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Restoring - General discussions that apply across many different years and models => Processes, Products & Techniques => Topic started by: jwc66k on July 27, 2017, 03:03:58 PM

Title: Zinc Plating -
Post by: jwc66k on July 27, 2017, 03:03:58 PM
I picked up some parts I had zinc plated a little while ago, and got a relatively new finish (two years for this plate shop) on some items. It's referred to as "dull zinc", as opposed to "clear zinc". A comparison picture of two trunk strikers shows the difference. The dull finish replicates cadmium plating, aka soft silver, Ford finish code -S7. Finish code -S8 does not specify "chromate", see finish code -S9 and others, or dichromate, see -S35 and others. However, a chromate treatment does provide additional corrosion protection and is a good surface preparation for painting. Specifying zinc dichromate may result in a yellowish tint per its industry standards. My plater, Bob (a long time Silicon Valley business owner, over 50 years) recommends to get the correct zinc finish, use the terms "clear", "dull" or "gold". He also does black zinc but says that process is more expensive, higher materials and labor costs.
Jim
Title: Re: Zinc Plating -
Post by: caspian65 on July 27, 2017, 03:30:49 PM
Considering Cadmium plating is probably becoming obsolete, it seems like the only alternative.  Here are some parts that I had Cad plated about 10 years back... more silvery looking.  Unlike zinc plating, I had found Cad to be relatively consistent in the final finish.  Zinc could vary with either shiny silver or silver with bluish hues.
Title: Re: Zinc Plating -
Post by: Bob Gaines on July 27, 2017, 03:57:46 PM
With my home plating set up it is easy to get the dull zinc. Sometimes too easy as in when you want it shiny it comes out dull. You have to have the correct brightener agent added to the plating brew for it to come out shiny.
Title: Re: Zinc Plating -
Post by: J_Speegle on July 27, 2017, 06:03:27 PM
.................. My plater, Bob (a long time Silicon Valley business owner, over 50 years) recommends to get the correct zinc finish, use the terms "clear", "dull" or "gold". He also does black zinc but says that process is more expensive, higher materials and labor costs.
Jim

Yes the terms seem to be the challenge at times depending on where you are located. Suggest that anyone having someone do this for them to ask to see samples first and then confirm what the platters terms are for each so that you get what you expected to get. Also on more recent batches have found that allot fo local platers are now doing parts in baskets  rather than manually tying each part along a strand of bailing wire as was typical years ago. Often could save a few bucks if you just told the platter to leave them on the string and you would remove them. Also found some batches benefited by coating them in some oil to deduct the chance of oxidation over time 

Just what has worked for me
Title: Re: Zinc Plating -
Post by: jwc66k on July 27, 2017, 08:33:43 PM
Also on more recent batches have found that allot fo local platers are now doing parts in baskets  rather than manually tying each part along a strand of bailing wire as was typical years ago.
The "basket" process does not always give good results as it is "static", not moving. Electrical continuity is required to get an even look, and even more important, a consistent thickness (it's not much, 0.00015 to 0.0002). A more common process is "tumble plating". It has its drawbacks as scratches may develop and parts sometimes get lost in the tumbler. My plater currently wires most everything, but that process occasionally leaves a "bald spot" where the wire was attached. Almost all thicknesses are measured by elapsed time by a lot of platers along with voltages, temperature and acidity of the bath.
Back when I worked for a living, I preferred to have the tumble process used and specified as such. That was for very large quantities of the same small part. Times have changed.
Also foudn some batches benefited by coating them in some oil to deduct the chance of oxidation over time 
Before or after plating? I send all my parts bead blasted and dry (the current humidity is 33 percent).
Jim
Title: Re: Zinc Plating -
Post by: J_Speegle on July 27, 2017, 09:18:36 PM
.............. Before or after plating? I send all my parts bead blasted and dry (the current humidity is 33 percent).

After of course :) 

As for prep depends on the part and its condition. Nuts and bolt sort of things are stripped then wire brushed do to not leave a texture. Just a choice
Title: Re: Zinc Plating -
Post by: caspian65 on July 27, 2017, 11:45:33 PM
The local plater here referred to wiring parts as 'rack plating' and small parts/fasteners as 'barrel plating'.  Barrel plating a large batch of nuts/bolts has usually worked out well for me.  Sometimes there might be a couple pieces that didn't get rinsed/neutralized properly and develop some surface rust.  The rack-plated stuff has been hit and miss.  It was because I sent a few parts back for re-do that the big local plater decided they didn't want to do anymore 'hobby' plating for me.  Found another place, which has since gone out of business, that would do only rack plating.  They were cheap and quick, but the zinc they did was the trivalent plating where everything came out with a lot of bluish hues.  I found I could cut that down with steel wool and chrome polish, but was a bit annoying.