June 15, 2000 Quiz Question

Process Fingerprints

Perspective Meter:

The concept of the "process fingerprint" was outlined by Dr. Chi-Kai Shih of DuPont at the recent International Polymer Processing Society Meeting in Shanghai [PPS-16 Proceedings, p. 348 (2000)]. For any polymer processing operation, he listed four basic requirements which should ideally be satisfied by a process measurement in order to consider it a process fingerprint:
  • The measurement is in-line or on-line (not off-line) and thus provides real-time data.
  • The measurement is sensitive to all key process and material input variables for the process.
  • The key elements of product quality are a function of the measurement.
  • The results of the measurement are linked to the fundamentals of the process, such as polymer physics, chemistry, rheology, morphology, etc.

Dr. Shih provided an example of a process fingerprint for batch intensive mixing. He proposed that the mixing torque as a function of time was an appropriate fingerprint for this process. Although not ideal, this measurement generally satisfies the requirements listed above.

Many laboratory and some manufacturing batch intensive mixers are fitted with a torque transducer or power gauge to measure the mixing torque (or power) for the process.

The mixing torque is sensitive to many of the key process parameters (rotor speed, rotor geometry, temperature, component addition protocol, etc.) as well as many of the key material variables (composition, component concentrations, component rheologies, etc.)

For particular material systems, there are strong relationships between the torque profile and and product quality. This is probably the weakest link in this example, and in general the most difficult requirement to satisfy. One of the problems is that performance characteristics of the resulting material are not necessarily uniquely determined by the torque profile.

The torque profile is linked to fundamentals such as morphological changes, chemical reactions, etc.

Consider instead the reaction injection molding process for a polyurethane. Propose a "process fingerprint" for this process.
Explain how your proposed measurement does (or doesn't) satisfy the four points listed above.

Is that your final answer?
Check your work before looking at the solutions.

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