Galvanized frame

[supergg]

In the industrial park of the city I work in, we have a large galvanization plant. I can have my frame done for $500. Has this been done before? Is it a good idea? Should I do anything to the frame first besides blasting it?

thanks

[goransons]

I was always under the impression (which could be wrong) that the process of galvanizing metal actually weakens it. That might be something to look into. Also any future repairs requiring welding will be a pain in the rear, plus you have to be very careful with the fumes during the welding process.

Could you achieve the same protection with a painted on finish like Por-15 or even powder coating?

[supergg]

I think the galvanized finish is stronger. Also, the frame is dunked in a hot tank and it gets into every little spot.

[barts]

While there can be issues with galvanization affecting high-strength steels due to hydrogen embrittlement during acid etching, Airstream frames are made from common mild steel.... and can be safely galvanized. Note the widespread use of galvanization to protect steel cables and workboat parts.

As always, avoid the direct contact of aluminum with the frame in the presence of moisture to minimize problems with corrosion.... this is how rear end separation starts, and why the belly pan has such corrosion problems.

- Bart

[supergg]

Bart, does that translate to go for it?

[barts]

Originally Posted by supergg

Bart, does that translate to go for it?

Sure. I'd talk to them about the surface prep needed. If I remember correctly they'll blast just before dipping because you don't want even a hint of corrosion underneath, but you can likely save money if you can do the preliminary cleanup yourself.

The galvanizing process will tend to reduce the diameter of holes, with the amount depending on dip temperature, etc. You'll get better results, I think, if you open up the smaller holes a bit so that the as-galvanized holes have sufficient clearance for your bolts; you don't want to have to drill the galvanizing out of the bolt holes to get your elevator bolts through. Of course, you'll want to minimize any new holes in the frame to take best advantage of the new coating, so you'll want to drill holes up from underneath to fasten the floor, C channel, etc. Welding on the frame afterwards will be more difficult and locally remove the coating, so make sure to repair any damage to step slots, fill any unwanted holes in the tongue, etc. ahead of time.

Boat trailer frames for salt water use are frequently galvanized.

- Bart

[supergg]

That is a great point about the holes getting smaller and the boat trailers being galvanized. Thanks Bart.

I am friendly with the folks at the plant. I think they will let me take photos of the process. If I go ahead with it, I will have it done in the early spring.

[BIGED52]

It's a great idea for making the framing last longer. The issue of drilling any holes once the frame is finished can be eased by coating the bolt holes and bolts with Parbond, Acryl-R or Vulkem/Tempro when installing them. So if the holes are in need of being drilled out after the galvanizing is done just keep that in mind. This was a question I was having about the folks here doing stainless steel frames. It would seem that standard steel and galvanization would be just as effective and less costly for a frame update. Ed

[Phoenix]

As Barts mentioned, hydrogen embrittlement is sometimes a problem with acid prep and pickling; assuming that the frame will be sand blasted, acid dipped, then either hot zinc dipped or electroplated.

If the zinc is electroplated, platers should be aware of hydrogen embrittlement and bake the frame, if necessary, a process called hydrogen embrittlement relief, which drives out the hydrogen gas entrapped in the metal. If plated, I'd ask the plating shop about whether hydrogen embrittlement is a problem, and how they plan to address it.

Zinc is a sacrificial metal and used in boat anodes to reduce corrosion of drive units, etc., in salt water. I am unsure what effect zinc plating might have when sandwiched between the steel frame and aluminum skin. Perhaps, it will work like a boat anode and prevent the steel and aluminum from etching away, while the zinc acts like a sacrificial coating. However, I have no experience with this. Maybe, someone with boat or salt-water exposure experience can enlighten us.

As an aside, zinc is pretty soft. I suspect that reduced hole sizes might not be a problem, as I think running a bolt through the hole will easily remove the coating.

[barts]

Originally Posted by BIGED52

It's a great idea for making the framing last longer. The issue of drilling any holes once the frame is finished can be eased by coating the bolt holes and bolts with Parbond, Acryl-R or Vulkem/Tempro when installing them. So if the holes are in need of being drilled out after the galvanizing is done just keep that in mind. This was a question I was having about the folks here doing stainless steel frames. It would seem that standard steel and galvanization would be just as effective and less costly for a frame update. Ed

From a structural standpoint, I'd feel better about a galvanized frame than a stainless steel one. Stainless has some weird corrosion issues when partially covered and in the presence of chlorides (road salt); welding stainless can also cause interesting issues.

- Bart

[nickcrowhurst]

Galvanizing an Airstream frame is perfect. Bart is absolutely correct in every detail, IMHO, and I've been galvanizing sea-going yacht parts since 1974. You will find previous discussion of this on the forum by doing an advanced search on "+galvanized +frame". You will see that I have been recommending this for years.
One extra caveat is that the galvanizers will want to ensure there are no trapped air bubbles in the frame tubes, regardless of its orientation when it is lowered into the tank. Any such bubbles will be rapidly heated, and cause an explosion. This is prevented by drilling 1/4 inch holes in places such as the closed end of a tube or a sealed cross-member. You may wish to drill these in advance, having consulted the galvanizers, so that you can have some control over the location of the holes.
This is a great idea.
Nick.

[mrgreen]

I think galvinisation sounds great but i must say that my point is that i have a frame 40+ years old which is in bad shape due to leaks but if you keep the leaks out you shouldn't need it as you can get frames of that age with no rot if they are dry, but for $500 it would be hard to say no!, just my thoughts

[barts]

Originally Posted by Phoenix

If the zinc is electroplated, platers should be aware of hydrogen embrittlement and bake the frame, if necessary, a process called hydrogen embrittlement relief, which drives out the hydrogen gas entrapped in the metal. If plated, I'd ask the plating shop about whether hydrogen embrittlement is a problem, and how they plan to address it.

This is generally an issue with higher-strength heat treated steels; springs in particular have problems. A safe working limit is steels with
150k psi tensile strength or more should not be galvanized or chrome plated without post-etching heat treatment. Our Airstream frames are much lower strength than this and will not have any issues.

As an aside, zinc is pretty soft. I suspect that reduced hole sizes might not be a problem, as I think running a bolt through the hole will easily remove the coating.

This is true for electroplated steels; the hot-dip process provides a much more rugged coating; the bottom layers are actually a zinc-iron alloy. Cleats, chain and other marine hardware is hot dip galvanized for protection; despite rugged service, the coating resists removal.

- Bart

[dwightdi]

Like previous posters have stated, zinc galvanizing is a sacrificial protective coating. That means that any break in the coating down to the base steel will be protected against corrosion, as long as there is still zinc coating in the immediate area. Zinc is also sacrificial to Aluminum so aluminum in contact with the zinc will also be protected. I worked for Johnson/Evinrude as their marine materials engineer and conducted many Florida test to identify the required galvanized coating thickness required for protection in various salinity of oceans and temperatures. All galvanized coatings have a specific useful life expectancy but is significantly better than just paint coating. Unless the paints are based on zinc rich formulas or zinc chromate, they are inferior to galvanize.