In works where so many special manufactures have been developed, the arrangement of the building-the design, position, and working of the machinery at present used-must necessarily have been arrived at only by hard-earned experience. The building is constructed of slag-cement coucrete throughout; the main building has 4 floors, the size of which is 46 ft. by 33 ft., whilst the slag-sand stores, gantry, engine-house, lime-house, etc, occupy 97 ft. by 47 ft. The slag-sand is brought from the blast furnaces in large wooden railway trucks, holding between 7 and 8 tons each, and is run up an incline by the locomotive into a gantry. The bottom doors of the trucks are opened, and the slag-sand is dropped or emptied into hoppers below. These hoppers are capable of holding about 600 tons of slag-sand, or storage enough for 1 week for 3 machines, and should be kept constantly filled. From these hoppers it is drawn into large wheelbarrows, and is taken up by a double-acting hoist to the top of the building. This hoist is driven from the main shafting in the mill, and is worked by 2 belts, one crossed, the other open, for the purpose of reversing the cages.
The cages can be made to stop themselves at any floor, and have a self-acting brake to prevent any movement of the cages after the straps are thrown off, the action being most simple and effectual.
The sand-barrows are taken from the hoist at the top of the building, through a passage, and tipped into the hopper which supplies the brick-presses. Selenitic lime is fed into a small hopper, by hand, from a chamber or floor above. At the bottom of these sand and lime hoppers are the measuring apparatus, which accurately measure both the lime., and the sand in the proportions necessary. From the measuring drums the material falls upon sifting and mixing apparatus, from which it falls through the floor into the brick-press. This press has been designed especially for the purpose, and has many new points. It is of immense strength. The pressure is obtained by 2 cast-steel cams, which are fixed upon a forged steel shaft 7 1/4 in. in diameter; this shaft, resting on bearings between 2 strong frames, is put in motion by very powerful double-geared spur-wheels, the first motion shaft having a heavy fly-wheel upon it to steady and equalize the pull upon the strap. The pressure cams act against rollers fixed upon 2 steel cylinders or rams. These rams transmit the pressure, to the moulds under the table. The table is circular, and contains 6 pairs of moulds, so that 4 bricks are pressed at one time, the table remaining stationary during the operation.
At the same time the bricks are being pressed, 2 other pairs of moulds are being filled up with material, whilst the other 2 pairs are delivering up the 4 bricks already pressed at the previous revolution of the cam shaft. The bricks are pushed out of the mould by smaller pistons, which are acted upon by separate cams. The moulds are lined with changeable steel plates 3/16 in. thick, and the sand and lime are fed into 2 pug-mills. These pug-mills are fitted with 6 knives each, so as the more thoroughly to mix and chop the spongy slag with the lime. The table is shifted round by a kind of ratchet motion. Immediately above the pressure-cylinders are 2 pressure-stops, which are held down by the heavy-weighted levers. These levers, therefore, receive the whole pressure put upon the bricks; and in case there should be too much sand getting into the moulds, they simply lift up and relieve the strain. The weights can be weighted at option, and thus form an exact gauge of the pressure upon the bricks. The moulds are generally filled so as just to lift the levers in ordinary work.
The filling is easily regulated by the set of the knives on the pug-shafts, which press the material into the mould, and one side of the pug-mill cylinder is made to open, so that the knives are accessible at any moment.
The pug-mills are filled by means of measuring and mixing apparatus placed on the floor immediately above the brick-press. The mixing and measuring apparatus is very simple and efficient, and works without trouble.. The slag-sand is tipped into a hopper by large barrows, which are lifted up by a hoist. At the bottom of this hopper there is a revolving cylinder, with ribs cast upon it, which, revolving under the hopper, carries a certain thickness of sand, previously regulated to the requirements of the press. The slag then falls upon a sieve, which separates any large pieces in a solid state, and at the same time allows the sand to fall through the sieve like a shower. The lime is fed into a separate hopper, and is regulated by a feed-roller of smaller size; it passes down a shoot, which forms part of the slag-sand sieve, where it meets the shower of sand, falling together with it - thus getting thoroughly mixed.
On the right side of the slag gantry and hoppers is the mill for preparing the selenitic lime. The lime, after being ground under edge-runners, is passed through a sifting apparatus, the wire of which has 24 meshes to the inch; it then falls into a hopper, is taken by barrows through a passage to the hoist, and lifted to the lime chamber before mentioned. In a line with this mill, and parallel with the slag gantry, are the stores for the lime, gypsum, and iron oxide; whilst behind the lime-house are the engine and boiler.
The hardening-sheds are 3 in number, and should be each about 100 ft. by 40 ft. The floor must be perfectly smooth and level, as an uneven floor spoils the bricks. The sheds should have plenty of ventilation, and require to be cool in summer. Great care is necessary in stacking these bricks; as they come off the barrows, they are placed on edge quite close together, and stacked 6 in height, and when once here in position, there is little or no loss afterwards.