Abstract:
An injection moulded part design which may be reflected in a part and the mould for making the part has a continuous alternating arrangement of thicker and thinner panels each extending from a gate area along a direction of flow to a transition line. Beyond the transition line the arrangement of thicker and thinner panels is inverted with the thicker panels continuing as thinner panels and vice versa along the direction of flow.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to injection moulded plastic parts. More particularly, the invention relates to part designs utilizing thin wall sections for reduced material consumption. 
       BACKGROUND OF THE INVENTION 
       [0002]    There is an ongoing desire to make injection moulded parts such as containers, cups, closures, lids, pails, etc. with less material both to reduce weight and to reduce material cost. A challenge presented by thinner parts is in filling the mould. The thinner a part is configured the more pressure is required to force melt into the space defined between a mould core and a mould cavity. 
         [0003]    A technique used in getting melt to zones in injection moulded parts that are difficult to fill in is the use of “flow leaders” which are in effect channels of greater thickness than the adjacent part to enhance material flow through a larger cross-sectional area of the flow leaders. Such an approach however doesn&#39;t work well with parts in which weight reduction through very thin walls is desired. As described in more detail below, once the disparity in flow rates between the thinner and thicker areas exceeds a certain amount poor part quality can ensue. 
         [0004]    It is an object of the present invention to provide a part design which is injection mouldable yet of thin wall and lightweight configuration. It is a further object of the present invention to provide such part design which is conducive to parts having large flat surfaces. 
       SUMMARY OF THE INVENTION 
       [0005]    An injection moulded part design and a mould for malting the part has a continuous alternating arrangement of thicker and thinner panels each extending from a gate area along a direction of flow to a transition line. Beyond the transition line the arrangement of thicker and thinner panels is substantially inverted with the thicker panels continuing as thinner panels and vice versa along the direction of flow. 
         [0006]    The transition line may extend transverse to the direction of flow uninterruptedly across a plurality of the thick and thin panels. 
         [0007]    The transition line may correspond to a transition between a bottom of the part and a side wall of the part. 
         [0008]    The part design may be arranged wherein the thicker sections do not transition into thinner sections in portions of the part where strength is paramount to thickness. Such portions may correspond to corners and edges. 
         [0009]    The transition from thicker to thinner sections and vice versa may be offset. 
         [0010]    The part may, without limitation, be a closure, container, cup, pail, bucket or a long flat part such as a lid or a tray. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0011]    Preferred embodiments of the present invention are described below with reference to the accompanying illustrations in which: 
           [0012]      FIG. 1  is a perspective view from above of an injection moulded part according to the present invention; 
           [0013]      FIG. 2  is a pictorial representation illustrating flow front advancement as a function of time across the bottom of a part according to  FIG. 1 ; 
           [0014]      FIG. 3  is a pictorial representation illustrating flow front advancement as a function of time up the side wall of a part having thicker and thinner areas extending uninterrupted from a gate area across a bottom and up the wall of a container; and, 
           [0015]      FIG. 4  is a pictorial representation illustrating flow front advancement as a function of time up the wall of a part according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0016]    An injection moulded part according to the present invention is generally indicated by reference  10  in the accompanying illustrations. The part  10  is illustrated as a container with a bottom  12  and a side wall  14 . Other parts are however feasible including, without limitation containers, closures, cups, pails, buckets and long flat parts which have no side wall portion such as lids, trays, etc. All shapes such as round, oval, rectangular, etc. are also feasible. 
         [0017]    The part  10  comprises a continuous surface defined by an alternating arrangement of thicker panels  20  and thinner panels  30 . The thinner panels  20  and thicker panels  30  extend from a gate area  40  which corresponds to where melt initially enters a mould in which the part  10  is formed. Although gate area  40  is illustrated it will be appreciated that multiple gate areas are feasible depending on part configuration. The thicker panels  20  and thinner panels  30  may vary in thickness as required for strength and for fill pattern during forming. 
         [0018]    The thinner panels  30  and thicker panels  40  extend from the gate area along a direction of flow which extends generally radially outwardly from the gate area  40 . The term “direction of flow” refers to the direction in which melt flows through the mould in filling up the mould after being introduced into the gate area. 
         [0019]    The thinner panels  30  and thicker panels  40  extend to a transition line  50  extending about the part  10  where the bottom  12  meets the side walls  14 . Although such an arrangement is convenient for the part  10  illustrated, in other part configurations, such as large flat parts, the transition line  50  may be coplanar with the balance of the part  10 . Although the transition line  50  is illustrated as a thin band, such need not be the case as it may have zero length. In other words, the thinner panels  30  may transition into the thicker panels  40  directly. 
         [0020]    Beyond the transition line  50 , the part  10  continues to be comprised of an arrangement of thicker panels  30  and thinner panels  40 , however the arrangement is generally inverted from what it is on the opposite side of the transition line  50 . While the inversion could be total, in the part illustrated this isn&#39;t the case in its corners  16  and side edges  18  as it is expected that the benefit of greater thickness in these areas will structurally enhance the part  10  to an extent that exceeds the benefit of reducing the weight of the part by thinning these areas. A further benefit of the “non-inversion” is that the thicker portions act as true flow leaders to help fill the corners. 
         [0021]    Although the illustrations depict the thicker panels  40  as directly opposite the thinner panels  30  they do not have to align exactly as general or substantial alignment may suffice. Also there may be more than one transition line  50  spaced apart on the part  10  as required to control flow. 
         [0022]    The benefit of the present invention may be seen by comparing the flow front advancement as illustrated in  FIG. 3  depicting a part  60  lacking a transition line where the thicker panels  40  align with the thicker panels  40  and the thinner panels  30  align with the thinner panels  30  with  FIG. 4  depicting a part according to the present invention having a transition line  50 . 
         [0023]    Reference is first made to  FIG. 2  which illustrates the distribution of melt shortly after injection in a part  10  having a bottom configuration according to the part  10  of  FIG. 1 . The leading edge of the melt, known as its “flow front” is depicted by reference  100 . 
         [0024]    Reference  120  depicts the flow front  100  in the regions of the thinner panels  20 . Reference  130  depicts the flow front  100  in the region of the thicker panels  30 . It is apparent that the rate of advancement of the melt is greater in the regions of the thicker panels  30  as the flow front  100  is further advanced in the regions  130  than it is in the regions  120 . 
         [0025]    Reference is now made to  FIG. 3  which illustrates the flow front  100  later in the injection cycle for a part  60  having a thicker areas  63  and thinner areas  62 . The flow front  100  is significantly advanced in the regions  130  which correspond to the thicker areas  63  as compared with the regions  120  corresponding to the thinner regions  62 . 
         [0026]    Reference is now made to  FIG. 4  which illustrates the flow front  100  as it advances along the side wall  14  of the part  10 . As compared to the flow front  100  in  FIG. 3  the flow front  100  in  FIG. 4  is much more even without pronounced peaks and valleys as is the case with the  FIG. 3  arrangement. The flow front  100  of the  FIG. 4  arrangement is significantly better for forming a part  10  of good quality avoiding the possibility of trapping air/gas within the part  10  as the flow front  100  wraps around. 
         [0027]    It will be appreciated that the part design of the part  10  of the present invention relates back to the mould design. Accordingly the present invention extends to mould design as well as the resulting part. 
         [0028]    The above invention is described in an illustrative rather than a restrictive sense. Variations may be apparent to persons skilled in such arrangements without departing from the spirit and scope of the invention as defined by the claims set out below.