Abstract:
According to the present invention, a manifold mounting arrangement is provided wherein a leg manifold is securely mounted midway along its length rather than at its sprue bushing and whereby thermally induced length changes are accommodated outwardly from its centre. Additionally, a first end of the leg manifold is clampingly secured between a sprue housing and a manifold insulator to avoid movement of the first end toward the sprue upon a sprue break portion of the injection moulding cycle.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to moulding apparatus for the injection moulding of plastics. More particularly, this invention relates to the mounting of a “leg manifold” in a multi-level stack moulding arrangement. 
     BACKGROUND OF THE INVENTION 
     In designing multi-level, multi-cavity stack moulds, such as 2, 3 or 4 level moulds, consideration must be given to maintaining balanced melt flow. It is often ideal to originate melt flow from a central axis of the mould for each level. This may require a melt flow path which originates at the mould axis, extends radially outwardly through a “leg manifold” to the edge of the mould, crosses a “level” through a crossover nozzle and returns radially inwardly back to the central axis through a further leg manifold displaced longitudinally along the mould axis from the first leg manifold. The number of leg manifolds will depend on the number of mould levels. Typical arrangements where radially inward and outward melt flow paths are present are illustrated in U.S. Pat. No. 5,846,472 (three level) and U.S. Pat. No. 5,458,843 (two and four level). 
     As injection moulding apparatus are principally made of metal which expands significantly between room temperature and its operating temperature, provision has to be made to accommodate thermal growth/contraction of the leg manifold by amounts on the order of 0.125 inches (approximately 3.3 mm). FIG.  1  schematically illustrates a typical axial cross-section through a “prior art” mounting arrangement. A leg manifold  10  is illustrated as providing a fluid conduit between a sprue bushing  12  located on the central axis  14  of the mould and a crossover nozzle housing  16  disposed generally parallel to but radially outwardly of the central axis  14  of the mould. The leg manifold  10  is located on the central axis  14  by a means such as a first manifold insulator  18  having a first locating spigot  20  which engages a socket  22  in the leg manifold  10  across from the sprue bushing  12 . 
     In theory at least, the leg manifold  10  will expand radially outwardly from the mould axis  14 . The end of the leg manifold adjacent the crossover nozzle housing  16  is clamped between the crossover nozzle housing  16  and a second manifold insulator  24 . The second manifold insulator  24  has a second locating spigot  26 . The second locating spigot  26 , is received in a slot  28  in an injection plate  30  against which it presses. While, it is intended that longitudinal movement should be accommodated by movement of the second spigot  26  in the slot  28  and sliding movement between the leg manifold  10  and the crossover nozzle housing  16 , often this doesn&#39;t occur. Instead the first locating spigot  20  ends up being sheared off in turn pressing the leg manifold  10  toward the sprue bushing  12  and misaligning the sprue bushing  12  in its locator ring  30 . 
     A further disadvantage to the prior art design is that there is no clamping force applied to the sprue bushing end of the leg manifold  10 . When “sprue break” occurs in the injection moulding cycle during which the injection machine nozzle is disengaged from the sprue bushing  12 . The sprue bushing is slidably received in a locating ring  32  and therefore doesn&#39;t “clamp” the leg manifold  10  against the first manifold insulator  18 . Repeated engagement and disengagement of the injection machine nozzle and sprue bushing  12  has a “hammering” effect on the leg manifold  10  which eventually causes curvature of the leg manifold away from the sprue bushing. 
     It is an object of the present invention to provide a mounting arrangement for a leg manifold which better accommodates thermal growth and shrinkage than the above described arrangement. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the present invention, a manifold mounting arrangement is provided wherein a leg manifold is fixedly secured at a central location along its length rather than at its sprue bushing and whereby thermally induced length changes are accommodated outwardly from this central location. Additionally, a first end of the leg manifold is clampingly secured between a sprue housing and a manifold insulator to avoid movement of the first end toward the sprue upon a sprue break portion of the injection moulding cycle. 
     More specifically, a manifold mounting arrangement for a leg manifold of an injection moulding apparatus is provided. The manifold mounting arrangement includes an injection plate, a manifold plate secured to the injection plate and a cavity defined between the manifold plate and the injection plate. The leg manifold, which has first and second opposite ends, is disposed in the cavity. The first end of the leg manifold is located by a first manifold insulator extending between the first end and the manifold plate and by a sprue housing having a flange extending between the leg manifold and the injection plate. The second end of the leg manifold is located by a second manifold insulator extending between the second end and the injection plate and by a crossover nozzle housing having a flange extending between the leg manifold and the manifold plate. The leg manifold has a melt passage extending through it which fluidly communicates at the first end with a sprue passage extending through the sprue housing and at the second end with a crossover nozzle passage extending through the crossover nozzle housing. The leg manifold is further supported along its length between central manifold insulators which extend between the leg manifold and the injection plate and between the leg manifold and the manifold plate. The first and second manifold insulators are positioned to allow longitudinal movement of the first and second ends of the leg manifold relative respectively to the sprue housing and the crossover nozzle housing in response to thermal expansion and contraction of the leg manifold. The central manifold insulators constrain the leg manifold from longitudinal movement to limit such movement to the first and second ends. 
     The central manifold insulators may be secured by respective securing means extending into the injection and manifold plates and at least some of the central manifold insulators may be provided with projections or recesses which engage corresponding projections or recesses in the like manifold to constrain its longitudinal movement. 
     The securing means may include a socket extending into the manifold plate and a socket extending into the injection plate for respectively receiving the second and the first manifold insulators. 
     The securing means may alternatively be threaded fasteners. In a preferred embodiment, the central manifold insulators are disposed about midway along the length of the leg manifold so that normal movement is divided approximately equally between the first and second ends relatively respectively to the sprue housing and the crossover nozzle housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present invention are described below with reference to the accompanying drawings in which: 
     FIG. 1 is a schematic view of an axial cross-section through a prior art manifold arrangement; and 
     FIG. 2 is a schematic view of an axial cross-section through a manifold mounting arrangement according to the present invention for a leg manifold. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A manifold mounting arrangement according to the present invention is generally indicated by reference  100  in FIG.  2 . The arrangement  100  mounts a leg manifold  110  in a cavity  102  defined between mating surfaces of an injection plate  104  and a manifold plate  106 . 
     The leg manifold  110  has a first end  112  and a second end  114  opposite the first end  110 . A first manifold insulator  120  is positioned between the first end  112  and the manifold plate  106  to limit movement of the first end  112  toward the manifold plate  106 . Unlike the prior art arrangement, the first end  112  is free to slide relative to the first manifold insulator  120 . The first manifold insulator  120  may be received in a recess  122  in the manifold plate  106  to secure it to the manifold plate  106 . Other securing means, such as threaded fasteners might also be used or it might be formed as part of either the leg manifold  110  or the injection plate  104 . 
     Across from the first manifold insulator  122 , on the opposite side of the first end  112  of the leg manifold  110  is a sprue housing  130  which extends through the injection plate  104 . Unlike the sprue bushing  12  in the FIG. 1 embodiment, the sprue housing  130  includes a flange  132  which engages the injection plate  104  to prevent its withdrawal from the injection plate  104  (to the left as illustrated). In other aspects, the sprue housing  130  is similar to a sprue bushing. It mates with an injection machine nozzle  140  through an anti-drool device  150  and may extend through a locating ring  152 . 
     The first end  112  of the leg manifold  110  is in effect “clamped” between the first manifold insulator  120  and the sprue housing  130 . In other words, the first end  112  is pressed up against the sprue housing  130  to sealingly engage the sprue housing. Given enough force to overcome friction between the first end  112  and the first manifold insulator  120  and the sprue housing  130 , the first end can slide at least vertically (as illustrated) relative to the first manifold insulator  120  and the sprue housing  130 . Furthermore, the first end  112  is prevented by the sprue housing  130  from moving toward the injection machine nozzle  140  (to the left as illustrated) upon “sprue break” (i.e. when the injection machine nozzle  140  separates from the anti-drool device  150 ). 
     The second end  114  of the leg manifold  110  is clamped in a manner similar to the first end  112 , but between a second manifold insulator  160  and a crossover nozzle housing  170 . The second manifold insulator  160  is secured to the injection plate  104  by suitable securing means such as a recess  162  in the injection plate  104 , threaded fasteners, welding or may be integrally formed with the injection plate  104  or leg manifold  110  (not shown). The crossover nozzle housing  170  has a flange  172  which engages the manifold plate  106  to limit movement of the nozzle housing  170  away from the injection plate  104  (to the right as illustrated). 
     As with the first end  112 , the second end  114  of the leg manifold presses up against the cross-over nozzle housing to sealingly engage the crossover nozzle housing  170 . Given enough force to overcome friction between the second end  114  the second manifold insulator  160  and the crossover nozzle housing  170 , the second end  114  can slide vertically (as illustrated) relative to the second manifold insulator  160  and the crossover nozzle housing  170 . 
     The leg manifold  110  has a melt passage  116  extending through it. The melt passage  116  communicates at the first end  112  with a sprue passage  134  extending through the sprue housing  130 . The melt passage  116  fluidly communicates at the second end  114  with a crossover nozzle passage  174  extending through the crossover nozzle housing  170 . 
     The leg manifold  110  is further supported along its length between a pair of central manifold insulators  180 , one of which extends between the manifold plate  106  and the leg manifold  110  and the other of which extends between the leg manifold  110  and the injection plate  106 . The manifold insulators  180  are received in respective recesses  182  and are provided with projections or locating spigots  184  which engage corresponding recesses  186  in the leg manifold  110 . Accordingly the central manifold insulators  180  constrain the leg manifold against the longitudinal movement (vertical as illustrated) in the region of the central manifold insulators  110 . This has the effect of limiting longitudinal movement of the leg manifold  110  resulting from thermal expansion or contraction to the first and second ends,  112  and  114  respectively. 
     In a preferred embodiment, the central manifold insulators  180  may be located about midway along the leg manifold  110  as suggested by dimensions A,A in FIG.  2 . This has the beneficial result of dividing thermal expansion and contraction approximately equally between the juncture of the leg manifold  110  and the sprue housing  130  and between the juncture of the leg manifold  110  and the crossover nozzle housing  170 . This in turn minimizes the overall restriction to melt flow imposed by misalignment between the melt passage  116 , the sprue passage  134  and the crossover nozzle passage  174 . 
     Some benefit would be realized from the arrangement  100  even if the central manifold insulators  110  were disposed closer to either the first end  112  or the second end  114  of the leg manifold  110  in view of the slidability between the first end  112  and the sprue housing  130 . Also, a benefit would be realized by virtue of the locating effect of the sprue housing  130  on the first end  112 , which is discussed above. 
     Although a spigot and recess arrangement is illustrated to secure the leg manifold  110  to the central manifold insulators  180 , other arrangements may be utilized. For example: the spigot and recess may be reversed as between the central manifold insulators  180  and the leg manifold  110 ; each of the leg manifolds  110  and the central manifold insulators  180  may have both spigots and recesses; only one of the central manifold insulators  180  need engage the leg manifold  110 ; other securing means such as welding, threaded fasteners or forming the central manifold insulator as part of the leg manifold  110  or as parts of the manifold plate  106  and the manifold plate  104  may be utilized. 
     If a sprue bushing is to be utilized in lieu of the sprue housing, another manifold insulator may be mounted adjacent the sprue bushing to limit movement of the first end  112  toward the injection machine nozzle  140  on sprue break. 
     Although four manifold insulators are illustrated, more may be used to provide further support along the leg manifold  110 . 
     Although single branch manifolds have been described, the above arrangement may be adaptable to multi-branch manifolds such as used in 3-level stack moulds. 
     The above description is intended in an illustrative rather than a restrictive sense. Variations to the specific structure described may be apparent to persons skilled in the art without departing from the spirit and scope of the present invention which is defined by the claims set out below.