POTMETAL..............the word that brings tears to a platers eyes and groans from his mouth. Its the metal from hell!

Potmetal is a slang word for a zinc based alloy that was used to form most of the trim parts on cars up into the 70s. Zinc in itself is a little difficult to plate. Then add 40 or 50 years of sitting in the weather, low current density areas that collect the rain, snow and pollution and you have a recipe for hair loss when you try to plate it! The only thing that can make it worse is if you happen to be working on a part that came from a Chrysler product that had a 12 volt POS. ground. That set up turns all of your trim into anodes! (I know, I have a 55 Dodge)

Well in spite of the difficulty, it can be plated. I wont say that I have the best method, but, I'm pretty sure it ranks up there with some of the best. Plus, its simple to do. No cleaners or cyanides involved.

Over the past 6 years I have worked with a lot with pitted pot metal.

It is probably one of the hardest metals to plate.

The process I use has had many refinements and changes. This is the

best one I have come up with so far but is always open for

improvement.

You can change it to fit your needs if that's what works for you.

1. If the part is greasy, degrease it by scrubbing it in hot dish

soap and water.

2. Dry it off

3. Sandblast the part very, very well. You will be stripping the

old chrome off, cleaning out the pits, and scouring the surface of

the part to give the initial strike plate a nice surface to plate

onto.

****( I use garnet for my blasting media. It strips the chrome and cleans the metal quite well. Silicon carbide is great also but really eats away at your gun. I have not had much luck with glass bead for stripping the chrome.)***

4. When you're blasting the part, make sure EVERY pit is clean.

If there is a small bit of black in the pit it will cause you to

blister in that area later on.

5. Next I will sand any casting lines off and shape lumpy areas

if needed. I use 80 grit sandpaper for this. You can also file if

needed. If you have any cracks, "V" them out so you can solder them later.

6. From this point on DO NOT touch your part with your bare

hands. Use nitrile gloves. Rubber gloves leave residue on the part.

7. Put the hanger on the part that will hold it in the tank.

Sometimes I put it on prior to the last sandblasting. You will also

want to wire up any robbers or auxiliary anodes at this point.

8. Now I go into my NEUTRAL NICKEL STRIKE bath live. By this I mean

with the power on and hooked to the NEG bar. Lower the part into the

bath. I set my voltage at a very high setting initially so that the

plating will get into the low current areas. Lift the part out every

15 seconds to make sure you're not burning any of the high current

areas.

9. If you start to burn (and you will) the high current areas back

the voltage down about 2 volts. If you see dark spots showing up in

the low current areas turn the voltage up. Once you do this about 10

times you will start to understand how to make it work. There's a

learning curve on this so practice on some scrap pot metal and NOT

YOU'RE PARTS!

10. Once you get the plating going at a nice dove grey color leave

the part in for 15-20 min. This will give you a nice strong strike

plate on the part.

11. After 15-20 min in the strike bath take it out and rinse it well.

12. Plate in the acid copper for 20-30 SECONDS...yup seconds. Why?

This will change the color of the surface so when you start to solder

in the next few steps you can see where you're soldering. It's hard

to see your solder on a grey back ground like the nickel. I will sand the

part with 100 grit sand paper to remove the copper, this way all of the

pits are now a nice contrast of copper with the top surface in nickel.

Don't plate a lot of copper on the pot metal. What happens if you do is you will

have a temp. difference between the copper and the pot metal that

will be too great as you heat it up to solder it will start popping

the plating and blistering it. Very depressing!

13. Pull the part out, rinse and let dry.

17. If the surface turns all different reds, purples, and blues, you

can sand it lightly with some sandpaper. It will make the pits stand

out.

14. If the part is big, I will put it in the oven at 300 deg to heat

the whole part up. That way you're not putting a propane torch to it

for a hour trying to heat it up. Small parts can be heated up with a

torch.

15. Once the part is hot, start filling the pits with solder.

TECHNIQUES FOR SOLDERING

This is a list of things that I have learned over the years on how

to solder pitted pot metal. Don't despair when you get blisters on

Pot metal. It is probably the hardest metal to plate. You will have

lots of learning experiences, but, hopefully this list will help.

1. If the part is long and skinny, trace it out on some paper

first. The heat from soldering will warp the pot metal and this way

you can bend it back into shape after you are done soldering.

2. If the metal is very thin, be CAREFUL not to heat it up too

hot and drop it out on the floor. VERY DEPRESSING! There

is a very, very fine line between melting the solder and melting the

part!

3. On thin parts heat a small area and solder it. Then move to

the other end of the part and solder it. That way you don't overheat

the part.

4. I use a torch with MAPP or Propane gas in it to heat fat big parts.

Once I get to the small thin areas I have a little butane pencil

torch to work those areas with.

5. For small pits and thin metal use a thin solder

6. For big fat parts use a thicker solder.

7. Heat the fat parts first and solder them. This will allow

the heat to transfer out to the thinner parts as you're soldering.

Once you start on the thinner parts the fat part will start to cool

and draw heat from the thin areas helping to keep them from

overheating.

8. Keep the flame of the torch moving. Don't concentrate it on

one area. You run the risk of melting the part down if you do.

Remember Zinc (pot metal) melts at 785 F. Your solder melts at around

400F. That's not much of a window to play with. Practice on some

scrap before attempting to work on good parts.

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20. Once all the pits are filled with solder then you have to get the

flux off. If it is a water based flux simply rinse under hot water.

If it is an acid/resin based flux you will have to take it off with a

MEK or another type cleaner.

21. Now your part should look like something that fell out of the

sky. Time to start sanding....

22. I start with 80 grit and then move to120 grit. If after sanding

with the 120 grit you see some more pits then make sure to fill them.

You don't want to have to solder after you have a thick plate of acid

copper on. Your part will blister badly.

23. Sand down again and repeat the above steps until the part is

smooth.

24. Next I sandblast again with very low air pressure. This cleans off the flux and also gives the surface a good texture to bond too.

25. Now you're ready to Re-Strike the part in your strike bath. Give

the part another 20 min. strike, rinse and go into the acid copper

for 1-1 ½ hours.

26. Rinse the part and sand with 120-220 grit.

27. Activate and replate in acid copper for another hour.

28. At this point if your can sand with 400 grit and get the part

smooth, then do it. If you still have some small pits then sand with

320-400.

29. I always like to put about a half hour of acid copper on at about 3/4 the

normal currnet after this for buffing.

30. Sand with 400-600 grit and buff your part.

31. Clean, activate, and plate with nickel/chrome.

The project piece is well corroded, pitted, and broken in half. But, its salvageble!!!!!	Close up of the broken area. Note that there are also cracks in the potmetal.	This shows the cracks "V"d out. I do this with a 1/8 round carbide bit in a dremel tool.
I clean up the bottom side very will with a grinder. This is the area that will have a beef up plate to hold it together.	This picture shows the part after I have straightned all the bent up areas. I do this AFTER I groove the cracks. This allows the metal to bend easier without cracking more. Notice I also grind the edges of the cracks some also. This will allow a good fill of solder later when your filling that area.	I also shape the part at this point by removing casting lines, bends and other defects.
Now is the time to sandblast the living snot out of the part. Blast both sides very good. Notice there are some pits that are deep and darker? These cannot stay this way. It will not plate and blister later on. There is corrosion deep down in those pits.	Use the grinder or a drill with a drill bit to dig out the pits that are deep or still have corrosion in them. Take your time here. Inspect the part very well. If there is ANY corrosion left in one of those pits its going to cause you to loose your hair later on!!! Can you say BLISTER!	This is the part ready for the nickel strike. From this point on, DO NOT touch the part with your bare hands. Use nitrile gloves. Rubber gloves leave marks. I have put robbers on at this point. You can also see the little copper splice plate in the bottom of the photo. Thats whats going to hold the part together and give it strength.
The part as its coming out of the Neutral nickel strike. Notice that the robbers did thier job? See how built up they are. I went into this bath at about 5 volts initially. After 30 seconds dropped down to 4 and then after a few minutes dropped it down to 3 volts. This really blasts the plating onto the part and does not allow the metal to sit bare in the bath too long.	After rinsing, the part goes into the acid copper bath for 15 SECONDS. I do this so that I can sand the copper off easyly and it highlights the pits. This helps as you heat the part up with the torch. If you dont have a contrast of colors then the metal turns all kinds of colors and makes it difficult to see the pits for filling.	Notice the contrast after the part is sanded? This helps to highlight the pits once the heat hits the part and it starts turning all kinds of funky colors
The part is now soldered. Keep the solder off of the cracked edge at this point. You have to be able to fit it together with the beef up plate and solder it together.

PROBLEMS...NOT THE END OF THE WORLD!!

Little black spots or rings showing through the plating after I pull it from the tank	Usually this is because all of the bad corrosion was not initially cleaned out of the pits. The chemicals reacted with the corrosion.
Plating is peeling	Couple of reasons here....Usually it comes down to poor surface prep. Not all the buffing compound was removed or contaminates in the rinse water. Another reason could be too high of amperage. Basically you baked the plating off. Either way you will have to take all the old plating off and start over.
Small pits in the finish after plating.	Couple of things could cause this. First it is usually not a good agitation of the bath during plating. Make sure your air bubbler is putting out BIG bubbles. Second your bath could have dirt or organic matter in it. If this is the case run it through some coffee filters.
Blisters!!!!	Blisters are usually from one of two things. Either the part was not cleaned well enough prior to the next plating or......the acid copper broke through to the base metal (zinc) and caused a reaction IE: BLISTER!
Part wound up across the room in a violent manner against the wall. Dog is also running the opposite way and wife is asking if your OK?	Yup Ive been there too!! TAKE A BREAK!!!! Re-think the whole procedure out. E-mail me with any problems if you need help.