ANODIZING FAQs


 
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FREQUENTLY ASKED QUESTIONS ABOUT ANODIZING

WHAT IS ANODIZING?   

Anodizing is a process for finishing aluminum alloys that uses electrolytic oxidation of the aluminum surface to produce a protective oxide coating.  The anodic coating consists of hydrated aluminum oxide and is considered resistant to corrosion and abrasion.  Coatings are 0.1 to 1.0 mil thick and are essentially transparent, although they may be colored.  Unlike most other finishes, anodizing preserves the natural luster, texture, and beauty of the metal itself.  The anodized coating is hard, durable, will never peel, and, under normal conditions, will never wear through.


WHAT IS THE PURPOSE OF ANODIZING?

The purpose of anodizing is to form a layer of aluminum oxide that will protect the aluminum beneath it.  The aluminum oxide layer has much higher corrosion and abrasion resistance than aluminum.  There are some types of anodizing that produce a porous oxide layer that can be colored with organic dyes or metallic pigments giving the aluminum a decorative and protective finish.  In short, the main purposes for anodizing are corrosion resistance, abrasion/wear resistance, and cosmetics.


IS ANODIZING SAFE?

When it comes to coatings, anodizing is a safe and environmentally friendly technology, as clean a process as is available today.  Anodizing is an acceleration of a natural oxidation process.  It does not produce harmful or dangerous by-products, and will not damage human health or the environment.  Other benefits include:

  An anodized finish will not break down or decompose
  The finish is non-toxic
  It is heat-resistant to 1,221°F (the melting point of aluminum)
  Anodizing uses simple water-based chemicals that can be treated easily and that release no harmful by-products
  The liquid by-products can be recycled and returned to the process
  Solid by-products can be separated for other uses such as:  aluminum manufacturing, baking powder, cosmetics, newsprint, and fertilizer
  The primary by-products are harmless -– aluminum hydroxide and aluminum sulfate can be used as filters in the sewage treatment process of municipal sewage treatment plants


HOW DO I DETERMINE THE PROPER ANODIZING FINISH TO USE?

This is determined by the final use of the part and the physical specifications and characteristics needed such as color, hardness, indoor or outdoor use, resistance to high UV levels and fading, and resistance to corrosion.


WHAT ALLOYS ARE RECOMMENDED FOR ANODIZING?

Most aluminum alloys will build aluminum oxide in an anodizing tank, so the answer to this question depends on the anodizing process and the desired result.  Copper containing 2000 series are generally the most difficult to anodize and 5000 or 6000 series are the easiest.


CAN PARTS WITH BRASS OR STEEL HARDWARE BE ANODIZED?

No.  The part being anodized must only be aluminum.  Anything else will be destroyed in the process.


WHAT CASTING ALLOY IS RECOMMENDED FOR ANODIZING?

Castings are challenging to anodize because they are often porous.  The alloy preferred for anodizing castings is 518.  C443 is also good, but it is not inherently corrosion resistant.  These are also the alloys preferred for painting since paint pretreatment will attack a poor casting similar to anodizing chemicals.


WHAT ABOUT WELDING?

Parts can be welded prior to anodizing.  The use of 5356 welded rod is strongly recommended, though some discoloration will still occur.  4043 is the worst choice because it will turn a smutty black when anodized.  Grinding away the weld before anodizing will result in decreased mechanical integrity and will not solve the appearance variation problem.  It is not a good idea to weld after anodizing because most welding processes require electrical conductivity and the anodic coating must be ground away where the weld will be applied.  This also results in an unsightly mess around the welding area.


HOW DO I PREPARE PARTS FOR ANODIZING?

Preparations:

  Anodizing Finish Pre-Treatment
  Clear/Color Coating Store Aluminum Properly
  Aluminum Alloy Fabrication
  Low Heat Welding Dyeing/Coloring

Step-by-Step:  Prepare to Anodize Aluminum Parts

Each anodic coating has unique properties that makes selecting the best choice for your particular needs your first decision.  Once a coating is selected, there are a number of steps you'll need to be aware of before the actual anodizing process is started.  These are the steps to take in order to help you customize the correct anodizing process and obtain the high quality finished product you need:

  1. Decide what pretreatment, if any, you want:  • etch (matte)  • clear anodize (satin)
  2. Specify whether you want the metal left clear or colored.  If colored, provide a sample of the color you want.
  3. Prepare your job.  Proper handling and care is important if you want to get consistent results.  When ordering materials and fabricating your job, please keep the following in mind:
      Store all aluminum in a manner that prevents metal-to-metal contact when moisture is present, whether it is to be anodized or not.  Contact can result in "water etch."  While minor water etch can sometimes be removed, severe water etch will ruin your metal.
      Choose the right alloy.  Some alloys and tempers respond better than others to pretreatment and anodizing.  You should always use the same alloy throughout any one job.  Variations can lead to color differences after anodizing.  Our consultants can advise you as to the proper alloy for your specific application.
      Have all fabrication work (cutting, welding, bending, grinding, buffing, etc.) completed before anodizing.  You will not want to disturb the anodized coating on a fabrication.
      When performing welding operations, use the lowest heat possible for optimal performance.  Excessive heat from welding can affect the properties of nearby metal and lead to irregular discoloration after anodizing.
      Use the proper alloy welding wire to prevent your weld from becoming charcoal gray or black after anodizing.  Your welding supplier can recommend the correct wire.
      Avoid using paints, varnishes, etc. on surfaces to be anodized.
      Avoid applying adhesive tapes.  They often leave glue residues.  We use water-based cleaners that are effective on fabrication oils and buffing compounds but not on materials that require solvents.
      Once fabrication is complete, schedule anodizing as soon as possible.  Aluminum is an active metal and, when unprotected, is subject to damage from fumes, mists, and even oily fingerprints.  The longer it sits out the more pronounced the damage can be.  While the aluminum anodizing process will clean up your metal a bit, it will only do so much.  However, an "etch" pre-treatment will minimize, and even remove, much surface "noise," such as small nicks, scratches, and die lines.


HOW ARE SPECIFIED AREAS OF A PART PROTECTED AGAINST ANODIZING?

Various masking products can be used to protect the areas you don't want anodized.


IS THERE DIMENSIONAL GROWTH DURING ANODIZING?

Yes.  Anodizing is the process of electrochemically converting the surface of an aluminum part to aluminum oxide.  Aluminum oxide occupies about two times the volume as that of raw aluminum.  Therefore anodizing will cause parts to grow dimensionally.  This factor should be taken into consideration when designing parts that will be anodized.  Typical standard clear and color anodizing creates an aluminum oxide film in the range of 0.0002 to 0.0008 inches (0.005 to 0.020 mm) on each surface.  Hard anodizing is typically in the range of 0.0005 to 0.003 inches (0.013 to 0.076 mm) with the most common being 0.002 inches (0.051 mm).  The process of hard anodizing a part to 0.002 inches film thickness will therefore grow 0.001 inch on each surface or 0.002 inches in overall dimension.


WHAT ABOUT RACK MARKS?

Electrical contact must be made to each part that is anodized.  The more electrical current required, the bigger the electrical contact must be.  The size of the contact therefore depends on the anodizing process and the size of the part being anodized.


CAN ANODIZING HIDE SCRATCHES AND DENTS?

The rule of thumb is that if you can feel a scratch by rubbing your fingernail across the surface then you will be able to see the scratch after anodizing.  Any imperfection on the metal (dents or deep scratches) must be corrected prior to anodizing.  It is always helpful for the finisher to understand the application.  It is also good for the finisher and client to agree on a viewing distance.  If a part is to be viewed from 10 feet away, such as a window or roofing component, then the inspection may be relatively insensitive to scratches.  However, if the part is to be viewed from 24" or closer, then even a scratch which you cannot feel may be unacceptable.


HOW LONG DOES ANODIZING TAKE?

It only takes a few hours to process and pack a part.  Most anodizers need anywhere from a few days to a few weeks to plan, process, and invoice for projects.  Lead times of longer than four weeks for anodizing are rare.


HOW DO I CLEAN ANODIZED ALUMINUM?

Cleaning anodized aluminum is easy with the right technique.  Because anodizing is so hard, you want to use an abrasive cleaning technique with a gentle soap.  Do not use harsh acidic or alkaline cleaners because they may destroy the finish.  Use solvents with care as they may stain the finish.  It is best to try a test area first.  One recommended technique is to use an abrasive cleaning sponge with mild dish washing liquid.  Always try a test small area first to prevent a widespread problem.


CAN AN ANODIZED PART BE STRIPPED?

Although stripping is a common practice, and many parts can be re-anodized, there may be concerns associated with the removal of anodic oxide from a part such as a loss in the base material.


WHAT IS HARD COAT ANODIZING?

Hardcoat refers to a very thick and hard anodic coating.  This kind of anodizing is accomplished with a bath similar to the standard sulfuric process, but with the temperature reduced to about 32°F to slow the dissolution rate.  A higher voltage is applied to enable the coating to continue to build after the insulation value of the coating starts slowing down the coating formation.


WHERE ARE ANODIZED PARTS MOST COMMONLY USED?

Because anodizing is such a versatile process, there are thousands of different applications.  A few of these include:

  Appliances Electronics
  Aviation Machinery
  Automotive Lighting
  Food preparation equipment Furniture
  Sporting goods Marine
  Architectural products such as windows and doors

 

Durable Printed Products, Inc. ~ DBA Anodizing Graphics of Texas
819 Success Court ~ Stafford, Texas, 77477
Office 281-499-6640 ~ Toll Free 800-822-8795 ~ Fax 281-261-0524

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