non-welding question - Cornish beam engines

Hi

I've posted a question about Cornish beam engines on rec.crafts.metalworking

Should that be of interest to anyone...

Rich Smith

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It is. I've bought and read quite a lot about the Industrial Revolution in Britain and America, such as "English and American Tool Builders" and the Holtzapffel series. Before it began we were about at the level of the Romans, or in some fields like public water and sewer behind them.

Monty Python what have the Romans ever done for us?

Monty Python what have the Romans ever done for us?

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My cellular Internet service has improved somewhat with a plan and phone (hotspot) change but I still don't have enough monthly data for videos, and got a ways behind while setting up and testing. They promise 10GB starting next month. The change to 5G is disrupting legacy services like mine.

At least I'm not paying $200 a month for cable TV.

Romani eunt domus! My first-year Latin teacher was a female version of that Centurion.

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. Etc.

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.

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. Etc.

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.

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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 them.

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.

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Expert opinion:

"Tests carried out by TWI have shown that when subject to shear or bending loads welded wrought iron can fail at unexpectedly low loadings ..."

The TWI advice isn't exactly in line with what a friend of mine - a direct-talking West Country boilermaker - says. Basically... You may be able to do full penetration (double-)V butt electric-arc fusion welds with the joint transverse to the grain, so the grain passes into the weld metal and resumes on the same axis and orientation on the other side of the weld. You do not do a fillet weld on / with wrought iron.

Hope have got this right.

The "welding" mentioned here is electric arc welding.

There will be a lot of welding with wrought iron and that will be forge welding. I cannot speak from experience though. Been shown where forge welds are an integral part of wrought iron bridge structure.

A common problem we have here in the UK is that some Agency raises the query whether a riveted bridge is wrought iron or steel, resulting in a couple of lads in a Ford Transit van have a stop at that bridge added to their day's driving around, where they get out a 9-inch angle-grinder with a slitting disk and cut a square of metal out of the *tension* flange. (it will be the lower / underside of the bridge and the first and most convenient thing such party will encounter - hence inevitable outcome) That then leaves a difficult and expensive rectification job to keep the bridge in service, whether it was fine before or not.

The TWI advice isn't exactly in line with what a friend of mine - a direct-talking West Country boilermaker - says.

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I took that to mean the original forge welds, not modern repairs that fully melt the iron and allow the included slag to float out. Before the Bessemer and open hearth processes, nearly pure wrought iron couldn't be melted in any appreciable quantity, because the nitrogen in air cooled a flame well below iron's 2800F / 1538C melting point.

Wrought iron could be welded with pressure because it becomes soft and sticky at yellow/white heat, but the welds may contain unknown amounts of slag and flux that weaken them. Ideally the weld progressed along a line and squeezed out the flux, but that became less certain as the size increased.

The open hearth process added heat exchangers that preheat the incoming air enough to reach melting temperature. The chemist had to work fast to sample the melt and analyze and correct its composition. That might have been my job if the Army hadn't redirected me into electronics.

Dissolved carbon reduced the melting temperature enough to produce small amounts of high carbon tool steel (wootz, crucible) or larger amounts of higher carbon cast iron, which melts at much lower temperatures a fire in unheated air could reach.

I've seen slightly different values for some of those. It varies with purity.