Classic cars forum & vehicle restoration.

[rcx822]

I'm getting some parts zinc plated, I've removed everything from my car that's removable and would fit in a 1m tank, so wishbones, springs, trailing arms, brackets etc.

I took it all down to the zinc platers to show them the parts before it all went to the sand blasters.

But one thing surprised me, the zinc platers said they won't do the fuel tank. They said that it's due to the acid dip, that the acid would get inside the tank and would cause rust. In that case I thought it best to show them a gearbox bracket that is made of two C section profiles welded together to form a kind of box section that would also fill with acid. They said that would be fine. I didn't think to ask them why this bracket is ok but the tank is not and now I'm a bit concerned.

The zinc platers also told me that EVERYTHING needs to be sand blasted because the acid won't remove any old paint. But this gearbox bracket cannot be sand blasted inside. There will always be inaccessible paint inside of it. So how can it be zinc plated?

And I thought an acid dip does remove old paint, and the only reason for sand blasting parts is to prolong the life of the acid.

I'm also concerned that these zinc platers made no mention of the thickness to which they will zinc plate. The last zinc platers I went to asked me what thickness I want. So the differing thickness of zinc plating might explain why some zinc plated parts rust after 6 months, e.g. cheap Screwfix bolts, and others, like the zinc plated "bash plate" armour under my 4x4, which takes a pounding off road, is totally rust free after 7 years of abuse.

What do people think?

[ukdave2002]

The only experience I have had getting stuff chemicaly dipped is with SPL in Birmingham. With their process everything gets removed unless it's solid steel, including paint, filler, aluminium and solder. As many old fuel tanks were soldered together, you wouldn't have it dipped with their process unless you were happy soldering it back together.

Of course different firms may use a different concoction of chemicals that will affect materials differently, the term Acid Dip is probably used to generally describing any chemical dip.

Dave

[Phil - Nottingham]

Could also be due to the fact they do not want to contaminate their dipping tank chemicals - modern fuel tanks are not soldered but a number of mine are including the S2 Land Rover's
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[rcx822]

Most parts came back from the zinc platers pretty good but a few are poor. The seams and some of the welds caught some of the pre-processing fluids and then leaked out onto the zinc. I don't know if the platers just didn't rinse properly or if welds and seams are generally a problems. I'm going to ask some other zinc platers what they think.