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Zinc Electroplating

Started by sutekh, 13 April 2023, 08:42 AM

sutekh

So, I removed the valve cover on my 300SD a few weeks ago to adjust the valves and decided to have it polished while it was off (looks great IMO!) During the process though, I got a very good look at my myriad accelerator linkages, and they all looked exactly like what they are: 45yr old metal parts that have been exposed to lots of heat and moisture.

Certainly wouldn't do to underscore their aesthetic inadequacy by placing them atop a mirror-polished valve cover! All the local plating shops in my area have closed up in recent years, and the thought of sending all of these very hard to get parts (which all to well aware of having first considered replacing them outright) off to any of the distant, expensive, and dubiously reviewed outfits I contacted just didn't appeal. So I decided to do it myself :)

In principle, the process is pretty straightforward: Place your part in an electrolyte bath connected to the negative side of a DC source, with the positive end connected to a sacrificial zinc anode. In practice though, there's a bit more nuance to getting it to work well. After removing, sand-blasting, and acetone cleaning everything, I tried a few different electrolyte solutions, voltages, and current settings. Ultimately, the process outlined here proved most effective:


Once suitably galvanized, anything you want to be shiny needs to be polished: I started with a brass brush and followed up wth Metal Brite compound and elbow grease.

You should now have bright and shiny silver parts, but they don't yet have the yellow-gold cadmium OE finish. Enter Caswell yellow chromate:


This stuff is apparently pretty nasty, even diluted with distilled water, but with gloves and dip wires, I never came into contact with it. After another acetone bath, immerse the parts in the yellow chromate solution for 20-30s, and voilà!

Color depth is determined by solution concentration and immersion time, so there's some trial and error involved. Also, anything left rough (like the cable retainer pictured at center below) soaks up color much more quickly.

The pic I took was pretty dark and doesn't do the parts justice, so I'll most a few more in situ once I get everything re-installed. 2nd pic is of my electrolyte bath with one of the shift rods for my forthcoming manual conversion being galvanized :)

raueda1

An interesting and ambitious project! Wonderful! I had a similar challenge but went a different path:  ultrasonic cleaning followed  by further cleaning with sand blaster using walnut shell blast media.  Then off to THIS place.  You're in SLC so it's local and reasonable pricing.  They do LOTS of old car work.  I ended up doing virtually everything under the hood as well walnut blasting other stuff for a nice satin finish (WUR, thermostat housing, etc).  And, like yourself, polished the valve covers.  Everyone should polish their valve covers! Looks fabulous.  Cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

sutekh

Quote from: raueda1 on 13 April 2023, 09:42 AMAn interesting and ambitious project! Wonderful! I had a similar challenge but went a different path:  ultrasonic cleaning followed  by further cleaning with sand blaster using walnut shell blast media.  Then off to THIS place.  You're in SLC so it's local and reasonable pricing.  They do LOTS of old car work.  I ended up doing virtually everything under the hood as well walnut blasting other stuff for a nice satin finish (WUR, thermostat housing, etc).  And, like yourself, polished the valve covers.  Everyone should polish their valve covers! Looks fabulous.  Cheers,

Thanks Dave! I think I too hastily dismissed Quality Plating when I called them last year about some chrome plating and they told me "Sorry – No car parts" (which their site reiterates). Sounds like that's just for chrome and I should give them another look!

rumb

#3
Simple bead blasting and having plating shop finish is an easier path and high quality finish.
Here in Denver min order is $110, but that does and huge bucket of parts.

I've also done the Caswell system.  I think your process left out the use of  "zinc brightener additive" in the zinc bath - that's what makes it shiny. I use a bit more than they call for to make sure nice and shiny.  It worked well for a few small parts, but took a looooooooong time.

https://caswellplating.com/electroplating-anodizing/zinc-plating-kits.html

Here's my last batch about a month or so ago from Denver Metal Finishing.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio

sutekh

#4
Quote from: rumb on 13 April 2023, 12:50 PMI think your process left out the use of  "zinc brightener additive" in the zinc bath - that's what makes it shiny.

First link outlines the use of sugar / Karo for brightening. Worked quite well on the parts I plated at lower current / polished afterward. Your photo is brighter, but my ball joint linkages look almost exactly like what you've pictured in better lighting.

I may re-do the two brackets just to lighten them up a bit (lower current + less time in the yellow chromate).

I looked into the Caswell system (did buy their yellow chromate solution) and it's close to $300 for what amounts to ~$20 in material at the local grocery store!

raueda1

Quote from: sutekh on 13 April 2023, 10:05 AMThanks Dave! I think I too hastily dismissed Quality Plating when I called them last year about some chrome plating and they told me "Sorry – No car parts" (which their site reiterates). Sounds like that's just for chrome and I should give them another look!
Here's what they did for me.  My build even has the hard core rat rod and rice rocket dudes gasping.  ;D
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

sutekh

Quote from: raueda1 on 13 April 2023, 07:27 PMMy build even has the hard core rat rod and rice rocket dudes gasping.  ;D

Gorgeous! I'd love to see it sometime if you ever bring it to any of the various local shows or cars and coffee events.