The wooden machine in Fig. 89 costs from 350 to 400 francs; the Dupuy machine costs 600 francs and weighs 400 kilos - that is to say, nearly the same as the other. The output, as we have said, is from 300 to 400 bricks per hour; labour is always paid by piece-work, at an average of 4 to 5 francs per thousand.
This kind of machine is extensively used in the neighbourhood of Paris, Rouen, Amiens, Saint-Quentin, etc., as well as abroad. But it must not be forgotten that all kinds of clay cannot be used with them. Weak vegetable moulds only can be treated, as the strong clays and potter's clays stick to the moulds and cannot be demoulded.
To a certain extent the stamping presses, which we shall describe in connection with high-class bricks (Figs. 158-166), may be used for moulding certain raw clays coming from the pit. The clay is prepared as in the case of the preceding machines. It should be as fine as possible, without lumps, and neither too damp nor too dry. The press-mould is movable. By means of a handle it is brought forward in front of the table, there it is filled, then returned to its former position, and with a rapid, violent blow the lever is depressed; the cap falls sharply and compresses the clay. The latter flies back and brings the lever forward again. The workman takes hold of it and replaces it in its former position. During this movement the movable bottom of the mould is taken away and the brick comes out. The output hardly reaches 200 to 250 bricks per hour.
Fig. 94. Hand Press for moulding Coarse Clay (Chambrette Bellon).
This inconvenience does not exist in the perfected press shown in Fig. 94. The moulds, three in number, are fixed on a plate which revolves round one of the uprights of the machine. Compression is no longer exerted by the action of the cap only, but the lever acts simultaneously on the movable bottom and the cap, and so the two faces of the brick are equally pressed. The motion of the lever produces at the same time an automatic demoulding by means of a cam and jointed lever. The plate is kept by gear in its position of compression.
The working of the machine is simple. While a boy takes away the brick which has just come from,the mould, another fills the empty mould, and a third workman turns the plate and works the lever.
The remarks we have made on these lever presses apply to the preceding machines, the use of which can only be interesting in certain special cases.
For complete description of these machines see paragraph on Stamping of Bricks (p. 161).
Fig. 95. Press for making Bricks from Dry Clay (Johnson).
The machines used in this kind of moulding are of American or English construction; they act by strong compression in moulds on dried, pulverised, and moistened clay.
The pressure on each brick exercised by the pistons is as much as 125 tons! Therefore these powerful machines, a model of which is represented in Fig. 95, are constructed in a very solid manner. They absorb much power, and for a production of
2500 to 3000 bricks an hour a 25 horse-power steam-engine is required.
The number of moulds varies from 2 to 6, and the bricks go from the machine straight to the kiln.
In the Whittaker machine (Fig. 96) the pressure is also exerted by a piston, but each brick receives two compressions successively.
Fig. 97 represents a section of the machine. The powder arrives from the upper storey by a conduit furnished at its lower end with a hose which takes the clay into a mould. The mould when full is pushed under a piston, which makes a first compression; then the brick is pushed under the second piston while the first mould is filled with clay. The second compression completes the brick, which, when demoulded, is placed on an endless band by the same motion which brings the clay to be pressed under the first piston.
Fig. 96. Press for making Bricks from Dry Clay (Whittaker).
The bricks thus formed by great pressure require no drying; they are taken direct to the kiln,
Fig. 97. Section of the Parts of the Whittaker Press.
The mechanism moving the different parts of the machine is easily understood by the annexed figures.
Fig. 98. Press for making Bricks from Dry Clay, with Revolving Plate (Boulet).
The Boulet machine (Fig. 98) differs from the foregoing in the arrangement of the moulds which are placed in pairs on a movable table. They are rilled by hand; during the compression the table is motionless, then it turns automatically, and the pressed bricks are at the same time removed from the moulds.
Another machine with a turning table is represented by Fig. 99. A special arrangement in this machine permits of bricks with hollows perpendicular to the surface being made by it.
The principle of these machines consists in the compression of the clay, which has been suitably prepared and made into a more or less firm paste, into a space one end of which is formed of a special piece pierced with a hole and called a die. Through this opening, which has various shapes and sizes, the clay issues in the form of a continuous smooth-faced prism, and is received on to a special waggon, where it is cut into the required lengths. There are three essential parts in these machines: 1. The machine proper, simple or with attached apparatus for the previous preparation or crushing of the clay,
Fig. 99. Press with Revolving Table (Bemhardi Sohn).
2. The die, a very important instrument, which gives the shape to the bricks.
3. The cutter, which divides the prism of clay into bricks when it comes from the die.
Each of these parts requires a special description, for the parts and their arrangement, although the same result is aimed at, are different with different makers.