Page 257 - Injection Molding Advanced Troubleshooting Guide
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248 26 Dimensions
Non-return valve
Machine performance
26.3.3.1 Machine: Nozzle Tip
When troubleshooting dimensional issues it is important to verify that the correct
pressure is being supplied to the cavity. One often-overlooked problem area is the
nozzle tip. If the wrong tip is being used the pressure drop from the machine will
be higher. Care must be taken to ensure that the correct orifice is used as well as
the correct style (i.e., nylon versus general purpose). Nozzle tip orifice and style
must be documented and matched every time with the mold. Figure 26.4 shows a
cavity pressure comparison between the same process running with a general-pur-
pose 3/16-in tip and a general-purpose 5/32-in tip. On this process a one-size
change in tip orifice had a huge impact on the plastic conditions. Tip orifice cannot
be taken for granted, ever!
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Figure 26.4 RJG eDART cycle graph showing variation in cavity pressure between cycles run
with a 3/16-in versus a 5/32-in nozzle tip
One method for ensuring that the correct nozzle tip is always used is to weld a 7/8-
in nut on the side of the mold and then store the tip for that mold threaded into the
nut. Every time a mold change is performed the nozzle tip is swapped for the one
stored on the mold.
