CHAPTER XV
THE M.G. OR CYLINDER MACHINE-THE VAT OR BOARD
MACHINE
THE M.G. machine (Figs. 101 and 102) is a modification of the Fourdrinier.
machine, designed to produce papers having certain distinctive characteristics
as to surface.
The single-cylinder (or M.G.) machine is so called because it usually has
only one drying cylinder in place of the tiers of cylinders arranged on Four-
drinier machines. It is sometimes called a 'Yankee' machine.
The wet end is exactly the same as that of the ordinary Fourdrinier, havkg
chests, sand-tables, strainers, wire part, couch rolls and—in the case of ordinary
machines—press rolls as well
When the web leaves the press rolls it is led on to a felt, usually of special
make, and this felt leads it into a nip between the large drying cylinder and
a press roll or press rolls. The pressure exerted at the nip causes the wet web
to stick to the polished surface of the hot cylinder, and it passes round the
cylinder to the reel.
The cylinder is the most important part of the machine, is made of cast
iron, or a mixture of iron and steel, chromium, etc., and is from 8 to 15 feet
in diameter. The surface must be entirely free from blemishes of any kind if
perfect paper is to be made, as any holes or depressions or fbt places will seriously
affect tie surface of die paper. It should also be capable of taking on a good
'skin' or surface to which dust and fluff from the web will not adhere; or if
it does adhere, should clean easily at the doctors.
The cylinder must at all times be absolutely dean and smooth if the beautiful
mirror-Hke gloss, so necessary to the majority of M.G. papers, is to be main-
tained.
These large cylinders are no doubt very difficult to cast, but a really good
one is worth almost anything to the mill which possesses it.
On most machines the cylinder is fitted with a hood or cover, which
fits closely round the surface of the cylinder for about three-quarters of
its circumference. Under this hood there are, on some machines, a series of
steam-pipes so placed that they are very close to the web of paper as it passes
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