Aluminum Finishes

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Aluminum Finishes Page 1 of 27 1

AluminumFinishes1. Mill Finish

2. Anodized Finish

3. Powder Coated Finish

4. Super Durable Powder Coated Finish

5. Polyvinylidene Flouride (PVDF) Finish

6. Alodine

7. Chromated Finish


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Aluminum Finishes 2

1. Mill Finish

Simply meansthe raw or barefinish of material

as it comes outof the extrusionor millingmachines.


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Aluminum Finishes 3

2. Anodized Finish

Anodizing, or anodising, is an electrolyticpassivation processused to increase the thickness of the natural oxidelayer on thesurface of metal parts.

A - History:

Anodizing was first used on an industrial scale in 1923 to protect Duraluminseaplane parts from corrosion. This early chromic acid process was called

Bengough-Stuart process. In 1927 Gower and OBrien patented the first sulfuric acid anodizing process.

This remain the most common anodizing electrolyte.

Oxalic acid anodizing follows in was patented in Japan in 1923 and laterwidely use in Germany, particularly for architectural applications.

Anodized aluminum extrusion was popular architetural material in the 1960sand 1970s, but has since been displaced by cheaper plastics and

powdercoating.
http://en.wikipedia.org/wiki/Electrolytehttp://en.wikipedia.org/wiki/Passivationhttp://en.wikipedia.org/wiki/Oxidehttp://en.wikipedia.org/wiki/File:Cheap_carabiners.JPGhttp://en.wikipedia.org/wiki/Oxidehttp://en.wikipedia.org/wiki/Passivationhttp://en.wikipedia.org/wiki/Electrolyte


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Aluminum Finishes 4

Anodized Finish History (continued)

In most recent major development, the phosphoric acid anodizing processso far is only used as pretreatments for adhesives or organic paints.Although a wide variety of proprietary and increasingly complexvariation of all these anodizing processes continue to be developed byindustry.


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Aluminum Finishes 5

Anodized Finish (continued)

A - Advantages: Increases corrosion resistance and wear resistance.

Provides better adhesion for paint primers and glues than baremetal.

Prevent galling of threaded components.

Increase surface hardness.

Allow dyeing (coloring). Improved lubrication and adhesion.

It is non- conductive.

B - Disadvantages:

Have a much lower thermal conductivity and coefficient of linearexpansion than aluminium. As a result, the coating will crack (butwill not peel) from thermal stress if exposed to temperaturesabove 80C.
http://en.wikipedia.org/wiki/Corrosionhttp://en.wikipedia.org/wiki/Corrosion


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Aluminum Finishes 6

Anodized Finish (continued)

Anodic films are most commonly applied to protect; Aluminumalloys, Titanium, Zinc, Magnesium, Tantalum and Niobium.

This process is not a useful treatment for iron or carbon steelbecause these metalsiron oxide (also known as rust) flakes off,

costantly exposing the underlaying metal to corrosion.

Anodizing is one of the more environmentally-friendly metalfinishing processes.


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Aluminum Finishes 7

Anodized Colors & Film Thickness

Chromic acid = 0.5m to18m (0.00002 to 0.0007)

Sulfuric acid = 1.8m to25m (0.00007 to 0.001)moderate

= 25m to 150m (0.001 to0.006) hard anodizing

Organic acid = up to 50m

Phosphoric acid = see ASTMD3933

Film thickness range from0.5m to 150m.


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Aluminum Finishes 8

3. Powder Coating Finish

Powder coating is a typeof coating that is applied asa free-flowing, dry powder.The main difference betweena conventional liquid paintand a powder coating is thatthe powder coating does notrequire a solvent to keep thebinder and filler parts in a

liquid suspension form.
http://en.wikipedia.org/wiki/Solventhttp://en.wikipedia.org/wiki/Solvent


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Aluminum Finishes 9

Powder Coating Finish (continued)

Polymer film-forming processes

Upon application by spraying, brushing, or various industrial processes, surfacecoatings undergo what is known as film formation. In most film-formation processes,a liquid coating of relatively low viscosity is applied to a solid substrate and is curedto a solid, high-molecular-weight, polymer-based adherent film possessing theproperties desired by the user. For most common applications, this film has a thicknessranging from 0.t to 500 micrometres (0.0005 to 0.5 millimetre, or 0.00002 to 0.02

inch.).

Coatingsbefore the 1960s were often liquids of low solids content, from whichconsiderable organic solvent was emitted into the atmosphere during film formation.Environmental and economic pressures have forced a reduction of solvent levels infilm-formation processes. As a result, there are now three major types of filmprocesses: Evaporation of solvent or carrier liquid; Cross-linking of low-molecular-weight, low-viscosity polymer precursors; and coalescence of small particles.

For specific coating, the overall film-formation process actually may be a mixture ofthese three.


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Aluminum Finishes 10


The coating is typically applied electrostatically and is then curedunder heat to allow it to flowand form a "skin." The powder may be athermoplastic or a thermosetpolymer. It is usually used to create ahard finish that is tougher than conventional paint. Powder coating ismainly used for coating ofmetals, such as "whiteware", aluminiumextrusions, and automobile and bicycle parts. Newer technologiesallow other materials, such as MDF (medium-density fibreboard), tobe powder coated using different methods.

Normally the powders cure @ 200C (390F) in 10 minutes. Thecuring schedule could vary according to the manufacturersspecifications.
http://en.wikipedia.org/wiki/Thermoplastichttp://en.wikipedia.org/wiki/Thermosethttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Thermoplastichttp://en.wikipedia.org/wiki/Thermosethttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Household_appliancehttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Bicyclehttp://en.wikipedia.org/wiki/Bicyclehttp://en.wikipedia.org/wiki/Household_appliancehttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Bicyclehttp://en.wikipedia.org/wiki/Medium-density_fibreboardhttp://en.wikipedia.org/wiki/Medium-density_fibreboardhttp://en.wikipedia.org/wiki/Medium-density_fibreboardhttp://en.wikipedia.org/wiki/Medium-density_fibreboardhttp://en.wikipedia.org/wiki/Medium-density_fibreboardhttp://en.wikipedia.org/wiki/Medium-density_fibreboardhttp://en.wikipedia.org/wiki/Bicyclehttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Household_appliancehttp://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Thermosethttp://en.wikipedia.org/wiki/Thermoplastic


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Powder Coating Finish - Advantages

Emit Zero or near zero volatile organic compounds (VOC). Can produce much thicker coatings than conventional liquid

coatings without running or sagging.

Overspray can be recycled and thus it is possible to achievenearly 100% use of coating.

Production lines produce less hazardous waste than conventionalliquid coatings.

Capital equipment and operating costs are generally less thanconventional liquid lines.

Items generally have fewer apprearance differences betweenhorizontally and vertically coated surfaces than liquid coated

items. Wide range of specialty effects can easily accomplished compare

to other coating processes..


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Powder Coating Finish - Disadvantages

Not easy to apply smooth thin films. As the film thickness isreduced, the film becomes more and more orange peeled intexture due to the particle size and TG (glass transitiontemperature) of the powder.

For optimum material handling and ease of application, mostpowder coatings have a particle size in the range of 30 to 50

micrometres and a TG > 40C.Powder Slurry process is a specialized operation where powdercoatings is less than 30 micrometers or with a TG < 40C.

Powder coatings have a major advantage in that the overspraycan be recycled. However, if multiplt colors are being sprayed in a

single spray booth, this may limit the ability to recycle theoverspray.


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Powder Coating Finish

Types of Powder Coatings:

Thermosets variety incorporates a cross-linker into theformulation. When the powder is baked, it reacts with otherchemical groups in the powder polymer and increases the molecular

weight and improves the performance properties. Thermoplastic variety does not undergo any additional reactions

during the baking process, but rather only flows out into the finalcoating.

The most common polymers used are polyester, polyester-epoxy

(known as hybrid), straight-epoxy (Fusion bonded epoxy) andacrylics.


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Removing Powder Coating:

Methylene Chloride is generally effective at removing powder coating.

Organic solvents (Acetone, thinnerss, etc.) are completelyineffective.

Most recently MC is being replaced by Benzyl alcohol with greatsuccess.

Can also be removed with abrasive blasting.

98% sulfuric acid commercial grade also removes powder coatingfilm.

Certain low grade powder coats can be removed with steel wool,

though this might be a more labor-intensive process than desired.


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Powder Coating Colors:


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4. Super Durable Powder Coated Finish

Super Durable Powder Coating - Specially formulated tosatisfy the highest requirements of the building industryregarding aesthetic performance, UV and humidity resistance.Outstanding properties regarding gloss retention and resistanceto color change are combined with optimum functionalproperties ensuring the highest levels of protection.

A. Application:

Primary areas of application are aluminum extrusions andcladdings for architectural work. When screen-printing orsealants are in use, we advise separate trials to ensurecompatibility and that the required performance criteria aremet.


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Super Durable Powder Coated Finish(continued)

B. Advantages:

Has an expected lifetime which is 3X as long as todays high qualityarchitectural powder coatings. Backed by a 25 year guarantee.

Cost effective compared to expensive fluorocarbon-based wet paint.

Truly environment friendly because its solvent free and recyclable.

It surpasses Qualicoat Class II industry requirements. Available in a wide range of colors and in three gloss levels; high

gloss, reduced gloss and matt finish.

C. Disadvantages:

Shall be keep in a dry cool area. Max 25C/ relative humidity 60%.


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5. Polyvinylidene Flouride (PVDF) Finish

PVDF is a specialty plastic material in the fluoropolymer family; it isused generally in applications requiring the highest purity, strength,and resistance to solvents, acids, bases and heat and low smokegeneration during a fire event. Compared to other fluoropolymers, ithas an easier melt process because of its relatively low meltingpoint of around 177C.

A. Usage:

A fine powder grade, KYNAR 500 PVDF or HYLAR 5000 PVDF, is alsoused as the principal ingredient of high-end paints for metals. ThesePVDF paints have extremely good gloss and color retention, andthey are in use on many prominent buildings around the world, e.g.the Petronas Towers in Malaysia and Taipei 101 in Taiwan, as well

as on commercial and residential metal roofing.
http://en.wikipedia.org/wiki/Petronas_Towershttp://en.wikipedia.org/wiki/Taipei_101http://en.wikipedia.org/wiki/Taipei_101http://en.wikipedia.org/wiki/Petronas_Towers


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Polyvinylidene Flouride (PVDF) Finish(continued)

B. Advantages:

Resistant to most acids, alkalis, salts, halogens, alcohols andchlorinated hydro-carbons

High mechanical strength,

Operating temperature range -20C to 140C

Displays high excellent flame retardant properties.

C. Disadvantages:

Strong polarized solvents, such as ketones and esters, can causethe material to swell.


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Polyvinylidene Flouride (PVDF) Finish

PVDF Colors


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6. Alodine Finish

Alodine is a coating based onTitanium Metal Oxide (TiO2)electrodeposited from the electricalassisted hydrolysis of metalcomplexes. The TiO2 Coating providessuperior corrosion and wear resistance

for harsh and demanding applicationssuch as marine and high temperatureengine environments.

Alodine is a brand ofChromateconversion coating products used onaluminum alloy and to a lesser extentmagnesium alloy metals, primarily inthe aerospace industry.
http://en.wikipedia.org/wiki/Chromate_conversion_coatinghttp://en.wikipedia.org/wiki/Chromate_conversion_coatinghttp://en.wikipedia.org/wiki/Aluminum_alloyhttp://en.wikipedia.org/wiki/Magnesium_alloyhttp://en.wikipedia.org/wiki/Magnesium_alloyhttp://en.wikipedia.org/wiki/Aluminum_alloyhttp://en.wikipedia.org/wiki/Chromate_conversion_coatinghttp://en.wikipedia.org/wiki/Chromate_conversion_coating


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Alodine Finish (continued)

A. Advantages:

A new electrolytic process provides a 3-12 micron thick layer ofTiO2

Virtually eliminates corrosion Drastically improves wear resistance Enables the use of lower cost materials (e.g., aluminum instead of

stainless steel) Excellent bonding capability when combined with branded

adhesives. Provides superior wear, corrosion, and thermal protection over

aluminum, titanium, and aluminized surfaces Thousands of times harder and more flexible than paint Impervious to fuel and fuel vapor, powertrain lubricants, oil, and

ethylene glycol Withstands temperatures up to 600C (1112F) without corrosion

performance loss


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7. Chromated Finish

Chromate coatings - are soft andgelatinous when first applied butharden and become hydrophobic asthey age. Curing can be acceleratedby heating up to 70C, but highertemperatures will gradually damage

the coating over time. Some chromateconversion processes use briefdegassing treatments at temperaturesof up to 200C. Coating thickness varyfrom a few nanometers to a fewmicrometers thick.
http://en.wikipedia.org/wiki/Hydrophobehttp://en.wikipedia.org/wiki/File:Stampings_steel_zinc_chromate_conversion_coating.JPGhttp://en.wikipedia.org/wiki/Hydrophobe


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Chromated Finish (continued)

A. Chromate Conversion defined:

When aluminum and aluminum alloys are immersed in acontrolled chromic acid bath with special additives, a chemicalconversion reaction occurs at the metals surface. This reactionproduces a complex, non-crystalline, non-porous coatingconsisting of a thin aluminum oxide film with entrapped chromates

and dichromates. The coatings corrosion resistant properties aredue primarily to the chromates, specifically the hexavalentchromium.

A type ofconversion coating applied to passivate aluminium, zinc,cadmium, copper, silver, magnesium, tin and their alloys to slow

corrosion.
http://en.wikipedia.org/wiki/Passivatehttp://en.wikipedia.org/wiki/Corrosionhttp://en.wikipedia.org/wiki/Corrosionhttp://en.wikipedia.org/wiki/Passivate


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The protective effect of chromate coatings on zinc is indicated bycolor, progressing from clear/blue to yellow, gold, olive drab andblack. Darker coatings generally provide more corrosion resistance.Chromate conversion coatings are common on everyday items suchas hardware and tools and usually have a distinctive yellow color.


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B. Typical Applications:

Aluminum frames and weldments for the computer anddefense industries. Chromating technology deals effectively withpoor drainage and entrapped chemicals, a complex problemcommon to frames manufactured of welded tubing and pipe

Aluminum extrusions, tubing and structural assemblies.These can be chromated in lengths of 4800 to 6000mm and crosssections of 1200 to 1500mm.

Any aluminum part that requires painting for corrosionresistance.


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C. Advantages: Low-cost option for corrosion and wear protection

A bonding agent for paint and adhesives

A lubrication carrier

Final finish

Minimal electrical resistance No effect on critical dimensions, in most cases

Documents

Aluminum Finishes