New System Measures Moisture In Pellets During Processing

Self-calibrating system measures pellet moisture in real time and can adjust dryer controls accordingly.

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After four years in development, a new system for measuring moisture directly within plastic pellets continuously as they exit the drying hopper was introduced commercially at the Fakuma 2015 show in Germany in October. The Moisture Meter from Moretto S.p.A. in Italy (U.S. office in Columbus, Ohio) uses a specific frequency of electromagnetic waves to measure moisture content in a range of 15 to 500 ppm with what’s said to be ±1.5% accuracy (minimum ±5 ppm).

In the measuring chamber, an emitter and receiver take measurements four times a second. Data are exported via RS485, USB, or Ethernet link. These real-time moisture measurements can be used to certify production conditions for especially quality-conscious industries like medical and automotive, where Moretto sees the greatest demand for the system.

The system can be configured in two ways: The most basic can be used with any drying system, not just Moretto’s. It places the meter just under the drying hopper. If used with a Moretto system, the moisture measurements can provide closed-loop feedback to the dryer controls, which can adjust conditions to ensure materials are properly dried without wasting time and energy for overdrying.

A more elaborate version utilizes two Moisture Meters—a “crown” unit at the top of the drying hopper to measure initial moisture before drying, and one at the outlet of the hopper to measure final moisture level after drying. This approach is designed for use with Moretto’s top-of-the-line Eureka drying system, which is called Eureka Plus when it includes the Moisture Meter. The user enters the resin type and desired moisture level into the touchscreen interface, and data from the crown unit are used by the system to set up the drying process automatically. Moretto says the Moisture Meter is self-calibrating and is unaffected by colorants or additives.

At least 24 Eureka Plus systems with Moisture Meter have been installed and are being used in production—mainly for PET packaging.

The only other commercial real-time, online drying system is the Moisture Master from Novatec, Inc., Baltimore, which uses electrical capacitance measurement (see Mar. ’12 Close Up). Novatec says multiple units are being used in the medical industry.

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