What exactly is hardcoat anodizing?

[TestedTwice]

Sorry if this is in the wrong section; I can't find an answer to this by searching. I just get websites that offer to anodize my stuff.

I have a 7075-T6 Eagle Arms/Armalite lower receiver and I'm not sure if it's type-III hardcoat anodized, or just standard anodizing. My question is, what exactly is type-III anodizing for? Does it add actual STRENGTH to the receiver, or is it just to protect the finish a little better?

 

[Nullcone]

You're looking for Type III:

https://en.wikipedia.org/wiki/Anodizing#Sulfuric_acid_anodizing_.28Type_II_.26_III.29

Anodizing thickness increases wear resistance, corrosion resistance, ability to retain lubricants and PTFE coatings, and electrical and thermal insulation.

The article explains things pretty well.

 

[Arizona_Mike]

You are only going to find type 3 on receivers. Type 2 will not hold enough dye to be completely opaque.

 

[oldandslow]

tt,

Probably the best and most simple explanation on hard coat anodizing can be found at the Caswell Plating site, www.caswellplating.com. Look up their Metal Finishing Forum section and then the Anodizing Forum sticky on Hardcoat Anodizing. When I first started anodizing it was a big help.

A short summary is that Type 3 is thicker than other types and done by passing higher voltages through a sulpheric acid solution at temps about 32 degrees (F). Type 2, which can be successfully done by the home user, is easier and done with lower voltages and higher temps (68-72 degrees F). It also takes colored dyes easier than type 3 and the thickness is less than the 0.001plus inches of type 3.

The prep work before anodizing is very important or your finished product will be flawed. I usually bead blast my parts then run it through several types of cleaning soltions and etch with a sodium hydroxide bath before my item goes in the sulpheric acid anodizing tank. Good luck.

best wishes-oldandslow

 

[Steel Horse Rider]

O&S: Thanks for your simplified explanation of the anodizing process. When Burris made their scopes here in Colorado I serviced the chiller for the acid tanks at Berthoud Anodizing who anodized all of Burris scope tubes. I always wondered actually how the process worked but never had the time to ask them about how the process worked. That and the fact that the room where the acid tanks were located was not exactly a comfortable setting.