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Prototype Surface Finishing: Anodizing Aluminum

Anodizing aluminum is an effective surface finishing technique being used by the producers to increase the surface properties of aluminum prototypes.

Categorys:Prototype Finishing & Painting

Anodizing aluminum-Feature image


Posted on Aug. 2nd, 2018 | By Mandy, WayKen Project Manager

In order to create a greater number of efficient prototypes, manufacturers are employing a number of rapid prototyping techniques. These techniques are cost-effective as well as time-saving, producing a large number of prototypes in lesser time. But the products produced mostly requires surface finishing to increase their surface properties and to be presentable to the customers.

There are a number of surface finishing techniques used to make the product presentable including powder coating, electroplating, passivation, anodizing etc. Anodizing aluminum is one of the most effective surface finishing technique being employed these days by the manufacturers to increase the functional effect of the model finishing process.

Anodizing

It is an electrochemical process that is used to increase the durability and resistance against corrosion by the formation of an oxide layer on the surface of the metallic product. The oxide layer increases the thickness of the product, protecting it from corrosion and wear. Furthermore, an anodized surface provides better adhesion to paint primers as compared to bare metal. Aluminum is the most suited metal for the anodizing process.

In anodizing aluminum, the aluminum prototype is dipped into the electrolytic solution bath along with the cathode. When the electric current is passed, hydrogen is released from the cathode and aids in the formation of an oxide layer on the surface of aluminum.

Other metals such as titanium, magnesium etc. can be anodized but the oxide layer formed as a result of anodizing aluminum is many times thicker than that of any other metal. Anodizing aluminum has made it one of the most widely used metal in the production of industrial and domestic products.

Although aluminum metal upon exposure to room temperature forms a layer of oxide that will protect it from corrosion and wear, the layer of oxide film formed by anodizing aluminum is 100 times thicker than that formed naturally. Anodizing methods can be generalized from the type of electrolytic solution used. Sulfuric acid and chromic acid are the two electrolytes that are used in the industries these days for anodizing aluminum.

Electrolytic conditions are the important parameters that are used to determine the thickness of a layer formed. These include electrolytic concentration, acidity, solution temperature and the amount of current passed through the solution. When anodizing aluminum, dilute solutions and high voltage is used to produce thicker and harder oxide layer. The thickness of the oxide layer is decided upon the application of metal. Brighter surfaces have a less thick layer of oxide as compared to dull surfaces.

anodized aluminum blue

Processes after Anodizing

Many processes can be done on the anodized surface according to describing as below:

1. Dyeing

After anodizing aluminum, a porous surface is created which can easily accept any color of the dye. Dyeing may be done during or after the anodizing process to reduce the dye bleed out. Color may be induced on the surface by electroplating any metal in the pores of the anodic coating. Dyeing can also be done during the anodizing process by mixing organic acids with the electrolytic solution. The acid type will depend upon the color that is supposed to be induced on the aluminum surface.

2. Sealing

Sealing is the process used to seal the pores created as a result of anodizing aluminum after dyeing. This makes the surface more corrosion resistant and increases the dye retention. This is usually done by dipping the surface in boiling hot deionized water or steam converting the oxides into hydrates causing the pores to close. It can be also be done by cold sealing in which a sealant is impregnated at room temperature. This is done by dipping the product into the sealant bath at room temperature. Cold sealing is more popular because it is an energy-saving process.

Sealing after anodizing aluminum

3. Printing

Printing may be done by the digital printer or sublimation transfer after anodizing aluminum. Any image or graphics can be printed on the surface of the product by incorporation of dyes in the pores before sealing. Graphics can also be made by hand using airbrush or paintbrush. Sealing process is done after the printing of graphics to seal the pores and to increase the dye retention. This prevents any corrosion as the pores are sealed.

Benefits of Anodizing Aluminum

Anodizing aluminum in addition with high surface finish provides many other benefits as described below:

1. Durability

The lifespan of most anodized products is longer as compared to other techniques. Moreover, the anodized products are easily maintained making it one of the most used processes in the industries.

2. Cost

Initial cost of anodizing aluminum is very less. Also given the durability manufacturers prefer anodizing over any other operation because it is a far cheaper option over longer terms. The maintenance cost of the anodized products is also less.

3. Resistance to UV

Processes carried out after anodizing aluminum can offer great resistance to Ultraviolent radiations of the sun providing a surface finish for a longer period of time.

4. Easy to be Maintained

Scars and wear during the fabrication, transportation, installation, dirt cleaning are almost nonexistent on anodized surface. An anodized surface can be brought to an original appearance by cleansing with mild soap and rinsing. Therefore maintenance cost of anodized products is also very less. Low maintenance cost combined with low initial cost makes it a favorable option for the manufacturers.

5. Aesthetics

A number of processes can be carried out during and after the anodizing which can be used to give the product the desired aesthetics. Dyeing of the product before and after the anodizing can give the product any desired color. Moreover, the electrolyte used during anodizing can offer almost any color to be dyed. Printing the graphics with the digital printers or with airbrush/paintbrush can also be done on the anodized surface due to pores generated after anodizing.

6. Health and Safety

Anodizing aluminum offers no harm to human health. An anodized product is also chemically stable and nontoxic. It is heat resistant up to the melting point of aluminum and will not decompose. Since it is a process in which naturally occurring oxides are reinforced upon the surface so it is non-hazardous and does not produce any harmful side products. Therefore compatible with today’s environmental concerns.

Anodizing aluminum-Image 2

Applications

Anodizing aluminum improves its surface finish and properties which are widely used in domestic and industrial applications including

  • Automotive
  • Aviation & Aerospace
  • Buildings & Architecture
  • Electronics
  • Food Manufacturing / Preparation Equipment
  • Home Furnishings
  • General Manufacturing
  • Marine Industry
  • Medical / Dental Equipment
  • Sporting Goods

anodized aluminum radiator

Hence the use of rapid prototyping is not enough given the product is not appealing. Many methods can be employed for surface finishing of the products but anodizing is the best among all in terms of cost, enhancing the properties and aesthetics. So the manufacturers are anodizing aluminum given its vast applications in different industries including the automotive, aerospace industries etc. Anodizing makes aluminum corrosion resistant and gives the required aesthetic to the product which is appealing to the customers.

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