Metal finishing Q&As since 1989
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Black anodize Color Fading Problem
Q. I have black anodized tire valve caps that are being produced. These valve caps are quickly fading to a bronze/gold type color in less than four months. The problem seems to occur in both hot and cold climates. The internet research that I have done seams to point to U.V. exposure and perhaps an improper sealing technique. I have two questions.
1. What do you think would be the most suitable sealing technique keeping in mind the harsh salt/road film environment that a tire valve cap endures?
2. What parameters should be set for U.V. testing and what exposure times would predict the sealing efficacy?
Thank you in advance for your help.
Sacha
product designer - Canada
July 23, 2009
First of two simultaneous responses --
A. You left out a critical factor--the UV stability of the dye. Till you use the best performing dye, the rest is a mute point. Nickel or cobalt salt based seals have been a fairly accepted standard for a quality seal.
I am not aware of a universally accepted fade test, but there must be some out there. I will guess that it uses a specific amount of light, probably from a xenon lamp of a given size (and distance).
- Navarre, Florida
July 24, 2009
Second of two simultaneous responses --
A. Aluminum is no place for a valve cap. (1) All organic dyes fade in the sunlight. (2)Salt (sodium chloride) attacks aluminum, and aluminum oxide, and hydrated ("sealed") aluminum oxide. (3) Job shops notoriously neglect quality control on the seal tank which is the weakest and therefore easiest to contaminate solution in the house. Get a copy of ASTM B136 (or use the seal test in my book) and test for sealing before you ship.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
July 24, 2009
A. Yes a good nickel seal is necessary. However, using a good HBL dye should also do the trick
Steve Tanner- Garland, Texas
August 12, 2009
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