Table of Contents
- Anodizing I &II &III
- Processing
- Benefits
- Application
Type
Aluminum anodizing is typically referred to by its three types.
- Type I
is chromic acid anodize which is very thin.
- Type II
is the conventional sulfuric acid anodize which can be decoratively dyed nearly any color.
- Type III
hardcoat anodize, is done under more exacting process conditions resulting in a harder, denser, thicker, and more abrasion resistant coating. Hardcoat thicknesses can vary from 0.0005 to 0.0030”, but is dependent on the specific alloy being anodized.
Processing
HARDCOAT TYPE II
Under normal circumstances, the aluminum is anodized using a prescribed set of parameters:typically, Type II anodizing is performed in a sulfuric acid bath containing 180-200 grams per Liter of acid and a small amount of dissolved aluminum. The operating temperature is controlled between 68-72º F. Current densities can range from 5-18 amps per square foot (ASF), but commonly are run at 12-15 ASF.
The power supply is a DC rectifier. The aluminum part being anodized is made the anode (or positive pole) in the system. The most efficient cathodes (or negative pole) are 6063t6 aluminum.
Current is applied to the system for a prescribed time, and at the desired current density to achieve the oxide thickness required (oxide thicknesses can range from 0.1 mil to 0.8 mil). The resulting porous oxide can then be colored or sealed.
HARDCOAT TYPE III
Type III (Hardcoat) anodizing differs from the typical Type II room temperature anodizing in a number of ways:
The anodizing bath parameters for Type III (hardcoat) anodizing are similar to type II (room temperature) anodizing in that the acid and aluminum concentrations can be virtually the same. The difference becomes apparent when you consider the other operating parameters.
Type III anodizing is performed in a sulfuric acid bath containing 180-200 grams per Liter of acid and a small amount of dissolved aluminum. The operating temperature is controlled between 28-32º F but in some instances an acceptable oxide can be achieved at slightly higher temperatures. Current densities can range per square foot (ASF), but commonly are run at 24-30 ASF. from 24-40 amps
The power supply is a DC rectifier. The aluminum part being anodized is made the anode (or positive pole) in the system. The most efficient cathodes (or negative pole) are 6063t6 aluminum.
Current is applied to the system for a prescribed time, and at the desired current density to achieve the oxide thickness required (oxide thicknesses can range from 0.7 mil to 3.0 mils). The resulting porous oxide can then be colored or sealed but limitations on final color will determined by the oxide produced and color used.
Benefits
PERFORMANCE BENEFITS OF ANODIZING WITH HARDCOAT TYPE III
- Increased abrasion resistance
- Increased wear resistance
- Increased corrosion resistance
- Improved aesthetics (see Appearance below)
- Dielectric properties/coating is an electrical insulator
- Improved lubrication
- Readily sterilized, non-contaminating for medical instrumentation
Application
COMMON APPLICATIONS THAT ARE HARDCOAT TYPE III ANODIZED
- Aerospace: wear resistance, dry lubrication, longevity & electrical insulation
- Firearms: corrosion and wear resistance
- Machinery: abrasion resistance for high-speed machine parts
- Electronics: uniform emissivity & a high dielectric
- Oil & Gas: corrosion protection & wear resistance.
- Cookware: corrosion protection & non-stick properties
- Molds & Dies: improved release properties & abrasion resistance
- Sporting Goods: improved durability & performance