When it comes to protecting metal, a few options are available to create a protective, non-corrosive layer. Corrosion can ruin any steel structure, from steel girders in high-rise construction to manifold covers in small engines. Two corrosion protection methods can increase hardness and corrosion resistance and prolong the life of steel structures.
The two are similar in how they protect but couldn’t be any more different. Let’s look at powder coating vs. galvanizing and when to use one or the other. Or even both!
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Galvanizing can be done with two different methods. Zinc is a critical component, but it is applied to steel to create a protective alloy that is very different.
Hot dip (HDG) vs. electro-galvanized
Hot dip galvanization (HDG) is a process that takes cleaned and treated steel and submerges it in a molten zinc bath. The zinc metal at these temperatures bonds with the steel to form a very hard, corrosion-resistant alloy sandwiched between the steel itself and the outer layer of pure zinc.
Eliminating exposure to oxygen prevents corrosion, which zinc does exceptionally well. The zinc/steel alloy is incredibly hard and also improves the hardness and structure of the steel substrate. Since it is submerged, the zinc will galvanize all steel surfaces that come into contact with the bath.
Electro-galvanizing is similar to HDG in that zinc is applied to a steel substrate and bonded to it at a molecular level by submerging the steel in a zinc-rich solution and using electrolysis to plate the exterior of the steel with zinc metal. A cathode and an anode are used to transfer zinc onto the steel through a medium with electricity.
Temperatures are much lower in this process, and any zinc/steel alloy created is negligible compared to HDG processes. This method takes longer than hot dip galvanization and creates a much thinner layer of zinc. The benefits of electro-galvanizing are a more even distribution and shinier surface than a hot dip method, which makes it more aesthetically pleasing in architectural or artistic applications.
Typically, HDG lasts longer, increasing the steel’s hardness, and even if the surface is scratched down to the steel, the zinc will continue to protect the steel underneath. However, hot-dip can be done on a much larger scale and provides extremely long-lasting protection and strength for large steel pieces such as traffic signal poles, structural supports, and beams.
Electro-galvanizing is generally valued for areas that will be less susceptible to punishment and need to look more pleasing to the eye.
The process is similar to HDG and electro-galvanizing and involves three steps.
- Prep: The steel to be galvanized is cleaned, usually through sandblasting or even a chemical wash, to remove oil, dirt, and other debris which would inhibit the metallurgical bonding process. Flux is applied to the surface, which eliminates oxidation and allows the zinc to bond to the steel.
- Galvanizing: In HDG, the steel is submerged in a molten zinc bath, allowing the component to bond with the zinc. Allowing the steel to cure in the zinc bath also eliminates outgassing and ensures a uniform layer is created. In electro galvanizing, the process is similar, without molten zinc. Instead, the substrate is submerged in the chemical bath, and the electrons passing from cathode to anode do the work, electroplating the surface.
- Inspection: The material is inspected for consistency and impurities and moved on as a finished product.
Powder coating vs. galvanizing is a different process but similar in that it bonds a polymer or metallic coating to a metal substrate. Powder coating is almost like a dry painting with heat treatment.
The coating is a protective layer that can create a layer of protection resistant to impacts, marring, and damage by distributing kinetic energy to a broader surface area. Powder coating protects metal substrates by bonding a layer of non-corrosive polymer to the exterior of a metal surface.
The process is similar to galvanizing as the metal substrate is prepped and cleaned. Still, the rest of the process is very different.
- The metal is cleaned and sandblasted to allow the polymer to attach itself without dirt, oil, or debris interfering, similar to painting.
- Next, the powder coating process uses an electrode to create a positive charge on the powder, which is blown with compressed air towards a negatively charged metal substrate, such as steel, aluminum, or other metals. The voltage can vary from 10,000 to 100,000 volts depending on what is required.
- The powder only attaches to the charged metal, which is then cured with a heat treatment to get the powder to polymerize on the exterior of the metal.
Benefits of Powder Coating vs. Galvanizing
The benefits of powder coating vs. galvanizing are that powder coating uses only a few pieces of machinery and materials, such as a powder coating gun, powder coat, air compressor, and an oven for heat treatment. The powder only requires curing at around 400 degrees Fahrenheit for an hour or so, as opposed to hours of submersion in molten zinc or an electrolysis bath as with galvanizing.
Powder coating is touch-ready as soon as the metal has cooled down enough to handle. The expense of powder coating is much less than galvanizing, especially HDG, and the waste materials can be recycled and repurposed for future jobs.
Galvanizing is also beneficial since the steel and zinc can be melted down and recycled with 100% of recovery on the steel substrate and 70% recoverability of the zinc. Galvanized steel is much more robust, however, it is longer-lasting than powder coating since the coating affects the metallurgical properties of the substrate and does not just provide a protective layer.
Powder coating vs. galvanizing, however, allows you to use various colors, textures, and portability in the process that you don’t get from galvanizing. Also, suppose a mistake is made with powder coating. In that case, you can remove the powder coating before heat treatment and start over again.
When to use one or the other or both
Depending on what you need to use, the components for the process are the main driver of when to use powder coating vs. galvanizing. Large steel structures which require strength and enduring years of punishment will probably require an HDG process. In contrast, materials that need protection with a focus on aesthetic quality will probably sway your decision towards powder coating. The good news is you can do both.
Galvanized steel components can be prepped and powder coated for added protection and a better aesthetic look. Outgassing, however, after an HDG process may create bubbling or distortion with a powder coating if the galvanized metal isn’t adequately cured and outgassing is taken into account. Powder-coated objects, however, cannot be galvanized since the polymer coating would interfere with the process.
Minnesota Industrial Coatings has the experience to help you decide which is better for your needs: powder coating vs. galvanizing, or even both. Contact us today to see how we can serve your metal protection needs.