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The Twilight of Bronze Cannon
Posted: Wed Nov 04, 2015 1:57 pm
by VMI77
http://weaponsman.com/?p=26801
Article sample:
Wrought, which today we would call Forged, iron, was a superior metal — in theory. In practice, it was hard to make. Two early forged cannon were made for USS Princeton in 1843. One, called Orator, was found to be deficient due to cracks, and was reinforced with welded-on bands for greater strength. The other, Peacemaker, was not as thoroughly tested, and during a demonstration for dignitaries on 28 Feb 1843, its breech shattered, killing a variety of people from the personal slave of President John Tyler to the Secretaries of State and the Navy. In the freak accident, the gun crew and gunnery officers of the ship (who were hands-on in service of the gun in front of the VIPs) were not seriously injured, while the fatalities were among the watching VIPs. The captain of the ship, Robert F. Stockton (who had supervised the design of the ship and the guns) was standing with the VIPs, and survived with severe injuries.
Re: The Twilight of Bronze Cannon
Posted: Wed Nov 04, 2015 2:12 pm
by oljames3
Re: The Twilight of Bronze Cannon
Posted: Wed Nov 04, 2015 9:43 pm
by treadlightly
Interesting! That article touches on Rodman casting, which was key to producing the huge Dahlgren guns of the Civil War. The largest Dahlgrens, I think produced during the Civil War, hurled a 1,000 pound with a 100 pound charge (700,000 grains of powder, just think of that). I think the gun had a range in excess of 5000 yards and weighed around 100,000 pounds.
Without the Rodman casting technique the casting of such a barrel was impossible. The problem with conventional casting is that the outside would cool to a solid while the inside was still gooey. As the inside finally solidified, it contracted within the already solid outer surface. The stresses were enormous and led to internal, hidden rips in the metal, pulling voids in the structure of the barrel.
In the Rodman method, a water jacket was inserted where the bore was going to be, after the iron was poured. Water was pumped through the jacket and fires were kept burning against the outer surface.
That caused the inside to solidify first. When the outside finally solidified, the contraction of the outside part cooling around an already solid core put the metal under intense compression, instead of extreme tension. Fascinating stuff.
