HR in moulds for small mouldings

The development of heating equipment and miniaturisation of heating elements are enabling the nozzle axis pitch to be made smaller. Recently designed nozzles with a diameter of 10 mm, heated by a 230 V current, are beginning to compete with nozzles fitted with 5 V heaters. 

Because of the typical areas of use - microelectronics, precision parts for mechanisms and parts for medical technology, etc., high temperature engineering plastics are increasingly used here, which makes it necessary to apply very restricted thermal injection parameters (even down to 2 °C). In such instances it is still best to use low voltage heaters with a rectilinear temperature characteristic. 

Since the critical point for many plastics is the time spent by the melt under a thermal load, attention should also be given to the combined time spent in the HR and the injection machine cylinder (see Chapter 3.1). When small HR moulds are used, one major problem is selection of an injection machine small enough not to be operating below the lower limit of the machine s nominal injection capacity (0.25 without an unnecessary increase in the multiplicity of the mould. 

Machine designs have recently appeared in which a multiple nozzle with valve pins, typical of an HR system, was used as an injection machine nozzle [5, 6]. The mould itself does not then have a gating system apart from the gates in the cavities. 

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