Fundamental Information on
Stumbling on Solutions Using A Trial and
A Knowledge Based Approach
Drivers for Change
Introduction of New
products or Formulations to Address Performance Issues
Benefit of Experience
The FT4 Powder Rheometer from Freeman
Powder Properties that can be Determined by
Other Factors that can be Assessed
Using a Rheometer
Where Knowledge of Powder Properties
Can be Useful
Effective Powder Management
Do you completely understand all aspects of your powder process, formulating,
specifying and manufacturing product in an optimal manner on the basis of
underlying knowledge? Or do you, like many other producers, rely heavily on the
experience of formulators, supervisors and operators running sub-optimally but
well enough to get by? Here we discuss how your experience can be fully
exploited by correlating process observations with measurable powder parameters.
This approach brings improved understanding, which in turn leads to cost
reductions and a lowering of the risks associated with change.
Fundamental Information on Powder Behaviour
For powder processors, fundamental information has always been elusive
because of the complexities of powder behavior. How to determine the combined
effects of attrition, segregation, moisture adsorption, consolidation during
storage and many other variables amounts to a serious challenge. Consequently
the development of new formulations, process design and process operation, have
all tended to rely heavily on previous experience.
Stumbling on Solutions Using A Trial and Error
A trial and error approach to problem-solving is common and although
time-consuming can be successful. Different solutions are assessed; one proves
optimal and processing or formulation development continues. The limitation of
such an approach is that the reasons for the success, or indeed the original
problem, often remain unknown. A ‘fix’ has been developed but understanding has
not necessarily increased.
The experience base that develops from working in this way is highly valuable
but can only improve operation within a well-mapped window, unless more widely
applicable process knowledge can be extracted from it. This is possible if
aspects of experience are correlated with specific powder characteristics.
Understanding which aspects of a powder make it behave, in a certain way,
provides the underlying knowledge necessary to make changes away from the
established operating regime. We can extrapolate outside the box, rather than
simply interpolating within it.
For example, tests have shown that the propensity of a material to flood from
a hopper can be predicted from dynamic studies of basic flow energy and aeration
behavior. In an analogous way consolidation behavior during storage can be
assessed through systematic consolidation studies. Many such correlations exist;
the key is identifying those of relevance for a particular process or product.
A Knowledge Based Approach
Quantifying and understanding experience is a valuable way of exploiting the
experience base within a company. It is also an excellent starting point for a
shift from experienced-based to knowledge-based operation. This paper outlines
how to achieve this goal, beginning with an examination of the drivers for
Drivers for Change
Continuous improvement is now a ubiquitous feature of manufacturing life, the
alternative being a drift towards uncompetitiveness; change is inevitable. There
are two key ways in which processors can improve their competitive position;
they can reduce variable costs or improve product performance. Variable cost
reduction goals may include:
- increasing throughput – by increasing reliability/reducing the frequency of
stoppages or by processing at a faster rate
- reducing waste – by, for example, ensuring that more of the product meets
the required specification without re-work
- switching to alternative, lower cost feed materials
- automating process control
In order to pursue these goals, processors need to understand what changes to
make and/or the impact of these changes on the process and product. For example,
effective troubleshooting requires identification of the root cause of the
problem; adoption of an alternative feed demands careful assessment of the
potential impact on all aspects of the process; automation requires the
identification of critical controlling parameters and an understanding of how
these influence process behavior and product quality.
Introduction of New products or Formulations to Address
Companies may introduce new products or formulations to address specific
performance issues. Potentially this is even more demanding, particularly if it
involves the introduction of a new powder product. In this case the following
questions need to be answered:
- Will the new formulation process well in the existing equipment?
- If the existing equipment is unsuitable can it be modified or is a new unit
- Are the existing storage facilities suitable for the new product? Is it
particularly sensitive to pressure, temperature, humidity, vibration etc?
- Will the new product give the customer the required performance? Will it be
adversely affected by storage and handling procedures at the customer site? Will
it process well in their equipment?
The aim is often to develop a blend that will process well in existing or
identical equipment. Successfully introducing a new material with the minimum of
pre-production trials has enormous benefits, reducing both time-to-market and
The Benefit of Experience
Companies that process powders have, typically through a combination of
knowledge, experimentation, and trial and error, learned how to manufacture
products that meet the required specification.
Gathering this experience will have incurred significant, unquantified costs.
Where a range of products is manufactured, some powders may be particularly
tricky to handle, requiring constant monitoring or the attention of an expert
operator. Others may process easily, even at high rates, giving excellent
product quality. Relatively frequent unplanned stoppages may be viewed as an
inevitable feature of day-to-day operation.
Historically, sensitive and reliable powder characterisation methods have not
been available and reliance on subjective human assessment therefore remains
widespread. It is unusual to find QC specifications for flow properties of a
material, or even bulk properties. This is despite the fact that tests have
shown that dynamic measurements can differentiate between samples of the same
specification, identifying those that will process poorly [See ref].
Batch-to-batch variability, of either feed or product, is also common. This
can give rise to a wide range of processing problems – bridging in a hopper,
blockage in a feeder, excessive aeration, or variability in product quality,
dose weight or composition. The problems may be clearly linked with a change in
material, but the underlying reasons for the poor performance are not
understood. This is primarily because so many factors can be responsible for a
change in powder behavior. Moisture content, fines, particle size, shape and
texture, air entrainment, adhesion and a wide range of other parameters are all
On the basis of process experience it is possible to classify materials using
‘Processability Rankings (PR)’. For example, a PR of 2 may describe a
trouble-free powder that processes consistently and easily at high rates. A PR
of 9, on the other hand, may indicate a difficult powder that needs constant
monitoring and processes to a variable product. This is a useful way of starting
to quantify experience.
Valuable information can also be generated by:
- recording the symptoms and circumstances of any unplanned shutdowns or lost
- correlating performance with supplier, if more than one is used
- correlating in-house batch variability with customer feedback
- comparing powder performance on parallel production lines
- identifying periods when the plant performs poorly; for example is
performance worse on a Monday morning after a weekend shutdown?
Investigating and analyzing experience in these ways highlights powders that
are optimal in terms of processing and product performance. Relevant powder
characterization gives insight into why these powders behave as they do.
Relevant Powder Characterization
Powders are complex materials and can be difficult to characterize well.
There are many measurement techniques, all of which give some insight into
powder behavior. Historically, however, many have been unreliable and overly
Options for process relevant characterization improved greatly with the
development of powder rheometers and dynamic test methodologies. More recently
these instruments have evolved into fully automated universal powder testers
with a range of complementary measurement methods, making them an ideal tool for
powder processors. It is now relatively easy to measure powder properties that
correlate directly with processing performance.
The FT4 Powder Rheometer from Freeman Technology
Rheometer from Freeman Technology provides automated test programs for the
measurement of shear, bulk and dynamic properties. Samples may be analyzed when
consolidated, conditioned, aerated or even fluidized, allowing the impact of
air, a critically important variable, to be fully explored. Conditioning, -
gentle agitation of the powder prior to measurement - ensures that samples are
always measured in the same baseline state, giving the instrument exceptional
reproducibility and repeatability.
The Freeman FT4 Power Rheometer
Powder Properties that can be Determined by Powder
Using instruments such as the FT4 Powder
Rheometer from Freeman Technology, databases of powder properties can be
established. Measured data may include:
- Flowability parameters - Basic Flow Energy (BFE), Specific Energy (SE) etc
- Shear properties – yield locus, unconfined yield stress (compression
strength), cohesion, internal angle of friction
- Bulk properties – bulk density, compressibility , permeability
Other Factors that can be Assessed Using a Rheometer
In addition, many other factors (de-aeration behavior,
de-blending/segregation, caking, effect of moisture and attrition) may be
investigated to generate the most complete picture of the powder. The resulting
database provides the information for rationalizing process experience. Close
correlation of powder properties and processing experience provides the key to
confident product and process development.
Where Knowledge of Powder Properties Can be Useful
For example, consider a filling process in which blend A processes well at
high rates (PR=2) while blend B is problematic (PR=6). One goal may be to
improve the processability of B by slightly changing the blend. Alternatively,
completely new formulations may be in development, the aim being to manufacture
a third product on the same line. In either case it would be highly advantageous
to understand the properties of A that give it such excellent performance.
By measuring an array of powder properties for blends A and B it is possible
to determine differences between the two samples, thereby identifying parameters
that need to be controlled to achieve the required performance. Intuitively, for
filling operations, it is likely that variability in flow energy, de-aeration,
compressibility and/or shear strength characteristics will provide the key.
Identifying which of these are critical gives a blueprint for the type of powder
that will process well on the line; other powders meeting this specification are
also likely to be a good match.
Effective Powder Management
By correlating experience with powder properties, processors can operate in a
much more effective way. It becomes possible to:
- Establish effective QC criteria for both feed and product
- Understand and address the causes of batch-to-batch variability
- Assess in a process-relevant way, differences in alternative suppliers’
- Define the characteristics of materials that will process well on a given
- More effectively match powder and processing equipment
- Reduce the risk associated with introducing new formulations
- Improve the performance of marginal formulations.
Decisions and actions are based on understanding and knowledge gained from
quantifying experience and therefore have a greater likelihood of success.
Powders are complex, and characterization methods have historically been
unreliable. Manufacturers handling powders have therefore learned to rely
heavily on human experience and subjective assessment. This has created a wealth
of valuable knowledge that enables operation within a defined window. The
drivers for process and product improvement are however strong, making change
inevitable. Extracting information from past experience, in a form that can be
used to move forward, is the key to confident renewal.
With state-of-the-art powder testers such as the FT4 Powder
Rheometer from Freeman Technology, shear, bulk and dynamic powder properties
can be measured easily. Powders can be characterized in a consolidated,
conditioned, aerated or even fluidized state. These instruments deliver the
fullest insight into powder behavior allowing identification of the key
parameters influencing process performance.
This is not a first principles analysis. Defining powder flow properties in
terms of particle size, shape, hardness and many other variables remains beyond
our current capabilities. It does, however, allow formulators and manufacturers
to rationalise behavior in terms of parameters that can be measured
reproducibly, and to differentiate between alternative materials in a
process-relevant way. This is a significant step forward towards optimised
operation that is based on product and process knowledge.
Freeman, R F (2007). Measuring the flow properties of consolidated,
conditioned and aerated powders : a comparative study using a powder rheometer.
Powder Technology 174, 25-33
Source: Freeman technology
For more information on this source, visit Freeman