 
If this were not the Electrical or Nuclear Age, it would certainly
deserve to be remembered as the Paper Age, for never has so much paper
been used or printed upon, by so many people or for so many purposes.
Paper making is a fairly complex process and involves the use of machines
which include a wide variety of rollers, wheels, semi-liquid pumps
and wire gauze, all comprising a proportion of copper alloys.
Good papers are made from rags, straw, grasses, etc., and newsprint
from pulpwood trees. The principal method of making paper by machine
is worth outlining. First, the raw material is 'digested' in vats,
i.e. it is cleaned, bleached and softened in an acid solution. The
digester is equipped with copper or brass cooling pipes, while the
evaporation of the surplus liquor involves copper evaporator tubes
and sometimes copper cylinder - applications where copper is chosen
for its high thermal conductivity. The bleached stock, a thick semi-fluid
mass, is pumped into beaters, where the fibres are chopped up and
shredded and the whole is reduced to an even consistency. This is
the most important operation in paper making. The beater comprises
a large revolving roll or cone, in stone, steel or bronze, into which
are set numerous sharp-edged, flat-ended beater bars; these oppose
similar bars set in a baseplate. A beater roll may be 1.5 meters (5
ft.) in diameter, and weigh 10 tons or more with up to 160 bars. Normally
the beater bars are made of 94/6 tin bronze; but aluminum bronze and
other alloys are also used. On leaving the beater trough the paper
material is an even pulp. It is pumped into feeeding tanks, from which
it is spread over the surface of a rapidly moving endless wire cloth
screen, 40 to 60 mesh, or occasionally even finer. This screen, known
as the Fourdrinier wire, is a weave of brass or copper rollers. In
one giant machine, the screen is 8.1 meters (26 ft 8 in.) wide and
30 meters (100 ft.) long. As the pulp passes along, surplus moisture
is drawn out from below by suction, and the screen is a small wire-covered
hollow cyliner called a dandy-roll, which smooths the upper surface
of the pulp and at the same time impresses a watermark into it if
required. The product now resembles wet paper. It passes over a very
large perforated suction roll, then between heavy pressing rolls,
and next through smoothing rolls, the lower of which is usually made
of bronze or gunmetal. Finally, it traverses a vertical stack of rolls,
commonly five in number, where it is calendered or given its surface
finish. The paper is then would into rolls.
Plunger, vacuum or centrifugal pumps are necessary to handle the fluid
stock and these include a large number of copper alloy components,
as do the vacuum boxes. |
