Topic: Seat track mounting plates

[EJackson]

Has anyone found any new info on the finish for these plates?  I'm ready to do something with mine--they are definitely a dark copper/bronze sort of finish.  Some are real dark, almost black actually, while others are more of a copper color.  I found a rattle can that is nearly identical in color to at least half of my plates but was hoping to plate them.

Just out of curiosity, is there zinc plating under the bronze finish? The pictures suggest that there is. If so, I would venture that it's either a dyed chromate conversion coating or perhaps an extra-thick undyed one.

To be honest, I don't know what the original spec is.  I would guess some kind of zinc with coloring.  Maybe "bronze" zinc, if there is such a thing?!  I've played around with rattle cans in the past to get something that looks close.  If you have a local electroplating shop, they might be able to help.

+1

Ed.

[J_Speegle]

Just out of curiosity, is there zinc plating under the bronze finish? The pictures suggest that there is. If so, I would venture that it's either a dyed chromate conversion coating or perhaps an extra-thick undyed one.

Finish is allot darker than any dichromate finish I've seen on anything plus the lack of the rainbow effect.

But until we get it tested we'll never know for sure

[EJackson]

Finish is allot darker than any dichromate finish I've seen on anything plus the lack of the rainbow effect.

But until we get it tested we'll never know for sure

Jeff, I agree but the lack of rainbow effect could be explained by the dye, or d>>lambda per thin-film optics (http://en.wikipedia.org/wiki/Thin-film_interference (hope its OK to post the link))

If I can only find my (now 20 year old) batch of yellow chromate coating solution, I want to do the experiment to see if I can replicate it.

Ed.

(edited: link fixed)

[CharlesTurner]

I've seen a bit of dichromate appearance on these plates before.  Even on the dark ones.

[Twilight65]

 I spoke with the guy that did all my plating and he had not seen it before. Said maybe he could duplicate it by using thin coat of Black Zinc. I also noticed when I was restoring my convertible that the glove box door latch had the same coating on it (Latch not plate), a kind of a bronze color.
Dave

[EJackson]

It is also possible that the brown/bronze color is due to a contaminated black chromate bath. Based on the spec sheet for a commercially available product, the brown color could result from drag-in of "...chlorides, cyanides, or nitrates from prior dips or the plating bath."

www.accu-labs.com/Chromates-and-Conversion-Coatings/560.pdf

I spoke with the guy that did all my plating and he had not seen it before. Said maybe he could duplicate it by using thin coat of Black Zinc. I also noticed when I was restoring my convertible that the glove box door latch had the same coating on it (Latch not plate), a kind of a bronze color.
Dave

That might be why your plater has never seen it before, especially if he's meticulous with maintaining bath chemistry.

NB: I used to be a process engineer in a previous career, for a while setting up plating and thin-film deposition processes, so a lot of this looks like stuff I've dealt with before. It's still only speculation at this point--one of my favorite sayings is "In God we trust, all others must bring data."

Ed.

[petersixtfive]

Dark florentine bronze is the coating
Also included some extra info


There are many finishes or coating applied to fasteners; some corrosion protective, some decorative, or there may be no added coating at all. Specifications for fastener coatings are contained in a number of Australian standards.


(Black - Self Colour)
   An 'as produced' finish on carbon steel products having an oil residue which provides some shelf life but no real corrosion protection when in use.
Today, less than 20% of carbon steel fasteners would be purchased plain finish.
   Stainless steel, brass and other non-ferrous materials protect themselves through a reaction of the surface to oxygen, creating a protective chromium oxide film.


Zinc Plated
   The most economic and common fastener finish, comprising a thin coating of zinc applied either by electroplating or mechanically. A shiny silver grey appearance, it will normally be enhanced by a chemical chromate passivation conversion which applies a harder surface film. This can be clear (bluish tinge), or iridescent yellow which is thicker and gives marginally better protection.
    Clear is referred to as zinc, zinc clear, blue zinc.
    Yellow is referred to as zinc plate gold (ZPG), zinc yellow chromate (ZYC), zinc di-chromate, zinc yellow pass.

Cadmium Plated
   Formerly a popular electroplated or mechanically applied finish, looking like but giving slightly better protection than zinc and providing increased lubricity; also chromate converted. Very seldom used today due to its toxicity and environmental non-acceptability. If specified, it is usually through habit, error or ignorance and possible confusion with zinc.

Galvanised
   A very heavy coating of zinc applied by hot dipping in a bath of molten zinc, then centrifuge spinning for even distribution and removal of the excess, or mechanically cold welding a zinc powder in a barrel rumbling process. The hot dip finish is rougher and duller than electroplated finishes but because of the thickness achieved, gives considerably enhanced protection. Often it is wax coated to provide assembly lubrication.

Phosphate
   A thin, dull grey phosphate coating obtained by insertion in a solution containing phosphoric acid. Gives a lower level of protection than zinc in mild environments, but gives an excellent base for painting or organic lubrication. Often used in automotive industry.


Electro Base
   A brass finish applied by electroplating. Appears similar to brass and is used in furniture or architectural fittings.

Black Japan
   A black enamel dipped finish, used in black fittings or furniture.

Black Zine
   An electroplated zinc flash and black chromate dip - used in dark finish appliances.

Light Bronze Antique
   Copper electroplated and dipped, medium brown for matching oxidised copper fittings.

Dark Florentine Bronze
   Copper electroplated and dipped, dark brown for matching oxidised copper fittings.

Copper
   Electroplated, used as a base for nickel or for improved conductivity.

Tin
   Electroplated, used to facilitate soldering.

Nickel
   Electroplated over copper, hard bright silver finish. Often used in electrical appliances and areas of condensation - not sacrificial.

Chrome
   Electroplated over nickel, very hard, bright, reflective finish; easy to clean or polish. Used in heavy condensation areas - not sacrificial.


With sacrificial protective coatings, the thicker the deposit, the longer the protection; however, there are practical and economic limitations to the thickness applied.

Zinc electroplating can provide thicknesses from a negligible flash of colour, for appearance, through normal commercial coatings of 3-5 microns (µm), to specified heavy coatings up to 12 microns (0.0005 in). Electroplating does not give an even cover; thicker concentration of deposit occurs on corners, points, thread crests and thinner concentrations on thread flanks and roots. This may cause thread galling on coatings above 8 microns average and adjustment by over - tapping of the nut may be required.

Hot dip galvanising will allow much heavier coatings, the normal commercial coating is approximately 50 microns (µm), which necessitates the over-tapping of the mating thread and is the maximum practical to avoid serious compromise of the fastener's strength. Unlike electroplating, the concentration of deposits is in the thread roots and internal corners. For this reason, thread diameters of less than M10 are not normally galvanised unless a subsequent light re-roll of the thread is performed.
Nuts supplied with galvanised bolts will have over-tapped threads to allow for the galvanised build-up on bolt threads and to reduce assembly galling.

Mechanical coating will result in a more even deposit and the point of over-tapping will be raised above 15 µm. Comparable thicknesses can be achieved but costs are generally much higher.


High tensile or hardened fasteners above PC 8.8 or SAE Grade 5 are susceptible to hydrogen embrittlement in the cleaning and coating process, particularly electroplating. They absorb hydrogen atoms which concentrate in areas of stress, causing minute cracks which can suddenly and violently fail in service.

To avoid this potential, the hydrogen atoms can be diffused by baking the product immediately after plating, prior to chromating at a temperature of 190°C to 210°C for a period depending upon the grade and size of the product.

For this reason, it is most unadvisable to plate PC 10 or SAE Grade 8 and higher products after purchase, unless the Plater is also able to perform and guarantee the de-embrittlement process.


Service life of coatings prior to first signs of corrosion will vary considerably depending upon thickness and environment.
Experience suggests the following:




Stainless Steel is self protecting, as shown below





Apart from general corrosion (rust) caused by exposure of uncoated materials there are several other types of corrosion which effect ferrous and non ferrous materials.       

   
They include:
2. Pitting
3. Crevice Corrosion
4. Stress Corrosion Cracking
5. Galvanic Corrosion   
   
- Further information on types 2,3 and 4 may be available in future publications. Please consult your local representative if required.   
   
- A selection chart to provide guidance on limiting the effects of type 5 - is referred to below   

Galvanic Corrosion   
In addition to corrosion being caused by exposure of uncoated materials, it is also caused or enhanced by the combination of dissimilar or incompatible materials.   The following chart gives guidelines for the selection of materials or finishes based on this galvanic action:



Key
A   The corrosion of the base metal is not increased by the fastener.   D   The plating on the fastener is rapidly consumed, leaving the bare fastener material.
B   The corrosion of the base metal is marginally increased by the fastener.   E   The corrosion of the fastener is increased by the base metal.
C   The corrosion of the base metal may be markedly increased by the fastener.       NR Not recommended.
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[jwc66k]

Excellent. If you intended pictures or links to be included they are not present. Also I think that a more detailed description of chrome plating might be helpful.
I found that if I prepare the surfaces to be plated before I send the items to the plater (I have a small batch of gold zinc that went out yesterday) I get back a better product. Preparations may include tumbling, degreasing, buffing and bead blasting.
Jim

[Bob Gaines]

Excellent. If you intended pictures or links to be included they are not present. Also I think that a more detailed description of chrome plating might be helpful.
I found that if I prepare the surfaces to be plated before I send the items to the plater (I have a small batch of gold zinc that went out yesterday) I get back a better product. Preparations may include tumbling, degreasing, buffing and bead blasting.
Jim

+1 .FYI don't let your plater talk you into cad gold if wanting Zinc Dichromate because the Cad offers better protection. It has a substantially different look. My plater thought he was doing me a favor by doing the cad. Wrong.

[J_Speegle]

I've found that part of the challenge is platters from different areas, or even ones close by can use different terms for the same finishes. Often I've had to take an example in to illustrate what I need done. And as mentioned allot depends on how good the original piece is that will be plated and how it was prepped.

[EJackson]

Dark florentine bronze is the coating

I'm skeptical as to your conclusion....

According to your description of dark florentine bronze, it is a coating over a copper plate. Based on the photos provided I don't see any copper, just brown coating on white metal.

Here's where the analysis (SEM EDX) Jeff wrote about would be helpful, as any copper would show up in the results.

Ed.

[EJackson]

One of my former colleagues, a material scientist and a old Mustanger to boot, offered to help with the analysis. He is currently at the University of Delaware. He was pretty sure the analysis could be done for about $30, I'd be willing to cover the cost to answer this one definitively.

If anyone is willing to part with an example for analysis, I can forward it to him. SEM EDX (or EDAX as I used to call it) is non-destructive but I can't guarantee I can return it undisturbed. The seat track mounting plate is probably the largest part that the equipment can accommodate, although it's been over fifteen years since I've had anything like this done.

PM me if interested in donating a part. In the meantime I'll look through my collection to see if there is anything like this as well.

Ed.

[J_Speegle]

Will see if I have a nice strong bronze one around to donate

[EJackson]

Will see if I have a nice strong bronze one around to donate

That would be great.

Ed.

[EJackson]

Hello All,

I wanted to provide an update on this topic. I received a nice example of a seat track plate with the 'bronze-like' coating from Jeff about six weeks ago. I forwarded it (the 'test' sample), along with a 65 glove box latch catch that I had, with a black zinc coating (the 'control' sample) for scanning electron microscopy with EDAX capability. The materials engineer scraped off a bit of each coating, then took SEM pictures of the scrapings (the samples themselves were too big to fit in the SEM chamber) and analyzed the surfaces for metals, oxides, etc.

Yesterday I received the results. Hopefully I've got this to attach properly:

The first is a jpg picture of the 'control' and the 'test' samples. The other files are the two analyses in Microsoft Word format.

The bottom line is this: the black zinc coating consists of zinc, oxygen and chromium with a bit of another element (either sulphur or molybdenum). Some carbon is also in the analysis, most likely due to contamination (e.g. fingerprints). No surprises here.

The bronze colored coating consists of the same elements, but in a much different proportion. It has a lot more of the moly or sulphur than the black zinc does, which most likely accounts for the color difference.

What is clear is that the two coatings are related to each other compositionally. In addition, there is no other metals present in the coating (e.g. copper) which would rule out the theory that it is florentine copper.

Whether the sulphur or moly is in the coating by design or by accident is not clear. Here is where an experienced plating process engineer could shed some light.

I hope this is helpful--I enjoyed the opportunity to provide something tangible to the discussion.

Ed.