Frequently Asked Questions
What is hot-dip galvanizing?
It is an industrial process which involves dipping clean steel in a basin filled with molten zinc at 450°C to create a metallurgical bond between zinc alloys covered by a layer of pure zinc. The first alloy so created is as strong as the base metal. This is what gives hot-dip galvanizing its excellent resistance to abrasion. The smooth and clean outer layer of zinc absorbs shocks, while the underlying layers provide excellent basic protection to the metal.
How does Galvanisation Québec meet industry standards?
We observe the standards and procedures issued by the Canadian Standards Association (CSA) and the American Society for Testing and Materials (ASTM) to the letter in our galvanizing process.
Our customers can obtain copies of test results and certificates of compliance. Just make a request on the purchase order given before we undertake the work.
Our basins’ safety equipment allows for double dipping. There are therefore solutions for parts whose size exceeds our basins’ capacity. We will gladly discuss this with you. The solution exists, don’t worry!
The zinc layer is sometimes brighter in certain areas; why?
The product’s final appearance depends largely on the chemical composition of the steel and the coating’s thickness. Foundries produce different steel compositions, thus creating varying results in terms of appearance, but not efficiency.
Our experts have their own recipes to add to zinc additives needed to produce a glossy, matt or marbled (spangled) finish. That being said, the appearance does not alter the anti-corrosion properties of galvanizing.
How do you minimize the risks of distortion of parts to galvanize?
These risks can easily be avoided by simply selecting steel so that the thicknesses are the same in each sub-assembly to be hot-dip galvanized. By avoiding the use of steel with a thickness of ≤1/16″ and by choosing, when possible, symmetrical designs, the risk of part deformation and distortion is much reduced.
White rust; what is it and how can it be avoided?
White rust is often mixed up with the term "wetstoragestain" which is a slight corrosion that is much less severe. You can avoid storage spots by storing steel immediately after galvanizing, by making sure not to expose non-protected surfaces to moisture or water or by applying a passivation surface treatment. However, white spots will fade as soon as the galvanized steel is exposed.
Cold galvanizing; does it exist?
No. This term is used to describe the application of zinc-rich paint, which is appropriate for galvanized surface repairs. As we explained earlier, galvanizing is a metallurgical reaction that occurs between a metal and zinc, producing a zinc-steel bond of about 3,600 psi. The application of a zinc-rich paint does not produce any chemical reaction. The strength of the bond, when using this paint, is only a few hundred psi.
Why are parts perforated before galvanizing?
You need to drill vent holes prior to dipping the parts in order to evacuate the air and allow the free flow of liquid when cleaning and galvanizing. To provide complete protection, zinc must flow into all part and structure cavities.
Can you paint galvanized steel? If so, how?
Yes. While the first reason to do so is aesthetics, the application of paint – while observing the standards - extends the life of galvanized materials. The part's age determines which surface preparation will be needed before painting it to obtain optimal protection. The ASTM D 6386 document, entitled Practice for preparation of Zinc (hot-dip galvanized) coated iron and steel product and hardware surfaces for painting provides all the necessary information.
What is the life of galvanized parts?
The zinc corrosion level and the duration of protection depend on the quality of the coating (thickness) and the number of corrosive elements present in the immediate environment. In a rural environment, where traffic is light, the small amount of corrosive emissions allows galvanizing to last more than 100 years without any maintenance.
However, in an industrial or marine environment, where there are large quantities of corrosive elements (chlorides, sulfides), the life of galvanized items varies between 50 and 100 years.
Visit the AGA website to obtain more details on this.
Is it possible to require a given thickness of zinc on my parts?
The answer is no. The thickness of the zinc layer during the hot-dip galvanizing process is determined by the chemical composition of the steel and the condition of its surface. A longer soak time in the molten zinc basin will produce one of the two following effects:
- 1. A marginal increase in the thickness of the coating;
- 2. A significant increase in coating thickness that will result in weakening the topmost layer of zinc, which could then peel off.
What is double dipping?
This is a process of gradual dipping used for parts whose size does not allow their dipping in a single dip. However, this method cannot be used to obtain an additional coating.
Is there a risk when there is contact between the galvanized steel and other metals?
Zinc is said to be a noble metal, which means that it "sacrifices" itself by corroding, leaving its electrons behind to create a bimetallic coupling to protect metals. It is therefore recommended to isolate galvanized steel, so that it will not be in direct contact with other metals. Rubber or plastic, two non-conductive substances, are often used as insulation. If assembly is required after galvanizing, we recommend using galvanized hardware. If welding is required, cover the weld runs with a zinc-rich paint.