The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Hard Chroming Problems

Our machine shop repairs and makes new parts for Centrifugal air compressors. We grind down journals on pinions and hard chrome them oversized. We then finish grind them to size. We have been having problems with our chrome bath. The last pinion that we chromed we could peel off the chrome by rubbing it.

The chrome was soft and dull looking. We have had these chrome machines for about 14 years now and haven't had any major problems. Our hydrometer reading said we have to much chromic acid concentration in the solution.

How do you lower the chromic acid besides putting a dummy rod in and just chroming it?
We are sending some samples out for testing for the first time since we have had the machines.

Everything that we know about chroming we have learned by on the job and by the seat of our pants. We know that we need a solution mix of 75:1 to 100:1. We chrome at 130 degrees F.

Thank you for any help you can give us.

Greg B [last name deleted for privacy by Editor]
machine shop - Mayfield, Kentucky, United States
2003

I am amazed that you have gone that long controlling your bath with a hydrometer as it measures the concentration of everything and not just the chromium. You also have no idea of tramp metals or trivalent chrome, both can have nasty effects on chrome when the concentration gets high enough. I would recommend that you look into training someone on wet analysis for the chrome and a centrifugal analysis for the sulphate. I would also strongly recommend the acquisition of a porous pot. Hard Chrome Consultants in Cleveland has the least expensive one on the market and it works great if you follow the instructions. Gets rid of excess trivalent and many metal ions. What have you done to keep your anodes active? How are you activating your parts? If you have too much chrome in the tank, take out a couple of buckets and replace it with water. Add it back in when you need more chrome. This will also add back in a small amount of sulphate, but drag out will normally require adds anyway. I like ratios of 90 to 115 better, 130 is a great temp if it is uniform in the tank.

James Watts
- Navarre, Florida
2003

---

Thank you for the help. I did as you said and took out some chrome and added water. The hydrometer reading is fine now. Right now we have to go over 6 volts to get the required 2 amps per square inch. We think we need to clean our anodes to do this. I have a book called the Handbook of Hard Chromium Plating by Robert K. Guffie. It is helping me out a lot. I am determined to try and start doing the right things to make our chroming operation run as it should. We have been doing to many things by the seat of our pants.

Does anyone know of a company that sells products for Krome King chroming machines.

Greg B [last name deleted for privacy by Editor]
Machine Shop - Mayfield, KY, United States
2003

Guffie's book is an excellent resource. Another one is from Hard Chrome Consultants in Cleveland. A tiny operation. Half of the book is self serving BS, but the other half is the best advice that I have seen and is in plain english. The author is dead and his son runs the shop. The book is very poorly arranged and has so many additions that you may have to add your own flags to the second index. forget the first one.

Voltage is extremely dependent on anode to cathode spacing. 6 V is typical for most boxed tank anodes. I am a strong believer in conforming anodes. 4 volts with a half inch spacing will plate about 0.003 per side per hour. The real beauty of the system is that you can adjust the anode to a point that only a tiny fraction of the grinding is required. It is not plate to size but can be quite close if you really work at it. Adjust means removal of some of the anode grid or adding some to it in selected places. Requires good note keeping of size shape voltage tank temp and tank analysis.

Read the part in the book about anode passivation. Yellow anodes are non functional! It takes quit a bit of dummy work to get them back to black. When not in use, I took anodes out and stored them in a tank of water to keep them from going yellow in the plating tank.

James Watts
- Navarre, Florida
2003