"Jim Wilkins" <
murat...@gmail.com> writes:
>> ...
> Wrought iron's random weld weakness imposed severe limits on pressure
> vessels, both boilers and cannon.
Not random - strong in direction of grain, but totally unreliable in
any other direction?
You could work around that with plates [in-plane design stresses
resulting from boiler pressure] and riveted structures with lapped
joints [clamped together and no forces trying to delaminate the metal]
?
> ... Look up Armstrong's rifled cannon
> for more info.
There's Woolwich Arsenal (and other?) rifled muzzle loaders all over the
place where I am working in Portland.
"Effective" range in kilometres compared to a couple of hundred metres
(?) with smooth-bore cast-iron canons.
Their concentric shrink-fit (?) structure of machined cylinders is
totally obvious to see. I'd seen them in books when I was a kid and
now for the first time in this job I'm doing I am walking past them
all the time.
Wrought iron would perform well by reason of stresses in the
direction of the grain of the metal given by forging.
I think it was only the cast iron which failed - and the engineer knew
and explained the limitations of the then achievable design.
I understand there were two things which were the undoing of the Tay
bridge
* wind-loadings weren't correctly assessed then (but were after this
experience) - not Bouch's fault really
* the railway operators got blase/ and had a flexible relation to the
severe speed limits specified
> Savery's 1698 steam engine used pressure to force water upward, but
> the workmanship of the time was inadequate to contain the
> stress.
Yes, but it had other limitations - particularly it could not lift
more than the about 10 metres of a "Toricelli" (sic.) vacuum with
water. As I understand it. So it was a first for applying fossil
fuel at a demonstrable level, but didn't have what it took to be a
usable device.
?
> ... Newcomen's 1712 engine and others for the next hundred years
> avoided pressure for safety reasons.
Yes - Newcomen's engines the boilers had no pressure at all -
apparently you could seal leaks with clay.
Boulton and Watt's engines operated at about 5psi - barely any pressure
at all.
The Newcomen engine was a "coal guzzler" and almost infeasible in
Cornwall, which has no coal.
It endured a long time at collieries, where it could consume waste
fines of no saleable value.
Apparently the "duty" of the generation of engines
* Newcomen - about 4~1/2million, rising to about 12million with
vastly improved mechanical detail (precision cylinder boring, etc.)
* Boulton and Watt - maximum about 30million
* "Cornish cycle" - maximum about 100million, but "blunted" back to
about 70million to 80million to lower peak forces giving the unfailing
reliability needed.
All according to
"The Cornish Beam Engine"
D.B Barton
> ... Boiler operation was a very
> uncertain art until Bourdon introduced a practical pressure gage in
> 1849.
You only had to have a feedwater water head of a few feet above the
boiler to keep it filled, and if it went over pressure it would push
water back up into the header and blow off steam - impossible to
over-pressurise. However - even that bare puff of pressure was
enought to burst boilers as they corroded, with horrible consequences.
Plug for a the book of a friend of a friend - both boilermakers by
Trade:
https://www.sledgehammerengineeringpress.co.uk/publications/historic-steam-boiler-explosions/
Alan McEwen
Historic Steam Boiler Explosions
Sledgehammer Engineering Press Limited (his own publishing house)
But come Cornish engine pressures of then "astronomical" 45psi
pressure - yes you would do well to have a safety-valve and
pressure-gauge...
> Trevithick in England and especially Oliver Evans in America advocated
> the greater efficiency of high pressure steam in opposition to Watt
> who feared the bad publicity of boiler explosions. Being further away,
> Evans was less inhibited and created lighter and more efficient high
> pressure engines that enabled American river steamboats. Since the
> Cornish engine was stationary it could be built of a great mass of
> cheap material.
>
https://en.wikipedia.org/wiki/Oliver_Evans
> Evans even experimented with supercharging the firebox but concluded
> that it would demand far too much of blacksmiths.
>
> This describes early marine steam engines which needed to be fairly
> light weight and fit into confined hull spaces, resulting in some
> clever but strange designs.
>
https://www.naval-history.net/WW0Book-Sennett-MarineSteamEngine.htm
> -jsw
Trevithick yes.
Apparently one of a number of talented Cornish engineers of the time.
One interpretation is that the Cornish cycle engine was the
combination of a Trevithick high-pressure engine "front-end" feeding a
Boulton&Watt separate-condenser "back-end" all on / in one cylinder...
The North American connection / steam-boats is a lead I must follow.
Efficiency - I have found this in the interim time
https://www.asme.org/wwwasmeorg/media/resourcefiles/aboutasme/who%20we%20are/engineering%20history/landmarks/194-kew-bridge-cornish-beam-engines.pdf
"Kew Bridge Beam Engines"
"...
One important side effect of the Cornish engine’s intermittent action
is that each up and down stroke is a separate power entity. So its
high efficiency – an 80-inch engine in Cornwall attained 11% overall
in 1835, a staggering figure for the time – is virtually unaffected by
the pumping rate. Maintaining efficiency over a wide range of load
factors is a problem with prime movers even today.
..."
The maximum for a single-stage high-pressure steam engine exhausting
to atmosphere peaked at about 12% maximum - if you got everything as
optimum as could be ?! - so that 11% 150years before and that
maintains over all loadings deserves serious respect.
Best wishes,
Rich Smith