spark test for steel, time for an update with modern abrasives?

cyanidekid · Sep 19, 2018

the grinder spark test of steel and iron alloys is a classic technique.

to review for the unfamiliar, its a quick field test that uses the spark "trace" coming from the grinding of iron and steel alloys. observing its color, length, and how it "bursts" or terminates when the trace disintegrates is used to differentiate between general classes of steel alloys.

this technique was most useful a century ago when there were far fewer alloys, and most grinding wheels were made pretty much the same way with the same abrasives.

today, with a plethora of both alloys and abrasives it has lost a lot of its usefulness. recently I have been trying to ID some misery stock I picked up free, and have found the spark trace to be VERY different depending on the wheel or disk, and that has me wondering if anyone has done an update with a specific wheel and some known test specimens? posted on the tube? before I went down that rabbit hole just wondering if anyone has already gone there or done that?

kenton · Sep 19, 2018

My welding instructor recommended getting a handful of known steel and cast iron samples and comparing the known sample's sparks to the mystery material.

eKretz · Sep 19, 2018

In my experience, this was always done with a plain aluminum oxide bench grinder wheel - which are still a dime a dozen (not really, but plentiful and easily available) almost everywhere. You want a very light touch for the spark test, don't press in with a lot of force.

cyanidekid · Sep 19, 2018

eKretz said:
In my experience, this was always done with a plain aluminum oxide bench grinder wheel - which are still a dime a dozen (not really, but plentiful and easily available) almost everywhere. You want a very light touch for the spark test, don't press in with a lot of force.

I think I might have one of those turkeys around somewhere...

thing is, most of the time, I'm going to have an angle grinder in my hand when I'm checking, and I only use the good stuff on them. I'm also wondering if a zerconia-alumina ceramic sanding disk, or a cubitron wheel would have a better diagnostic result or, possibly be less effective.

guess I'll have to do that cubitron video!

adama · Sep 19, 2018

Wheel dia and hence surface speed is everything, hence a few known goods to compare is the gold std for spark testing, motitor and grinder differences would make You tube videos pointless. That said Xref guns keep getting cheaper and are a far better bet for real alloy content.

john.k · Sep 19, 2018

Unfortunately the Xrf guns cant detect the tiny percentages in HSLA steels,and to do that you need lab standard eqipment....in a lab........a grinder will tell if its cast/nodular iron,low carbon steel ,or high carbon....which is about all you need for welding....One of the worst accidents I have witnessed was caused by a welder thinking large ductile castings were weldable to a steel fabrication......the welds broke as soon as they were loaded up and a barge bow ramp fell on two painters .

cyanidekid · Sep 19, 2018

adama said:
Wheel dia and hence surface speed is everything, hence a few known goods to compare is the gold std for spark testing, motitor and grinder differences would make You tube videos pointless. That said Xref guns keep getting cheaper and are a far better bet for real alloy content.

eerr.. no, not quite pointless. the spark is not THAT sensitive to speed, and you can prove that to yourself by sweeping a sample across a sanding disk on an angle grinder. the "surface speed" will change by a factor of 2.5 at least, but the nature of the spark won't change dramatically, mostly it will vary in the quantity of sparks, and somewhat in brightness. the curve, if present, and the nature of the "starburst" stay reasonably consistent .

the abrasive, its condition, binder and type of wheel do have a dramatic affect on the spark, thus the wheel brand, grit, and type need to be the same for sure.

DMF_TomB · Sep 20, 2018

cyanidekid said:
the grinder spark test of steel and iron alloys is a classic technique.

to review for the unfamiliar, its a quick field test that uses the spark "trace" coming from the grinding of iron and steel alloys. observing its color, length, and how it "bursts" or terminates when the trace disintegrates is used to differentiate between general classes of steel alloys.

this technique was most useful a century ago when there were far fewer alloys, and most grinding wheels were made pretty much the same way with the same abrasives.

today, with a plethora of both alloys and abrasives it has lost a lot of its usefulness. recently I have been trying to ID some misery stock I picked up free, and have found the spark trace to be VERY different depending on the wheel or disk, and that has me wondering if anyone has done an update with a specific wheel and some known test specimens? posted on the tube? before I went down that rabbit hole just wondering if anyone has already gone there or done that?

.
spark test not 100% reliable. many a time i thought i had cast iron and when i drilled it i got long stringy chips so obviously i was wrong
.
some steel alloys and cast irons are almost the same spark look.

eKretz · Sep 20, 2018

Yes, that's why you need to compare to known material.

DMF_TomB · Sep 20, 2018

eKretz said:
Yes, that's why you need to compare to known material.

1018, A36, 4140, 8620, 303, 304, 316, M2, M42, 1090, cast iron, ductile iron, literally a shop can gave 10 or 20 different metals or alloys and many when 10 machinist spark test 70% are wrong in what they think spark test says
.
definition of "critical" if wrong will it cause significant economic loss or injury to anybody if wrong. basically will anybody care if you are wrong about spark test ??
.
not many parts where if your are incorrect it will not matter or nobody will care about it or be effected by wrong decision
.
i remember melting in foundry furnace what i thought was scrap aluminum. when i took furnace lid off the bright white burning light was my first clue it was magnesium. many metals look similar

eKretz · Sep 20, 2018

A spark test is not meant to identify alloys of steel precisely. It gives an idea of low carbon, high carbon, iron, etc. The problem of "10 machinists.... different results" is exactly why you don't just let any knucklehead do the spark testing. One needs to know what to look for and recognize the telltale differences in the spark shape, number of branches, sparkles at the end being long or short, continuing to spark after they separate etc.

Anyone who would produce a crucial weldment using unknown steel deserves what they get.

adama · Sep 20, 2018

eKretz said:
Anyone who would produce a crucial weldment using unknown steel deserves what they get.

Yeah problem is going by history its not normally them that get it but some other poor sod.

Videoing and lighting then moitor would totaly distort anything but the shape of the sparks, the 3m cubitron discs i use on typical mild steel throw harldy any sparks compared to a hard slow cutting old alox grinding wheel too, there also really dull, super abraiseves are definatly not your friend, getting the swarf to ignition point and how it burns in air realy kinda defines the bushy like hot sparks of a high carbon steel.

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