Home Forums General Discussion Shot Peening Process, Intensity, Coverage Lance Peening

We do internal (lance)peening on 4.5 m"m holes
We use a s110 cast shots and intensty of 5-7 N. We did some experiments to substitute to CCW14 and we had some problem with the surface roughness. With S110 on a 30HRC strip we got 10-12 Ra and on the same strip with the same blasting parameters we got 30-40 Ra. On an Almen strip both shotes gave the same roughnes of 2-4 Ra.
The part is 30HRC how dos it affects the residual stress on the part if any? and why dose it occur
I know that roughness has a negative affect ot the fatigue resistance.

Almen A strips have a hardness of 44-50RC so that they are much harder than your part material. The depth of indentations depends on the hardness of the impacted material. Therefore you will have shallower indentations on the strips than on your part material. That explains why the roughness is less for the strips. The effect of deep indentations on fatigue resistance depends on the shape of the indentations. Conditioning of cut wire reduces the sharpness of edges but does not produce spherical particles. Double and special conditioning gives further improvement. Examine your CCW shot using a microscope.

Thank you for your help
The cut wire is well rounded
My question is why the big difference in roughness between S110 and CW-14 and can I ignore it when there is no requirement for surface roufhness?
The only way I can messure roughness is on an Almen Strip comper ther two strip one shot by S110 and the other by cw-14

When cast steel shot is properly maintained the particles are very round (spherical). Cut wire starts as a cylinder and is pre-conditioned into a shape we often refer to as a soccer ball, meaning it is basically spherical but it is not as smooth as the cast steel.
The peening effects will be similar (compression etc) but the surface roughness will be different (until the cut wire shot becomes very, very round). I'm not aware of any studies that show a detrimental influence on fatigue life due to these differences in surface roughness.