Home Forums General Discussion Shot Peening Process, Intensity, Coverage endless saturation curve

Hello everyone,
one of our shot peening machine (tunnel type, with 3 turbines) is now running on 1,2mm shot (before it was 1mm).
I'm trying to use saturation measurement performed by a colleague (but who never analysed/drawn the curve...).
As it's a tunnel, peening time is adjust by conveyor speed
Measurement are performed with C plate (with A we had 0.76mm at 2min, 1.20mm at 8..... so A is not suitable)
The strange stuff is that we have lower saturation value with the new large shot! Turbine are compatible for the new diameter shot.

[img]https://ibb.co/cwrzVC1[/img]

What should I conclude? on 1,2mm shot saturation curve, measurements was stopped to soon? I have drawed a new curve with an imaginary 16 minutes points (trying to achieve a plateau), it naturally increase the saturation value. Result looks more logical. But I'm not so sure it would reach that plateau on the next point. It seems to keep rising, after 16min, it would be 32minutes crazy long.
Did you ever had such curve, who keep rising? What to conclude, lower saturation value, but 4 and 8 minutes points are much higher than before.
In SAE J443, we can read: It should be noted that Almen strips exposed for extended periods may exhibit arc heights significantly greater than the “intensity” value.


Thanks to all who read that.
a nice day to all shot peener!

EDIT: I have tried with another curve solver (according to SAE J2597), and found intensity of 0.19 with 1mm shot and 0.229 with 1.2 shot, more logic.
Did you have already experienced such difference with different solver?
Maybe something goes wrong in my excel, strange, but you can observe on the picture in previous kind of an angle in the curve

Jean,

In order to help I'll need some so more information.
You say the peeing "time" is adjusted by the speed of the conveyor.
1) Am I understanding you correctly that the test strip holder passes through the machine from the left to the right or right to the left?

1.1)If this is true could you base your saturation curve on the number of passes through the machine at the same speed and not time?

1.2)What is the speed of the conveyor?

2) You have 3 turbines or wheels, can you turn them on and off independently?

3) Does each wheel peen the same test strip location?

4) At each arc height reading what would you estimate the coverage percentage to be on the test strip?

Hello Walter, thank you for your post,
some answers:
1) Am I understanding you correctly that the test strip holder passes through the machine from the left to the right or right to the left?
yes

1.1)If this is true could you base your saturation curve on the number of passes through the machine at the same speed and not time?
it could be possible, it what discussed as one possiblity


1.2)What is the speed of the conveyor?
at first point, it's 10m/min


2) You have 3 turbines or wheels, can you turn them on and off independently?
This is something I ask since a lots of time, for the moment everything run at the same time

3) Does each wheel peen the same test strip location?
No, one plaquette for each turbine, but, everything run a the same time, so result is a bit a mix of everything

4) At each arc height reading what would you estimate the coverage percentage to be on the test strip?
coverage is 100% since the first passage

jJean,

4) At each arc height reading what would you estimate the coverage percentage to be on the test strip?
coverage is 100% since the first passage

You are peening the test strips way too long! At the point of saturation the test strip should be close to 100% coverage with peening coverage uniformly distributed on the test strip.

Your machine may not be capable of producing a 4-point saturation curve. It sounds like you may not be able to send the test strip though the shot stream fast enough to have anything less than 100% coverage on the strip. If true, then you have what is known as a Type 2 Curve. See SAE J443 "In some cases, saturation curves can appear as exemplified in Figure 2 (Type 2) and occur only when process variables do not permit the attainment of earlier data points."

Thank you very much Walter!
interesting answer
For drawing a type 2 saturation curve, I would still need much homogenuous result, isn'it? Here I clearly have the iconic rise of a type 1 saturation curve at the begining
If test strip is 100% covered, and max residual stress is obtained at 100% coverage, what mechanism make the almen plate continue to bend? recrystalisation? Almen plate is already made out of hard material and fine structure.

Two mechanisms contribute to Almen strip curvature. These are: plastic deformation and residual stress. Plastic deformation will continue after notional 100% coverage. Recrystallisation is not a factor.