Ok, a former collegue of mine posted me a question:
They have some 1 1/2 or 2 inch steel plate, I'm guessing A36. Its used in a non-structural application. Anyways, the steel has a fairly thick layer of scale on it. Its all plated after its been welded to another part using GMAW-S. Yeah I know GMAW-S on that thick of material!!!? Don't ask!!! The method used to remove this scale is by placing said part in a surface sander.
Ok, my collegue is advocating using a rosebud to heat it up to pop off the scale. One of his co-workers thinks that heating up the material in this manner, how ever brief it might be, would change the metal at the molecular level possibly messing the steel up.
What do yous think?
Here is my theory: Although its not a structural application I consulted the Good Book (D1.1) for some insight. That thickness of steel, when used in structural applications, with that poorly chosen and not qualified welding process, the preheat should be a minumum of 150 degrees F. My thinking is since that grade and thickness of material, when used structurally needs preheat then whatever heat that might be generated by the rosebud, or 10 passes through a surface sander, wouldn't happer the properties of the steel.
And I think I use commas too much. :-)
Hey Bryon
I don't think sanders or rosebuds are very good at removing mill scale.. Neither are a top choice
Sanding discs just load up and loose their edge... Rosebud will prolly only make more scale rather than "popping it off"
I guess if he is just welding thin little clips or something like that (thick to thin) than short circuit may not be such a bad choice..
To get the best results on Moderate mill scale and GMAW short circuit transfer mode try ER70S-6 filler rather than -3 and also run C02 100%.. The Carbon Dioxide will provide the deepest penetration you can get with short circuit and is also going to provide the best performance over the scale. The sweet spot in parameters is a bit more narrow than with a mixed gas, but so what. A good operator can just pay attention eh?
A grinder is the way to remove the silly scale.. much faster than a rose bud, much more efficient than sanding discs.
Hi Lawrence,
Believe it or not, I found that those flap discs do a better job at removing tough mill scale than a grinding disc....at least the mill scale that we see on base plates for columns....Our shot blast machine is by far the easiest method as it takes very little manual labor to sit the pieces in a basket and let the conveyor run them through....LOL
It depends on which sanding and grinding disk you’re comparing. I've had hard stone wheels skip around on some of the thinner but tough scales, and some very nice sanding pads chew through the thickest layers like it was a coating of flash rust. The hard wheels were a cheap no name brand and the sanding disk were some of the 3M Red disks that they make for stainless. With that being said, one of the Sigma Green hard stones that we have kicking around work is a real destructive device. Nothing stops that disk when you put it to metal, mill scale or otherwise. It’s like an arc gouger on a 5" grinder.
Flap wheels, as in the orange( Norton’s brand) disks with the strips of abrasive over lapped and glued together, can work real good if you get the zircon disks and not the alum oxide. I'll leave the technical reasons as to why they work up to you guys, my guess is that zircon oxide is harder than aluminum oxide and can stand up to attacking the though mill scale better.
John has the right idea though, why do it yourself when the machine does it so much nicer with so much less work. ;)
Adding a few pennies worth
-Clif
Damn it. I forgot to add. The scale is on the top and bottom of these plates. They have been cut round and the edge that is getting welded on is not in question. The scale is being removed for asthetics on the top, since its being plated and on the bottom so it will fit flush on on the faying surface.
I think all those methods are viable, but I'm just trying to clear up differences in their 2 opinions about the change, or lack thereof with regards to heat.
Thanks guys.
a couple of plates or a whole truck load of plates?.....
--whole truck load, have them blasted,
--just a couple use a grinder/flapdisc.
A friend of Mine uses muriatic acid to loosen scale before sand blasting, claims it cuts blasting time way down. Use at Your own risk.
At the auto frame plant they used CO2 and globular transfer to weld heavy plate weldments. Great penetration and more spatter than You could shake a stick at. Looked like somebody spilled a bag of shot on the job.
Yes, Dave, muriatic acid (commercial name for hydrochloric acid) removes scale faster and better than sandblasting. However, muriatic acid is a strong one, it releases harfmul fumes and it's essential to know how to handle it, both from an operational and safety points of view, before using it. So, it should be used under the supervision of a chemist. Furthermore, muriatic acid alone isn't sufficient. A suitable inhibitor should be added to the acid so it removes only the oxide leaving the sound metal untouched.
Giovanni S. Crisi
needle gun is the way to go if ya aint got one of them id grind it the preheat aint goin a hurt a thing and it will pop o ff some of the scale
ironsport,
please understand my point of view and don't get upset.
This Forum is open to every inhabitant of this planet called Earth who's interested in Welding. So, a considerable number of frequentors (me included) don't have English as their mother language. They have learned English at school, or with a private teacher (my case) or at institutions supported by the American and British governments. In either case (school, private teacher or institutions) what's taught is the English language, not slang nor cockney.
So, I think that you people who have English as your mother language should post your opinions in English, not slang, as a courtesy to those of us who don't understand that particular language spoken in the USA, and perhaps Canada.
I confess I haven't understood your message at all. How many of you people who live outside English speaking countries have understood it?
Giovanni S. Crisi
Giovanni,
Allow me to translate:
A needle scaler is what he suggests. If I don't have one of those then he suggests grinding off the scale. As far as the preheat is conscerned, it shouldn't be a problem. It will remove the scale.
I had to read it a couple times myself and my first language IS English. :-)
I hope that helps.
Bom dia!
Thankyou, Byron, now I've understood what ironsport meant.
Boa tarde!
Giovanni S. Crisi
PS:
Bom dia: (good morning) is said before noon.
Boa tarde (good afternoon) is said from noon to when the sky gets dark.
Boa noite (good evening AND good night): is said from when the sky is dark to the next morning.
I profusely apologize for my unintended butcherey of the english language I myself had no problem understanding what I said but different strokes for different folks. I would be the first to admit my typing skills leave much to be desired. i certainly did not mean to annoy anyone.I am a weldor been doing it for 30 years . Internet communication is very fresh to me it is something I will try to be much more careful with in the future .Have a great day.
ironsport,
there's nothing you should apologize for. You've just written the same way you're used to speak. Just be a little more careful next time.
Giovanni S. Crisi
If by "surface sander" you mean sandblasting, then it's the best way to remove scale from a steel surface. Trying to burn the oxide with a torch isn't as efficient. Acid cleaning (pickling) is used in surfaces that are impossible to sandblast, like the inner surface or piping, for example.
Depending on the final use you intend to give to steel, there are three types of sandblasting, according to The Steel Structures Paining Council of the USA (SSPC):
Commercial sandblasting (the less stringent)
Sandblasting to near white metal (an intermediate one)
Sandblasting to white metal (the most stringent).
You can found them at www.sspc.org/standards/scopes.html#sp
Giovanni S. Crisi
Sao Paulo - Brazil
If the steel is not taken over 1100 degress there wont be any harmful changes.
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