Page 125 - Injection Molding Advanced Troubleshooting Guide

112 13 Cavity Instrumentation

knowledge of the equipment to set up correctly. Current monitoring equipment
utilizes auto calibration and plug and play smart transducers making cavity pres-
sure monitoring easily accessible.
See Figure 13.1 for a typical cavity pressure transducer. Be aware that transducers
come in different load ratings, different cable lengths, and different styles includ-
ing strain gauge and piezoelectric.

Figure 13.1 RJG button style cavity pressure transducer

Cavity pressure transducers are most often installed under an ejector pin and the
pin transfers the pressure from the cavity to the transducer. Another technique is
to install a pressure transducer at the mold surface. In both cases the transducer
will provide pressure data of the plastic in the mold. Long unsupported pins can
lead to deflection that will show as an uptick in-cavity pressure after second stage
is complete (this can also indicate mold deflection).
A web search will show that there is a wide variety of producers of cavity pressure
transducers including RJG Inc., Priamus System Technologies, and Kistler Group
among others. Decision of the brand, type, and size must be determined before the
mold can be machined for installation.
Some of the information that cavity pressure monitoring can provide from inside
the mold include:
ƒ Cavity pressure at all points of the cycle
ƒ Actual mold fill time