WOOD PULP

53

MECHANICAL PULP

Those intended for mechanical pulp are passed to the grinders after having
all knots drilled out. The wood pulp grinder consists of a revolving stone of
about 31 to 4i feet diameter and 2 to 2\ feet on face. This is mounted on
a heavy shaft and enclosed in a heavy metal case on which are strong metal
boxes fitted with hydraulic pressure arrangements to hold the logs and keep

[Nokia Mtitbolag

FIG. 13.—TOWING A 'RAFT* OF LOGS ACROSS A LAKH TO THE PULP Mm

them pressed against the revolving face of the stone. Inside the case, behind
each box, is a water spray which washes off the particles of wood as they are torn
from the log.
The stone is kept rough on the tearing surface by frequent dressing with
special tools; the quality of the pulp and the output depend very much on the
condition of the stone. If the stone is smooth the output will be small, and
the pulp will be fine and 'dusty' on the paper-making machine. Coarse stones
give a greater output of longer-fibred pulp.
There are several kinds of mechanical pulp, named according to the method
of grinding—viz. cold ground, hot ground, and cooked or steamed — i.e.