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 2222

Alkaline non-cyanide zinc problem


(1998)

We currently have a problem where we can't achieve a blue finish after passivating. Have tried 3 different passivates (2 hexavalent and 1 trivalent) in last 5 days with no progress whatsoever.The zinc deposit looks OK until it starts to dry when it takes on a hazy, bloomish type of appearance over all current density ranges. Prior to this problem appearing we had plated satisfactorily with our existing passivate for 10 years.

Any ideas ?

Dougie Lightfoot
- Fife, Scotland


(1998)

It is much more difficult to passivate an alkaline non cyanide zinc deposit than a cyanide one. Most suppliers have an additive named conditioner or purifier for the zinc bath. Try to add it to your solution.

Also check your rinses, they have to be much more clean than for a cyanide deposit.

How is your iridescent chromate? Usually the iridescent is less sensitive then the clear chromate.

(I notice that you are from Fife in Scotland and it reminded me of the Macbeth....)

sara michaeli
sara michaeli signature 
Sara Michaeli
chemical process supplier
Tel-Aviv, Israel



(1998)

Dear Dougie ,

Sorry for the long wait for a reply , but you problem could most probably be overcome with a predip before passivating in either

1 ) 5 % Hydrochloric Acid

2 ) 2 % Nitric Acid

remember the Caustic Film of Alkaline non - cyanide Zinc plating solutions is very tenacious , usually effective rinsing after plating can only be achieved in rinses that are violently agitated with air or solution movement then acid dipping prior to chromating

regards
John

John Tenison-Woods
John Tenison - Woods
- Victoria Australia


(1998)

Estimado colega:

Nosotros hemos padecido este problema con el pasivado azul durante varias semanas, pero en los ultimos dias hemos probado el pasivado azul IRIDITE (no recuerdo el n), distribuido por MAC DERMICK (por lo menos en Espana) y los resultados son estupendos muy azules y sin iridiscencias ni amarilleos, pruebalo.


Miguel Angel MartÌn
GHSA - Madrid/Spain


(1999)

Thanks for the suggestions, the problem was eventually traced to a deterioration in the incoming water supply. Calcium and other minerals in the water prevented the chromate in the passivate working. We added Ammonium Bifluoride to the water prior to adding the passivate concentrate passivate and this cured the problem immediately.

We had considered the possibility of poor quality water but had discounted it out of hand as historically the water in this area had always been of very high quality.

A lesson learnt, albeit an expensive one.

Dougie Lightfoot
- Fife, Scotland


(1999)

Dear Dougie

We have seen this problem many times, particularly in the south of England due to water quality. At Canning we have a trivalent blue pass TRIPASS ZB which overcomes these problems without pretreating the water.

Yours sincerely

ALAN GARDNER
Wm. canning [now MacDermid] - B'ham UK



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.