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13.3 USING THE INDUSTRIAL GRINDER
This is used to grind pre-forms, bottle necks, polymer plaques, pieces of polymer extrudates and thick
sheet samples to approx 8mm chips.
One complete pre-form is usually sufficient for chipping and drying.
If only the bottle necks are to be used, then several bottle necks (usually about three) are required.
Cut the bottle necks from the bottles as close to the threaded portion as possible using tin snips or a
small clean hacksaw.
Polymer plaques, thick sheet samples or chunks of polymer extrudate should be cut using tin snips or
a small clean hacksaw until they are small enough to fit into the pulverisette sample inlet port.
Using tongs, place the selected sample or samples in a Dewar Flask containing sufficient liquid
nitrogen to immerse the sample completely.
WARNING: ALWAYS WEAR SAFETY GLASSES AND HEAT RESISTANT GLOVES
WHEN HANDLING LIQUID NITROGEN WHICH IS AT -196ºC
Leave the samples immersed in the liquid nitrogen until the liquid nitrogen has ceased to boil,
showing that the sample has been cooled to the correct temperature.
Ensure that a clean collecting bowl is fitted to the bottom of the grinder.
Start the motor on the industrial grinder.
Carefully remove the cooled sample from the liquid nitrogen using tongs and place it in the safety
interlock sample part of the pulveriser.
Open the interlock to drop the cooled sample into the sidearm and immediately lift and lower the
plunger arm to push the sample onto the pulveriser blades.
Switch off the motor as soon as pulverisation has ceased (usually a few seconds after lowering the
plunger arm).
Wait until the rotor has stopped then unclip the receiving bowl containing the coarsely chipped
sample.
Clean the pulveriser using a jet of clean compressed air or nitrogen to remove any polymer chip
remaining on the rotor blades or coarse sieve.
Follow the procedure shown in SECTION 10 - SUPPLIED PET (POWDER) to grind the chips to a
powder then test using the PET Plus.
74 PET Plus User Manual
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