finishing.com -- The Home Page of the Finishing Industry

HomeFAQsSuggested
Books
Help
Wanteds
Advertise
on this site
FORUM
current topics
Live! From Pine Beach NJ: The world's most popular metal finishing website, and the internet's friendliest corner

topic 17026

380 Anodize "Smutty" Finish


2002

We anodize a die cast composition 380 part. On occasion the parts have a "smutty" film on them that can be wiped off. We've been told that this condition happens when the silicon content of the 380 is high. Is this accurate? Is there any way to prevent this occurrence outside of changing the material?

Frank Coates
- Naples, Florida


2002

Apparently every 380 recipe is different from caster to caster, also the wall thickness causes a different amount of silicon to be on the surface, thinner areas tend to have more silicon (and other JUNK) than the thick areas.

Never alkali etch a casting, alkali removes aluminum and not silicon, you want to do the opposite. On most heavy wall 380's a simple 50% Nitric Acid with 1 pound per gallon ammonium bifluoride will remove the smut.

Some anodizers down in Florida swear by the Tri-Acid which adds sulfuric acid to the above, however going back to September 1950 I have never seen a casting that was improved by tri-acid versus simple Nitric/F.

In all cases the electrolytic action of the anodizing should pull off the smut and render as good finish as can be formed on the given "380" casting. Try wiping off the smut on one and leaving the smut on another to see if the smut is interfering with the anodic film formation, if not then the problem is the casting and not the smut. We only worry about smut when we are chromating.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como
and co-author of The Sulfamate Nickel How-To Guide


2002

IF You ETCH THE 380 PLEASE FORGET IT THE BEST REMEDY IS MASS FINISHING WHICH REMOVE SCALE AND APPROACH TO A BRIGHT SURFACE.

TO AVOID DESMUT IN ANODIZING You HAVE TO FIND BEST current DENSITY (ALWAYS LOWER THAN ORDINARY CD) AND LOW VOLTAGE.

WORKING WITH FLUORIDE IS DANGEROUS.

HADI KHOSRAVI
- Tehran, Iran



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

ADD a Q, A, or Comment on THIS topic START an UNRELATED topicView CURRENT HOT 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


©1995-2019 finishing.com, Inc., Pine Beach, NJ   -   About finishing.com   -  Privacy Policy
How Google uses data when you visit this site.