The invention of the Hoffmann continuous kilns, by perfect-ing to such a degree the firing processes, has also been one of the causes of the development of machinery in brickworks. Economy cannot be a factor favourable to the development of machinery, for if, in works having a large output, the cost of mechanical manufacture is no larger than that by hand, in works of moderate size, where there is a long cessation of work in the winter, interest and sinking-fund are factors to be taken into consideration. But what has gained the day for machines is that they allow of the manufacture of articles impossible to make by hand.
Per thousand: 3500/10,000 = 0 fr.35
Thus in the great centres of consumption, England, Germany, America, where millions of bricks are used annually, they are nearly all made by machinery. In France also numbers of brick and tile works produce by machinery.
The machines that have been invented for the mechanical manufacture of bricks, are as numerous as they are varied; but if we consider how a parallelopiped, regular like a brick, can be made out of clay, we must come to the conclusion that two processes only can be utilised: the first consists of compressing a certain quantity of clay by some means or other in moulds of the required shape; this is the principle of machines working by compression. The other process consists of forming out of clay suitably prepared a long prism having two of the dimensions of the brick, and of cutting it afterwards at regular intervals to get the third dimension. It is in this way that machines working by expression act.
In practice these principles may be applied in many different ways, hence we have a variety of machines possessing one common principle.
In classifying machines we must note the manner in which they carry out one of these principles, and also the degree of dampness of the paste used; it is evident that machines intended for treating firm or semi-firm clays are not suited for treating hard clays, and vice versa.
This being so we have the following classification: -
I. Machines working by compression
1. On soft clay.
2. On semi-firm, or firm clay
By gradual pressure.
3. On dry clay.
II. Machines working by expression
With semi - firm or firm clay
By propelling cylinders.
By pug-mill with expelling screws
With hard clay.