Letter 2107

Hardcoat

--

having,promblem color matching hardcoat.very tight range,for color.must be a medium grey,and,thickness of 0015-0017. current density is used,and we control the time.aare there many factors in the process. time,current density,bath makeup,racking. parts,are approx.1 sq. ft. in area. thank you, stan

stanley vilakis

Stan,

It is a tough job.

What kind of material are the parts you want to anodize? Hard coatings on aluminum alloys usually have intrinsic cplors, so they are generally dyed in black color. If you want a medium grey color, you need a clear hard coating using special process with proprietary additives. Although raising temperature might help a little bit, it will reduce hardness and could cause burning problem, especially for 2000 series and 7000 series.

Ling

Ling Hao
- Grand Rapids, Michigan

The factors you mention are important and along with tank temperature, part temperature, and agitation are all inter-dependent. Note the term part temperature. Agitation must be uniform throughout the tank to maintain the parts at the same temperature. This is especially true if you are using high current density, e. g. 36 asf. Hopefully your ramp up is automatic.

You didn't mention the alloy but there is one factor you may or may not have any control over: alloying elements affect color, and the content of the alloying elements of a particular alloy can vary quite a bit. For example, the silicon content of 6061 is listed as 0.4-0.8%. Silicon is one element responsible for turning hardcoat grey. We could also talk about the importance of consistent temper, but you get the idea.

Those of us who have been involved in color anodizing for many years learned very early to establish not one color standard, but two- an acceptable light and an acceptable dark standard. AAMA has established this as standard practice in their specifications. Considering all the variables you need to control, and the likelihood for color variation, you may need to establish this practice.

Phil Johnson Madison Heights, Michigan