The process is of no use for ordinary bricks, although many manufacturers subject them to it.
Fig. 168. Universal Stamping Press (Jager).
In choosing a machine, lightness is desirable, but rigidity must not be neglected. The double guiding of the cap and the easy lubrication of the frictional parts must be taken into consideration as well as the distance apart of the rods; this should be great enough for bricks of at least 0.30 metres (1 foot) to be stamped.
Cast-iron moulds give more clean-cut shape than those lined with bronze, and they do not wear out so quickly. But with the former the removal of the brick requires a lubrication of all the faces of the mould, while with bronze-lined moulds it is sufficient to sprinkle the bricks with powdered dry clay, and this is done when they are in stacks or on the waggon when brought up to be stamped.
Notwithstanding the necessary lubrication, which increases the cost of stamping, owing to the oil used (generally resin oil), and the decreased output (due to time lost in greasing), preference should be given to cast-iron moulds if we wish to have fine products. The same press can stamp several kinds of products;it is sufficient to change the mould, the bottom plates, and the cap.
Fig. 169. Friction Stamping Press (Jager).
We have already stated that bricks cannot be stamped immediately after they come from the expression machine; they must be left to gain firmness, until they are in a fit state, neither too hard nor too soft, to take the shape of the mould. When space allows, they are placed on edge on a level tiled floor, or on boards, whence they are afterwards removed to the press. This can easily be moved, and is placed in a convenient position. It is better to carry out the process on the ground-floor on account of the shocks produced by the action of the press.
If space is limited, the bricks are placed on shelves, and when they are ready to be stamped, the press is brought near them.
A workman takes the bricks from the shelves, and puts them in the mould.
Name of Maker:
Weight of machine in kilos
Price in francs with mould complete
Lever and cam.
Lever and cranks.
Special press without., mould.