Torpedo heated internal

With internal heating it is also possible to use nozzles with a heated internal torpedo for non-standard methods of melt distribution (Figure 9.26). In case (a) the cavities are... 

Nozzles with heated torpedo. The simplest kind of tip nozzle with torpedo (Figure 4.21a) is internally heated by a cartridge heater and attached directly to the manifold (mould plate) with internal heating. It thus serves at the same time to heat the feed channel in the manifold. The end of the nozzle is supported by three pins or short ribs in the bottom of the chamber. Sealing of the channel between the plates is provided by an external frozen layer of melt. 

Use of an internal channel heating system, coupled with the low manifold plate temperature, have enabled torpedoes to be set within the manifold and for them to be used to heat the exit channels. A torpedo is normally fitted in a fixed manner (see Figure 4.93), but there is also the potential to fasten it in such a way that it can move (Figure 4.93b). 

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). 

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. 

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 system with external heating enables the channels to be purged relatively quickly. A system with internal heating does not allow the channels to be purged completely, and in some cases it is necessary to take the manifold apart and clean the channels, torpedoes and insulation chambers manually. Some systems are designed in such a way as to allow the channels to be opened up (see Figure 4.91) sometimes this can even be done on the machine without removing the mould. 

The difficulties with color change restrict the field of application of internally heated systems. The following combination can be found more often Externally heated manifold and internal heating in the nozzle area, equivalent to the design of the gate elements as a torpedo or as a thermal conductive tip. 

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