n4 MODERN PAPER-MAKING
man will be guided by circumstances. If colour and furnish permit, the stuff
service system need not be emptied, and here the sequence of colours, furnishes,
etc., is important.
Waste occurs every time a chest has to be washed out, and by arranging
lots in proper sequence, starting from a low shade and working up to yellows
and blues, for instance, this waste will be cut down to the minimum. The
stuff gate being shut, more water should be put on and the level of the shutes
and strainers maintained until the stuff loses so much consistency that the wire
can no longer form it into a web. The machine may be slowed and the stuff
run up the press roll when the proper substance is lost. This will save a great
deal of fibre that might otherwise be run down the drain.
When it is necessary to empty the chests and service system, the simplest
plan 'is to run a good supply of water into the chest when the pump shows
signs of losing grip. The pump will take the water from the chest and flush
the remainder of the' fibre from the pipe and stuff box. The pulp recovered
by these means may not be so clean as the ordinary broke, owing to the flush
of water disturbing the sand traps, but it may be used with care in lower qualities
of paper. When it is realised that in the bottom of the chest, in the stuff pipe,
stuff pump, stuff box, shutes, strainers and connecting pipes, there may be
from 50 to 200 Ib. of fibres, the importance of a little care in this .connection
is manifest. A careless shut-down may easily cost the mill ^50. Again, when
starting up it is a very wasteful and reprehensible practice to run the first flush
of water and stuff down the drain in order to get full weight on putting the
wire in gear.
The machine should be slowed down, so that a start can be made with
the first flush of stuff. It is quite a simple matter to speed up after a few
minutes.
When starting up the machine it will be found that the paper does not
come up to the proper shade for some time. This is due to the use of fresh
water at the start, and when the backwater begins to circulate, the colour
loading, etc., gradually work round. In very deep shades the colour will be
nearly | hour before it is quite settled. Ordinary white paper coloured with
a little ultramarine blue will come up in 15 to 30 minutes.
Also, no doubt, however well the machine has been washed up, the paper
will contain specks of dirt, strings of fibres from the strainers and bits of coloured
pulp from the previous lot. In some mills it is customary to run the web up
the press rolls for a time on starting. Others get the web right away to the
reel as soon as possible. In the first case the wet broke is easiest to repulp,
but has the disadvantage that the handling of it is more difficult and often leads
to its getting dirty. In the second case the machinemen, once the paper is