MACHINE DRIVES 217
intermediate wheels and shafts into action. Later on two steam engines were
used, of which one drove the wet end at a constant speed and the other the
machine itself from the wire onwards. This was a great improvement, but
the steam engines were of too heavy a type, with a limited range of speed, and
'speed wheels' were still necessary. Their heavy flywheels, parts and long
stroke prohibited a high speed, so there was only a limited range of speed at
which they could be used with any efficiency.
The reciprocating action of these heavy engines caused the belts to swing,
and the sections of the machine were very jerky and unsteady, and this was
the source of endless broke.
Many had no variable governor drive, and the speed was altered by hanging
more or less weight on the governor lever. As the necessity for higher speeds
arose, and to dispense with the inconvenience and loss of shutting down to
change speed wheels, the smaller type of high-speed light engines was developed,
and proved a great advance in steadiness and efficiency.
In the old type of belt drive the usual arrangement comprised a series of
gear wheels of various sizes, which had to be changed to suit the speed required,
The first press rolls were driven dkect through a clutch on the main shaft. On
this shaft were three pulleys, from which one belt drove the wire shaft, one
the shaft for the main stack of drying cylinders, and the third the shaft for the
second press. On the cylinder shaft were the pulleys of the smoothing rolls,
the second stack of drying cylinders and the calender rolls. From one or other
of the calender roll shafts, belts extended to the cooling rolls, winder, etc,
The sections of the machine were put in gear by means of toothed clutches,
which started them up with a sudden jerk, imposing a great strain on the belts,
and specially on the teeth of the cylinder gearing. In fact, the engine had to
be slowed down to put the cylinders into motion, and unless this was done the
wheels were sure to be stripped of teeth*
The tension of the 'draws* was regulated by sticking on the pulleys, to
increase their diameter, pieces of 'packing', strips of old coudier covers, old
dry felts, etc., by means of resin boiled with oil and pitch. This had to be done
when the machine was mailing, and was a troublesomc^.difficult and dangerous
operation. The tendency of the pull of the belts was to drag the 'packing'
into lumps, and in hot weather the resin refused to remain sticky enough, so
tfeat pieces fell off aad had to be cxmtoidDfy replaced. When a piece of packing
could not be got off a pulley, & piece had to be stuck on the other to get the
draw correct, and the belts frequently stretched and broke under dbe strain*
The provisions of tbe 1937 Factory Act preclude the use of this type of drim
The introdactia& of the high-speed engine and variable speed electee
motors made it pQsstWe to arrange a drive which has none of these