Welding long channels, want to keep them straight

abstruse · Mar 22, 2021

I have to join two 10 ft. steel channels that are 10" wide and 2" deep. Besides clamping them straight on a heavy beam and doing a lot of small tacks first, are there any tricks to keep the welded joint from pulling the channels into an angle?

I can MIG, TIG or stick.

implmex · Mar 22, 2021

Hi abstruse:
I was taught to stitch weld things like that if I wanted to minimize distortion.
It's a pain in the ass to do, and you may violate the customers requirements if you just do it without getting their approval first.
If you stitch the vertical legs first it might give you a better chance to stabilize it a bit but they're only 2" high so it may not help as much as you'd like.

Are you planning to weld everything from one side only or can you flip the channel around as you need to?
How thick it the cross section?
If you can hit the 10" leg from both sides alternately it will probably help you too, but it's a lot of flipping.

I haven't welded for a living for over forty years, so take all I say with a good dose of skepticism.
I encourage you to ask again in the welding subforum....there are a lot of people there who know this turf a gazillion times better than I do.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

gbent · Mar 22, 2021

How, exactly, are you joining them? Butt, back to back, face to face?

abstruse · Mar 22, 2021

Thanx, Marcus. Customer won't complain since I'm the customer. I'll butt weld the channels, but I can scab on a plate or smaller size channel on the inside of the main channels because only the front side shows. Actually, I thought about adding the scab channel before doing most of the welding.

The cross section is a bit over 1/8", maybe 5/16".

It'd be a bit tedious to flip the channels, but I can stand them on edge and do a vertical weld on alternate sides, with both sides being convenient to access. I can grind a bevel on each angle before welding.

My choice of methods would be MIG. These things aren't highly stressed -- they're only holding a 20' x 8' pool shade that is cantilevered when deployed and spooled up at the angle when not deployed.

cyanidekid · Mar 22, 2021

yes, definitely use a reinforcing flitch plate. it doesn't matter how much you clamp it. its still gonna move. so you have to anticipate that. years of experience will tell you how much shrinkage to anticipate, and you will still be wrong. cut and go again.

johansen · Mar 22, 2021

i welded a box beam out of 9" by 14 pound channel iron

i kept flipping it over clockwise.. not realizing a put a helical screw into what i was doing that was impossible to take out.

Phil in Montana · Mar 23, 2021

You need to tell us where the welds are going to be, a box, a i beam, ect or just 2 piece,s made 20 ft long...Phil

gbent · Mar 23, 2021

For a butt weld getting the beam straight should not be a problem. Tack it straight, starting with the flanges then the web. Leave a gap. After tacking, weld the inside of the web first. This is closest to the neutral axis and will produce the least pull. Weld the inside of the flanges next. If you get a bend after welding completely, grind out the long side and reweld. Flame straightening can also be used.

If you put a reinforcement over the weld, make sure you fish mouth the ends and don't weld across the ends. Never weld crosswise on a beam.

It sounds like you are making a cantilever support. This is a flimsy beam in the off axis. It will need to be braced securely to prevent rolling.

AJ H · Mar 23, 2021

Last place I worked had a fab shop. For long/big stuff we would always use pulse spray with metal core wire. Seemed like because it was faster the heat into the part was less and therefor the distortion was less.

BT Fabrication · Mar 23, 2021

Only way to keep it straight is to clamp it to something flat. as you weld, it will move 100% due to weld shrinkage. how much changes joint to joint. if moves too much, cut it out and weld again. no real scientific way to do it.

magneticanomaly · Mar 23, 2021

Clamp to something that won't move, vibrate while welding and cooling, flame straighten as needed.

Scruffy887 · Mar 23, 2021

Phil in Montana said:
You need to tell us where the welds are going to be, a box, a i beam, ect or just 2 piece,s made 20 ft long...Phil

The real question to get a good answer.

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Welding long channels, want to keep them straight

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