CHAPTER Xffl
THE FOURDRINIER MACHINE (Continue!)
deckle straps to machine drive
Deckle Straps.—These are the endless rubber bands which keep the stuff
on the wire. They are composed of flexible rubber with a core of harder and
stronger material to give them stability. They should be of sufficient weight
and bulk to prevent the stuff from flowing under or pressing them outwards.
They are carried on flanged pulleys, movable outwards or inwards to suit
different widths of web. Often deckle straps are far too big and heavy, and
the)r cause a strain on the wire, and frequently damage it. A deckle strap
should never be heavier or longer than is absolutely necessary. It is possible
on some machines to manage with deckle straps only about 7 feet between
centres, depending on how the stuff parts with its water. Various means have
been suggested and tried out in order to supersede the rubber deckle strap, but
in our experience these have been very unsatisfactory on the whole, and we
are inclined to think that, at the present time, there is nothing available which
will give such general satisfaction as the ordinary rubber decide strap.
A trickle of water must be continually run on the inside of the straps; other-
wise they will soon become dry and stick to the pulleys. If this happens a
strap may stop, and this often means a ruined wire, owing to hard rolls of
pulp going through the couch rolls. Bruises or cracks on the edge next the
wire will result in a little leaf being formed on the edge of the paper, with
a corresponding thin place behind it.
This may be picked up by the press rolls and cause a break there or at the
dry end of the machine. If the edges of the strap are rough, uneven, dirty,
or have a hard lump, the same trouble will result. If a strap is too long, the
return portion will swing and sag and cause it to move forward on the wire
with a jerky motion. If too short, or with perished and sticky places, it will
drag and make rolls of pulp on the deckle edge.
It is important tfcat the side that runs on the wire should be slightly concave,
otherwise there will be a continuous bad edge. It often happens that a strap
is kuiscd or otherwise damaged when changing a wire. Therefore too great
care cannot t« takes to see that they are skilfully handled, placed where there
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