Stack moulds

Front gating via a distribution system (indirect) in a stack mould. The HR system has made it possible for stack moulds to be developed (Figure 1.4d), with two, even three parting lines. 

The potential for further development of stack moulds and for design of moulds with gating via a long core. 

The nozzles (Figure 4.41a) is equipped with a centrally located cylander with an annular piston, which may be driven by compressed air at a minimum of 0.6 MPa (closure force around 2 kN) or hydraulically at a maximum of 3 MPa (closure force around 10 kN). The drive is transmitted to the pin via a traverse cross beam. Because of its small length, this nozzle is also used in stack moulds. 

The main element in each stack mould is the central plate containing the HR manifold and nozzles and the cavities. One difficult problem which is crucial to the design of the HR system is the way the melt is to be fed to the manifold. 

For design reasons it is difficult to use shut-off nozzles in stack moulds. Problems arise from the installation in the moulds of cylinders, which by nature are of substantial height. 

Figure 9.9 Stack mould with HR manifold adapted to work with angle injection machine Reproduced with permission from Arburg)...

Figure 9.10 Diagram showing the operation of a stack mould with axial central melt flow to manifold [8]. a - closed manifold b - open manifold Reproduced with permission from G. Bagusch and U. Kolter, Kunststoffe, 1995, 85, 6, 759, Figure 2. 1995, Carl Hanser Verlag)...

Figure 9.12 Fragment of a 16-cavity stack mould for a bottle base using pneumatically-operated shut-off nozzles Reproduced with permission from Mold-Masters)...

A simple stack mould design is provided by a shut-off nozzle with an annular cylinder (Figure 9.13). An example of a very compact manifold design with shut-off nozzles and an integrated drive combined with the nozzle casing is illustrated in Figure 4.43. 

In view of the advantages of HR systems with internal heating (described in Chapter 4.2.2), they are also used in stack moulds. Of particular importance here is the potential to reduce the mould height. Figure 9.14 shows a fragment of a stack mould with a long sprue bushing, internally-heated manifold and two-way torpedo. A characteristic feature of this system is that the manifold is the mould plate. 

Serious problems are encountered in the design of stack moulds with two cavities (1+1), since in this instance it is not possible to use a central melt feed to the manifold via a sprue bushing. It is then necessary to design a system that delivers the melt from the side of the manifold. 

Figure 9.13 Location of shut-off nozzles with ring cylinder in stack mould Reproduced with permission from PSG Plastic Group GmbH)...

Figure 9.14 Example of use of an HR system with internal heating in a stack mould 1 - sprue bushing 2, 3 - cartridge heaters 4 - manifold 5 - two-way torpedo Reproduced with permission from D-M-E Belgium)...

A completely different concept of an HR system in a stack mould (Figure 9.17) was used to mould two parts of a pallet from PP (6.3 kg and 2.3 kg). There are two manifolds in this mould... 

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