Rotaryphile

Hi Ladyflyer: I have set up hard chroming rigs in as small as 500 ml. Pyrex beakers, with ordinary hardware store flashing lead for anodes. I hang the anodes on each side of the beaker from the work, for external work, and use several times as much anode area as work area. For internal work, you need a lead anode positioned more of less in the centre of the bore, and about 2/3 to 3/4 the bore diameter, to leave sufficient space for circulation of the bath in the annulus. You also need additional anodes for internal work, since anode area must always be kept larger than work area, or the bath will tend to poison with trivalent chromium. You don't need to worry about calculating current density - just vary the voltage across the work until you get the deposit you want - nice and shiny. Usually takes about 3.5 volts, depending on anode spacing and bath temperature. I don't usually strip previous chromium from ABC or AAC liners; a good acid cleaning, rinsing, and, most importantly, reverse current etch in the bath, should work just fine. Chromium cannot be applied directly over aluminum or its alloys - you have to zincate plate the part first - one reason for not removing existing, worn chromium from AAC liners.

I have never heard of cynanide gas coming from hard chroming process, but it does generate an aerosol of hexavalent chromium, which has been implicated in all sorts of health problems, although to the best of my knowledge, people who worked for years in chromium plating did not appear to have grossly unusual health difficulties, but it is better to be safe, and use adequate ventilation, and if you plan on doing it for a business, be much more careful than if you are doing one or two liners or pistons a year. I keep a lid on the bath while I am plating, and an exhaust fan drawing air from over the bath. There are commercially available additives for the bath that produce a foamy surface that stops aerosols from getting loose.

The bath usually plates about 0.001 inches per hour, so building up a typically worn ABC liner only takes ten minutes or so to get back to the original fit.