ipo MODERN PAPER-MAKING
Many machinemen prefer to run an hour or two with no water on the
cover until it fills up to a working condition.
At all times it is inadvisable to rub the hair or nap of the jacket the wrong
way if the stuff shows signs of going up the roll. Only a momentary improve-
ment is obtained. A hot and strong solution of soda ash is far more effective,
and this should be used when the cover requires cleaning, instead of using
the force jet. As one of the chief causes of wear in a cover is the plucking
out of the nap by the meshes of the bare wire, the new cover should, if possible,
be started with a full-width deckle and fall widths should also be run as long
as can be arranged.
The Guard Board.—The function of the guard board is to clean and dry, as
far as possible, the cover of the couch roll. As pressure is the integral part of
this action, it will be readily recognised that its use will be the chief factor in
shortening the life of the cover. For this reason various kinds of appliances
have been tried, and many ways of fixing, pressing and covering the rubbing
edge of the board have been resorted to. We will not go into details of these,
or the special designs applied to high-speed machines, but confine ourselves to
the types that are commonly used for machines in general. A guard board is
usually constructed from one piece of good wood (pitch pine), strengthened
and made rigid by another piece at right angles, fixed at the back of the board;
or in some cases this is replaced by a rod of iron used as a 'stringer'. It is covered
on the rubbing edge by a piece of old couch cover, and there are two ways
of fixing and using it* It may be fixed to the brackets which hold the couch
roll, sliding in a guide, and being pressed down by springs; sometimes there
are no springs, and the board is pressed down by hand and fixed in position fay
bolts. If the brackets are of the modern type which swing with the couch roll,
the board will of course rise and fall with the roll; but if the brackets are of the
older fixed type, the roll is apt to lift the board and let water pass.
A board of this kind must be very carefully used. The machineman is
sometimes tempted, when running very wet or fine staff, to squeeze it very
hard down on the cover, when he may very easily reduce the life of the latter
by half. A safer and more efficient type is the swinging board. This is hung
on pivots on the brackets and the pressure is applied by weights hung on short
fixed levers on the back of the board. Being free to rise and fall, it does not
require to be so heavily pressed on die roll, and the pressure is more easily
controlled and observed This kind, owing to the angle at which it touches
the roll, has die advantage of allowing a deeper flow of .water to be used to
dean the cover, and therefore washes away any fragments of fibre that may
come up die roll A fixed board requires to be set opposite the point of pressure
of the couchers, and die angle admits of a very shallow flow.