I'm thinking of strengthening old steel sheets (They are in a good condition for their age but there are some signs of usage and mild corrosion). I've been thinking of galvanizing them. Are there any other ways to strengthen older steel sheets?
As far as I know, galvanizing actually doesn't do all that much in terms of hardness and strength. It almost only improves corrosion resistance and that is it. You can try other hardnening techniques though.
It doesn't improve strength? I was under the impression that galvanizing offered an extra layer of protection and therefore more hardness. What hardening techniques would you recommend? Sorry if this is a stupid question.
Galvanizing is a heated process and then sheets are rolled or flattened etc, that could hardened the sheets..
I couldn't find any proof that galvanizing improves strength. In fact, high-strength steels can lose some of their strength and can become brittle due to hydrogenic reaction. There are lots of ways to improve old steel sheets other than galvanizing, including enhancement of other properties such as hardness (something that you're apparently looking for). Try boronizing for example?
As far as re-galvanizing, not sure that it's possible, unless you contact a steel foundry and get their recommendations. No way you could use the hot dip galvanize process if your talking sheet stock. Not sure on every process of galvanizing, but I understand that the Hot Dip Galvanizing liquid is 800 degrees plus and that would warp sheet stock and if you where to try and flatten the sheets, I think you would get separation between the metal and the hot dip galvanize.
Lightly sand blast the sheets and spray them with a cold galvanize compound spray..
Re-galvanizing? I'm pretty sure my sheets haven't been galvanized in the first place but I'll look into it and get back to you.
My bad I read your question incorrectly
You may look into a really good paint, instead. It will be a lot cheaper and easier to work with. This is an expensive paint, and may be overkill for your application: Fluorokem HS - Protective & Marine but it should provide good uv protection and should last a long time.
First step is to contact a paint specialist. I usually call Sherwin-Williams and ask to speak with someone in technical support, Contact Us - Sherwin-Williams Protective & Marine Coatings .
Just as a side note, I called about what type of paint to put on my shed floor. They recommended an epoxy paint and it has lasted 5 years so far, with me dragging wood, a generator, all manner of stuff over it and it hasn't damaged the paint. It was $100/gallon but it was money well spent. A good epoxy paint holds up well, apparently.
I'm not sure what your constraints are, but I would look into flame spray coatings as a possible solution. Here's a source:\
Plasma Spray Coatings | Thermal Spray Coating
That may be what our structural guys were referring to. Apparently there is a way of spraying molten zinc onto steel and it adheres. I'm not 100% sure it is as good as hot dipping, but it provides a much thicker layer of zinc. Here's an article about it:
Metalizing steel bridges in the field | International Metal Fusion Corporation
I think you'd want to bring in someone with experience to have them coat those plates. The parent metal probably has to be cleaned to a certain SSPC and prepped. A quick search just turned up:
Zinc Spray Metallizing | American Galvanizers Association
An additional concern I'd have is whether you are annealing the steel when you spray the zinc onto the plates. If it's just plain steel, it shouldn't be a problem.
improving don't think old steel can be improved much. Best thing that you can do is #1 try to preserve them with coatings. Improving old steel sheets can also be done by using them to make parts...send em to the forge and have a knife made out of them if the carbon content is good.....
What is the purpose of these sheets?Are you just trying to preserve them?I don't think you can "strengthen" them... strength is a material property that no amount of paint or galvanization (or even thermal coatings) will significantly improve.
As mentioned by others, galvanizing is just a coat of zinc over carbon steel against rusting and has nothing to do with strengthening the material
If the steel you have is rusted or a orange-irony color it is regular steel. Galvanized steel is the color of the chain link fence in your back yard. Galvanizing will not improve the strength of your steel (if anything it will be a verrrry minimal change in strength)
The only ways to improve the PROPERTIES (hardness, strength) of the steel you have is to heat treat through quenching or stress hardening.
Without knowing the properties of the steel is hard to say what method of heat treating to use or how well it will work. Typically for heat treating to work well you need a high carbon steel to begin with.
To stress harden you can put the material through processes like shot peening, manual peening, or rolling. Think black smithing techniques. This is the reason cold rolled steel has better strength properties than hot rolled steel given the same chemical composition.
You can add bends in the material to increase the moment of inertia the material has. Think of an I-beam vs a flat sheet of steel.
More information about what you plan to do with the sheets would help in giving advice.
I think Bjorn Sorenson and Evan Dlugopolski are getting to where we need to be. What do you plan to do with these old steel sheets? Are they already formed and installed? Are they sitting in inventory rusting away and you want to use them? Answers to these questions would go a long way toward to determining what can be done. As said before galvanizing is really just a corrosion resistance practice and can cause other issues (welding can be hazardous) and probably isn't what you are looking for. Some of the other suggestions would cost more than scrapping old sheet metal and buying the correct strength of material. Depending of course what you have and what it is being used for.
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