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

on this site
current topics

topic 0138

Rack plating with acid zinc

A discussion started in 1995.
Add your Q. or A. to restore it to the "Current Topics" discussions.


Q. From a conventional potassium chloride, boric acid system what affect does high zinc (ex. 5.5 oz/gal) or low zinc -2.5 oz/gal) have on:

A. Plate thickness distribution from high to low current areas?
B. Overall rate of plate thickness?

1. What affect does replacing boric acid with ammonium chloride have on A & B above?
2. What affect does high temp.( 110 deg vs. 85 deg.) have on A & B.
3. What is recognized as Max. voltage level in chloride zinc rack system?
4. Is a zinc plate rate of 1/10 Zn in 10 min. at 10 amps/sq.ft. considered avg., below, above ?

I realize this is a lengthy question, however, any input would be greatly appreciated.

Erik Esarlano

A. Hi, Erik.

A. The theoretical effect of higher metal concentration is an increased tendency for plating thickness to track the geometry of the current flux--that is worse thickness distribution…
B. …but faster plating.

1. I think the function of the boric acid is the same as in a nickel bath--i.e., as a pH buffer to offset the tendency of the bath to rise in pH as water hydrolyzes into hydrogen bubbles (which leave the bath) and hydroxyl ion (OH, alkali which remains in the bath). I don't know how effective ammonium chloride is in this regard or if it serves a different function.
2. In theory, raising the temperature has the same effects described above under raising the metal concentration. But in actuality, brighteners degrade faster at higher temperatures; I believe that proprietary brighteners for ammonium chloride baths can take 110 or more, while those for potassium chloride baths are much more limited.
3. Voltage depends on anode to cathode distance, but 6 to 12 volts is pretty common.
4. Sounds right on target, but the math can be checked on page 791 of the Metal Finishing Guidebook.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

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


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.