Aluminum is the most sought-after material for building various structures.
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Being durable and lightweight, this metal does the job just right.
However, its durability, longevity and appearance can be enhanced by choosing the right finish.
Nowadays, powder coating has gained a lot of popularity making it a desired finish. If you are new in the world of finishings and are unaware of what powder-coating aluminum is, then you are at the right place.
This article will take you through the entire process of powder coating along with its benefits, making you realize the utmost importance of powder coating your aluminum pieces. Let’s get started!
The process of powder coating involves a dry powder that is used as a finishing material.
This powder is applied to the metal surface followed by baking the metal to make sure the protective layer is firm enough.
You can powder coat any material including aluminum. There is also a wide selection option of colors to powder coat aluminum, such as clear, white, black, brown etc.
This process elevates the appearance of the metal by giving it a matte or glossy look while increasing its life.
If it is done accurately, you won’t have to worry about protecting your aluminum products from the damage caused by wear and corrosion.
Horizontal powder coating means the application of coating powder to a surface placed in a horizontal orientation.
The horizontal powder coating involves 2 shifts, making the whole process take around 48 workers. The production capacity of horizontal powder coating is only 500 metric tonnes of aluminum.
This process involves six steps, making the production process complicated. The only advantage it has is the low equipment investment.
Vertical powder coating means spraying the powder to coat a surface placed in a vertical orientation.
The vertical powder coating cuts down extra time taken along with the labor. This process takes only 24 workers and is able to cater to around metric tonnes of aluminum.
The production process is also simpler, involving just three steps. The only drawback of this process is its high investment in equipment.
To powder coat aluminum, there are many types of finishings and processes that can be used. Below we have gathered some of the best ways to powder coat your aluminum products:
One of the most popular choices for powder coating is polyester.
The process simply involves an electrostatic spraying of electrostatically charged powder. This makes the polyester particles stick to the metal.
However, there are two types of polyester powder coatings available in the market currently. The first is the triglycidyl isocyanurate (TGIC) and the other, most preferable one is the TGIC-free. It is liked because it offers an ideal consistency and is much more suitable for large-scale production usage.
This type of coating utilizes a type of polyester which is a bit more sturdier than the normal ones.
There are many pros that come with the utilization of super durable polyester for coating your aluminum products. Firstly, it protects against rust.
Moreover, it also shields the metal from harmful UV rays. Its longevity sets it apart – it can outlast regular polyester by up to ten years.
If you’re after a sleek, glossy finish, particularly for outdoor structures like window frames or roofs, this will be your best choice.
Epoxy is slightly more expensive than the other coatings. However, it is extremely durable and tough.
If your aluminum pieces are exposed to heat or extreme environmental conditions, use epoxy to coat them. It also takes care of the aesthetics with a wide color range.
This is the top-tier, the priciest, but also the sturdiest. It’s reserved for products that’ll be up against severe temperatures or conditions.
With fluoropolymer, the color options are fewer but can be tailored as per your demand.
This coating is similar in strength to epoxy, but it’s especially useful outdoors. It’s a popular pick for items that need to resist chemicals, from car parts to doorknobs. One cool feature is that dirt and stains don’t show up easily on it.
However, there are some downsides. It can be costlier than epoxy and might not be the greenest option due to the fumes it releases during its application.
In essence, the right powder coating depends on your needs, whether it’s longevity, aesthetics, or resilience against the elements. Each category from the above holds its unique strengths and uses.
Aluminum has a natural ability to resist corrosion. However, in some circumstances, it seems necessary to powder-coat aluminum to provide extra protection.
Powder coating of aluminum can help you prolong the life of many things for example playground equipment, and sign boards.
Let’s go through the top six reasons why you should be using powder coating as a finishing process:
By powder coating aluminum you provided your product with added protection against corrosion.
The metal base is safeguarded against oxidation and other forms of severe weathering. This increases the durability and the longevity of your product.
On top of this, the powder coating also provides a scratch-resistant thick layer. This also helps in protecting against stresses that can cause the product to wear out.
The choice of colors for powder coating is immense. You can pick any color you like. There are many variations available too, including, matte, gloss, and wrinkle.
These colors are resistant to fading along with providing your product with UV protection. Hence, this makes powder coating ideal for achieving an aesthetic finish.
You won’t have to renew the color for up to 20 years despite the tough environment you expose the product to.
Powder coating is sprayed on the parts and whatever is oversprayed can easily be collected. This allows it to be reused.
The ability to reuse powder coating allows more parts to be covered. This helps you minimize the wastage. Hence, you can benefit from a cheap finishing process.
The process of powder coating is environmentally safe. It doesn’t involve volatile organic compounds like those present in the paint. There are no carcinogenic or other toxic compounds. Hence, it causes no harm to the technicians during the application process.
If you are wondering how the process of aluminum powder coating takes place then here are the five basic steps involved in the process.
The pre-treatment is a bath that involves the removal of all the unwanted particles. This is essential to get rid of the dust and grease. After this, your product has a clean surface.
It involves spraying electrostatically charged powder paint on your aluminum products.
The positively charged powder binds with the electrically grounded profile. This step takes place in a spray booth.
This step involves baking the aluminum product by passing it through a curing oven.
The coated powder paint adheres to the aluminum products. You also get an even coating through this step.
After the process of curing the aluminium products require cooling. Once they have cooled down, an inspection is done. This ensures that the paint is evenly spread.
There are many tests like scratch test, punch test, and microns test carried out. They check the surface thickness and adhesion of the paint. This helps in maintaining the quality of the coating.
Finally, another layer of protection is added to the aluminum product. It is fed through a machine in which protective films attach all of its sides.
This prevents the powder from peeling off and makes your product scratch-resistant. Hence, it can be safely delivered to you without any damage.
These are all the simple steps involved in the aluminum powder coating process.
Number 3-Akzo Nobel.
A Dutch multinational company that is famous around the globe for creating paints and performance coating for industrial and consumer use.
From its headquarters in Amsterdam, it has become the world’s third largest paint manufacturer.
This is a Norwegian multinational chemical company. Being the largest manufacturer it provides decorative and performance paints and coatings.
The company focuses on constant innovation and creativity to stay up to date with the changing trends.
This American company is a global supplier of paints, coating, and other materials. It has been named among the top 500 American Fortune companies.
It functions in 70 countries making it famous for its high-quality products. This is why it has become the world’s top coating company.
The process of Anodizing involves an electrolytic passivation procedure. You can use it to thicken the metal’s natural oxide coating.
Using this procedure the metal becomes more resistant to corrosion and wear. You also get an adhesive surface which can be used for paint primers and adhesives.
This method is liked because of its ability to provide your product with an enhanced aesthetic effect. You can get a distortion simply by reflecting light on it.
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To anodize aluminium you can utilize Sulphuric acid. This provides you with a porous surface, making the dying process easier. You simply have to apply a sealer after the color application.
However, you are offered a limited range of color selections. This is because the final shade depends upon the alloy base.
Paint is widely used as a finishing material because it’s accessible and cheap.
When choosing paint as a finishing product for aluminum components you need to keep the environmental risks in mind.
The harsh chemicals filled in the paint are considered carcinogenic. They are also combustible, placing you in danger of a fire hazard. Paint usage is a significant factor in the contribution of ozone layer depletion.
Furthermore, paint gets wasted more owing to evaporation. You cannot gather it and use it again.
The process of powder coating involves spraying an electrostatically charged colored powder over a material.
For aluminum, this procedure has many benefits. There is little wastage as the excess spray is easily collected for reuse. You will also enjoy a less hazardous environment because the powder coating lacks any solvents.
Despite being a new method introduced in the market, powder coating has left a lasting impression. If you seek aesthetics, durability, and sustainability then choose this method. It is also suitable for many aluminum products like windows, railings, and roofing.
All the finishing methods that we have covered above have their own perks and drawbacks. However, powder coating proves to be the only option whose advantages outweigh its disadvantages.
At Wellste corporate, our utmost priority is to provide high-quality powder coating. We do this by utilizing a highly effortful process of inspection called Cross-Cut Testing. In easier words, it means paint adhesion testing.
The process of cross-cut testing involves making small cuts through the coating layer. This allows us to inspect how the adhesion and coverage have taken place.
This method comes with the advantage of ensuring the detection of any issues in the quality. Our team can efficiently identify insufficient coverage, adhesion problems, and many other defects.
Furthermore, the cross-cut testing helps us in meeting the desired standards of coating. We need to make sure we coat your products in a way that they are highly resistant to corrosion.
Our entire focus is to make your product more durable and appealing. Hence, we prioritize our quality control at all times.
Here are some common defects that cause imperfections in the coating:
When the oxide skin is not removed properly large burrs form. Aluminum material also gains flaws when it is insufficiently heated. Pre-treatment fails to remove many of these particles because they are very tiny.
To remove these flaws, aluminum products are brushed and cleaned before the pre-treatment. An alkaline etching tank also ensures the removal of such defects.
It is difficult to remove the aluminum chips as they aren’t blown away easily. During the washing, they may stick to the aluminum surface.
These big flakes result in projecting particles during coating. Hence, it is vital to take these flakes off before the coating process.
If the operator fails to clean the coolant off the aluminium then the coolant will dry to form glue spots. It cannot be removed by pre-treatment.
This causes the coating particles to spread densely. To remove this defect you can use small clips to clamp the labels.
A layer of dust can settle on the aluminum surface. If it is not cleaned then the paint will become dense and uneven.
These hard particles can also scratch the coating. Hence, to remove these large particles, aluminum should be covered with a cotton cloth temporarily to prevent dust from settling.
There can be linear defects caused by filaments from cotton work clothes and cotton threads. These burrs make the coating defective. Hence, the operators are required to wear rubber or canvas gloves which don’t produce filament.
It is important to clean the hanger with compressed air to remove the paint slags, iron powder, and even debris. This will ensure good electrical conductivity for coating.
The temperature of the powder should be lowered before packing. If not then larger pieces harden making the powder coating perform poorly. Hence, it is important that you pick a powder that is reputable and check it using a mesh screen.
Conclusion
In conclusion, powder coating is the best choice when selecting a finish to protect aluminum surfaces. This will add shine to your aluminum products while increasing their durability and longevity. This process is also safe for the environment, making it more desirable.
However, it is important to properly prep and clean the aluminum before powder coating it. By this, you can prevent the drawbacks associated with powder coating.
To ensure your aluminum products are properly powder coated, make sure you choose a reliable service company.
Food and beverage cans preserve the taste and nutritional values of their filling for up to several years. As a consequence of such long storage times, the interactions between the packaging and the food need to be minimized. Cans are typically coated with an organic layer that protects the integrity of the can from effects of the food and prevents chemical reactions between the can’s metal and the food. To fulfill the technical and legal requirements, can coatings should withstand the production and sterilization processes (1, 3), be universally applicable for all food and beverage types (2), prevent chemical migration into food in quantities that endanger human health (4), adhere to the can even after non-intentional deformation (5), resist aggressive food types and protect the metal of the cans (6), and preserve the food and maintain its organoleptic properties over several years (7).
Cans are made of three different materials: aluminum, tin-coated steel (tinplate) and electrolytic chromium coated steel (ECCS). Can bodies are either formed as 3-piece welded cans (3PC), 2-piece drawn and redrawn (DRD) cans or as 2-piece drawn and ironed (D&I) cans. Independently of the material and the production process, most cans are coated internally and externally with films of 1 to 10 µm thickness. Coatings are usually applied to both sides of planar metal sheets or coils by roller coating before the cans are formed. Alternatively, coatings are sprayed on preformed cans. Tin cans are used without internal coatings for light colored, acidic juices and fruits (e.g. pineapple, pears, peaches), because tin is more easily oxidized than the food, thus preventing darkening and flavor changes caused by oxidation of the fruits. Food cans are usually pressure-sterilized with the exact conditions depending on the food type. However, beverage cans may be pasteurized or sterilized in the sealed cans or filled under aseptic conditions.
More than 300 billion beverage cans are produced globally each year. In , 90% of the beverage cans were made of aluminum; the remaining 10% consisted of steel. Furthermore, it was estimated that 75 billion food cans were sold globally in . In , about US $30 billion and US $9 billion were globally earned with beverage and food cans, respectively. In , the global production capacity of can coatings was estimated to be 800’000 metric tons, which corresponds to a market value of €2.8 billion.
Many different can coatings are commercially available, but most of them are based on a limited number of chemicals functionalities (Table). Coatings contain different additives, e.g. agents to increase surface slipping as well as abrasion and scratch resistance of can coatings, lubricants, anti-foaming agents, adhesives, scavengers for hydrochloric acids, and pigments.
Epoxy-based coatings have the highest market share of more than 90%. However, can manufacturers and food companies have started to replace BPA-based epoxy coatings by alternatives as a consequence of toxicological evidence, public discussions, and recent regulatory decisions. Acrylic and polyester coatings are currently used as first generation alternatives to epoxy coatings and, more recently, polyolefin and non-BPA epoxy coatings were developed. Further inventions include BPA capturing systems and top coatings. Most of these alternative coatings are more expensive than epoxy coatings and may not display the same array of characteristics with respect to their stability and universal applicability yet.
Epoxy coatings
In the s, epoxy resins were introduced as coatings for aluminum and steel cans. Their stability, protective function, and technical properties made them the most commonly used coating material. Most epoxy coatings are synthesized from bisphenol A (BPA, CAS 80-05-7) and epichlorohydrin forming bisphenol A-diglycidyl ether epoxy resins. Many different blends of epoxy coatings were developed with epoxy-phenolic coatings being the most important subgroup. Other blended resins are e.g. epoxy amines, acrylates, and anhydrides.
Oleoresins
First can coatings were made of oleoresins, which are mixtures of oil and resin extracted from plants. Oleoresins are rather flexible and easily applied, but do not adhere well to metal surfaces, have a limited corrosion resistance, and need long curing times. Furthermore, they may change the organoleptic properties of food.
Vinyl
Vinyl coatings are synthesized from vinyl chloride and vinyl acetate. They are highly flexible and stable under acidic and alkaline conditions, but they do not adhere well on metal and do not withstand at high temperatures. Vinyl coatings need plasticizers and stabilizers and are often blended with other resins. Vinyl organosols are prepared from suspensions of resin in organic solvent. Organosols offer comparably higher chemical resistance, thermal stability, and adhesion properties than vinyl coatings.
Phenolic
Phenolic resins are composed of phenols and aldehydes. They are highly corrosion resistant and protect cans from sulfide staining. Phenolics have low flexibility, do not adhere well to metal, and may change the odor and flavor of foods. They are applied as coatings for drums and pails, but unblended phenolic resins are not used in food and beverage cans. However, phenolics are common crosslinkers (e.g. in epoxide resins) and increase their resistance.
Acrylic
Acrylic resins are most commonly synthesized from ethylacrylate. They have a clean appearance and display corrosion and sulfide stain resistance, but they are brittle and may change the taste and odor of foods.
Polyester
Isophthalic acid (IPA) and terephthalic acid (TPA) are the main carboxylic acids used in polyester coatings. Polyester resins are easy to handle during the production process and adhere well to the metal surface, but they are usually not stable under acidic conditions and have a poor corrosion resistance. Alternatively, polyethylene terephthalate (PET) coatings are used to laminate beverage cans, but adhesives are needed to bind the PET onto the metal.
Polyolefins
Coatings that are based on dispersions of polyolefins have recently entered the market. According to the manufacturer, the final polyolefin coating exhibits corrosion protection, adhesion, and flexibility without impacting the flavor of the food.
U.S.
Polymeric and resinous coatings are covered under 21 CFR 175.300. This code lists permitted starting substances and specifies test conditions and migration limits. Can coatings meeting these specifications are compliant with the law. In May , California’s Office of Environmental Health Hazard Assessment (OEHHA) added BPA to the list of chemicals known to cause reproductive harm under Proposition 65. Manufacturers, distributors, and retailers now have to inform the consumers of BPA-containing products with a clear and reasonable warning regarding the chemical hazards (FPF reported).
Europe
Can coatings are not regulated by an EU-wide legislation, but national measures are in place in the Netherlands, Belgium, the Czech Republic, Greece, Italy, Slovakia, France, and Spain. Harmonized regulations for specific chemicals known to migrate from can coatings exist for bisphenol A diglycidyl ether (BADGE) and its derivatives (Commission Regulation EC /) and for inorganic tin (Commission Regulation EC 242/). A draft of a Commission Regulation on the use of BPA in varnishes and coatings currently suggests a specific migration limit of 0.05 mg/kg food (FPF reported). In France, the use of BPA is prohibited in FCMs including all packaging, containers and utensils intended to come into direct contact with food (LOI n° -729) (FPF reported).
Most studies investigating chemical migration from food cans focused on BPA, BADGE and their derivatives. Especially the amount of data for BPA provide a good basis for exposure estimates. However, the total migrates from cans may also contain oligomers, catalysts, reaction accelerators, epoxidized edible oils, amino resins, acrylic resins, various esters, waxes, lubricants, and metals. Furthermore, non-intentionally added substances (NIAS) such as impurities, reaction by-products and degradation products generally constitute a part of the migrate. Exposure estimates for these, often complex mixtures are much more difficult or even impossible to calculate, because many NIAS are unknown or unidentified substances.
A correlation exists between the human exposure to BPA and the consumption of canned food and, to a far lower extent, canned beverages. In , a study showed that BADGE and its derivatives were detected in all test samples from the U.S. and China and that urinary concentrations exceeded those of BPA by 3 to 4 times.
Can coatings generally release complex chemical mixture into the food and only few of the migrants were thoroughly tested. Extensive toxicity data exist for BPA covering many different endpoints such as reproductive and developmental effects as well as neurological, immune-modulatory, cardiovascular and metabolic effects. In , BADGE was judged to not raise concern for genotoxicity, carcinogenicity, reprotoxicity and developmental toxicity. However, more recent studies indicated some effects on reprotoxic and developmental endpoints.
Many migrating substances are completely unknown, but they may strongly contribute to the toxicity of the migrate. In , cytotoxic effects of migrates from epoxy- and polyester-based coatings were tested using a series of assays. The results of one of these assays showed that only about 0.5% of the cytotoxic effects measured in the migrate from epoxy coatings could be traced back to the amount of BPA, BADGE and BADGE·H2O. This example illustrates the importance of tests targeting the final migrate and not only single substances during risk assessment.
FPF Dossier
Why are cans coated?
Can production and market data
Coatings: properties and alternatives
Migration, exposure & biomonitoring
Health effects
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