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Page 39 of 105
7.2.
Preparing Granular and Powdery Samples
The MAX
®
4000 can be used to test a wide range of products from finely ground,
low-moisture powders to high-moisture slurries.
For best results, the sample should
be of a uniform particle size distributed evenly over the sample pan.
If sample
material is collected into a jar or sampling bag, shake the jar or bag to produce a more
thorough mixture. Note, however, if there is a large variation in particle size, shaking will
tend to distribute larger particles to the top. Liquid samples should also be mixed or
shaken to ensure a more homogeneous mixture. Large chunk samples, such as charcoal
or cookies, should be crushed or ground to smaller pieces approximately 1/4" or less in
diameter.
For best results, take care not to over-grind the sample, causing it to
heat up and causing moisture loss.
Some samples, such as dried vegetables, may also need to be ground. The smaller
pieces will easily release moisture during testing, leading to shorter test times and more
repeatable results. Solid, granular sample material should be shaken onto the pan from
a spoon; shaking sample directly from the collection jar will usually deposit only the larger
granules, not a representative mixture. Samples should be evenly distributed over the
sample pan.
7.3.
Preparing and Testing Liquid Samples
Some liquid samples will dry slowly, even at high temperatures. Drops or puddles may
form on the pan and dry slowly as the sample concentrates. A skin may form which limits
evaporation from the interior. Long test times (greater than 25 minutes) and low percent
moisture (or high percent solids values) suggest incomplete drying. Pre-dried glass-fiber
filter paper (AZI P/N: 990-0003) and flat-bottomed pans (AZI P/N: 990-0010) are
recommended to successfully test samples such as these. Call AZI consumable parts
sales for more information.
The glass-fiber filter paper serves as a support for the liquid sample. The sample is
absorbed through the paper for more even and rapid evaporation to reduce test times.
Waffle-bottom sample pans are
not
recommended for use with filter paper; the liquid
sample may soak through the filter paper and collect in puddles in the pan's depressions.
Liquid samples or slurries can be spooned or poured onto the sample pan; however, a
pipette or sampling straw will collect a uniform mixture of the sample. Samples should be
evenly distributed over the sample pan.
Occasionally, some samples cannot be absorbed into the filter paper. At the end of the
test, examination of the sample pan shows the sample sitting high above the filter paper
with a thick crust. The crust may be singed from the heat or even show bubbling where
vapor has been trapped beneath the surface. Percent solids results will be high or
percent moisture results will be low. Samples such as these are treated differently: After
the sample has been added to the sample pan, remove the pan from the test chamber
and place it onto a flat surface. Grasp part of the filter paper (tweezers are suggested)
and flip it over so that the sample lies between the pan and the paper. Squash the sample
with a flat-bottom glass or jar to a uniform layer. Return the sample pan to the test
chamber and close the lid. The upper filter paper surface absorbs moisture from the
sample and minimizes bubbling and spattering to produce more accurate, reproducible
results.
