Table of contents
What is Galvanizing?
Importance Of Powder Coating
What is Powder Coating on Hot Dip Galvanized Steel?
Using Galvanization and Powder Coating Together
Types Of Powder Coating
most common methods to remove powder coating
Conclusion
Introduction
Powder coating is a type of coating that is applied as a free-flowing, dry powder. Unlike conventional liquid paint which is delivered via an evaporating solvent, powder coating is typically applied electrostatically and then cured under heat or with ultraviolet light. The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a hard finish that is tougher than conventional paint. Powder coating is mainly used for coating of metals, such as household appliances, aluminium extrusions, drum hardware, automobile, motorcycle, and bicycle parts. More advanced technologies allow other materials, such as plastics, composites, carbon fiber, and MDF (medium-density fibreboard), to be powder coated using different methods that require less heat and time.
On the otherhand ,Powder coating adds to the steel’s durability, helping the frame to withstand damages better and last longer. Corrosion resistant. moisture and humidity can cause metal frames to rust. When applied to steel, powder coating provides a protective barrier that helps prevent corrosion.
What is Galvanizing?
Hot-dip galvanizing involves the immersion of iron or steel workpieces into a bath of molten zinc heated to a temperature of approximately 840 F. The zinc alloys with the surface of the base metal to form a protective coating. The zinc reacts with the oxygen in the atmosphere to form zinc oxide. The most important benefit of hot-dip galvanization is enhanced protection against corrosion.
Similar to powder coating, galvanizing is the process of applying an extra layer of protection. However, galvanizing is the process of adding a layer of zinc as a coating. The zinc coating gives metal objects tough protection against rust and corrosion.
The most common method to achieve galvanization is hot-dipping, in which parts are submerged in a bath of molten zinc. First, the base metal is thoroughly cleaned and then the base metal is fluxed to remove any remaining oxides. The metal is then dipped into the heated zinc.
Galvanic Corrosion (also known as bimetallic corrosion or dissimilar metal corrosion) is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte.
A primary difference between galvanized and powder coating is the way they protect the surface of the workpiece. Galvanization provides sacrificial protection, meaning the coating will absorb corrosive materials before they can reach the metal object. Powder coating works by forming a protective barrier that prevents destructive materials from penetrating and reaching the surface.
The ability of hot-dip galvanization to deter corrosion makes it an excellent choice for protecting outdoor objects that are vulnerable to the elements, such as iron and steel gates, fences and guardrails. However, powder coating offers greater flexibility for decorative applications — coatings are available in numerous colors and textures — making it better suited for indoor products. Various pretreatment methods are also available to bolster the powder coating’s corrosion protection capabilities.
Corrode simply means to eat away or be eaten away especially by chemical action as in the oxidation or rusting of a metal.
Importance Of Powder Coating
Powder coating provides a hard finish that is tougher than conventional paint. Powder coating adds to the steel’s durability, helping the frame to withstand damages better and last longer. Because of its durability and resistance to abrasion and corrosion, powder coated steel require little to no maintenance. Moisture and humidity can cause metal frames to rust. When applied to steel, powder coating provides a protective barrier that helps prevent corrosion. Unlike other treatments that can easily crack, peel, chip, scratch and corrode, powder coated steel frames are more durable and can withstand the environment better. Because of this, colors stay brighter and vibrant longer than other methods. The powder coating process has little impact on the environment. It requires no harmful solvents and does not emit vapors or fumes like liquid paint does.
Powder coating is durable and could be used as a finish for a variety of surfaces, not just metal. The chemical bonds gives a superior coating that makes it suitable for both machinery and everyday items. It holds well to extreme weather and physical impact, meaning it’s resistant to scratches, abrasions, and chips.
What is Powder Coating on Hot Dip Galvanized Steel?
Powder coating over hot dip galvanizing is a two step coating process. In the first step, the steel part is galvanized with a layer of zinc. The zinc layer provides cathodic and barrier protection, preventing the steel from oxidizing, resulting in a longer part life. Galvanizing is a four-step process that requires exceptional attention to details and procedures to ensure quality in the finished part. Duncan Galvanizing uses a hot dip galvanizing process under strict quality control to ensure conformance to ASTM standards.
The second step is the application of a powder coating to the galvanized part. The powder coating is applied to the part and heat cured, which bonds the powder to the galvanized part. The finished metal powder coating protects both the steel part and the galvanized layer, and provides an attractive exterior finish to the part. This process can be difficult to perform properly if quality control procedures are not in place, and can result in uneven coating and pinhole spots where the coating does not adhere. In order to maintain quality, powder coating must be performed within 12 hours of the part being galvanized and all parts have to be free of dust or grease.
Using Galvanization and Powder Coating Together
It’s possible to combine hot-dip galvanizing with powder coating to form a duplex system for protecting metal materials. The galvanized zinc serves as a base coating that enhances corrosion protection. The powder coating provides a top layer that slows down the rate in which corrosion consumes the underlying zinc. The powder coating can also improve the aesthetic appeal of the metal object.
Types Of Powder Coating
There are two types of powder coating
Thermoset
Thermoplastic
Thermoplastic Powder Coating finishes become liquid and very soft when heated. This eliminates chemical bonding. This process makes the powder coating both reversible and reusable.
Thermoplastic coatings tend to be thicker and hence more durable compared to thermoset coatings. For this reason, they can be used for a plethora of things from metal, auto parts, and even refrigerators. Thermoset Powder Coating is quite different in the fact that it forms chemical bonds once cured, making it impossible to recycle it. It is suitable for high heat areas because the bonds prevent it from melting away. This type is much cheaper compared to thermoplastic.
Different coatings also have varying lifespans. For instance, coatings that have fluoropolymers and urethanes can last longer. They are designed to withstand extreme conditions and are better suited for outdoor products. The longevity of the powder coating finishes will highly depend on several factors. These factors include the quality of preparation, type of powder coating used, and the environment in which the product is exposed. Powder coating finishes can last up to 20 years, but due to the consistent use, exposure to UV light, and outdoor environment may break it down faster.
Powder coating is well known for its adhesion and durability, and is commonly used for automotive parts, construction equipment, offshore platforms, and more.
However, the qualities that make powder coating such a great coating can become big challenges when you need to remove it.
The most common methods to remove powder coating are:
Chemical stripping
Burn-off in oven
Media blasting
Chemical stripping methods also known as caustic or solvents method works by causing the powder coating to dissolve, soften, and/or swell. At this point, the coating will fall off or have to be washed off. Chemical stripping can remove powder coating completely and evenly. Chemical stripping also has disadvantages. The toxic chemicals are dangerous to work with, as they can easily burn the operator’s skin and eyes. Proper PPE (personal protective equipment) is required. Disposal is also tasking because both the used stripper and the water used to rinse the part are considered a hazardous waste and must be disposed of accordingly. Chemical strippers leave behind a perfectly smooth surface, so you may need to scuff up the surface before applying a new coating. This adds an extra step to the process. One exception would be if the surface was given a proper anchor profile before the original coating was applied.
Burn-off in oven also known as burn-off or bake-off or fluidized bed method uses very high temperatures to burn off powder coating, which turns to ash and must then be washed off. Thermal stripping is quite popular because it’s one of the quickest ways to remove powder coating. It doesn’t come with the same environmental concerns of chemical stripping. The extremely high temperatures required to remove powder coating may warp or damage parts. Like chemical stripping, this method does not leave an anchor profile which is critical for the reapplication of paint or coating.
Media blasting, abrasive blasting, which includes both traditional sandblasting and dustless blasting, uses media propelled at high speed towards the surface to strip off the powder coating. Dry blasting can take place in a blast cabinet or a blast room, whereas dustless blasting requires minimal or no containment. Traditional sandblasting can be a slow process for powder coating removal, and is not always favored. Because the dustless blasting process introduces water, it increases the mass and energy that the machine is putting out, making it dramatically faster than dry blasting. The water also cools the powder coat, making it brittle. This allows it to flake off as opposed to getting gooey, like it does with the heat generated from dry blasting because dustless blasting uses water to suppress the dust plume, the process is environmentally friendly and does not require bulky containment. This makes it perfect for blasting items that cannot fit into a blast cabinet, or cannot be moved.
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