Thread: Long weld

Hit there!
Still working on my ramp, weekend work very slow

I would like to know from the experts out there what would be the correct procedure to weld a 4m long flat bar 60x5 perpendicular to a 4m long RHS 150x50x3 duragal.
I have to make 2 of this things. This flat bar will be supporting the deck made of 240x45 M12 H3 pine.

I was planning to do 100 mm weld and then 200 no weld on both sides but I spoke to the galvo people who will do the hot dip and they said that in order to guarantee no rust it will have to be welded all along with no gaps.
So all weld it is. I have already tack welded both RHS pieces together to eliminate bending and will start welding the flat bar (one to each of the beams) .......... I would like to know the best way to avoid it pulling to the side of the weld and keep it square...............your replies are appreciated.

Originally Posted by Marc

Hit there!
Still working on my ramp, weekend work very slow

I would like to know from the experts out there what would be the correct procedure to weld a 4m long flat bar 60x5 perpendicular to a 4m long RHS 150x50x3 duragal.
I have to make 2 of this things. This flat bar will be supporting the deck made of 240x45 M12 H3 pine.

I was planning to do 100 mm weld and then 200 no weld on both sides but I spoke to the galvo people who will do the hot dip and they said that in order to guarantee no rust it will have to be welded all along with no gaps.
So all weld it is. I have already tack welded both RHS pieces together to eliminate bending and will start welding the flat bar (one to each of the beams) .......... I would like to know the best way to avoid it pulling to the side of the weld and keep it square...............your replies are appreciated.

Not quite the answer you're after, but my first thought is to make it out of two pieces of flatbar spaced appropriately to let the gal fully flow through the gap and have it all braced with gussets. That way there are no cavities for rust to start in and minimal continuous welding length
Cheers
- Mick

Don't fully weld that or you will create a whole world of hurt for yourself and potentially distort the beams near beyond repair.
Put basically, your galvaniser is wrong.
The best way to tackle the job is to space the flat bar 1mm or so away from the 150X50 and stitch weld it 50mm on top, miss 150, weld 50 on the bottom, miss 150 and so on. Spacing the flat bar out 1 or 1.5mm allows the galvanising to penetrate, (think solder almost), and form a good bond that does not fail. Been there done that on disabled personnel loaders that were exported worldwide.
Even though your plan to back to back the RHS is fairly sound, it will not counteract 8M of fillet weld and your beam could well distort in both axis.
When you stitch your flat bar, crank that welder up good and hot and run your welds in quickly. They don't need to be too big either - 25mm of 6mm fillet will hold a tonne.

Originally Posted by WelderMick

Not quite the answer you're after, but my first thought is to make it out of two pieces of flatbar spaced appropriately to let the gal fully flow through the gap and have it all braced with gussets. That way there are no cavities for rust to start in and minimal continuous welding length
Cheers
- Mick

Yes, that will probably work too, just a lot of additional work and the length of weld would be about the same since I will have to weld each gusset all around against the RHS and against the flat bar.

Originally Posted by Karl Robbers

Don't fully weld that or you will create a whole world of hurt for yourself and potentially distort the beams near beyond repair.
Put basically, your galvaniser is wrong.
The best way to tackle the job is to space the flat bar 1mm or so away from the 150X50 and stitch weld it 50mm on top, miss 150, weld 50 on the bottom, miss 150 and so on. Spacing the flat bar out 1 or 1.5mm allows the galvanising to penetrate, (think solder almost), and form a good bond that does not fail. Been there done that on disabled personnel loaders that were exported worldwide.
Even though your plan to back to back the RHS is fairly sound, it will not counteract 8M of fillet weld and your beam could well distort in both axis.
When you stitch your flat bar, crank that welder up good and hot and run your welds in quickly. They don't need to be too big either - 25mm of 6mm fillet will hold a tonne.

That was my first thought Karl, I called them to ask how big of a gap I need to leave for the galvo to flow behind the flat bar, and they told me that wouldn't work and to weld the whole length ... you say 1.5mm is enough? That would be a much easier way to do it. 50mm of weld every 300 top and bottom staggering it.
Any particular sequence? Should I start at each end of the 4m RHS ? Leave to cool down every how much? or does not matter?
Thank you both for your answers.

We used to use a piece of .9mm mig wire and that worked very well, so anything in the 1-1.5mm range should be fine.
As to sequence, set it up so that your flat bar is vertical, mark out your beam with your welds and misses and just start from one end and work yourself along welding both sides of your flat bar as you go, then flip the whole thing over and do the other beam if they are still tacked together.
It always pays to remember that a weld contracts more width ways than length ways as well, so by this method, you are giving yourself intermittent length way welds, minimising potential distortion.

Thank you Karl that will be easy. I also have a roll of 0.9 in the machine. I'll use a piece of 1.5 flat bar to keep the gap consistent and clamp a piece of SHS next to the flat bar to keep it square. ..........Hooroo.........Marc

Last question if you don't mind ... This 60x5 flat bar will need to be drilled for 10 mm SS bolts all along. The galvo will reduce the size of the hole but I don't know by how much. Would 12 mm be too much? 11? .......... your reply is appreciated...........Marc

I'd drill it 12 mm, most of the galvanising should drain off, allowing the 10 mm bolt to go through, if built up, should be able to be drilled to 10 mm without a problem.
Kryn

Originally Posted by Marc

Last question if you don't mind ... This 60x5 flat bar will need to be drilled for 10 mm SS bolts all along. The galvo will reduce the size of the hole but I don't know by how much. Would 12 mm be too much? 11? .......... your reply is appreciated...........Marc

Standard structural clearance is +2mm and that will be plenty for what your needs. I probably wouldn't use stainless in this case as I reckon galvanised bolts - not zinc or cadmium plated, but proper galvanised, will be your best bet. Stainless bolts are a PITA and expensive too.

12 mm good I got an annular cutter 12mm just the ticket.
Karl ... looked up the galvanisers web site and they say I need 2.5mm gap minimum to avoid run off on a butt joint, meaning the acid bath will not drain off the gap completely and steam will blow the zinc out the butt joint if it is too narrow ... (?)

Originally Posted by Marc

12 mm good I got an annular cutter 12mm just the ticket.
Karl ... looked up the galvanisers web site and they say I need 2.5mm gap minimum to avoid run off on a butt joint, meaning the acid bath will not drain off the gap completely and steam will blow the zinc out the butt joint if it is too narrow ... (?)

When we built the disabled personnel loaders mentioned in a previous post, we butted a 50X50X3 SHS onto a 100X50X3 RHS with the 0.9mm gap and never had an issue. The galvaniser was Industrial Galvanisers and if anybody could stuff up galvanising, they could!
When you think of it, there is very little pickling solution to run out or a 6mm wide joint, you therefore have two options. A, run the 1.5mm gap, or B, increase the gap to 2.5mm, which will be no real hardship and quite weldable although you may need to drop your power a little..
I would probably take option B, even though I have full confidence in the 1.5mm gap, as your Galvaniser may potentially refuse to dip your beams if they don't like what you've done. A third option is to find someone that you can talk to at the galvanisers and explain your individual job. I think I'd still go option B to avoid any drama.

Thank you for that Karl, I actually spoke to a different galvanising mob and they quoted 1.5mm not 2.5
They said that the acid will wash through the 1.5mm gap and then the zinc should fill in the gap.
If I go for the bigger gap, would I still stitch weld 50 mm skip 150 and then the other side or will I have to weld both sides 50 mm and skip and both sides again?

Originally Posted by Marc

Thank you for that Karl, I actually spoke to a different galvanising mob and they quoted 1.5mm not 2.5
They said that the acid will wash through the 1.5mm gap and then the zinc should fill in the gap.
If I go for the bigger gap, would I still stitch weld 50 mm skip 150 and then the other side or will I have to weld both sides 50 mm and skip and both sides again?

I reckon you should be good to stick with the original sequence.
You're lucky to have a couple of galvanisers to choose from, down here we have only one which means pricing is less than kind and quality is what they decide to give you on a given day.

i have two places nearby, I am sure there are many more. One a small place charges $1.9 per kilo, the other a larger industrial place $1.07. The flip side of the larger place is that they take no notice of any instructions you give, for example not to quench. Surprisingly they were more forthcoming with this business of a gap, when the smaller place was adamant that I must weld the lot or bust. Go figure!
The previous job I took to them, 4 PFC that are now bolted down to a concrete platform, I asked it not to be quenched yet they did.

I cleaned it up as best as I could and painted it with Dulux Luxepoxy4 This two pack undercoat designed for non ferrous metals is amazing, it sticks like glue and the finish is very hard. They use this to paint bridges and street lamps and stuff like that. Even though it is an undercoat, it does not need top coat unless for cosmetic reasons.