Hard Chrome Plating Questions and Answers

2-4 ASI Density

Q: Our company plates hard chrome on hydraulic rods as well as other parts. For many of these parts we apply a flash chrome plate prior to plating with hard chrome. Is there any rule of thumb as to whether we should be using a current density of 2-4 ASI? 

A. No, I do not have a rule of thumb for this particular plating step. If you talk with individuals who are in the hard-chrome-plating business as well as read the printed literature, you soon find out that there are multiple opinions as to whether a flash is required in most situations. When you talk about flash plate, I assume you are thinking in terms of a ramping of the current density for a short period of time until you reach the required current density for doing the chrome plating. Since I don’t have a good answer for you, I’ll ask our readers if they have any thoughts on this. If you do please respond to me through Products Finishing magazine. 

Teardrop Shaped Pits

Q. We are a landing gear repair station that hard chrome plates in a standard hexavalent chromium bath. Recently, some of the plated parts have shown rough areas with pits that are teardrop shaped and have a tail that goes up. We have tried a number of different adjustments to our plating bath to no avail. The chemistry has remained the same and within specifications given by our chemical vendor. Do you have any ideas as to what is causing this problem? 

A. The two most common causes of pitting and services in a hard chrome plating bath are contaminants on the surface of the part and sticking bubbles. Since you mentioned that the tear-shaped pits have tails that go up, I think that your problem is sticking bubbles that are caused by the evolution of hydrogen gas that is always part of the hard chrome plating process.

You should try increasing the flow of plating solution on the surface of your parts by pumping of the solution. You should also try “jiggling” on a regular basis to remove the bubbles from the surface. If possible, you might also consider using a modern mist suppressor designed for use in hard chromium plating. You would have to discuss this with your chemical vendor.