These machines, which imitate hand work, operate upon soft clay previously prepared by a vertical or horizontal pug-mill attached to them. The wooden mould, which has six or seven compartments, is placed under the press, and when it is full is automatically expelled; a workman smooths the surface of the bricks with a scraper and passes the mould to the demoulder;the latter places the bricks on a board, which is carried to a drying ground or room. The empty mould is dipped in water and put under the press again. These machines, largely used in America, are suitable for thin clays which draw badly.
Fig. 88. Vertical Machine for Soft Paste worked by Horse-gear.
With a horse the machine in Fig. 88 (2800 fr.) produces 600 to 900 bricks per hour; with two horses (2500 fr.) from 1200 to 1800 bricks. The machine (Fig. 87) which is worked by steam power (6300 fr.) produces from 3000 to 5000 bricks.
The oldest of these, and the one always used in a large number of works which make bricks of vegetable mould (lehm or tableland ooze), is composed (Fig. 89) of a low and very thick wooden table, pierced with a square hole at one end. Into this hole a copper double mould (Fig. 90) is introduced and fastened to the table by bolts which pass through the thickness of the table. The bottom of each mould is closed with a T-shaped piece of wood (Fig. 91) called chandelle, the top of which is covered with a copper plate. The two pieces are moved up and down smoothly in the mould by rack-work connected .with two pinions worked by a winch. This motion is guided by an iron rod passing through each of the two T-pieces and resting on a strong cross-bar which joins the two uprights of the machine.
Fig. 89. Lever Press for moulding Vegetable Moulds.
Fig. 90. Cap and Double Mould.
Fig. 91. - "Chandelle".
A first lever, movable round an axis, is connected by a chain to another lever, which is attached at one end to one foot of the table. This chain holds the lever by a collar which slides on an iron guide fixed to the lever. A wooden counterpoise called a mouton, which is pivoted on an axis, rests on the horizontal lever and keeps them both raised.
The working of this machine is simple and requires two men, at the most three. The clay is prepared as we have said. The workman who manages the lever takes a shovelful of this clay and throws it into the two moulds; the latter must not only be full but must overflow. He puts aside his shovel quickly, and, with the aid of his comrade, compresses the clay by striking it with his fists; then with a quick motion he takes the excess off the moulds, one corner of which he discloses in order that the man who takes the cap (Fig. 90) may be able to see the place where he is to put it. Meanwhile the other man has placed himself at the end of the lever and leans upon it. The pressure is transmitted to the clay by the lever called brebis. After having given two or three pulls, the moulder quits the lever, which is drawn back by the counterpoise called mouton. The demoulder takes off the cap and turns the winch; the bricks come out of the mould, and the demoulder takes away the one on his side and puts it on a barrow with a platform which contains about fifty of them. His comrade puts his on the brebis, whence the other takes it to place it on the barrow. Meanwhile the moulder has taken a handful of powder from the table and has sprinkled the moulds, - the winch, left to itself, having been returned to its first position by the weight of the movable pieces forming the bottom of the moulds, - then he throws another shovelful of clay into these latter, and the process continues as before.
When a barrow is full the moulder pushes it forward a few metres and substitutes an empty one. The other workman has meanwhile been bringing as near as possible to the machine the clay which has been drawn in advance to replace that used. When the second barrow is full, the two moulders expose their productions in drying-places, generally open-air ones. Sometimes this part of the work is done by a third man who, in the intervals, prepares and draws the clay. These three men are able to make from 300 to 400 bricks an hour.
The length of the chain is so adjusted that the end of the lever touches the ground when the strongest pressure is used. This method of manufacture, simple as it is, requires a certain skill to be quickly carried out. Especially is this the case in putting on the cap, for it must at first trial be placed just over the moulds, and this is difficult owing to the excess of clay on the table. If it is put on badly one corner of the plates will strike against the mould, and compression cannot take place; it will have to be readjusted, and time will be lost. The moulder, too, must have the knack of putting the same quantity of clay in each shovelful, in order that the bricks may have a uniform thickness. The fulling of the clay should be uniformly done, otherwise the bricks will be thicker at one end than the other. Bricks made in this way require to be fired thoroughly to acquire cohesion, and never, even when res tamped, have the tenacity or the quality of blended bricks.
The machine above described has been modified in different ways. The framework is made of cast-iron (Fig. 92), the cap is hinged and held by a stirrup; the pressure instead of acting from above acts from below. The adjustment of the cap is thus simplified, and can be done by a young man.
Fig. 92. Lever Press with Cast-iron Frame (Boulet).
Fig. 93. Lever Press with Cast-iron Frame (Dupuy).
In the Dupuy machine also (Fig. 93) the cap is movable about a hinge. The lever by its special position makes the operation more rapid, for the workman, instead of having to go from the moulds to the end of the lever, has only to turn round, and thus output is increased.
Another improvement is in the dcmoulding. In ordinary machines, in order to keep the bottom of the moulds at the level of the platform, the workman is obliged to hold with his knee the winch which controls the pinions.
In the Dupuy machine the demoulding is done by the lever which, in the figure, the workman is holding in his hand. The bottom of the moulds is held by a special catch, and when the bricks are taken out the assistant, by means of the little lever at his side, releases the catch and the bottom falls into its place again. The moulds are of bronze, as also are the plates of the cap and bottom. As these latter wear out rather quickly in consequence of the friction, a hollow is formed between them and the sides of the mould, through which a little clay is forced under compression, and this makes seams in the bricks. It would be troublesome to be always renewing the plates. Therefore they are made of malleable bronze, and every two or three weeks they are beaten on an anvil to lengthen and broaden them, then they are fixed to the mould by screws or bolts.
The moulds also get worn; the only inconvenience of this is the progressive increase in the dimensions of the brick; when it becomes too large, the moulds are renewed.