162 MODERN PAPER-MAKING
reason for this is that, generally, the weight of the slices and pulleys will cause
the cross-bars to sag down a little as they are moved towards the centre, and
this must be allowed for, or the apron will be nipped between the plate and
the wire.
When the brass plate is fixed or cast in one piece with the deckle pulley
fittings, the upright pillars of the cross-rods may be raised. There is usually
provision made for this adjustment by having the pillars threaded and held by
two nuts.
It is generally found necessary to pack a handful of soft stuff at the outside
of the apron on the breast board to prevent fibres coming out and getting under
the deckle straps. This arrangement is very efficient and gives a sharp, clean
deckle edge to the web of paper. Another method is to fix the apron down
on the breast board all across its length and arrange a piece of weft-worn old
couch cover on the brass plate, so that the empty space between the deckle
pulley and deckle strap and the apron is closed up. This projects in a knee
shape about i| inches over the apron, and allows the deckle to be changed
without so much risk of tearing the apron, but is not very effective and requires
very skilful handling to give a clear deckle edge.
When changing deckles, the apron ought never to be strained or pulled
very strongly, or it may then refuse to lie flat. Stuff will then run under the
raised part and make continuous streaks or rolls in the paper. A very good
plan for getting the apron to lie and remain flat is to utilise an old apron for
supporting the new one. The old apron should be cut to about two-thirds of
its width and put on underneath and along the new one. This helps to bridge
the gap between the lip of the breast board and the highest part of the breast
roll, and takes a great deal of strain and wear off the top apron. The lip or
wire edge of the apron must coincide with the centre of a tube roll, and all tube
rolls under the apron should be kept well oiled and running freely, otherwise
air will be drawn through with the wire, causing little holes or clear spots in
the paper.
After being put on and once made wet, the apron should never be allowed
to get dry; a trickle of water ought to run on to it during the week-end and
when there is a shut long enough for it to dry up.
When shutting down, all fibres and any dirt, sand, etc,, must be washed
off with the hose-pipe from the apron, breast board and connecting devices,
towards the breast box. If allowed to get on the wire, it will often be found
that these hard substances will pass to the couch rolls and stick in the cover
or the guard and score or cut the top couch jacket, A very soft brush or piece
of soft felt ought to be sufficient for cleaning the apron, if cleaning is done as
often as it should be. This is one of the jobs that the machineman should do