What Is A Mid-Point Sieve?
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:
- Average Opening ±19µ
- Opening Dimension of 396µ not exceeded by more than 5% of the openings
- maximum individual opening 502µ
The mid-point would have a variation in Average Opening of ±9.5µ, 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.
Where Should Mid-Point Sieves Be Used?
When a process requires a high level of repeatability, mid-points can be used on all sieve tests. However, the predominant application for the mid-point sieves is as master stack. A master stack is used to check and recalibrate sieves used in everyday testing.
About The Construction
The Mid-Point Sieves supplied by CSC are produced by Endecotts, Ltd. The company is an ISO certified manufacturer. Endecotts manufacturing tolerances for these mid-point certified sieves are so tight that approximately 30% of the mesh inspected is discarded as not suitable for Endecotts Mesh Certified Sieves. To get a mid-point sieve, samples of mesh certified sieves are selected for the final mid-point check. Only the sieves that fall in the middle of the ASTM tolerances are tagged Mid-Point and a special certificate form is prepared showing the result of the inspection. One of the special benefits of the Endecotts sieve construction is a fillet. The fillet covers the solder connection between the the mesh to the frame. This keeps particles from being caught in the crevices and makes cleaning easier.
Summary
If your process must have traceability and the precision and repeatability of your sieve testing results is critical to your process or customer requirements, Mid-Point sieves should be considered for the master stacks and for every day testing of supercritical processes.
Mid-Point Sieve Inspection Report
Available Sizes