extrudate from the pre-heat period. Make the final cut-off
exactly when the time interval selected (see Table 1) is reached.
Collect and weigh the extrudate specimen. If the extrudate
specimen contains visible bubbles, discard it and begin the test
again. If the initial cut-off was initiated outside of the tolerances
of the pre-heat period or the piston position requirements,
discard the specimen and repeat the test with readjusted
piston position after the initial purge, or change the weight.
9.10 Once the extrudate is cool, weigh to the nearest 1 mg.
9.11 Multiply the weight of the extrudate by the appropriate
factor shown in Table 1 to obtain the flow rate in grams per 10
min.
NOTE 16—Some labs have found it helpful to take interim cuts of the
extrudate at uniform time intervals during the specified extrusion time
period. The individual cuts may give an indication of the presence of
bubbles which may be masked due to their size or to opacity of the sample
which will result in test error. This technique is particularly helpful in the
case of highly pigmented materials.
9.12 Purge the remainder of the sample from the bore and
follow the extrusion plastometer manufacturer’s instructions
for removing the die from the bore. Swab out the cylinder with
cotton patches and the cylinder bore cleaning tool. Thoroughly
clean the die and the piston to remove all residues (Note Note
17).
NOTE 17—The die may be cleaned by dissolving the residue in a
solvent. A better method is pyrolytic decomposition of the residue in a
nitrogen atmosphere. Place the die in a tubular combustion furnace or
other device for heating to 550 6 10°C and clean with a small nitrogen
purge through the die. This method is preferable to flame or solvent
cleaning, being faster than solvent cleaning and less detrimental to the die
than an open flame. In certain cases where materials of a given class
having similar flow characteristics are being tested consecutively, interim
die cleaning may be unnecessary. In such cases, however, the effect of
cleaning upon flow rate determination must be shown to be negligible if
this step is avoided.
9.13 In case a specimen has a flow rate at the borderline of
the ranges in Table 1 and slightly different values are obtained
at different time intervals, the referee value shall be obtained at
the longer time interval.