Three-plate mould

This type of mould, also often referred to as a three plate mould, is used when it is desired to have the runner system in a different plane from the parting line of the moulding. This would be the case in a multi-cavity mould where it was desirable to have a central feed to each cavity (see Fig. 4.38). In this type of mould there is automatic degating and the runner system and sprue are ejected separately from the moulding. 

The runners and sprues are necessary in a mould but they are not part of the end-product. Unfortunately, it is not economically viable to discard them so they must be re-ground for subsequent reprocessing. Regrinding is expensive and can introduce contamination into the material so that any system which avoids the accumulation of runners and sprues is attractive. A system has been developed to do this and it is really a logical extension of three plate moulding. In this system, strategically placed heaters and insulation in the mould keep the... 

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%. 

Transfer moulding may actually be carried out on a compression press using a three-plate tool but this is not considered by the author as a wholly successful means of moulding, and should only be used for special applications. 

PEI is also used in so-called moulded intercoimect devices (MID), because of its unique plating capabilities. PEI allows the combination of electrical fimctions with the advantages of injection moulded three-dimensional mechanical components in electrical control units, computer components, telecom and mobile phones, internal antennae of duplexers or microfilters, and fibre optic connectors. 

Figure 4.5 General assembly and operation of a typical three-plate mould...

On three-plate moulds too, pencil-form connections should be avoided for this reason. 

The screw caps are manufactured in pairs, using a three-plate mould. 

After compaction and once the metal extension collar is removed, the soil material is flattened by means of a straightedge (knife or spatula) until it is even with the top of the mould. Afterwards, the soil specimen with the steel mould is inverted and clamped on a perforated base plate (a coarse filter paper is added to the interface of the perforated base plate and soil specimen). Sufficient annular weights (usually three) are added on the compacted soil material in the mould in order to produce a surcharge equal to the weight of the overlying layers. Soil material, mould and surcharge weights are immersed in water (water level shall be 25 mm above the specimen s surface). At the same time, a tripod with a dial indicator is placed over the mould and its initial indication is recorded. The whole system remains undisturbed for 96 h. 

At least 24 aggregate particles are placed in a steel mould in a single layer with their flattest surface down. The interstices between the aggregates are in-filled with fine sand to approximately three quarters of their depth. The rest of the mould is in-filled with epoxy resin, and a metal plate, which has been precoated with grease, is placed on top. After the resin hardens, the specimen is removed from the mould, cleaned thoroughly from any sand and transferred to the abrasion machine. 

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. 

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