weldable rust inhibiters

Date 05-25-2001 16:19

I really don't like the so called weldable primers (or any paint) because I am not convinced that they do not affect weld quality. Also someone has to breath the fumes.
However, we do use them from time to time at the customer's request. We usually use a mist coat of zinc based primer and try to keep it to 1 mil or less. On small jobs, we have used either cold-galv or aluminum paint spray bombs.
It seems that whenever we use those we can get decent looking welds and not too many wedability complaints.
I've heard of paints sold for that purpose, such as "Bloxide", but have never tried them.
CHGuilford

By mbutler (*)

Date 06-12-2001 12:39

I agree with you concerning weld quality and fumes when using the weldable primers. But how can you control corrosion when the product you are welding results in inaccessible interior surfaces? In some cases the interior surfaces cannot be entirely protected from moisture, for example if the assembly is spot welded, seam filler can be applied, but this is not a complete solution.

By CHGuilford (****)

Date 06-12-2001 13:43

I really don't a foolproof way to stop corrosion in inaccessible areas. I don't even know what you are manufacturing but a few thoughts are:

Use Inorganic Zinc paint and go light in the weld zones. It will withstand around 700 degrees when cured properly so not as much will burn off.

Use a weathering steel if practical. Or maybe even stainless steel.

Galvanize the product after welding. Of course distortion may be a problem with sheet metal.

Paint the product in a dip tank.

Metallize with a zinc/aluminum material. Not feasible in inaccessible areas but the sacrificial action of the coating may slow down corrosion.

Use cathodic protection if the weldment is intended to be stationary.

Accept the fact that corrosion is going to happen and plan on replacing the item every so often. (doesn't this happen with automobiles, unfortunately?)

Allow extra material thickness to compensate for corrosion over an expected service life.

Redesign the parts to allow seal welding.

I'm just having some fun with this but the point is there are many ways to retard corrosion but few that can totally stop it. All methods have pros and cons. I hope you find one that works well for you.
CHGuilford

By kam

Date 06-13-2001 11:39

Not looking for a paint or a primer. Completed assembly does not get painted. I just want a "rust inhibitor" to give some protection from the elements. Would be nice to have a product that does not leave a heavy oil film on the surface either (then porosity would become an issue).

Also concerned about other additives in the product that might adversely affect weld quallity (i.e. introducing additional hydrogen into the process). Are there any chemicals that should be avoided prior to welding?

How about chemicals that could affect the weld after it has been welded?

real basic process
low to mild carbon steels
90 /10 gas
GMAW-P

Thanks
kam

By mbutler (*)

Date 06-13-2001 16:52

Thank you for the thoughtful reply. The specific job I was thinking about was a truck cab repair, in fact the manufacturer has since changed the process so that they are dipping the assembled cabs in a tank. I will use the weldable zinc spray and go very light around the actual weld area. In regards to cathodic protection, in the absence of liquid immersion or coating the surface, what conditions have to exist to make it work properly in a vehicle or other dry product?

By CHGuilford (****)

Date 06-15-2001 16:35

You pretty much answered your own question regarding cathodic protection. It wouldn't do much good unless the protected item was constantly wet. The other way is to galvanize or metallize with aluminum/ zinc so that the coating corrodes in preference to the steel when water is present.

Just another thought for the previous post... How would anti- spatter spray work for preventing/ retarding rust? I've never tried that but I would think it might give some limited protection if the active ingredients are not hygroscopic (I don't have an MSDS handy).
CHGuilford