Except in a few cases it is preferable to submit the clay to a previous pugging before sending it to the cylinder machine. Thus a good installation is one in which the two machines are so arranged that the clay passing from the pug-mill is at once absorbed by the moulding machine.
Fig. 108 represents an installation of this kind composed of a pug-mill (Fig. 60) and the cylinder machine of Fig. 101.
Another installation of the same kind (Fig. 109) combines the pug-mill of Fig. 62 and the machine with propelling cylinders of Fig. 104.
Any kind of clay can be treated by an installation of this type, provided it is friable and contains no very hard particles which would require special crushing. The mixture of rich and shortening clays is carried out in the pug-mill, as are any other mixtures required,
Fig. 108. Cylinder Expression Machine combined with Pug-mill (Joly).
We stated, when speaking of pug-mills, that the clay underwent, by the action of the knives in those machines, a certain pressure which drove it through the orifice of issue, this expulsion being facilitated by the presence near that orifice of screws of various forms.
This being so, if the orifice is provided with a die and the parallelepiped of clay is received on a cutting-table, we have a brick-making machine. This is a most simple machine, giving good results with clays which are free from all foreign substances, and easily worked. These machines are called vertical or horizontal according to the position of the pug-mill.
These machines do not differ from pug-mills of the same type (see p. 74). The orifice of issue is provided with a die, and a cutting-table is joined to the machine. Theoretically any pug-mill can be made into a brick-making machine; practically, as we said above, special clays are required to get good results under these conditions.
Fig. 109. Cylinder Expression Machine combined with Pug-mill (Sachsenberg).
Fig. 110 represents a Whitehead pug-mill with two issues, transformed into a brick-machine, and worked by a horse-gear fixed to the shaft of the mill. In this way power is more economically applied, but it must not be forgotten that the supply of clay and removal of bricks are rather difficult in these machines on account of the horses.
These are the same machines but more powerful and of greater output.
In the Whitehead machine (Fig. 111) the gearing is separate, but there are simpler arrangements in which the pug-mill supports the driving-gear.