Figs. 77.

The Manufacture Of Malleable Iron Continued 10049

78.

The Manufacture Of Malleable Iron Continued 10050

70.

The Manufacture Of Malleable Iron Continued 10051

80.

The Manufacture Of Malleable Iron Continued 10052

81.

The Manufacture Of Malleable Iron Continued 10053

Figs. 77, 78, 79 and 80, represent four amongst numerous other sections of railway iron; these bars are produced in rollers turned with counterpart grooves; as before, the shaded portions represent fragments of the lower rollers, and the upper rollers are supposed to occupy the spaces immediately adjoining the section of the rails. For these also, three, four, or more grooves, varying gradually from that of the roughly prepared bar, to that of the finished rail, are employed, and this in like manner saves the necessity for adjusting the distance between the rollers during the progress of the work.

All the foregoing rolls are supposed to be concentric, and to produce parallel bars and plates of the respective sections; but in making fish-bellied railway bars, (no longer used,) taper plates for coach springs, and similar tapered works, the rollers whether plain or grooved arc turned eccentrieally, so as to make the works respectively thicker or deeper in the middle, as in fig. 81; this requires additional dexterity on the part of the workman to introduce the material at the proper time of the revolution, upon which it is unnecessary to enlarge.

The general effect of the manufacture of malleable iron is to deprive the cast-iron of its carbon, this is done in the puddling furnace; the original crystalline structure gives way to the fibrous, from the working under the hammer and rollers, by which every individual particle or crystal is drawn out as it were into a thread, the multitude of which constitute the fibrous bar or metallic rope, to which it has some resemblance except in the absence of twist. The rod may now be bent in any direction without risk of fracture; and the superior kinds, even when cold, may be absolutely tied in a knot, like a rope, when a sufficient force is applied.*

Should it however occur that the first operation, or shingling process, were imperfectly performed, the error will be extended in a proportional degree throughout the mass; which will account for the general continuance of any imperfection throughout the bar of iron, or a considerable length of the wire in which the reduction or elongation are further extended; and to which evil all metals and alloys, subjected to these processes of elongation, are also liable.

Malleable iron is divided into three principal varieties, first, red-short iron; secondly, cold-short iron; thirdly, iron partaking of neither of these evils; and which may be so far denominated pure malleable iron.

* One of these ties may be seen at the Architectural Society's Rooms, Lincoln's Inn, and another at the Institution of Civil Engineers. The bars of iron are two inches diameter, and the openings in the loops measure only 6 1/2 by 3 1/2 inches. The ends of the bars were turned through each other whilst hot, forming circles of about three feet diameter, and when quite cold they were gradually drawn to this small size with the hydrostatic press used in proving chain cables, by the gradual application of a force equal to about twenty-six tons. Considerable heat was evolved, sufficient to melt wax placed on the metal, and the friction at the rubbing surfaces was so great as fairly to brighten the metal, although a plentiful supply of grease was applied.

These curious and fine specimens of iron were manufactured and tied at Messrs. Hartford, Davis & Co's Chain Cable Works, Ebbw Vale, South Wales, under the direction of C. Manby, Esq., now Secretary of the Institution of Civil Engineers.

The first kind is brittle when hot, but extremely soft and ductile whilst cold; this is considered to result from the presence of a little carbon. The cold-short withstands the greatest degree of heat without fusion, and may be forged under the heaviest hammers when hot, but it is brittle when cold; this is attributed to the presence of a little silex. The third kind is considered to be entirely free from either carbon or silex, etc, and to be the pure simple metal; but in the general way the characters of iron are intermediate between those described.

From one and a half to two tons of pig-iron, have been used to produce one ton of malleable iron; but the average quantity is now from twenty-six to twenty-seven tons for each twenty tons of produce. The No. 3 cast-iron, called also forge pig, ballast, and white cast-iron, is the kind principally used, as it contains least carbon, the whole of which should be expelled in the conversion of the cast metal into wrought iron.*

It appears to be unnecessary to attempt any minute description of the different marks and qualities of iron; first, as these descriptions have been minutely given in many works, some of which are alluded to at the end of this chapter; and secondly, as in common with most other articles, the quality of iron governs the price. The quantity used by the amateur will be comparatively inconsiderable, he will be therefore disposed to ask for the best article, and to pay the best price.

I will only add, that little can be known of the character of iron from its outside appearance, beyond that of its having been well or ill manufactured, so far as regards its formation into bars. The smith is principally guided by the fracture when he breaks down the iron, that is, when the bar is nicked on opposite sides with the cold chisel, laid across the anvil upon a strip of iron near to the cut that it may stand hollow, and the blows of the pane of the sledge-hammer are directed upon the cut.

The judgment will be partly formed upon the force thus required in breaking the iron; the weakest and worst kinds will yield very readily, when small, sometimes even to the blow of the chisel alone, and will then show a coarse and brilliant appearance, entirely granular or crystalline; this iron would be called very common and bad. If, on the other hand, the iron breaks with difficulty, and the line of separation, instead of being moderately flat, is irregular, or presents what may be called a hilly surface, the sides of which have a fibrous structure, and a sort of lead-coloured or a dull grey hue, this kind will have a large proportion of fibre, which is the very "thew and sinew" of iron, and it will be called excellent tough iron. Other kinds will be intermediate, and present partly the crystalline and partly the fibrous appearance, and their relative values will depend upon how nearly they approach the one or other character.

* Pages, 21 - 23 - 32, Mushet.

Another trial is the extent to which iron, when slightly nicked, may he bent to and fro without breaking; the coarse brittle kind will scarcely bend even once, whereas superior kinds, especially stub, charcoal, and dented irons, will often endure many deflections before fracture, and when nicked on the outside only and doubled flat together, will bend as an arch and partly split open through the center of the bar, somewhere near the bottom of the cut made with the chisel, the entire fracture presenting the beau-tiful fibrous appearance, and dull leaden hue before described. - See Appendix, Note P, page 958 of Vol. II.