Joining bar

[Andy from Workshopshed]

hi all, I'm new to the forum but have been reading bits and pieces for sometime.

I'm new to MIG and am slowly getting the hang of joining chunky steel plates together and producing a weld that looks at least a bit like the ideal. So I'm reasonably happy the the machine is setup right.

However, I tried welding some bars together yesterday and the metal started forming small orange bubbles, some which then popped. I ground the joint back to see if it was solid and not surprisingly it was pitted as you can hopefully see in the picture below. It did not seem to matter if the bar was horizontal or vertical.

Is there something specific about joining bar? Any suggestions as to what I was doing wrong?

Thanks in advance,

Andy

 

[malcolm]

Having the weld full of bubbles is a fairly classic sign of a lack of shielding gas. You would also expect a lot of spatter and welds covered in brown rusty dust rather than looking like chean metal.

Can you hear a decent hiss of gas coming continuously out of the torch? (not just a spurt when you first press the trigger). Also are you welding outside? - the wind blows shielding gas away easily. Disposable bottles and regs can be a pain.

 

[1styear]

That is called porosity it has many causes here are a few it can happen

• If there is not enough shielding gas, or way too much should run mig at about 18Lpm or more depending on the situation
• If the metal is unclean e.g. rusty, oily, painted
• If the MIG wire is contaminated

and various other reasons but they are the three main causes.
Also when you get porosity you should grind out all the porosity that you can and then re-weld it.

 

[Andy from Workshopshed]

Thanks for the comments.

The weld was not covered in rusty dust it was a slate grey colour but there was lots of rusty dust generated around the area of the weld. You can see from my image that the inside of the bubbles have this coating. The surface was lumpy like a ricecrispy cake.

I did not notice a lot of spatter when I was using welder but that does not mean it was not happening.

Was welding inside but had a very large extractor fan quite close to the work.

Will check gas and extractor next time.

Thanks again.

 

[Bsmith]

Think the orange bubbles popping would be rust, salt or some other foreign contaminate. I'm sure yours isnt as its painted, but actually rebar is a high tensile steel and should never be welded or heated if its going to be used as rebar in concrete.

 

[Andy from Workshopshed]

I thought the black surface layer was just oxide not paint but I suppose that could be affecting things.

You'll be glad to know it's just a small tabletop sized sculpture, I'm using the bar for it's appearance not for it's structural qualities.

 

[Welderpaul]

Think the orange bubbles popping would be rust, salt or some other foreign contaminate. I'm sure yours isnt as its painted, but actually rebar is a high tensile steel and should never be welded or heated if its going to be used as rebar in concrete.

Granted this is not a structural item, but with the correct procedures, rebar can be welded and heated. We make quite a few 'cast-in accessories' for people, almost always means welding rebar. We often weld large diameter rebar on site, under the watchful eye of the structural engineer. - Usually when laps/splices have been missed, or someones cut something they shouldnt.
Specialist jointing sockets can be used, these are quite fancy but REALLY expensive.

So there you go. If you wernt bored before, you are now

 

[Sid]

Welderpaul, would you typically use an arc welder for joining rebar?

 

[Sparkey]

Yes you can but mig is easier to use...it all depends if you ave to weld on site or in a workshop i guess...

 

[Bsmith]

Yea ok Andy, I use rebar for all different kinds of jobs too. I usually weld it and often heat it to make it easy to bend, It does the job and it always seems easy to get hold of some off-cuts from a building site etc.
Thanks for putting me right Paul. The engineers and safety people with the company I used to work for would not allow heating or welding of the rebar which was used in their concrete foundations. It would often displease the steel fixers when we would said NO to them as a little weld here or there could have covered up a huge mistake. They had an engine driven guillotine and bender and the rebar was always worked cold.
Not bored, Thanks again, Brian (",).

 

[Bsmith]

I would suggest joining rebar with arc and 7016 0r 7018 rods for a stronger job.