Date: Tue, 16 May 1995 06:44:15 -0700 (PDT)
From: Peter Snidal <psnidal@cln.etc.bc.ca>
Discussion here on the subject of replating rusty fittings got me going; went to the local library and did a little research; made notes for myself, and thought I'd toss them up for any who are interested:
ELECTROPLATING Steel with Zinc
Disclaimer: The substances mentioned herein are in most cases *Dangerous* to Handle. Use a faceshield, or at minimum, goggles, heavy rubber gloves,avoid inhalation of fumes, work in a well ventilated environment, choose your containers carefully, especially for storage between usage, and if anything goes wrong, you never heard of me. Read the labels on Everything, and heed them. This Ain't No Disco!
The following material is taken from a wonderful little book which is
part of a wonderful little series called Workshop Practice, printed of
course in The Land Of The Meccanno Set. I have ungratefully forgotten
the Author's Name. Book is no.11 in the set, and I recommend them all.
_Screwcutting in the Lathe_ will have you making your own bolts in
less than an hour!
Current Density: Amps/ft^2 or Amps/dm^2 relative to area of cathode plates - varies with electrolyte being used
Power Supply - must be Full Wave Rectified DC ~12V,12A - 6V tap is good
Cleaners:
Alkaline Cleaner - No. 1 Alkaline
6oz/gal NaOh (40gm/l)
Na2CO3 4 oz/gal (25)
NaSiO4 (if that's trisilicate) 4 oz/gal
Use between 60 and 80 C Immerse from 2 - 10 minutes
Acid Cleaner - No. 1 Pickle
HCL (conc) 200ml/l into water.
nb:!: Mixing: Add HCl to water SLOWLY, STIRRING
CONSTANTLY - this is the stuff of acid-throwers;
use gloves, face mask, RESPECT THIS STUFF!
- Use at room temp; Plastic or Glass Tank
-Buffering: .8oz/gall to lessen attack on base metal
-a Pickle removes rust and scale prior to plating
- No. 2 Pickle
H2SO4 (conc) 55ml/l (9oz/gal)
Immerse for 1 - 4 min at room temp
Electrolytic Cleaner - to follow chemical cleaning
- in either event, in a metal tank, made slightly Anodic
(+) at a Current Density of ~10-30 a/ft^2 for 2-10 min.
- No. 1 Alkaline cleaner is a good electrolyte for this
The Plating Itself:
Electrolytes:
1) ZnCl2 Bath
3 oz/gal (29gm/l) ZnCl2, add to 2 pts H2O
20 oz/gal (120) NH4CL2 add to 6 pts H20
Mix the two for a good steel plating electrolyte
Plating CD: 14-28 A/ft^2 @ 15-20 C.
Deposit Rate: .001"/80 min @ 14a/ft^2
2) ZnOH Bath - Very Caustic
6 gm/l ZnOH
55gm/l NaOH (that's why)
Dextrin 1%
Add NaOH to 6 pts H2O and stir till dissolved.
Add ZnOH and finally Dextrin Top up to 1 gal.
Plating Current Density: 2 - 20 Amps/ft^2
@ 15-20 C.
Electrodes: - suspended in electrolyte, in a glass/plastic tank
The Anode - the + electrode - gives over its mass to The Cathode - the - electrode - what you're plating
Anode for Zinc Plating: Zinc, of course recommended: 3 X 4 in. pieces, or 6X6 perforated sheets
Cathode Augmentation - may in some cases be necessary -hanging a piece of scrap steel beside the cathode material being plated is sometimes necessary in cases of too much current density, etc. Sometimes a piece of sheet metal on each side of the cathode is necessary. Experiment.
These are suspended in the electrolyte, and must of course be insulated from one another and reliably connected to the wires from the power supply.
Burning in Electrolyte: For best results, plate a piece of scrap for an hour or so, longer at lower current is even better.
The higher the CD, the faster the deposit rate, the more uneven will be the deposit.
Enjoy--------