Sprue bushing manifold

Name Gate Nozzle Manifold Sprue bushing... 

A type (a) mould of three-plate design with heated sprue bushing is converted using an HR manifold and nozzles with side gating. The cycle time has been reduced by 35%, and the production cost has fallen by 43%. 

Function. Central nozzles and manifold nozzles differ only in that the former are designed to interact directly with the injection machine nozzle. Both a central and a manifold nozzle may be in the form of a hot sprue bushing leaving a small sprue and intended mainly for gating to a cold runner. 

The channel must be polished. In the centre of the manifold is a sprue bushing (1), on the opposite side is a support pad (3) taking the pressure from the injection machine cylinder and a pin (4) aligning the manifold. A second pin (5) located in the end of the manifold sets its angular position. The manifold is pressed against the HR nozzles located in the mould by pressure pads (6) on the opposite side of the manifold. The transfer from the... 

In the example given, the manifold comprises a sprue bushing, two T-junctions, six bushings and four nozzles. 

The figure shows examples of solutions to this problem with the rheological balance maintained. Because of the flow disruptions that occur, it has been necessary to eliminate the central channel located opposite the sprue bushing channel. In Figure 4.71b a two-level manifold has been used, with a central channel with a diameter that is smaller than the diameter of the outside channels. In Figure 4.71c, a manifold with two small-diameter inclined channels has been used. 

Figure 4.85 Matching of injection machine nozzle and sprue bushing of manifold...

In view of the low temperature of the manifold plate, the sprue bushings must be heated. Both external and internal heating is used (for the use of a torpedo, see Figure 4.92). 

The numbers 1-8 have been given to the nozzles/cavities, starting with the nozzle which is nearest to the guide pillar with the smallest diameter, and proceeding clockwise. The numbers 9-11 have been allocated to the manifold zones in a similar sequence (9-10 - side distributor channels, 11 - main channel), and 12 has been allocated to the sprue bushing as the final component of the system. 

Figure 5.16 Example of marking of heating zones 1-8 - nozzles 9-11 - manifold 12 - sprue bushing (Reproduced with permission from D-M-E Belgium)...

Heat conduction from the manifold takes place chiefly via the spacer pads and fastening bolts, and perhaps also via the non-heated sprue bushing. A diminution in heat losses caused by conduction may be attained by ... 

The manifolds most frequently used have a very long heated sprue bushing located on the mould axis and operating on the principle illustrated in Figure 9.10. As can be seen, the melt flowing out of the sprue bushing may, when the mould is taken away from the injection machine nozzle, gets into the ejector plate space. 

Figure 9.11 Stack mould with split sprue bushing a - diagram of mould b - view of manifold Reproduced with permission from Arburg)...

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. 

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