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Etching Free Caustic Soda Limits

We want to do a project on the reduction of the usage of caustic soda [affil links] in the Anodising Plant. The current limit of free caustic soda we are using in the etching tank is 60g/l-80g/l. Can we reduce it to 40g/l-60g/l. Is it practically possible or is it going to affect the texture of the aluminium surface.

Mobius Shumba
Quality Assurance Officer - Harare, Zimbabwe
2007

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First of two simultaneous responses -- 2007

Reduction of free caustic soda concentration at the same temperature will reduce the speed of the etch. In theory, you can obtain the same etch with either, but it will take longer for the more dilute solution. In the real world, the etch is not absolutely identical depending on numerous factors, but probably will be close.
In the theoretical world, it will take the exact same amount of caustic for a given amount of etch. In the real world, the more dilute solution does not drag out as much caustic, so you will see some reduction in use.
In the real world, you need to do some testing, in the lab, to find an optimum concentration and then try it on the line. Time is money as well as material is money, so you will be doing a minimal cost benefit calculation.

James Watts
- Navarre, Florida

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Second of two simultaneous responses --

I would much prefer 40 grams per liter. 40 grams per liter will work fine, you will not see a difference, you will save on drag-out, you can transfer with less streaking, but you may have to increase time of immersion 20% to 40%.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2007