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How the Powder Flow Analyser Operates


The Powder Flow Analyser

 

The PFA vessel in use

Stable Micro Systems Ltd. use the test frame and vertical drive system provided by a universal Texture Analyser, and add the rotational drive and software functionality to form the Powder Flow Analyser - an accurate and reliable method of measuring the flow characteristics of powders.

Powder Flow Analysers can be purchased as completely new working systems, or you can take your existing Texture Analyser and attach the Powder Flow Analyser to extend your range of testing solutions from powders to end products.

A patented helically machined rotor can be programmed to move through a powder column in different ways, depending upon the characteristic that is to be measured. Due to the unique precision profile of the rotor's blade, the sample can be physically displaced in many different ways. The Test Settings of blade path angle and tip speed determine the mode of Controlled Flow achieved within a sample column. 

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. Manufacturers can assess and avoid typical problems such as batch and source variation of ingredients, caking during storage or transportation and problems with discharging from hoppers or bins.

Once programmed, the optimised test can provide identical controlled flow conditions when completing the same test programme. Test Settings can be optimised to show the maximum differentiation between similar products, or to imitate the process or storage handling conditions, experienced by the product.

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

A typical test starts with conditioning the powder column to remove operator loading differences.

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:

Helical blade tip path

Blade action diagram

A Lifting/Aerating 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.

The use of a Compaction/Compressing 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.

The Powder Flow Analyser Controlled Flow* provides:


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.

The patented helical blade
The most important tool for 
powder flow measurement
is provided by a patented* 
precision blade.

From an engineering perspective:
The patented 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 CNC machining, it allows Stable Micro Systems to achieve very reproducible, and highly discriminating results from a reliable, simple and lost cost accessory.

Commenting on the patent, Jim Walker, technical director at Stable Micro Systems, said: "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."

Stable Micro Systems
Patented Helical Blade:

Helical blade

Non-helical blade used on other
powder measuring instruments:

Non-helical blade

*Patents granted and applied for: US 7201040 / EU 1448973 / HK 1071429 / JP 4322676 / US 6481267 / AU 774211 / JP 2000-351017 / NZ 508253

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