I have often ranted about the limited range of ASTM 11 sieve mesh standards as it relates to individual sieve certification. We at CSC have tried to help clearly distinguish between different levels of inspection and/or degrees of conformity. We outlined three levels of sieve certification. These are working sieves, mesh certified sieves and mid point sieves. There are summary definitions of these categories on the CSC Web site.
In June of this year, the ASTM E-11 committee, published a revised standard for test sieves. Among other things, it tightened up the specifications on maximum opening size. In addition, the new standard changed the way the specification is defined. It also provides a standard and definition for three levels of mesh certification. These levels are named: Compliance Test Sieves, Inspection Test Sieves and Calibration Test Sieves.
In addition to detailed specifications of the construction of test sieves the ASTM E11-9 defines the following characteristics of the three compliance levels:
- Compliance Test Sieves – This level states that the sieve cloth (mesh) was inspected prior to mounting in the sieve and that the cloth meets the requirements of the standard. Part of the standard for a Compliance Test Sieve is that the standard deviation of the openings measured will not exceed that for a confidence level of 66%. The certification document does not require any statistical documentation.
- Inspection Test Sieves – In these sieves, the cloth(mesh) is inspected after mounting in the sieve. The Inspection Test Sieve must have a standard deviation of the openings measured that does not exceed the number needed for a confidence level of 99%. An inspection document shall be included that states at a minimum, the value for the average aperture size, separately in both the warp and shute direction of the sieve cloth.
- Calibration Test Sieves – In these sieves the cloth (mesh) was inspected after mounting in the sieve. The inspection standard for this sieve requires that the standard deviation of the openings measured does not exceed that for a confidence level of 99.73%. A Calibration Test Sieve certificate shall include at a minimum, the number of aperture and wire diameters measured, the average aperture size, standard deviation and average wire diameter, separately in both the warp and shute directions of the sieve cloth.
Because current sieve definitions and calibration standards are based on older definitions and certifications, it may be some time before these newer tolerances and definitions are instituted in the field. Further it will take sieve manufactures time to switch their processes to these newer definitions and certifications.
The changes stated in ASTM E11-09 have defined the specific measurement and calculation details that define three confidence or assurance levels for test sieves. I would expect that over time these new standards will replace the current less defined variations.
Let me know what you think will happen. Do you think this is a good change?