218 MODERN PAPER-MAKING
Instead of heavy belts in series, the engine drives a shaft, usually overhead, from
pulleys on which each section is separately driven through bevel wheels, the
smaller of which is of hide> giving a smooth and noiseless motion. Light
belting (4 to 6 inches) is used, and cone pulleys supersede the packing method.
In another type— 'White's drive'—the power is transmitted by a system
of ropes instead of an overhead shaft, and cone pulleys with light belts are
used to vary the speeds of the sections. No clutches are used, the driven cone
pulley being raised by a lever so that the belt is put out of action, and has no
wear and tear unless the section is being run. When starting up, the pulley
is lowered into the loop of the belt and the section starts gradually as the belt
is tightened up. This has shown itself to be a very efficient, smooth and steady
drive.
The Marshall Drive.—The Marshall drive transmits power to the various
driving sections of the machine from a line shaft ninning parallel to the length
of the machine. Each unit allows a certain amount of speed adjustment, and
turns the drive through a right angle to couple to a driving shaft which lies in
a cross-machine direction.
In every stage of its development the unit has consisted" of a shaft carried
by bearings and stands from the machine house floor, and driven from the
line shaft by clutch-operated cone pulleys, the latter being provided with
belt-regulating gear to give speed adjustment. The shaft of each unit has
fitted at one end a bevel pinion which gears with a bevel wheel on the section
driving shaft.
The advances made in the design of the Marshall drive since its first inception
consist mainly of improvements to the gear wheels, and the replacement of
ordinary bearings by anti-friction bearings of the roller or ball type.
The first arrangement of gear wheels would almost certainly have an iron
pinion with cast teeth, working in conjunction with a mortise wheel having
teeth of hornbeam or birchwood fitted into a cast-iron rim. Later, both
wheel and pinion would have cast teeth, and then in turn these would be
replaced by gears with machine-moulded cast-iron teeth, and eventually by
machine-cut teeth. IJp to this period the gear wheels'had worked without
my serious attempt being made to enclose them, and lubrication consisted of
an application by hand of heavy oil or grease at frequent intervals. With
the advent of bevel gears made from high-tensile steel and having spiral teeth,
ihe Marshall cfcive entered the field of precision engineering. Gears that were
now only about half the diameter of the originals, but transmitting the same
ower, required protection both from dust .and from the effects of faulty
It thus became necessary to enclose the 'gears in cases that were