Ralph,
That just makes so much sense. You can run 3 times the volume, while only drawing 1/3 amperage needed. Just adjust your time intervals. This means your rectifier is not constantly overloaded or at max draw time. This would also lead to lower acid temperatures wouldn't it ?
Actually, it has nothing to do with overloading the rectifier. Let's assume you have a certain type of gold plating bath that provides the best plating at a current density of 10 amps/square foot (asf) of surface area on the parts. Let's say that the total surface area of all the parts you are running in a load add up to 1 square foot and, at 10 asf, to get the gold thickness you want, it would take 15 minutes. If you ran them on a rack, you would simply adjust the current to 10 amps and remove the rack after 15 minutes. However, in a plating barrel, it is well known in the plating industry that, in general, only 1/3 of the parts make contact at any given time. Therefore, if you were to apply 10 amps, the parts in contact would have a current density (CD) of 30 asf, which would surely burn the parts. To counteract this, you only apply 3.33 amps and triple the time to 45 minutes.
I am speaking of averages. Depending on such variables as the shape of the part, the 1/3 thing could be a little off. It might be 25% or 40%. After running several batches of the same parts, the astute operator will make adjustments to the amperage and the time. However, the total number of amp-minutes (amps x time) will remain the same.
Chris, Did you notice that will the Barrel plating process that you overall gold consumption for say 100,000 pieces or some large volume would run higher than when plated on a rack all at the same time. I'm figuring that will barrel plating their is just a little more uneven plating thickness on some parts more than others. It would only make sense in large volumes though. But then again i think that's the purpose of barrel plating.
Except for the plating efficiency of the particular gold bath (which is a constant for a particular type of bath - assuming the bath is up to par), the gold consumption is only related to amps x time = amp-minutes. In the example above, on a rack, the gold consumption would be directly related to 10 x 15 = 150 amp-minutes. In a barrel, it would be related to 3.33 x 45 = 150 amp-minutes. Same number of amp-minutes. Therefore, in each case, the same theoretical amount of gold consumption.
In a barrel, the plating would be a little more uniform than on a rack. On a rack, e.g., the parts on the perimeter of the rack would receive more current than those in the center of the rack. In a barrel, everything constantly changes position and every part ends up receiving about the same average amount of current over a period of time.
If a valence 1 gold bath operates at 100 efficiency (which it never really does), it will deposit .122 grams of gold for each amp-minute. For the example above, it will deposit 18.37 grams of gold in 150 amp-minutes, whether the parts are plated on a rack or in a barrel (theoretically, at least). It's all amps and time (Coulomb's Law). When stripping, it's the same thing in reverse, although the efficiency may vary more in practice. Amps and time.
The main purpose of barrel plating is to eliminate the labor that would be required to rack or wire the parts. The same with stripping.
Your friend, Chris
