NEWSPRINT 275
Speed
Speed Increase Stretdi
f.p.m. f.p.m. Per Cent
Couch ............ 1045 — —
First press............ 1108 63 6.0
Second press .......... 1120 12 i.i
First drying cylinder ...... ,.1129 9 0.8
Sweat cylinder.......... 1130 i o.i
Pope reel drum.......... 1130 o o.o
Total wet end stretch........ — 84 8.0
Total dry end stretch........ — i o.i
Grand total for whole machine...... — 85 8.1
The moisture removed by a modern press part is indicated by the following
average figures:
Moisture Content Vacuum Used
Per Cent Inches
Couch ................ 79 16
First press................ 68 17
Second press .............. 66 22
Obviously it is important to remove as much moisture as possible by pressing,
in order to reduce the amount of drying required to a minimum.
The Dryer Part—The most difficult problem in the drying of newsprint is
ventilation. The greater the width of a machine the greater is the difficulty
of removing the moisture-laden air uniformly across the machine. It is the
general practice to fit hoods by means of which the damp air is collected and
discharged to atmosphere by a battery of usually six to eight fans situated above
the back of the machine. Coupled with this system, hot air is blown in through
trunking under the dryer section. The fundamental defect of methods of this
kind, however, is that air cannot pass directly upwards past the drying cylinders
because of the felts and the paper itself Various methods have therefore been
tried to promote adequate circulation between the cylinders, and the Grewin
system is a typical example. In this system relatively small quantities of hot
air are blown into the dryer section alternately from the front and back of
the machine* The nozzles are placed as near to the paper as possible, so that
fresh dry air may be brought continuously into contact with it.
In spite, however, of all the attempts made to improve the uniformity of
drying, it is all too frequently necessary to have to try to compensate for
uneven evaporation by loading the presses or crowning them specially to
give the lowest moisture content in that part of the sheet where the drying is
least efficient.
In tackling drying problems on news machines the fundamental feet must