166 MODERN PAPER-MAKING
It thus becomes a question of adjusting the weight of the head of stuff to giv<
a pressure sufficient to force the stuff forward at the correct speed. Until the
introduction of the Voith box very little attention had been paid to this im-
portant subject, and in most cases the stuff came slowly forward until caughl
by the wire, and it was then whisked suddenly forward and rolled into waves
and generally disturbed, when it should have been coming under the action
of the shake and been properly felted together.
It can therefore be said that the use of the flow box helps very considerably
in forming a better and stronger sheet. The amount of stuff for a given sub-
stance and speed is, of course, still regulated by the stuff and back-water taps,
but the head of stuff behind the box, to give the required speed of discharge
on to the wire, is regulated by the opening of the lips of the gate.
The correct adjustment of the gate and head of stuff must, of course, be
found by the machineman himself, according to the substance he is making
and the speed of the machine, just in the same way as he had to find these
adjustments with his slices. The adjustment, however, is far more easily con-
trolled, both for the whole width of the machine—by turning a wheel—and
for any individual unequal patches by screwing the adjusting spindles up or
down. It has one great disadvantage, however, in that it cannot be used satis-
factorily where there are many changes of deckle width. When a slice is used
it should be high, so as to allow a deep pond to be worked; 18 inches is not
too high for a machine running up to 650 feet per minute, and very much
higher for fast speeds and free stuff
The Wire.—The wire is the most delicate and expensive part of the machine
equipment. It may be described as a sheet of fine wire gauze, joined by a
seam to form a continuous band.
The fineness of the wire, its texture and mesh, are made to suit the class of
paper for which it has to be used, and the speed at which it is to be run. The
wire is made of bronze of various alloys of copper, tin, etc., and these are
varied by the makers to obtain a combination of strength, durability, and
wearing qualities.
Machine wires may be obtained in a wide range of mesh and quality, and in
various types of weave. The old weave seems now to be giving place to long
crimp, flat-warp; and twill types of weave for which various advantages are
claimed, and the wire-makers are continuously experimenting with different
weaves, to give strength and wearing qualities, and smoothness to the under
side of the sheet of paper, so that the surface of the under side may be as nearly
as possible equal to that of the top side.
Great praise is due to the energy and extensive research work of the paper
machine wire manufacturers, who do their utmost to give the paper-makers