FAQ's

What is the purpose of anodizing?
The purpose of anodizing is to form a layer of aluminum oxide that will protect the aluminum from corrosion. The aluminum oxide layer has a much higher corrosion and abrasion resistance than the aluminum itself.  There are some anodizing processes that produce a porous oxide layer that can be colored with organic dyes or metallic pigments, giving the aluminum a decorative and protective finish.

 

Is anodized aluminum NSF certified?
Yes.  Lorin ClearMatt® products meet NSF/ANSI 51 Standards for surfaces with food contact.  Lorin ColorIn® and Classic Colors meet NSF/ANSI Splash Zone 1 Standards for surfaces other than the direct food zone that is subject to routine splashing or spillage.

 

How do I clean anodized aluminum?
Cleaning anodized aluminum is easy with the right technique. One recommended method is to use an abrasive cleaning sponge with mild dish washing liquid.  Do not use harsh acidic or alkaline cleaners because they may negatively impact the finish.  Use solvents with care as they may stain the finish.  Regardless of the technique, be sure to try a test area first.  For more detailed information, obtain a copy of Care of Aluminum, The Aluminum Association.

 

Can anodized aluminum be cleaned with an alkaline solution, pH of 10 or greater?
Factors such as concentration of the detergent solution, duration of exposure, and temperature will influence the results. If the anodized aluminum is cleaned at room temperature and promptly rinsed with clean water, then there should be no problem. If cleaned at an elevated temperature or with prolonged exposure without rinsing, then the cleaning solution would start to attack the anodic oxide and etch the metal.  Mild soap is generally preferable to acidic or alkaline detergents for routine maintenance cleaning.

 

How often should I clean an anodized aluminum surface?
It helps to maintain the beauty of the surface if it is at least washed with a mild soap and rinsed when surface dirt becomes apparent.  We recommend at least an annual cleaning. 

 

Can I weld anodized aluminum?
Yes.  Anodized aluminum can be welded after anodizing.  Because most welding processes require electrical conductivity, the anodic coating must be ground away where the weld will be applied. The recommended welding techniques include TIG Welding, Laser Welding or the Pulse Technique. The use of 5356 welded rod is also recommended to minimize the color difference of the weld and the sheet, though some discoloration will still occur.  Customers have also had positive results after making slight modifications to the design so that the weld is on a non-visual component of their finished product, or by lightly touching up the weld with a metallic pigmented paint.

 

Can anodizing hide scratches on the surface of the aluminum?
The usual rule of thumb is that if you can feel a scratch by rubbing your fingernail across the surface of the aluminum, you will be able to see the scratch after anodizing.  It is always recommended that the anodizer and customer establish visual quality requirements before the anodizing process takes place.  

 

Can I use my existing tooling to fabricate anodized aluminum?
Yes.  Fabricating pre-anodized aluminum is very similar to other metals with slight adjustments required in air bending with a press brake or the stroke and tooling adjustments in a stamping or blanking operation. 

 

What is the minimum order quantity of a coil anodized aluminum product?
Stocked Anodized Finished Goods Inventory:  The minimum order quantity for stocked anodized finished goods inventory is 1,000 lbs or the smallest coil available.  Non-Stocked Anodized Inventory:  Lorin requires a minimum of two machine lengths for non-stocked anodized inventory.  The net weight will vary dependent upon the gauge of the aluminum specified.  Custom Metal Purchase Order:  The minimum order quantity as specified by our supplier is required.  However, our Inside Sales staff will do their best to provide you with the quantities you require.

 

What are an Architectural Class I and Class II Anodize Coating?
Class I and Class II anodic coatings are designations created by the Aluminum Association for the purpose of codifying the specification of anodized aluminum. The American Architectural Manufacturers Association (AAMA) publication, AAMA 911-92, Voluntary Standards for Anodized Architectural Aluminum, includes the following definitions from The Aluminum Association publication #45, Designation System for Aluminum Finishes: 

Class I.  High performance anodic finish used in exterior applications receiving periodic maintenance such as curtain walls. Minimum coating thickness of 0.700 mils (18 microns). 

Class II.  Commercial anodic coatings used in interior applications or exterior applications receiving regularly-scheduled cleaning and maintenance such as store fronts.  Minimum coating thickness of 0.400 mils (10 microns).

 

Are there different kinds of anodizing?
There are many different types of anodizing.  When we talk about anodizing, we generally are talking about sulfuric acid anodizing that produces a porous oxide layer and the most common anodizing process.  There are other anodizing processes where other electrolytes are used such as chromic acid, phosphoric acid and sulfuric-boric acid.  Using these different electrolytes produces oxide layers with different properties than those produced with sulfuric acid.

 

How do you color anodized aluminum?
There are two different ways that Lorin colors anodized aluminum:

Organic and Inorganic Dyes:  The freshly anodized metal is immersed in a solution that contains dissolved dyes either using an organic or inorganic compound.  The porous anodic coating absorbs the dye compound.  The intensity, saturation and hue of the color is controlled by using various process conditions.  Colors requiring organic dye compounds are not UV stable and should be used for interior applications only.  Colors requiring an inorganic dye compound can be used for exterior applications. 

Electrolytic Coloring (a.k.a. "two-step"):  After anodizing, the metal is immersed in a bath containing an inorganic metal salt compound.  Electrical current is applied which deposits the metal salt compound into the anodic coating using tightly controlled processing conditions.  Electrolytic coloring is UV fade resistant and recommended for exterior applications.

 

What does it mean to chemically brighten the aluminum sheet?
Chemical brightening is a process for increasing the specularity or brightness of aluminum by leveling the microscopic roughness or "peaks and valleys" on the surface of the aluminum.

 

Does anodizing affect the mechanical properties of aluminum?
Mechanical properties of aluminum, such as ultimate and yield strength, along with percent elongation, have been tested after anodizing without exhibiting any significant difference in the strength of the aluminum.

 

What anodize coating thickness should I specify for my product?
In general, thicker coatings are used for products to be used outside or in corrosive environments, and thinner coatings are used for parts to be used in interior applications.  When anodized products are to be used out of doors, anodized film thickness is usually specified at 0.000400" minimum or 0.000700" minimum. Parts used in automotive applications are usually specified at 0.000300".  Parts used in interior applications are usually specified between 0.000100" and 0.000350".  There are some applications where coating thickness of 0.00001" is used. 

 

Does exterior anodized aluminum appear to change color under different light conditions?
Many factors influence the appearance of anodized aluminum architectural components.  Many architects and designers find that to be one of the most attractive features of anodized aluminum: their buildings assume a slightly different character depending upon the weather, the time of day, the season of the year, or the angle of observation.  Differences in appearance will also be influenced by the alloy, anodic film thickness, surface texture of the aluminum, and the finishing process of the anodizer.  Critical to all this is the angle of observation, especially as it relates to the primary source of illumination.  If the product is colored, another level of complexity is added, since the shade and hue must also be controlled.

 

How is the corrosion resistance of anodized aluminum in sea water areas?
Anodized aluminum is very suitable for applications involving exposure to sea water and is routinely used for parts such as sail boat masts and railings. Corrosion resistance is excellent; however, the parts should be kept clean. The buildup of dirty surface deposits can provide sites for corrosion, particularly if there is any associated acidity.

 

I understand that the colors on anodized aluminum may derive from metallic salts or from organic dyes.  How lightfast are these colorants in an indoor application?
Generally speaking, organic dyes are well suited for indoor applications and have enjoyed such use for over 50 years.  Like any dyed fabric or painted surface, it is best to minimize direct sunlight exposure.  The ‘Two-Step’ electrolytic coloring process can provide various bronze tones to a deep black finish [including Lorin’s Antique Copper Series that are impervious to ultraviolet light and can be used for interior applications.  The use of inorganic dye compounds can also produce shades of gold from light champagne to a dark ten-carat gold finish and highly resistant to ultraviolet light.

 

What tests are used to evaluate an anodized finish?
There are many different tests used to evaluate anodized finishes. Some of the most commonly used tests are as follows: 

ASTM B136-84, Standard Method for Measurement of Stain Resistance of Anodic Coatings on Aluminum. 

ASTM B137-95, Standard Test Method for Measurement of Coating Mass Per Unit Area on Anodically Coated Aluminum.

ASTM B680-80, Standard Test Method for Seal Quality of Anodic Coatings on Aluminum by Acid Dissolution. 

ASTM B117-07, Standard Practice for Operating Salt Spray (Fog) Apparatus.

 

What does the term anodize rack marks mean?
In a batch anodizing process, an electrical contact must be made to each part that is going to be anodized.  The more electrical current required, the larger the electrical contact area must be.  At the point of the electrical connection, the passing current causes a burn mark and/or pit in the area of the contact on the part.  Rack marks are NOT part of the coil anodizing process.  

 

What alloys are recommended for anodizing?
Most all aluminum alloys will build an aluminum oxide layer in an anodizing process.  The recommended aluminum alloy depends on many factors such as application, visual requirement, formability, and anodize thickness.  The primary aluminum alloy used in a coil anodizing process requiring visually pleasing appearance [lack of visual imperfections] is a 5005 alloy.

 

Is anodizing environmentally friendly?
Yes.  It is not difficult for anodizers to comply with all federal and state environmental regulations. There are no heavy metals or VOC’s [Volatile Organic Compounds] used in the anodizing process.

 

What anodized aluminum colors are available that are fade resistant?
Anodized aluminum products that have inorganic dyes or metal salts using a two-step electrolytic coloring process qualify as fade resistant.   Colors range from various shades of gold, light to dark bronze tones, copper and deep black. While organic dyes will color shift with UV exposure, the color shift is often gradual and have lasted for over 50 years for interior applications.  

 

What sort of heat exposure will an anodized aluminum finish survive?
The aluminum oxide layer could thermo craze with continuous heat exposure at 300° - 375° Fahrenheit, but will not remove the protective layer.  Aluminum has a melting point of 1,220o Fahrenheit.

 

Can you eliminate anodize crazing?   
All anodized aluminum can experience crazing when subjected to extreme temperatures or fabrication.  You can minimize anodize crazing by increasing the bend radius, maintaining temperatures less than 350oF, and reducing the anodic layer thickness. Crazing does not impact the protective characteristics of the anodic layer. 

 

How does anodized aluminum compare against other metals in terms of corrosion resistance?
Aluminum is naturally corrosion resistant and does not break down or degrade with exposure to water or humidity like other metals.  Lorin’s Antique Copper does not leave weathering stains or patina [corrode] like real copper.  Lorin’s ColorIn® does not chip, flake or peel [leading to corrosion] like painted aluminum.  Lorin’s GoldBrite® does not tarnish [corrode] like brass.  Lorin’s AlumaPlus® does not fingerprint [stain] like stainless steel.

 

How does anodized aluminum compare against other metals in terms of dent resistance?
Based on calculation alone, an anodized aluminum product using 5005 ½ hard temper material has 25% higher dent resistance than stainless steel.

 

How is the visual consistency of an anodized product within the anodizing process?
Because anodizing is a finishing process, Lorin Industries, through our proprietary processes, are able to control the gloss, optics and color values of our anodized product.  In addition to producing material to stringent industry standards, material is reviewed for consistency throughout the production run.  Lorin Industries employs the most current technology in production techniques, test equipment and quality systems to ensure that only the highest quality material is produced and shipped.  Lorin’s process automation, statistical process control (SPC) methodology, traceable documentation and ISO 9001:2000 Certification are a few of the production methods that keep us apart from our competition.  Lorin’s success also comes from knowing and clearly understanding our customers’ requirements, to ensure they receive only the highest quality product, every time.

 

What can be done to fix scuffs and scratches on the anodized surface?
Keep in mind that the oxide layer is three times harder than the aluminum itself and has excellent abrasion resistance.   This surface hardness will protect against scuffs and abrasions.  Minor scratches in a colored anodized material are typically repaired with touch-up paints or permanent markers.  Clear anodized material, if scratched, will build its own oxide layer over time and self heal to hide the scratched finish, unlike other materials.

 

How do anodized aluminum products help me in securing LEED points for my architectural project?
LEED initiatives were designed to create a common standard and promote the use of “healthy” building products.  Buildings get LEED certified, but the products used in those buildings can help in qualifying for points.  Lorin products can help in qualifying for LEED points based on the following criteria:

Energy & AtmosphereLorin ClearMatt® products meet Energy Star Standards for total solar reflectance and thermal emittance, making them an excellent choice for roofing and exterior product applications where the designer is looking to maximize the building efficiencies with no negative impact on the environment through coating outgassing (No VOC’s emitted).

Materials & Resources – Anodized aluminum products typically use high-purity aluminum alloys with little to no recycle content.  Lorin is currently working with our suppliers to develop a high scrap content alloy that can be anodized with visual quality in mind.  We are also developing a high scrap content alloy that shows the imperfections in a controlled and uniform way so the consumer can see that the metal is recycled but not compromise the beauty of the anodized aluminum finish. In the meantime, the anodized aluminum used in a project today is 100% Recyclable tomorrow.

Indoor Environmental Quality - Anodized aluminum products do not outgas or emit toxic fumes like other coated materials. The anodizing process is 100% natural and will not negatively impact air quality.


Can you anodize continuous cast aluminum? 
Yes, although you must consider the quality requirements for deciding on continuous cast or direct cast aluminum.  In the continuous cast process molten aluminum is cast into a continuous strip and rolled to its final gauge.  No additional steps are taken to homogenize or remove impurities.  As a result, the quality of the finish is very poor and inconsistent, making it unsuitable where visual quality is important.