158 MODERN PAPER-MAKING
outside rises until it reaches the desired level, when it is run down to the lowest
breast box.
This is an excellent strainer for high-class papers, as the plates are easily
changed for finer or coarser cut, according to lite quality of the stuff, and for
cleaning. The plates may be well immersed in the stuff, and light substances
such as rubber, chips of wood, etc., float to the surface and are run off to the
auxiliary. Every part is easily accessible for cleaning purposes, and if it is
kept in good order there is no waste of stuff from rubber ends, etc.
No spray pipe can be used, therefore all the uncleared fibres and knotty
stuff collect on top of the plates and must be periodically removed by
the machine assistants. This always causes a rush of stuff to the wire,
together with tangled masses of fibres and dirt, and is the worst feature of this
strainer.
The strainer vat may be cleaned out, the plates taken off and blown by
the steam force jet and replaced in 2 to 3 hours by two men. It is not advisable
to run this type of strainer uncleaned for more than a week. Long strings of
fibres collect about the inner surfaces of the plates, and are very apt to come
away in lumps which do great damage to the wire. Also, it is not unusual for
one of the bolts holding a plate on to break or come out, leaving a hole through
which the stuff will pass unstrained. It will be readily seen that these strainers
are rather expensive to run and keep in good condition, but nevertheless they
have proved 'very efficient in fine mills.
Auxiliary Strainers.—]& almost every mill auxiliary strainers or 'back
blotters' are used to deal with'the stuff rejected by the machine strainers, and
they do not usually receive as much attention as they should, either from the
machinemaa or those in authority. The idea of the auxiliary strainer is that it
should deal with all the lumps, and heavy stuff rejected by the machine strainers,
and also with any scum which may run over, and with the water used to clear
the slits. All these contain valuable paper-making material or chemicals, such
as size, alum, etc., and if they can be recovered there is a great saving and also
a reduction in the mill effluent.
This strainer usually consists of an ordinary flat jog strainer, with a fine cut
plate, and it is often placed away in a corner at the back of the other strainers,
'out of sight and out of mind5. It should be placed in a prominent position
whenever possible, so that the machineman may see it always receives proper
attention, and that others- who pass may also see it.
In the case of rag stock, the heavy uncleared lumps and strings which gather
in the trough of the strainers, together with the top scum, containing rubber,
wood, etc., and the water from the spray pipes, should all be run into it and
strained. A good many of the lumps and strings will be broken up, especially