5.1 Centrifuge:
5.1.1 Use a centrifuge capable of spinning two or more
filled cone-shaped 203-mm (8-in.) centrifuge tubes at a speed
that can be controlled to give a relative centrifugal force (rcf)
of between 500 and 800 at the tip of the tubes (see 5.1.6).
5.1.2 The revolving head, trunnion rings, and trunnion cups,
including the cushions, shall be soundly constructed to withstand
the maximum centrifugal force capable of being delivered
by the power source. The trunnion cups and cushions shall
firmly support the tubes when the centrifuge is in motion. The
centrifuge shall be enclosed by a metal shield or case strong
enough to eliminate danger if any breakage occurs.
5.1.3 The centrifuge shall be heated and controlled thermostatically
to avoid unsafe conditions. It shall be capable of
maintaining the sample temperature during the entire process at
60 6 1°C (140 6 1.8°F). The thermostatic control shall be
capable of maintaining the temperature within these limits and
operate safely if there is a flammable atmosphere.
5.1.4 Electric powered and heated centrifuges must meet all
safety requirements for use in hazardous areas.
NOTE 3—Some heated centrifuges maintain the bowl at a pressure
slightly below atmospheric pressure and reduce the hazards associated
with vapors and gasses, produced by samples and solvents used in the
tests, by discharging any vapors to a non-hazardous area.
5.1.5 Calculate the speed of the rotating head in revolutions
per minute (r/min) as follows:
r/min 5 1335=rcf/d (1