5.5 Compounding materials other than rubber, carbon black,
and oil may be added to miniature internal mixer batches more
precisely and with greater ease if they are previously blended
in proportion to the mass required by the recipe. Such blend
may be made in a mortar and pestle, by mixing for 10 min in
a biconical blender with intensifier bar turning, or by mixing in
a blender9 for five 3-s periods and scraping the inside of the
mixer to dislodge materials stuck to the sides after each 3-s
mix. Caution: If mixed longer than 3 s, the stearic acid may
melt and prevent good dispersion.
5.6 Unless otherwise specified, carbon black shall be conditioned
by heating for 1 h at 125 6 3°C (257 6 5°F) in a 1 B
oven or equivalent, in accordance with Specification E 145.
5.6.1 Place the carbon black in an open vessel of suitable
dimensions so that the depth of the black is no more than 10
mm (0.4 in.) during conditioning. Store the conditioned carbon
black in a closed moisture-proof container until cool and then
use for weighing and mixing.