RE-USE OF WATER 351
If, however, the mill makes its own wrappers from time to time, or has a
machine engaged in the manufacture of wrapping papers, it will pay to recover
all this fibre in order to assist in making up the furnish of the wrapping papers.
This is not only economical, but it also enables a really good wrapper to be
made, on account of the rag fibres contained in the refuse.
The method employed to save this material is simple, and consists of running
the waste washing water, overflow or cleanings from auxiliary strainers, waste
from the wire pit and press pit into large tanks built up of perforated tiles.
Here the water drains away, leaving a large proportion of the fibres lying in
the bottom of the tank and round the sides. The tanks are periodically cleaned
out and the stuff is taken up to the beaters to be furnished for wrappers. The
tanks should be of a sufficiently large capacity to deal with all the water from
the rag-washing engines, which contains only a small amount of fibre, and they
must also be capable of dealing with the stuff from the machine wire pit when
changing or washing up.
If this work is being properly and carefully carried out by the machineman
the amount of effluent should not be excessive, but there will always be some
waste from the bottom of the chest, the sand traps and strainers, and a small
amount from the wire pit.
In mills making lower grades of paper the methods employed vary accord-
ing to the general lay-out of the mill and the grades being manufactured, the
amount of waste which has to be dealt with and the capacity of the mill to
re-use this waste in lower-grade papers.
It may be taken as a general rule that most of the recovered stuff will have
to be used in a paper of a lower grade, quality or colour from that which pro-
duced the waste water.
The most satisfactory method is as follows:
All water from the machine wire pit, press roll pits, wire save-alls and
suction boxes should be collected in suitable tanks at the back side of the machine,
whence it can be pumped back to any or all of the following places:
1. The machine back-water tank for supplying the mixing box.
2. The beater supply tanks.
3. The machine chests.
4. The sprays at the machine.
When the machine starts up, assuming the back-water service system to
be empty, it will be necessary to use fresh water to dilute the stuff coming
into the mixing box from the stuff tap, but as soon as the machine has
started and the back water has had time to get round, the fresh water may