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Finishing WorkshopColumbus, OhioMay 16-17, 2017

Anodizing 101

Introduction

• Importance of step by step methodology

• Overview

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Aluminum

Aluminum

Aluminum

• Certain problems can occur which the anodize process cannot correct

• Die lines• Buffing• Different soils• Corrosion• Zinc• Incorrect alloy ratios• T-52• Soft Metal

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RACKING

Racking• Racks have two functions:

1. Transfer parts from one tank to another

2. To act as the electrical conductor

• Racks are consumable and will wear out

Racking

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Racking• Problems associated with worn racks:

1. Parts falling into chemical tanks

2. Cannot carry current

3. Produce incorrect film thickness

4. Produce incorrect color

5. High chemical consumption

Racking• Rack preventive maintenance (PM)

• Clean contacts

• Completely stripped splines

• Good spacing

Load Bars

• Contact pads should be kept clean

• Heat is a sign of resistance and current is not getting to the parts

• Load bar preventive maintenance (PM)

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Rinsing

Rinsing

• One of the most important steps in the anodizing process is rinsing

• Three main purposes for rinsing:1. To remove the chemicals from the surface2. To end a chemical reaction3. To prevent cross contamination

Rinsing

• Rinse water should be clean and overflowing if possible

• Counter-flowing can help with high water usage

• Draining:1. Reduces contamination2. Reduces cost by keeping chemicals in the tank

• Rinse tanks must be dumped periodically

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Keep chemicals in the tank!

Cleaning

Clean

• The purpose of the cleaner is to remove soils from the surface

• The majority of anodizing lines use an alkaline cleaner, which is good for removing extrusion soils

• Cleaners must be dumped periodically

• The proper time temperature and concentration should be used to produce a clean, water-break free surface

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Is it clean?

Clean

• If the surface is not properly cleaned, pitting can occur

• Preferential etch may occur if parts are not cleaned properly

Etch

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Etch

• The purpose of the etch is to provide a uniform matte finish

• The etch can also be used to chemically mill parts and remove minor surface defects

Etch

• Three types of etch baths:

1. Conventional Etch (No-Dump)

2. Caustic Recovery Etch

3. Acid Etch

Etch

• Conventional etch

• High caustic and aluminum

• Contains additives to keep the aluminum in solution

• Produces a smooth matte finish

• Etch times can be long

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Etch

• Caustic Recovery Etch

• Equipment removes aluminum and keeps caustic

• Cannot use chelators

• Produces a sellable waste

• Bath has low aluminum levels

• Sensitive to contaminates

• Finish is not as good as conventional etch

Etch

• Acid Etch

• New technology

• Produces a superior smooth matte finish

• Can hide many die lines and extrusion defects

• Not sensitive to zinc contamination

• Reduces sludge in waste treatment

Acid vs Alkaline Etch

180s Acid Etch 10 mins NaOH

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Etch

• All etch baths must be maintained (time, temperature, concentration) to produce a consistent finish.

Desmut / Deoxidize

Desmut / Deoxidize

• The desmut is used to remove the residue left behind after the etching process.

• What is the smut?

The alloying ingredients which are insoluble in caustic

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Desmut / Deoxidize

• Problems associated with desmuts:

1. Drag out – Concentration too low

2. Neutralization – Drag in of etch bath

3. Over-usage – Parts in the bottom of the tank

Anodizing

Anodizing

• Anodizing is a electrochemical process in which the surface of the aluminum is oxidized, producing a porous film.

• This porous film can be colored and sealed.

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Anodizing

• Anodizing is performed by immersing the aluminum in sulfuric acid and applying DC power.

• The aluminum is the anode and the side electrodes are the cathodes.

• The anodizing film is controlled by the current and time so proper contact is very important.

Anodizing

• Important points about anodizing:

1. Concentration

2. Temperature

3. Anodize Additives

4. Time

5. Electrical Connections

AnodizingArchitectural Requirements:

Coating Weight

Class I (0.7 mil) 27.0 mg/sq. in.

Class II (0.4 mil) 15.5 mg/sq. in.

Coating Density

All Classes 38 mg/cubic inch

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Anodizing

• Anodizing problems:

1. Burning

2. Uneven coating

3. Pitting

4. Soft coating

Anodizing

• Anodizing is the most important step in coloring.

• If the anodizing is not done properly, the coloring process will not produce the desired results.

Coloring

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Coloring

• There are three basic methods of coloring:

1. Two step electrolytic coloring

2. Organically Dyed

3. Integral Coloring

Electrolytic Coloring

• In this process, anodized parts are immersed in a solution containing a metal salt (tin).

• AC power is applied and the metal is deposited into the bottom of the pore.

• Most problems that develop in electrolytic coloring are due to the anodizing not being done correctly.

• If the anodic film is not properly formed, the color uniformity will not be acceptable.

Coloring

Electrolytic Coloring Components

• Tank

• Counter Electrode

• Power Supply

• Chemistry

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Electrolytic Coloring

• Problems associated with electrolytic coloring:

1. Extrusions not colored2. Dark ends light center (picture framing)3. Light ends dark center (reverse picture framing)4. Non-uniform color across the extrusion5. Color wrong shade6. Light color complete load 7. Dark color with red undertones8. Lighter color with green undertones

Electrolytic Coloring

Electrolytic Coloring (Two-Step)

• Electrolytic coloring is the 2nd electrical step in the 2-step process of Anodize and Electrolytic Color

• Electrolytic coloring IS dependent upon the characteristics and consistency of the anodizing step.

• Because the Two-Step system consists of the two electrochemical processes, BOTH steps are affected by the following:

• Good electrical contact.• Tight bath chemistries and temperatures.• Work load distribution and spacing.• Adequate power supply.

Dyeing

• Dyeing occurs by the dye being absorbed into the pore.

• Dyeing occurs from the top of the pore down. Electrolytic coloring starts at the base of the pore and works up.

• No current is used in dyeing. Minimal equipment.

• Certain colors require specific film thicknesses

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Dyeing

• Similar problems can occur in dyeing just like electrolytic coloring.

• Dye pH is critical.

• Dyeing can generate pits and white spots.

• Dyed parts are not as light-fast as electrolytic coloring.

Integral Coloring

• Not widely used.

• Anodizing and coloring occur in the same tank at the same time.

• This process uses the alloy components to generate color.

• This process is done under cold conditions and very high power.

• Special alloys and tempers are needed for this process.

Coloring• As a best practice for any type of coloring, anodizing must be

preformed properly to yield the desired results.

• Final end use will determine the best coloring method used.

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Sealing

Sealing

• The final step in the anodizing process is sealing.

• Sealing of anodized aluminum changes the anodic coating to make it:

Non – Staining Non – Absorbing Non – Reacting Non – Corroding

Sealing

• There are three types of seals

1. Hot Water

2. Mid Temp Seal (Low Temperature Seal)

3. Cold Seal

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Hot Water Seal

• Parts are placed in hot water (210oF)

• The pores are swelled shut

• This process is environmentally friendly.

• This process takes a tremendous amount of time (up to 60 minutes for Class 1)

• This process takes a tremendous amount of energy

Mid Temperature Seal

• The parts are sealed similarly to hot water sealing except metal is precipitated into the pores

• Special surfactants speed up the chemical process – 10 to 12 minutes for Class I coatings.

• Adhesion is fair when compared to hot and cold seals

• Smut is significantly less than hot water

Cold Seal

• A chemical reaction occurs when a metal (usually nickel) and an accelerator react forming a compound that plugs the pores

• This type of seal uses less energy

• Adhesion is very good with cold seals

• Metal and fluoride must be controlled

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Sealing Comparison

Sealing

• All seals must be controlled properly to achieve the desired results.

• Time, temperature, concentration and pH are critical

• Seal baths have to be dumped periodically to maintain quality

• Proper rinsing before and after is needed to reduce the possibility of smut

“Seal Smut”

• All smut does not come from the seal bath:

• White powder (yellow tint) – Electrolytic color

• White powder (green tint) – Nickel seal or seal rinse

• Iridescent (black) – Deoxidizer not working, over-plating from electrolytic color or black dye problems

• Iridescent hard to wipe – Seal time, low pH rinses

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Conclusion

• Quality anodizing can occur if there is:

• Proper racking• Good chemical control of baths• Good rinsing• Proper drainage• Understanding the chemical and/or electrical

function of each bath

Thank You

Thank you for attending the Anodizing 101 Workshop.

Please feel free to contact Houghton or the AEC with any additional questions.

Daryl Jones : dbjones@houghtonintl.comLinda Newman : lnewman@houghtonintl.com