The anodizing process - page 1
AS/NZS ISO 9001:2000 Certified
If you are interested in wanting to know the basics about the anodizing process ... please read on.
WHAT IS ANODIZING?
Anodizing successfully combines science with nature to create one of nature's best metal finishes.
It is an electrochemical process that thickens and toughens the naturally occurring protective oxide. The resulting finish, depending on the process, is the second hardest substance known to man, second only to diamond. The anodic coating is part of the metal, but has a porous structure which allows secondary infusions, (ie organic and inorganic colouring, lubricity aids, etc.).
ANODIZING DEFINITIONS AND METHODS
While the chemical anodizing process remains the same for all applications, the mechanical methods vary according to the two physical types and shapes of metals used.
Batch Anodizing involves racking parts and immersing them in a series of treatment tanks. Extrusions, sheets or bent parts, castings, cookware, cosmetic cases, flashlight bodies and machined aluminium parts are just a few of the items that are batch anodised.
The appearance can be inproved through special pre-treatment procedures, this makes the aluminium look like pewter or stainless steel.
The surface of the aluminium itself is toughened and hardened to a degree unmatched by any other process or material. The coating is 30% thicker than the metal it replaces, since the volume of oxide produced is greater than that of the metal replaced. The resulting anodic coating is porous, allowing relatively easy colouring and sealing.
Hard Anodizing is a term used to describe the production of anodic coatings with film hardness or abrasion as their main characteristic. They are usually thick by normal anodizing standards (greater than 25 microns) and they are produced using special anodizing conditions (very low temperature, high current density, special electrolytes). They find application in the engineering industry for components which require a very wear resistant surface such as pistons, cylinders and hydraulic gear. They are often left unsealed, but may be impregnated
with materials such as waxes or silicone fluids to give particular surface properties.