Dummying Tanks before Starting electroplating

Dummying is the common term for dummy plating, or using a scrap piece to plate, usually at lower or higher then normal current densities.

If you were constantly nickel plating zinc or copper or brass parts, you would frequently dummy plate the bath at low current densities to PREFERENTIALLY remove the copper and zinc.  Normally, the dummy has a large surface area, to maximize the amount of material removed.  In my experience, a large piece of corrugated sheet metal is used with a current density close to 5ASF or lower.

There are other uses for dummy plating.  In a hex chrome bath, it can be used to remove chlorides and activate the anodes.  These dummies are usually very small to prevent the buildup of tri chrome.  You can also perform a high-current density dummy plate to remove excess brightener.

A separate dummy tank is usually one that is used to perform the dummying in.  You can also do a continuous dummy, where you use a small tank with a separate rectifier, anodes, and dummy panel to perform the dummying continuously.  Usually, you pump the solution into the tank, which is higher in elevation than the main tank.  As the dummy tank fills, it overflows back into the main tank.  Many platers use them in high-production shops to minimize down time.

One thing to consider with the current price of nickel.  While dummy plating targets a certain contaminant (usually), you are still plating a majority of your normal metal.  That is to mean, in a nickel bath, you can try to dummy out zinc, but the majority of the deposit on the dummy panels will still be nickel.  The zinc content will be higher than on a normal deposit, but it will still be mostly nickel. 

Those type of panels tend to work very well.  They can also be rotate 90 degrees to help remove shelf roughness in a pinch.  The smaller you make the "shelves" the more uniform the surface area will be, and generally the more effective the panels will be.  This will allow you to HCD dummy the bath without affecting the LCD chemicals, and vice versa.  With panels that have larger folds, you tend to build up a lot of plating on the corners and very little in the concave areas, making the panels less efficient.

1.  The purpose of a dummy is to prevent the use of "good" parts from being wasted while trying to plate in the bath.  While you could sacrifice parts every time you needed to remove Cu/Zn/Fe/etc from a bright nickel bath (for example), if is usually cheaper (and easier) to use a piece of scrap material, like to corrugated panels pictured above.  Regarding what amount of current density (HCD v. LCD), you should be able to set your rectifier to the appropriate range.  The variations in the corrugated panels expand that range somewhat, but you don't typically want to stray too far from your target current density.

2. You can plate your dummy at any current density.  Each has it's own reasons.  LCD dummy-ing tends to remove certain metallic contaminants from nickel baths (Cu/Zn/Fe top name a few), while HCD dummy-ing can help remove other metals (Cr for example).  Also, HCD dummy-ing is used frequently in hex-chrome baths to drive off chlorides and activate lead anodes before actual production begins.  And sometimes you want to consume some excess brightener, so you target the optimal current density with the dummy.

3. I typically use 2" pleats,90' bends, horizontilly arranged.  This works well for my nickel baths.  For my hex chrome baths, I prefer straight, iron rods, ususally 1/2" dia.  Like the kind they typically use for rebar in concrete work.

Some people like to use expanded metal, but I've not seen its benefits.  To each his own, I guess.