Surface Wear Effects on Shot Peening

[driveline]

I have an application that has seen significant fatigue life improvement in a lab test by adding shot peening to the process. 30x to 50x life improvement. The problem is, the lab test does not simulate all of the service conditions. The part can undergo significant surface wear, beyond the max compressive layer. What can be done to reduce the wear without adversely affecting the fatigue life?

 

[Carburize]

Better lubrication??

 

[driveline]

Carburize,

The wear occurs at contact from a loose joint (can't change this) and from abrasion along the surface of the part (can't change this either). Lubricant would work at the first wear area for a while, but it would not last long in the second area. It would have to be a permanent coating or surface treatment, low cost too. Sorry I have to be so vague. Any help?

 

[Carburize]

OK - I suggest you call Timken R&D in Canton OH and discuss their recently developed family of specialized surface treatments - they probably have one which will meet your requirements.

 

[aspearin1]

Could you use a more spherical peen?

Aaron Spearin, EIT
ChemE, M.E.
"The only constant in life is change." -Dan Andia; 1999, Chemical Engineering Progress

 

[rmw]

Shot peening puts millions of tiny locations of "case hardening" on the surface of the part, increasing the properties at the surface for a variety of purposes, fatigue life being among the chief uses. If these miniscule peened locations are eroded or corroded away, the beneficial effect is lost.

Now, to answer your question, after shot peening, a metalspray application of a wear resistant metal compatable with the base metal would give wear resistance, assuming the flame spraying did not heat the surface to a point that normalized the peening.

rmw

 

[diamondjim]

Did you mean 30 to 50 percent increase
by shot peening? I know they are coating
many of our gear cutters and other tools
with some special coatings and have increases
the tool life by 300 percent. Shot peening
does help to improve the surface finish as
well as put compressive stresses into the
parts which improves or relieves tensile
stresses, so your are getting several
advantages by shot peening.

 

[driveline]

The peen media is cut wire which I am told forms the best shape for peening. The life improvement is 30x to 50x, not 30 to 50%. I have been told this is an extreme example, usually 10x life improvement at best.

I am not familiar with the flame spray prcocess. Is this the same as flame hardening? Would nitriding be a better option? I want to avoid reheating the part if possible.

 

[TVP]

Flame spraying is not the same as flame hardening. The process is also called thermal spray or HVOF (high velocity oxy fuel), and it is used to deposit hard materials like tungsten carbide onto other substrates.

 

[rmw]

Flame spraying is also used, amoung lots of things, to give a hard surface for boiler tubes in high erosion zones with solid fuels like coal, and wood. It is also used in chemical recovery boilers in the pulp and paper industry to give not only abrasion resistance, but corrosion protection to furnace tubes in the furnaces, where the smelt bed is located.

The flame is used to convey the metal coating, and does not heat the part appreciably.

rmw

 

[ccw]

Hi Driveline,
How about industrial chrome plate?

 

[diamondjim]

Driveline,
What is the material and heat
treatment of your material that
you see such high improvement
in life by the shot peening.
Thanks for sharing this information.
You might want to submit an article
to several gear technology magazines
as this is very interesting.
I have read many gear articles on
shot peening and have never seen
such high results. Many manufacturers
would be interested in your results
as well as the designers of gears.

 

[driveline]

Diamondjim,
The material is AISI 5160, heat treated to 38 HRC.

 

[Christian62]

Well, If coating is impossible (lubrified liner etc. on your part or the other part) then use a peening that induce deeper compressive stress. You can look at LPB (Low-Plasticity Burnishing) or Laser Peening or Water Peening.
Good Luck