Anodic Oxidation

Since the founding of our company, our engagement in anodic oxidation has led to significant accomplishments.

Anodic oxidation, also known as anodising, is an electrochemical technique used to increase the natural oxide layer on metal surfaces, especially aluminium. In this process, the metal acts as the anode in an electrical circuit while submerged in an electrolytic solution. When an electric current passes through, it causes an oxide layer to form on the metal's surface. This layer enhances the metal's resistance to corrosion and wear and can be dyed for aesthetic purposes, making anodising a popular choice in various industries like aerospace, automotive, and consumer goods.

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Understanding Anodic Oxidation at Coler Supply Solutions

This technique utilises an acid bath and electrical current to create an anodic layer on the base metal. In essence, it involves affixing a controllable and robust oxide film onto the components, as opposed to depending on the thin oxide layer naturally produced by the material itself. This process is akin to other surface treatments such as bluing, phosphating, and passivation applied to steels, which are known for their significant corrosion resistance and surface hardening capabilities.

The method's efficacy lies in its precision and adaptability in controlling the thickness and properties of the oxide layer. This controllability allows for tailored surface characteristics to meet specific requirements, such as enhancing the wear resistance or electrical insulation of the treated parts. Additionally, the oxide film formed through this process is integrated with the underlying metal, providing a seamless and strong bond that significantly improves the longevity and performance of the metal surface. This makes it particularly valuable in industries where durability and resistance to environmental factors are crucial, such as in aerospace, automotive, and marine applications. Moreover, the process can be modified to alter the aesthetic appearance of the metal, offering a range of colours and finishes that enhance the visual appeal of the final product.

Anodic Oxidation Classifications

Category I:

  • Type I and IB – Chromic Acid Anodising
  • Type IC – Substitute for Type I and IB Non-Chromic Acid Anodising

Category II

  • Type II – conventional coating for sulfuric acid bath
  • Type IIB – non chromate alternatives to type I and IB coatings

Category II

  • Type III – hard anodizing
  • Each type of anodic oxidation has specific reasons

Types I, IB, and II anodising are all employed for components requiring corrosion resistance to a certain extent. For parts necessitating specific fatigue resistance, such as connection and structural elements on aircraft, Types I and IB are preferable due to their thinner coating films.

In situations where Types I and IB necessitate non-chromate alternatives, Types IC and IIB are recommended. These variants align with environmental protection standards by avoiding the use of chromates.

Type III anodising is primarily aimed at enhancing wear resistance through a thicker coating. This makes it more effective against wear compared to other types, but it can potentially decrease the fatigue life of the component. Common applications for Type III anodising include gears, valves, and other parts subject to sliding actions.

Compared to uncoated aluminium, all types of anodising improve the adhesion of paint and other bonding agents. In addition to anodising, some parts may require further treatments such as colouring, sealing, or the application of additional materials like dry film lubricants. If colouring is needed, the part falls under Type II anodising, whereas uncoloured components are classified as Type I.

Understanding Anodic Dimension Change

Dimensional Changes Post-Anodising: The foremost factor to consider is the dimensional alteration resulting from anodic oxidation. Engineers or designers usually account for this by specifying post-treatment dimensions on technical drawings. This practice ensures that the final component aligns with required specifications. However, in rapid prototyping, where speed is of the essence, reliance on detailed drawings is often minimal. Instead, solid models — digital 3D representations of parts — are used. This shift in approach demands a nuanced understanding of how anodic oxidation alters dimensions, necessitating adjustments in the solid model to accurately reflect these changes.

Surface Enlargement in Treated Parts: Anodic oxidation typically results in the expansion of the surface area of the treated parts. This enlargement means that external dimensions, like the outer diameter of a cylindrical part, increase, while internal features, such as holes, decrease in size. This phenomenon is attributed to the growth of the oxide layer both internally and externally on the metal surface. Therefore, meticulous planning during the design phase is crucial to ensure that the final dimensions align with the intended use of the part.

Thickness of the Anodic Layer: The expansion in size is often proportional to the thickness of the anodic layer, which can increase the overall dimensions of the part by up to 50% of the layer's thickness. Understanding the relationship between the anodic layer's thickness and the resultant size increase is vital for accurate design and manufacturing.

Variability in Coating Thickness: The thickness of the anodic layer varies depending on the alloy used and the specific controls applied during the processing. This variability must be carefully considered by designers, particularly when precision is paramount. In some cases, especially with thicker Type III coatings, post-treatment machining such as grinding may be necessary to achieve the desired final size. However, this additional step can increase both time and costs.

Impact on Edge Radii and Internal Angles: The process of anodic oxidation is less effective on sharp corners, which is especially true for thicker Type III coatings. Consequently, designers must consider the radius of edges and internal angles in their designs, avoiding sharp corners where the anodic coating may be less effective. The specific corner radii for different thicknesses of Type III coatings are often guided by standards such as Mil-A-8625.

In summary, successful application of anodic oxidation in manufacturing, particularly in rapid prototyping, requires a comprehensive understanding of how the process affects material dimensions. Designers and engineers must carefully consider the changes in surface area, thickness variations, and the impact on specific geometric features. By doing so, they can ensure that the final product not only meets aesthetic and functional requirements but also adheres to stringent industry standards.

Understanding Wear Resistance

Enhanced Surface Stiffness and Wear Resistance: Hard anodizing creates an oxide layer on the surface of the part, leading to increased surface stiffness. This process is highly beneficial for parts that require enhanced wear resistance. The unique characteristic of hard anodizing is its high adhesive force; approximately 50% of the oxide layer penetrates into the aluminum alloy, while the remaining 50% adheres to the surface. This dual action results in a robust coating that is resistant to wear and tear. Applications of hard anodized aluminum include products like baseball bats, bicycle frames, and flashlights.

Properties of the Hard Anodized Layer: The hard anodising process typically produces a layer thickness ranging from 30 to 50 micrometers, with a hardness of about 500HV. This layer boasts exceptional corrosion resistance and wear resistance. Additionally, the hard anodizing layer is non-toxic and safe for human contact, making it suitable for a wide range of applications, including kitchen appliances like rice cookers, medical device packaging, air and oil cylinders, and printing rollers. Moreover, this coating is durable and maintains its integrity under high pressure and temperature conditions, offering not only functional benefits but also aesthetic appeal.

Impact on Surface Dimensions: The hard anodizing process alters the surface dimensions of the treated parts to a certain degree. Therefore, precise allowance calculations are essential to ensure that the final product meets the desired specifications. This dimensional change is a critical consideration in the manufacturing process, requiring accurate forecasting and adjustment in the design stage.

Advancement in Hard Anodizing Technology: To meet the diverse needs of various industries, hard anodizing oxidation factories are continually improving their technologies. This advancement is driven by the need for mechanical machining convenience, weight reduction trends, and environmental protection requirements. In many instances, hard-anodized aluminum alloy is replacing stainless steel in specific components, offering a lightweight yet durable alternative.

Range of Hard Anodizing Technologies: The field of hard anodizing encompasses a wide array of technologies, including thermochemical hard-oxidation, physical vapor deposition (PVD), chemical vapor deposition (CVD), physicochemical vapor deposition, high-energy in vitro hard-oxide coating, diamond film coating, and multicomponent and multilayer composite coating technologies. These methods offer varied benefits, such as increased toughness and wear resistance, compared to other oxidation processes like conductive oxidation, which produces a significantly thinner layer (0.01-0.13 micron) and offers less wear resistance.

In conclusion, hard anodizing is a sophisticated and versatile surface treatment that significantly enhances the mechanical properties of aluminum alloys. Its application across various industries underscores its effectiveness in improving wear resistance and surface stiffness, while also being environmentally friendly and aesthetically pleasing. The continuous advancement in hard anodizing technologies ensures that it remains a critical process in modern manufacturing, adapting to evolving industry demands and environmental considerations.

Understanding Colour With Dyes

Anodic oxide films, emerging from the anodizing process, possess the distinctive capability to be colored, offering a range of advantages for various applications.

Key Advantages of Coloring Anodic Oxide Films:

Aesthetic Enhancement: The primary appeal of coloring anodic oxide films lies in their aesthetic enhancement. This capability allows for a wide range of color applications, catering to diverse design preferences and branding requirements. The visual appeal of colored anodic oxide films is particularly significant in consumer-facing products, where appearance can strongly influence consumer choices.

Optical Benefits: In optical systems, colored anodic oxide films play a crucial role in reducing stray light. This reduction enhances the performance of optical instruments, contributing to more precise and accurate measurements.

Assembly and Identification: The application of color on anodic oxide films aids in the contrast and recognition of different components during assembly processes. This enhancement is particularly useful in complex assemblies, where identifying parts quickly and accurately can significantly streamline the manufacturing process and reduce errors.

Anodic oxide films, emerging from the anodizing process, possess the distinctive capability to be colored, offering a range of advantages for various applications.

Key Advantages of Coloring Anodic Oxide Films:

Aesthetic Enhancement: The primary appeal of coloring anodic oxide films lies in their aesthetic enhancement. This capability allows for a wide range of color applications, catering to diverse design preferences and branding requirements. The visual appeal of colored anodic oxide films is particularly significant in consumer-facing products, where appearance can strongly influence consumer choices.

Optical Benefits: In optical systems, colored anodic oxide films play a crucial role in reducing stray light. This reduction enhances the performance of optical instruments, contributing to more precise and accurate measurements.

Assembly and Identification: The application of color on anodic oxide films aids in the contrast and recognition of different components during assembly processes. This enhancement is particularly useful in complex assemblies, where identifying parts quickly and accurately can significantly streamline the manufacturing process and reduce errors.

Considerations in Anodic Oxidation:

Fading of Anodic Oxide Films: A notable concern with anodic oxide films is their tendency to fade, especially when exposed to UV light or high temperatures. This fading is more pronounced with organic dyes compared to inorganic ones. Despite this, many vibrant colors are achievable predominantly through organic dyes, necessitating a balance between color choice and longevity.

Dye Responsiveness and Anodizing Types:

Type I Anodizing: This type, known for its thinner coating, struggles to achieve deep black hues. Often, even when black dyes are used, the resulting color may appear grey, limiting the effectiveness of the coloring process without additional specific treatments.
Type III Anodizing: With its thicker coating, Type III anodizing tends to produce dark grey or black shades on certain alloys, thus restricting the spectrum of available colors. However, thinner Type III coatings can sometimes accommodate multiple colors.

Type II Anodizing: This is generally considered the most versatile and effective for color applications, providing a broader range of color options with better dye absorption and retention.

In conclusion, the coloring of anodic oxide films enhances both the aesthetic and functional aspects of anodized parts. While it offers significant benefits in terms of visual appeal, optical efficiency, and component identification, challenges such as dye fading and limitations in color application across different anodizing types must be considered. Type II anodizing emerges as the most favorable option for a wide range of colors, balancing these considerations effectively. With ongoing advancements in anodizing techniques and dye formulations, the potential for coloring anodic oxide films continues to expand, promising more durable and vibrant color applications in various industries.

Understanding Electric Conductivity & Composite Coating

Understanding Electric Conductivity

Despite the inherent electrical conductivity of the base metal, typically aluminium, an anodic oxide layer formed through anodising acts as a highly effective insulator. This insulating property is one of the key benefits of anodising, as it enhances the electrical safety and performance of the metal parts.
However, this feature can also present challenges in certain applications where electrical grounding is essential. In such scenarios, particularly in the case of electronic components or metal chassis that require grounding for safety or functional purposes, a special consideration is needed.

To address this, a transparent chemical transmission layer can be applied to targeted areas of the anodised component. This layer, while maintaining the overall integrity and insulating properties of the anodic oxide layer, allows for electrical conductivity in specific zones where grounding is necessary. The application of this layer must be done with precision to ensure that it only covers areas where electrical transmission is required, without compromising the protective qualities of the anodic oxide layer in other regions of the component.

In the manufacturing and quality control process, it's important to verify whether parts have undergone the anodising process.

Understanding Composite Coating

Anodised parts offer the unique advantage of being amenable to secondary machining, which allows for further enhancements to their properties post-anodisation. This process involves applying additional treatments or coatings to the anodised surface to improve its performance and durability.

One popular method is the application of paint to the anodic coating. This technique enables the attainment of specific colours that are not achievable through conventional dyeing processes. The use of paint not only enhances the aesthetic appeal of the anodised parts but also potentially increases their corrosion resistance. This dual benefit makes painting a favoured choice in applications where both appearance and longevity are key considerations.

Another notable treatment is Teflon immersion, particularly effective for Type III hard coatings. This process involves immersing the anodised part in Teflon, significantly reducing the friction coefficient of the anodised surface. The reduced friction is especially beneficial in applications involving moving parts, such as in mould cavities and areas where parts slide or make contact. By decreasing friction, Teflon immersion enhances the operational efficiency and lifespan of the components, making it a valuable addition to the anodising process.

Main Considerations

Types I, IB, and II anodising are all employed for components requiring corrosion resistance to a certain extent. For parts necessitating specific fatigue resistance, such as connection and structural elements on aircraft, Types I and IB are preferable due to their thinner coating films.

In situations where Types I and IB necessitate non-chromate alternatives, Types IC and IIB are recommended. These variants align with environmental protection standards by avoiding the use of chromates.

Type III anodising is primarily aimed at enhancing wear resistance through a thicker coating. This makes it more effective against wear compared to other types, but it can potentially decrease the fatigue life of the component. Common applications for Type III anodising include gears, valves, and other parts subject to sliding actions.

Compared to uncoated aluminium, all types of anodising improve the adhesion of paint and other bonding agents. In addition to anodising, some parts may require further treatments such as colouring, sealing, or the application of additional materials like dry film lubricants. If colouring is needed, the part falls under Type II anodising, whereas uncoloured components are classified as Type I.

Why Choose Coler Supply Solutions?

To ensure that your manufacturing plan operates efficiently and with the flexibility required to maintain high-quality standards, it's crucial to implement strict project flow management. Here's a concise guide to achieving this:

Product DFM Analysis

Mould Design

Mould Making

Mould Trial

Sample Approved

Large Volume Production

Quality Control

Packing

Delivery

Customer Aftercare