From a processing perspective - productivity and quality are universal objectives. When powders are involved their characteristics can greatly affect the efficiency of the process. Understanding powder flow properties is therefore very important. Examples of questions that can arise in everyday processing are:
Why is this batch a problem?
Will this alternative source of material be ok?
Will this material transport ok by road?
Can flowability be improved by using a flow additive?
Is this new powder suitable for this (existing) process line?
How readily will this material release entrained air?
Will this powder dose satisfactorily?
Understanding powder behaviour is also important in other contexts. For example optimising formulations to achieve favourable processing characteristics and establishing QC criteria so that flow performance can be verified at all stages of manufacturing.
Working with industry and providing answers to questions like the above using the FT4 Powder Rheometer is our business. If this is of interest to you – please read on.
Powder processing is challenging and has relied extensively on very experienced operators to overcome problems and ensure that production targets are met. Some formulations will be easy to process and others will be problematic. Batch to batch variability will be commonplace with certain products and ways and means of resolving these issues may have evolved from long experience.
Resolving the processing issue however, allows production to continue but usually does not provide an understanding of why the problem occurred – what was the underlying cause? Inevitably it will recur and process efficiency will be compromised on an ongoing basis.
Our perspective is that learning from this experience and understanding the root causes of processing problems is now possible. This can be done by measuring the powder characteristics of powders that flow well and not so well. This applies to different formulations and to batches of material. Hence we can determine the optimum powder characteristics for each piece of plant whether a hopper or a tablet press. The compatibility of a new formulation with each item of plant can then be determined with confidence.
Powders are blends of solids, liquids and gases, usually air, and their flow properties or rheology, may be affected by perhaps 100 or more factors. These include particle characteristics such as size range and shape, environmental factors such as air content, temperature and vibration, and chemical interactions such as those which produce caking.
Flowability depends on all these factors and describes how easily a powder will flow. Broadly powders are either cohesive or non-cohesive. A free flowing powder is non-cohesive – particles are separate and when unconfined are able to move individually – for example dry sand when spilled. However, such powders may easily aerate and even fluidise so that control within the process becomes difficult or even hazardous. ‘Good’ and ‘bad’ are relative terms in powder processing.
Cohesive powders are not free flowing. Their particles attract each other and more energy is required to make them shear or flow. The agglomerates formed trap air which makes the powder spongy and compressible. However, they are dust free, not prone to segregation, unlikely to suffer attrition and will not fluidise, all of which may be advantageous. In a confined, slightly pressurised environment they are better able to flow round corners into the recesses of moulds for example, unlike free flowing coarse materials. However, cohesive powders are sticky and reluctant to flow from hoppers or into recesses on dosing machines. Generally they are more problematic during processing.
To summarise, quality and productivity depend on powder and plant characteristics being matched and this in turn, requires a comprehensive understanding of powder behaviour.
The FT4 has become a truly universal powder tester offering dynamic, shear and bulk properties measurements in one instrument. The patented dynamic measurement of flowability pioneered by Freeman has been complemented by the development of a series of high-precision accessories.
During dynamic testing the rotational and axial forces acting on a patented helical blade are measured as it passes through a sample. Basic flow energy is determined from these data and is regarded as a measure of the rheology or resistance to flow of the powder. A unique conditioning step eliminates the influence of processing history so that extremely reproducible baseline measurements are generated for aerated, conditioned and consolidated samples.
Combining dynamic measurement with bulk properties and shear properties measurements allows the characterisation of powders in a range of complementary ways. For example, bulk density, permeability and compressibility can be determined easily and a family of shear cell accessories deliver accurate, conventional shear stress data for samples down to 1ml.
All testing is automated and utilises the unique conditioning methodology so that exceptional levels of reproducibility of data are attainable. A library of test programs are provided and the test data is stored securely in binary file format.
Study the flowability of conditioned, consolidated and aerated powders
Measure bulk density, permeability and compressibility
Generate high precision shear strength data
Quantify the impact on flowability of many variables such as moisture, segregation and attrition
Optimise formulations
Construct a database of powder characteristics for all your powders
Predict processability
Analyse abnormal process behaviour
Establish QC criteria for raw materials, intermediates and final product
Detemine optimum powder characteristics for each item of plant
Most powder processing companies have vast experience of which powder types are trouble free and which are most problematic during storage, handling and processing. Each material may be given a processability ranking and this can be correlated with the measured flow properties. Many benefits result from this – batch variability may be investigated methodically and new formulations may be assessed for compatibility with the available processing plant.
In summary matching powder properties and plant is the key to obtaining high productivity and good product quality.
Powders are our business. We sell a precision instrument that we are intensely proud of, but we’re pragmatists who understand that, for you, it’s all about solving your day-to-day processing problems.
With new customers we look at any process-related issues and normally would measure some samples to tell you what we can discover about your powder. We report on the results and explain how they relate to the way in which the material might behave during processing.
When you’re convinced and purchase an FT4, we follow through with exemplary service during installation, commissioning and training. Regular follow-up and updates ensure that you continue to get the best out of your instrument throughout its lifetime.
Why not start the ball rolling and put us to the test? See what we can tell you about your powder.
Our Experience in your industry
Flow Additive Studies How fumed silica flow additive can transform the flow properties of starch
Sampling Guidelines for sampling powders to obtain representative samples for powder testing
The FT4 Powder Rheometer was developed to measure the flowability and processability aspects of powders.
The main benefits are to measure and match the characteristics of both materials and processing machinery, so that the consistency and efficiency of powder processing can be improved.
