sarabande
Well-Known Member
I've seen proper hot-dip galvanising tanks, but wondered if one can zinc coat a small object with a layer of zing by electrolysis. What bath and what anode/cathode would be needed, please ?
D I Y galvanising (not painting)
- Thread starter sarabande
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JumbleDuck
Well-Known Member
MM5AHO
Well-Known Member
Galvanizing and electroplating are quite different processes.
Galvanizing is an alloying reaction between iron and zinc. It requires molten zinc (melting point about 419C) typically about 450C. Its important that the steel is chemically clean, no oxides. Where the steel isn't clean, there will be no zinc coating. Cleaning is typically by immesion in acid, in Europe that's usually hydrochloric. After cleaning there is a layer of flux (ammonium chloride and zinc chlorides mixed together) before immersion in zinc.
Holding the zinc molten is the problem. Iron slowly dissolves in molten zinc forming crystals of iron-zinc alloy which sink to the bottom. To prevent that, galvanizers use a special steel that dissolves slower. Plain carbon steel will dissolve at a rate of about 2mm/hour off the surface. The special steel will last 10-15 years, during which time it will reduce from 50mm thick to about 25-30mm. No electric current or voltage is used between the steel and the zinc. The coating thickness is often about 100 microns (0.1mm)
Electroplating is an electrical process using a cold solution of zinc dissolved in an aqueous liquid. By passing a current between a piece of suspended zinc and the steel item, all supended in the solution, zinc migrates to the steel and deposits there. Coating thickness varies from 5 microns to 20, and depends on time, current etc.
The coating is not alloyed to the surface and can sometimes be peeled off.
The life expectancy of zinc coated steel is directly proportional to the thickness of the zinc.
Galvanizing is an alloying reaction between iron and zinc. It requires molten zinc (melting point about 419C) typically about 450C. Its important that the steel is chemically clean, no oxides. Where the steel isn't clean, there will be no zinc coating. Cleaning is typically by immesion in acid, in Europe that's usually hydrochloric. After cleaning there is a layer of flux (ammonium chloride and zinc chlorides mixed together) before immersion in zinc.
Holding the zinc molten is the problem. Iron slowly dissolves in molten zinc forming crystals of iron-zinc alloy which sink to the bottom. To prevent that, galvanizers use a special steel that dissolves slower. Plain carbon steel will dissolve at a rate of about 2mm/hour off the surface. The special steel will last 10-15 years, during which time it will reduce from 50mm thick to about 25-30mm. No electric current or voltage is used between the steel and the zinc. The coating thickness is often about 100 microns (0.1mm)
Electroplating is an electrical process using a cold solution of zinc dissolved in an aqueous liquid. By passing a current between a piece of suspended zinc and the steel item, all supended in the solution, zinc migrates to the steel and deposits there. Coating thickness varies from 5 microns to 20, and depends on time, current etc.
The coating is not alloyed to the surface and can sometimes be peeled off.
The life expectancy of zinc coated steel is directly proportional to the thickness of the zinc.
doug748
Well-Known Member
You can electroplate with zinc very easily and cheaply using bits and bobs from around the house and workshop, plus some bits of zinc anode from down the boatyard.
It is no use for items above deck, too thin and fragile but might be useful for small items in the cabin. It's great for small bits of cars or motor cycles, where it is just not economic to send them to a plater who would probably lose them anyway. Things like nut and bolts.
The finish is not as bright as commercial work but can be jollied up with a light polish with a brass wire brush.
The workpiece needs to be mechanically clean first plus a degrease, maybe:
Caustic Soda soak and/or 20% Hydrochloric Acid pickle or brick cleaner
Use white vinegar for the bath with Epsom salts at 1/4lb per quart and ditto Sugar 1/4lb per quart.
Submerge the zincs around the sides of the bath, maybe four (square plastic container) and connect to the power +
Suspend the workpieces from the - wire in the solution.
Connect up some form of 3 - 6v supply with a simple means of control.
Switch on to go, can be a quick at 10 mins. Too fast and bubbles start and the plating begins to go black.
It is no use for items above deck, too thin and fragile but might be useful for small items in the cabin. It's great for small bits of cars or motor cycles, where it is just not economic to send them to a plater who would probably lose them anyway. Things like nut and bolts.
The finish is not as bright as commercial work but can be jollied up with a light polish with a brass wire brush.
The workpiece needs to be mechanically clean first plus a degrease, maybe:
Caustic Soda soak and/or 20% Hydrochloric Acid pickle or brick cleaner
Use white vinegar for the bath with Epsom salts at 1/4lb per quart and ditto Sugar 1/4lb per quart.
Submerge the zincs around the sides of the bath, maybe four (square plastic container) and connect to the power +
Suspend the workpieces from the - wire in the solution.
Connect up some form of 3 - 6v supply with a simple means of control.
Switch on to go, can be a quick at 10 mins. Too fast and bubbles start and the plating begins to go black.
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