Zinc Plating vs Galvanising
I have a vehicle bulkhead (firewall) which I intend to restore by cutting the rust out and welding new pieces of plate in.
Once finished, I am planning on getting it either hot-dip galvanised or zinc plated.
The bulkhead on this particular type of vehicle is very prone to rusting, so many owners have them plated after restoration. They are almost always spray painted after plating.
Would hot-dip galvanising or zinc electroplating be a better option for this application? I have read that hot dip galvanising can cause the thin steel plate bulkhead to warp. This is what lead me to consider electroplating. Would electroplating leave a sufficient zinc coating to protect against corrosion in the same way that hot-dip galvanising would?
What are your thoughts?
I can't tell you for sure which is better but I can tell you that the Hot dip bath should be about 860deg F and the part needs to be pre heated so the galvanize (zinc) will stick as it goes into the bath. Their is another process though called aluminizing ( Aluminized steel - Wikipedia, the free encyclopedia ) the corrosion resistance of aluminized steel is far superior to galvanize. The catch is aluminum at that temp ~1200 deg F is exceptionally corrosive to anything that stays in the bath like the dipping rig. The parts that say in the bath are just considered throw away parts so the process caries a premium in cost but its well worth it. As a side note most new cars in the a and b pillars are made out of high strength steel that has been aluminized thru a continuous aluminizing bath.
Hot dip galvanizing would almost certainly offer better corrosion resistance than zinc plated.
Zinc plated is like a cheapie hardware store bolt. Put it out in the rain and it will rust. Hot dip galvanize is like a radio tower. It lives out in the rain for years and doesn't really rust.
This is the specifications of the zinc plating at the company that is located fairly close to me:
Jackson Plating Ltd - Zinc Plating - Zinc Electroplating - De-embrittlement
Zinc electroplating is basically a cheap process that provides a little corrosion protection. Adding an Iridite coating (Chromite Conversion Coating) will double the corrosion protection of the zinc, plus give better paint adhesion. Hot dip galvanizing would be preferred in any aspect of corrosion resistance for your application.
Aluminizing is done at very high temps. Somewhere around 1650 F. You would get a lot of distortion when doing sheet metal with that process.
Nobody suggested powder-coating?
My experience involves keeping metal alive on my sea farm--boat trailer, boat and pump fittings and fasteners.
Hot-dip galvanizing is vastly superior to zinc plating. The plating is essentially useless, I wouldn't even bother.
Your welds, and especially the HAZ around the welds, will corrode more quickly than the base metal. That's what we find on repairs on steel-hulled boats. A good prep process for hot-dip galvanizing will help prevent this.
If you are looking to save money you might sandblast the completed project then paint with a good zinc-rich paint, then a protective layer of paint over that. It won't form the nice chemical bond between the base steel and the coating that hot dip will though, but it will be at least as good as zinc plate and a lot cheaper.
If you go this route, make sure your zinc rich paint has a t least 95% zinc in it. The spray paints sold in hardware stores to cover scratches in a galvanised coating is often 93% and the 2% difference matters when painting a clean surface.
I found a product in my local welding supple that I've just applied to a new trailer, over the existing hot dip galvanizing. Check back with me in a few years to see if its effective
This is the stuff: http://www.zrcworldwide.com/p_zrc
It is possible that you will get some heat warpage from galvanizing.
After all, it is taking it up to 800 or so.
Usually its not too bad, and can be hand bent back into shape with thin stuff.
But it definitely can happen.
I agree that the hot-dip would be a better option, but it does have it's own downfalls as mentioned. Another option would be a chemical substrate. I used this product several years ago on the chassis, suspension & some body parts (firewall included) of a '63 Chevy. Pretty tough stuff, but I didn't expose it to any extreme environments, either.
POR-15 Black Rust Paint Quart
No affiliation with the product. Just happy with the outcome.
Whats this the bulkhead off? Any plating or galvanising will only work on clean metal. Galvanising will get all the internal crevasses if done right, but again they have to be clean metal, scale - light rust will be removed in the pre galvernising pickle, but oils, grease and paints won't! Plateing won't get any internal surface even if its clean because of how it works. The best plating i have seen (high grade military spec) only managed about a year in a marine environment. But its relay not the way to go if you have seams or internal cavities to coat.
However galvanising will cause all thin - panel work to distort to varying degrees. I have a series 3 land rover, just got some new under wing shields and got them galvanised. Yep they have distorted, but there simple enough to straighten out good enough to do there job. The bulkhead on a land rover would be damn near impossible to straighten. You can get them to dip it at lower temps to reduce distortion, but its still a issue.
The key thing i find is you need to use good paint or good under seal on a well prepared surface. So long as it won't chip it will protect the surface below it. I tried the zinc rich primer route on my front bulkhead, caused adhesion issues with the top coat and really failed prematurely. The zinc protects the steel by turning to zinc oxide. Paint stops this till it gets a chip then the zinc oxidises and the paint falls off in sheets.
For internal channels and such i find you can't beat enlarging the drainage holes (having any moisture - mud wash out is key to Verichal corrosion protection IMHO and coating generously in wax oil or a equivalent. So long as the wax oil is straight on good bare metal in enclosed protected areas it works brilliantly. Areas going on 15+ years with zero signs of corrosion and this land rovers been used in all weathers pretty near every day.
The other option you have is looking for some one that does full dip "inversion coating" i think it goes as. Basically dip the complete bulkhead in a vat of the same stuff used on modern cars. Its a cold process so no distortion issues and it paints over lovely. Problem is no one in Suffolk does it, your way some do i believe. Its probaly by far the best option, then combined with good paint + underseal your easy going to get 10+ years out of it, a lot more if you touch up any paint chips.
I can't add much to what's already been said, but I wanted to let you know that you can touch-up a defect or new weld bead on a hot galvanized part by gently (!) heating the defective area to 800F or so, and then smearing on a stick of zinc/lead/tin like a crayon. Lots of companies make these sticks, some without the lead content. Really useful for when you screw up a freshly dipped part with a slipped wrench, etc. For work pieces that are only a few square feet, it is definitely possible to bypass the hot dip tank altogether and just use the heat-and-smear technique. Depending on the piece, sheet metal warpage can be reduced by clamping down the piece to a welding table and then doing the heat-and-smear.
Here's a link to the "crayons" made by Rotometals:
REGALV Galvanizing repair stick
I realize this doesn't solve your problem directly, but I hope it is peripherally useful.
"Audi produces 100% galvanised cars to prevent corrosion and was the first mass-market vehicle to do so, following introduction of the process by Porsche, c.1975. Along with other precautionary measures, the full-body zinc coating has proved to be very effective in preventing rust. The body's resulting durability even surpassed Audi's own expectations, causing the manufacturer to extend its original 10-year warranty against corrosion perforation to currently 12 years (except for aluminium bodies which do not rust)."
Fastening the bulkhead back into the car will most likely damage whatever you do. You need to consider the repair of the system you use. Every corosion prevention system you use must be 100% or it will fail.
No Steve, that's the beauty of galvanise, its a electrolytic protection. A scratch wont corrode for a decade or more.
As to damaging galvanised stuff on assembly, the galvanising i get done is near bomb proof. So long as you don't try to bend it far it will not fail. Its certainly more than tuff enough to handle reassembly, unless your using something like barbed wire for lifting slings! I can highly recommend the galvernisers in great yarmouth, "British metal Treatments" A slipped spanner will not take there galvanising off! Am a very satisfied customer of there's. They acid etch the steel prior to flux then into the zinc bath.
Thanks for the replies everyone.
Adama: I also have a Series 3 Land Rover. This is what the bulkhead is for. The one that is on there at the moment is too far gone to recover, so I bought another which needs some repair work. The difficult part will be removing the paint from between the two panels below the vents. So far I haven't worked out a way to do this.
There is not really a easy way and its kinda anyone's guess what they painted them with. The other big issue i have with mine is the lack of quality of the steel land rover made them from, its more like compressed plywood than steel. Add in the number of overlapping seams (that are bare metal from new) to create rust traps and its fighting the inevitable to a degree. If its in good shape just wax oiling the inertia gaps really will work well. Losing the rubber floor mats and getting the doors to be a good fit will massively extend the foot well life's too!
The problem with galvanising them is that it causes the panels to oil can, that is not easily straightened on something like that. But it depends on how you want it too look, some people are doing it, The door pillars would look fine, but the foot - gearbox wells and probably the front bit around the vents would be the problem areas.
Bulkhead Repair Part 3
Personally I hate the way it would oil can, would not be something i would go for. All the panel's would look dented. But if you can get it clean enough especially in the seams it could be a really good way to go and would easily give it a good 3+ decades of life if not more if kept away from salt water.
My problem is my front radiator bulkhead between the wings. Its repairable but its kind a case of diminishing returns. I really hate welding to the metal land rover made stuff from, its just a porosity nightmare. No one does them at all currently and there's a really nasty bunch of pressed in flange shapes. Current thoughts are to completely make my own, possibly from aluminium even, simplify the shapes and just increase the gage of material a bit, Probably jump up to 3mm for most of it so its easy to TIG to save messing with the flanges. Like this i can keep her on the road too in the mean time. Other option is to tool up for it and possibly offer galvanised steel ones for sale. But its going to end up a expensive bit to make. Hence i am not sure if they would sell.
I should add i am after a 100% working land rover, its my main form of transport. I am not nor ever have been interested in keeping it "Original" I want it to work, to be reliable and to reduce future maintenance needs.
I thought about the overlapping seams as well when I looked at mine. Obviously it would be almost impossible to clean them out.
Perhaps I will simply shot blast, repair and spray paint it. If it lasts say another 10 years then that would be more than enough.
I have wondered before if there is any way of finding a Land Rover that's spent its life in somewhere hot and dry like Saudi Arabia. The metal would probably be virtually rust free.
I doubt it, desert areas often swing wildly temperature wise at night, hence even low humidity will condense out. Plus its the metal there made from, its just not "real" steel. Modern steel when it rusts will flake of as lumps, land rover steel just looks like wet non water proof ply when it rusts, loads of layers all gradually separating.
You have to remember, land rovers were made as work horses, but never had any requirement about corrosion in the design speck. I have friends that repair old minis, MGB and other "British" classic cars. Fighting and reversing corrosion goes with the territory. It was the foreign import cars that really forced that to change, the fully corrosion resistant dipped chassis, superior oil seals and a whole bunch of other things.
Runny warm or even slightly thinned wax oil is the best i have found for overlapping seams. It really did penetrate well on some of the bits i have had to repair at a later date due to previous, pre wax oil protection corrosion.
The best advise i can give you on your repair efforts, is fully weld seams, minimise overlaps. Don't plate over corrosion, cut it out then weld in a patch. Personally i also avoid seam sealer, It has caused more corrosion by creating mud - moisture traps than it has prevented on mine. Then Grit blast it clean, or at least DA sand it for some key and use a good etching primer ( i some times think the primer matters more than the paint when it comes to actual protection) and good paint. Wax oil it last with one of the probe type sprayers in all the hidden bits. Whilst wax oiling last seams counter intuitive but it wipes up easy were it runs out and won't then cause you any paint adhesion issues like it would in the opposite order.
Above all when you reassemble use copper eze on every thing, you will thank your self for it when your undoing bolts 5+ years later!