"Richard Smith" wrote in message
Rifled Muzzle Loader - RML64lb 64cwt
Did someone on the thread about Cornish beam engines (cornish-cycle
beam engines) reference in construction techniques about the
1860's-ish rifled muzzle loader artillery / guns of the time?
There's loads of them lying around where I am working.
There's (at least) one outside the base which I could photograph -
but we are living in "the land of perpetual darkness" right now near
the winter solstice, from going to work and coming back from work.
However, wikipedia page shows exactly the same
Made of concentric cylinders of wrought iron.
Heat-shrunk on concentrically?
Apparently the then propellant was faster-burning than you'd like for
a propellant, leading to a short fat "bottle-shaped" gun and robbing
advantage from a breech-loader. Where whatever mechanism could
withstand that pressure / force was so clumsy and slow to operate that
firing rate was no greater anyway. And your barrel was short for
ramming a shell down it from the muzzle.
As far as I've read, one of the limits capping-off the evolution of
the Cornish beam engine by 1850-ish with about 50psi (3bars) operating
pressure is that is you have a higher operating pressure and a shorter
steam cut-off early in the stroke for maximum expansion, the initial
"jolt" force on the beam was too great, and they had to "ease off"
from "duty" of over 100million (foot-pounds of water to a bushel of
coal). Reliability - cracking the (cast-iron) beam and the mine
flooding as you had to replace it - seems dropped back to "duty" of
about 80million and accepted bit higher coal consumption in return for
the decades-long reliability.
I referred to Armstrong's preceding RBL, Rifled Breech Loader, which he
didn't consider safe for sizes over 12 pounder, apparently due to its
longitudinally forge welded wrought iron barrel. The surrounding rings were
only a partial solution. The 110 pounder version on HMS Warrior was fired
with reduced charges that greatly reduced the shell's range and
effectiveness. Although this claims the reduction was due to poor obturation
I think I've seen evidence that it was also to avoid barrel explosions. The
RML replaced the RBL after it didn't live up to its promises.
That was another example of the limitations of forge-welded wrought iron
under high stress. They couldn't know how much slag and flux had been
trapped in the weld until it broke, and apparently larger welds were worse.
In common with other contemporary designs the breech had problems that could
have been solved with a brass case for the charge. Military authorities
required decades of failed experimenting to convince them to waste that much
brass per shot.
Initially the base was iron, before they accepted that the entire case
needed to be one piece of brass. 0.577" is 24 gauge.
It was known at the time though not fully accepted that the burning rate
could be controlled by pressing the powder into cylinders with one or more
longitudinal holes. The powder burns on the surface and the outside area
decreases as the cylinder burns, while the holes become larger to
compensate. The bottle shape came from crude early measurements of peak
pressure along the bore. Prior to electronic strain gauges the only way to
determine it was to have the pressure deform little copper or lead slugs in
holes leading into the bore.
The inconsistency and relative weakness of wrought iron has been implicated
in the Titanic disaster. Central portions of the hull were joined with
hydraulically-driven steel rivets but at the ends where the huge riveter
wouldn't fit they were softer hand-driven wrought iron.
However the fatal leakage was into the #5 and #6 boiler rooms in the wide
part of the hull, below the first funnel. The whole front third of the hull
flooded. That part is now inaccessible, buried in mud. This survivor was
standing right beside the rupture in #6 and also observed and reported the
lesser damage in #5. He was ordered topside to help with the lifeboats after
his duty station flooded, as Titanic had far too few deckhands to both lower
and crew all of them. The ship's officers themselves were manhandling the
last spare lifeboat toward the davits when the top deck submerged under
The article I referenced mentioned that Cornish mining declined after 1850,
so perhaps less available capital prevented updating the engines with
stronger frames and beams. Cheap steel was still a few decades away.
Industry, locomotives and propeller-driven ships needed smaller, faster
rotating engines that could be better balanced and delivered a more constant
flow of power to a shaft. The compound engine had the potential to make
better use of high pressure steam than the Cornish beam engine, so although
it was a good design to operate a reciprocating pump rod it was a dead end
for other applications. US oil well pumps are still beam engines.