Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

Hard chromium plating rate is way low

"Hard Chromium plating"
by Robert K. Guffie

on AbeBooks
(rarely)

or eBay
(rarely)

or Amazon

(affil links)

Q. I am a plating processes engineer. Our firm begins to run a hard chromium plating line using standard hard chromium plating solution. Bath temperature is 57 °C. The solution analysis is:
Chromic acid - 250 g/L, Sulfate - 2.63 g/L, Chromic acid/sulfate = 95.
Chromium (+3) 2.5 g/L (1%), Chloride 0 ppm, Fe 119 ppm, Ni 3 ppm, Cu 19 ppm, Al 1 ppm, Pb 22 ppm,
Zn 0 ppm, Co 0.6 ppm, Se 1 ppm.
We plate small shafts of 6 mm diameter using cylindrical conforming anode about 2 cm around the shaft.
Our customer permit to plate at current density of 31-47 A/dm². (2-3 A/in²), so we plate it at 45 A/dm².
According to the book of Mr. Guffie (page 35) ⇨
plating rate should be at 30-35 microns per hour at the same conditions. Canning Handbook [on eBay, Amazon, AbeBooks affil links] (page 463) gives almost the same data (25 microns per hour).
We experience plating rates of 10 microns per hour.
Please advise, what could be the reason for so slow plating rate in our solution and how it could be improved.
Thank you