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Topics Covered
Background
The Freeman FT4 Powder Flow Instrument
Shear Property Measurement
Calibrating for Powder Dynamic Flow Properties, Compressibility and Permeability
Background
Although the use of reference materials for instrument calibration is common practice for many analytical methods, the situation for powder flow testing is somewhat different. Historically, powder characterization techniques have tended to be somewhat ill-defined, subject to operator variability, and not universally applicable, reducing the relevance of a reference standard. However, over the last decade steps have been taken to address these issues and Freeman Technology has led the way in combining precision-engineered instrumentation with closely defined, automated test methods to deliver extremely high reproducibility.
The Freeman FT4 Powder Flow Instrument
The FT4 powder rheometer uses patented dynamic methodology, a fully automated shear cell and several bulk property tests, including density, compressibility and permeability, to quantify powder properties in terms of flow and processability. High reproducibility underpins the sensitivity of the instrument maximising its value for research, manufacturing and troubleshooting applications. Here the development of a reference material for in-house calibration is a logical step, since it allows users to confirm that they are consistently accessing optimal system performance.
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Shear Property Measurement
The one area of powder testing where there are already well-established calibration data is for shear property measurement. These data relate to a single reference standard, a fine, cohesive limestone with the designation CRM116 (or BCR 116), supplied by the EU Institute for Reference Materials and Measurements. This limestone has a mean particle size of around four microns and is very stable with respect to its environment. It can be tested repeatedly, within certain limits, without degradation or variation in results.
Calibrating for Powder Dynamic Flow Properties, Compressibility and Permeability
Freeman Technology has now extended the calibration data set for CRM 116 to include dynamic testing and bulk property measurement (compressibility and permeability). Test protocols and acceptable results ranges are now in place. Calibrating the performance of the FT4 is therefore simply a matter of running the automated test sequence and comparing the data generated. To assist with this process Freeman Technology provides suitably sized aliquots of the reference standard (since it is only usually available in three kilogram batches) and recommendations relating to storage and in-lab use.
The multi-faceted powder characterisation delivered by the FT4 differentiates sensitively between similar samples making the instrument a valuable tool for analysing and controlling: new formulations, batch-to-batch variability, manufacturing problems and product performance. While this sensitivity stems from the way the instrument is engineered and through its automated operating procedures, calibration provides an extra level of reassurance that optimal performance is being consistently achieved. This gives users the utmost confidence in results enabling them to fully exploit the capabilities of the instrument for maximum gain.
Table 1. Table showing dynamic FT4 calibration data for CRM116 including: Basic Flow Energy (BFE), Stability Index (SI), Flow Rate Index (FRI) and Specific Energy (SE).
| 50mm Dynamic Test |
| Test Parameter |
Maximum |
Minimum |
Typical |
| BFE (mJ) |
610 |
538 |
574 |
| SI |
1.43 |
1.08 |
1.26 |
| FRI |
2.17 |
1.94 |
2.05 |
| SE (mJ/g) |
7.57 |
7.02 |
7.29 |
Source: Freeman Technology
Author: Tim Freeman
For more information on this source, please visit Freeman Technology.