616 



NAVY, UNITED STATES. 



The relative advantages of these two meth- 

 ods are still only in part decided. In this 

 country opinion and practice have favored the 

 making of thin plates by rolling, since in such 

 plates homogeneity of structure and uniformity 

 of strength are less likely in this way to be sacri- 

 ficed, and the manufacture is much more rapid ; 

 while for thick plates, in order to secure close 

 interlacing of the fibres and uniform tenacity, 

 working under the hammer has been preferred. 

 The thin rolled plates are formed from bar 

 iron or blooms, produced in the usual manner. 

 The blooms for the thick plates are usually pro- 

 duced from " scrap iron," selected, but of mixed 

 description, piled in fagots of a convenient size, 

 brought to a welding heat in a furnace, and re- 

 duced under the steam hammer to a solid mass. 

 Several of these blooms are then laid in a pile, 

 four or more layers deep, and successively 

 crossing each other in length, conveyed in -this 

 condition into a large furnace in which they 

 are again heated until the whole becomes high- 

 ly malleable, and under the steam hammer are 

 then welded into a portion of a plate ; and ad- 

 ditions are made in like manner to one end of 

 this, until the material requisite for a single 

 plate has been in this way united. The plate 

 so produced can be of almost any size desired, 

 and it is finally brought to more uniform con- 

 dition and surface by one or more heatings 

 followed by working under the hammer. The 

 plates of the Roanoke, forged and built up in 

 this way, were of a usual length of 12 to 15 ft., 

 and width of about 3 ft., their thickness gen- 

 erally 4r, inches, and their weight 4,000-7,000 

 Ibs. Such a plate is a sort of oblong plank of 

 iron: other plates of irregular outline required 

 for special parts of the ship's sides are shaped 

 by appropriate machines. 



These plates are next drilled for the bolts, 

 and those requiring it are also bent to fit the 

 part to which they are to be applied. By 

 means of " templets," or fac similes, in thin 

 board, marked with spots corresponding to the 

 holes already bored in the wooden body, or 

 drilled (as the case may be) in the parts of the 

 iron hull upon which they are to be fastened, 

 the successive courses of plates, numbered in 

 their proper order, are then marked for the 

 bolt-holes and drilled ; after this the holes are 

 usually " countersunk," in order, that the bolt- 

 head may enter so as to stand even with the 

 outer surface. The plates are finally bent to 

 the shape they may be required to have, by the 

 action of powerful hydrostatic presses. The 

 required curvature is readily given to the plates 

 for upright turrets, by placing them one at a 

 time between a curved bed upon the upper sur- 

 face of the movable platform of the hydrostatic 

 press, and a fixed frame of like curvature above, 

 and forcing the plate upward until it is shaped 

 between the two, as in a mould. These plates 

 are, at different works, bent either cold or 

 heated. The plates for the sides of the ship 

 require to be bent to a great variety of curves, 

 and the expense of preparing a corresponding 



number of moulds is obviated by employing an 

 iipper and a lower " die," each consisting of a 

 series of strong iron bars, these being severally 

 capable of being raised or depressed, as re- 

 quired, and at either end, by the action of stout 

 screws which fix their positions. Above the 

 upper die, which is movable, is a heavy iron 

 casting to give it weight, while the lower die 

 is stationary. A templet, representing any re- 

 quired plate, being placed between the two 

 dies, the upper and lower sets of bars have 

 their ends raised or lowered by the screws, 

 until each bar exactly fits upon its own part of 

 the templet ; and the upper die being then 

 raised to some distance, and the templet re- 

 moved, the plate, already heated to a highly 

 soft and ductile condition, is placed upon the 

 lower die ; the upper being then let fall, the 

 weight with which it is loaded suffices at once 

 to bring the soft plate to the required shape ; or 

 any slight departure from this is corrected by 

 tightening the bars, at points where it is requi- 

 site. 



In England, the two modes of producing the 

 single thick plates under the hammer, and by 

 the rolls have each their advocates. The ham- 

 mered plates of the Thames Iron Works are 

 thus made : The best scrap iron being selected 

 and cleaned, is piled, heated, hammered into a 

 bloom, and then rolled into bars 6 inches broad 

 by 1 thick; these bars are cut up, piled and 

 again hammered into a slab ; several of these 

 slabs are laid upon each other, heated, and 

 hammered into the form of part of a plate ; and 

 the process being repeated by like additions at 

 the end of this, the requisite length of plate is 

 gradually produced. In other cases the ham- 

 mered plate is more simply produced by suc- 

 cessively welding together lumps or masses of 

 scrap iron, to the required length. It has been 

 objected to such, and in a degree to all ham- 

 mered thick plates, that the iron under this 

 mode of working becomes hard and brittle, 

 and must lack a continuous and uniform tena- 

 city. To this it has been replied that in prop- 

 erly made hammered plates, though somewhat 

 hardened, the iron does not lose its fibrous and 

 tough character, that by the requisite anneal- 

 ing, as observations on drilling and bending 

 the plates and experiments upon targets show, 

 the toughness of the iron is preserved and per- 

 haps improved by the working ; while the 

 solidity and- freedom from blisters or other 

 faults in the incorporation of the parts are 

 greater with the hammered plates. 



Messrs. Brown & Co., of Sheffield, among 

 others, advocate and practise the making of 

 the plates by rolling. The dimensions usually 

 required for the frigates now building in Eng- 

 land are length 15-18 ft., width 2 ft. 6- in. 

 to 3 ft. 10 in., thickness 4- in. The weight 

 of an unfinished plate of usual size, as it comes 

 from the rolls, is 80-140 cwt. ; a few inches 

 being cut from the sides and ends, the weight 

 of the finished plate ranges from 60 to 110 

 cwt. In the making of a 5-ton plate, bars of 



