Finishes that can be used on Aluminum Extrusions

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Finishes that can be used on Aluminum Extrusions

2020-11-09

In the extrusion of machine components and load-bearing structures, surface treatments are very rarely needed, as the surface finish already meets satisfactory levels. The quality of the extruded aluminum is not affected by its surface finish.

For extruded aluminum parts where surface finishes are however required, the following is used:

Mechanical Surface Treatments
Anodizing
Painting
Powder Coating
Screen Printing
Function Specific Surfaces
Profile Designs

Mechanical Surface Treatments
Techniques used for finishing aluminium surface using mechanical surface treatments includes:

Polishing:
Smoothing the aluminum surface, the gloss and quality of the polish is determined by your specific requests and requirements. After a surface has been polished, it will normally also be anodized . To achieve a high gloss finish, polishing will often be by what is called bright anodizing.

Anodizing
One of the most common surface treatments used for aluminium finishing, anodizing is a process used in order to increase the translucent film of the aluminum oxide or, to increase the thickness of the natural film already present on aluminum extruded surfaces.

Anodizing in aluminum extrusion is used to:

Enhance the surface's resistance to corrosion.
Give aluminum surfaces a coating that is electrically insulating.
Create a 'dirt repellent' surface so that it meets strict hygiene requirements (seen in aluminum extrusions used for food processing).
Creating a function specific surface finish (this is seen in abrasion resistant or slip surfaces in machine parts).
Maintain a surface's 'as-new' appearance.
Create a base 'coat', readying the surface for the application of printing inks or other adhesives.
Provide a decorative aluminium finishing that has durable colors and a gloss.

By anodizing aluminum surfaces, manufacturers are able to achieve an increased resistance to corrosion. This is especially true in cases where the pH is between four and nine. When in contact with strong, alkaline substances, aluminum surface are subject to damage. This is seen on construction sites where extruded aluminum parts can come into contact with gypsum, lime and cement. By covering the visible surfaces with tape, this damage can be prevented.

Painting
Offering a limitless choice of colors and repeatability, powder coating is one of the most wide spread methods of aluminium finishing.

In pre-treatment phases, degreasing, pickling the surface and chemical treatments are preformed.

Chemical Treatments: Being either chrome-free or chrome-based, chemical treatments are able to deliver a good adhesion as well as an effective resistance to corrosion.

Powder Coating
With an almost limitless choice of colors, powder coatings are applied to aluminum surfaces and cured without the use of solvents. In wet coating plants, a high level of the paint used is lost through evaporation, but in a powder coating plant, up to 98% of the powder is use. The powder not used is then recalculated via a reclamation system and reused.

Powder coatings have no risk of blistering or running.

The coating thickness for this process is usually between 60 µm and 140 µm, and in some cases the thickness of the powder coating has to be taken into account during the determining of the tolerances and the profile's dimensions.

Screen Printing
Also known as silk-screen printing, this process involves the original design to be reproduced on a transparent film, which is then placed on a fine-meshed screen. From here, it is exposed to develop photographically, after which the screen is fitted into a frame.
Either through manual or automatic processes, a squeegee is dragged along the screen, transferring the design onto the printing surface.

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