CEMENTING FURNACES.
63
carry plates 8 metres (26 ft. 3 in.) long and 3.500 metres
(11 ft. 6 in.) wide, or several plates of smaller dimensions.
When plates are subjected to the cementing process,
after having been moulded to template, they are placed
one above the other with spaces between them, which
constitute gas chambers. A cast-steel frame is put between
When the furnace has been préparée!, the plates are
put in and the openings are closed with firebricks.
the gas pipes are then fixed, openings being provided for
this purpose in the furnace walls. These pipes, or tuyeres,
are of copper, and are kept cool by a stream of water,
i Each one is fitteel with four passages—one for the gas
Fig. 143. 2,000-Ton Hydraulic Forging Press. (See page 60.)
each pair of plates ; this frame completely encloses the gas
chamber ; and to prevent any gas escape, an asbestos strand
is fitted between the plates and the frame. The sides of
the frame, which correspond with the length of the furnace,
are drilled and fittod with gas pipes ; tliese are placed about
20 in. apart. On the hearth are placed steel blocks, which
carry the plates to be treated. The outside surfaces of tlie
plates are covered with sheet iron, in order to prevent
oxidation.
miet, one for the water inlet, the third for the water outlet
and the fourth for the outlet of the gas when it has re-
mained some time in the gas chamber. Three branches
are connected to the collecting pipes by means of india-
rubber tubes. This arrangement suits for all the thick-
nesses of plates, as the flexibility of the connecting tubes
allows of advancing tlie tuyeres more or less deeply into
the furnace, accord ing to the size of the plates. The part
of tlie tuyere which penetrates the furnace has a fireproof