On the Economy of Machinery and Manufactures eBook

This eBook from the Gutenberg Project consists of approximately 313 pages of information about On the Economy of Machinery and Manufactures.

129.  Coins and medals.  The whole of the coins which circulate as money are produced by this mode of copying.  The screw presses are either worked by manual labour, by water, or by steam power.  The mint which was sent a few years since to Calcutta was capable of coining 200,000 pieces a day.  Medals, which usually have their figures in higher relief than coins, are produced by similar means; but a single blow is rarely sufficient to bring them to perfection, and the compression of the metal which arises from the first blow renders it too hard to receive many subsequent blows without injury to the die.  It is therefore, after being struck, removed to a furnace, in which it is carefully heated red-hot and annealed, after which operation it is again placed between the dies, and receives additional blows.  For medals, on which the figures are very prominent, these processes must be repeated many times.  One of the largest medals hitherto struck underwent them nearly a hundred times before it was completed.

130.  Ornaments for military accoutrements, and furniture.  These are usually of brass, and are stamped up out of solid or sheet brass by placing it between dies, and allowing a heavy weight to drop upon the upper die from a height of from five to fifteen feet.

131.  Buttons and nail heads.  Buttons embossed with crests or other devices are produced by the same means; and some of those which are plain receive their hemispherical form from the dies in which they are struck.  The heads of several kinds of nails which are portions of spheres, or polyhedrons, are also formed by these means.

132.  Of a process for copying, called in France clichee.  This curious method of copying by stamping is applied to medals, and in some cases to forming stereotype plates.  There exists a range of temperature previous to the melting point of several of the alloys of lead, tin, and antimony, in which the compound is neither solid, nor yet fluid.  In this kind of pasty state it is placed in a box under a die, which descends upon it with considerable force.  The blow drives the metal into the finest lines of the die, and the coldness of the latter immediately solidifies the whole mass.  A quantity of the half-melted metal is scattered in all directions by the blow, and is retained by the sides of the box in which the process is carried on.  The work thus produced is admirable for its sharpness, but has not the finished form of a piece just leaving the coining-press:  the sides are ragged, and it must be trimmed, and its thickness equalized in the lathe.

Of copying by punching

133.  This mode of copying consists in driving a steel punch through the substance to be cut, either by a blow or by pressure.  In some cases the object is to copy the aperture, and the substance separated from the plate is rejected; in other cases the small pieces cut out are the objects of the workman’s labour.

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On the Economy of Machinery and Manufactures from Project Gutenberg. Public domain.
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