Zinc Cobalt passivation, thickness to be controlled

We have been doing zinc-cobalt passivation. Problem we face is of controlling the thickness of metal deposited on the product. The passivation we do is done on ball bearing dust shields. The shields are hanged on a copper wire and inserted in the bath, the shields near the electrodes, i.e., top and bottom have higher thicknesses. Suggest the reason for this non uniform thickness, we are ready to pay for consultation charges in case the problem can be solved. Also refer some good literature on this subject which we can get.

Any electroplating process will have higher thickness outside compared to inside and at the bottom. You could try out vigorous agitation and faster filter pumping to obtain better uniformity in the thickness. You could also try alkaline process to achieve better trow.