PULPING BROKE

109

is a slow process; when ready, the whole vat is tilted with the help of heavy-
counterweights, and emptied into trucks.

The Edge Runner or Kollergang (Fig. 3 5}.—This machine is peculiar and
clumsy-looking in construction. It consists of a rather shallow circular vat
the bottom of which is of hard stone, usually granite. Through the centre is
a vertical shaft, driven from below. At right angles to this shaft, and forming
a T, another shaft carries two stone rolls, which partly roll and partly drag
on the stone bottom of the vat.

These rolls are on opposite sides of the vertical shaft, and cover all the stone
bottom, slightly overlapping each other. A usual size of roll is 6 feet in dia-
meter, 10 inches across the face and weighs about 3 tons. They are usually of

[Messrs. Massoti, Scott and Co. Lid.
FIG. 35.—SECTIONAI VIEW OF KOLLEHGANG OR EDGE RUNNEB, SHOWING DBIVING MECHANISM AND
BASE STONE
granite with the running faces roughened to grip the pulp. They are driven
from 10 to 15 travel revolutions per minute. The power required is about
30 h.p. and the output with strong papers 4 to 6 cwt per hour.
A steel scraper or blade follows the rolls round the vat and pulls the stuff
from the outer edges under the rolls for treatment Sometimes the stone
bottom is made concave and the faces of the rolls are cut to correspond to
induce the pulp to fall under the rolls by its own weight.
The action of the edge runner is not only a rolling one—it is something
more. The stones being pulled round in a small circle, there is also a twisting
or screwing motion going on, similar to what takes place when a garden roller
is turned in a small space.