Nozzle control

Further differences from hydraulic nozzles (controlled by sheet and ligament breakup) are the stronger increase in drop size with increasing surface tension and decreasing gas density. 

D) Tube-side channels and nozzles control the flow of the tube-side fluid into and out of the tubes. The tube-side channel may be bolted to the shell by flanges (as shown in the drawing) or welded directly. 

Section I of the ASME code for fired boilers requires that the PSVs reach their full lift at a pressure not greater than 3% over their set point. Section VIII of the ASME code for unfired vessels does not provide a blowdown requirement, and the industrial practice is about 7%, which means that the normal operating pressure must be under 93% of set pressure. The position of the adjustable ring on the PSV nozzle controls the blowdown. This position establishes a secondary orifice area as the valve opens and closes. 

Cold runner systems have a similar temperature control requirement to the plasticising and injection unit, since the cold runner acts as an extension to the nozzle, controlling the rubber temperature to preclude any build up of scorched material while it awaits injection into the mould. 

Figures 4.15c-g shows how nozzles are used in cold runner gating. Nozzle 4.15(c) is a point-gate nozzle, while nozzles (d)-(g) are of the sprue-gate type. The sprue length may be reduced by shortening the nozzle, but it should be remembered that a longer sprue helps in nozzle control.

Sequential moulding is based on mutually independent opening and closing of the nozzles in the mould cavity in such a way as to allow the weld lines to be shifted until they reach an optimum position. This technique is used for products of large area and with numerous apertures which cause weld lines to appear. The use of simulation clearly provides a good starting point for optimisation of nozzle control. 

Nozzle control takes place using one of the following methods ... 

For each axis (EF,V), the detection/correction algorithm uses the values of angular deflection of the nozzles controlled by the pilot, the measured position of the trays distributing each cylinder and provides the estimated position of each distributing tray of each controlled cylinder. 

Group nozzle control, operated from a speed governor by a hydraulic servo motor, results in economic partial-load performance combined with desirable speed-governing characteristics. 

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