The fact that rolling is so much cheaper than forging has led engineers to design their pieces so that they can be made by rolling, i.e. to make them straight and of uniform cross section. It is for this reason, for instance, that railroad rails are of constant uniform section throughout their length, instead of having those parts of their length which come between the supporting ties deeper and stronger than the parts which rest on the ties. When, as in the case of eye bars, it is imperative that one part should differ materially in section from the rest, this part may be locally thickened or thinned, or a special part may here be welded on. When we come to pieces of very irregular shape, such as crank-shafts, anchors, trunnions, &c., we must resort to forging, except for purposes for which unforged castings are good enough.
 | |
| Fig. 37.—Steam Hammer. | |
A, Round bar to be hammered. B, Anvil. C, Anvil block or foundation. D, Falling tup. | E, Steam piston. F, Piston-rod for lifting tup and driving it down. G, Steam cylinder. |
131. Forging proceeds by beating or squeezing the piece under treatment from its initial into its final shape, as for instance by hammering a square ingot or bloom first on one corner and then on another until it is reduced to a cylindrical shape as shown at A in fig. 37. As the ingot is reduced in section, it is of course lengthened proportionally. Much as in the smith’s forge the object forged rests on a massive anvil and anvil block, B and C, and is struck by the tup D of the hammer. This tup is raised and driven down by steam pressure applied below or above the piston E of the steam cylinder mounted aloft, and connected with the tup by means of the strong piston-rod F. The demand for very large forgings, especially for guns and armour plate, led to the building of enormous steam hammers. The falling parts of the largest of these, that at Bethlehem, Pa., weigh 125 tons.
The first cost of a hammer of moderate size is much less than that of a hydraulic press of like capacity, as is readily understood when we stop to reflect what powerful pressure, if gradually applied, would be needed to drive the nail which a light blow from our hand hammer forces easily into the woodwork. Nevertheless the press uses much less power than the hammer, because much of the force of the latter is dissipated in setting up useless—indeed harmful, and at times destructive—vibrations in the foundations and the surrounding earth and buildings. Moreover, the effect of the sharp blow of the hammer is relatively superficial, and does not penetrate to the interior of a large piece as the slowly applied pressure of the hydraulic press does. Because of these facts the great hammers have given place to enormous forging presses, the 125-ton Bethlehem hammer, for instance, to a 14,000-ton hydraulic press, moved by water under a pressure of 7000 ℔ per square inch, supplied by pumps of 16,000 horse power.
Table IV.—Reduction in Cost of Iron Manufacture in America—C. Kirchoff.
| Place represented. | Operation represented. | Period covered. | Cost, Profit and Production, at End of Period in Percentage of that at Beginning of Period. | |||||||
| From | To | Cost. | Profit per Ton. | Production per Furnace &c., per Day. | ||||||
| Ore. | Fuel. | Labour. | Total. | Total excluding raw Material. | ||||||
| A large Southern Establishment | Manufacture of Pig Iron | 1889 | 1898 | 79 | 64.1 | 51.9 | 63.4 | .. | 47.9 | 167.7 |
| North-eastern District | ” ” | 1890 | 1898 | 103.7 | 97 | 61.1 | 65.8 | .. | 33.9 | 163.3 |
| Pittsburg District | ” ” | 1887 | 1897 | .. | .. | 46 | .. | 44 | .. | .. |
| Eastern District | Manufacture of Bessemer Steel Ingots | 1891 | 1898 | .. | .. | 75 | 64.39 | .. | .. | 107 |
| Pittsburg | ” ” | 1887 | 1897 | .. | .. | .. | .. | 52 | .. | .. |
| Not stated | Rolling Wire Rods | 1888 | 1898 | .. | .. | .. | 63.6 | .. | .. | 325 |
132. Statistics.—The cheapening of manufacture by improvements in processes and machinery, and by the increase in the scale of operations, has been very great. The striking examples of it shown in Table IV. are only typical of what has been going on continuously since 1868. Note, for instance, a reduction of some 35% in the total cost, and an even greater reduction in the cost of labour, reaching in one case 54%, in a period of between seven and ten years. This great economy is not due to reduction in wages. According to Mr Carnegie, in one of the largest American steel works the average wages in 1900 for all persons paid by the day, including labourers, mechanics and boys, were more than $4 (say, 16s. 6d.) a day for the 311 working days. How economical the methods of mining, transportation and manufacture have become is shown by the fact that steel billets have been sold at $13.96 (£2, 17s. 8d.) per ton, and in very large quantities at $15 (£3, 2s.) per ton in the latter case, according to Mr Carnegie, without further loss than that represented by interest, although the cost of each ton includes that of mining 2 tons of ore and carrying them 1000 miles, mining and coking 1.3 tons of coal and carrying its coke 50 m., and quarrying one-third of a ton of limestone and carrying it 140 m., besides the cost of smelting the ore, converting the resultant cast iron into steel, and rolling that steel into rails.
Table V.—Reduction in Price of Certain Products.
| Date. | Yearly average Price in Pennsylvania, gross tons. | ||||
| Bar (Wrought) Iron. | Wrought Iron Rails. | Steel Rails. | No. 1 Foundry Pig Iron. | ||
| 1800 | $100.50 | Hammered | |||
| 1815 | 144.50 | ||||
| 1824 | 82.50 | ||||
| 1837 | 111.00 | ||||
| 1850 | 59.54 | Best refined rolled | $47.88 | $20.88 | |
| 1865 | 106.46 | 98.62 | $158.463 | 46.08 | |
| 1870 | 78.96 | 72.25 | 106.79 | 33.23 | |
| 1880 | 62.04 | 49.25 | 67.52 | 28.48 | |
| 1890 | 45.83 | 25.182 | 31.78 | 18.41 | |
| 1898 | 28.65 | 12.392 | 17.62 | 11.66 | |
| 1900 | 44.00 | 19.512 | 32.29 | 19.98 | |
| 1906 | .. | 23.032 | 28.00 | 20.98 | |
| 19081 | 31.00 | 18.252 | 28.00 | 17.25 | |
1 July 1st.
2 Old. i.e. second-hand wrought iron rails.
3 1868.