RUNNING THE MACHINE 225
Therefore, though a lifting gear at the breast end gives a little more chance
of varying the conditions, it is by no means a necessity for an ordinary machine.
By using the slices intelligently and getting the proportion of stuff and water
correct, its absence will not necessarily be a disadvantage.
The behaviour of the stuff and water on the wire is a very interesting study.
It will be found that in every case there are long fibres and fibrilk, some of the
latter so fine as to be nearly powdered. On emerging from under the slices,
if the water is nicely proportioned, the long fibres fell to the under side of the
sheet, and the fibrillae remain for a time in suspension with the water. The
action of the shake, contrary to what one might expect, keeps these finefibrillae
suspended for a time, until they are sifted into the spaces between the longer
fibres, and by the gradual drawing out of the water by the tube rolls they
remain there permanently. As the stuff approaches the first suction box, the
action gradually ceases, so that the suction sets the sheet without altering the
disposition of the fibres. It seems to be a fairly general belief that the shake
turns the fibres from their 'end-on' flow from the apron. But a simple experi-
ment will show that this is a fallacy. Take a few matches and float them in
a rectangular tray. Give the tray a sideways shake and the matches will arrange
themselves broadside on to the direction of the shake. Close observation
will show a similar action on the wire when the stuff is beaten rather raw and
long. It must be remembered that the shake does not make zjlow, but, what
is quite a different thing altogether, a wave.
Actually, with a well-fibrilkted stock, the longer (or any) fibres are not
moved much, if at all, from their endways flow. Moreover, the end-on flow
of the fibres from the apron is not so pronounced as is generally supposed.
The passage under the slices tends to turn round fibres that are pointed end-
ways, especially the longer and bulkier ones. These, being entangled with
fibrillae, will naturally remain very much in the position in which they emerge.
If they do alter their position, it will be towards placing themselves end on,
because the shake is forcing them to this position.
An examination of paper made with and without shake will sbow this to be
correct. The increase in strength given by the shake is due to the fibrilk
being spread and sifted'into what would otherwise be bare spaces, or air
spaces, and making a uniform in place of a 'ptchy* paper. If there is too
little water with the fibres, the fibrilk will not be so sifted, because their
carrying medium is absent. If too much water, they will not have settled
before reaching the suction box, but will still be in a suspended state. Then
too much suction will have to be used, and the whole fabric of tie sheet will
be disturbed.
A long wire is not always an advantage in making strong papers.