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.
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.
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'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.
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.
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.
The transition line may extend transverse to the direction of flow uninterruptedly across a plurality of the thick and thin panels.
The transition line may correspond to a transition between a bottom of the part and a side wall of the part.
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.
The transition from thicker to thinner sections and vice versa may be offset.
The part may, without limitation, be a closure, container, cup, pail, bucket or a long flat part such as a lid or a tray.
Preferred embodiments of the present invention are described below with reference to the accompanying illustrations in which:
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.
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.
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.
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.
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'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.
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.
The benefit of the present invention may be seen by comparing the flow front advancement as illustrated in
Reference is first made to
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.
Reference is now made to
Reference is now made to
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.
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.
Number | Date | Country | Kind |
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2631762 | May 2008 | CA | national |