History of Phosphating

Phosphating has a long history and is one of the earliest surface treatment techniques in modern metal processing. Its development has gone through several stages.

In 1869, the discovery of phosphate coatings in the UK showed that they could effectively protect metals from corrosion over extended periods. This led to the first patent for phosphating, laying the foundation for its technological advancement.

From the early 20th century, phosphating began to be applied to industrial products, driving further development and entering a phase of practical application.

Now, phosphating processes have evolved to meet diverse needs, focusing on low-temperature processing, reduced residue, and environmentally friendly, non-toxic formulations.

Types of Phosphating

Unlike most surface treatments that result in a single color, phosphating can produce various colors—gray, iridescent, or black—depending on the phosphating agent used.

Iron Phosphating

This process creates a rainbow-like or blue coating, often called color phosphating. The phosphating solution, primarily composed of molybdate, forms a rainbow-colored film on steel surfaces. It is mainly used as a base layer for coatings to enhance corrosion resistance and improve adhesion of the topcoat.

Zinc Phosphating

This produces a gray coating, known as gray film phosphating. The solution typically contains phosphoric acid, sodium fluoride, and emulsifiers, forming a gray phosphate film on the metal surface. It serves as a base for processes like powder coating, painting, or electrophoresis. The gray film also provides some corrosion resistance and can be used alone as a protective coating on surfaces like galvanized steel, cold-rolled steel, or aluminum.

Manganese Phosphating

This results in a black or dark gray coating, often called black phosphating. Using a manganese-ion-containing solution, it forms a black phosphate film with superior rust resistance, making it ideal for long-term corrosion protection. Its low friction coefficient makes it suitable for components subject to frequent friction, such as automotive parts and fasteners.

Principles of Phosphating

Phosphating works by triggering a chemical reaction between active sites on the metal surface and phosphate ions in the solution, forming a dense phosphate conversion coating. During this process, impurities like oil and rust are removed, exposing more active sites to facilitate the reaction.

Steps in the Phosphating Process

Phosphating typically involves the following steps:

Pre-treatment: Removes oil, rust, and oxide scales to provide a clean surface for the phosphating reaction.

Phosphating Reaction: The metal is immersed in a phosphating solution, where a chemical reaction forms a phosphate conversion coating. The solution’s formula and process parameters significantly affect the coating’s quality and performance.

Post-treatment: Includes rinsing, drying, and passivation to remove residual chemicals and enhance the coating’s corrosion resistance and durability. Each step is followed by rinsing to remove residual chemicals, ensuring the next step proceeds smoothly. After phosphating and rinsing, the workpiece is dried to complete the process, ready for further processing or use.

Phosphating is a simple and practical method for corrosion protection in modern metal surface treatments. It plays a critical role as a pre-treatment step and has significantly advanced the surface coating industry. However, challenges remain, driving improvements toward energy efficiency, environmental friendliness, non-toxicity, and higher efficiency.

Why Does Phosphating Produce Multiple Colors?

The ability of phosphating to produce various colors depends on factors like the coating formation mechanism, phosphating solution formula, process parameters, and post-treatment. Below, we explore these in detail.

Coating Formation Mechanism

The phosphate coating forms through a chemical reaction between active sites on the metal surface and phosphate ions in the solution. Different metals and phosphate ions produce distinct chemical combinations, resulting in coatings with varying colors and properties. For example, iron phosphate films typically appear gray-black, while zinc phosphate films may be light yellow or gray.

Phosphating Solution

The solution’s composition significantly influences the coating’s color and performance. Typically containing phosphates, additives, and auxiliaries, the solution’s phosphate type and concentration alter the coating’s composition and structure, affecting its color. Additives like organic dyes or inorganic pigments can also be included to produce specific colors.

Process Parameters

Parameters like temperature, time, and pH affect the reaction rate and extent, influencing the coating’s composition and structure. For instance, higher temperatures can accelerate the reaction, creating a denser, more uniform coating, while longer processing times result in thicker, more robust coatings. These changes impact the coating’s color and performance.

Post-Treatment

Post-treatments like rinsing, drying, and passivation can alter the coating’s surface state and chemical properties, affecting its color and performance. For example, different passivating agents can modify the coating’s color and corrosion resistance during passivation.

Conclusion

With advancements in technology and industry, phosphating is increasingly vital in metal surface treatments. Future developments will focus on efficiency, environmental sustainability, and multifunctionality. Optimizing solution formulas and process parameters can produce more uniform and dense coatings, while eco-friendly phosphating agents and additives will reduce pollution and waste. Additionally, combining phosphating with other surface treatments, like spraying or electroplating, can further enhance metal surface performance and aesthetics.

About SogaWorks

SogaWorks is an all-in-one online platform for custom mechanical parts, connecting over 1,000 top-tier factories to serve startups and major companies. We offer flexible manufacturing solutions for rapid prototyping, small-volume testing, and large-scale production with services like CNC machining, 3D printing, urethane casting, and injection molding. Surface finishes include anodizing, sand blasting and phosphating. With our AI-powered quoting engine, SogaWorks can deliver quotes in 5 seconds, match the best capacity, and track every step. This cuts delivery times and boosts product quality.

Surface Finish: What is Phosphating Coating?最先出現(xiàn)在SogaWorks。

Principle of Acid Stainless Steel Passivation

The corrosion resistance of stainless steel primarily stems from adding more than 10.5% chromium (Cr), for example, 16%–18% in 316L stainless steel. Chromium readily oxidizes, quickly forming a dense Cr?O? oxide film on the steel surface. This film significantly enhances the steel’s electrode potential and corrosion resistance in oxidizing environments. The corrosion resistance of stainless steel relies on this extremely thin (about 1 nm) and dense passivation film, which acts as the primary barrier, isolating the base metal from corrosive media. If the passivation film is incomplete or damaged, stainless steel can still corrode.

When stainless steel is exposed to air, it forms an oxide film, but this film’s protective properties are inadequate. Acid pickling removes an average surface layer of about 10 μm, where the chemical activity of the acid causes defective areas to dissolve faster than other parts of the surface. This process results in a more uniform and balanced surface. More importantly, acid pickling and passivation preferentially dissolve iron and its oxides over chromium and its oxides, eliminating the chromium-depleted layer and enriching the surface with chromium. Under the action of an oxidizing agent, a complete and stable passivation film forms. This chromium-rich passivation film can reach a potential of +1.0V (SCE), close to that of noble metals, significantly enhancing corrosion resistance stability.

Significance of Stainless Steel Passivation

The primary reason for the widespread use of stainless steel is its corrosion resistance, which extends the lifespan of components made from it. However, stainless steel is not immune to rust. All stainless steel materials, unless plated or coated, typically undergo passivation after pretreatment (such as acid pickling to remove black scale, polishing, etc.) for use as finished products or in assemblies. Evidence shows that only through passivation can stainless steel maintain long-term passivation stability, thereby improving its corrosion resistance.

Related Post: Does Stainless Steel Rust? Everything You Need to Know

Methods of Passivation

Depending on the operation, stainless steel acid pickling and passivation can be performed using six methods: immersion, paste, brushing, spraying, circulation, and electrochemical. Among these, immersion, paste, and spraying are particularly suitable for acid pickling and passivation of stainless steel chemical tankers and equipment.

Immersion Method

The immersion method is ideal for stainless steel pipelines, elbows, and small components, offering the best treatment results. The parts are fully submerged in the pickling and passivation solution, allowing complete surface reaction and the formation of a dense, uniform passivation film. This method is suitable for continuous batch operations but requires periodic replenishment of the solution as its concentration decreases. Its drawbacks include limitations due to the shape and capacity of the acid tank, making it unsuitable for large equipment or overly long or wide pipelines. Prolonged disuse may reduce effectiveness due to solution evaporation, and it requires dedicated venues, acid tanks, and heating equipment.

Paste Method

Stainless steel pickling and passivation paste is widely used and available in various commercial products, typically composed of nitric acid, hydrofluoric acid, corrosion inhibitors, and thickeners in specific proportions. It is suitable for on-site applications, such as treating weld seams, weld discoloration, ship deck tops, corner dead zones, escalator backs, and large-area passivation inside liquid tanks.

The paste method’s advantages include no need for specialized equipment or venues, no heating requirements, flexible on-site operation, and one-step pickling and passivation. The paste has a long shelf life, with each application using fresh paste, and the reaction stops after passivation, avoiding over-corrosion. It is less affected by subsequent rinsing time, and weak areas like welds can be further strengthened. However, the worker’s operating environment is poor, labor intensity is high, costs are higher, and the treatment effect on the inner walls of stainless steel pipelines is less effective, requiring a combination with other methods.

Spraying Method

The spraying method is suitable for fixed, enclosed environments with single products or equipment with simple internal structures, such as spray pickling processes on sheet production lines. Its advantages include fast, continuous operation, simple operation, minimal impact on workers, and high solution utilization, as the pipeline can be re-pickled during the transfer process.

Considerations of Passivation

Pretreatment for Acid Pickling and Passivation: If grease or other contaminants are present on the stainless steel surface, they can affect the quality of pickling and passivation. Generally, alkaline detergents or cleaning solutions should be used to clean the inner walls of the tank first.

Control of Chloride Ion Concentration in Pickling Solution/Paste and Cleaning Water: Excessive chloride ions can damage the stainless steel passivation film. Some pickling solutions or pastes use chloride-containing corrosive media like hydrochloric acid or perchloric acid as primary or auxiliary agents to remove surface oxide layers, which is detrimental to corrosion prevention. Standards, such as CB/T3595-94 for stainless steel pickling and passivation paste, require chloride ion content to be controlled between 25 ppm and 100 ppm. Cleaning water should also have chloride ion levels below 25 ppm, which can be achieved by adding sodium nitrate as a chloride ion corrosion inhibitor to tap water during construction.

Waste Liquid Neutralization and Environmental Discharge: Acid pickling and passivation waste liquid must meet national environmental discharge standards. For example, fluoride-containing waste can be treated with lime milk or calcium chloride, while chromium-containing waste can be reduced with ferrous sulfate.

Quality Inspection of Passivation

The quality of stainless steel pickling and passivation can be inspected according to standards like CB/T3595-94 for stainless steel pickling and passivation paste or ISO 15730 for surface passivation film inspection after electrolytic polishing, grinding, and pickling passivation. Common inspection methods include:

Visual Inspection: The pickled and passivated stainless steel surface should be uniformly silver-white, smooth, and aesthetically pleasing, with no visible corrosion marks. Weld seams and heat-affected zones should have no oxidation discoloration, and there should be no uneven color spots.

Residual Liquid Inspection: Use phenolphthalein test paper to check the rinsing degree of residual liquid on the stainless steel surface; a neutral pH value indicates a pass.

Blue Dot Test: The blue dot test is based on the principle that incomplete passivation films or iron ion contamination will result in free iron ions, which react with potassium ferrocyanide solution to form a blue precipitate according to the reaction:

K? + Fe2? + [Fe(CN)?]3? → KFe[Fe(CN)?]↓

Test Method: Dissolve 10g of potassium ferrocyanide in 50ml of distilled water, add 30ml of concentrated nitric acid, and dilute to 1000ml with distilled water in a volumetric flask to prepare the blue dot test solution, which has a one-week shelf life. Drop the test solution onto the test paper attached to the stainless steel surface; if blue dots appear on the test paper after 30 seconds, the surface is deemed unqualified.

About SogaWorks

SogaWorks is an all-in-one online platform for custom mechanical parts, connecting over 1,000 top-tier factories to serve startups and major companies. We offer flexible manufacturing solutions for rapid prototyping, small-volume testing, and large-scale production with services like CNC machining, 3D printing, sheet metal fabrication, urethane casting, and injection molding. With our AI-powered quoting engine, SogaWorks can deliver quotes in 5 seconds, match the best capacity, and track every step. This cuts delivery times and boosts product quality.

What is Stainless Steel Passivation?最先出現(xiàn)在SogaWorks。

In this paper, we will delve into the methods of implementation of titanium anodizing, the form of the process, as well as the pattern of change in the color of titanium after anodizing and its application in industrial manufacturing.

What is Titanium Anodizing?

Anodizing is an electrochemical process that uses electrical and chemical action to treat the oxide layer of titanium. The titanium part acts as an anode (positive electrode) and is immersed in an aqueous electrolyte solution, such as trisodium phosphate (TSP) or various salts. When energized, the water molecules undergo hydrolysis and break down into hydrogen and oxygen. The electrical potential forces the oxygen to rise to the surface of the titanium and deposit it on a thin layer of titanium oxide. Oxidized metal parts such as titanium act as anodes in electrical circuits. By forming a tough and tightly packed oxide film, these metal surfaces effectively block the penetration of ions, thus preventing or slowing down further corrosion. Overall, titanium anodizing is the electrolytic oxidation of the surface of a titanium (or titanium alloy) part to make the surface properties appropriate for the part’s intended use.

How to Anodize Titanium

To further understand the process of anodizing titanium parts, here are 4 major steps: cleaning, setting up anodizing equipment and tools, electrolysis, control of voltage, current and temperature, and post process.

Step 1: Cleaning

Cleaning is the first step in the process. Before anodizing titanium, it is important to ensure that the surface is free of any contaminants that may affect the adhesion and uniformity of the oxide layer; oil and grease can hinder the anodizing process and may leave imperfections in the anodized titanium that can affect the uniformity and consistency of the color.

Typically, to effectively clean titanium parts, a combination of detergent and water should be used to remove surface contaminants. This step typically involves soaking the titanium part in a cleaning solution and then rinsing with deionized water to remove any residual cleaner. Ensuring that the titanium surface is completely clean will assist in the proper formation of the oxide film during the anodizing process.

Step 2: Setting Up Anodizing Equipment and Tools

Setting up your anodizing equipment is a critical step in ensuring the success of your titanium anodizing process. You will need specific tools and materials, including a power supply that provides the necessary voltage, an anodizing tank with electrolyte, and a cathode, usually made of aluminum foil or stainless steel. The titanium sheet that serves as the anode is connected to the power source, while the cathode is placed in the electrolyte tank.

During setup, it is important to wear rubber gloves to ensure safe operation of the equipment and to avoid contamination. The electrolyte usually consists of sulfuric acid and must be mixed to the correct concentration to facilitate the anodizing process. Precise control of voltage and current is required to form the desired oxide layer on the titanium surface. The anodizing equipment should be checked for proper function to ensure consistent results. Once everything is set up, the electrolysis process can proceed, which is the heart of titanium anodizing.

Step 3: Electrolysis Process

The electrolysis process is an anodic oxidation conversion process that gives titanium parts enhanced surface properties. In this stage, the titanium part is immersed in an electrolyte bath and a direct current is applied through a power supply. The current causes the titanium surface to oxidize, forming an oxide film. The thickness and properties of the oxide film can be controlled by adjusting the voltage and residence time of the titanium in the electrolyte bath.

Step 4: Control of Voltage, Current and Temperature

During the anodizing process, control of voltage, current and temperature is critical to achieving the desired oxide thickness and surface properties. The supply voltage is usually adjusted for the desired oxide film thickness and color, and the current density should be carefully regulated. Typical current densities range from 15-30 amps/sq. ft. to ensure a uniform oxide layer on the titanium surface. Temperature control is also critical; the electrolyte temperature should be maintained between 60 and 75 degrees Fahrenheit to optimize the anodizing reaction and prevent overheating.

Step 5: Post-treatment

Post-treatment is the final step in the titanium anodizing and is critical to sealing and protecting the newly formed oxide layer. Once the anodizing is complete, the titanium part needs to be thoroughly rinsed to remove all electrolyte solutions to prevent any adverse reactions or corrosion. Next is the sealing process, where the anodized titanium part is immersed in a hot deionized water or nickel acetate solution to seal the pores of the oxide layer.

Color Effects of Anodized Titanium

Anodized titanium oxide takes on a range of vibrant colors that are produced by varying the thickness of the titanium oxide layer on its surface. Typically, achievable colors include bronze, purple, blue, light blue, gold, rose, magenta, cyan and green. However, certain colors (e.g., red) cannot be produced by anodizing due to the physical limitations of the interference effect of the oxide layer. Color is directly dependent on the voltage applied during the anodizing process, with the voltage required for different colors ranging from roughly 0 to 100 volts.

A simplified titanium anodizing color chart by voltage is shown below:

It is important to note that not all colors can be achieved with the titanium anodizing process. Due to the physics of the optical interference phenomenon, red cannot be achieved by conventional anodizing. Currently, the closest colors to red are magenta, rose (reddish-purple) or violet.

Advantages of Titanium Anodizing

1. Enhanced corrosion resistance, proper titanium anodizing can improve the corrosion resistance of titanium and prevent wear and tear

2. aesthetic versatility, through the light interference effect without the need for dyes to obtain bright permanent colors, the color will not fade.

3. Cost-effective and eco-friendly, the process is relatively inexpensive compared to other coatings and avoids the use of harmful chemicals

4. Reduces material friction and wear, anodized surfaces have a higher hardness and reduce material transfer during the friction of mechanical parts

Disadvantages of Titanium Anodizing

1. The precise control of process parameters is difficult, titanium degradation oxidation is extremely sensitive to parameters such as voltage, current, temperature and electrolyte composition, so it is necessary to constantly monitor the fluoride concentration and immersion time, in addition to this any change in the parameters such as tank chemistry, solution temperature, ramp time and other factors may produce oxides of slightly different thicknesses. Precise control of these parameters is challenging in practice.

2. Material limitations and shape complexity increase process difficulty, different grades of titanium alloys react differently to anodizing, not all titanium alloys can be effectively anodized, thus limiting design flexibility

3. Limitations in oxide film performance, while titanium anodic oxides provide some protection, they are limited in thickness and may not provide sufficient protection for high wear applications, and titanium anodizing in oxidant-free environments (e.g., methanol) may not completely prevent corrosion and may even lead to stress corrosion cracking in high titanium alloys.

Titanium Anodizing Applications

Titanium and its alloys have become core materials in the aerospace field due to their light weight, high strength-to-weight ratio and high temperature resistance. However, its susceptibility to corrosion, high oxygen reactivity and surface adsorption problems have restricted wider application. Anodizing can effectively improve the wear resistance, corrosion resistance and optical stability of titanium materials, giving them a unique advantage in precision areas such as space equipment.

Titanium alloys strengthened by anodizing excel in extreme environments and have been expanded into demanding applications such as medical implants, chemical equipment, food processing systems and marine engineering. The technology also enables precise coloration of the material’s surface, which is used in a wide range of applications such as tool size marking, jewelry design, and the surface treatment of high-end consumer products such as bicycles and golf clubs, combining both functionality and aesthetics. The details are as follows.

• Aerospace: For corrosion-resistant parts such as fasteners and structural components, weight reduction and durability are critical.
• Medical: Implants (e.g., dental screws, joint prostheses) benefit from biocompatibility and osseointegration properties.
• Mechanical parts: Valves, pumps and mechanical parts utilize reduced friction and wear resistance.
• Decorative: Jewelry, watches and architectural elements utilize vibrant, fade-resistant colors.
• Electronics: Electrically passive surfaces are ideally suited for insulating components in sensitive equipment.

Conclusion

Titanium Anode Oxygen transforms titanium from a cold industrial material into a work of art through controlled voltages and processes. Whether it’s creating sparkling jewelry or enhancing the performance of aerospace components, the possibilities are endless. Try titanium anodizing today and find the perfect balance between function and aesthetics in your designs!

About SogaWorks

SogaWorks is an all-in-one online platform for custom mechanical parts, connecting over 1,000 top-tier factories to serve startups and major companies. We offer flexible manufacturing solutions for rapid prototyping, small-volume testing, and large-scale production with services like CNC machining, 3D printing, sheet metal fabrication, urethane casting, and injection molding. With our AI-powered quoting engine, SogaWorks can deliver quotes in 5 seconds, match the best capacity, and track every step. This cuts delivery times and boosts product quality.

Titanium Anodizing: Process Analysis and Color Effects最先出現(xiàn)在SogaWorks。

What is Surface Finish?

Surface finish is composed of three distinct elements – roughness, lay, and waviness  However, it is not uncommon in machine shops for the term surface finish to be used to describe only surface roughness.  Roughness is the most commonly specified aspect of surface finish.

Lay

Lay is the term used to describe the dominant pattern on a surface and the orientation of that pattern.  Lay is generally produced by the manufacturing process and can be parallel, perpendicular, circular, crosshatched, radial, multi-directional, or isotropic (non-directional). 

Lay refers to the primary pattern on a surface and the orientation of this pattern. It is usually a by-product of the manufacturing process. The different types of lay can be parallel, perpendicular, circular, crosshatched, radial, multi-directional, or isotropic (without any preference direction). 

Waviness

Waviness refers to those surface finish variations that are most broad in spacing. In most generalizing ways, periodic irregularities on the surface are larger than the sampling length used for the measurement of roughness. Still, they are less small, shorter and more regulated than to not be flatness flaws. It is common for surface waviness to occur due to warping in the heating and cooling, or due to machining errors said errors being a consequence of chatter or deflection. 

Evaluation length is used to measure waviness and a waviness profile is generated in this length. The waviness profile does not include any irregularities in the surface due to roughness, flatness, or form variations. The distance between the peaks of the waves is called waviness spacing (Wsm), while the wave height is established by parameters like average waviness (Wa) or total waviness (Wt). Waviness specifications are less common than roughness specifications, but for bearing races or sealing surfaces they are very important. 

Surface Roughness

Surface roughness can be seen as the closely spaced peaks and valleys on a surface, and it is the result of the material condition and production process used.

Criteria for Evaluating Surface Roughness

Sampling Length

The sampling length is a specified reference length used to evaluate surface roughness. It should be chosen based on the actual formation and texture characteristics of the surface. The selected length must accurately represent the roughness features of the surface. When measuring, the sampling length should follow the overall contour direction of the surface. The purpose of defining and selecting a sampling length is to minimize the influence of waviness and form errors on roughness measurement results.

Evaluation Length

The evaluation length is the total length used for assessing surface roughness. It consists of one or more sampling lengths. Since surface roughness can vary across different areas of a part, a single sampling length may not fully represent its roughness characteristics. Several sampling lengths are taken to obtain a more accurate assessment, Typically, the evaluation length includes 5 sampling lengths.

Reference Line

The reference line is the baseline used to determine surface roughness parameters. There are two types:

• Least-Squares Mean Line: Geometric contour line that minimizes the sum of squared deviations of all points within the sampling length. It provides an ideal mathematical representation of the surface profile.
• Arithmetic Mean Line: This line ensures that the areas of the profile above and below it are equal within the sampling length.

The least-squares mean line is the ideal reference line, but it is difficult to apply in practice. Therefore, the arithmetic mean line is commonly used instead. A straight line with a similar position is often used as an approximation during measurement.

Surface Roughness Terminology

Ra – The numerical average of all the peaks and valleys across the evaluation length. It’s also called the Center Line Average (CLA).

Rz – The average of consecutive highest peaks and lowest valleys. The vertical distance between the highest peak and lowest valley, the distance between the second-highest peak and the second-lowest valley, etc. This is usually done for the five biggest deviations, and then an average is calculated.  It helps eliminate errors since Ra is relatively insensitive to some extremes.

Rmax – The vertical distance between the highest peak and the lowest valley, calculated within the sampling length.

Rp – The calculated distance between the profile’s tallest peak and the mean line within the evaluation length.

Rv – The calculated distance between the profile’s lowest valley and the mean line within the evaluation length.

Surface Roughness Conversion Table

The table below represents the conversion between industry-standard units for surface roughness measuring purposes. Awareness about the conversion of one alternative industry-standard unit—for example, surface roughness Ra in metric and imperial—to ISO might well be helpful on how you want your surface finish to be. 

How to Measure Surface Roughness

There are several methods to measure surface roughness, generally, it can be divided into 4 types: contact measurement, non-contact measurement, comparison with known samples, and in-process methods.

Contact Stylus Profilometer

Contact measurement is the most commonly used method. This diamond stylus moves up and down as it encounters peaks and valleys, the displacement is converted into digital values and displayed on the profilometer screen. This method often measures up to 20mm. Profilometers should not applied for soft or easily deformable surfaces, as the contact may alter the surface texture.

Non-contact methods

The non-contact measurement uses optical or light to measure the surface roughness with direct contact, such as laser scanning confocal microscopy and laser triangulation. A beam is projected on the surface to measure diffraction and reflected signals. these methods are ideal for soft material, and complex geometries for their non-contact to the surface. However, the accuracy is easily affected by the reflectivity and color of the surface. 

Comparison methods

Comparison methods use surface roughness samples generated by specific processes or equipment. manufacturers can evaluate roughness parameters by comparing the surface against the sample with tactile and visual senses.

In-process methods

in-process methods such as inductance, which measures surface roughness using magnetic materials and electromagnetic energy. Then, the parametric value measured can help find out comparative roughness parameters. 

How to Choose the Suitable Surface Roughness?

In some applications, surface roughness may not matter much. However, it holds significant importance in several other scenarios. In critical uses, surface roughness can have an impact on the functionality, performance, durability, and appearance of parts. It also affects the machining time and cost.

The requirements for the surface roughness level in CNC machining vary depending on different applications. There is no such thing as an inherently good or bad surface roughness level; instead, it all boils down to whether it meets the specific requirements. Thus, determining the appropriate CNC machining surface roughness for your part is of great significance. The following factors should be taken into account during the selection process.

Functionality and Purpose

When choosing the right CNC machining surface roughness, the intended use of your part is the most important consideration. Surface roughness can affect the characteristics of your part and how it interacts with other parts and the working environment. It can influence the friction coefficient, noise levels, wear – resistance, absorption capacity, optical properties, load-bearing capacity, durability, electrical conductivity, lubrication, and many other functions and properties. The table below details the various functions of CNC machined parts, how surface roughness impacts these functions, and the corresponding recommended surface roughness levels.

The table below shows the common roughness for different manufacturing processes.

Cost and Production Time

Achieving a smoother surface roughness in CNC machining demands more machining work. To obtain low roughness values, slower machine speeds, finer feeds, and shallower cuts are necessary. For Ra levels of 0.4 and below, additional polishing might be required. The precise manufacturing process and these extra steps take more time and effort, which in turn drives up the production cost.

About SogaWorks

SogaWorks is an all-in-one online platform for custom mechanical parts, connecting over 1,000 top-tier factories to serve startups and major companies. We offer flexible manufacturing solutions for rapid prototyping, small-volume testing, and large-scale production with services like CNC machining, 3D printing, sheet metal fabrication, urethane casting, and injection molding. With our AI-powered quoting engine, SogaWorks can deliver quotes in 5 seconds, match the best capacity, and track every step. This cuts delivery times and boosts product quality.

Surface Roughness: Ra Standard, Measure Methods最先出現(xiàn)在SogaWorks。

Overview of Sand Blasting

Sand blasting uses compressed air to blast tiny particles at high speeds onto a part’s surface. It is used for cleaning, roughening, removing rust, or stripping paint from the surface of the part. The force of the abrasives changes the physical properties. Sandblasting is very important in many fields, and it serves as a controlled surface finish through mechanical action.

The sand blasting process begins in the 1870s. General Benjamin Chew Tilghman noticed the capability of sand to abrade glass that was used for windows in the desert, and he then obtained a patent. In 1904, An improvement was introduced by Thomas Wesley Pangborn, who added compressed air to the process. This change made the process adaptable and efficient and made it widespread use in various industries.

Steps of Sand Blasting

1. Preparation: Make sure to choose the right sandblasting equipment and abrasives, according to the part material, shape, and size. Ensure that all equipment is in working condition, including compressor pressure and the gun nozzle. A safe environment must be ensured such as wearing safety glasses, masks, and protective clothing.
2. Fixing the workpiece: Ensure the workpiece is secured on the workbench to avoid movement during blasting. This keeps the process even and accurate. Special fixtures are needed to keep large or oddly shaped pieces in place.
3. Setting the equipment: Adjust the settings per the workpiece and goals. This includes air pressure adjustments, distance setting between the gun and the workpiece, the angle of the gun, and the abrasive flow rate. For thin pieces, set a lower pressure to avoid damage. and increase the abrasive flow rate for rough surface.
4. Starting blasting: Once everything is ready, the workpiece will be held in the gun and moved with a pre-defined path and speed. Keep the movement smooth to avoid overblasting or underblasting.
5. Quality Check: After blasting, inspect the workpiece for cleanliness and roughness. If any areas are not fully treated, do some more blasting on those areas.
6. Cleaning Up: Once everything is complete, clean up the area, collect any unused abrasives, and store the equipment.

Sandblasting Equipment

According to the abrasive supply method, sandblasting equipment can be divided into 3 types:

Suction Sandblaster

The suction-feed sandblaster operates using compressed air. Because of the high-speed airflow in the spray gun, there is a lower pressure in the gun that causes abrasives to be sucked in through a pipe. The abrasives are subjected to a pressurized air beam and propelled toward the surface needing to be treated.

Pressure Sandblaster

The pressure-feed sandblaster also operates using compressed air. In this system, compressed air pressurizes a tank where abrasives are mixed. The abrasives are pushed into the conveying pipe through a valve, then accelerated by the air and sprayed onto the surface. abrasives mixed with air in a tank are pressurized with compressed air pushed through a conveying pipe by a valve and blasted on the surface.

Wet Sandblaster

The wet sandblaster uses a grinding fluid pump to supply a mixture of abrasives and water into the spray gun. Compressed air then accelerates the fluid as it enters the gun and sprays it onto the surface. This method combines abrasives with water to help clean and treat the surface.

A wet sandblaster uses a pump to carry a mixture of water-based abrasives into the blast gun. The air compresses the fluid into the gun, where it is thereafter projected onto a surface requiring treatment.

Sand Blasting Media

Aluminum Oxide

The most common abrasive for sand blasting. Aluminum oxide is sharp, durable, and can be reused many times. It comes in different hardness grades and particle sizes, making it suitable for a wide range of projects.

Glass Beads

Glass beads are safe, non-toxic, and free of heavy metals and silica. Their spherical shape helps polish to leave a bright and smooth finish. They can be reused multiple times.

Plastic blasting Media

Plastic media works well for aggressive stripping and will get you consistent results. it can strip paint from metals, plastics, and composites.

Silicon Carbide

Silicon carbide is the hardest abrasive and cuts quickly. It begins with small pieces and breaks while blasting. This media can be reused and is often used for etching glass and stone or for removing heavy rust.

Garnet

This abrasive is based on the complex silicate mineral garnet, which has high cutting force， uniform grain size and lower dust pollution.

Steel Shot

Steel shot consists of small steel balls used to clean and polish metallic surfaces. It strips off some material, bearing a shiny and smooth surface.

Steel Grit

Steel grit is used for aggressive blasting; it works quickly and can take off a variety of contamination. It is effective for etching into metals as long as the surface can withstand it.

Organic Compounds

Organic abrasives like corn cob and walnut shells are green. Corncob is used for delicate blasting work on wood, while walnut shells offer a more abrasive stripping action.

Sand Blasting Media Comparison Table

Cleanliness

Cleanliness measures how well impurities are removed from a workpiece after sandblasting. There are two main international standards for cleanliness: the U.S. “SSPC-” standard from 1985, and the Swedish “Sa-” standard from 1976. The Sa- standard has four grades: Sa1, Sa2, Sa2.5, and Sa3, it is commonly used worldwide.

Sa1 Grade – This is the lowest level, like the U.S. SSPC-SP7 grade. It involves simple manual brushing and sandpaper grinding. The coating protection is only slightly better than no treatment. For Sa1, the surface should be free of visible oil, grease, rust, and paint, but minor contamination may remain.

Sa2 Grade – Equals to the U.S. SSPC-SP6 grade. This level uses sandblasting, the basic cleaning method. The workpiece surface should be free of visible grease, dirt, rust, and paint, but defects may cover up to 33% of the surface. Slight rust and paint in dents are acceptable.

Sa2.5 Grade – This is a used standard in the industry, known as near-white cleaning. It’s often used as an acceptance standard. The surface should have no more than 5% defects, such as small shadows or slight discoloration, rust, or paint defects.

Sa3 Grade – The highest level, equal to the U.S. SSPC-SP5 grade, also called white cleaning. The surface must be completely clean, with no defects, rust, or paint allowed. There can be no shadows or discoloration at all.

Sand Blasting Roughness

The sand blasting grains impact and bounce outward. This impact creates indentations on the surface of a few thousandths of an inch, which is called the basic pattern. The rebound will make some surfaces protrude a few thousandths of an inch outward. The lower parts are called “valleys” and the higher parts are called “peaks”. Each sand grain impacting the surface will create a “valley” and a “peak”, which is the reason for the formation of roughness. It is expressed in MILL (mil), and one mil is 1/1000 second.

Why is Sand Blasting Necessary?

Sand blasting uses high-speed sand flow to process the part surface so that the workpiece surface gets a certain degree of cleanliness and roughness, the process improves the mechanical properties and aesthetic appearance of the workpiece.

Pre-treatment of Coatings or Plating Layers

Sand blasting removes impurities like dirt, grease, and oxides from surfaces. It leaves a uniform, rough texture that improves the bond between parts and their coatings or electroplating. Different abrasives create varying levels of roughness to suit different needs.

Cleaning and Polishing of Rough Surfaces

Sand blasting cleans dirt such as oil and rust from castings, forgings, and heat-treated parts. It also polishes the surfaces, making them smoother and more visually appealing. The process reveals a consistent metallic color, enhancing the workpiece’s appearance.

Deburring and Surface Aesthetics

Sandblasting removes small burrs from workpieces, making the surfaces flat and safe. It also creates rounded edges where surfaces meet, improving the workpiece’s overall look.

Improving Mechanical Properties

Sand blasting creates a uniform, fine texture on parts, allowing lubricating oil to be stored on the surface. This improves lubrication, reduces noise, and extends the lifespan of machinery.

Stress Relief

Sandblasting reduces stress on a workpiece’s surface by hitting it with abrasive pellets. This strengthens the surface and is commonly used for parts like springs, tools, and aircraft blades.

Sand Blasting Explained: Process, Media and Functions最先出現(xiàn)在SogaWorks。

What is Alodine Coating?

Alodine coating involves applying a chemical solution containing chromates on the surface of aluminum alloys. This surface finishing process forms a thin, protective conversion coating that adheres to the surface of the metal part to improve its corrosion resistance and prepare it for further finishing such as painting or anodizing. Compared to anodizing, Alodine coating is faster and does not require electrical current, which makes it a more affordable and efficient choice for many price-sensitive clients.

Solutions for Alodine Coating

The type of Alodine solution used depends on the material type, primer, and specific color requirements. Common solutions include:

• Alodine 600: Produces a yellow coating on aluminum surfaces.
• Alodine 1200, 1200S and 1201: Produces a light gold to brownish-yellow finish.
• Alodine 1000 and 1500: Keeps the aluminum surface in its natural metallic color.

The typical formulations for these solutions are detailed in the table below:

Types of Alodine Coating

Different types of Alodine coatings are available, each tailored to specific requirements. The most common classifications are based on the MIL-DTL-5541 standard, which specifies two primary types:

Type 1 (Hexavalent Chromium Coatings): These coatings contain hexavalent chromium and are highly effective in providing corrosion resistance. However, due to environmental and health concerns, their use has been increasingly regulated.

Type 2 (Trivalent Chromium Coatings): As an alternative to Type 1, Type 2 coatings use trivalent chromium, which offers similar performance with reduced environmental impact. These coatings are often transparent and have become the preferred choice in many industries.

Alodine Processes

The implementation of Alodine coating can be carried out through three primary methods: immersion, spraying, and brushing. Brushing is the most commonly used approach in aircraft structure repairs. The specific steps for the Alodine process are as follows:

1. Surface Cleaning

Before applying the solution, the aluminum surface must be thoroughly cleaned to ensure optimal coating adhesion.

For areas with oil residues (such as aviation hydraulic oils), use a clean cloth or sponge soaked in solvents like MEK, acetone, or MIBK to wipe the surface clean. If no oils are present, deionized water can be used to remove impurities. For specific applications like shot-peened surfaces, use a Scotch-Brite pad soaked in deionized water to clean the surface as per BAC 5748 standards. This involves multiple cleaning passes, each using a new pad, followed by rinsing with deionized water and drying with a clean cloth.

After cleaning, the surface should be bright and free of contaminants. Allow at least 15 minutes for the surface to dry completely before proceeding.

2. Applying Solution

In cases where the work area is near sensitive components like composite honeycomb cores, wires, or gaps, ensure proper masking to prevent accidental exposure to the Alodine solution.

Alodine 600/1200 Series: Use pneumatic spray guns or nylon brushes to coat the work area with the Alodine solution evenly. Keep the surface wet for 2–3 minutes. A golden or yellow-brown color will appear, indicating the formation of the protective layer. Wipe away excess solution with a clean cloth or sponge. If uneven coloration or residue is observed, lightly sand the area with 600-grit sandpaper, rinse with deionized water, and reapply the solution.

Alodine 1000 Series: Similar to the 600/1200 series, apply the solution uniformly and keep the surface wet for 3–5 minutes. Avoid direct sunlight during application. Any issues such as solution pooling or powdery residue require the same remediation steps: light sanding, rinsing, and reapplication.

3. Cleaning and Drying

Clean the treated surface with a water-soaked cloth or sponge to remove excess chemicals. Handle the soft and easily damaged coating with care. Use a clean, dry cloth to wipe the surface and allow it to dry at temperatures up to 54°C (130°F). Alternatively, dry the surface at 44–54°C (110–130°F) for 20–35 minutes to enhance corrosion resistance. Once dried, apply the primer paint promptly, ideally within 16 hours, to maximize coating protection.

Benefits of Alodine Coating

Alodine coating offers several advantages, making it a popular choice for aluminum surface finishing:

Thin and porous oxide layer: The Alodine conversion coating is typically thin, measuring around 0.5–4 μm. Its soft and porous nature provides excellent paint and coating adhesion without altering the mechanical properties or dimensions of the workpiece. This makes it an ideal primer layer for further surface treatments.

Cost-effectiveness process: The Alodine process is quick, does not require electrical power, and involves simple equipment. These factors contribute to its low production costs, while still delivering a strong, corrosion-resistant finish.

Conductive coating: Unlike some other surface treatments, Alodine produces a conductive coating. This property helps stabilize contact resistance and ensures effective electrical conductivity, crucial for applications in the electronics and aerospace industries.

Low-temperature requirement: Most Alodine treatment steps are conducted at room temperature, except for the alkaline cleaning stage, which typically operates at around 60°C. This reduces energy consumption and minimizes environmental pollution in the production environment.

Durable solution: Alodine solutions are stable, have a long usage life, and are easy to maintain. These features make them suitable for large-scale, continuous production with minimal disruptions.

Improved corrosion resistance: The Alodine coating provides exceptional protection against corrosion, significantly extending the lifespan of aluminum components even in harsh environments.

Enhanced fatigue performance: Research indicates that Alodine can help predict and improve the fatigue life of aluminum alloys under varying stress conditions. By quantifying corrosion pits as equivalent elliptical surface cracks, the treatment aids in a more accurate reflection of the material’s real-world performance.

Applications of Alodine Coating

Alodine coating is widely used across various industries, including:

• Aerospace: Protecting aluminum airframe components from corrosion.
• Automotive: Enhancing the durability of aluminum parts exposed to harsh environments.
• Electronics: Improving the performance and longevity of enclosures and heat sinks.
• Marine: Providing corrosion resistance for aluminum parts used in coastal or underwater settings.

Alodine vs Anodize

Alodine provides corrosion resistance and enhances the adhesion of the coating. It creates a thin, soft layer that typically ranges from 0.5 to 4 μm in thickness. This process is energy-efficient, requiring less power to complete, and it operates at room temperature. However, Alodine offers limited color options, typically in yellow, brown-yellow, or natural tones, which can restrict its aesthetic appeal.

On the other hand, anodizing is a more complex electrochemical process that produces a thicker, harder coating, typically between 5 and 25 μm, the thickness depends on which type of anodizing is applied. This coating is more durable than alodine, which offers higher surface hardness and better resistance to wear and scratching. Anodizing is a non-conductive process, which can be advantageous in parts that require electrical insulation. However, it needs more energy due to the electrochemical process and operates at high temperatures. One of anodizing’s greatest strengths is its wide color selection, ranging from clear to a variety of vibrant shades, which provides more versatility in aesthetics.

Conclusion

Alodine surface finishing is a versatile and effective method for enhancing the properties of aluminum and its alloys. By providing superior corrosion resistance, improved paint adhesion, and compliance with industry standards, it plays a vital role in the manufacturing of durable and high-performance components. Understanding the types, benefits, and applications of Alodine coating can help manufacturers make informed decisions about their surface finishing needs.

Alodine Coating 101: A Comprehensive Guide最先出現(xiàn)在SogaWorks。

Overview of Chrome and Aluminum

Chrome is a silvery-white metal with strong passivation properties. It quickly forms a protective oxide layer in the atmosphere, which helps it maintain its shine over long periods. Chromium is highly stable in corrosive media such as alkalis, nitric acid, sulfides, carbonates, and organic acids. Chromium has unique properties such as high hardness (800 HV), excellent corrosion resistance, and good heat resistance, which makes it widely used as a protective and decorative coating.

The advantages of aluminum and its alloy include high strength, low density, lightweight, and ease of processing. They can be made into parts that require a high strength-to-weight ratio, as well as complex casted components that are difficult to machine. However, aluminum and its alloys have some shortages such as intergranular corrosion, low surface hardness, and poor wear resistance. To overcome these weaknesses and extend the lifespan of aluminum parts, electroplating can be used to deposit a chrome coating on the surface.

Process of Chrome Plate Aluminum

Can you chrome plate aluminum? The answer is, of course, yes. It is well recognized that electroplating of aluminum is tricky, and the root cause of this problem is the highly active chemical behavior of this metal. Because aluminum has a very negative electrochemical potential (-1.67V), a strong affinity for oxygen, and a tendency to oxidize easily, working with this metal can be tricky. The higher coefficient of expansion of aluminum, compared to most metals, also contributes to internal stress in the plating layer. Aluminum is an amphoteric metal means it is unstable in both acid and alkaline environments. Besides, the surface of an aluminum part generally contains residual electrolytes from cracks and micropores, which can negatively affect the adhesion of the plating layer. Therefore, the key to successful electroplating of aluminum remains in solving the problem of adhesion.

The pretreatment of aluminum and its alloys is needed to make a high-quality coat. The conditions which the surface should comply with are as follows:

• A completely clean surface free from oxidation and oil contamination.
• The metal directly contacting the aluminum should have a lattice constant very similar to that of aluminum and a relatively small atomic radius.

Chrome Plate Aluminum Operations

The step-by-step guide for chrome plate aluminum is as below:

1. Degreasing with organic solvents

Commonly used organic solvents include gasoline, carbon tetrachloride, trichloroethylene, etc. Surface oil stains can be removed by soaking, manual brushing or ultrasonic cleaning.

Here, we use gauze and gasoline to wipe the oil stains on the surface of the parts.

2. Degreasing with alkaline washing

Remove the oil stains on the surface of the aluminum parts, dissolve the surface oxide film, expose the matrix crystallization, and make the parts have an ideal surface state before plating.

3. Acid pickling and brightening

The purpose of this operation is to remove the residues from alkali corrosion, as well as other surface contaminants, ensuring that the substrate’s crystalline structure is fully exposed. Depending on the base material, different solution preparation methods should be selected.

4. Zin-Nickel Immersion Film

We have adopted a primary zinc-nickel alloy immersion method. The chemical zinc-nickel alloy process is developed from the zinc salt immersion method, overcoming many of the shortcomings of the chemical zinc salt immersion process. It is more suitable for pre-treating a variety of aluminum and aluminum alloy parts. After chemical zinc-nickel treatment, the resulting alloy displacement layer has a dense, bright crystalline structure, and good adhesion, and eliminates the need for the toxic cyanide copper pre-plating process. Additionally, this method produces less solution waste during treatment, making it easier to clean and more user-friendly in operation.

The solution preparation method is as below:

Using a zinc-nickel alloy solution containing ferric chloride helps to improve adhesion and corrosion resistance. When preparing the solution, ferric chloride and potassium sodium tartrate are dissolved separately first and then mixed to prevent the hydrolysis and precipitation of ferric chloride.

5. HEDP copper plating

The chemical displacement layer obtained through zinc-nickel immersion is very thin. If any electroplating solution penetrates the zinc layer and corrodes the aluminum substrate, it will lead to a poor-quality coating. The electroplated layer itself must also have a certain level of toughness.

To achieve a fine, bright, and dense crystalline structure with good adhesion, parts should be treated by HEDP copper plating. This step helps deposit a copper layer with strong adhesion on the zinc-nickel alloy layer, ensuring a solid bond between the chrome plating and the substrate.

The solution preparation method and conditions are as below:

If the surface quality of the part substrate is high or the requirements for the coating quality are not particularly strict, the HEDP copper plating process can be omitted and bright copper can be plated directly.

6. Bright copper plating

The anode of this process is a phosphor copper plate, and the sulfate copper plating process is used to improve the brightness of the workpiece and shorten the nickel plating time.

7. Nickel plating

Nickel plating solutions must be carefully maintained, ensuring that there are not too many impurities, especially organic contaminants. Otherwise, the plating may develop bubbles or peel off, and it could increase the brittleness of the coating.

The primary and secondary brighteners in the nickel plating bath should be properly balanced to reduce the hardness and tension of the plating. This helps to minimize the internal stress within the coating and improve its ductility.

8. Chrome plating

The chrome plating formula requires appropriate adjustments depending on the pre-plating process used. Additionally, the appearance of the plating can vary significantly due to the different additives used in the process.

After plating, a hydrogen removal treatment is necessary. The baking temperature should be 160°C, and the baking time should be 1 hour. This hydrogen removal process helps to eliminate the internal stress formed between the plating layer and the substrate, improving the adhesion strength between them.

Chrome Plating Performance Test

The chrome plating layer not only offers excellent corrosion resistance and a smooth, glossy appearance, but provides strong adhesion, high hardness, and good wear resistance.

Tests for the adhesion of chrome plating include heating, bending, and impact methods. After testing, no peeling or delamination was observed, indicating good adhesion.

Hardness testing should consider factors such as part size, substrate material, plating thickness, indentation diameter, and applied load. The Vickers microhardness tester is commonly used for measuring the hardness of the plating layer. Depending on the thickness, a load of 5g to 200g is applied to ensure the indentation depth reaches 1/7 to 1/10 of the plating thickness. A Rockwell hardness tester can be used for chrome plating layers thicker than 100 μm.

Wear resistance is typically assessed using thickness reduction, mass loss, volume wear, abrasive media consumption, cutting thickness time, and radioactive isotope methods.

Experiments have shown that chrome plating with a Vickers hardness of 7355 MPa to 7845 MPa exhibits significant wear resistance. The thickness of the chrome plating also has a direct relationship with its wear resistance and affects the service life of the coating.

How to Chrome Plate Aluminum and its Alloys最先出現(xiàn)在SogaWorks。

What is Powder Coating?

Powder coating is a finishing process in which a dry powder is applied to the surface of parts using electrostatic spraying equipment. The powder carries an electrostatic charge, allowing it to be evenly attracted and held onto the part surface. Once the powder has been applied, the powder-coated parts are exposed to high temperatures.

The coating is made of a special resin, pigment, filler, curing agent, and other additives, they are mixed in a certain proportion and then prepared by hot extrusion, crushing, and screening. They are stable in storage at room temperature, and after electrostatic spraying, heating, and solidification, a smooth and bright permanent coating is formed, to achieve the purpose of decoration and corrosion protection.

Advantages of Powder Coating

Increased efficiency. Since the film is formed in a single application, productivity can increase by 30-40% compared to traditional methods.

Energy savings. Powder coating reduces energy consumption by about 30%, making it more energy-efficient than conventional coating techniques.

Reduced Pollution. This process does not involve the emission of harmful organic solvents such as toluene or xylene, which are commonly found in paints, leading to less environmental pollution.

High coating utilization. The powder coating process boasts an excellent material utilization rate of over 95%, and excess powder can be recovered and reused, minimizing waste.

Superior coating performance. The thickness of the coating can reach 50-80μm in a single application. The adhesion, corrosion resistance, and other performance indicators of powder coatings typically outperform those of traditional paint processes.

High yield. Before curing, the coated items can be re-sprayed, ensuring a higher yield and better quality of the final product.

What is Anodizing?

Anodizing is an electrochemical process that produces a protective oxide by immersing metals ( aluminum) in an acid solution. The oxide film has a thickness of 8-120μm, which gives the aluminum parts resistance to corrosion and an aesthetic appeal.

Unless otherwise specified, the anode in anodizing is usually made from aluminum or its alloy, and the cathode is a lead plate. The aluminum and lead plates are immersed in an acid solution containing sulfuric acid, oxalic acid, or chromic acid, where, through electrolysis, the surfaces of the aluminum get an oxide film.

Anodizing can be divided into 3 types: Clear anodizing, anodizing type II and anodizing type III.

Advantages of Anodizing

It improved corrosion resistance. Type II anodizing provides a protective oxide layer on the aluminum surface, it is able to protect aluminum from harsh environments such as moisture, chemicals, and saltwater. This improved corrosion resistance makes anodized aluminum an ideal choice for components exposed to mild or challenging environmental conditions.

Exceptional hardness. The oxide layer formed during Type III anodizing is much harder than that produced by Type II. It can reach a hardness of up to 60-70 HRC (Rockwell Hardness Scale), making it highly resistant to wear, abrasion, and scratching.

Enhanced durability. As the oxide layer is generated by a chemical reaction, unlike paint and coatings, it bonds precisely to the aluminum surface and is not easy to flake off.

Aesthetic appeal. Type II anodizing produces a porous oxide layer, this structure makes it possible to absorb various colors. The anodized aluminum surface can maintain its color over time. These aesthetically pleasing finishes bring designers more flexibility in aesthetics.

Anodizing vs Powder Coating: What are the Differences？

Process. Anodizing is an electrochemical process that uses electric current to form a layer of oxide. On the other hand, powder coating is an electrostatic spraying technology in which the dry powder is adsorbed on the surface by an electrostatic charge and then cured by heating to form a coating. These coatings are organic and consist of resins, pigments, and hardeners.

Substrate. Anodizing is usually used for specific metals such as aluminum and titanium, while powder coating can be applied to a wider range of materials, including metals like stainless steel, aluminum, plastics, wood, glass, etc.

Color and appearance. Color and appearance. Powder coating offers a broad range of color options by mixing pigments and curing agents. Anodizing acheives colored appeal by immersing the aluminum parts into a coloring solution before curing. Typically, powder coating has a wider range of color options than anodizing.

Durability. Anodizing forms a hard oxide film on the metal surface, which is tightly bonded to the substrate. The coating hardness can reach 300 HV (depending on the anodizing type), and the coating is not easy to wear or flake. Powder coating is cured on the surface of the part at high temperature, and is not as hard as the oxide layer. The coating is easily damaged by friction and scratches, and the coating may peel, crack, or wear.

Corrosion resistance. Corrosion resistance is one of the key differences between anodizing and powder coating. The oxide layer formed by anodizing is not only hard but also provides excellent corrosion resistance by effectively isolating the substrate from the external environment. Anodized aluminum parts have excellent corrosion resistance when exposed to marine climates, high-humidity environments, industrial chemicals, etc. Powder coatings also provide some corrosion resistance, but they generally do not perform as well as the anodized when exposed to extreme environments. For example, when exposed to rain or salt spray conditions, the coating may crack and result in corrosion of the metal surface.

Cost. Anodizing generally costs more than powder coating. This is because anodizing requires specialized electrochemical equipment and higher energy consumption, while powder coating equipment is simpler and material costs are lower. For large-volume production, powder coating is usually a more cost-effective option. However, The additional cost of anodizing may be worth it in specific applications, especially where high durability and special protection are required.

Repair and maintenance. Once the anodized coating is damaged, it is difficult to repair. Since the oxide film is closely bonded to the substrate, scratches or damage on the surface cannot be easily repaired and usually require replacement or re-surface treatment. Powder coating, on the other hand, has a strong repair ability, especially when the coating is damaged, it can be restored to its original state by re-spraying.

How to Choose Between Them?

When selecting anodizing or powder coating, there are several critical factors to consider in order to choose the best and most cost-effective method for your application. Here are some key factors to consider:

Cost

Powder coating is generally less expensive than anodizing, especially for large production runs. The overall cost may slightly differ by factors such as part size, and the type of powder used. Anodizing requires specialized equipment and higher electricity consumption during the process, thus it costs more. However, Anodizing can provide enhanced durability and corrosion resistance for certain applications despite of higher cost.

Tips: Evaluate your needs, and choose a process that gives you the right balance between cost and performance for your application.

Color

Powder coating does not have any significant limitations when it comes to offering color variants. Since the colors can be added to the powder coatings by mixing them with a wide range of colorants, they can be colored-matched very precisely. Anodizing has more limited color options. The dyes used in anodizing are absorbed into the porous oxide layer, resulting in less vibrant and more muted colors.

Tips: For applications requiring specific or vibrant colors, powder coating is the better choice. If a metallic color is acceptable, anodizing may be sufficient.

Durability and resistance

Anodizing forms a layer of oxide that is bonded to the base material; hence, it can yield wear and resistance to harsh conditions. Powder coating applies a protective coating layer on the base material, it can also provide some corrosion resistance. But it bonds more loosely and is easier to scratch and flake.

Tips: For applications to be exposed to heavy tears and harsh environmental conditions, anodizing provides much better durability and protection.

Surface preparation

In anodizing, sandblasting is commonly used to clean the surface and remove impurities, ensuring good adhesion. Similarly, anodizing requires thorough cleaning before the process to avoid imperfections. Powder coating has lower requirements on the surface quality of raw materials. Powder coating can cover the extrusion lines on the surface of the profile, conceal some defects on the surface of the aluminum profile, and improve the surface quality of the finished aluminum profile.

Surface quality

Powder coating produces a smooth, shiny finish. This finish is visually to appear highly uniform and gives a sleek look. Anodizing provides a matte or satin finish since the process involves forming a porous oxide layer, which is not as smooth as the coating. The finish is generally more rugged.

Conclusion

Both powder coating and anodizing have their specific advantages, and the choice depends upon which factors are most important for your project. Powder coating has wide color ranges with intense colors, but more limited corrosion resistance and durability. Anodizing, on the other hand, provides hardness and resistance, especially where withstanding heavy wear is a factor. While anodizing is more expensive, it has better corrosion resistance and durability. It is better to consider several factors such as price, color requirements, and durability before you select one.

At Sogaworks, we specialize in delivering high-quality, precision CNC machining services from China and anodizing services tailored to satisfy the needs of our clients. We offer a comprehensive range of surface finishing services, including powder coating and anodizing. With our advanced equipment and expert engineers, we deliver durable, reliable, and cost-effective solutions for customers in various industries.

Finishing Showdown: Anodizing vs Powder Coating最先出現(xiàn)在SogaWorks。

Anodizing is a process in which aluminum is placed in an electrolyte solution as an anode and an aluminum oxide film is formed on its surface by electrolytic reaction. The thickness of the anodized film of aluminum can reach tens to hundreds of microns. It has good mechanical properties and corrosion resistance, wear resistance, and weather resistance.

Principle of Anodizing

A chemical reaction occurs at the cathode:

A chemical reaction occurs at the anode:

The acid chemically dissolves the aluminum and the formed oxide film, and the reaction is as follows:

The formation and dissolution of the oxide film occur simultaneously. Initially, the growth of the film is faster than its dissolution, causing the film thickness to increase. As the thickness grows, its electrical resistance increases, which in turn slows the growth rate of the film until the dissolution rate equals the growth rate, at which point the film thickness stabilizes. The process can also be explained by the voltage-time curve during anodizing.

The anodizing voltage-time curve can be divided into three stages:

Stage 1: Formation of the Non-Porous Layer – In the segment from point ab, the voltage rises sharply from zero to maximum value within a few seconds. This voltage is called the critical voltage, which indicates the formation of a continuous, non-porous thin film on the anodized surface. The thickness of this non-porous layer is proportional to the forming voltage and inversely proportional to the dissolution rate of the oxide film in the electrolyte.

Stage 2: Formation of the Porous Layer – In the segment from point bc, the voltage drops slightly by 10%–15% after reaching its maximum value, which indicates that the non-porous layer begins to dissolve in the electrolyte, forming a porous layer.

Stage 3: Thickening of the Porous Layer – In the segment from point cd, after about 20 seconds of oxidation, the voltage rises gradually and steadily. This indicates that as the non-porous layer continues to dissolve to form the porous layer, a new non-porous layer is also forming. This means the porous layer continues to thicken, with both film formation and dissolution occurring at the base of each film cell. Once the rate of film formation and dissolution reaches dynamic equilibrium, further oxidation will not increase the thickness of the oxide film.

What is Type II anodizing？

Type II anodizing, also known as sulfuric acid anodizing, is a specific class of anodizing process that creates an oxide film with a thickness of 0.00010” and 0.0005” inches on the aluminum surface. The process involves immersing aluminum in a sulphuric acid electrolyte. When a direct current is applied to the electrolyte, oxygen atoms combine with aluminum atoms on the surface of the part to form an oxide film.

Benefits of Type II Anodizing

Type II anodizing provides many benefits, such as improved performance, durability, and visual appeal.

Improved corrosion resistance. Type II anodizing provides a protective oxide layer on the aluminum surface, it can protect aluminum from harsh environments such as moisture, chemicals, and saltwater. This improved corrosion resistance makes anodized aluminum an ideal choice for components exposed to mild or challenging environmental conditions.

Enhanced durability. As the oxide layer is generated by a chemical reaction, unlike paint and coatings, it bonds precisely to the aluminum surface and is not easy to flake off.

Aesthetic appeal. Type II anodizing produces a porous oxide layer, which makes it possible to absorb various colors. The anodized aluminum surface can maintain its color over time. These aesthetically pleasing finishes give designers more flexibility in aesthetics.

What is Type III anodizing？

Type III anodizing, also known as hardcoat anodizing, is another class of anodizing process that is similar to Type II but forms a thicker layer of oxide film. It is done at a lower temperature and higher voltage.

Benefits of Type III Anodizing

Types III anodizing has its advantages for critical components that must work under certain conditions.

Exceptional hardness. The oxide layer formed during Type III anodizing is much harder than Type II. It can reach a hardness of up to 300-500 HV, making it highly resistant to wear, abrasion, and scratching.

Greater thermal shock resistance. Thicker oxide films can effectively buffer thermal expansion and contraction caused by temp. Changes and reduces cracking caused by thermal stress.

Good electrical resistance. Aluminum reacts with the acid in the electrolyte and produces aluminum oxide(Al2O3)during the anodizing process. Aluminum oxide is a hard and electrically resistant material. On the other hand, the aluminum oxide produced by Type III is much thicker and denser than Type II. Thus, the anodized aluminum parts have better electrical resistance.

Difference Between Type II and Type III Anodizing

There are several distinctions between Type II and Type III anodizing, some of the distinctions include:

Process parameters. Both anodization methods involve immersing aluminum as the anode in a sulfuric acid solution. The difference is that Type II uses higher temperatures and lower voltages, while Type III uses lower temperatures and higher voltages and produces a thicker oxide layer.

Oxide thickness. Type II anodizing forms a thinner oxide layer that is corrosion resistant, while Type III anodizing produces a thicker and denser oxide layer that improves hardness, wear resistance, and electrical insulation properties.

Corrosion resistance. Type III anodizing forms a much thicker and denser oxide layer than Type II, providing significantly improved corrosion resistance. The thicker oxide is like a barrier against aggressive chemicals, high humidity, and abrasive elements, which means Type III anodized aluminum has better corrosion resistance.

Hardness. Type III anodizing forms a much harder layer, significantly enhancing the hardness of the aluminum surface. This layer can reach hardness levels of 350-550 HV.

Dimension and tolerance. Type II anodizing typically adds only a thin coating thickness resulting in minimal dimensional change, Type III anodizing adds a thicker coating with greater dimensional change that may require adjustments to the design and tolerances.

Price. Type III anodizing is generally more expensive than Type II because it requires lower temperatures and higher voltages. This results in a thicker oxide layer formation and takes longer.

Below is a table showing the main distinctions between Type II and Type III anodizing.

Conclusion

There are distinct advantages to both Type II and Type III anodizing. Type II anodizing exhibits special suitability in applications requiring adequate corrosion resistance, generally in less severe environments. On the other hand, Type III anodizing is ideal for more demanding situations, offering improved corrosion resistance and increased hardness. The difference between these two classes of anodizing process can be vital in choosing the right treatment for aluminum parts to enhance their performance and extend their lifespan.

At Sogaworks, we specialize in delivering high-quality, precision CNC machining services from China and anodizing services tailored to satisfy the needs of our clients. We offer a comprehensive range of surface finishing services, including Type II and Type III anodizing. With our advanced equipment and expert engineers, we deliver durable, reliable, and cost-effective solutions for customers in various industries.

Anodizing Class Comparison: Type II vs Type III最先出現(xiàn)在SogaWorks。