J442_200605 Test Strip, Holder, and Gage for Shot Peening

Recommendation: Replace “Edge Type: Number 1 round” with “Edge Type: Number 1 (does not apply to ends of strip)

Rationale: edge type number one includes several variations, all of which are acceptable for the purpose of the test strip. Although the “round” edge may have nicer appearance the use of square edge number one or other variants does not affect the performance of the test strip. Relaxing this requirement will give the strip producers more flexibility in procuring raw material and will not be detrimental to the performance of the test strip.

Recommend deleting tempering temperature of 371 °C (700 °F)

Rationale: This is not the correct tempering temperature for the desired hardness range. Since the objective is to produce strips of certain hardness it should be left to the discretion of the producer to select the tempering temperature, which could be influenced by carbon content or as-quenched hardness.

Recommend deleting “Flatness: Measured as the reading on the Almen gage for each strip type is as follows:” and replacing with “Pre-bow:“ the arc height as measured by the Almen gage prior to peening. The maximum allowed pre-bow for each type of strip is as follows:”

Rationale: Pre-bow is the arc height measured on the Almen gage prior to peening. The Almen gage does not measure flatness per se.

Recommendation: add sentence “One or two additional holes may be used to facilitate mounting the holder to a fixture. The hole(s) may be threaded and shall not extend into the strip contact surface of the holder.”

Rationale: Several commercially available holders already accept the practice of mounting the holder by use of extra threaded holes. This provides a convenient method of attaching the holder to a fixture. The addition of such holes that do not degrade the performance of the holder should be allowed.

Recommendation: “A zero block, approximately the size of an Almen strip in length and width or large enough to contact the Almen gage 4-balls and indicator tip, with a minimum thickness of 5 mm shall be used to set the zero datum of the Almen gage. Flatness of the zero blocks shall be within ±.001 mm. Lapping the surface to achieve flatness is recommended.

Rationale: It is common industry practice to use a zero block similar to these dimensions but there has never been dimension or tolerance criteria established in J442. However, SAE J443 Section 5 states: “General – Prior to use, the zero position of the gage shall be checked with a flat calibration block (see SAE J442), and, if necessary, adjusted.” Therefore, to be consistent with J443 we need to add the zero block to J442. The flatness tolerance of ±0.001 mm can be easily met and inspected by standard commercial practices.

Recommendation: add a tolerance for distance between back post -0.5 to +2.0 mm.

Rationale: the absolute distance between the posts (i.e. the 20 mm span from centerline) is not critical. Only the distance of the edges of the posts to the centers of the ball centerlines (1.69/1.49 mm) is critical. Some older gages did not maintain the 20 mm ± 0.5 mm tolerance but they, nevertheless, still functioned appropriately. Spacing the back posts 20 mm with a tolerance of +2.0 mm and -0.5 mm has no influence on the accuracy of the strip reading. It would seem to be unnecessarily rigorous to disqualify a gage for this reason.

Recommendation: Replace “Any visual signs of wear…” with “Visual signs of wear or flat spots on the ball greater than 1.0 mm (.039 inch).“ Posts should be inspected for grooves that may interfere with proper seating of the test strip on the 4-ball platform and, if necessary, replaced.

Rationale: Virtually any use of the gage will produce “visual signs of wear” thereby rendering the gage useless. The present accept/reject criteria are entirely subjective leaving interpretation to auditors and inspectors. Inspection for flat spot of 1.0 mm can be easily accomplished using 5x to 10x magnification and a simple scale or calipers. This is the procedure used by several aerospace companies.