When we work on soft or firm pastes, we use the screw or propelling roller machines described on pp. 114 and 123, with a modified die. For hard pastes we must have recourse to the piston machines called "galettieres." Fig. 371 represents a machine of this kind in which two pistons compress the clay alternately in two boxes, having the dies in one face.
M. Dumont, one of the promoters of hard-paste manufacture, has invented a double "galettiere " (Figs. 372 to 375), composed of a cast-iron frame supporting two compression boxes in which move two pistons worked by two cranks fixed to the same extremity of a vertical shaft, the lower end of which has a large toothed wheel driven by a small pinion. All this gear is hidden in such a way that there is no danger in approaching the machine - a very important advantage.
The dies are of conical section, and metallic plates, whose distance can be regulated by small screws, allow of the section of the issuing orifice being altered to suit requirements, or compensate for wearing away.
The clay, having been passed between granulating cylinders, or pugged, is thrown on to a sheet-iron plate, which is pierced with two openings corresponding to those of the compression boxes. When one of the pistons has done its work and returns, it uncovers the orifice of the box, and the clay at once falls into it; the piston continuing its motion compresses the clay and drives it out in the form of a continuous slab, which passes between two rollers held by flanged springs. The lower roller, called the greaser, dips into a little reservoir of oil, and in its rotation lubricates the bottom of the slab. The upper roller, called the cutter, carries one or several blades, the distance of which, measured on the circumference, is equal to the length of a tile. In turning, these blades come in contact with the slab and cut it into the required lengths.
Figs. 372 to 375. Double-action "Gatettierc" (Dumont).
The slabs thus cut are firm enough to be carried in the hand without losing their shape; a boy takes them, and places them in piles on a waggon which carries them to the presses. During this handling, the oil on the bottom of each slab is partly deposited on the top of the one below, and thus both faces become lubricated for stamping.
The advantages of this "galetticre" are: its small volume, its hidden mechanism, the use of one hopper for the two boxes, automatic cutting and greasing.