The extensive destruction of the ordinary cast-hon chairs about fifteen years since, induced Mr. Scrivenor, in 1832, to attempt their formation of malleable iron by the rolling and die-pressing process. The following account we derive from the specification of the patent.
In the preceding Fig. 1, a b represent a pair of cast-iron rolls designed for this object, and put in motion by the usual mechanism employed in iron-works. It will be observed that the series of grooves or indentations in their peripheries correspond with the several shapes which the metal is intended to take in its progress through these rollers, until it at length attains the exact shape required to form the chairs or pedestals. Thus, for example, the grooves at cd must be adapted to receive an ordinary short thick bar of wrought iron, about two feet long, and six inches square, properly heated for rolling. The bar is first passed through the rollers at c d, which causes it to assume the shape shown at j. It is then passed in succession through the other grooves on the rollers at k k, l l, m m, n n, whereby it successively takes the form shown at e f g h. Having thus obtained a long bar of iron of the sectional form shown at n, it is next cut into lengths for chairs, which is effected by the mill shears shown at Fig. 2, which are worked by the engine. These shears are provided with steel jaws to receive the chair as shown at v w, in order that in cutting off the chair it may not be forced out of shape.
The opening between the cheeks of the chair for the reception of the rail are at present left parallel; the next process is therefore to give these parts a more suitable form for holding down the rail. This is effected by making the chair red hot, and placing inside the recess a mandril of the required shape, with which it is again passed through another pair of rolls shown in the annexed Fig. 3; by these the recess is impressed with the required form to adapt it for receiving the intended keys.
We have never seen any of the wrought-iron chairs of the kind just described in use; probably from the difficulty of bestowing upon them that finished form which is requisite, at a sufficiently low price. Although the brittleness of cast-iron seems at first sight to render it an improper substance for chairs, yet a little reflection on the other hand will show that it affords such facilities to the judicious engineer to provide the most effectual remedy to its natural defect, as to render it in our opinion even more advantageous than wrought-iron. The immense breakage of cast-iron chairs a few years since was in a great measure owing to injudicious forms, and not a little to bad execution in the foundries, rather than to the nature of the material. This fact is satisfactorily proved by the perfection of form and superior execution of the cast-iron chairs and fastenings on the South Eastern and Dover Railway, manufactured we understand by Ransome and May of Ipswich, which will be described a few pages onward.