-- The Home Page of the Finishing Industry
Serious Education & the most FUN
you can have in metal finishing smiley

No popups, spam, registration or passwords
on this site
current topics
topic 6217

Anodising after chromic acid stripping.


On occasion we have to strip off a black dyed, anodised layer,clean the component and anodise and dye again.

We strip off the layer with chromic acid. After this treatment and water washing, the new anodised layer is never as thick or as black as before.

Why is this?

Is it to do with using chromic acid, insufficient washing or to do with the aluminum surface.

Any suggestions gratefully received.

Nick Winstone-Cooper
- Bridgend, South Wales, UK


To answer this question properly, it would help to know the process parameters you are currently employing.

1) Are these wrought products or castings? What alloys?

2) What do you mean when you say the oxide is never as thick as before? Do you mean that for a given voltage (I am assuming you are voltage anodizing these instead of current density anodizing) and process time you do not get the same oxide thickness? Or do you mean that you cannot achieve a given oxide thickness no matter how long you run or how high a voltage you use?

3) What are your anodizing process parameters (times, voltages,temperatures, etc.) What dye do you use and what process parameters do you follow?

4) How thick an oxide do you put on during the initial coating?How thick is the oxide after the second attempt?

Sjon Westre
- Minden, Nevada

If you have a question in mind which seems off topic, please Search the Site

ADD a Comment to THIS thread START a NEW threadView CURRENT TOPICS

Disclaimer: It's not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & Devices

©1995-2018, Inc., Pine Beach, NJ   -   About   -  Privacy Policy
How Google uses data when you visit this site.