M_D, I have a racking question for you:
Since titanium won't anodize under the anodizing conditions for aluminum, it would be reasonable to think that that two things are occurring:
1. When the surface area (SA) of the racking is much larger than the SA of the combined work (like in your picture) the rack will draw the majority of the current and dissipate most of the power.
2. Since the titanium won't anodize here, the electrical bulk resistance of the titanium SA will show a low resistance (lower than the work) and will remain constant.
It seems that because of 1 & 2 there going to be a current density problem with the work, the racking is setting the current density (not the work). Worse still, since the work and the rack are electrically in parallel, the constant resistance shown by the rack will lower the current density of the work as its coating builds up. This can be substantial when the rack is much larger than the work. In effect, this defeats constant current operation as far as the work is concerned (where it counts).
This can be reduced by only operating with lots of work; so that the work SA is much larger than the rack SA, or insulating the non contacting areas of the rack, reducing its SA. Plastic goop or something like that would probably work.
Have you experienced any problems with this?
|