The Shot Peening Dictionary
The following is an alphabetical list of terms and their definitions common to the shot peening industry. In no way do we presume to suggest that this list is complete. In fact we need your help to make it both accurate and as extensive as possible. Additional terms & definitions, corrections and/or comments are welcome! Please send us your suggestions by using the e-form at the bottom of this page.
Shot Peening Terminology
- Aluminoslicate glass beads: To be used for surface finishing of highly wear resistant castings of hardness more than 9 in mohs scale. Nominal composition of the beads is: Fe 54%, Silicon 36%, Aluminum 11%.
- Automatic: a class of peening machine that precludes use of manual movement of either the shot stream or the workpiece but relies upon mechanical means to provides these features.
- Cognizant Authority: entity responsible for approving specification or drawing departures and interpretations.
- Coverage: the extent of obliteration of the original surface by dimples produced by impact from individual shot particles and is expressed as a percentage. Complete coverage, or full coverage, is defined as 98% dimpling of the original surface. Coverage requirements of 200% or 300% are obtained by extending the exposure time by a factor of 2,3 etc. NOTE: 200% coverage is not synonymous with 2T coverage. 2T coverage is the doubling of time required to bring an Almen strip to saturation.
- Full Coverage: Full coverage, complete coverage and 100% coverage are synonamous terms and defined as complete dimpling or obliteration of the original surface of the part to be peened (not Almen strip).
- 200% Coverage: Coverage that is achieved by exposing the peened part to the blast stream for twice the time needed to achieve 100% coverage. NOTE: 200% coverage is not synonymous with 2T.
- 1T: The exposure time on the saturation curve needed to determine intensity.
- 2T: Twice the exposure time of 1T to achieve a 10% increase in arc height on the saturation curve Note: 2T is not the same as 200% coverage.
- Intensity: A measure of the energy of the media stream. The intensity is determined from interpretation of an Almen saturation curve. It is the first point on the curve (not necessarily an actual data point) commonly referred to as "T", that meets the following criteria: the arc height curve increases by 10% when the exposure time is doubled (or "2T").
- Intensity Determination: A process of determining the peening intensity using a minimum of four (4) Almen strips and generation of a graph using a smooth fit curve to determine the intensity value. Intensity determination is usually done at original machine set-up or after changes to any major process parameter or component.
- Intensity Verification (or Confirmation): A process of affirming that the peening intensity is within tolerance of the value established during intensity determination. Only one (1) Almen strip is needed (at each required location) and it is exposed at a time equal to or greater than the saturation time (1T) and less than double saturation time (2T) established during intensity determination. For example, if an intensity of 6-10A is required and the intensity determination was 7.2A, then the intensity verification would have to be within 6.2A and 8.2A. However, the intensity verification must also conform to the peening intensity limits specified on the drawing.
- Intensity Determination Tolerance: the tolerance of peening intensity listed on the drawing requirements (for example 6-10A) which allows for repeatability and angle of impingement considerations.
- Intensity Verification Tolerance: the variation allowed for confirmation compared to the original set-up intensity determination. The tolerance for "A" and "C" intensities is +/- 0.001 inch and the tolerance for "N" intensities is +/-0.002 inch.
- Media: any of the commonly used materials used for peening, such as cast steel shot, cut wire shot, ceramic bead, glass bead, or peening balls. See AMS 2431
- Nominal Size: approximate size of media in ten-thousandths of inch. Example: S-110 = 0.011 inch. Used in determining minimum fillet radius requirements. The size of the media maintenance screen opening for 20% Passing.
- Saturation Curve: A plot of data points exhibiting the relationship of Almen strip curvature and exposure to the blast stream.
- Tracer: a special fluid applied to a part to assure correct shot impingement (targeting) and to measure the degree of coverage. It is recommended to establish the removal rate of the tracer proportional to actual coverage.