NEWSPRINT

267

taper to give the required larger clearance between the gkss tube and the cone.
Rotameters are obtainable already calibrated over the range of flow-rate
desired.

From the proportioner, then, the stock is complete with colour, loading
and alum, and after further refining it is ready for the machine.

In dealing with the correct furnishing and preparation of the stock for
making newsprint, stress must be kid on the importance of selecting pulps
which are suitable for the purpose, and on the need for keeping out of the
system foreign material likely to affect adversely
the quality of the sheet, or cause breaks on the
paper machine. Methods of evaluating pulp
quality have advanced very considerably during
die past few years, and in modem newsprint mills
the testing of the quality of shipments is an im-
portant part of laboratory control work. The
tests made include freeness determinations, the
estimation of shive content and the preparation
and examination of laboratory sheets. Detailed
information about methods of this kind is avail-
able in the technical literature and in the reports
of committees which have made a special study
of the subject

The precautions taken to prevent foreign matter
getting into the paper consist firstly in keeping a
careful control of the cleanliness and general con-
dition of all pulp used; this is usually done when
the pulp is first received at the mill and is tested
for moisture content. Secondly, coarse grids are
fitted at various points in the pipe lines, in boxes
which may be isokted and cleaned out periodically
without interrupting production. The final point
for holding back unwanted material is at the
strainers through which the stock passes immedi-
ately before flowing to the breast box,

Strainers and Slice.—The finally prepared stock,
regulated to a uniform consistency of 2\ to 3 per cent, and containing dyes,
alum, and loading, is pumped to a head box, from which the required quantity
of stock flows through the stuff valve to be mixed at the mixing pump with dbe
back-water recovered from the wire pit It is important to have a
pressure of stock behind the stuff valve, as this is the valve that is

FIG. 113.—THE ROTOSPRAY FOR CLEAN-
ING CLAY AND OTHER LOADINGS AND
COLOURS. THKALSOHAS AHOMOCEN-

EER FOR SEPARATING THE PARTICLES
AND GIVING AN EVEN HOW Of CLEAN
SLURRY