THE MANUFACTURE OF BUILDING BRICK. 231 



condition. In order to prepare the clay for disintegration, it is 

 usually stored in sheds for some time before being used, and is then 

 broken up either in a disintegrator or dry pan before passing to the 

 screen. The latter is commonly from 12 to 1 16 mesh. The molding 

 machine consists of a steel frame of varying height and heaviness, 

 with a delivery table about three feet above the ground, and a 

 press box sunk into the rear of it. The charger is connected with 

 the clay hopper by means of a canvas tube, and consists of a 

 framework which slides back and forth over the molds. It is 

 filled on the backward stroke, and on its forward stroke lets the 

 clay fall into the mold box. As the charger recedes to be refilled, 

 a plunger descends, pressing the clay into the mold, but at the 

 same time the bottom of the mold, which is movable, rises slightly, 

 and the clay is thus subjected to great pressure. The plunger 

 then rises, while the bottom of the mold ascends with the freshly 

 molded bricks to a level with the delivery table. These are then 

 pushed forward by the charger as it advances to refill the molds. 



The faces of the mold are of hard steel and heated by steam 

 to prevent adherence of the clay. Air holes are also made in the 

 dies to permit the air, which becomes imprisoned between the 

 clay particles, to escape. If this were not done, the air in the 

 clay would be compressed, and when the pressure was released, its 

 expansion would tend to split the brick. The great pressure 

 necessary to form the clay is generally applied by means of a 

 toggle joint, and 1 to 6 bricks are molded at a time, according to 

 the size of the machine. At Winslow Junction, N. J., and at 

 several localities -in other states, an hydraulic dry-press machine 

 is used. In this the pressure is produced by a pair of hydraulic 

 rams acting from both above and below and is applied gradually. 



The advantages claimed for the dry-press process are, that 

 in one operation it produces a brick with sharp edges and smooth 

 faces. There is practically no> water to be driven off, as the 

 clay has been pressed in a nearly dry condition, hence drying 

 tunnels can be dispensed with, although sometimes used. When 

 hard burned, dry-pressed bricks are as hard as others, as can be 

 seen from tests of New Jersey brick given on later pages. On 

 account of the method of molding, dry-press bricks usually show 

 a granular structure. 



