The expression of the clay is performed by a machine of some kind furnished with a suitable die. The transformation of the slab into tiles is effected in various ways. The Joly cutting-table (Figs. 376, 377) is provided with two rollers; the lower one has a projection corresponding to a hollow in the upper one, and the latter has blades fixed longitudinally upon it. When the slab passes between these rollers, it makes them revolve; the projection on the lower roller presses down the paste at regular intervals, thus forming the hook, while the blade cuts the tile to the required length (Fig. 376). The workman has only to take up the tiles and place them on boards (Fig. 377) to be scraped; then they are carried to the drying-sheds. A cutting-table of this kind produces from 1200 to 1600 finished tiles per hour.
Fig. 376. Front View.
Fig. 377. Side View.
Another method, suited to thick tiles, requires a somewhat different die: the prism of clay comes out with a projection in the middle, of the same section as the required hook. The die is arranged either for one tile (Fig. 378), two side by side (Fig. 379), two, one over the other (Fig. 380), or four tiles (Fig. 381).
The special cutting-table (Fig. 382) cuts the prism into slabs of the required length, and, at the same time, another horizontal wire takes off the projecting rib at the surface, leaving a small part which is to form the hook.
Figs. 378 to 381. Dies for Hooked Flat Tiles.
Fig. 382. Cutting-table for Hooked Flat Tiles.
When two tiles come out one over the other, the rollers of the cutting-table have a notch in the middle which allows the lower rib to pass, and there are two horizontal wires to remove the ribs.
These tiles are of different shapes, but are all manufactured in the same manner, by stamping between two plaster or metal moulds of the desired form. A great number of mechanical methods of producing the necessary pressure may be devised; the simplest is the screw press. Cams and levers have also been used, and for large production the presses called " revolver" are utilised.
Fig. 383. Screw Press, worked by Hand (Jager).
There are three classes of machines -
A. Screw Presses : (1) Worked by hand; (2) by steam.
B. Cam and Jointed Lever Presses,
C. Revolver Presses.