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2008 Anodizing Conference Abstracts
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Abstracts
Abstracts for the 2008 Anodizing Conference are organized by General Sessions and the following Focus Sessions: Practical, Technical, Academic.

General Sessions

Purification and Recovery of Anodizing Baths and Bright Dip Rinse Water
Paul Pajunen, P.Eng.; Eco-Tec Inc.

Metal finishing processes such as anodizing involve operations in which metals are dissolved by acids. Process acids are considered spent and need to be discarded even though they still contain unused free acid. The recent punishing and dramatic increases in sulfuric acid and phosphoric acid prices have prompted many anodizers to investigate the implementation of acid recovery and purification techniques. A well-established method of anodizing bath purification employs a process called resin sorption. Not only is sulfuric acid cost reduced, but other benefits include a predictable, consistent bath operation resulting in improved product quality and productivity enhancements. This presentation will review the resign sorption process, outline critical design features and parameters, and provide field performance data and operating experiences of resin sorption installations for sulfuric acid anodizing purification and phosphoric acid.


Trivalent Chromium Seals for Anodic Coatings
Danielle Rosenquist, Director of Product Development; METALAST International, LLC

As the demand for higher efficiency and more environmentally friendly chemicals increases in the anodizing industry, research facilities and private industry alike have looked into new alternatives for current anodic seal techniques. Hexavalent chromium in the form of dichromate is one of the most widely used seal components in the industry and also one of the most carcinogenic. European Directives such as ROHS, WEE, and ELV, which ban the use of chromium in many applications including anodic sealing, have already been implemented in Europe. The trend is quickly spreading to the United States where job shops are already experiencing a demand from their customers for hex-free products. This paper is meant to communicate the known and projected strengths and weaknesses for using trivalent chromium products as an alternative for dichromate and other hexavalent chromium based seals.


Improving Anodize Wear and Corrosion Resistance by Combining Modified Electrolyte Chemistry with Advanced Waveform Pulse Ramp Technology
Fred C. Schaedel; Anodic Tech Services - (ATS), Alpha Process Systems - (APS)

The latest developments in Process Tank Modified Chemistry which promote the formation of harder more wear resistant anodic coatings with enhanced corrosion resistance will be presented. Advanced Electrical Waveforms and Electrochemical Pulse-Step-Ramp Technology which has been proven in production on commercial, military, and aerospace applications will be discussed, including Data Logger Graphs covering most Aluminum Alloys.


A Comparison of Etching Processes: Alkaline, Mechanical, and Acid Etching of Aluminum
Wayne Chandler, SIC Technologies

Alkaline etching of aluminum has been the traditional method of surface preparation for anodizing, used to produce a pleasing matte appearance on aluminum parts. With the price of caustic rising, with landfill space diminishing, and with aluminum extruders competing internationally for business, interest in acid etching as a method of producing a matte appearance has risen. This talk presents comparisons of the appearances and various physical properties of the matte surfaces produced on aluminum using mechanical blasting, acidic, and alkaline chemical solutions.


Interfacial Phenomena and Anodizing: Ramifications and Process Solutions
Jude M. Runge, Ph.D.; CompCote International, Inc

Why do some alloys anodize easier than others? Why do some components manufactured from the same alloy, through the same anodizing process, on the same rack, sometimes at the same time, exhibit different finish appearances, and sometimes different finish performance? This paper offers some answers to these questions by discussing the impact of various phenomena at the aluminum–electrolyte interface and some process solutions to yield acceptable finishes with even the most difficult alloys.


Political Prognostications and Regulatory Roundup
Charles T. Simmons; Thompson & Simmons, PLLC

November 4, 2008, is “E-Day,” which promises to be as momentous as that other famous letter day of American history. The outcome could decisively set the course for U.S. legislative, regulatory, environmental, energy, economic, and social policies at home and internationally. Voter discontent is usually outcome-determinative, and the build-up to E-Day has shown many sources and reasons for bitterness. In addition to putting the opposing Democrat/Republican parties’ energy and environmental regulatory policies in perspective and present an impartial analysis of what could be expected under an Obama or McCain administration, this presentation will address several important regulatory initiatives that are expected to come to the fore during the next administration. Chief among them is the EPA’s regulation of greenhouse gases under the Clean Air Act. Time permitting, the basics and deadlines for the European Registration, Evaluation, and Authorization of Chemicals (REACH) regulation will be reviewed, along with an overview of the upcoming Globally Harmonized System (GHS) of hazard communication.


Focus Session 1: Practical

Identity Crisis: Job Shop or Captive Shop
Rick Rosenfield (Tom Michel presenting), Douglas Alexandria Finishing

Identifying important aspects of job and captive shop requirements are identified in this presentation. How does a dual shop (some captive, some job shop) operate in a very complex environment? Who are your customers? Who has what priority? Do you invest in new equipment for job shop increase? How do you stay sane in the predicament?


Is Tradition Costing You Customers and Higher Rejects?
Charles Schultz, Vice President Sales & Marketing, Serfilco, Ltd.

Major advances in the way anodizing solutions can be filtered, purified, and agitated will be reviewed. Special attention will be given to cartridge filtration systems, advanced methods of solution purification, and pumped eductor agitation systems.

An overview of automatic filtration systems, enhanced by pumped eductor agitation, including detail on sizing appropriate systems and a review of various case histories, together with a comparison between batch and continuous purification of rinse and the seal process will make the case for breaking with tradition in order to reduce operation costs, improve process control and reduce rejects.


Quality Control in Anodizing from the Architectural Perspective
Srimay Basu, Dubai Aluminium Company, Ltd.

Anodizing has always been recognized as an important medium for enhancing the durability of aluminum. For decades, anodizing has been the architectural finish of choice because of its outstanding complement to aluminum as a lightweight and attractive manufacturing component. In light of recent efforts toward continuous improvement, it would appear that the use of anodized aluminum may be in decline. Perhaps decision-makers in the architectural fields are trying to avoid the risk of color variation, inability to offer various colors, or inconsistent quality. This paper addresses some of the many factors that come together to yield consistent quality in anodizing.


Focus Session 2: Technical

Racking Concepts & Computerized Surface Area Calculation of Load
Leonid Lerner, Sanford Process Corporation

The resistance of a piece of wire (aluminum or titanium racks) depends on its length, and its cross-sectional area or thickness. The longer the wire is, the greater its resistance. If one wire is twice as long as a wire of identical diameter and material, the longer wire offers twice as much resistance as the shorter one. A thicker wire, however, has less resistance, because a thick wire offers more room for an electric current to pass through than a thin wire does. The Sanford Surface Area Calculator will calculate the surface area of one particular part in metric and non-metric systems. Review of existing Surface Area software will also be discussed.


Automatic Racking
Petter Isakson, Ahlins i Habo AB

Labor-intensive racking methods can add significantly to the cost of production. Traditional efforts toward automating the process have relied on consistent production orders with substantial quantities of uniform parts per year. Job shop customers may be reluctant to invest in solutions perceived to be costly, or to commit to long-term contracts that enable an anodizer to invest in automation. This presentation describes an alternative that makes automation flexible, without requiring special tools, feeders, racks or the like. The solution presented in this case study includes a pallet tipper, transport belts, two industrial six-axis robots, and a vision system to identify parts. The cell uses two types of rack to produce more than 200 vastly different parts, including extrusions, sheet, and cast aluminum.


A Parametric Study of PTFE Coating Process in Anodizing Aluminum
Mike Sung, Ph. D., Sanford Process Corporation

A study using an experimental design of PTFE coating process is presented. The effects of four major process parameters of the coating process, i.e. polymer concentration, immersion coating time, air spray, and water rinsing time on residue defect, coating weight, and Taber abrasion test were investigated. The study was conducted starting with two level factorial experiments to identify the most significant parameters in the PTFE coating process, and concluding with response surface methodologies to establish and optimum operating condition for the PTFE coating of anodized aluminum. It was observed that coating immersion time and rinsing water time were identified to be the key parameters, an operation process condition for the coating that provided elimination of residue defects and satisfactory Taber abrasion test was determined to be an immersion time of 2 minutes with flowing water rinse time of 1 minute.


Focus Session 3: Academic

Effect of Extrusion Microstructure on Formation of Streaking Defects on the Surface of Anodized Aluminum Extrusions
Hanliang Zhu and Arne K.Dahle, ARC CoE for Design in Light Metals, Materials Engineering, University of Queensland, Brisbane, Australia; Xinquan Zhang and Malcolm J. Couper, Rio Tinto Alcan Technology, Thomastown, Australia

Surface appearance is an important characteristic of high quality aluminum components for the automobile and construction industries. Surface defects, such as streaking, are often present on anodized extrusions of 6xxx-series alloys, increasing the fabrication cost of these products. Moreover, streaking often becomes visible only after etching and anodizing treatments, rather than in the as-extruded condition, making it difficult to identify the original causes of these defects.

During anodizing, a transparent oxide layer is formed on the metal surface; this metal/oxide interface is the prevailing surface for reflecting light. Any surface imperfections in the metal/oxide interface will increase the diffused part of the reflected light, ultimately resulting in streak defects. Surface imperfections include etching pits, grain boundary grooves and/or grain etching steps; they are created on the extrusion surface as the result of uneven surface microstructuring during etching. Hence, the severity of surface imperfections depends on the surface microstructure of the extrusion. In this study, the effect of microstructure variants such as intermetallic particles, grain size, grain orientation and precipitation on the formation and severity of surface imperfections, as well as the occurrence of streaking defects, are investigated.


A New Phase Space Interpretation of the Formation of Anodic Oxide Films
Digby Macdonald, Penn State University

The phenomenon of passivity is responsible for our ability to employ reactive metals, such as aluminum, in our metals-based civilization and results from the formation of a thin corrosion product on the metal surface that effectively separates the reactive metal from the corrosive environment, thereby inferring kinetic stability on the system. The “passive film” is found to generally comprise a defective oxide (or hydride) barrier layer adjacent to the metal and a precipitated, outer layer that may contain species present in the solution. For many systems (e.g., Ni, Zn, stainless steels, and iron in some environments) passivity is conferred on the system by the barrier layer, and it is these systems that are of primary interest in this paper.

The stability of the barrier layer of a bi-layer passive film that forms on a metal or alloy surface, when in contact with oxidizing aqueous environments, is explored within the framework of the Point Defect Model (PDM) using phase-space analysis (PSA), in which the rate of growth of the barrier layer into the metal, (dL+/dt), and the barrier layer dissolution rate, (dL-/dt), are plotted simultaneously against the barrier layer thickness. A point of intersection of dL-/dt with dL+/dt at positive L indicates the existence of a metastable barrier layer with a steady state thickness greater than zero. If , where the latter quantity is the barrier layer growth rate at zero barrier layer thickness, the barrier layer cannot exist, even as a metastable phase, as the resulting thickness would be negative. Under these conditions, the surface is depassivated and the metal may corrode at a rapid rate. The boundaries for depassivation may be plotted in potential-pH space to develop Kinetic Stability Diagrams (KSDs) as alternatives to the classical Pourbaix diagrams for describing the conditions under which metals or alloys exist in contact with an aqueous environment.


Effect of Microstructure of AlMg0.8Cu and AlMg0.7Si on the Optical Quality of Anodic Film
N. Tabrizian; P. Møller; R. Ambat, H. N. Hansen,
Department of Mechanical Engineering; Technical University of Denmark

During conventional and decorative anodizing of aluminum alloys, self-coloring of the anodized layer is usually a problem, resulting in unwanted color shades or uniform discoloring. To a large extent such coloring is believed to be controlled by the alloy constituents and microstructure of the aluminum substrate; mainly the alloying elements and their chemical stability in the anodizing bath, grain structure, and secondary phases with size varying from nanometers to micrometers. However, very little is known at present about the influence of these factors on the appearance of the resulting anodized layer.

An important aspect is the entrapment of the intermetallic particles of impurity elements in the oxide film in undissolved or partially dissolved state. Presently, the increasing use of recycled aluminium invariably contains higher amounts of impurity elements and intermetallic particles. Therefore, it is important to know the influence of various microstructural features on the appearance of the anodized layer.

In this paper the effect of microstructure of an extruded 6063 alloy on the appearance of the anodized layer is investigated in detail. Microstructural investigation of the substrate using SEM and EDX has been carried out to understand the distribution of intermetallic particles as a function of extruded profile thickness. Morphology of the anodized layer was investigated using Light Optical Microscopy, SEM, EDX, and Glow Discharge Optical Emission Spectroscopy (GDOES).

Color measurements were carried out using CIE Lab. Results show that the coloring of the anodized layer in general is influenced by the alloying elements, the intermetallic particles and their size and distribution, and dissolution behavior in the anodizing electrolyte, which will be the focus of this paper.