Practical considerations

Part size & shape limitations: Your barrel platable parts are limited.

Part size and shape limits

Part size and shape limits

Your barrel platable parts are limited.

While some of these examples were "staged" to illustrate the potential problem, all of these situation DID occur either during testing, or actual plating operations.

Batch sizes

A barrel requires a minimum number of parts in it, just to maintain contact with the dangler.  In my particular design, that turns out to be about 45-50 square inches worth.  Any less than that and the dangler looses contact often.

Maximum is dictated by how heavy all the parts are, how sturdy your barrel is, how strong your motor is, and how much current you can supply.

Current density

After considering the nature of the electrical contact (the dangler touches only a few parts, which in turn contact a few more parts, which in turn contact some more parts, etc.) it's clear that the contact "area" can be rather small at times while parts are tumbling.  It's logical then to run as little current as possible so as to preclude any overload at the contact points.

And checking in at commercial plating operations bears this out:  barrel plating tends to be done at lower current densities.  ie, as low as you can go and still get good plating.

Anode shadow

In conjunction with current density, you have to consider anode exposure.

Electricity will ALWAYS take the path of least resistance, so parts buried within a pile will not get much current!  Parts on the outer edge of the pile, directly exposed to the anode,  will get the lions share of the current.

So a "shadow fudge factor" should be applied.  Unfortunately, this is not a cut-and-dried number, you just have to eyeball your pile, and guess at the percentage of parts buried in the middle of it.  Then reduce your total current by that percentage.  And this will be different for small vs. large piles of parts.

eg.  I normally run at 80 ma/sq-in (old formula electrolyte) with wire-hung parts.  In barrel runs, I use 50-60 ma/sq-in, since only the outer parts are being plated.

Plating time

And since not all parts are plating all the time, you have to add some time to the plating run, about equal to the percentage you reduce current by.

Electrolyte

Caswells old formula electrolyte, with a current density range of 70-100 ma/sq-in, would seem better suited to barrel operations.

The new formula doesn't specify a range, just 140 ma/sq-in.  It might be worthwhile running some test pieces to find the lowest current density that still gives good plating, and use that for the start point when barrel plating.

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