Bright dip anodizing is commonly used to enhance the aesthetics and corrosion resistance of aluminum workpieces.
But what exactly is bright dip anodizing? And what benefits does it provide?
Bright Dip anodizing is an electrochemical process for metals that produces a glossy look with a highly reflecting surface finish. It involves two phases: Bright dipping etches the surface to remove any microscopic roughness, producing a shiny surface, followed by anodizing to enhance the corrosion resistance of the workpiece.
This article provides a detailed guide on bright dip anodizing by going through its process, benefits, and applications.
The article also discusses the factors that affect the cost of bright dip anodizing and the grades of aluminum best suited for the process.
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What is Bright Dip Anodizing?
Bright dip anodizing is a chemical treatment that enhances the appearance and corrosion resistance of aluminum parts.
Although it is best suited for aluminum, you can also include bright dipping in the process of anodizing steel, bronze, gold, etc.
In addition to the benefits of anodizing such as protection from scratching, fading, and corrosion, bright dipping provides a highly reflective sheen and smooth surface finish to the workpiece.
However, the addition of bright dipping increases the cost of anodizing the workpiece, making it important to consider the requirement before opting for bright dip anodizing.
| Steps involved in Bright Dip Anodizing | |
|---|---|
| Step 1 | Cleaning of workpiece |
| Step 2 | Racking |
| Step 3 | Bright dipping |
| Step 4 | Desmut |
| Step 5 | Anodizing |
| Step 6 | Dying/Coloring |
| Step 7 | Seal/Packing |
| Step 8 | Testing/Inspection |
Step 1: Cleaning of Workpiece
In this first step, any burr, swarf, or unwanted excess material from the aluminum part is removed.
It can be performed by using different surface cleaning processes, such as sandblasting, sanding, chemical etching, or laser etching.
Step 2: Racking the Workpiece
Racking is a material holding method used during the bright dip anodizing process.
It serves two purposes: it physically holds the parts and provides a secure electricity supply to the parts during bright dip anodizing.
The parts must be securely held during the process otherwise will fall off the rack or be lost in the tank.
Throughout the process, the parts are gripped on a conductive rack.
It must be noted that the contact point between the workpiece and the racking system will not be anodized, and will leave a rack mark on the part.
Therefore, it is always advised to include an expendable profile in the workpiece for raking, which can be removed after anodizing.
Step 3: Bright Dipping the Workpiece
Bright dipping is an etching process in which the workpiece (aluminum part) is immersed in a phosphoric/nitric acid bath to remove a very fine layer from the surface.
This material removal produces a bright surface finish but with some irregularities on the surface.
Therefore, the process is followed by desmutting to eliminate any microscopic surface irregularities, producing a smooth and shiny surface that facilitates producing a bright anodizing layer.
Step 4: Anodizing the Workpiece
During anodizing, the parts are submerged in the acid electrolyte tank and an electrical current is supplied to the bath.
The reaction during anodizing forms a protective oxide layer (coating) on the surface of the alloy, which protects it from corrosion, scratching, and fading, extending the life of the workpiece.
Depending on your requirement, you can select the best-suited anodizing process for your application.
Although there are three types of anodizing, bright dipping is only suitable for type II and type III anodizing.
Type II - Sulfuric Acid Anodizing
Type II anodizing is the most commonly used anodizing technique for bright-dipped aluminum parts. In this method, sulfuric acid is used instead of chromic acid.
Sulphuric acid is an electrolyte solution that forms porous structures efficiently, which can help in absorbing the dye/color.
As a result, type II anodized parts can be dyed with various colors for decorative applications.
Compared to Type I, Type II anodizing produces a thicker anodizing layer ranging from 2.5-25 µ, which improves the abrasion resistance of the workpiece.
Unlike type I anodizing, type II anodizing does not require special waste treatment to dispose of the chemicals, making type II anodizing comparatively cheaper.
Type III - Hard Anodizing
Type III anodizing also involves immersing the workpiece in a sulfuric acid bath, but at a higher voltage, and current density, while maintaining a temperature lower than Type II anodizing.
It produces a much thicker (>25 µ) and more porous coating layer.
The thick coating layer increases the part dimensions, making it suitable for limited applications which require high corrosion and wear resistance.
Also, this type of anodizing produces dark film, which is not suitable for applications where color anodizing of aluminum workpieces is required.
Due to the higher current and voltage requirement, followed by a longer anodizing time, type III anodizing is generally more costly than type II anodizing.
Step 5: Dying/Coloring the Anodized Workpiece
Anodized parts contain tiny pores on their surface, making them suitable for dying. The anodizing dye or color penetrates the pores and forms an integral part of the oxide layer.
Bright-dipped anodized aluminum parts can be dyed in different colors such as Blue, Red, Green, Purple, Gold, and Black to enhance the aesthetic look.
Apart from that, you can also paint the anodized surface to get more flexibility in the choice of color.
There are various factors that determine the brightness of the anodized surface, such as the grade of aluminum, its surface finish, etc.
Generally, high-tempered aluminum alloys are best suited for bright dip anodizing, as they facilitate the production of surfaces with greater luster and brightness.
Step 6: Sealing the Anodized Surface
Sealing locks the absorbed dye/color on the porous anodized layer.
It protects the decorative coating from corrosion, staining, and fading.
Sealing is the final step of anodizing is performed by using a selling agent to lock the pores after adding the desired color.
Benefits of Bright Dip Anodizing
Bright dip anodizing provides the following benefits:
- Bright dip anodized surfaces have a lustrous, mirror-like finish.
- Thorough cleaning of the surface ensures a smooth surface finish, free from deposits.
- The final workpiece has an improved visual appeal.
- The workpiece will be protected from corrosion, scratching, and fading.
- It provides the ability to add different colors to the coating.
- The workpiece will have a longer lifespan.
Factors that Affect the Cost of Bright Dip Anodizing
The cost of the bright dip anodizing can be varied based on various factors.
Thickness of the Coating
The thickness of anodizing plays an important role in determining the cost.
Generally, the thicker the coating, the higher will be the cost.
Therefore, a thick coating is only advised when abrasion resistance is the decisive factor, irrespective of the cost.
Ease of Racking
The racking of the workpiece directly affects the cost of anodizing.
When outsourcing your bright dip anodizing project, it is important to ask the service provider about their racking technique and design your part accordingly.
This is because, a custom/unique racking system will reduce the batch capacity of the service provider, thereby increasing the cost of anodizing.
Type of Anodizing
Type I anodizing process requires the installation of a specialized wastewater treatment facility, whereas type III anodizing requires a higher voltage and current density facility, making it more expensive than the type II anodizing process.
Therefore, it is recommended to go for type II anodizing for bright dip anodizing, unless the application demands other types of anodizing.
Part and Batch Size
Bright dip anodizing services typically cost around $0.5 to $1 per square inch or even $200 per part.
Therefore, as the area of the workpiece increases, the cost of bright dip anodizing also increases.
Apart from this, some service providers have minimum batch charges of around $50. This means that, despite the small size of your workpiece, you will be charged $50 for the service.
As a result, it is more economical to anodize bulk products, rather than anodize a single unit.
Customized Services
The service provider may charge for additional services like adding custom color, buffing, media blasting, dry film lubrication, custom packaging, etc.
Therefore, it is essential to choose the correct service provider for your application.
Applications of Bright Dip Anodizing
As bright dip anodizing comes in a variety of colors, it is typically used in different applications where an aesthetically pleasing surface finish with excellent wear resistance is desirable.
Construction Industry
The bright dip anodizing process produces attractive, low-maintenance parts for use in commercial buildings and skyscrapers.
These parts are used for highly durable exteriors, roofs, lobbies, staircases, escalators, curtain walls, ceilings, architectural accent pieces, window frames, light reflectors, etc.
Commercial Industry
Aluminum bright dip anodizing transformed the fabrication of computer hardware, food and beverage containers, home appliances, and consumer products.
It allows to produce a lustrous attractive look to the product while enhancing its durability, making it last long and withstand the harsh environmental conditions.
Automotive and Manufacturing Industry
Bright dip anodizing is used to enhance the corrosion resistance of automobile parts and manufacturing equipment while providing pleasing aesthetics.
It is generally used for coating the body of the machine and other automotive parts like rims, mirrors, etc.
Recreational and Sporting Goods
Bright decorative colors are widely used in the manufacturing of recreational and sporting equipment such as flashlights, paintball guns, baseball bats, bows & arrows, tennis rackets, baseball bats, etc.
Metals Suitable for Bright Dip Anodizing
Aluminum is considered one of the best materials for bright dip anodizing because of its ability to produce a thick oxide layer.
This enhances the corrosion resistance and lifespan of the aluminum parts.
| Aluminum alloy Grades | Alloying Constituents | Coating Properties | Characteristics |
|---|---|---|---|
| 1100-0 | Pure Aluminum | Clear, bright | Pure aluminum, coating can be damaged easily |
| 2011, 2024 | Copper | yellow, poor protection | Poor appearance and corrosion protection |
| 3002 | Manganese | Grayish-brown | Difficulty in maintaining consistent color |
| 4043, 4343 | Silicon | Dark gray | Heavy black color, Visually not appealing |
| 5052, 5357, 5457 | Magnesium | Clear, good protection | Best for anodizing |
| 6061, 6063,6463 | Magnesium and Silicon | Clear, transparent, good protection | Best for anodizing |
| 7016, 7029, 7075 | Zinc | Clear, good protection | superior protection, Excessive zinc content can produce a brown coating |
5XXX and 6XXX series alloys are higher tempered than 2XXX and 7XXX series alloys, and therefore, produce a lustrous and bright anodizing coating.
However, 6061 aluminum alloy, commonly known as structural aluminum, produces a comparatively dull coating, making it the least favorable alloy for bright dip anodizing, from the 6XXX series.
On the other hand, 6063 and 6463 aluminum alloys, which are commonly used in architectural applications, have a brighter and more reflective surface, making them the most commonly used aluminum alloys for bright dip anodized.
It is important to note that bright dip anodizing does not remove surface scratches, die lines, or rolling marks from the alloy. Additional buffing is required to remove these marks.
Apart from aluminum, you can also use bright dip anodizing for other non-ferrous metals, like magnesium and titanium.
Final Thoughts
Bright dip anodizing is a surface treatment that produces a lustrous protective coating on aluminum.
Higher-tempered 5XXX and 6XXX series aluminum alloys are best suited for bright dip anodizing as they produce a bright coating with a lustrous surface finish.
Bright dipped anodized parts can be dyed in different colors, making them suitable for cosmetically enhanced commercial, construction, automotive, industrial, recreational, and sporting products.
Type II anodizing is most commonly utilized for bright dip anodizing due to its simple processing conditions and lower cost compared to Type III anodizing.
Bright dip anodizing is not a common practice due to its higher cost, and therefore, it is advised to select the right service provider who has prior experience in bright dip anodizing, such as Chicago Anodizing Company.
Frequently Asked Questions (FAQ)
What safety precautions are required during bright dip anodizing?
The safety precautions required during bright dip anodizing include wearing rubber gloves, a face shield, safety goggles, and an apron during the process. Appropriate exhaust hoods must be installed to dispose of the fumes generated during bright dipping.
Can I bright-dip anodize steel and stainless steel workpieces?
No, you cannot bright-dip anodize steel and stainless steel workpieces. Bright dip anodizing causes material to dissolve into solution, which can lead to the corrosion of steel and stainless steel workpieces.
Does bright dip anodizing enhance the strength of the aluminum part?
No, bright dip anodizing does not enhance the strength of the aluminum parts but it improves the chemical and abrasion resistance of the part.
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