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Joined: Apr 1999
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J
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J
Joined: Apr 1999
Posts: 341
Likes: 1
Dear Jack,

I have a tumblast from Wheelabrator that I need to shot peen some small steel parts about three inches long by 3/8" made in the shape of a half-moon.

The parts tumble around in the Tumblast to be peened.

My question: Should I put the Alman block and test strip in for "x" amount of minutes to test it or should I use a different method?

Thank you,

Mark

Joined: Apr 1999
Posts: 341
Likes: 1
J
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OP Online Content
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J
Joined: Apr 1999
Posts: 341
Likes: 1
Dear Mark,
This is a very interesting topic. The exposure of the Almen strip in this type of machine is somewhat random and can cause some concern.

First I'll describe a common industry practice and then an alternative. Later I'll mention some issues to be aware of during testing.


1. Yes. You will need several Almen strips. Place the strip and holder into the machine with a batch of parts to be peened. The first strip is exposed for a brief period. The second strip for a longer period and so on until the arc height readings don't continue to increase with longer exposure times. Plot the data onto a graph for a "saturation" curve and determine the intensity using the 10% rule (arc height increase by 10% when exposure time is doubled).

2. The above process can be very time consuming because it takes a while to accumulate dents on the Almen strip. The strip orientation to the blast stream is always changing and it can also be masked by the small components you are peening. An alternate method is to make a fixture and mount the strip in a stationary manner in the shot stream without the mill (tumbling action). You will have to activate the shot flow rate for brief periods, perhaps 5 seconds, 10 seconds, 20 seconds and so on. This method is much faster since your accumulation rate for dents on the strip is greatly improved.

3. If you are curious you can try another experiment. Place a strip and holder into the machine with a standard load of parts. Turn on the mill (tumbling action) but do not activate the shot flow. Run the machine like this for about one minute and then measure the Almen strip arc height. If the impact of the parts onto the Almen strip is such that you can read an arc height even though you have no shot impacts then you can demonstrate why you should be using method number 2.

Note: a simple computer program that generates the saturation curve and interprets "intensity" is available from our web site for FREE. Click on this link http://www.shotpeener.com/learning/solver.htm


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