CLAYS or NEW YORK 665 



The molding macliine consists of a massive frame of forged steel 

 about 8 feet high. 3 feet up from the ground is the delivery- 

 table, into which the press box is sunk. Connected with the hopper 

 above the machine by means of two canvas tubes is the charger. 

 This slides back and forth on the table. It is filled on the backward 

 stroke and on its forward stroke lets the clay fall into the mold 

 bos. The charger then recedes to be refilled and at the same time a 

 plunger comes down pressing the clay into the mold. As the upper 

 plunger descends, a lower plunger which forms the bottom of the 

 mold moves upward, so tliatthe clay receives pressure from above 

 and below. The upper "^plr.'ger then rises, and the lower plunger 

 ascends till the lower suiiace of the brick is even with the lable. 

 Again the charger comes forward, shoving the green brick for- 

 ward on the table, the lower ^lunger drops and the mold box is 

 once more filled with clay. Th faces of the mold are of hard steel 

 heated by steam to* prevent adnerence of the clay. Air holes are 

 also made in the dies, but are apt to become clogged up. The pres- 

 sure from above is applied by a toggle-joint arrangement, and it is 

 maintained by the manufacturer - f the Boyd dry clay presses that 

 the pressure exerted on each brick is 150 tons. One to six bricks 

 can be molded at a time, according to capacity of machine. On a 

 four brick machine about 20,000' are molded in a day. 



The hydraulic dry press machine is in use at Oanandaigua, 

 IsT. Y. In this, the pressure is produced by a pair of hydraulic rams, 

 acting from both above and below. The pressure delivered at first 

 is light, being only 240 pounds the square inch (Missouri clays. 

 Mo. geol. sur. 11: 502), and this is followed by a pressure of 

 3700 pounds, which completes the pressing. 



A difficulty encountered in the dry press and semi-dry press 

 methods is the imprisonment of air in the brick under pressure, 

 with the result that the compressed air tends to split the brick when 

 the pressure is released. This can be obviated partly by allowing 

 the plunger to descend very slowly, giving the air time to escape, 

 and also by leaving small vent holes in the top and bottom of the 

 mold. 



