Aluminum Finish

Aluminum Finishes

1. Mill Finish2. Anodized Finish3. Powder Coated Finish4. Super Durable Powder Coated Finish5. Polyvinylidene Flouride (PVDF) Finish6. Alodine7. Chromated Finish

1. Mill Finish

Simply means the raw or bare finish of material as it comes out of the extrusion or milling machines.

2. Anodized FinishAnodizing, or anodising, is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts.

A - History: Anodizing was first used on an industrial scale in 1923 to protect

Duralumin seaplane parts from corrosion. This early chromic acid process was called Bengough-Stuart process.

In 1927 Gower and O’Brien 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 later widely use in Germany, particularly for architectural applications.

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

Anodized Finish

A - History: (cont.) In most recent major development, the phosphoric acid

anodizing process so far is only used as pretreatments for adhesives or organic paints. Although a wide variety of proprietary and increasingly complex varuation of all these anodizing processes continue to be developed by industry.

Anodized FinishA - Advantages: Increases corrosion resistance and wear resistance. Provides better adhesion for paint primers and glues than bare metal. 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 linear

expansion than aluminium. As a result, the coating will crack (but will not peel) from thermal stress if exposed to temperatures above 80°C.

Anodized Finish

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

This process is not a useful treatment for iron or carbon steel because these metals’ iron oxide (also known as rust) flakes off, costantly exposing the underlaying metal to corrosion.

Anodizing is one of the more environmentally-friendly metal finishing processes.

Anodized Colors & Film Thickness

Chromic acid = 0.5µm to 18µm (0.00002” to 0.0007”)

Sulfuric acid = 1.8µm to 25µm (0.00007” to 0.001”) moderate= 25µm to 150µm (0.001” to 0.006”) hard anodizing

Organic acid = up to 50µm Phosphoric acid = see ASTM

D3933Film thickness range from 0.5µm to 150µm.

3. Powder Coating Finish

Powder coating is a type of coating that is applied as a free-flowing, dry powder. The main difference between a conventional liquid paint and a powder coating is that the powder coating does not require a solvent to keep the binder and filler parts in a liquid suspension form.

Powder Coating Finish

Powder Coating Finish

The coating is typically applied electrostatically and is then cured under heat to allow it to flow and form a "skin." The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a hard finish that is tougher than conventional paint. Powder coating is mainly used for coating of metals, such as "whiteware", aluminium extrusions, and automobile and bicycle parts. Newer technologies allow other materials, such as MDF (medium-density fibreboard), to be powder coated using different methods.

Normally the powders cure @ 200°C (390°F) in 10 minutes. The curing schedule could vary according to the manufacturer’s specifications.

Powder Coating FinishA - 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 achieve

nearly 100% use of coating. Production lines produce less hazardous waste than

conventional liquid coatings. Capital equipment and operating costs are generally less than

conventional liquid lines. Items generally have fewer apprearance differences between

horizontally and vertically coated surfaces than liquid coated items.

Wide range of specialty effects can easily accomplished compare to other coating processes..

Powder Coating FinishB - Disadvantages: Not easy to apply smooth thin films. As the film thickness is

reduced, the film becomes more and more orange peeled in texture due to the particle size and TG (glass transition temperature) of the powder.

For optimum material handling and ease of application, most powder coatings have a particle size in the range of 30 to 50 micrometres and a TG > 40°C.

Powder Slurry process is a specialized operation where powder coatings is less than 30 micrometers or with a TG < 40°C.

Powder coatings have a major advantage in that the overspray can be recycled. However, if multiplt colors are being sprayed in a single spray booth, this may limit the ability to recycle the overspray.

Powder Coating Finish

C – Types of Powder Coatings:

Thermosets variety – incorporates a cross-linker into the formulation. When the powder is baked, it reacts with other chemical 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 final coating.

The most common polymers used are polyester, polyester-epoxy (known as hybrid), straight-epoxy (Fusion bonded epoxy) and acrylics.

Powder Coating Finish

D – Removing Powder Coating:

Methylene Chloride is generally effective at removing powder coating. Organic solvents (Acetone, thinnerss, etc.) are completely ineffective. Most recently MC is being replaced by Benzyl alcohol with great

success. Can also be removed with abrasive blasting. 98% sulfuric acid commercial grade also removes powder coating

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

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

Powder Coating Finish

E – Powder Coating Colors:

4. Super Durable Powder Coated Finish

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

A. Application: Primary areas of application are aluminum extrusions and

claddings for architectural work. When screen-printing or sealants are in use, we advise separate trials to ensure compatibility and that the required performance criteria are met.

Super Durable Powder Coated Finish

B. Advantages: Has an expected lifetime which is 3X as long as today’s high quality

architectural powder coatings. Backed by a 25 year guarantee. Cost effective compared to expensive fluorocarbon-based wet paint. Truly environment friendly because it’s 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 25°C/ relative humidity 60%.

5. Polyvinylidene Flouride (PVDF) Finish

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

A. Usage: A fine powder grade, KYNAR 500 PVDF or HYLAR 5000 PVDF, is

also used as the principal ingredient of high-end paints for metals. These PVDF paints have extremely good gloss and color retention, and they 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.

Polyvinylidene Flouride (PVDF) Finish

B. Advantages: Resistant to most acids, alkalis, salts, halogens, alcohols and

chlorinated hydro-carbons High mechanical strength, Operating temperature range -20°C to 140°C Displays high excellent flame retardant properties.

C. Disadvantages: A strong polarized solvents, such as ketones and esters, can

cause the material to swell.

Polyvinylidene Flouride (PVDF) Finish

D. PVDF Colors

6. Alodine Finish

Alodine is a coating based on Titanium Metal Oxide (TiO2) electrodeposited from the electrical assisted hydrolysis of metal complexes. The TiO2 Coating provides superior corrosion and wear resistance for harsh and demanding applications such as marine and high temperature engine environments.

Alodine is a brand of Chromate conversion coating products used on aluminum alloy and to a lesser extent magnesium alloy metals, primarily in the aerospace industry.

Alodine FinishA. Advantages:

A new electrolytic process provides a 3-12 micron thick layer of TiO2

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 600°C (1112°F) without

corrosion performance loss

7. Chromated Finish

Chromate coatings - are soft and gelatinous when first applied but harden and become hydrophobic as they age. Curing can be accelerated by heating up to 70°C, but higher temperatures will gradually damage the coating over time. Some chromate conversion processes use brief degassing treatments at temperatures of up to 200°C. Coating thickness vary from a few nanometers to a few micrometers thick.

Chromated FinishA. Chromate Conversion defined: When aluminum and aluminum alloys are immersed in a

controlled chromic acid bath with special additives, a chemical conversion reaction occurs at the metal’s surface. This reaction produces a complex, non-crystalline, non-porous coating consisting of a thin aluminum oxide film with entrapped chromates and dichromates. The coating’s corrosion resistant properties are due primarily to the chromates, specifically the hexavalent chromium.

A type of conversion coating applied to passivate aluminium, zinc, cadmium, copper, silver, magnesium, tin and their alloys to slow corrosion.

Chromated Finish

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

Chromated Finish

B. Typical Applications:

Aluminum frames and weldments for the computer and defense industries. Chromating technology deals effectively with poor drainage and entrapped chemicals, a complex problem ccommon to frames manufacturerd of welded tubing and pipe

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

Any aluminum part that requires painting for corrosion resistance.

Chromated Finish

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