Ask the Expert Question-and-Answer Archive

by Ron Joseph

June, 2005

Glare of Sunlight from Aluminum Tubing

Q. I am constructing a large beam antenna made of aluminum tubing of various diameters. The antenna will weigh about 100 lbs. and will be mounted on a tower, exposed to the weather at all times. To reduce the glare from sunlight, I would like to apply a flat black enamel or latex paint to the tubing. The aluminum is newly manufactured 6061ST. I understand that a conversion coat of some kind will be necessary. I don't wish to reduce the yield strength of the aluminum. Perhaps there may be other means to reduce the glare such as glass bead abrasion?

A. Glass bead abrasion might work well and provide physical adhesion to the black enamel or latex. However, with a conversion coating you get both physical and chemical adhesion. The success of your paint job will to some extent also depend on weather conditions. If the antenna will be subject to corrosive elements, such as high humidity, marine environments, etc., the conversion coating will provide considerably more corrosion protection than the bead blasting.

I understand why you are reluctant to subject the tubing to the acidic solution of the conversion coating; therefore, you might need to conduct stress tests to determine if the pretreated aluminum is affected by the process. Metallurgical labs can perform such tests with ease.

I guess you can see from my answer that I would lean toward the conversion coating process.

Best wishes,

Ron Joseph

Q2. Thank you. Perhaps a conductive Alonine (iradite) process in a 'dull' gold as in old mil-spec hardware would be all that I would need. It may be dull enough.

A2. You might also consider applying Alodine (or Iridite, Chemfilm) and follow with a dull black powder coating. A powder coating job shop will be able to do the work for you.