Freeman Technology Ltd

The Uniaxial Powder Tester (UPT) from Freeman Technology provides an accurate and repeatable measure of the uniaxial unconfined yield strength (uUYS) of a bulk solid – a parameter widely used to assess and rank the flowability of powders. The UPT also quantifies key fundamental powder properties including Bulk Density and Compressibility. It is a quick, reliable and easy to use device which delivers value to scientists, process engineers and QC analysts working in a diverse range of bulk solids handling industries. The UPT offers a low cost powder testing solution.

The Automated Shear Cell modules for the FT4 Powder Rheometer allow assessment of powders in terms of shear strength. Using a shear cell on the high-specification FT4 platform enables the automatic generation of accurate and reproducible shear information. This is in addition to bulk properties data and the comprehensive flowability data provided by a standard FT4 measurement (in accordance with ASTM Standard D7891).

A range of shear cell options is available to suit different sample sizes and applications:

• 85ml powder volume using 48 mm diameter shear head
• 10ml powder volume using 24 mm diameter shear head
• 1ml powder volume using 24 mm diameter shear head

Fully automated testing

Each shear cell is delivered with a library of testing programs in which the following stages are fully automated:

• The standard conditioning cycle that prepares the sample for testing
• A 'pre-shear' stage during which the powder bed is sheared to maximize the major principal stress
• A single series of tests at a particular pre-consolidation stress, which may be sufficient for powder characterization. For example, a powder may be pre-consolidated to 10 kPa and then sheared at 9, 6 and 3 kPa, with pre-consolidation to 10 kPa between each test
• More comprehensive, multi-stage testing to produce a range of yield loci corresponding to different pre-consolidation stress levels. Usually a given sample will be suitable for repeated shear testing to obtain the required set of yield loci. In this case the entire evaluation is automated.

Parameters derived from shear testing:

• Yield loci – shear strength vs normal applied stress
• Cohesion – shear strength at yield when normal stress is zero
• Internal angle of friction
• Unconfined yield strength or compression strength
• Major principal stress
• Flow function (the plot of unconfined yield stress versus major principal stress) Particular benefits of the Freeman shear cells:
• Relatively low cost – being an FT4 accessory
• Pre-conditioning of sample to obtain a homogenous powder bed
• Fully automated shear testing and data analysis
• Ability to evaluate non-consolidated powders
• 1 ml minimum sample size

The FT4 Powder Rheometer® was originally designed with one purpose in mind - to characterise the rheology, or flow properties, of powders. This remains a primary function today, but the instrument, accessories and methodologies have been continuously developed to the point where the FT4 is now considered a universal powder tester.

In addition to the patented dynamic methodology, where a powder’s resistance to flow is measured whilst the powder is in motion, the FT4 also includes a shear cell for measuring the powder’s shear strength, a wall friction kit to quantify how the powder shears against the wall of the process equipment (in accordance with ASTM Standard D7891), and also accessories for measuring bulk properties, such as density, compressibility and permeability. This range of measurement capabilities makes the FT4 a truly universal powder tester and the world’s most versatile instrument for measuring and understanding powder behaviour.

FT4 Powder Rheometers are installed around the world in a diverse range of industries including chemical, pharmaceutical, additive manufacturing, toners, foods, powder coatings, metals, ceramics, cosmetics and many others. They deliver data that maximise process and product understanding, accelerating R&D and formulation towards successful commercialisation, and supporting the long term optimisation of powder processes.

The FT4 is supplied with a variety of accessory kits, including the Aeration Control Unit, which allows fine control of air flow through powders under test to evaluate fluidisation behaviour. The bulk properties of powders are affected by the presence of entrained air which fills the spaces between particles. The removal or addition of this air can radically change the flow properties of a powder - often by a factor of 100 or even 1000. When aerated, the contact between particles is reduced and less energy is required to cause flow. For some powders, complete separation of individual particles results in fluidisation when the powder behaves as a fluid. This reduction of flow energy is described by the Aeration Ratio (AR), which can be measured automatically using the Aeration Control Unit on the instrument.

The Aeration Control Unit is under the direct control of the FT4's control system allowing the following types of automated testing, with no operator involvement:

• Aeration or fluidisation assessments to determine response to increasing levels of aeration - up to fluisation velocities where appropriate
• De-aeration testing to determine how readily a given powder releases entrained air following aeration
• Permeability profiles derived from measurements of pressure drop across a powder bed at varying levels of consolidation stresses.

With an operating range down to a velocity of 0.02mm/s, this Unit also delivers the high degree of control at very low rates that is essential for characterising powders sensitive to the addition of a very small quality of air.

A series of educational guides are available from Freeman Technology on powder characterisation for industrial applications. They provide a valuable foundation for those with little prior knowledge of powders, as well as being a useful resource for anyone looking to expand their understanding of the factors relevant to product development and processing performance.

Understanding powder behaviour is an essential precursor to efficient processing. ‘An Introduction to Powders’, the first in the series, focuses on how the three components of powder – the particles, surrounding air and any moisture present – interact to define powder behaviour, and provides answers to the most frequently encountered powder processing problems throughout industry. The guide goes on to explore the importance of powder flowability across a range of industrial processes, explaining the significance of operational conditions in the context of powder processing.

Once the fundamentals of powder behaviour are understood it is beneficial to review the strengths and limitations of the different types of powder testing techniques available. ‘Choosing a Powder Tester’ addresses important questions facing powder processors looking to invest in powder testing instrumentation. These include: what powder testing techniques are available, what should powder handlers look for in a testing method and what features make powders more or less suitable for industrial applications?

It is also important to assess the potential economic benefits a powder tester can deliver. ‘The Value of Powder Testing’ explores key questions associated with such an investment. These include: what makes powder test data valuable, how does powder testing deliver an economic return, and, how can I identify ways in which powder testing might deliver value for a specific process or R&D laboratory? The guide also provides example studies to demonstrate how to estimate potential gains.

Each guide is written in a straightforward easy to understand style and draws on 15 years’ of experience in powder characterisation.

Lenterra flow measurement systems provide an in-line, real-time analytical tool  for enhancing process understanding, and improving manufacturing efficiency and quality in number of industries. The flagship products, the Drag Force Flow (DFF) and the RealShear™ Wall Shear Stress (WSS) sensors, ue fibre optic technology to enable users to obtain important information without interrupting the manufacturing process.

The Drag Force Flow (DFF) sensor is mounted on a stationary base, and contains two optical strain guages, made up of Fiber Bragg Gratings, which are connected to an Optical Interrogator via a fibre optic cable. When immersed, the DFF sensor bends under the force of the flow and quantifies the drag force, allowing the user to determine in-process properties of materials.

The RealShear™ Wall Shear Stress (WSS) mounts flush with a pipe or vessel wall enabling real-time direct measurement of wall shear stress, flow rate and viscosity during flow or mixing without the need to disrupt the process, allowing users to make ‘on-the-fly’ process adjustments. The RealShear WSS employs a floating element attached to a cantilever beam that deflects in response to shear force which transmits to a Fiber Bragg Grating. The shift in wavelength is proportional to shear stress.

The data collected allows for optimised cycle times, reduced costs, and improved product quality and consistency.