Grinding welds to reuse the metal

[Glenn]

Can you grind out the welds in order to separate pieces of metal so they (the pieces) can be disassembled and reused in other projects?

Does the metal once it is welded (and the welds ground out) loose any strength in that area making it weak? Should this metal be used for less critical applications?

What method do you suggest for removing the larger welds? Can they be cut or gouged with an ox/ac torch and then cleaned up with a grinder?

[irnsrgn]

Which brings up the question. Why was it welded in the first place to form part of a structural member if the weld was going to affect it adversly?
As is common with most inexperienced welders and farmers, they adversly effect the structural integrity of the joint to start with by using the biggest rod they can find and set the welder on the highest setting making the whole thing just below the molten state in the misbegotten idea that they are saving time and electricity by putting a humongous weld in in one pass, Bigger is Better you know.
And besides that, with only one big weld, you don't have to waste time chipping flux and cleaning for another pass. That flux is hard to weld over and besides the flux is actually what holds the stuff together anyway its a lot smoother than the weld under it, so if it looks better it must be stronger.

[saintjohnbarleycorn]

remove your welds with a oxy acetylene, it is surprising how fast and clean you can remove welds. they also make gougers that are compressed air and electric, the gas method works very well though.

[Glenn]

Cutting or grinding the head off a rivet releases the rivet. Same with a bolt. The question came up as many times there are things (fabrications, equipment, etc) that have materials that can, if disassembled, can be used elsewhere.

There is no current project in mind. I just wanted to start a discussion so when the need arose, we (collectively) had some idea of what could be done.

[Milt]

I'm not sure, but I think the question on strength of pre-welded metal has not been answered by anyone here yet. Anyone know, or was Jr. saying that it depends upon the metal snd the type of original weld?????????????.

[Rutterbush]

irnsrgn,
You've touched a nerve.

..."That flux is hard to weld over and besides the flux is actually what holds the stuff together anyway its a lot smoother than the weld under it, so if it looks better it must be stronger"...

I hate being on the road anywhere near a home made trailer. Most of those who DIY purchase a cheap machine and the salesperson points them toward the E-6013. Good rod if used properly. I've recently seen trailers upside down and busted apart on the median and shoulder of the road.
I could write all day of new impatient students who enroll to build a trailer. Thier, I need it NOW and I'm paying to rent the equipment and have you do it, attitude pays no heed to my you need to learn to weld first response.

As I said, You've touched a nerve.

Glenn,
Welding electrodes should be used as irnsrgn indicates. Electrodes should be run at the lowest possible amperage to get a good weld. This is defined as the lower end of the manufacturers amperage guide. If the guide lines say this electrode should weld with 90 to 100 amps, then try 95 amps. Can you make a sound weld with 94 amps? Can you make a sound weld with 93 amps. When an amperage is found that will not allow a sound weld to be made, then turn the amperage up one or two or?.
When a weld is made the base metal has a heat affected zone (HAZ). I'll compare it to a hardened edge on a Japanese sword. When welding the heat makes the grain of the base metal grow. The further from the weld the smaller the grain. If the weld is ground out, band sawed or cut with anything which doesn't bring the base metal up to normalizing heat, then the HAZ is still there. Effectively you are welding on the area which has grain growth and a possibility of cracking. BUT making the weld could bring this area up to a normalizing heat.
Think of that Japanese sword. If the sword were heated to 400

[Ice Czar]

of course "effecting the grain" is what annealing, forging, hardening and tempering is all about
provided your doing all that (especially the forging) there shouldnt be any great amount of weakening. At least for most typically hand forged applications. Salvaging stock for other applications where its simply re-welded into a new structure might pose some issues in highly stressed structures. But then your getting into engineering, metal fatigue, load bearing, ect. Its possible to over engineer much of that even with pre-used steel. In really critical aps, say an engine mount that is under a weight constraint probably a good idea to use virgin stock.

[MLMartin]

i would not recommend running the amps as low as possible to make a good looking weld ever. in the shop i work at we make and repair many things from trailers and industrial chippers to high grade stainless parts in food plants. most of all the broken welds i see daily on equipment look great, vary smooth on top even ripple pattern, But there COLD. cold welds do not penetrate well and sometimes only adhere to the toes of the weld. im not saying run rods way to hot buy any means i know you can destroy just as many things getting way to hot. find a comfortable temp then run just a little hotter. it is a little more challenging to run rods a little hot but your much safer to ensure good tye in.

and yes big welds do not always mean strong. many people do over size welds, this will cause stress at the side of the weld. welds should only be slightly stronger than the parent metal.

[Glenn]

What I had in mind was dis-assembling and reusing the structural members, such as angle iron, flat bar, beams etc. Would the neat affected zone from welding and cutting out the weld create a substantial weakness to where that area or section should be down graded to a non-structural use?

[Ice Czar]

depends on the stress and loads its being asked to handle
what are you making?

one definition of engineering is:
as cheaply as possible that is just good enough

whereas over engineering something is relatively easy, but more expensive

[Dodge]

As far as mild steel goes, as long as actual weld bead is not now part of the material to be used, in effect making the piece longer, wider, etc. e.g. a 6" long piece of angle iron with 1/4" of weld on each end should not be considered a six and a half inch piece of usable material, you should be fine. Grind, cut with torch, plaz, sawzall, abrasive wheel, what ever, grind down to stock metal, re-use. Carbon steel would be a different matter, however. Heat treating procedures would need to be considered then. I know that there are light poles and transmission structures out there that may have had the wrong base or attachment put on, cut off re-used and even cut off again and re-used again and you drive by and under them all the time. Happy motoring :D

[Frosty]

If you're concerned with the HAZ when salvaging steel just grind it back 1/2-3/4" from the weldment.

Overamping to get penetration is probably the most common mistake made by inexperienced or poor weldors. While I don't necessarily agree that you should use the minimum amperage possible you should use the lowest amperage workable. It may be a small difference but it is significant. Most failure initiation points can be found at the start or stop of a bead, the fewer there are while maintaining a proper weldment the better.

Most pretty weldments you see with zero penetration, usually on one side are made by inexperienced or poor weldors using GMAW or mig. They're known as the lawyer's welder for a reason.

Then again if you know what you're doing a mig just fine, you can make a proper weld in inhospitable conditions, out of position, imperfect rod selection, amperage, etc.

It's the weldor that makes the weld, not the welder.

Frosty

[Ten Hammers]

Ok here's my 5

[irnsrgn]

from actual experience welding for a living for 50+ years including building, modifing and repairing carnival rides, there is way to much emphasis put on deep penetration. Penetration means that when welding up two pieces that have a V, J or a space between the edges of a butt weld you get completely thru the joint and in best case scenario you have a perfect looking little weld bead on the back side. This is usually called the ROOT pass. After the root pass you should be more concerned with complete FUSION of the the welds and or parent metal with what you are depositing by welding.

Undercut at the edges of the weld bead suggests you are using to much heat or amps to make the weld. Overlap at the edges of the weld bead suggests to cold or not enough amps to make the weld or moving too slow or too much deposit rate.

To prevent a cold lap or non fused starting point with a large lump, start a little ways away from the starting point and then go back over the area after its warmed up a bit and start the bead.

If you look closely you will see a small crater at the end of a weld if you just pull off to stop, and after a bit by carefully looking at the crater you will usually see a small crack in it. To prevent this make a small circle at the end of the bead before pulling off or just reverse direction a bit before pulling off.

Back to the original question, if the pieces you want to take apart have only a fillet weld on one side and its not overly long, usually just an adjustable wrench used to pry the piece toward the side that has the fillet weld will generally break the weld easily, or just hitting it with a decent sized hammer will also suffice.

[Glenn]

Let me simplify my question.

Say a piece of angle iron is welded in 4 places across a 8 foot length. Grind or cut out weldment to separate the piece of angle iron from the parent structure. Is this recovered piece of angle iron as sound a piece of metal as a new piece of angle iron? Can you expect them to both to support the same load? (the difference being the areas of weld and grinding). Same concept for flat bar, sq bar or any other shape.

It would seem recovered metal would be less structurally sound due to some stock removal, and the heat affected zones at the welds.

Cutting these zones out would seem to provide good sound metal as the zones were removed.

It would also seem that if you planned ahead in such a way that the old weld would fall in such a place as the new weld would go, weld over weld, there would be little loss of structural strength.

I am just asking the question in order to make a proper decision of new vs used materials when building a project where structural quality and integrity is a concern.

[acoop101]

Most pretty weldments you see with zero penetration, usually on one side are made by inexperienced or poor weldors using GMAW or mig. They're known as the lawyer's welder for a reason.

Frosty

Aren't GMAW and MIG the same thing?:confused:
As fare as heat affected zones they wouldn't change the metal properties for forging since you are heating them up. I can't tell u guys the number of times I've seen welds blown to xxxx from using too much heat (i teach welding and this seems to be a common problem.)

[GrandLordKhorne]

Glenn:

If the weld was made properly in the first place and removed properly when removed, than as long as you make your new set of welds the right way (meaning heat treat on metals that need it, ext) than it will have no ill effect on the quality of metal. You haft to remember, in most structural shapes they are cut and shaped with grinding and torch anyways, so you will have HAZ zones all over the piece, what maters is do you have HAZ cracks from improper procedure or material loss from over grinding. So the answer is, do it right and you can re-use a piece as many times as you like. The only place I do not suggest this is with metals used in super critical applications (space shuttle parts and such) where metal chemistry is important because stress may approach 100% of acceptable load by design. But if your designing that way without a safety factor than you have a whole other set of problems.




On the subject of welding:

To be completely honest, as a weld inspector. The most common mistake I see in the field is being in a big rush. More often than not, when I fined a bad weld it is because a welder did not do pre heat, post heat, chip slag or something to that extent. The most common mistake I catch my friends and hobby welders doing is too hot or too cold, which is a mistake I think comes to inexperienced welders in phases. Generally some one new to welding (in my experience) will weld blazing hot thinking that is how you get metal to fuse, the result being loads of HAZ cracks and often poor bead characteristics. They then tend to eventually turn the heat way down and discover that all of a sudden there bead looks really good to them (but it general sits super proud to the surface), resulting in a lot of cold laps and lack of fusion. I would argue that the right welding input has little to do with the min possible or the max penetration or what gives the prettiest bead. In fact, I fined that more often than not, it is the prettiest bead on a job that is unsound, normally because the welder that made it fresh out of trade school is worried that if he makes an ugly bead I will reject it and instead of paying attention to how to make a sound bead makes a pretty one instead.

The right and only way to determine proper welding input and characteristics is by experience and trial (this is why they have welding procedures for critical structures and welding qualifications for welders building the structures). Welding rod size is only one factor in picking the right setup to weld a section. The biggest mistake I think most amateurs with some experience make is saying

[Travis Covington]

GLK, Thank you You nearly quoted my old college instructor. It takes a lot of practice to know when something is right. If people don't use the guidelines they put everyone at risk. And knowing how to use those guides is part of experiance.
Travis

[Frosty]

Aren't GMAW and MIG the same thing?:confused:

Nope. While MIG (Metal and Inert Gas) is a type of GMAW (Gas Metal Arc Welding) the reverse isn't true.

I run 75/25 in my little wire feed, 75% argon/25% CO2. CO2 isn't an inert gas so it can't properly be referred to as MIG.

If I switch out to an argon or helium bottle then it's MIG.

It may seem like a minor distinction but the devil's in the details. And it's often the details that keep bad things from happening.

Frosty

[Ice Czar]

Lwhere structural quality and integrity is a concern.

maybe

stressprimer

for every design there is a point of failure, design failure or material failure
so the design can compensate for a weakened material, or the stressstrain might be lower than the failure point of a weakened material. But it really comes down to specifics not rules of thumb. When its a critical application, a bit of over engineering and paranoia in material selection is probably a good thing.

[ThomasPowers]

I have a rancher friend who broke the frame of his pickup and asked me why it kept breaking after he welded it up again---no preheat/postheat on an alloy frame that has do not weld stamped into it...gets scarey out here too

[Dodge]

Glenn:

"...and by adjusting speed and arc can make a good weld every time, which comes from an outstanding knowledge of puddle and arc characteristics which we should all strive to achieve. It is also worth noting that more can be said about weld quality based on the characteristics of the puddle during the weld than the characteristics of the weld face after it cools."

Ok, that was my 2psi, thank you for your time.
GLK

I agree fully on the puddle note! Puddle during the weld is everything. The art to welding is in puddle control:)