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"Lifetime of Chemicals in Aluminum Anodizing"

June 12, 2019

Q. Hello all,
I am an Intern at my company and my team and I are tasked with developing an anodizing system suitable for our company. We do our own metal work and have been having problems with quality and lead times from our local Job Shops. We do not produce a huge amount of metal to be anodized (about 60 sq-ft/month), however we feel that it will still be worth while for us to anodize ourselves. We plan on doing only Type II clear and a few black coatings at about 0.4-0.6 mils thick. We will be anodizing 6061 and 5052 alloys.

We have purchased the "Aluminum How To" Book and I have essentially read the entire thing cover to cover.

The setup that we are looking at right now is 20 gallon tanks (That is the liquid volume we are planning, actual tank size is 24 gallons.) I just still had a few more specific questions:

1. With running approx 60 sq-ft/month, how often would our anodizing solution need to be decanted and refreshed? (We are trying to get an idea of monthly run costs, I know that titration is the empirical way to determine this).

2. If we aren't going to be running full time, will we need to worry about degradation of chemicals while we are not using them? Will any of the tanks have a problem sitting for a week or two unused? (We would pull out all cathodes, heaters and other components that could be problematic).

Thanks for the help!

Jake O'Bryan
Manufacturing Engineering Intern - Kansas City, Missouri

June 18, 2019

A. Hi Jake,
1) You only decant when the aluminum content goes too high. By 'refreshed' if you mean 'replenished', you simply titrate the solution to determine whether you need to top it up with fresh Sulfuric.
2) The tank is fine to sit around idle for weeks on end. It's a good idea to cover it when not in active use just to prevent contamination, or absorption of atmospheric water if it's humid out.

Rachel Mackintosh
Plating Solutions Control Specialist /
Industrial Waste Water Treatment - Brattleboro, Vermont


June 19, 2019

A. With that little production the anodizing tank will require maintenance maybe every 6 months, or even longer

I suspect seal tank will require more attention, my personal experience with couple types of nickel acetate hot seals is that the anti smut additive can last from 1-3 months, depending on the amount of work, as I understand, the anti smut additive deteriorates over time even when sitting idle.

use reasonable tight covers for all tanks when they are not in use to limit evaporation and CO absorption

if (and you should) use a heat exchanger in the acid tank to control the temperature, you can easily process that amount of work in couple days, to be honest, the trouble of bringing the process in-house for that little amount of work may not be worth the effort.

Janis Ziemelis
- Riga, Latvia

June 20, 2019

1-Dissolved aluminium value in anodizing tank should be 5-15 gr/lt. So if this value exceeded up to 15 gr/lt, you can decant the anodizing tank. Number of decant issues depend your production's density. You can analyse your anodizing tank daily and you can follow process with this way...
2-Anodizing baths can stay for weeks as idle position...there won't be any harmful effect by itself, but you must focus on etching bath. If your etching bath stays under 100 °F for days then probably you will see black etching bath convert to brown etching bath; moreover,aluminium hydroxide will be precipitated under the tank. Keep temperature of etching bath up to 100 °F when idle times of etching bath.
Good Luck,

alaattin tuna
- TURKEY, sakarya

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