Process control during the production of polyoxymethylene using NIR spectroscopy

The situation

Polyoxymethylene (POM) is a plastic used for items such as gears, housing parts, coffee machines, zippers and toothbrushes. It is a very important component in the area of mechanical engineering, electrical engineering, vehicle construction, and the medical technology sector. The quality requirements for this plastic are very stringent, which is why the production must be closely monitored.


In the polyoxymethylene manufacturing process, the composition of various components must be kept within narrow limits. Methanol must be checked by means of gas chromatography together with other ingredients. To control the process within the narrow tolerance range, measurements must be taken several times a day in a laboratory.

The sample collection and laboratory measurement are not only very time consuming but also cumbersome and error-prone. In the time between sampling and measurement (about 45 minutes), the process continues without direct control, which entails considerable risks. Production of 200 to 300 tons / day requires fast and efficient control of the process to efficiently dispense ingredients, adjust concentrations, and avoid uncontrolled polymerization. If production managers or process engineers do not react quickly enough, this can cause for entire batches to be discarded or that the plant will be shut down. Both scenarios can cause losses of millions of dollars.


The solution

Because NIR spectroscopy does not require sample preparation, numerous polymer and plastic attributes for qualitative and quantitative parameters can be quickly measured inline or atline. The continuous measurement with optical immersion probes in real time enables online measurements and monitoring in the control room. Measurement results within seconds or minutes ensure accurate monitoring of concentration, pressure, temperature and pH. With this online measurement, deviations and trends are immediately seen so that the process can be controlled quickly and efficiently. To ensure the entire process even further, laboratory gas chromatographs are also used at regular intervals. A specially integrated sieve surrounding the measuring head in the river shadow prevents clogging of the measuring area of ​​the immersion submerged by solids (clots or particles) occurring in the composition.



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