BEATING WOOD PULP 103
Wood pulp fibres are short enough in themselves to need little cutting,
and they have not the structure or stability to produce extensive fibrillation.
This brings us to the obvious conclusion that it is possible to find beaters more
economical than the hollander for the treatment of wood fibres. Not that any
improvement in the quality of the paper made from wood pulp in a hollander
can be looked for by using any other type, but because it is uneconomical to
have to drive a heavy roll, whose weight is never fully used, and because of
the slow and uncertain circulation of the hollander.
The beating of wood fibres is confined in a very great measure to clearing
fibre clusters and 'brushing' the fibres so that they are roughened by the partial
fibrillation of their surfaces.
This suggests a type of beater with a lighter roll and quicker and more
perfect circulation than the hollander. Many good beaters of this lighter type
are now in use, such as the Taylor and Tower beaters, which have separate
circulators and light rolls, and are found to be perfectly efficient in beating
wood, esparto, and straw.
Many qualities of chemical wood pulp show a surprising degree of fibrilla-
tion when examined under the microscope, after careful heating, and run well
on the machine. They are suitable for the cheaper kinds of typewriting papers,
and down to 15 Ib. in Large Post will take nice water-marking. Under that
substance it is difficult to water-mark an all-wood furnish without a great deal
of trouble with dandy 'pick-ups', but very thin papers may be made with
a plain wove dandy roll. The reason for the trouble with dandy picks is the
shortness of the fibre. Certain qualities of wood pulp are, however, now
available which take a good deal of beating and produce long, wet stuff.
Wood pulp produced by the soda or sulphate processes has better bulking
qualities than sulphite pulp, but tends to be too free and raw for these papers.
Under the beating of wood pulp comes the important operation of treating
newsprint stock and stuff for cheap printings and supercalendered papers.
In these cases we have the best examples of 'free beating' as opposed to the
beating of cotton and linen for the manufacture of writing papers.
The beating of newsprint is usually divided into two operations; the first
consists of soaking and mixing the strong sulphite and mechanical pulps in a
large hollander type engine, which has a roll with single and equidistant bars,
as opposed to the usual clumps of three or four bars. The sulphite is furnished
first and then the moist mechanical and broke, or the broke may be mixed
up in a separate engine. The chief requirements are maximum speed in fur-
nishing and the elimination of wire bands and bits of wood from the bale
wrappings, as these are liable to do damage later when the stuff is passing
through the refiners*