over nozzle parts. The cooling plate engages ends of the cross over nozzles during mould filling and provides a melt transfer passage therebetween. Once the mould is filled, the cooling plate acts to dissipate heat from the melt transfer passage thereby promoting solidification of melt therein. Accordingly melt solidification in the sprue is assured with more certainty than prior art designs enabling relatively fast mould cycling with minimal risk of drool. 
     More particularly, an anti-drool cross over nozzle arrangement for a sprue gated melt transfer system is provided which has a first nozzle member having a melt outlet end with a melt outlet for discharging melt and a second nozzle member having a melt inlet end with a melt inlet for receiving melt. A cooling plate is mounted between the first and second nozzles. The cooling plate has first and second receptacles respectively for registering with and receiving the melt outlet end and the melt inlet end during a mould closed stage of an injection moulding cycle. The cooling plate has a melt transfer passage extending between the first and second receptacles for providing fluid communication between the melt inlet and the melt outlet during the mould closed stage. 
     The cooling plate may be carried by either the stationary or moving side of the mould, being attached thereto by a cooling plate attachment assembly. The attachment assembly may react to movement of an injection moulding assembly incorporating the melt transfer system between the mould closed configuration and a mould open configuration for the first and second receptacles to respectively engage the inlet and the outlet ends in the mould closed configuration and to be spaced apart therefrom in the mould open configuration. 
     The attachment assembly may mount the cooling plate to the stationary or the moving side of the mould (as applicable) for relative axial displacement parallel to a mould axis of the mould. The attachment assembly may include biasing means urging the cooling plate away from respective of the stationary or moving side of the mould. 
     The attachment assembly may include guide pins extending between the cooling plate and the respective of the stationary side and the moving side of the mould along which the cooling plate is slidable. The biasing means may be springs extending between the cooling plate and the respective of the stationary and the moving sides. 
     The melt transfer passage may be parallel sided to retain a plastic spigot formed by cooling of the melt therein as the mould is moved toward the mould opening configuration. 
     The melt transfer passage may narrow toward the melt inlet to cause a plastic spigot formed by cooling of the melt therein to stay attached to the outlet end as the mould is moved toward the mould open configuration. The melt transfer passage may alternatively narrow toward the melt outlet to cause a plastic spigot formed by cooling of the melt therein to stay attached to the inlet end as the mould is moved toward the mould open configuration. 
     The cooling plate may include a cooling passage extending therethrough for passage of a cooling fluid therealong to assist in removal of heat from the cooling plate. 
     The cooling plate may be secured to one of the first nozzle member and the second nozzle member. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       Preferred embodiments of the present invention are described below with reference to the accompanying illustrations in which: 
         FIG. 1  is a schematic axial sectional view illustrating an anti-drool cross over nozzle arrangement according to the present invention in a mould closed configuration; and, 
         FIG. 2  is a view corresponding to  FIG. 1  but illustrating the arrangement in a mould open configuration. 
         FIGS. 3 through 7  are axial cross-sectional views illustrating various nozzle tip configurations. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     An anti-drool cross over nozzle arrangement according to the present invention is generally indicated by reference  100  in the accompanying illustrations. The arrangement  100  is shown mounted between a stationary side  103  of an injection moulding apparatus (the balance of which is not shown but would be familiar to those skilled in injection moulding technology) and a moving side made up of parts  101  and  102 . The moving side  101 ,  102  is movable parallel to a mould axis  150 . 
     A melt channel  115  provides melt to a first nozzle member  120 . The first nozzle member  120  has a nozzle housing  113  and a melt outlet end  111  with a melt outlet  122 . A heater band  112  encircles the nozzle housing  113  near the outlet end  111  to provide heat (if required) to the nozzle housing to control melt viscosity at the melt outlet  112 . 
     A second nozzle member  107  is associated with the moving side  101 ,  102 . The second nozzle member  107  has an inlet end  132  having a melt inlet  130  for receiving melt. The melt inlet  130  fluidly communicates with a melt channel  114 . 
     A cooling plate  110  is mounted between the first nozzle member  120  and the second nozzle member  107 . The cooling plate  110  has a first receptacle  117  for registering with and receiving the outlet end  111  of the first nozzle member  120  during a mould closed stage of an injection moulding cycle as illustrated in FIG.  1 . The cooling plate  110  further has a second receptacle  118  for registering with and receiving the inlet end  132  of the second nozzle member  107  during the mould closed stage as also illustrated in FIG.  1 . The first and second receptacles,  117  and  118  respectively, should register with the outlet end  111  and inlet end  132  in a substantially fluid sealed manner to avoid the escape of melt therebetween. 
     The cooling plate  110  has a melt transfer passage  116  extending between the first and second receptacles,  117  and  118  respectively, to provide fluid communication therethrough between the melt inlet  130  and the melt outlet  122  during the mould closed stage. After melt flow is abated, in other words, once the moulds in the injection moulding machine to which the arrangement  100  is affixed are filled, the cooling plate  110  will dissipate heat from melt in the melt transfer passage  116 . This will cause solidification of the melt in the melt transfer passage  116  and in the melt inlet  132  and the melt outlet  122  adjacent thereto prior to separation of the components in the mould opening stage of the injection moulding cycle. This aids in avoiding melt seepage otherwise known as “drool” and hence the description of the nozzle arrangement  100  as “anti-drool”. 
     The cooling plate  110  is illustrated as being carried by the moving side  101 ,  102 , however it might alternatively be carried by the stationary side  103 . A cooling plate attachment assembly consisting of pins  108  and a biasing means such as the springs  109  illustrated. 
     The springs  109  urge the cooling plate  110  away from the inlet end  132 . Accordingly, as illustrated in  FIG. 2 , the cooling plate is spaced apart from the inlet end  132  as the moulding assembly incorporating the arrangement  100  is moved toward its mould open configuration. The pins  108  have heads which limit the displacement of the cooling plate  110  thereby resulting in the cooling plate  110  also being spaced apart from the outlet end  111  in the mould open configuration. 
     The movement of the cooling plate  110  away from both the outlet end  11  and inlet end  132  controls the amount of heat removed by the cooling plate  110 . Having the cooling plate spaced apart from the inlet end  132  and the outlet end  111  ensures that the cooling plate  110  doesn&#39;t continue to “freeze off” the melt outlet  122  or the melt inlet  130 . 
     As the moulding assembly is moved toward its mould closed configuration (in other words, as the moving side  101 ,  102  is moved toward the stationary side  103 ) the outlet end  111  urges the cooling plate  110  toward the inlet end  132  of the second nozzle member  107 , against the force of the springs  109 . 
     Although the use of springs  109  is shown in the illustrative example, other means may be devised for effecting relative movement of the cooling plate relative to the first nozzle member  120  and the second nozzle member  107 . For example a mechanical linkage or screw splines might be used. Also biasing means other than springs  109  might be utilized, such as a fluid pressure responsive piston slidable along a bore which may for example be coupled to the pins  108 . 
     Air cooling may be relied upon to dissipate heat from the cooling plate  110  in some applications. If enhanced heat dissipation is required, further cooling may be provided by a cooling passage  140  through which a coolant fluid, such as water, may be passed to aid in removal of heat. 
     Upon cooling and ensuing solidification of the melt in the melt transfer passage  116 , a “spigot” of plastic will form therein. The melt transfer passage  116  may be configured in different ways depending on whether the spigot is to remain therein or to attach to the outlet end  111  of the first nozzle member  120  or to the inlet end  132  of the second nozzle member  130 . The configuration of the melt transfer passage  116  illustrated is of generally constant diameter (i.e. “parallel sided”) which will result in the spigot remaining therein. If the melt transfer passage  116  narrows toward the melt outlet  122 , the spigot will tend to stay attached to the melt inlet  130 . Conversely, if the melt transfer passage  116  narrows toward the melt inlet  130 , the spigot will tend to stay attached to the melt outlet  122 . 
     To further cushion the arrangement  100  during mould opening and closing, a cover plate  106  may be placed between the second nozzle member  107  and the moving side  102 . Furthermore, the second nozzle member  107  may be slidably received in a socket member  105  and springs  119  mounted between the moving side  102  and the second cover plate  106  to urge the cover plate  106  and second nozzle member  107  away from the moving side  102 . A manifold  104  may be provided through which the melt passage  114  extends and receives melt from the second nozzle member  130 . 
     It will be appreciated that the amount of heat provided to and retained by the cooling plate  110  will be a significant factor in optimizing performance of an injection moulding arrangement utilizing such a feature. Accordingly nozzle design may play a significant role in system performance. It is expected that nozzles with hotter tips and greater surface area will provide more heat to the cooling plate  110  than nozzle arrangements with less surface area and lower operating temperatures. 
       FIGS. 3 through 7  illustrated various configurations for the first nozzle member  120  and in particular its melt outlet end  111 . Similar designs may be applied to the second nozzle member  107  and its melt inlet end  132 . 
       FIG. 3  illustrates a nozzle member  120  which is a “one piece” configuration having a melt outlet end  111  in the form of a tip  160  machined in the nozzle housing  113 . This is a relatively simple configuration but not readily reconfigurable other than by remachining. 
       FIGS. 4 through 7  illustrate three-part nozzles in which the nozzle housing  113  receives a nozzle tip  170  and a threaded collar referred to as a “nozzle cap”  172 . The nozzle cap  172  threadedly engages the nozzle housing  113  and abuts against a flange  174  extending about the base of the nozzle tip  170  to secure the nozzle tip  170  in the nozzle housing  113 . 
       FIG. 4  illustrates an arrangement wherein the nozzle tip  170  extends from the nozzle housing  113  beyond the nozzle cap  172 , wherein the melt outlet  111  has a breadth generally about the same as that of the nozzle tip  170  and wherein a nozzle tip melt passage  178  diverges radially outwardly at the melt outlet  122 . 
       FIG. 5  illustrates an arrangement wherein the nozzle tip  170  extends beyond the nozzle cap  172  and the melt passage  178  is generally “straight through”. This is referred to as a “through tip”. 
       FIG. 6  illustrates an arrangement somewhat similar to that of  FIG. 4  but wherein the nozzle cap  172  extends beyond the nozzle housing  170  and the melt passage  178  narrows toward the melt outlet  122 . 
       FIG. 7  illustrates an arrangement similar to that of  FIG. 6  but wherein the nozzle tip  170  and nozzle housing  172  are generally coterminal. Another embodiment which is not illustrated would be similar to that of  FIG. 7  but wherein the nozzle tip  170  protrudes beyond the nozzle cap  170 . 
     The  FIGS. 6 and 7  embodiments provide a greater contact area between the nozzle cap  172  and the cooling plate  110  thereby increasing heat transfer therebetween. The  FIG. 4  arrangement allows the nozzle tip  170  to extend into the melt transfer passage  116  in the cooling plate  110  in the mould closed configuration. 
     In the  FIG. 5  embodiment, melt does not impinge directly upon the nozzle cap  172  from the melt passage  178 . This arrangement therefore isolates the melt outlet  122  somewhat from the effects of the cooling plate  110 . 
     The above description is intended in an illustrative rather than a restrictive sense. Variations to the exact embodiments described may be apparent to appropriately skilled persons without departing from the spirit and scope of the invention which is defined by the claims set out below: