Thread: Copper block idea - advice?

Copper is used as a chill block regularly.
It shouldn't be necessary though. I've welded a lot of 1.6 SHS with a stick welder and it's quite achievable. I prefer a 4112 electrode, but I have used RB26's as well.
What are you using? AC, DC+ or DC-? What sort of amps?
You need a shortish arc and to concentrate more on the box side than the open ended side of the joint.

Oh, I can do it alright. But it's not uncommon for me to mess up my fitment slightly and with those particular joins a millimetre off makes a huge difference. I use a BOC Smootharc, usually around 42A-48A, DC+. RB-26 because I wanted to standardise on one rod instead of the half dozen or so I previously went through. And they get a good rap on the forum and they're dirt cheap. I do wish there was an RB-20 though.

As I'm sure you know, the difference between zero penetration and a blow through is less than a second on this thin wall stuff. I thought that using a copper block as a mould to build up a clean, straight "pad" might be a great idea. But if the copper melts on the first attempt it's a waste of time and copper.

My usual technique if I'm really concerned about poor fitment or holes is tack after tack on 25mm shs then go over the tacks with a finish pass when there's enough material and the gaps disappear.

I also have taken to using discarded rod ends as filler rods to fill holes, which works well. Stick the rod in the hole, turn up amps a bit and tack it in place and then go over it with a smoothing pass for aesthetics.

You are right, 1.6 is pretty unforgiving. My favourite electrode for 1.6 was and is, Murex Speedex 12 in the 2mm size. I've even welded 1.15 wall conduit with them.
In the application you describe, it wouldn't surprise me if you needed a slight rebate in the copper block to allow the metal to achieve its full with once slag is taken into account. I recall an article in a welding journal where this was required when hardfacing the edge of 12mm bisalloy plate.
Sometimes really shoving the electrode in and almost choking it can head off a blow through or when fit up is not as good as you hoped.
Give it a try and see how you get on. My gut feeling says you will want a bit of 10 or 12mm copper at a minimum so as to dissipate the heat if more than a couple of build ups are done in quick succession and watch your fingers, that heat will travel pretty quickly.

Aluminium works well also,my piece is about 100X75X12, have used it many times for poor fitup work. If you are constantly getting burn through you could try going a bit faster or tilting the job on an angle. Just because a rod is cheap, it doe'snt necesarily mean it's economic.
Kryn

angle tacked to channel.jpgAttachment 286091Attachment 286091

Originally Posted by Legion

I do a lot of stick welding with 1.6mm shs. When I need to butt no matter how well I fit it up the chamfer on the flat side of the join makes it very difficult to avoid blowing holes with rb-26 rods. .

If you use a chamfer prep on a butt ,that is your problem.Use a square edge preparation. Only remove paint or gal coating by scuffing avoid removing any material thickness. The whole process is about minimising heat input into your material.

Try these things:

• Extremely good fit up - see above and below where cnr radius was left too big.
• Weld using electrode positive
• Use extremely short arc length-flux coating touches work
• Travel speed is really quick- it does take some practice to stay on the weld bead alignment
• Set up your weld position to allow semi vertical down - somewhere around 30 - 40 degrees off horizontal

See the pics of a 1.6 to 2mm edge join above and below.It was welded using all these techniques.Success has more to do with the techniques used rather than the inverter type used in my opinion.
Cheers
Grahame

No, I don't do a chamfer prep Grahame. I mean the chamfer due to the radius of the SHS corners.

butt_chamfer.png

With that tiny internal corner of the butted SHS it's already hard work. If my measurements or cut are a millimetre off it becomes difficult and time consuming to make a nice weld.

I end up tacking and joining tacks. My original thought for this thread was to build up that radius corner to a square corner, so that the butt had a squarer fit up.

I do direct the arc towards the tube side and sometimes leave it there apart from the odd whip across. Directing the arc directly at the butt side is a recipe for disaster once any heat gets into it.

Impatience doesn't help. I should tack, tack, tack and then go to another join but often my projects are big and unwieldy and I can't be bothered moving them around just for a minute so I just wait too short a time then go back into it while the join is still too hot.

I will try the semi-vertical down technique.

I have used graphite as a backing block in the past. Hard to find large pieces tho.

Dean

Originally Posted by Legion

I do a lot of stick welding with 1.6mm shs. When I need to butt no matter how well I fit it up the chamfer on the flat side of the join makes it very difficult to avoid blowing holes with rb-26 rods. I have some idea that copper won't fuse with steel so I had an idea to use a scrap copper block, clamp it to the area where I'm going to butt and then run a bead along the chamfer to build it up square. This would then give a nice square "flange" to butt the other piece of shs to and also a bit more material to sink heat. But given the lower melting point of copper, surely it will just melt away if I'm running a bead along it? I thought it would be nice if I could unclamp the copper and it would come away clean with a new straight edge on the steel.

copper backing bar will work fine. But use the smallest electrode possible and turn the amperage down to around 70 or a little less. Also focus the arc on the radius (edge) of the SHS as this gives heat more volume to disperse. Let the weld pool bridge its way across the gap by intermittently guiding the arc very briefly across the gap. Increase welding speed to prevent too much heat build up and you probably wont need the backing bar. If it gets too hot, cease welding until the steel loses it's hot orange colour.