Anodizing 101. A primer for Anodizing today

Transcription

1 A primer for Anodizing today

2 Wiki-Pedia says: Anodizing, or anodising, is an electrolytic passivation process used to increase the thickness and density of the natural oxide layer on the surface of metal parts. This process is of no use on carbon steel because rust puffs up and flakes off, constantly exposing new metal to corrosion. But on many other metals, anodizing increases corrosion resistance and wear resistance, and provides better adhesion for paint primers and glues than bare metal.

3 Anodic films can also be used for a number of cosmetic effects, either with thick porous coatings that can absorb dyes or with thin transparent coatings that add interference effects to reflected light. Wiki-Pedia says:

4 Wiki-Pedia says: Anodization changes the microscopic texture of the surface and can change the crystal structure of the metal near the surface. Coatings are often porous, thick ones inevitably so, so a sealing process is often used to improve corrosion resistance.

5 Wiki-Pedia says: The process derives its name from the fact that the part to be treated forms the anode portion of an electrical circuit in this electrolytic process. Anode + (pos) Work piece Cathode (neg) Cathode (neg) Acid Electrolyte

6 Wiki-Pedia says: Anodizing can prevent galling of threaded components. Anodic films are generally much stronger and more adherent than most paints and platings, making them less likely to crack and peel. Anodic films are most commonly applied to protect aluminum alloys, although processes also exist for titanium, zinc, magnesium, and niobium.

7 An overview Materials Anodized Assemblies Brake Metal Castings Coil Material Extrusions Sheet & Plate Small Parts Chemical Finishing Bright Dip Etching (Caustic) Etching (Acid) Type I (Chromic) Type II (Sulfuric) Type III (Hardcoat) Sealing Teflon Seal Dichromate Seal Boiling DI Water Nickel Acetate Mid-Temperature Trivalent Chrome Seal Other Mechanical Finishing Fabrication Services Special Services Conversion Coat Coloring

8 Introduction Economics and Environmental concerns Productivity and Efficiency Support and Troubleshooting Understanding the process is key to success

9 Steps to a Quality Anodized Finish Raw Aluminum Mechanical Finishing Racking Cleaning Rinse Etch/Bright Dip Rinse Anodize Rinse Color Rinse Seal Rinse

10 Raw Aluminum Problems Die Lines Buffing Different Soils Corrosion Effect Too deep, hard to remove Burning, too much compound, comet pits Cleaner not Effective Pitting, staining

11 Alloy and/or Material Temper Problems Zinc Fe, Si, Mg ratio T-52 (overaged) Soft Metal Effect Spangling Bright surface or Rough Surface Smutting Bad etch, smut or grainy appearance

12 Racking Used to transfer from tank to tank. Acts as an electrical conductor to deliver power to parts. It is consumable. Problems not always where it appears.

13 Racking Practices No worn out racks Clean Contacts Uniform Distribution of Parts Rack of Similar Alloy Load Bars

14 Rack Types Spline, Twist, Stack, Welded Bolt Clamps, Spring Clamps.

15 Rinsing Soil Residue Soil Breaking Surface Tension Dissolving Soil Soil Lift Off Clean Surface

16 Cleaning A clean surface will be soil free and water break free You need the right cleaner for the soil, environment and materials involved. Alkaline cleaners Acid cleaners Both???? Bath life factors Problems with Cleaners Does not clean Spent Solution Low concentration Wrong chemistry Too cold Etching High Temperature Temp beyond cloud point Redeposits soil Dirty bath Crystal on Surface High concentration Bath is spent

17 Purpose Uniform surface Esthetically appealing Types of etching Conventional Recovery New generation recovery Acid Etching Tank maintenance Critical controls Additive levels Temperature Etching

18 Desmutting & Deoxidizing Purpose A desmut will remove residue from the finishing process. An oxidizer will remove oxides in addition to smut. All desmut/oxidizer solutions are acidic with proprietary additives. Usually run at ambient. Problems usually are caused by low concentration. Drag out not brought up to strength Neutralization Drag in of alkaline residue Excess usage Parts in bottom of tank consuming chemicals

19 If the smut or oxides are not removed, you may create stains in the finished product. Deoxidizing for too long will create acid etching and will form smut which is not soluble in acid. This often results in a stain. Desmutting & Deoxidizing

20 Anodizing A controlled electrochemical process in which the surface of the aluminum is oxidized producing a porous aluminum oxide. Anode + (pos) Work piece Cathode (neg) Cathode (neg) Acid Electrolyte

21 Anodizing This step in the process is critical for coloring. Inconsistency in managing this step will lead to failures and non-uniformity at other steps in the process.

22 Anodizing As you see in this photograph, the surface is very porous. The pores can be filled with organic or inorganic color and sealed to provide an anodic oxide coating that protects the aluminum substrate.

23 The thickness of the resulting anodic oxide is controlled by time and current density. The structure, i. e. cell size, pore diameter and the barrier thickness are determined by voltage. Anodizing Faraday s Second Law: Film thickness is proportional to Current and Time. Thickness in mils = ASF * T 720

24 Anodizing Guidelines for maintaining uniformity throughout the process: 1. Concentration levels must be maintained within narrow specifications. Acid: +/- 5 gram/liter Aluminum: 8 12 grams/liter 2. Temperature fluctuation will affect uniformity most. H 2 SO 4 conductivity changes dramatically with temp changes. Uniform coloring requires consistency between multiple anodizing tanks. Temperature: +/- 2 degrees Farenheit

25 Anodizing Guidelines for maintaining uniformity throughout the process: 3. Additives reduce the dissolution effect of H 2 SO 4 on the anodic film. 4. Electrical connections tend to corrode with time. Acidic corrosion can lead to uneven current distribution and uneven anodic films. Cleaning and monitoring connectivity must be a regular practice.

26 Anodizing Problems in this step are usually seen in the color or seal steps. 1. Burn Marks Current density too high or no additive Bad or dirty contacts To quick of a ramp on the rectifier.

27 Anodizing Problems in this step are usually seen in the color or seal steps. 2. Uneven Coating Worn out cathodes Too quick of a ramp. Anode to cathode ratio off. Too much load for tank. Bad part distribution on the rack.

28 Anodizing Problems in this step are usually seen in the color or seal steps. 3. Pitting Contamination of solution, chlorides, nitrates or sodium.

29 Anodizing Problems in this step are usually seen in the color or seal steps. 4. Soft Coating Low current density. Temperature too high. No additives to protect coating.

30 Coloring Coloring is created by depositing material or dyes in the pores of the anodic coating or by dispersing particles in the coating. There are 3 basic methods used for anodized aluminum. 1. Electrolytic coloring 2. Organic or inorganic dyes 3. Integral

31 Electrolytic Coloring In this process, parts are immersed containing a metal salt such as tin. AC power is supplied and the metal is deposited at the bottom of the pore.

32 The Electrolytic Cell Counterelectrode Positive/Negative (+/-) Anodized Aluminum work piece with anodic coating. Power Supply Alternating Current or Modified AC. Negative/Positive (+-) Counterelectrode Positive/Negative (+/-) Stannous Sulfate + Acid Electrolyte

33 Electrolytic coloring is accomplished by the electrical disposition of metallic particles near the base of the anodic pores. AC power is used to deposit metal at the bottom of the pore. Electrolytic Coloring

34 Electrolytic Coloring The depth of the metal deposit within the pores determines the color of the film that ranges from Champagne through various Bronzes to Black.

35 Electrolytic Coloring Various metals can be used such as:

36 Electrolytic Coloring The thickness and pore structure of the anodized film regulates the coloring rate and distribution. If the anodic film is not produced properly, color uniformity and color ability will be compromised.

37 Electrolytic Coloring Most problems arise from improper anodizing, although problems can occur from the coloring system itself. These problems are usually controlled by keeping bath chemistry constant. Coloring additives and sulfuric acid concentrations must be maintained, the temperature can not fluctuate and electrical power must be programmed correctly.

38 Electrolytic Coloring Problems Extrusions Not Colored Bad Contacts Broken Contacts Dark Ends Uneven Coating Wrong voltage on coloring power Wrong program on coloring power Non-uniform Color Across Extrusions Wrong ramp Chemistry of bath incorrect Uneven coating Color Wrong Shade Temperature of bath is wrong Time

39 Dyeing The pores of the anodic film produce a capillary action and will absorb easily. This property allows the use of organic or inorganic dyes to color anodized aluminum. Inorganic Dying Organic Dying

40 Dyeing Most dyes are designed so that dyeing is done by saturation of the pore to get the proper color and stability. To achieve this, temperature, ph, concentration and time must be controlled. Inorganic Dying Organic Dying

41 Dyeing Dyes need a certain depth of the pore to achieve the colors, which makes the anodizing step critical. Uniformity of thickness and pore structure is very important for uniform results.

42 Organic & Inorganic Dyes The inorganic dye (FAO or FSO) or the organic dye will absorb into the pores of the anodic coating. Inorganic Dying Organic Dying

43 Non-Uniform Color Uneven anodic film ph of rinse too low Dye ph wrong Dye activity too high White spots of surface Pits Holding sulfuric acid from anodize Poor rinsing Airborne contaminants Color not dark enough Film thickness too thin Rate of Dye off Concetration wrong; ph off Dye bath is old with aluminum build up Dyeing Problems

44 Electrolytic Coloring combined with Dyeing By combining Electrolytic Coloring and Dyeing, you have more color options. Dye Electrolytic Deposit

45 Integral Color Anodizing An Organic Acid such as Sulfophthalic Acid, is used in anodizing to produce anodic coating. The color results from insoluble particles within the anodic pores. A color range from light bronzes to black can be obtained. The depth of color is dependent on the thickness of the anodic coating and bath conditions.

46 Integral Color Anodizing This process makes use of the intermetallics (alloying material) in the metal to give color. As the anodic film is grown, particles are exuded into the film and color is dependent on the thickness. The process is usually done under cold conditions and high power. The alloy and temper play a major role in color uniformity and thickness determines color depth. Because of the cost, only 5 systems remain in the US. The main products are handrails and push plates where heavy wear occurs.

47 Sealing of Anodic Coatings Sealing of anodized aluminum changes the anodic coating to make it: Non-Staining Non-Absorbing Non-Reacting Non-Corroding Sealing can be accomplished by: Physically plugging with oils, waxes, paints or aqueous sealing chemicals Chemical change of the oxide layer through hydration Combining both using metal-based sealing salts

48 Sealing of Anodic Coatings This is the final step in the process. A good rinse prior to the sealing step will reduce contamination and allow the pore to be closed. Here are the 3 most common methods of sealing the anodic film: 1. Hydrothermic Sealing Hot 210 Deg. F Emersion in hot water with a ph of Film hydrothermically sealed converting the AL 2 O 3 to AL 2 O 3 *H 2 O Larger hydrated molecules fills the pores and seals it.

49 Sealing of Anodic Coatings 2. Nickel Acetate Low Temp Hot Deg. F Nickel co-precipitates into pores accelerating the hydrothermic sealing. 3. Cold Sealing Deg. F Nickel, the accelerator and the aluminum react to form a compound that plugs the pores.

50 Sealing of Anodic Coatings It is critical to manage the seal bath. Time, temperature, concentration and ph have dramatic impact on the finished seal properties. Improper seals lead to smut or a non-sealed part.

51 Sealing of Anodic Coatings Smut was once a necessary evil. Quality standards and increased production rates require no smut. Seal baths must be maintained to control the process. Use as recommended with regular dumping and recharging.

52 Sealing of Anodic Coatings White powder (Yellow tint) Electrolytic color dirty White powder (Greenish tint) Nickel seal Rinse after nickel seal dirty ph too high on Nickel seal Foam on seal tank Iridescent easily wiped off. Desmut tank not working Iridescent hard to wipe Off Too long of seal time Too soft coating Too low ph, rinse before seal Eliminate problems with the proper processing steps 1. Proper racking 2. Good chemical management of the baths 3. Good rinsing 4. Proper drainage of parts 5. Understand the function of each bath

53 Sealing

54 Anodizing Line Safety It is everyone s responsibility to see that the anodizing line runs safely. The 3 areas of concern:

55 Anodizing Line Safety 1. Employee Training 2. Safe design of facilities and equipment 3. Adequate safety equipment readily available

56 Anodizing Line Safety Employee Safety and Training Safety consciousness is mandatory for anyone working around an anodizing line. You must be aware of the potential risks and be able to react in case of an emergency. The employer must ensure that the equipment is appropriate for the job, is within easy access and that training is provided for new employees and refresher courses for existing employees. Management should assign a safety person who will be responsible for maintenance, supplies and monitoring the day to day operations. Equipment should be inventoried and readily available. One tool is a checklist. This outlines all of the checks needed as well as the time and the person conducting the activity. Studies show that 7 areas result in 80% of the reported citations.

57 Anodizing Line Safety 1. General Housekeeping 17% of citations. Blocked doors, improper storage and clutter, improper posting of signs and exits. 2. Mechanical Guards 16% of citations. Lack of adequate guards and shields around abrasive wheels, exhaust fans, belts and pulleys. 3. Electrical Problems 14% of citations. Improper grounding and potential exposure to live current. 4. Safety Equipment 12% of citations. Lack of adequate eye wash and safety showers, along with worker failure to wear personal protective gear. 5. Railings and Platforms 8% of citations. Slippery platforms and inadequate or missing safety rails. 6. Signs and Labeling 6% of citations. Failure to identify hazards, particularly open tanks. 7. Others 6% of citations. Availability of fire extinguishers and lack of poor ventilation.

58 Anodizing Line Safety Principles 1. Safety is first 2. Understand the risks 3. Provide Safeguards 4. Train for Action Laws and Guidelines Ontario Occupational Health & Safety Act and Regulations for Industrial Establisments OSHA Regulations 29CFR and 29 CFR

59 Anodizing Line Safety 1. Understanding the risks 2. Hazard Characteristics 1. Toxicity 2. Corrosivity 3. Flammability 4. Spontaneous combustion 5. Explosivity 6. Reactivity 3. Information Sources 1. MSDS s 2. Container labels 3. Process tank labels 4. Chemical Manufacturers 5. Plant Management

60 Anodizing Line Safety Wear Protective Clothing Goggles, face shields, rubber gloves, aprons, rubber boots and a respirator as required.

61 Anodizing Line Safety Store Chemicals Safely Avoid high traffic areas Allow for good ventilation Identify Risks with placards

62 Anodizing Line Safety Adopt Safety Habits 1. Never eat, smoke, drink or wear contacts in chemical environments 2. Know where the nearest safety shower, eye wash and emergency equipment is located. 3. Wear personal protective equipment 4. Avoid breathing fumes

63 Anodizing Line Safety Emergency Procedures 1. Eye contact: Flush immediately with water for minutes. Take other follow-up care as required by MSDS. 2. Skin contact: Flush with water for minutes. Seek additional care as required by the MSDS. 3. Inhalation: Leave area immediately and seek treatment as required by MSDS. 4. Ingestion: Contact medical personnel immediately with MSDS information.