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.