finishing.com -- The Home Page of the Finishing Industry
A website for Serious Education, promoting Aloha,
& the most FUN smiley you can have in metal finishing

HomeFAQsBooksHelpWantedAdvertiseForum
topic 6606

Help with Oxalic Acid and Hard Coating


(2000)

In our Hard Coat anodizing process we have run into an issue with oxalic acid clogging an associated heat exchanger. Our finished product quality has not been effected, only the maintenance of the system.

The bath is approx. 1800 gal solution of oxalic acid and sulfuric acid at 32 degree F. The solution is removed from the tank and pumped to a heat exchanger where the temperature is approximately 24 degree F. The Oxalic acid concentration is specified at 1.9 to 2.1 (right around the saturation point...I have a feeling). About 50% oxalic acid recrystalized during a lab experiment simulating the bath and add conditions. And to add to the story, about 6-8 inches of precipitated oxalic is on the bottom of the tank.

After discussions with the Oxalic representatives, the best answers I have come up with is that we are bouncing on the saturation curve (which I have not seen at 32 degrees)and have supersaturated the bath with Oxalic acid. Consequently, a portion of the oxalic drops out of the added water-oxalic solution (52 degrees F) and an additional amount drops out at the heat exchanger when the temp drops again. This crystal growth provides additional surface area for further growth and eventually clogs the exchanger.

The only solution (no pun intended) that I have developed is to flush the exchanger as a O&M item and look for a substitute for the Oxalic.

Well all that being said...any ideas.

Chris Mullin
- Greater Hartford, Connecticut, USA


(2000)

Put the heat exchanger in the anodizing tank, that should solve the problem(your anodizing tank is probably too small and of insufficient capacity). I mean make the tank bigger and run less parts per load. (Oh sure, if I could do that!)

How many amperes per gallon (of the solution in the anodizing tank) are you running?

pooky
tom pullizi signature
Tom Pullizzi
Falls Township, Pennsylvania

(2000)

Why do you use oxalic acid? at 32 °F

Keith Tranmer
- England



This public forum has 60,000 threads. If you have a question in mind which seems off topic to this thread, you might prefer to Search the Site

ADD a Q or A to THIS thread START a NEW THREADView This Week's 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


©1995-2017 finishing.com     -    Privacy Policy
How Google uses data when you visit this site.