Page 39 - Plastics News February 2020

FeAtures

robots, reversing conveyors, and diverters can be used are basically computers, and we all know that even the
to accomplish this. If none of these is an option, the best systems have software issues from time to time. If
machine must be set up to shut down when any out-of- the system is only looking for reject signals, that system
process condition is identified, and ejection must be cannot be considered failsafe, and if the system locks up,
prohibited, leaving the suspect parts in the mold. This it can continue to run until someone discovers the issue.
is undesirable for several reasons, one of which being Most of the third-party process-monitoring systems I have
that a process interruption can cause instabilities in the worked with will also accept a good-part signal if you
process. Automating is the best option and will allow you make that part of your system specification. A process-
to continue to mold, keeping the process stable. It is also monitoring system that requires a good-part signal to be
critical to ensure you have built in effective reject logic received and defaults to reject, is a system that is truly
in your monitoring to prevent the machine from running failsafe.
excessive scrap rates. It is important to remember that regardless of how tight
monitoring limits are set, the first step in effective process
Failsafe to Avoid Failures monitoring is the process development. Establishing limits
Is your process monitoring failsafe? Most monitoring for unstable processing conditions or tooling conditions will
systems are programmed to look for a reject signal. So, ultimately prove ineffective in preventing unacceptable
if the monitoring system doesn’t receive a reject signal, product from escaping. Once you have mastered process
parts are considered to be within process limits. So, what development, effective process monitoring ensures you’re
happens with a system crash? Remember, these systems always running to that process.

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39 Februar y 2020 Plastics News