Anyone able to help me improve further, on the basis of this recent experience?
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 :-)
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Ends:
The ends needed precision-cutting to present a right-angles in every direction / sense, for easy placement and 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
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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
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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.
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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?
Regards, Rich S