Dew Measurement in Plastic Drying Processes

In the drying of plastics, a good dew-point meter is essential as it can let you know if your dryer is working properly or if it may need to be repaired. The instrument does this by monitoring the air flow through the dryer and recording the humidity. However, a dew-point meter won’t tell you how much moisture is present in the resin that is drying, which can cause problem for molders that assume that if the air around the resin is dry, then the resin itself is dry.

Why the Industry Relies on Dew-Point Measurement

The widespread use of dew-point meters in the plastic molding sector is due to their low cost, wide availability, and they can provide a quick and simple reference for the operating status of the dryer. They often come pre-installed in resin dryers, with newer generation models being able to make changes to the dryer: automatically switching valves activating subsystems depending on the measured dew point.

Why Dew Point Measurement Isn’t Good Enough

If you are one of those molders that feel that using a dew point value is an accurate measure of if your resin is dry, you could be setting yourself up for numerous, potentially costly, mistakes. Dew-point meters can only tell you about the humidity of the air, and not the moisture within the resin. Also, if there is a fault in the meter or the thermocouple has been damaged, then it will still read the air around your sample as dry without actually heating the air to dry the resin and accurately record the moisture in your sample. The only way to truly be sure that the moisture content of your resin is correct before it goes to the mold is to use a dedicated moisture analyzer on the samples themselves.

Dew-point monitors are great for monitoring the overall drying process, but they can’t directly measure the moisture content of the resin. If you’re working to tight deadlines with demanding clients, you don’t want to have to run a whole process again because of partially dried material. This is why the dedicated moisture analyzer is so crucial.

The moisture analyzer is a key piece of equipment that every molder should have. It can single out a malfunctioning dryer or dew point meter as well as improving dryer efficiency, resin residency time and throughput. The company has a range of moisture analyzers to help you properly monitor this crucial variable in the injection molding process.

Arizona Instrument

This information has been sourced, reviewed and adapted from materials provided by AMETEK Brookfield Arizona


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