Galvanizing after arc welding

[John MIG]

Hi Guys

Can somebody please tell me if I can galvanize parts that have been welded using an arc welder , I have been advised that the area around & including the weld (slag removed of coarse before hand) will not galvanize properly. A black mark appears
Will I need to use a MIG?
Advise appreciated
Thanks
john

 

[madkayaker]

Galvanising after Arc should be the same as after any weld. A proper welder will be along shortly who will shed more light on this.

 

[TechnicAl]

I assume we are talking mild steel.

The galvanised surface may appear different. This is because the weld will have a slightly different composition to the plate. The Silicon content is the reason. Silicon "attracts" zinc so the steel with the higher Silicon content will "attract" more zinc. This is usually the weld. Given the same time in the bath the weld will have a thicker layer of zinc. It shouldnt go black though.

 

[John MIG]

I assume we are talking mild steel.

The galvanised surface may appear different. This is because the weld will have a slightly different composition to the plate. The Silicon content is the reason. Silicon "attracts" zinc so the steel with the higher Silicon content will "attract" more zinc. This is usually the weld. Given the same time in the bath the weld will have a thicker layer of zinc. It shouldnt go black though.

Thanks for the reply.
Yes, its mild steel box section I am welding. I have a MIG but may not have enough gas to finish the job so was curious to know if I could finish the job with my arc welder.
I assume all the welds will have to be completly free from slag.
Thanks

 

[TechnicAl]

If you do it with stick the difference will be less than with MIG, the Si content should be lower.
Yes you will need to clean off all the slag

 

[dannyweld]

is it Galvanizing or electric zinc plating? whatever it is ask your man to clean his tanks out. if its electric zinc plating it sounds like it could be a matter of drainage.

 

[Welderpaul]

If you do it with stick the difference will be less than with MIG, the Si content should be lower.
Yes you will need to clean off all the slag

Is there a welding wire with reduced levels of silicon such that the welds will not swell during galvanising?

What is the detrimental effect of using wire with reduced silicon?

 

[TechnicAl]

Silicon deoxidises the weld metal (prevents porosity). The S6, A18, SG2 grade has quite a high Si level to help it cope with rusty plate.

There are lower Si grades but they will be difficult to source.

Using 100% CO2 (as opposed to Argon mix) will reduce the Si content of the weld.