109

"The steam cylinder is of course omitted, and the hydraulic press, as described, is replaced by a double-acting press, the two parts of which are put in communication by a valve chamber with a spring poppet and a return valve."

STEAM PRESSES WITH OPEN FORMS.

The general principle of the continuous presses consists in compressing the plastic material in a form open at both ends by means of a stamp moving backward and forward. As the stamp moves backward a certain amount of the mixture to be compressed falls into the mould; during the forward stroke of the stamp this material is forced against that previously pressed, by which means this is driven still further forward toward the open end of the mould, and then, by automatic appliances or knives, cut into such number of briquettes as the stroke of the stamp will allow. In compressing, the stamp has no other resistance than that offered by the friction of the briquette mass in front of it. This friction is very considerable, and increases with the length of the mould.

The principal machines operating under this system with use of bond in compressing are the Evrard, which uses soft pitch as an agglomerant, and manufactures briquettes of cylindrical form, and the Bouriez, which is built on the same principle, but for brick-shaped briquettes, and is in use in many places in Belgium and Germany, including the cast steel establishment of Krupp.

The advantages claimed for machines of these systems are moderate cost and great simplicity of plant; but a greater power is required for operating them than for machines with closed forms.

The machines for compressing brown coal without bond are also constructed under this general principle.