A typical powder flow analysis test
A typical test starts with conditioning the powder column to remove operator loading differences.
During the test, axial force, time and distance are measured by a sensitive transducer and data is displayed and analysed in real time by Exponent software. Sample results can be ranked and compared to assess the impact of external conditions including humidity and moisture content, surface properties, electrostatic charge and particle or granule size, shape and distribution.
The Powder Flow Analyser is supplied with library tests, so operators can start testing quickly and conveniently after straightforward installation and calibration. Users can, however, fully program the instrument to carry out slicing, shearing, compressing, compacting and aerating cycles in any combination.
Controlled Flow Displacement
Depending upon the programmed rotation of the blade in terms of path angle, blade direction and tip speed the powder column can be displaced in a number of different ways to suit the process and properties to be measured.
Lifting/Aerating – this action allows the powder column to be conditioned, thereby giving independence from sample loading variations. It can also effectively measure particle cohesion and flow behaviour after compaction has been employed.
Compaction/Compressing – this method allows the measure of flow properties with changing compaction force and flow speed and provides an investigation of caking potential.
Slicing/Shearing through a powder column allows movement through the sample with minimum disturbance when required by moving at the same helical path angle as the blade profile. This may be desirable when required to move downwards through the column with minimum disturbance and therefore effect on the sample in order to measure a characteristic on the upward cycle of the test or when looking to 'cut' through a column in order to measure the strength of a cake that has been formed after compaction/consolidation to a specified stress in order to imitate storage conditions.
Controlled Flow Measurement
The Powder Flow Analyser Controlled Flow Measurement technology offers you the ability to physically displace the powder in a controlled manner that can be optimised to measure the differences between samples, or can be adjusted to be complementary to your process conditions.
The force resulting from the displacement is accurately measured and used to characterise and rank the sample.
From an engineering perspective: The precision blade is a true helix and can be mathematically described, unlike the blades fitted to other powder measuring devices on the market. The helical blade naturally cuts through the column of powder being tested and negates the need for complex torque measuring systems. Repeatably manufactured by Selective Laser Sintering and polished to a specific surface smoothness, it allows Stable Micro Systems to achieve very reproducible, and highly discriminating results.
Commenting on the blade, Jim Walker, Founder and Director at Stable Micro Systems, says: "The design of the blade is the single most important factor in achieving repeatable powder flow measurements. The non-helical blade used on other instruments is bent from a flat sheet and presents a large flat central area to the powder being tested. It effectively compresses a column of powder beneath the blade during its travel path through the sample. As a consequence, any axial force readings being taken are corrupted and these instruments are forced to rely on torque measurements because of the inadequacies of blade design."