216	MODERN PAPER-MAKING
machines are fitted with as many as five sets, of which the first two sets may be
of three rolls each. All rolls are cambered to take an increasing weight towards
the reel end, and are fitted for steam heating, and have doctors and guards
before each ingoing nip, The bottom roll of each set is greatest in diameter
and is driven. The other rolls are driven by the friction between their surfaces
and the paper.
After passing through the calender rolls the paper will have received its
surface finish, and as a result of the heat and friction of the rolls, it is always
charged with static electricity. Sometimes this charge is very high, especially
so when the rolls are very hot and the paper has been allowed to get a little
too dry. Then trouble is experienced with the laying of the sheets when the
paper is being cut. They are attracted to parts of the cutter and also to each
other, which interferes with the 'picking' or overhauling later on. To cause
this electricity to be discharged die paper is led from the calenders over a
water-cooled cylinder or cylinders. Where these are not fitted, copper wires
are stretched across the machine, close to the surface of the web, and earthed
to a water pipe or to the frame. Conditioned paper is, of course, freed from
all static.
The web is wound round on a wooden or iron bobbin by means of a friction
winder. A square spindle or bar is put through the bobbin and the latter is
secured in its place by 'keepers'. At one end of the spindle is a small cogged
wheel. The friction winder is composed of a shaft which carries a cogged
wheel to engage in that on the bobbin spindle. On the shaft are two steel
discs, one of which is fixed; the other is free to move sideways. Between
these discs runs a pulley which comprises two polished sides. Leather discs are
interposed between the fixed discs and the running pulley discs.
The pressure between these discs is adjusted by a screw handle and the
friction gives the necessary tension to the spindle and web of paper. Drum
winders are also used.
The Machine Drive.—Ike 'drive' is the term used to express the means
by which the various sections of the machine are connected to the source of
power, and includes the latter. Formerly one steam engine was used to drive
tbe various pumps, etc., of the wet end and also the machine itself In still
earlier times it was not unusual to find a water wheel doing the work. The
means of power transmission was by belts and shafting geared to the engine
with spur wheels; as the wet raid machinery cannot be varied very much in
speed, tbe range of speed for the machine was very limited,
To overcome this difficulty, intricate arrangements of 'speed wheels'
were used wbm voy heavy or light substances were being made. This
entailed shutting down and lifting on and off heavy gear wheels, or putting