Sheet Metal Fusion Weld Symbol

By Lawrence (*****)

Date 09-10-2014 19:00

The A3.0 term you are searching for I think, is "autogenous weld" rather than "fusion weld" A2.4 does not have a symbol for this (I don't think) an acrobat search came up empty.

I'm not sure what exactly what the joint looks like for real. A2.4 Fig 11 might provide the symbol and significance if you intend this autogenous weld to be CJP

GTAW is a prequalified process for AWS D1.3

3.2.1 Square Groove Welds in Butt Joints. Complete
joint penetration groove welds (CJP) made by the
SMAW, GMAW, GTAW, or FCAW processes in butt
or comer joints, which may be used without
WPS qualification tests, are detailed in Figures 3.1A and
3.1B.

GTAW in mild steel can be troublesome without filler, especially if there is any oxidation/mill scale on the base metal or if the steel is unkilled. Having some ER70S-6 filler in hand often stops the headaches associated with popping and sputtering that typically occur when doing structural GTAW on plain carbon steel. Not impossible, just something to be aware of from the outset.

By SCOTTN

Date 09-10-2014 19:24

yojimbo,

Sounds like mesh paneled rails. If these mesh panels are going to be powder coated after hot dipping, you may want to look into telling the galvanizer to skip the quenching process. I know that when we hot dip galvanize pieces that are to receive a top coat, we make notes on our p.o. and also write on the steel "do not quench", because the top coat will not properly adhere to the galvanize coating if it's been quenched. I don't know if there would be a problem with powdercoating, because my experience has been with top coats other than powdercoating. I just thought it might be worth mentioning. Another possible issue with the framed mesh panels, are possible "wrinkles" in the mesh panels due to the effects of the mesh being hot dipped in a vat that's typically around 850 degrees F. The bigger the frames, the more the mesh will have these "wrinkles".

By yojimbo (***)

Date 09-10-2014 20:21

Scot-

That's right, mesh panel frames, about 100 of them bolted to the outside of some existing, 40 year old out of code railings [they built them to 36" tall back then with horizontal rails spaced 12"!! Plenty of room for little kids to climb through and show Mommy their new balancing trick on the third story!!]. The frames will bring the spacing issue into code and we add a 6" top rail- everybody's happy.

Usually you manage to give people a good laugh around here but reading through your post initiated a minor anxiety episode. We just finished 2100 LF of galvanized and powder coated DOT railing early this year and the idea the powder coat was just waiting for winter to start peeling off was a little unsettling. But it is apparently standard ops for DOT and they put our coaters through a rigorous QA/QC pre-qualification of facility, manual, material and application. Every section of that railing was inspected at my shop for fabrication/weld compliance, inspected again at the galvanizer, and then inspected twice at the powder coater, 1st for the sweep blast prior to coating 2nd after coating requiring I believe 3-4 special inspection tests: a mill thickness, a hardness, a pull off and something else I don't recall. It could very well be just the difference between paint and powder coating or it may have to do with the pre-coating media blast, but it was their spec and procedure and followed to the gnats tail. Actually looked damn good.

I have heard of many problems galvanizing mesh. The 3 jobs I've done before with this system all worked very well without warping issues and that was with 6 GA. welded mesh. The problem, so my galvanizer tells me is created with different cooling rates between mesh and the frame material that is made worse when the mesh is welded to the frames. Maybe I just got lucky with our welded mesh frames but there were about 90 +/- all about 3' X 4' with both flat bar and angle frames and there weren't but 2 panels in the lot of them that showed but the most minor warping of the mesh. Installed you couldn't see it at all. This job will be using 2 X 2 and 3 X 3 crimped mesh, all 1/4", trapped inside the U edge frames but not welded to the frames- which is what the galvanizer always wants to see. First time working with the crimped mesh so we'll run a test piece or two through the zinc. Actually it was brought to my attention from the painter who also quoted this job [and may still be doing it as we don't yet have approval for powder coating, just a better price] that we would really want to galvanize the crimped mesh because the paint would never get in between the crimps and eventually cause rust stains. Good point to look out for and never occurred to me. The cost of the galvanizing is offset by being able to remove the Tnemic zinc primer coat if it's galvanized and also reduces the paint prep blasting to a sweep blast reducing both the painters and the powder coaters cost.

I will ask the QC guy at the galvanizer about the quenching issue. H'es pretty heads up and you have me curious now. Thanks for your response.

By yojimbo (***)

Date 09-10-2014 19:51

Lawrence-

Very helpful and happily pre-qualified. Will make matters that much simpler. With what you've provided I should be able to track down everything I'll need to satisfy the EOR with our submittals.

I take your point with carbon steel "fusion" welding w/out filler being problematic. I'd probably expect to have some small diameter wire in hand and we'll experiment to get it as productive as necessary. Only about 100 frames, flat welding, all bench work, should be a snap.

I'll be locating those code references you provided. Thanks again.

By Metarinka (****)

Date 09-10-2014 23:58

We would specify the welds as square groove welds with 0 root gap and melt through. I would still have a note on the drawing or tail to denote that the weld should be autogenous. sounds like you would allow wire you just don't need it for speed if the fitup is tight.

By yojimbo (***)

Date 09-11-2014 03:44

Metarinka-

That sounds about right. Will be checking the referenced specs Lawrence provided and putting this together. It's very far from aerospace work but engineers appreciate the details have been considered during review. Thanks.

By yojimbo (***)

Date 09-11-2014 03:46

Al,

I was wondering about that too. If we don't get a reply here I will be asking the QC guy at the galvanizer and report back.

By 803056

Date 09-11-2014 04:04 Edited 09-11-2014 04:06

My understanding of quenching is that the carbon or high strength low alloy steel would have to be austenitized. That would be above 1600 F for most steels used in construction.

I was under the impression that HDG is on the order of 1000 F.

Just looked it up. The temperature is around 900 F, so, the steel is not austenitized, so it ain't quenching in the metallurgical sense.

Al

By welderbrent (*****)

Date 09-11-2014 04:46

Typical misuse of terminology not properly understood by many vendors, both galvanizers and powdercoaters.

Wouldn't waste too much time on it, they're not quenching it, they may have a problem that shows up that they are attributing to the heat induced but since they don't understand proper terms and applications they just drew one out of the hat. Has happened to me many times while I had the shop here in AZ.

One more thing, somewhere above, mention of paint not getting between crimps, neither will powder coating. If they tell you otherwise they are filling you with pipe dreams. Want proof? Take a small section and get it galv'd then powdercoated and cut it apart with a cut off wheel so as not to burn out any powder that may get into the joint. Not happening. No more so than with normal spray gun and paint. All depends upon how thick and from how many angles it is applied. If applied thick enough you might get it to seal around the joint but don't bank on that either. In short order, with expansion and contraction the paint that is not properly bonded, just bridging a gap, will pop off and leave the joint wide open for moisture in and rust out. I give it two years at best.

No matter the coating or combinations of coating, the end result is only as good as the preparation. The larger the radius and smoother the transition the better it will be and longer it will last. With no actual bonding of the base materials there is bound to be inherent problems later.

He Is In Control, Have a Great Day, Brent

By yojimbo (***)

Date 09-11-2014 14:28

WelderBrent-
Incomplete top coating between the crimps was brought to my attention by the painting contractor who's looked at this job. His recommendation was to have the crimped wire mesh screen hot dipped galvanized to prevent the inevitable rusting at the criimps that would occur where the paint [or powder coating ] would not penetrate and provide coverage. Are you saying the galvanizing will not be effective in coating the crimps? If so, I'd bring this to the owner and suggest using welded wire mesh as an alternative. I meet with the prime on Friday onsite. I'd like to hear your opinion in this regard. Thanks.

By jwright650 (*****)

Date 09-11-2014 10:50 Edited 09-11-2014 10:59

Yup...bath has to be kept at a min of 850°F to remain molten and still wet out while cold chunks of steel are being dipped.
Quenching is part of the hot dip process not describing what is happening to the steel. Quenching helps with the shiny finish, while if the part is to be top coated with paint, they skip the quenching process and the finish has more "bite" for the paint to promote adhesion.

http://www.galvanizeit.org/specification-and-inspection/post-hdg-considerations/passivation

http://www.galvanizeit.org/specification-and-inspection/specifying-duplex-systems/preparing-hdg-for-paint

http://www.galvanizeit.org/specification-and-inspection/specifying-duplex-systems/preparing-hdg-for-powder-coating

EDIT*
whoops, I should read more before posting...Scott has covered most of what I just typed......

By SCOTTN

Date 09-11-2014 11:26 Edited 09-11-2014 13:44

Al, yojimbo,

With regard to the quenching, after a piece of steel has been galvanized, it's sometimes quenched or treated by the galvanizer in order to stop the reaction between the iron and zinc. The most common post treatments are water quenching, chromate quenching and phosphating. Water and chromate quenching will adversely affect the bond between the galvanized steel and the paint (referred to as a duplex system). That's why it's critical to communicate with with the galvanizer prior to galvanizing in order to avoid post treatments that can be detrimental to paint adhesion.

Edit: related links:

http://www.galvanizeit.org/images/uploads/publicationPDFs/Paint_Over_Galvanized_Steel_Duplex_Systems.pdf

http://www.apluspowder.com/GalvinizeArticle.pdf

http://www.galvanizeit.org/specification-and-inspection/post-hdg-considerations/passivation

Edit (Part 2)

I should have paid more attention to the links that John posted. The other day my wife said she was leaving me because I don't pay attention. I said "What??"

By yojimbo (***)

Date 09-11-2014 19:34

Scott, JW-

Good reading and info with the links. We are getting pricing for a welded wire mesh which we'll bring as a consideration for the owner. The galvanizer is throwing back caveats regarding coatings at the crimps. Welded wire would eliminate the concern and ease future maintenance. Might be the simplest solution.

By SCOTTN

Date 09-11-2014 20:25

Have I missed something? You were originally going to weld wires together to make these mesh panels? You didn't mention anything in your original post, so I thought you were actually using pre-welded wire mesh panels. That's what we've always used, along with the u-edging, unless we can get out of using it. We just raise the u-edging off the rails 1/8" all around for the galvanizing to flow through, and stitch weld them to the rails rather than seal weld them. Where the mesh fits inside the u-edging, we get a good bit of tack welds inside the edging to keep it in place. It's hard enough to do this, and seal welding is pretty much out of the question. We've always tried to get away from using the "u edging", regardless if it's galvanized panels or painted panels, and we've been very successful in getting it changed. We prefer flat bar to sandwich the mesh panels. We fit one side of the flat bar directly to the rail, making a frame, then we lay the mesh panel inside the flat bar frame, and stitch weld it to the flat bar frame. Then we flip the rail over and frame that side with the flat bar. The flat bar framse end up being stitch welded to the rail. The mesh panel ends up being stitch welded to one side of the flat bar frame on the inside. We've found this to be much easier and less expensive than the u-edging.

By yojimbo (***)

Date 09-16-2014 14:40

Scott,

The welded wire is a manufactured product we purchase. We want to use it instead of woven wire because the coatings will not protect the intersection of mesh at the crimped woven wire called out. Welding the mesh to a frame- so our galvanizer insists- will warp/wrinkle the mesh due to different cooling rates of the mesh and frame. We'll be using .244 wire and the U edging is 10 Ga. I'll experiment with a few panels- have some frames with the mesh tacked and some "floating" in the U edge- per galvanizers recommendation- and see which works best for us. To date we have never had any wrinkling in any mesh but we always use at least a 6 Ga. wire. I have seen a badly wrinkled condition after galvanizing in their yard with someone who used a 10 Ga. wire. I'll compare fabrication time/costs using the U edging this time and compare it to previous flat bar and angle frame construction for future reference.