246 MODERN PAPER-MAKING
If soft water is available for paper-making, it seems to be much easier to
keep the cylinder clean than if the water is very hard.
The papers made on M.G. machines are very varied in character and uses,
and the following are some of the most common: Pressings, manillas for
envelopes, litho papers for poster work, krafts, sulphite bag papers, common
cap and cheap wrappings, tissues and sealings.
The machine described is the commonest type, but there are many varia-
tions and modifications, of which the following are a selection:
1. An ordinary' Fourdrinier wet end, followed by several small drying
cylinders, which partly dry the paper before it is led to the large cylinder.
The overfelt of this machine receives the paper from the last of the small
cylinders, which are not usually very hot, and takes it to the cylinder press.
The felt is damped just before the press nip.
This arrangement enables higher speeds to be run, as the big cylinder is
relieved of some of the drying, and it does not have any detrimental effect
upon the high surface which is obtained on the paper.
2. The *lick-up* machine may have either a vat or Fourdrinier wet end,
but it does not possess a wet press. Instead, the wet felt passes round the top
couch rolls, and the web is transferred to it at the couch, carrying it to the
cylinder press and depositing it on the cylinder. The felt acts as wet felt and
overfelt, and is usually passed through a washer to cool and clean it on its return
journey from the cylinder to the couch roll. On this type of machine the under
side of the web sticks to the cylinder and receives the polished surface.
If the wet end is of the vat type, as described in the following section, the
web is made on the wire drum and transferred to the wet felt and thence to
the cylinder.
3. A combination of both the above-mentioned types makes duplex paper
in the following manner: The Fourdrinier wire part forms one side of the
sheets and the other side is made on a cylinder mould situated above the wet
end. The second web is led by a felt into the couch of the Fourdrinier wet
end and the two webs are united, couched and pressed together at the same
time, thus forming a duplex sheet or thin board. They are subsequently dried
on the cylinder in the usual way.
4. Heavy boards may be made by having a battery of cylinder moulds
exactly the same as those for the ordinary board machines, as described in
tfoe following pages,
It will be readily understood that the drying power of an M.G. machine
is very limited compared to some Fourdrinier machines with their long double
tiers of drying cylinders. For this reason it is usual to work the cylinder very
hot linked, as k>t as the paper can stand without blistering.