Endecotts Sieves for Master Stacks
A mid-point sieve has had the mesh inspected. The sieve is then selected as a mid-point if the results give tolerances that are in the middle of the ASTM standard. For example, the ASTM permissible variations for the mesh of a No. 40 sieve (425µ) are:
The mid-point would have a variation in average opening size of ±9.5µ, an opening dimension of 396µ not exceeded by more than 2.5% of the openings and a maximum individual opening of 463.5µ. The effect of this tightened tolerance is an improvement in variation of approximately 30%. These results are traceable to a NIST standard.
Available in the following options:
When a process requires a high level of repeatability, mid-points can be used on all sieve tests. However, the predominant application for mid-point sieves is as master stack. A master stack is used to check and re-calibrate sieves used in everyday testing.
The needs for woven wire mesh tolerances, tighter than the certified specifications of the older ASTM E112-04 were satisfied by mid-point sieves. These applications can be serviced by the new Inspection and Calibrationcategories found in ASTM E11-09 Specifications.
However, many quality control systems inspected under ISO 9000 Quality Management procedures have mid-point sieves as the traceable standard for sieve testing. Because of the difficult, long and complex procedure needed to change standards in an approved quality system, we continue to provide a full range of mid-point sieves.
In addition to the tightening of the wire mesh sieve certification standards by ASTM, there is a growing trend for the use of calibration techniques. These calibration techniques provide a check on the actual performance characteristics of a sieve and not a static measurement of a small sample of openings.
There are calibration techniques that are traceable to NIST or other national measurement bodies. Using methods such as calibration beads, makes it practical to only use Compliance Sieves throughout an operation. These calibrations can be used in standard quality management systems such as ISO 9000.