Valve gate nozzle

Valve gating nozzles used in sprueless molding also belong in the general category of shutoff nozzles, as do the nozzles which are used for impact molding. 

Gating nozzles, hot-runners and insulated runner molds, nozzle manifolds, and valve gating nozzles are used for obtaining sprueless moldings. Elimination of the sprue and runner system reduces costs through scrap and labor savings. 

FIGURE 2.63 Pneumatic needle drive with needle guide and valve gate nozzle... 

FIGURE 2.65 Valve gate nozzle with electromagnetic drive... 

The gate is the termination of a flow channel, and is a critical functional zone in an HR system. It governs the functioning of the nozzle, regardless of whether it is located in the nozzle or inside the actual mould cavity. The gate plays the part of a thermal or mechanical valve. Gate control concerns both melt flow control and gate closure (open time). 

Does this mean, that the amount of piping, fittings, gate valves, etc. should be minimized on a draw-offline, until the line drops 10 or 20 ft below the draw-off nozzle Yes ... 

Figure 2. Molecular beam mass spectrometer. Key A, nozzle-skimmer chamber B, middle chamber C, mass spectrometer chamber D, sampling nozzles E, skimmers F, choppers G, gate valve assembly H, mass spectrometer and I, nylon flanges permitting electrical biasing for detection of ions from coal burner.

Figure 9. View of the essential parts of the crossed beam apparatus using short-lived radioactive labeling and detection (23) Ay radioactive beam source By scrubber-furnace C, LN -cooled collimator D, shut-off plug Ey nozzle beam furnace and cryopump F, gate valve G, hodoscope H, LN -coohd beam trap 7, calibrated beam monitor /, silicon surface barrier detectors K, halogen crossed beam L, radioactive beam M, rotary feed-through used to close the source stopcock.

Shear heating of melt] injection rate too fast/injection pressure too high/gates too small/nozzle orifice too small < 0.8 of sprue bushing/nozzle dirty/sharp corners/injection rate too fast/shutoff nozzle used instead of a general purpose nozzle/improperly designed or defective non-return valve. 

Fluoroplastics feature high viscosity combined with a low resistance to shear stresses. Large channel diameters and very large gates, with a diameter of as much as 5 mm, are recommended [7]. This requires nozzles with a valve pin to be used. In a plasticised state, the melt has a strong corrosive effect on steel (chemical reaction of fluorine and iron). Steel with a high nickel content is therefore recommended, or else nickel coatings. To improve heat conduction, internal copper beryllium alloy inserts are used in the nozzles, which are pressed into elements made of hardened nickel steel. 

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. 

Inadequate quantity of material Check whether there has been a change of material. Increase shot size. Check screw nonreturn valve. Check machine nozzle and HR sprue bushing contact. Check whether there is any drooling of melt from sprue bushing when machine nozzle is withdrawn. Check leaktighmess of HR system. Check whether there has been a blockage of one of the gates - clean. 

Many diverse devices have been developed for feeding pipelines. Some are specifically appropriate to a single type of system, such as suction nozzles for vacuum systems. Others, such as rotary valves, screws and gate valves, can be used for vacuum and positive pressure systems. The approximate operating pressure ranges for various pipeline feeding devices are illustrated in Figure 4.13. 

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