Benefits of Anodic Oxide Films on Aluminum

  • Physical and Mechanical
    • Hardness
    • Wear Resistance
    • Lubrication
    • Membrane
  • Chemical
    • Corrosion resistance
    • Wettability
    • Adhesion
    • Catalytic properties
  • Electromagnetic
    • Insulating properties
    • Dielectric properties
    • Magnetism
  • Optical
    • Luninescence
    • Absorption
  • Thermal
    • Emittance
  • Reference

Anodizing Station

  • 5 gal buckets typically have
    • circumference of 35“ with diameter 11.14” (~11-3/16“) at bottom
    • top diameter is 12.5” or 12.19“
    • total height of 14.35”
    • height from bottom to first reinforcement ring is 11“

Workflow - Aluminum Parts

Henkel Surface Treatments

Step 0 - Workpieces

  • Slide Fit

Step 3 - Heat Treatment

  • Purpose of Heat Treatment
    • Harden surface of part
    • Relieve internal stress in the part
    • Soften/Anneal
    • Precipitation Harden
  • “Deformation parameters and aging to a T6 temper typically produces a moderately fine grain size (60 to 100 micrometers) that yields a uniform chemical potential across the surface.” [ASM-02A p. 602]
  • Commonly heat treated aluminum alloys
    • 2000 (aerospace)
    • 3000 (popular in canning industry)
    • 6000 (aerospace)
    • 7000 (except 7072) (aerospace)
    • 200
    • 600
    • 700 cast alloys
  • Temper Designations
    • F - as produced/fabricated
    • O - annealed
    • H - strain hardened (cold worked)
    • T - heat treated, with or without strain hardening
      • T3 - Heat treated and cold worked to improve strength
      • T6 - Heat treated, not cold worked, aged at elevated temperature
      • T8 - Heat treated, cold worked, aged at elevated temperature
    • W - heat treated and quenched
  • Example
    • 6061-T6 = heat treated, not cold worked, aged at elevated temperature

Step 4 - honing or polishing or pickling

  • honing - air blast (dry or wet) with 5 micron aluminum oxide (~ 1000 grit)
    • “Wet (sometimes called vapor blasting, vapor or liquid honing) or dry blasting is very effective in removing particulate soil, oxides, and scale (from a previous heat treatment). Blasting can also provide random, uniform micro-roughness, which may contribute to improved adhesion of electroplated deposits. Dry blasting is more severe than wet blasting, because the water acts as a cushion on the impingment of the abrasive particles. The abrasives are usually glass beads, aluminum oxide, silcon carbide, sand, or metal shot of varying particle sizes.” [NASF p. 7]
  • polishing - buff with a cloth wheel with Tripoli abrasive compound. Speeds about 2000 RPM.
  • pickling - acidic treatments on the workpiece to produce a lightly etched surface into which plating crystals can grow
    • acidic pickling using sulfuric acid or muriatic acid. 5-10 oz of acid per 1 gallon of water. Always add small amount of acid to a large amount of water to reduce the boiling of the water . Pickle the part for 1-2 minutes. [Hobbyist p. 18]

Step 6 - Degreasing

  • after machining to remove any cutting fluid
  • any solution containing sodium metasilicate is good such as automotive spray degreasers

Step 8 - Electrocleaning

Step 10 - Deoxidize

  • Degreasing and Deoxidizing Chemistries for Aluminum Alloy Surfaces
  • “Many commercial formulations based on other chemistries exist. Some of these can be found in” S. Wernick, R. Pinner, and P.G. Sheasby, The Surface Treatment and Finishing of Aluminum and its Alloys, Vol 1, 5th ed., ASM International, 1987, p. 220 [ASM-13a p. 1862 of 2597]

Step 11 - Degreasing

  • “Degreasing is performed by dipping the specimen in organic solvents, alcohol, acetone, kerosene, or trichloroethylene, or by wiping with cloths permeated with solvent.” [ASM-13A p. 1903 of 2597]
  • “Preparing aluminum parts for plating typically begins with solvent degreasing whenever possible. Solvent degreasing with the use of ultrasonics is even more effective.” [NASF Section 3 p. 4]

Step 12 - Etching

  • Chemical finishing of degreased aluminum surface
  • with Caustic Soda (NaOH) at 3-5% v/v concentration for 10-15 minutes (see [Dimetrics]) at room temperature
  • to dissolve the aluminum surface (chemical milling) to within specified tolerances or to produce a surface roughness [NASF p. 5.1]
  • Caustic Soap

Acid Etching

  • Acid Etching
    • ASM Handbook Vol 13a - Corrosion, p. 1904 of 2597

Step 13 - Desmutting

  • required if etching was done with city water

Step 20 - Neutralize

  • “Use 5% sodium carbonate as a neutralizer after rinsing” [NASF Section 8, p. 21]
  • use city water with 5-10% baking soda solution - pH between 9 and 10
  • 1 gal distilled water and 1/2 lb baking soda [Caswell 2003, p. 8]

Step 18 - Anodize

Anodizing Station

Bucket Floor

  • Background
    • if bucket is spilled, won't be harmful
  • Neutralizer - Baking soda
  • Rinse - City Water
  • Rinse - Distilled Water
  • Wash - dish soap

Bucket Stations

  • Background
    • station to chemicals from getting spilled
  • Bucket 1 - Caustic Soda
  • Bucket 2 - Degrease
  • Bucket 3 - De-oxidizer Desmut
  • Bucket 4 - Anodize
  • Bucket 5 - Dye
  • Bucket 6 - seal (this needs boiling water, so stainless steel pot on a hot plate might be better)
  • References

Safety Equipment

  • have a bucket of water with baking soda to neutralize and cleanup any sulfuric acid spill (add red food coloring so can tell isn't not just water). This is the same as the neutralizing bath.
  • well ventilated area, such as the garage with the door/window open, recommend having a fan to keep the air
  • face shield
  • rubber gloves

Direct Current (DC) Power Supply

  • voltage 15-20 volts
  • current 7.5-28 Amps per square foot (A/ft² or asf)
  • auto battery charger will work as DC power supply for Low Current Density (LCD) anodizing. Low range is 10-30 amps. Don't use the high range which is ~ 50 amps.
  • Formula
    • 1 amp for every 50 inch^2 for 240 min grow 1/1000“ film
    • 1 amp for every 25 inch^2 for 120 min grow 0.001” film

Wiring up Parts

Anodizing Bath Equipment

  • Plastic tanks/containers
  • Anti-Mist Balls or Fume Control Balls - small plastic hollow spheres (1/4 to 1/2“) to help hold heat in the bath, prevent evaporation and reduce fumes
  • Aluminum or Titanium wire or clip to hold parts
  • Anode
    • Aluminum part from which the anodic oxide will grow
  • Cathode
  • Aluminum cross bar
    • steel will rust and contaminate the bath
    • copper will corrode over time
  • Air sparging (bubble agitation, aeration)
    • aquarium air pump connected to a small diameter tube. The tube has small holes to release air. Place tube at the bottom of the tank, under the workpiece to create flow up and over the part to the O2 and H2 gas bubbles as well as circulated the anodizing bath.

Anodizing Bath Solution - Electrolyte

  • 160-180 g/L (approx 16-18%)
  • Battery acid to water ratio 1:4
  • Work should be performed under a hood or well ventilated area as gas bubbles of oxygen (O2) and hydrogen (H2) are released
  • Procedures of anodizing
    • Aluminum Anodizing by Hideaki Takahashi, ASM Handbook Volume 13A: Corrosion, Fundamentals, Testing, and Protection pdf

Sulfuric Acid (MIL-A-8625 Type II) Anodizing Process

  • “As the sulfuric acid content increases above 20%, the coating weight produced for a given current density and time becomes unacceptably low. This is why the optimal concentration is typically held at 15%.” [NASF Section 8 p. 5]
  • “Anodizing times are shorter for more clear coatings and longer if the coating is to be dyed and sealed.” [NASF Section 8 p. 5]

Anodizing Procedure

  • Ice water 32-40°F
  • Keep the part in the anodizing bath for minimum 30 minutes [Dimetrics] up to 1 hour [Gilmour]

Step 24 - Dye

Step 26 - Sealing

  • “Sealing is usually performed by dipping in boiling water…A 10 min sealing treatment is sufficient to seal the pores completely in boiling water…” (ASM Handbook Volume 13A Corrosion: Fundamentals, Testing, and Protection, p. 1907 of 2597)
  • Caswell sells an Anodizing Sealant (nickel acetate based)
  • Bright Dyes sells additional additives to nickel acetate to prevent smut when boiling (HT-70D), see Bright Dyes Finishing Additives
  • Anodic coatings produced by the sulfuric acid process can be sealed by immersing the parts in any one of several solutions. The principal sealing treatments are:
    • (1) Hot water sealing. Hot water sealing is the most common sealing treatment. It consists of immersing the parts in hot or boiling water [200 to 212F (93 to 100C)] for 10 to 30 minutes, depending on coating thickness. This treatment involves hydration and converts some of the surface aluminum oxide to crystalline alpha alumina monohydrate, which occupies a greater volume than the alumina from which it was formed. This increase in volume closes and effectively seals the pores. Hot water sealing does not affect the color or appearance of the film. It does increase the corrosion resistance of the coating, but not as much as does dichromate sealing. Steam is sometimes employed in place of hot or boiling water to speed up sealing.
    • (2) Dichromate sealing. The part is immersed in a hot [190 to 210F (88 to 99C)] aqueous solution containing 5 to 6% by weight of sodium or potassium dichromate for 20 to 30 minutes. This treatment imparts a yellow color to the anodic coating, but at the same time it also provides the best corrosion resistance of any of the sealing treatments. This is due to the absorption of corrosion inhibiting chromate into the pores of the film. Dichromate sealing is very useful as protection against stress corrosion in Duralumin and other high strength alloys, particularly in sections where traces of the corrosive sulfuric acid from the anodizing bath might remain. The dichromate treatment is sometimes used as a second sealer over dyed coatings that had first been sealed in a nickel acetate or cobalt acetate bath. To avoid yellowing of the applied color, the strength of the dichromate sealing bath is reduced to 1% sodium or potassium dichromate by weight. The second seal is used to further improve the corrosion resistance of the coating.
    • (3) Nickel or cobalt acetate sealing. Anodic coatings can be sealed by immersing parts in a hot [180 to 210F (82 to 99C)] aqueous solution containing 0.5 to 1% weight of nickel acetate or cobalt acetate for 15 to 20 minutes. This treatment is primarily used to seal porous anodic films after they have been colored with organic dyes. The nickel or cobalt salts are absorbed into the coating where they are precipitated as virtually colorless hydroxides, which help stabilize the color. The pores of the film are sealed in the same bath or given a further hot water sealing in a subsequent treatment.
    • [MIK-HDBK-132A p. 104-5 of 275] - MIL-HDBK-132 Rev A from EverySpec

Periodic Table of Elements

  • Periodic Table
  • Column 1 - electro positive - give electrons
    • Na = sodium likes to give away electrons
  • Group 7 halogen top right side - electro negative - want electrons
    • Cl = chlorine

Oxidation - Reduction: Transfer of Electrons

  • Oxidation-reduction reaction (abbreviated redox) is any reaction that involves the transfer of electrons from one substance to another
  • Oxidation is defined as the loss of electrons (LEO)
    • generally metals lose electrons to form positive ions
  • Reduction is defined as the gain of electrons (GER)
    • nonmetals gain electrons to form negative ions
  • LEO the lion says GER

Electrochemistry

  • LEO is A GERC (jerk)
    • Loss of electrons is oxidation an Anode (positive terminal)
    • Gain of electrons is reduction a Cathode (negative terminal)
  • Anode - positive terminal
    • lose electrons (loss of mass), or source of electrons
    • An Ox = anode oxidation
  • Cathode - negative terminal
    • gain electrons (gaining of mass)
    • Red Cat = reduction cathode

CSI

Blast Cabinet

Modifications

  1. portable sandblasting cabinet - move to outdoors when blasting
    1. Harbor Freight Mobile Base Cart - HF# 95288
  2. upgrade lighting
  3. shelf to store blasting media
  4. shelf to store dust collection / shop vac

Video Help

  • Ray's Garage - Tacoma Company Upgrades Part 9
  • asdf

Training

  • SSPC.org - The Coatings Society
    • Abrasive Blasting (C7) \$1020

Surface Treatments

Surface Coatings

Anodize

  • MIL-A-8625F, Type II
  • Provides corrosion protection and wear resistance to aluminum parts. Can be applied in a variety of colors or clear for decorative and architectural uses.

Brush Anodizing

  • Brush anodizing is a localized application of a colored oxide (aluminum oxide) on an aluminum substrate. The workpiece is the cathode (-) and the brush is the anode (+). Various electrolytic acid solutions can be used, usually sulfuric, which is placed on the brush. A low voltage DC rectifier is used to achieve the equivalent of 3+ amps/ft2 of anodizing contact area.
  • Aluminum Finishing, An AESF Foundation Educational Course, p. 22-3
    • Brush anodizing has a history of about 40 years in the US. The process is portable, not limited by tank size, and can re-anodize components that are already assembled. The process is labor intensive, but can often be justified on the economics when labor savings for assembly/disassembly are taken into account, or if the part is unusually large. As one might expect, the chief applications involve airline and aerospace repair work.
    • The technique utilizes a “brush” as illustrated here. Solution is pumped through the polyester felt or bonnet covers. Stainless steel perforated sheet instead of fabric tool covers are used with the gels. Phosphoric, chromic, sulfuric and hardcoat can be applied using this type of equipment. In some cases, the solution is a gel, instead of a free flowing liquid. The equipment and solutions for brush anodizing are commercially available.
    • Brush Anodizing
    • In the case of a repair job, the surface may first be stripped using a similar brush, reverse polarity, and stripping solution/gel.
    • Typical operating conditions are:
    • Anodize Type CD A/in2 Temp, ℉ Time
      Phosphoric 0.02 60-90 10-12
      Sulfuric 1.5 65-85 0.5-10
      Hard Coat 0.5 30-50 10-30
      Chromic 0.02 95-105 15-60
  • References

Brush Plating

Hard Anodize

Procedure

  • “In general, the anodizing process of an aluminum or aluminum alloy specimen consists of pretreatments (degreasing, etching, and polishing), anodizing, coloring, and sealing.

Surface Coating - Electroless Nickel

  • Provides very high corrosion and wear resistance. Also known as EN.

Standard Specifications

Surface Coating - Tungsten Disulfide

Procedure - Tungsten Disulfide

  • Step 2 - Hone
    • Using 5 micron (800-1500 grit) aluminum oxide powder as a fine abrasive, air blast the part to obtain a uniform matte appearance
    • Equipment
      • Blasting cabinet to reclaim aluminum oxide
      • brush to wipe down workpiece
  • Step 3 - Impingement
    • Using an air blast at <125 PSI and nozzle size, spray tungsten disulfide on the part until you see a uniform silver gray color film appearance
  • Step 4 - tape test
    • “A pressure-sensitive-film-backed tape with an adhesion of not less than 45 ounces per inch (0.49 N/mm), shall be applied to a flat surface of a coated specimen, rolled in place, and rapidly removed in accordance with ASTM D 2510, Procedure B. The lifting of flakes or particles of the coating from the specimen, exposing the basis metal, is not acceptable. A uniform deposit of powdery material clinging to the tape is acceptable.” [AMS2530A 3.4.1 Adhesion]

Specifications - Tungsten Disulfide

  • AMS2530A - Tungsten Disulfide Coating, Thin Lubricating Film, Binder-Less Impingement Applied
  • DOD-L-85645A

Honing

  • Grit to Mesh to Microns Conversion Chart
  • Aluminum Oxide (Al2O3), 5 micron
  • Aluminum Oxide (White Fused) Sandblasting Abrasive, Fine Grades 280 through 1200
  • Illinois Valley Minerals (IVM), LLC is a producer of brown fused aluminum oxide
  • AGSCO Corp in Wheeling IL
    • 50 lbs of #1000 Mesh White Aluminum Oxide at $6.107/lb = $305.35
    • Tom Guzek, tguzek@agsco.com
  • The Stutz Company - distributors of plating processes, chemicals and equipment for the electroplating industry
    • info@stutzcompany.com

Aluminum Oxide

Surface Preparation - Anodize Aluminum

  • Step by Step Procedure
  • Step 1: Cleaning aluminum parts
    • Option 1 - Acid Cleaning - fluoride cleaner consists of sulfuric acid, fluoride and surfactant
    • Option 2 - Sulfuric Acid
      • battery acid is 37% sulfuric acid
      • add distilled water
    • Option 3 - Lye/Caustic Soda (Sodium Hydroxide)
      • 5 grams (0.18 oz) caustic soda
      • 240 mL (1 cup) distilled water
      • soak object 2-4 minutes
      • “Aluminum is rapidly attacked by even dilute solutions of caustic soda at all temperatures.” (ASM Handbooks Online - M.Davies, Corrosion by Alkalis, Corrosion: Environments and Industries, Vol 13C, ASM Handbook, ASM International, 2006, p 710–726)
    • Graham's Salt (Sodium Polyphosphate)
    • Washing Soda or Soda Ash (Sodium Carbonate) used in swimming pools to raise pH
  • Step 2: degrease aluminum parts with any degreaser such as Simple Green
  • Step 3: de-smut the aluminum part
  • Step 4: Anodize in the acid bath at 12 amps/square foot for 45 min, keep temp at 70-72 degrees F
  • Step 5: remove parts from acid bath and rinse with distilled water
  • Step 6: Dye parts in warm dye, 100-140 degrees F
  • Step 7: Seal parts by placing in boiling distilled water for 20-30 minutes
    • asdf

Dave Mills Cleaning Procedure

  • Alkaline solution with agitation
  • Clean water rinse with agitation
  • Warm air dryoff
  • [Q] do you recommend using a fish tank air bubbler to agitation the solution, could I just submerge an air hose?

Education

Associations

Chemical Manufactures and Resellers

I got your contact info from https://www.lvf.com/industrial/contact-us.html

I'm working on a new business venture on surface treatments (e.g. anodizing aluminum) and will be buying substantial quantities but currently need small quantities for lab work. What is the minimum sample quantities I could get or minimum purchase amount for the following:

Aluminum Sulfate Copper Nitrate Oxalic Acid Potassium Permanganate Nitric Acid Sulfuric Acid

I reached out to Thatcher Company, they don't sell in small packages and suggest contacting you, Land View in Rupert,

thanks,

Jeff Jensen

Industry

Employment

    • Powder Coater
      • Powder Coater
        • Mountain Home, Idaho
        • In The Ditch Towing Products is the fastest growing manufacturing company in Idaho and we have an opportunity for a passionate, energetic person to join our Powder Coating/Paint Department. All you need is a desire to learn and a hunger to want to build a career.
        • We are currently seeking someone for the powder coating department to prepare product for painting, powder coat products to a high standard, check for defects in finish, and take necessary actions to correct those defects. The sky’s the limit in this position with unlimited opportunity for advancement. If you have great attitude and a desire to get better every day, we would love to teach you the skills you will need to succeed here. If you want to work in a clean organized shop that believes in helping people get what they want; this may be the job for you.
        • Here at In the Ditch, we are a privately owned business that’s been in Mountain Home for over 20 years with no plans to move. We have found great success by recruiting people who are excited about working here and buy into our culture. We truly believe in coaching and developing people who have a great attitude, work ethic and want to leave their mark on the world. At In The Ditch, we value people for their Enthusiasm, Commitment, Hard Work and Ability to do things better each day, not just for their certifications and degrees or for the buzzwords on their resumes. We love candidates that believe that our only opportunity to win in the marketplace will come by hiring and retaining the best people in the industry. If you have the desire to help us build a great company and want to surround yourself with people who share the same vision, please apply today.
        • Job Details:
          • Hold or position powder coat guns to directly spray onto products
          • Attach hoses or nozzles to machines, using wrenches and pliers, and make adjustments to obtain the proper dispersion of spray
          • Powder coat items and perform touch-up painting, using paint brushes
          • Set up and operate machines to powder coat a wide variety of metal products
          • Remove grease, dirt, or rust from surfaces in preparation for powder coating application using abrasives, solvents, brushes, washing, or sandblasters
          • Apply powder coating to protect product surfaces, using powder coatings guns
          • Place coated products in ovens for specified times to harden finishes
          • Place items or products on racks to coat or spray them, using hands or hoists
          • Inspect finishes of workpieces or finished products to ensure quality
          • Clean machines, related equipment, and work areas, using water, solvents and other cleaning aids
          • Transfer completed items or products from machines to drying or storage areas, using handcarts, or racks
          • Provide a great level of attention to detail and focus on given tasks
          • Drive fork lift to load/unload items as needed
          • Assist with other tasks as given

Newsletter

  1. 00.01 Cover - Title Page
  2. 00.02 Table of Contents
  3. 01.01 Chapter 1
  4. 02.01 Chapter 2
  5. 03.01 Chapter 3
  6. 04.01 References
  7. 05.01 Appendix A
  8. 05.02 Appendix B
  9. 99.99 Back Cover
  10. Change log
    1. version (1.2) YYYY-MM-DD Title
    2. latest to oldest
  11. Aluminum Anodizing by Hideaki Takahashi (ASM Handbook Volume 13A Corrosion)
  12. Excel Anodizing Calculator
  13. Safety Data Sheets (SDS)
  14. Shopping List - where to buy chemicals

References and Standards

Standards

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