Page 124 - Injection Molding Advanced Troubleshooting Guide

13 Cavity Instrumentation

Cavity instrumentation is one significant tool available for injection molding and
normally comprises the use of either cavity pressure transducers or thermocou-
ples. This chapter will provide a basic understanding of cavity instrumentation.
Many examples of data from in-mold instrumentation are used throughout this
book.
For a complete understanding of in-cavity instrumentation consider taking a
course specializing in scientific molding and molding instrumentation.

„ „13.1„ Cavity Pressure Technology

During the 1960s Rod Groleau conducted a number of studies on cavity pressure
and published a paper called “A Report on Injection Molded Part Size Control”. In
1969, Groleau co-founded a company called Control Process Inc., and began pro-
ducing the industry’s first strain gauge cavity pressure transducer and monitoring
system. In 1989, Groleau founded RJG Technologies and began supplying cavity
pressure transducers and monitoring equipment to the injection molding industry
[1].
Cavity pressure transducers have created a revolution in the molding industry.
With an instrumented mold it is now possible to understand what is occurring in
the mold. Without in-cavity instrumentation there is a gap between the machine
settings and the final part results. Cavity pressure transducers help fill this gap.
What occurs in the mold has always been a closed “black box” but now with trans-
ducers it is possible to see inside the box.
Cavity pressure monitoring capabilities have come a long way over the years. Not
too long ago the use of paper strip chart recorders for capturing process data was
state of the art. Progression over the years led to computer-based monitoring
systems that at first required careful calibration of transducers and intimate