6. Equipment for Mixing
6.1 Standard Mill:
6.1.1 The standard mill shall have rolls between 150 and
155 mm (5.9 and 6.1 in.) in diameter. The mill shall be
equipped with retaining guides, with a distance between the
guides at the nip of 250 to 280 mm (10 to 11 in.).
NOTE 1—If mills of other sizes are used, adjustments to batch masses
and mixing cycles may be required to obtain equivalent results.
6.1.2 The speed of the slow roll shall be 0.4 6 0.50 rad/s (24
6 0.5 rpm) and the ratio between slow and fast roll shall be
1:1.4. Other ratios may be used, but modifications in mixing
procedure may be required to obtain equivalent results. The use
of other than a standard mill shall be recorded with the reported
data.
6.1.3 Means shall be provided for controlling the mill roll
temperatures to the specified temperature 65°C (69°F).
6.1.4 The clearance between rolls shall be adjustable from
0.2 to 8.0 mm (0.008 to 0.31 in.) as a minimum range of
adjustment. Roll clearance shall be determined by means of
two lead strips 10 6 3 mm (0.4 6 0.1 in.) wide, at least 50 mm
(2 in.) long, and 0.25 to 0.50 mm (0.01 to 0.02 in.) thicker than
the roll clearance to be measured. The lead strips shall be
inserted, one at each end of the rolls approximately 25 mm (1
in.) from the guides, while a piece of compounded rubber, with
Mooney viscosity in excess of 50 ML 1 + 4 at 100°C (212°F),
approximately 75 by 75 by 6 mm (3 by 3 by 0.25 in.) is passing
through the center portion of the rolls. The rolls shall be at the
temperature specified for mixing. After the lead strips have
passed through the rolls, measure the thickness of the strips to
the nearest 0.02 mm (0.001 in.). Tolerance on a roll clearance
shall be 610 % or 0.05 mm (0.002 in.), whichever is larger.
6.2 Standard Internal Mixer—The standard internal mixer
shall have a chamber of 1575 6 50 cm3 volume and two rotors
with approximately 400-cm3 displacement volume, resulting in
1170 6 40-cm3 loading capacity. The slow rotor speed shall be
8.16 rad/s (77 rpm) and the gear ratio shall be 1:1.125. The
rotor wing tip to side clearance shall be 2.4 + 0.3, − 0.1 mm
(0.094 + 0.010, − 0.005 in.). The mixer shall be equipped with
a thermocouple for measuring and recording batch mixing
temperatures. The thermocouple shall be installed through the
end frame and shall protrude into the mixing chamber 25 6 2.5
mm (1 6 0.1 in.) measured along the top side of the
thermocouple probe. A ram that is 56 6 3 mm by 140 6 8 mm
(2.2 6 0.1 in. by 5.5 6 0.3 in.) shall exert a force of 1.27 6
0.06 kN (285 6 14 lbf) on the batch in the chamber. The sides
shall be hinged to swing open, made of cast stainless steel and
jacketed for controlling temperature by means of a circulating
liquid or steam. The end frames shall be of ductile iron that has
a 0.20 6 0.02-mm (0.008 6 0.001-in.) thick chrome plating on
the working surfaces. Rotors are of stainless steel, nitrided,
drilled, and equipped with rotary unions for controlling the
rotor temperature by means of a circulating liquid or steam.