PROJECTILES.

Lyttelton Times, Volume CXV, Issue 16666, 26 September 1914, Page 10

PROJECTILES.

! THE DUEL WITH ARMOUR- PLATE--1 In a nation’s fight for existence, a. 1 deciding factor will in nil probability bo whether or not uho projectiles can, penetrate the armour of the opposing vessels at a safe distance, says the* i “ Daily Telegraph.” For years thero j lias been in progress a never-ending ! duel between makers of projectiles and j of armour-plate, the struggle beginning at tho opening of the era of armoured. ■ vessels by the equipment of the French frigate Gloire with forged sheet-iron armour. This armour necessitated tho designing of guns of such power as to impart sufficient energy to their projectiles to enable them to break down ■ the resistance offered by the armour. ' In addition, it was required that the/ material of which tho projectile was made and its form should be such as to I produce complete perforation of the plate. I Cast-iron balls were first used, but such spherical projectiles were early , discarded, and cylinders with ogival | points were introduced. The fi rst ' l? ro ~ jectiles to be used with suebess against ( armour-pla.te were those of Palliser. These shells were made of cast iron, the point being cast in a metal mould and the cylindrical portion in ordinary refractory sand. The casting of the point in a metallic mould gave to the projectile at once 1 both its final form and j the necessary thermal treatment which j hardened it. In the manufacture of I the projectiles of the present day the process is infinitely longer and more complicated, but in principle it is the same, and approximates the more to tho Palliser process. The projectile, instead of being forged, is simply cast and subjected afterwards to thermal treatment. When materials distinct from ordinary wrought iron began to be used in the manufacture of armour plate, the Palliser projectiles were no longer capable of piercing them, and failed completely against the Schneider plates of homogeneous steel, as well as the English compound plates, and those hardened I by the Harvey and Krupp processes. The sanie process in metallurgical science which made it possible to improve the armour plate material contributed also by degrees to the perfecting of projectiles. Advantage was taken of chromium, which increases tho hardness and toughening capacity of steel in a i higher,degree than carbon, but without : increasing the brittleness, and a cer- ( tain proportion of this metal was added to the material used in the manufacture of projectiles. For some time chromium steel, or Holtzer, projectiles held the field, but when the ternary and quaternary steels (the latter containing nickel besides the chromium, j manganese and carbon of the former) ! came to be employed in the manufacture of the plates, the surfaces of which wore cemented to a certain depth and afterwards hardened, even chromium steel projectiles, tempered and hardened ns they were to an extraordinary degree, could not pierce the plates. I The invention of the cap, however, about the year 1890 gave the preponderating advantage to tho projectile in the struggle which for nearly half a century had been maintained between this and the armour plate. The cap is actually made of a softer material than j that used for the projectile, an extra mild steel being generally selected. , Tho steel for caps is melted in an open j hearth furnace, and is forged in round I bars after tlio removal of all surface cracks from the ingot, and it is then annealed and cut into' short lengths convenient for stamping. After stamping, the caps are oil hardened and tempered, which processes they share with i the projectile itself, and then they undergo the final thermal treatment. Exactly how the cap protects the point of the projectile has not yet been satisfactorily explained, but it is certain that, whereas unprotected projectiles ' are warded off by the plate, those with caps easily penetrate and pierce it com--1 pletely.