Summary for hard chrome thickness variation Discussion
Excessive thickness variations in hard chroming with old plating solutions are discussed as a bath-control problem rather than simply a uniform shift in deposit rate. Chao Wang asked why thickness becomes more variable as the electrolyte ages, even though new electrolyte gives consistent results. Aimee Longacre suggested checking the bath with weekly Hull Cell analysis and noted that the tank may simply need brighteners or purifiers. Dominik Michalek said the bath may be “riding” better as it ages, increasing efficiency and reducing process time, which could be a positive change. A third response gave a longer checklist of causes of thickness variation: anodes, shields, thieves, bath conditions, power-supply uniformity, surface preparation, anode area, chromic acid-to-sulfate ratio, temperature, catalyst, chloride contamination, trivalent chromium, and heavy metals. That answer also recommended DI water, regular dummying, and cleaning anodes.
Q. With new electrolyte, coating thickness varies very little from different batches. As time goes on (electrolyte gets old), thickness varies much larger. I think thickness should get smaller or larger, but not with a larger fluctuation. Why the fluctuation gets larger when the electrolyte gets old.
Chao Wang
– WX, China
December 29, 2011
Are you running weekly analysis of the plating solution by Hull Cell ⇦ huh?
? It could be as simple as needing to add brighteners or purifiers to the tank.
Aimee Longacre
– Savannah, Georgia, USA
First of three simultaneous responses — December 30, 2011
Hi Chao Wang,
you’re riding in the young lady and you seem to treat her well so the efficiency is increasing … be happy, saves you bit on process time and costs.
Happy New Year 2012
Regards,
Dominik
Dominik Michalek
– Melbourne, VIC, Australia
Second of three simultaneous responses — December 30, 2011
Third of three simultaneous responses — December 31, 2011
VARIATION IN THICKNESS:- ANODES/SHIELDS/THIEVES/CONTROL OF BATH CONDITIONS/UNIFORMITY OF THE POWER SOURCE/SURFACE PREPARATION.
ANODE:- LEAD-TIN MINIMIZE CORROSION.
RATIO OF CHROMIC ACID TO SULPHATE 100:1.1 TO 1.2.
TEMP/CATALYST (CHEMICAL SUPPLIER)
IMPURITIES:- CHLORIDE (USE DEIONIZED (DI) WATER ONLY)
TRIVALENT:- 1% OF CHROMIC ACID(2.25 G/LR)
(DO NOT USE CHROME TANK FOR REVERSE ETCHING)
USE SUFFICENT ANODE AREA.
DUMMY OUT SOLUTION REGULARLY USING MORE ANODE AREA. ( ANODE:CATHODE 30:1) 4 TO 6 HOURS DUMMY DAILY OR 24 UPTO 48 HOURS WEEKLY. CLEANING ANODES.
TRIVALENT REDUCTIONS SHOULD BE DONE AT HIGH TEMP./CURRENT
HEAVY METALS:-IRON/CU/NI.BELOW 5 G/LR COMBINED. IF HIGHER DILUTE BATH.
Ajay Raina
Ludhiana, Punjab, India
Generally, we find that the build up of iron over time reduces throwing power in the hard chrome bath, resulting in higher thickness variability. You probably need to remove impurities from your bath.
Kent Backus
Fort Worth, Texas, USA
January 16, 2012