Surface fatigue (Grinding)

[kempdawg01]

I am having a slight memory lapse since college. At our company we produce cement pumps for spray-in lightweight concrete. We use a progressive cavity pump(much like a screw pump). This part in ground in sand all day everyday.

Here lies my question. Is there a formula for surface fatigue (sand grinding away at the surface). I have useful information on the rpm of the pump and mechanical properties of the metal, but no way to relate them to surface grinding.

Thanks in advance for any light you can shed of my problem.

 

[chicopee]

Anotherword, you are trying to find out how much metal is being eroded from pump cavity and screw surfaces?

 

[MintJulep]

http://books.google.com/books?id=hoj0vpQCRo0C&printsec=frontcover&dq=slurry+erosion

 

[tbuelna]

kempdawg01,

Interesting question.

Classic metal fatigue failures usually initiate at points on the surface where there are stress concentrations due to corrosion pits, machining grooves, or surface damage due to operating conditions. In your case, the abrasive nature of the pumped media would seem to create an environment where the surface of the pump elements are continually experiencing material removal during operation. As long as the abrasive characteristics of the pumped media are consistent, the operation of the pump would seem to continually resurface (and also mechanically stress relieve) the pump elements. The pump elements would eventually wear out due to material loss, but provided they are not overstressed I can't imagine they would fail in fatigue.

The only exception I can think of would be if there were some sort of chemical in the pumped media that was having a corrosive effect on the pump elements.

Good luck.