304 MODERN PAPER-MAKING
Milne's patent damper consists of a short travelling wire cloth, which is
made to carry a certain amount of water in its meshes. Air jets blow this water
on to the paper. Any mesh wire may be used as required for the fineness of
the spray, and the speed and mesh control the quantity applied.
As only the amount of water carried can be blown on the paper, the damping
is very uniform and regular. The cheaper grades of paper are damped on the
making machine. Better grades are damped and rewound. All paper should
stand for at least twenty-four hours before being finished, so that the moisture
will spread through the substance of the sheet and reduce inequalities of
damping.
It seems to be a very general idea that best results are obtained by having
the paper cool before it is damped. This entails more expense and labour in
the use of a damper separate from the machine, but very few mills work this
method. The usual practice for super-calendered papers is to damp the web
as it is reeled on the making machine, while still in a very hot condition. Quite
satisfactory- results are obtained. As the damping, or application of water,
takes place immediately before the paper is reeled, very little evaporation can
take place in the short space of time before the sheet is covered by another layer
of warm and watered paper.
As warm water is more penetrative and diffusive than cold, it is only reason-
able to expect that it will more readily force its way into the fibres and produce
more uniform damping when the paper cools. There is no doubt that the
results of practical experience go to prove that the most satisfactory damping
is that carried out when the paper is hot off the machine.
THE SUPER-CALENDER
The super-calender (Fig. 132) is a stack of rolls usually eight in number,
but now being built with as many as sixteen. These are alternately of iron
and composition. The latter are built of discs of paper, made from cotton or
woollen fabrics and cotton rags and hemp. The laminations or discs of paper
are fitted on a heavy steel centre and compressed into a solid form. The roll
is then turned and buffed to the correct camber. The iron and paper rolls are
placed alternately, commencing with top and bottom rolls of iron. This
brings two paper rolls together in the centre of the stack. The reason for the
dse of iron and paper rolls is that the latter form what may be termed a cushion,
allowing the heated iron rolls to impart a high glaze to die paper, without the
blackening or crushing and reduction of bulk which take place between two
rigid iron rolls.
The two adjacent paper rolls bring the reverse side of the web into contact