CHAPTER Xn
THE FOURDRINIER MACHINE (Continued)
Connecting Pipes and Skates.—The height and situation of the strainers usually
decide whether the stuff is run to the breast box through pipes or open shutes.
Open shutes are easier to clean, but where pipes must be used they should be
of copper, have very smooth interiors and be easily taken apart for cleaning.
Dirt or any rough surface inside the pipes causes clumps of fibres to form.
This is very often the cause of a great deal of broke, as these lumps show up
very plainly as clear specks or spaces when the paper is finished. For the
same reason all shutes must be kept very clean, with no ragged wood or scale,
and inside edges should be bevelled or rounded.
The Breast Box.—This is an oblong box extending across the width of the
machine. It receives the stuff from the strainers and, overflowing along its
whole length, discharges it equally over the breast board. Some machines
receiving the stuff from low-level'pipes have a series of holes in the bottom of
the box. These are connected by smaller pipes to the main stuff pipe. The
stuff then flows over the edge of a board on to the breast board. This board
is sometimes the cause of clumps of fibres forming in the stuff, especially if its
edge is badly trimmed or dirty. The best form of box is V-shaped, whether
the stuff falls into it from above or enters at the bottom.
The consistency of the stuff should be equal at the sides and the centre.
Where it enters from a series of holes in the box, from one side only, the side
of the machine where it enters has always the closest and clearest water-mark,
owing to the finest fibres coming first over the edge. The longer and heavier
fibres are flung to the other side, and the machineman is often puzzled to know
why he cannot get a uniformly made sheet all across the machine.
The whole object of the breast box is to keep the fibres in suspension in
the water, and to prevent them from coming together and forming lumps, or
settling down, and to ensure an even flow on to the wire, and that all stuff is
of equal consistency across the whole width of the machine.
From the breast box the stuff passes on to the breast board, and thence to
the apron, or the projection slice. Where an apron is used some sort of con-
necting device is necessary to bridge the gap from the stationary box to the
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