Clear coating of titanium springs

[Theisk]

Hi
I have a couple of titanium springs in production, made for testing on downhill mountainbikes. The springs are made of Ti-3Al8V6Cr4Mo4Zr, which has been sand blasted after production of the springs.
My question is: Which type of clear coating should be used for this type of spring? They will be mounted on mountainbikes, so they need to handle a lot of abuse - sand, water, salt, stones etc. Temperatures will be from -20 to +50 degrees Celsius.

Do you have any suggestions?

Thanks in advance!
Theis, Denmark

 

[cloa]

Its Titanium it won't have any corrosion problem with salt and water.

 

[Theisk]

Thanks for your answer. I know corrosion isn't a big issue, but the clear coat will improve the overall "toughness" of the surface. Kronos springs describe their process here (but no clues about the type of clear coat):

http://www.springtime.vg/titanium-1.html

 

[Screwman1]

The surface of heat treated Ti is going to be much harder and more durable than any clear coating that you put on them. The addition of a clear coat will not increase the life in any way. That Kronos link is complete marketing fluff; there is no engineering basis to it. If coating titanium would increase the fatigue life, then why are titanium fasteners not coated for fatigue applications?
Don't do a "sand blast"; you need to do a controlled shot peen for service life enhancement.

 

[EdStainless]

I hope that you mean that it was carefully glass bead blasted.
If not then you should get them shot peened.

Any coating will only eventually fail, long before the springs do.
If you want to change the look then you might try heat tinting them. You can get some great looking surfaces.
It can even be done electrochemically to impart colors.

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Plymouth Tube

 

[CoryPad]

The Springtime site refers to a hard coat, which may mean anodizing, or even one of the new physical vapor deposition (PVD) coatings. I wouldn't think any of these would be necessary for this application unless it were to change the cosmetics or to cure a bad fretting problem at the spring seat(s).

 

[TomDOT]

Electrochemically anodizing titanium is fun. Unlike aluminum (which uses dyes for color) the oxide layer itself provides the color on titanium.

 

[1gibson]

Look up titanium anodizing color samples, you can get nearly any color you want by adjusting the voltage of the process. I've done it in the garage with an adjustable DC power supply and diet coke, definitely not rocket science!

 

[EdStainless]

The colors come from refractive interference. You change the density and thickness of the Ti oxide film to change colors.
The only place on the spring to really worry about is the ends where it seats. You could get some fretting there, though it is more likely that the mating part and not the Ti will suffer the worst wear and corrosion.

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Plymouth Tube

 

[Theisk]

Hi guys
A bit delayed, but thank you very much for your answers.
I have just recieved the springs from the manufacturer, and they sandblasted them instead of shot peening. I guess the communication with chinese factories can be difficult sometimes...

Nevertheless, I am now trying to find out what to do with them. I have contacted a local spring factory, which do surface treatments of springs. They can do the shot peening, but they usually do this for carbon steel and stainless steel - they are not familiar with titanium.
Do any of you know if stainless steel shots/balls will work fine with the titanium springs?

The factory also asked about heat treatment of the springs after shot peening - will this be necessary? If so, what temperature will be needed?

Thanks!
Theis