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Repairing galv chassis..


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How much is involved in galving a previously galv'd chassis?

My mates 90 was recently damaged by a truck. The damage to the rear cross-member area is pretty bad. He now plans to rebuild the 90 completely. It looks like he'll get away with welding on a new cross-member with the extension pieces. Once done, he wants to re-galv the whole lot.

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Not sure of the tech term but the process of galvanising changes the structure slightly of the metal.

The coating if welded on top off gives off evil fumes which are serious dangerous - cyanide spings to mind :lol:

You can get galv off, or mainly off, I would use a series of flap wheels on a grinder and unusually for me

a mask too, get the man off 1st, then swap to new wheel and redo gently until your using say a 120 flap

grade wheel and have a polished surfcae, then also clean before welding with say brake cleaner or thinners (let it dry 1st tho :lol:)

and then hold you breath when you weld, the qulaity of how well you have cleaned it will reflect the

new weld qulaity, a green glow + toxic fumes + horrible weld - sometimes reffered to as a "A Warne" :rofl:

....means not clean enough :(

Just take care and it's doable :)

Nige

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Hi the fumes wont kill you but will give you zinc fever (really BAD flu type symptoms)and as far as I know zinc behaves the same as lead or any heavy metal ie. it stays in your body for ever! as for re-galvanizing, check with the firm who you plan to use as they might not want to do it or will charge you a small fortune, for some reason they just don't like doing it, we had to send some structural steel back in after modifying and it cost us triple!...

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Have you considered having the new rear cross member galvernised prior to fitting, grinding the galvernise off the areas to be welded on chassis and cross member then once fitted just treating the welds with galverfroid, assuming the inside isnt left bear metal it should still last a heck of a long time and would save hundreds that you would spend having the entire chassis galvernised

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Wot he said! beat me to it, wear a proper mask as above and grind it outside in a decent breeze, when you've finished have a pint of milk!

Mike

Yeah been there, done that and had more than a few pints! :blush:

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I would just start with a fresh galvy chassis, by the time you add your time and costs up, not to mention the fact that the chassis could well now be 1" out further forward/ distored, i reckon you wouldnt be saving that much.

Will.

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I think we are all missing the obvious - you don't need to dip the whole chassis again.

Just weld on a new rear cross member (with the relevant precautions) then ask the galv plant to dip the end of the chassis only. That way you will only pay for the galv pick up on the cross member and rear end of the chassis.

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What I was thinking.

Is it actually stripped and string-lined now, so you can see the full extent of the damage?

We rebuilt a 6.5ton Iveco last year, it'd had a minor roll. We stripped the body and subframe off it (tilt and slide recovery vehicle), but it wasn't until the cab came off it that the bow in the front part of the chassis was evident.

By this time there'd been a lot of work done, so forward seemed the only way to go.

After the cost of having the chassis jigged, the man-hours involved in straightening the cab, replacing the steelwork on one corner of the bed, rebuilding the suspension, it wasn't a cost effective excersize.

Had we have known the full extent of the damage in the first place, we wouldn't have rebuilt it.

Our fault was, we only looked the chassis by eye, from underneath. We should have string-lined it properly to check the dimensions.

Bear in mind that as you weld the outer part of the chassis, you'll burn the galv on the inside. It will need waxoyling inside once done. A chemical dip won't take the original galv off properly, the only way to do this is to have it blasted (with a proper blaster, not one of those machine mart bucket jobs). Even then, the new galv won't take to the old galv on the inside of the chassis very well.

Sure the job's worth less that the price of a new galvy chassis?

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I think we are all missing the obvious - you don't need to dip the whole chassis again.

Just weld on a new rear cross member (with the relevant precautions) then ask the galv plant to dip the end of the chassis only. That way you will only pay for the galv pick up on the cross member and rear end of the chassis.

If only it was that easy! I'm afraid it still classed as "double dipping" the chassis would still need to be stripped of the old galv then shot blasted and acid dipped for the new galv to bond because the galv firm would not want to risk any violent reaction or contamination in the dip tank...

The trouble is hot dip galv works at about 460 deg C and starts degrading or peeling in service at about 200 deg C so the only way to "double dip" is to dip one end straight after the other...eg if the part was to long to fit in the dip tank.

Don't get me wrong I'm sure there will be a firm out there that will do it but be warned expect two things (1) it will look and be a right sh&ty mess and secondly don't expect it to last too long...

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Umm - are we all missing something really obvious, or is it just me?. Since it's all in electrical contact, won't the galv on the rest of the chassis act as a sacrificial anode for the exposed bit that you weld on, or is that only if the whole thing is immersed in an electrical substrate (ie the sea)?

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Not sure what you are getting at? :huh:

All I know is from jobs Ive done in the past if you weld on/near/too etc to galv, the place where you have welded rusts at an alarming rate even if you treat said area...

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Let me Google that for me :)

It is important to understand that for this mode of corrosion protection to function there must be simultaneously present an electron pathway between the anode and the metal to be protected (e.g.,a wire or direct contact) and an ion pathway between the anode and the metal to be protected (e.g., water or moist soil) to form a closed circuit; thus simply bolting a piece of active metal such as zinc to a less- active metal, such as mild steel, in air will not furnish any protection.

Seems Mr Electron has to find a way back too - a strong argument for keeping the truck coated in wet, sloppy mud year-round :)

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do get rid of the electrical corrosion stuff... why can't you just wire the car without using an Earth to the chassis/components? just wire it all back to the battery?

Positive earth??

G.

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What Boro said!

This is done a lot in industry (think railings, fences, stairways etc), where pre-galvanised parts are welded together (galvanising ground off, before an arc is struck!) and then the bare area treated with Galvafroid® Obviously in the case of a chassis the inside would need to be treated with good-old waxoyl. As some one else said the Zinc acts sacrificially to the steel so any gaps in the galvanising (as long as they were treated) should not be a big issue.

AD90

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Jeeez. What have i started! :D

Not liking the idea of it costing a lot to re-galv. We have got loads of time but not loads of money. Would it save expense if we took the appropriate breathing apparatus precautions and stripped all the external galv off ourselves, then got it acid dipped and re-galved?

If we got all the external galv off, the company trusted to do the re-galving wouldnt even know it had been galved in first place so wouldnt charge us for 'double-dipping' (ooer)... Thoughts?

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Where I use to work (making milking machines) most of the stuff was either Stainless steel or pre-galved steel. If the pre-galved steel was to be welded it was always done with an ARC welder (My job) as this would cut thro the galv and weld fine. After welded it was painted with Galvafroid and eitcher primed and sprayed silver.

Paul

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Jeeez. What have i started! :D

Not liking the idea of it costing a lot to re-galv. We have got loads of time but not loads of money. Would it save expense if we took the appropriate breathing apparatus precautions and stripped all the external galv off ourselves, then got it acid dipped and re-galved?

If we got all the external galv off, the company trusted to do the re-galving wouldnt even know it had been galved in first place so wouldnt charge us for 'double-dipping' (ooer)... Thoughts?

Even if they didn't see it, as soon as it was put in acid they sure would then! and you would have some explaining to do!

To be honest if you do your home work, you find that cold galving is sometimes the first choice eg. oil rigs,pipe lines and maritime vessels etc

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