Material CharacterizationNovember 22, 2021 2021-12-17 10:05
Various materials can be tested using a DFF sensor installed in a small mixer, with a probe permanently installed in a specific position, typically just above the blade, as seen in the figure. After a particular amount of powder is added to the mixer, flow force measurements are conducted at a rate of 500 per second. The mixer speed, the volumetric amount of powder, and the probe position are kept unchanged for a standard test. The material is characterized with two principal metrics of LIR technology: the mean force pulse magnitude (MFPM) that is the measure of flow force, and the Powder Consistency Factor (PCF) that characterizes the uniformity or cohesiveness of the powder (please refer to White Paper 13 for definition of MFPM and PCF). The two metrics and their uncertainties are obtained by averaging their values over the pre-selected measurement time, which is typically 10 to 30 seconds (see also White Paper 15).
Comparing material characterization of dry powders using an off-line LIR and FT-4 Powder Rheometer®
In a case study where an off-line LIR test station and FT4 Powder Rheometer® were used to concurrently measure characteristics of commercially available sugar powders, both the off-line LIR based on DFF sensor and FT4 Powder Rheometer can identify differences between a variety of different sugar powders. The comparable trends observed between the FT-4 basic flowability energy (BFE) and LIR’s MFPM data demonstrated how both of these techniques can be used to quantify the material’s resistance to forced, dynamic flow. The LIR, however, demonstrated superior sensitivity being able to resolve sugars with comparable flowability properties, and LIR tests produced better repeatability than standard FT-4 tests. The LIR tests also reported the Powder Consistency Factor (PCF), which is a measure of flow uniformity or cohesiveness for each sugar. The results were in good agreement with visual observation. Please see White Papers 15 and 16, as well as the article in the Powder and Bulk Solids magazine.
Characterization of grain samples
Force Pulse Magnitude (FPM), an output of the LIR measurement (see White Paper 3 for the description of the metric), is an effective characteristic that reliably differentiates powders with different masses/sizes of the particles. For example, in a mixing study with four grain samples, where each samples was mixed in a laboratory mixer for 120 seconds, the real time FPM data demonstrate highly repeatable levels which are clearly different between the four grains.
Measuring blends of small and large particles
In another example, two grain samples with small particles (SP) and large particles (LP), respectively, were blended as binary mixtures and tested in a similar conditions. Again, these trials produced highly repeatable data and evidence of blend uniformity, as seen on the plot. There also a positive non-linear trend between the percentage of large particles and the magnitude of the FPM signal.
Please see details of these studies in a publication of Powder and Bulk Engineering.