Manifold with external heating

In practice, hybrid systems are increasingly frequently encountered, where the manifold is simultaneously bolted on and clamped down, which reduces the risk of seal failure. Much attention is given to ensuring that manifolds with external heating can withstand leakage. Manifolds with screw-in nozzles have been developed for this reason. 

Hot-manifold mold n. An injection mold equipped with an internal heater located in the center of the melt stream in the manifold and nozzle system. This type of mold was developed for thermally sensitive resins to provide gentler heating and avoid the decomposition problems experienced with external heating techniques because of excessive temperature differences. 

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. 

Other options for gas dispensing cryogenic tanks are manifolds that can connect two to six cylinders together. These manifolds can provide flow rates of 250 cfh (cubic feet per hour), can set up a reserve of gas for uninterrupted flow when changing cylinders, and (with an economizer circuit) can cut loss due to evaporation. For extra-high-capacity gas demands, there are external vaporizing manifolds, which are a combination of the external heat exchanger and manifold n... 

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. 

In the classic D-M-E version, the manifold has large-diameter (24-50 mm) drilled flow channels in which cartridge heaters in a tubular body are located. The melt thus flows through an annular channel between 4 and 9 mm wide (see Chapter 1). Because of the heating pipe in the centre of the channel, the channels cannot cross over as in externally-heated manifolds, but must be connected adjacently. Torpedoes must also be connected with a butt joint to the flow channels. This creates certain restrictions as regards the mould cavity arrangement, and it is not easy to achieve a natural flow balance (see Figure 4.91). 

The Ele oCetl concept (Pig, 2.31) utilizes internal manifoldmg to distribute the electrolyte in the mamiet of some plate-and rranie heat exchangers (Fig. 2.31(a)) Such an arrangement helps to provide a compact reactor In special cases, individual compartments with external manifolds may be incorporated into the cell stack (Fig. 2.29). 

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. 

FIGURE 1.46 Externally heated hotrunner in the standard design with floating manifold a Manifold b support disk c tubular heating elements d centering pin e heating coil of the nozzle [24]... 

Injection The injection blow moulding machine is based on an extruder barrel and screw assembly which melts the polymer. The molten polymer is fed into a manifold where it is injected through nozzles into a hollow, heated preform mould. The preform mould forms the external shape and is clamped around a mandrel (the core rod) which forms the internal shape of the preform. The preform consists of a fully formed bottle/jar neck with a thick tube of polymer attached, which will form the body. 

Craig [312] reports on an investigation of the performance of a large diameter static mixer used as a continuous reactor for styrene polymerization. It was shown the mixer behaved adiabaticaliy. This was confirmed by computer simulation using models that had been verified experimentally. Better results were obtained with a static mixer that carries a heat transfer fluid supplied via manifold connections from external headers. A comparison of different static mixers with respect to thermal homogenization, pressure drop, and mixing efficiency was published by Mueller [313]. 

Tubular manifolds. An example of a tubular manifold is a design in which the flow channel is in a tube. The tube is heated by coil heaters in ceramic insulation and is set in a hole in a plate transferring the external load (see Figure 4.63). The low mass of the tubular manifold and its insulation by air gaps means the plate temperature is relatively low. Because of the very small temperature fluctuations, this manifold is recommended for the injection of plastics that are difficult to process, LCP, PA 66, PBT, PC, PEEK, PET, PSU, PVC with glass fibre, etc. 

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