You may be correct that hot dipping thinwall devices will warp them -- every finish has advantages and disadvantages. It has been replaced with hot dip galvanized flooring at enormous rework cost and cleanup cost because most people believe that hot dip galvanized finishes are not susceptible to zinc whiskers, or at least far less so.
Also people have died in hospitals when apnea monitors have shorted out due to zinc whiskers from their zinc electroplated enclosures. So, while I agree that some specs which call for hot dipping may be archaic, some are deliberate and based on far more current thinking that you may realize. It is crucial that if we feel a spec is wrong we alert the designer and get the spec changed, not unilaterally make a substitution -- because we simply don't know what issues the designer was planning for.
Hot dip galvanizing definitely changes thread dimensions, but it is common to cut threads to allow for that dimensional change, or to drill and tap nuts after galvanizing. Countless hot dipped nuts and bolts are in place on electrical transmission towers, bridges, and other installations; it is not an outmoded finish, and it offers corrosion resistance far superior to any other finish. Good luck in working it out, and thanks again.
Hi everyone, I believe that the thickness of the zinc coating for electro-galvanizing is far more controllable than the hot-dipped. Can anyone please give me an advise with regards to which is better in resistance to corrosion.
I am hoping to get comments and reply from you guys. Thanks and Best Regards. Hi, Darryl. As you can see, instead of starting a duplicate thread, we pasted your inquiry onto a thread that already partially answers it. Yes, electro-galvanizing is more controllable, but the thickness is usually far less and the corrosion resistance is therefore far less.
What's the difference between "galvanized" and "hot dip zinc" coated? There is a difference or is it that the procedure of making a hot dip zinc with the process gives the result "galvanized coated"? What is the difference between galvanized steel and hot dip galvanized; which one is best for kitchen project ladder.
Hi, Steve. To me there is no difference between the phrases "galvanized" and "hot dip zinc coated". Hi, Ramesh. A kitchen is not a highly corrosive environment, so I don't think you need a super corrosion-resistant finish; any zinc coating procedure may work fine.
To me, "galvanized" means "hot dip galvanized" with no distinction between them. But we cannot stop other people from using words in the fashion they use them, even if we consider it a sloppy fashion. Some other people have apparently started using the word galvanized to also refer to the much cheaper and much less corrosion resistant zinc electroplating. When people use words that way, you have no choice but to ask them what THEY mean when they use the term, and to specify things by specification numbers, rather than slang.
Thanks for this thread. It became clear to me the difference between Hot-dipped and Electro-galvanized. Hello and this is an interesting thread. I have recently completed some salt bath testing on pregalvanised product vs Hot dipped galvanised with results that seem to go against your thoughts. The hot dipped galv product failed both the scribed and unscribed tests at the hour mark whereas the pregalved product showed no corrosion on the unscribed test at hours and less than 1 mm crawl on the scribed test at We had 3 hot dipped pieces and 2 pregalvanised pieces.
I hear all the time that hot dipped is better and I am confused to know why? It seems that once any weakness is found in the hot dipped product the crawl between the hot dipped layer and the product it is supposed to protect becomes the weakness which is not found on Pre Galvanised product? Thanks, Michael.
Actually I thought it was a rather dull thread that only became interesting when you posted findings that do not match conventional thought on the subject :- But actually, there are several things that have to be said about your results.
First, salt spray testing is a QA measure to be employed to make sure that an established process has not gone south. It is NOT an appropriate way to gauge the corrosion resistance of one finish vs. Let me explain that rather than just claiming it -- Although galvanizing protects steel cathodically, what protects the zinc?
It protects itself with a coating of its own corrosion products. If it did not protect itself, it would just quickly react with the environment and dissolve away like uncoated steel does, or like zinc does when put into hydrochloric acid.
Indeed, if galvanized sheets are left tightly stacked in a moist environment, they do corrode that way, they get "wet storage stain", i. But that doesn't happen in actual service because in service the zinc slowly reacts with carbon dioxide in the air to produce tightly adhered, glassy feeling, zinc carbonate reaction products which are very effective in sealing the virgin zinc away from the air and slowing corrosion to such a crawl that galvanized structures can last 75 years and more.
But what happens in a salt-fog chamber? You are emulating the conditions for wet storage stain, not real life. The carbonate reaction products never form and the zinc just rapidly corrodes away into loose, non-protective, powdery corrosion products. The second problem here is that proper pretreatment is a necessary part of a coating system. The pre-galv apparently received an adequate chromate pre-treatment.
A chromate dip is not an appropriate pre-paint treatment for hot dip galvanized surfaces though; they require phosphatization. Thanks for the interesting posting.
Hello Ted and thank you for taking the time to review my question and posting an informative answer for me. Being new to the steel industry and more specifically Steel Tubular fencing, I am questioning "why" a lot of the time to understand our own product and how it compares to other similar products for both strength and weaknesses. This particular question came up when I lost a tender based on a supposed fact that hot dipped Galv will always outperform pre Galv'd product.
In fact the unflattering comment that our product was not fit for purpose in a marine environment was made. The marine environment was mtrs from a beach.
I expected at the least to be comparable to Hot dipped at that stage. Upon withdrawal from the galvanizing bath, either an air knife or mechanical wiper is used to remove excess zinc so producing a good surface finish. After galvanizing, the sheet is recoiled prior to a stockholder, the sheet being uncoiled and cut for sale so producing uncoated edges.
Tubes may also be galvanized using an automated process to EN Again Immersion times are relatively short and upon withdrawal, steam may blown down the bore of the tube to give an adequate surface finish. Again for resale purposes, tubes may be cut to size creating uncoated edges.
From a practical point of view strands of wire may only be coated using an automated process and this may be specified by EN This dull grayish film is relatively stable and adheres tightly to the surface of the iron or steel. In hot-dip galvanizing, the zinc chemically bonds and becomes part of the steel being protected. Though the concept of hot-dip galvanizing may seem simple, the process consists of several crucial steps Figure 2.
The steel first goes through three cleaning stages to prepare its surface for galvanizing; these are degreasing , pickling and fluxing. Degreasing is used to remove dirt, oil and other organic residues; a mild acid bath, or pickling, etches the steel and removes mill scale and iron oxide; and fluxing further removes any oxides and coats the steel with a protective layer that prevents the formation of further oxides on the steel surface prior to galvanizing.
Once the cleaning process is completed, and the structure has dried, it is ready to be immersed into the molten zinc bath.
Molten zinc flows in and around the iron or steel object, thus thoroughly coating it to protect all surfaces. The coated material is then removed from the bath and air-dried before inspection. Cold galvanizing is simply the application of a zinc-rich paint to the surface of a steel element to protect it from corrosion. Zinc paints may be applied by brushes, rollers, spray guns, etc.
Coatings may also be applied by the electrogalvanizing method as well. The zinc-rich paints used in cold galvanizing are different from conventional coatings due to the presence of a binding compound. These binders allow the zinc to mechanically bond to the steel to offer an effective level of protection. Like hot-dip galvanizing, cold galvanizing can provide barrier protection and also some degree of cathodic protection.
However, the zinc dust present in the paint or coating must be in high enough concentrations to promote electrical conductivity between the steel and the zinc. The surface preparation required for applying zinc-rich coatings is less demanding than hot-dip techniques.
Before coatings operations begin, the surface of the steel must be clean and dry. Usually, a wire brush is first used to remove rust or any other corrosion products that may be present. Dirt, grease, chemicals and other organic compounds must also be removed accordingly. Once the surface is prepared, the zinc coating is applied to the surface in as many coats as required. Although hot-dip and cold galvanizing both serve similar purposes, their method of application and performance differ significantly.
Cold galvanizing, unfortunately, does not offer the same level of protection as its hot-dip counterpart. Because cold galvanizing is simply a coating, it cannot bond with the metal on a chemical level and, as such, does not have the same durability, abrasion resistance and cathodic protection capabilities as hot-dip galvanizing. While cold galvanizing does not live up to the performance of hot-dip galvanizing, it does have its benefits.
Cold galvanizing is ideal for cost-effective and rapid application on smaller structures and components. Hot-dip processes are more expensive and better suited for larger structures, typically for heavy-duty industrial uses.
Related reading: Galvanization and its Efficacy in Corrosion Prevention. The choice of galvanizing method ultimately boils down to finding the right balance between cost and coating performance for a given application.
Written by Krystal Nanan Civil Engineer.
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