242

MODERN PAPER-MAKING

round the cylinder. Dry steam passes through these pipes and heats the moist
vapour which is being driven from the web of paper by the heat of the cylinder.
This assists the web to part with its water, and the vapour is drawn away from
the hood by means of a large pipe and fan which exhaust to it atmosphere.

On other machines the hood has no steam-pipes, and the vapour is exhausted
to atmosphere by means of a fan only. The process is really vacuum'drying
except that the vacuum is very low owing to there being no sealing of the
joints between the hood and the cylinder.

There are two distinct methods of drying the web on these machines, which

[Bentley and Jackson
FIG. lor.—DKHNG CYLINDER OF A LARGE M.G. MACHINE, SHOWING Two PBBSS ROLLS AND
COMPLETE HOOD
have a marked effect on the finished paper, both as regards under side and
surface.
In one method the top side of the paper—that is, the side farthest away
from the wire and wet felt of the machine—is brought in contact with the
surface of .die cylinder. In order to effect this, the web has to be led round
the cylinder in such a way that it finishes up at the front top of the cylinder
nearest Ac wet end of the machine, and immediately above the press rolls.
This method olmousiy gives the smoothest surface and the roughest under
side.