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Vanapplebomb
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Joined: November 03, 2010
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Location: Holland, MI
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 Posted: Mon Jan 30, 2023 1:04 pm Post subject: Prototype head studs |
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I have been prototyping some waisted shank head studs in my spare time. They are made out of 170,000 - 180,000 PSI rod with rolled threads. They are shorter than stock type 4 studs by 10mm, and the shank is larger at 8mm (stock is 7mm).
My question is on coatings.
Because it is relatively high yield strength (~12.9) and a Rockwell hardness of C38 - C40, I am not excited about electroplating anything, or any process that requires acid pickling. Free hydrogen generated by the process can migrate into the grain boundaries of the steel and cause it to fracture prematurely, even with a post process baking in an oven to drive out the hydrogen.
I am also passing on black oxide, since it has no corrosion resistance in and of itself. All it does is hold oil or wax as a barrier, which is very temporary.
I have been leaning towards zinc flake coating, or a zinc aluminum flake. There are a couple ways it can be mechanically applied. One method is by shot peening the flake onto the surface. The other is to use a binder, such as epoxy or polyester. Both really need to be sealed with a top coat. There are a few local companies that have zinc flake capabilities, with salt spray tests north of 1000Hr.
The epoxy bound zinc flake is pretty appealing due to its higher heat stability as well as excellent abrasion resistance.
Top sealing coats on zinc flake can include friction modifiers for more consistent coefficients of friction.
If anyone has other ideas they want to spitball, let me know. Curious to see what other ideas there are out there.
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jimmyhoffa
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Joined: February 16, 2014
Posts: 1057
Location: St. Louis
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| Posted: Mon Jan 30, 2023 1:16 pm Post subject: Re: Prototype head stud coatings |
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Mmm nice lathe. Lil' jealous. More rigid than mine.
What sort of epoxy zinc flake coating are you talking about? Sounds Like Steel-It, but zinc!
I have been VERY surprised by the corrosion resistance of black-oxide hardware on my toys that I experimentally sprayed with this:
https://www.eastwood.com/eastwood-heavy-duty-anti-rust-in-amber.html and I'm right here in the rust belt with ya! Just a lil' less rusty.
I'm sure it's either something else or something simple, knowing Eastwood, but it does work. Probably not exactly the solution you were shooting for, but I've been impressed.
I downloaded that last picture and zoomed way the heck in. Great job on the finish on that stud. I'm sure the round insert is doing you plenty of favors there, but that plane doesn't fly itself! 
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raygreenwood
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Joined: November 24, 2008
Posts: 21513
Location: Oklahoma City
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| Posted: Mon Jan 30, 2023 3:20 pm Post subject: Re: Prototype head stud coatings |
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| Vanapplebomb wrote: |
I have been prototyping some waisted shank head studs in my spare time. They are made out of 170,000 - 180,000 PSI rod with rolled threads. They are shorter than stock type 4 studs by 10mm, and the shank is larger at 8mm (stock is 7mm).
My question is on coatings.
Because it is relatively high yield strength (~12.9) and a Rockwell hardness of C38 - C40, I am not excited about electroplating anything, or any process that requires acid pickling. Free hydrogen generated by the process can migrate into the grain boundaries of the steel and cause it to fracture prematurely, even with a post process baking in an oven to drive out the hydrogen.
I am also passing on black oxide, since it has no corrosion resistance in and of itself. All it does is hold oil or wax as a barrier, which is very temporary.
I have been leaning towards zinc flake coating, or a zinc aluminum flake. There are a couple ways it can be mechanically applied. One method is by shot peening the flake onto the surface. The other is to use a binder, such as epoxy or polyester. Both really need to be sealed with a top coat. There are a few local companies that have zinc flake capabilities, with salt spray tests north of 1000Hr.
The epoxy bound zinc flake is pretty appealing due to its higher heat stability as well as excellent abrasion resistance.
Top sealing coats on zinc flake can include friction modifiers for more consistent coefficients of friction.
If anyone has other ideas they want to spitball, let me know. Curious to see what other ideas there are out there.
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I have approached this exact issue. Letting these studs rust is not good for their strength when they finally start to rust enough to pit.
Also the same issue. Zinc plating would be ideal...but not safe for strength due to hydrogen embrittlement unless you have a dedicated "post-bake" capability.
What I used is this:
I chose this one because its 48% solids of zinc. After the solvent evaporates that leaves about 93% pure zinc layer. I sprayed one thin layer, pay close attention to instructions and then a second layer with a bake after drying to get rid of all solvent.
There are several brands that work just as well.
The object is that this much zinc...in contact with the metal surface...does work just like plating as a sacrificial anode to prevent rust. The problem is that its a VERY weak coating. You can scratch it with your nail.
I thin painted it with a layer of either VHT SP 104 "flame proof" matte gray or the high temp Ford gray from VHT (good to 500F). I will have to look at my notes.
Either of these will give the paint a hard shell that does not scratch easily.
The cold galvanizing spray is actually better than real galvanizing for an application like this because galvanized zinc crystals actually starts to fail in the range of 450* F give or take and start to flake off.
Ray |
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Vanapplebomb
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Joined: November 03, 2010
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Location: Holland, MI
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| Posted: Mon Jan 30, 2023 5:24 pm Post subject: Re: Prototype head stud coatings |
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Jimmy, I have really liked the round button inserts. They leave a really nice surface finish, but it is borderline a forming tool, so anything more than a 15thou cut takes a lot of tool pressure. My 13” South Bend is rigid enough… but only just. It’s pushing it. I touched up the shank with some 320 emery cloth on the lathe. It didn’t take much with a button insert.
As for the zinc flake coating… basically it is 85-95% zinc or zinc aluminum flake powder by weight. The rest is a binder that cross links when cured… usually at 400 - 600 degrees F, or there abouts. Typical thicknesses are 0.0003” - 0.0005” with a sealer on top. It can be sprayed, but usually it is dipped and then spun to throw off the excess, leaving a nice uniform thickness everywhere. Often times there is a phosphate coating applied first for good surface adhesion.
In some ways it is similar to Steel It coatings as it contains a high solids content. The “cold galvanizing” paints are a similar idea, but nowhere near as tough as commercially applied zinc flake coatings.
My experiance with black oxide or phosphate coatings has been pretty poor. Doesn’t seem to keep rust at bay once the lite oil dries up. As soon as they dry, or it gets washed off, they rust right away.
I have never really looked into Steel-It before. All these high solid coatings are new territory for me. Lots of stuff to look into. 
Thanks for the input!
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Vanapplebomb
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Joined: November 03, 2010
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| Posted: Mon Jan 30, 2023 5:26 pm Post subject: Re: Prototype head stud coatings |
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Ray, I have used that exact product on fence posts before. Seems to be holding up well on its own, but seems really soft, even a year later. Did top coating it help toughen it up?
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raygreenwood
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Joined: November 24, 2008
Posts: 21513
Location: Oklahoma City
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| Posted: Mon Jan 30, 2023 7:34 pm Post subject: Re: Prototype head stud coatings |
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| Vanapplebomb wrote: |
| Ray, I have used that exact product on fence posts before. Seems to be holding up well on its own, but seems really soft, even a year later. Did top coating it help toughen it up? |
Yes, it did. Soft is the correct term. Its not weak in adhesion...its just soft.
Really this is the same exact "concept" as zinc flake...except it uses pure GRANULAR zinc. Same deal....as much zinc as they can suspend in the solvent and anywhere from 5-10% binder.
The difference with the zinc flake is that the binder is binding together "flattish" flakes which makes a higher strength film with many interlocking features and it will have a higher "pencil" hardness as a film. We see the same exact issue in high solids conductive silver inks when you are looking at flake vs granular.
The obvious problem is that flakes cannot spray through a rattle can orifice so they use granules of zinc.
But this makes a nice primer. Put a hard shell of something high temp...a urethane or polyester paint and it holds up pretty nicely. I will see if I can get a couple of pictures of the finished coat.
It makes it "workable" ofr this exact application. In something that was going to be handled a lot....maybe not so much. But I can guarantee they will never rust. Ray |
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RLFD213
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Joined: January 21, 2009
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| Posted: Mon Jan 30, 2023 7:38 pm Post subject: Re: Prototype head stud coatings |
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| If rust is a concern what about just getting them powder coated? Wouldn’t that seal things |
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chrisflstf
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Joined: February 10, 2004
Posts: 3439
Location: San Diego
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| Posted: Mon Jan 30, 2023 8:01 pm Post subject: Re: Prototype head stud coatings |
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| What type of coating does Arp use on their studs, for ex? |
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Vanapplebomb
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Joined: November 03, 2010
Posts: 5410
Location: Holland, MI
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| Posted: Mon Jan 30, 2023 8:30 pm Post subject: Re: Prototype head stud coatings |
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| RLFD213 wrote: |
| If rust is a concern what about just getting them powder coated? Wouldn’t that seal things |
Some of the high heat ones may work. My question is how high do you have to heat them to bake it, and would that mess with the temper of the fastener?
I have a buggy that is powder coated, and it has held up really well everywhere accept where things bolt to the frame. It peals up and starts rusting from underneath. Do you think nuts on the threads would do the same?
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Vanapplebomb
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Location: Holland, MI
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| Posted: Mon Jan 30, 2023 8:32 pm Post subject: Re: Prototype head stud coatings |
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Ray, that would be cool to see what they look like finished. Did you coat the whole part or just the shank?
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SGKent 
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Location: Citrus Heights CA (Near Sacramento)
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| Posted: Mon Jan 30, 2023 9:33 pm Post subject: Re: Prototype head stud coatings |
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CRC makes an instant galvanized spray,
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Tobias Bylund
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Location: Varberg - Sweden
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| Posted: Tue Jan 31, 2023 12:09 am Post subject: Re: Prototype head stud coatings |
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| What about Cerakote? It is baked on i believe, but not a a high temp really, and comes in almost any shade. Seems to be very scratch resistant as well. |
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UK Luke 72
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Albertoprop17
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Location: Valencia (Spain)
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| Posted: Tue Jan 31, 2023 1:55 am Post subject: Re: Prototype head stud coatings |
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What about cold bluing? Just takes a brush to put on it and instantly makes them black, protecting them with just a surface chemical reaction
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Tobias Bylund
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Location: Varberg - Sweden
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| Posted: Tue Jan 31, 2023 1:59 am Post subject: Re: Prototype head stud coatings |
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| I cold blue a lot of parts or tools, or touch up of already blued parts and tools, but i must say that i am a bit disappointed in the corrosion protection of cold bluing, it doesn't take long for them to start rusting again, so i mostly do it for aesthetics and for parts/tools that are kept indoors. I think true hot bluing is better, but that is a process that is a lot more involved |
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oprn
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| Posted: Tue Jan 31, 2023 4:23 am Post subject: Re: Prototype head stud coatings |
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I accidently left a brand new gun outside overnight. By morning the dew had rusted the barrel a lot! The blueing on that one did absolutely nothing to protect it from corrosion!
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esde
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| Posted: Tue Jan 31, 2023 5:34 am Post subject: Re: Prototype head stud coatings |
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One of the bake on header coatings should work perfectly. My local powdercoating outfit has a few that they cure in there regular oven with all the other coatings, and it is pretty tough. The cure temp is just a few hundred degrees so there shouldn't be any danger of changing the stud strength.
A real black oxide coating might be an option, these are much harder than the cold applied oil finished blackening finishes.
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raygreenwood
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Location: Oklahoma City
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| Posted: Tue Jan 31, 2023 8:12 am Post subject: Re: Prototype head stud coatings |
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SGKent said:
| Quote: |
| CRC makes an instant galvanized spray, |
Yes! and it is an excellent product! It was actually the one I was most familiar with and what I was looking for when I did the last set of studs....but everyone was out of stock.
I was a little leery of using a Rustoleum product...but was pleasantly surprised at how well it worked.
Albertoprop17 said:
| Quote: |
| What about cold bluing? Just takes a brush to put on it and instantly makes them black, protecting them with just a surface chemical reaction |
OK...a couple of things to understand up front.
1. Anytime you are doing a plating or coating that uses an acidic electrolyte to create an electrolytic or electrochemical reaction on ferrous metals....it frees up hydrogen atoms and links them at the surface. This causes "hydrogen embrittlement"....which causes fracture risk in HIGH TENSILE ferrous metals.
So...its said that hardware/bolts/nuts that are grade 5 or lower (or metric equivalent) have a much lower risk of this happening. It has to do with how much carbon is present in the steel. So with bolts of say class 8.8 that are small and low torque you "SHOULD" be able to get away with it...but most bolt and screw works do what is called a "post bake"....IMMEDIATELY after plating and rinsing to drive the hydrogen off.
Post bake for grade 5 is about 3 hours at 325F. The harder the steel ...like class 12.9...it could require up to 24 hours.
2. there are two main bluing processes. There is "Hot-caustic" based and cold acid based.
The "Hot caustic" process uses Sodium hydroxide. If the sodium hydroxide is 100% pure, no hydrogen is introduced into the process. This is the main method that professional gunsmiths use. You need to have your stuff together to do this.
And....if water has been added to the caustic....you just added H2O...that "H" is hydrogen.
The cold bluing method...uses an acid...usually nitric when done well...which causes less initial oxidization and is safer for the metal but much harder to handle.....or hydrochloric acid which is an oxidizing acid....both of which causes hydrogen embrittlement.
Bluing...which coats the surface in black magnetite is not really a rust proofing. Its a black oxide similar to what you get with phosphoric acid. Its main purpose is an even coating that holds an oil or wax...which you have to apply.....to keep rust from normal handling down.
In short....its really a "passivation" which is an initial oxygen sealer to slow down the start of rust...but does not prevent it.
And, in hot environments....it breaks down faster.
Not really what we want in this application.
Tobias Bylund said:
What about Cerakote? It is baked on i believe, but not a a high temp really, and comes in almost any shade. Seems to be very scratch resistant as well.
Cerakote would probably be excellent. However, its an exacting process and its a requirement that the parts are grit blasted with aluminum oxide or garnet sand to open up the surface and give it grip texture to fill.
There are possible issues with very high tensile studs and drawn steels like these studs and CV axles....with grit blasting or wire wheeling with carbon steel brushes. It can cause crack propagation....so I hear. But I would have to research it. For now i think it would be an excellent product.
esde said:
| Quote: |
One of the bake on header coatings should work perfectly. My local powdercoating outfit has a few that they cure in there regular oven with all the other coatings, and it is pretty tough. The cure temp is just a few hundred degrees so there shouldn't be any danger of changing the stud strength.
A real black oxide coating might be an option, these are much harder than the cold applied oil finished blackening finishes. |
Yes....I think many of the bake on coatings could work very well. But its one more thing to pay for ...and it has the problem of not having sacrificial anode rust protection. What that means is that anywhere the coating is scratched or worn through...like if a cylinder hole edge rattles up against the stud....it will rust.
See....the zinc...does not have to 100% always cover every square millimeter. Because its protection is "anodic"...electrolytic....if you even have zinc bonded to the surface very adjacent to an open spot in the coating...it protects it fairly well. To see this is a test is amazing.
I have seen small test plates of steel that are masked and spot plated with a 1" zinc spot or spot galvanized teh same way ...that are then sprayed with salt water, dipped in water and left out to test rust.
100 hours later....the plate is rusted everywhere but the zinc spot....and no rust in a halo ~1" all around the zinc spot.
High quality Zinc of some type/application is really the best anti-rust. Ray |
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Vanapplebomb
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Vanapplebomb
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| Posted: Tue Jan 31, 2023 8:27 am Post subject: Re: Prototype head stud coatings |
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| raygreenwood wrote: |
Tobias Bylund said:
What about Cerakote? It is baked on i believe, but not a a high temp really, and comes in almost any shade. Seems to be very scratch resistant as well.
Cerakote would probably be excellent. However, its an exacting process and its a requirement that the parts are grit blasted with aluminum oxide or garnet sand to open up the surface and give it grip texture to fill.
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Oh.. your right. I forgot about the grit blast for adhesion with that product… and these custom studs are polished on the shank. Thanks for the reminder, Ray.
This is why I love the forums. Lots of good ideas and constructive criticism. I appreciate all the thoughts guys.
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