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Aluminum Anodizing

VALIDATED Aluminum Anodizing for the Medical Industry
The Electrolizing Corporation of Ohio provides the safest non-burning hard anodizing process for hardcoating aluminum. Our aluminum anodizing produces superior wear and abrasion resistance, compared to conventional hardcoat, and it is available in several different colors. Unlike plating, which is 100% buildup, ECO's aluminum anodizing is 50% penetration and 50% buildup.
Aluminum Anodizing - Available in Colors

  MIL-A-8625 Type II & III
  ASTM B-580
  AMS 2469
  AMS 2471
  AMS 2472

Typical applications of aluminum anodizing include:
• Surgical Cases & Trays • Surgical Instrument Handles • Dental Components • Jet engine control valves, pistons and gears
• Race housings for bearings • Screw threads for hydraulic jacks • Aircraft landing gear components • Spraying systems & equipment
• Marine and architectural hardware • Medical handling and processing equipment • Textile machinery • Nuclear equipment
• Food processing & handling equipment

Aluminum Anodizing

Our hard anodizing process is the hardest anodic coating available, with greater abrasion resistance than conventional anodizing. Thicknesses range from .0001 - .003” (.00254 - .0762 mm) on many alloys, and meet abrasion resistance requirements of MIL-A-8625F Type III.

You can color-code parts to simplify assembly procedures and to reduce assembly and installation errors, or to enhance the appearance of trim and decorative hardware.

Aluminum Alloys for Anodizing
Anodizing is recommended for virtually all aluminum alloys. Difficulties can arise if an order of components is manufactured from different alloys, and this is not made known to the anodizer. Each aluminum alloy has a different rate of penetration and buildup. If different alloys are processed together, different thicknesses of oxide are formed on the different alloys. This can result in "out of tolerance" components.


Both Reynolds and Alcoa make high-stability tool plate (wrought and cast, respectively). Maximum practical coating is .0025 - .003” (.0635 - .0762 mm).
Sandcast Alloys. The most commonly used are 155, 156, 319 and 356, with 356-T6 used most often. The maximum practical coating is .003” (.0762 mm). Grinds and polishes very well. The porosity produced by sandcasting can cause pits in the coating, which hard anodizing will not fill.
Die Cast Alloys. The most commonly used are 218, 360, and 380, gray. The maximum practical coating on 218 is .0002” (.00508 mm); for 360 and 380 the maximum practical coating is .001” (.0254 mm). 360 and 380 are not as wear resistant as 218. Only 218 produces a hardcoat comparable to the hardcoat of wrought or cast alloys. The primary elements of die cast alloys 360 and 380 – silicone and copper – are detrimental to hard anodizing.

Important Facts About Aluminum Anodizing
  • Hard anodizing is not plating.
  • Hard anodizing works in two ways; it penetrates the part’s surface and it builds up a layer on the part’s surface.
  • The depth of penetration and amount of buildup are approximately equal, but can vary according to the aluminum alloy. The term “thickness” includes both the amount of penetration and the amount of buildup.
  • Hard anodizing a shaft .002” (.0508 mm) thick will increase the diameter of the shaft by .002” (.0508 mm). Plating the same shaft .002” (.0508 mm) thick would increase the diameter by .004” (.1016 mm), since plating is 100% buildup.
  • Before machining components, be sure to allow for the hard anodizing buildup, not a plating buildup.When you specify hard anodizing, use the term “buildup per surface” to make clear what you are requesting.
  • Exacting dimensions can be maintained with hard anodizing. Standard commercial tolerance is± .0002” (.00508 mm) on a coating thickness of .002” (.0508 mm).
  • The formula for cutting a V thread prior to anodizing aluminum is buildup per surface multiplied by 4. This will equal the pitch diameter (PD) change. A typical example: desired PD = .4050/.4091 (7/16 NF internal thread) and coating thickness of .0018 - .0022 (.0009 - .0011 buildup per surface). Maximum PD change will be .0011x 4 = .0044. Minimum PD change will be .0009 x 4 = .0036. Therefore you should machine the pitch diameter to .4094/.4127 to allow for the anodize buildup.
Hard Anodizing Wear Cycles
  • Allowing a tolerance on hard anodizing buildup means that that you must machine closer than blueprint dimensions. For example: if a shaft diameter is to be finished at 1.5 ± .001” (38.1 ± .0254 mm), and hard anodized .002 ± .0002” (.0508 ± .00508 mm) thick, .001 ± .0001” (.0254 ± .00254 mm) buildup per surface. Your blueprint should specify “machine to 1.498 ± .0008” (38.05 ± .02032 mm)” to achieve final finish at 1.5”(38.1 mm).
Ordering Aluminum Anodizing
Four kinds of information are crucial to processing your order accurately and quickly:
• Alloy • Buildup per surface • Masking requirements • Racking instructions
Hard anodizing can be applied to virtually any aluminum alloy. However, each alloy is different, so it is imperative that the alloy be properly designated on the drawing or purchase order.
Buildup Per Surface
Like other coatings, hardcoat will change the dimensions of the basic component. Unlike other coatings, however, half of the hardcoat is buildup and half is penetration. On your blueprints and purchase orders, be sure to allow for hard anodizing buildup, not plating buildup.
Racking - Aluminum Anodizing
It may be necessary to mask the coating from being applied to threaded or bored holes, ground points, mating surfaces and other areas. Areas to be masked must be clearly specified on the blueprint or purchase order. Because of the cost involved in this hand operation, it is usually more expensive to tap holes to a standard size and mask them rather than use oversized taps to compensate for hardcoat buildup. In most cases, it will be less expensive to coat the entire component, even if coating is required on only one area.
Proper racking is essential. Each component must be racked to maintain firm electrical and mechanical contact during the hard anodizing process. Since each rack contact point leaves a small void in the coating, it is important for the contact to be made in a non-critical area. Your suggestions on rack placement will facilitate processing.