oxy-propane pressures & conditions

I've recently had a "perfect" job to refine my oxy-propane cutting
conditions. "Goldilocks" ("just right") challenge.
I was doing paper engineering during the transition from oxy-acetylene
to oxy-propane - hence had to find my own way without much mentoring,
returning to steel fabs. now using oxy-propane for cutting.
The job was recovering steel to make temporary supports about 1 metre
(3ft) long - from heavy H-column used as beam. Cutting off all the
features from its previous application as a rack for tube.
Thickness 30mm.
Nozzle 1.6mm (1/16th-inch) oxy-propane.
None of the steel being recovered had any coating or paint on (nice
for me!).
All the severing was at fillet-welds - so the "retained" / "recovered"
steel made a nice guide to drag the torch along - reducing the number
of variables I needed to control, giving me a perfect focus on the
physics of the cut :-)
The ends needed precision-cutting to present right-angles in every
direction /
sense, for easy placement, and for good fit-up without gap
for welding.
I found
* 40psi (2.7Bar)
fairly powerful preheat flame, but not over-driving nozzle as makes
flame "feathery" and lose focus
* neutral flame (? - still blue, just before any more preheat
oxo. would make the flame become more pale blue)
cut with torch at right-angle (or very slight forward tilt) to surface
Severing redundant side-features of previous application:
Removing all other features was "severing", without accuracy or
neatness requirement.
I found
* 70psi / 4.8Bar
* most powerful preheat flame the nozzle would give (accepting some
loss of focus)
slightly oxidising preheat flame
* cut at up to 45deg tilt-forward into direction of cut
This gave fastest cutting speed - and not-bad cuts.
The rationale for the conditions are, respectively;
- 70psi is maximum before the kerf became wider than nozzle-bore
- oxidising preheat flame meant minor knocks of the oxo. and propane
valves didn't result in a big drop in flame temperature
- oxidising preheat flame made "sweating" before could ignite the cut,
especially when piercing, more obvious
- oxidising flame "sweating" and slightly rounding the top edge of the
plate cut doesn't matter for this "severing" application
Where needed a bigger kerf in awkward locations with corners, etc.
Almost as-above, but increasing oxo. pressure to 80psi / 5.4Bar gave a
kerf at least twice as wide - presumably due to turbulence of the
oxygen stream from over-driving the nozzle? - while still a rapid
cutting rate, still going in a straight line no side-to-side
oscillating the torch.
I'd got literally a ton of oxygen, and others use a higher pressure
than these, so that isn't a pressing issue...
I got reprimanded already that learning to use an oxy-fuel torch was
about 1 year of an apprenticeship, so in that context, my skill level
is going to be somewhat basic.
OK - anyone benefit me with their wisdom? How well am I doing?
Rich S
Reply to
Richard Smith
Loading thread data ...
Thanks for the data points.
Those who can, do. Those who can't, teach (or manage).
Right now American politics is boiling with the juvenile resentment those-who-can't have for those-who-can.
Reply to
Jim Wilkins
Hi Jim
I had a good week doing that work. I can only say - that's what I saw and found. For what it's worth... Yes it's raw data for you - observations, unexpected so pure and unbiased.
Since then had interesting new one - how to sever a beam which is resting close and tight up flat on the deck of your barge. Which means the lower flange is pressed against a plate you must not cut. A precision cut to length and at right-angles for further fabrication needed...
Regards, Rich S
Reply to
Richard Smith
I watched a neighbor's brother torch-cut a pressed-in wheel bearing race without leaving any visible mark on the hub.
When heating iron in a blacksmithing fire a crack can reveal itself by being bright red on one side and black on the other.
Reply to
Jim Wilkins
If you can cut out a clearance section of the upper flange and web maybe you could groove the cut line with a grinder and then jack the far end up to crack it.
Reply to
Jim Wilkins
One end is scrap / offcut yes. However, this is over 300m/1ft wide and 20mm thick, so it's not bad using grinder, but you'd never be able to speed it up and become a master of the task like using the oxy-p torch offers.
I did cut a "window" with the torch through the web on the "scrap" side of the cutting line going down to the lower flange, to let slag flow/blow-through and keep the cut as clear as possible.
Regards, Rich S
Reply to
Richard Smith
I was in the custom and prototype business so the many problems I was asked to solve were "can it be done at all once", not how fast repeatedly, which is a Production Engineer's jealously guarded turf.
formatting link

Reply to
Jim Wilkins
Hi Jim, all
Interesting article.
I perceive "my problem" as being "not with the flow" in a world where people are conforming to becoming exact-shaped pegs to fit into various "holes" designed by an unimaginitive senior level trimming the world to fit their ability.
I'd say the world needs different people. So the walking encyclopedia of Standards relating to "splunge grommets" is just as valuable as the overview person who stops at overall knowledge in order to keep a mind clear to reach across many topics and glue the organisation together, running between all in order to keep the group endeavour running true.
I've always, since my early days in the steelworks, perceived that the brief is rarely likely to be correctly formulated and all you know is there is a cry of pain in the organisation, and the best remit is always to find something which will take away the pain and in so doing advantage the Company.
My time in Turkey on the 3rd Bosphorus Bridge project was an ultimate demonstration of the need for a person going between unconnected groups and building a shared strategy for getting the job done.
There is a greater specialisation going even further than the "wall" thing. If a specification for a project (eg. a bridge) is a Product Standard, each organisation seeking to minimise its financial obligations will seek specialists in that Standard, who will determine whether a task is within their obligation or not part of their obligation. Problems: * no-one is then looking at where the project is going and whether it is on a path to a desirable outcome * every "Code combateer" negates each-other in fractal Code combat
(this has likeness to flood alleviation by installing drainage - if you are the only one doing it, it will work per description, but if everyone does it following the Code, the land will flood now by the river welling up from its course)
Anyway, coming back to Britain after the huge success of facilitating the 3rd Bosphorus Bridge project, I encountered, believe it or not (!), an impenetrable wall of functionaries measuring me for whether I would fit one of their exact-shaped holes ... ... ... oh well.
Hope this is in some meaningful relation to the point you were making.
Regards, Rich S
Reply to
Richard Smith
I've been the liaison between Engineering and Production, an utterly thankless task I wouldn't volunteer for. Eisenhower became Supreme Commander more for his diplomatic ability than his military background.
If eveyone is responsible then no one is. See the Titanic and Andrea Doria inquiries.
I know what you mean. Finding a fault in an hour didn't endear me to the Ph.D. who'd given up after two weeks on it. He had carefully followed the sacred rules but didn't realize he'd strayed into the no-mans-land bordering different sacred rules. I could see the problem just by looking at the photo plot of the circuit board's inner ground plane and spent the hour setting up a convincing demonstration.
The Peter Principle has people rising to positions they don't deserve and are desperate to defend against more talented challengers. If you can't improve yourself any further the only advancement option is to downgrade your rivals. Such toxic envy is the real basis of socialism.
German commando leader Otto Skorzeny was a very perceptive and innovative engineer who understood all this and chose as his second in command a smart lawyer who knew little of military tactics but was a master at manipulating the inept, hostile and self-serving Nazi bureaucrazy.
This book analyzes the sociology of good engineering management when politics doesn't interfere.
formatting link

When it came out I was the project manager's assistant on a similarly smooth-running job, a general-purpose computerized test station for analog integrated circuits and the test patterns on memory chip wafers.
formatting link
Sadly we completed it just as the economy turned down and capital investment vanished, so the impatient orders became rows of unsold machines and the company soon closed.
Nevil Schute's "Slide Rule" describes a (typically) more confrontational situation in which the Labour government was trying to 'prove' the superiority of central planning over private enterprise and didn't take well to evidence they were wrong.
formatting link

formatting link
"This led to the nicknames the "Socialist Airship" and the "Capitalist Airship". The Socialist Airship quite literally went down in flames due to mismanagement and the successful Capitalist Airship was then grounded out of spite.
The history of the Industrial Revolution is essentially the battles of engineers (your Stephenson and Brunel, our Fulton and Whitney) versus bureaucrats.
Reply to
Jim Wilkins
Somewhat like a statically indeterminate structure.
Reply to
Jim Wilkins
I just read a WW1 officers' manual that describes trench drainage in detail and laments how each section's individual interpretation of the rules and disregard for the next section makes the problem insoluble.
The rules demanded wider trenches for rapid 2-way and stretcher passage and narrower ones for better shell fragment protection, etc, with the result that everyone could quote a rule to justify doing whatever they fancied. I appreciate Captain Blackadder's situation more now.
Reply to
Jim Wilkins

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.