A VAST RANGE
OF POWDERS - A WIDE RANGE OF PARAMETERS TO MEASURE...
Video Clip showing the
of Conditioning Cycles.
To remove any user loading
variation and to normalise the powder column after filling and prior
to testing, test protocols include a conditioning process. Data is
not captured during this process but this ensures that each sample
starts after the same influence and hence provides outstanding reproducibility.
- when your products stick together and stand up for themselves.
Cohesiveness is the tendency for
particles of powder to cling together and agglomerate (form larger
clusters of particles). The PFA measures this cohesion
characteristic by moving the blade in such a way as to lift the
powder. A more cohesive powder will cling to itself and to the
blade therefore reducing the force exerted on the base of the
vessel. This is shown in the plotted data by a large negative force.
Cohesion Test works
The powder blade moves down
through the powder column using a "cutting" action to
minimise compaction. The upward part of the cycle then lifts the
powder and the force of the powder on the vessel base is recorded.
- Cohesion Index
The cohesion index is a useful
quality control measure as changes in powder specification
(formulation, particle size distribution, particle shape etc.),
storage conditions and test environment can all influence the
tendency of a powder to agglomerate. A change in the cohesive
properties of a powder may have an important affect on production
processes such as die filling that could impair production efficiency
and product quality.
This quick analysis allows
repeatable quantification of the cohesiveness of a bulk
solid. Test results can be used to compare the sample being
tested with previously analysed product, to assess if it is more
cohesive or more free flowing.
- when you need it...
- when you don't want it...
look at the Cake Height
will indicate caking
and speed of
of a powder.
test on eyeshadow
a Texture Analyser.
Caking is the tendency of a powder
to form large agglomerates during storage and transportation. The
tendency of a powder to cake is closely related to its cohesiveness
and generally a powder that is cohesive will also form a cake during
the caking test. The strength of the cake will depend on a
number of factors such as packing efficiency, particle to particle
interactions and moisture content i.e. humidity. Understanding
the caking properties of a powder are important as most powders will
be stored in hoppers or silos, or transported at some point in the
production process. A powder that cakes easily and forms a
strong cake may not discharge easily from a silo when
required. However the caking process can be intentional and a
desired result such as in a granulation process or when required to
form a 'cake'.
Caking Test works
The blade levels the top of the
powder column and measures its height. The blade then moves
down through the column and compacts the powder to a pre-defined
force (usually 750g). When it reaches this force it measures the
height of the cake and slices up through the powder. This
compaction cycle is repeated four more times. The 5th time the
target force is reached the blade slices through the compacted cake
of powder formed at the bottom of the vessel.
Caking strength can be a highly
desirable property of a finished product and can be assessed easily
using the Texture Analyser.
The tendency of a powder to cake
can give important data about the properties of the powder after
storage and transportation. The formation of strong, high height
cakes may lead to issues with discharge of powders from storage
hoppers or silos. Product settlement and cake formation may also
impact on customer perception of products, as it may appear that the
product is less voluminous than stated. Proper understanding of
the caking characteristics of powder may assist manufacturers in
minimising issues after storage or transportation.
Speed Flow Dependence - when decreasing/increasing sample throughput
creates a problem.
FLOW SPEED DEPENDENCE
of Powder Flow Speed Dependence
Powder flow properties may change
with increasing or decreasing flow speeds. For example a powder
may become more resistant to flow as it is forced to flow faster or
indeed it may become more free flowing as the flow speed increases.
This issue can lead to under/filling, for example, as a result of
process changes to meet increase output demand. The PFA measures
this characteristic by assessing the work needed to move the blade
though the powder at increasing speeds. An evaluation of the
flow stability of the powder is also made by comparing the work
needed to move the blade though the powder at the start of the test
compared to the work required to move the powder at the same speed at
the end of the test.
How the PFSD
The powder flow speed dependency
(PFSD) test provides 5 sets of 2 cycles at increasing speeds. The
downward parts of the cycles compact the powder and the upward
stroke of the cycle uses a lifting action.
The test measures resistance of a
powder sample as controlled flow is imposed at different
speeds. Powders that flow freely will transfer very little
resistance through the powder column in either a downward or an
upward direction. Conversely, poorly flowing powders exhibit
substantial amounts of force in either direction.
of the Data
PFSD gives important information
about the speed flow properties of a powder and this can be of
interest in a production environment. It may be necessary to
convey a powder through plant at a certain speed to meet production
volume requirements. The PFSD test can assess the suitability of
a powder for different conveying speeds or test a powder for
variations in speed flow properties from batch to batch. PFSD
can also give important data on the attrition characteristics of the powder.
COLLATE YOUR RESULTS
Once your range of tests are
performed, the collection of parameters you have obtained can be
collated into a 'fingerprint' of each sample.
Controlled Flow technology
enables the sample to be physically displaced in many different ways.
The Test Settings of blade path angle and blade tip speed determine
the mode of Controlled Flow achieved within a sample column. Once
programmed, the Test Settings can be exactly repeated test after test.
The Test Settings can be optimised
to show the maximum differentiation between similar products, or to
imitate the process or storage handling conditions, experienced by
Precision manufactured Rotor
Blades (optimised patent applied design), and test vessels ensure
that Powder Flow Analysers always provide identical controlled flow
conditions when completing the same test programme.
Nothing surprises us more than
what experienced users want to investigate. That is why for Research
& Development needs we allow the flexibility for you to not only
customise the test projects that we provide but also for you to
completely create your own test protocols to test in a different way
or analyse your data to collect additional parameters.
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