The purpose of sieving is to separate particles according to size. The challenge is getting individual particles to present themselves to the sieve openings without sticking together, blinding the mesh or changing during the test.
Dry sieve analysis
Dry sieving is the normal starting point for materials that are sufficiently free-flowing and stable in air. The sample is placed on the top sieve of a stack and agitated so smaller particles can pass through progressively smaller apertures.
It works well when particles separate cleanly and do not strongly adhere to each other or to the sieve cloth.
Wet sieve analysis
Wet sieving uses a liquid to help disperse and carry fine particles through sieve openings. It may be useful for materials that agglomerate, carry electrostatic charge, or produce fine dust that does not separate effectively when dry.
However, the liquid must not dissolve, react with or otherwise alter the material in a way that invalidates the test. The governing method should permit the approach.
Key differences to think about
- Material behaviour: free-flowing versus cohesive or agglomerated.
- Method requirements: whether wet processing is allowed or prescribed.
- Sieve configuration: whether the frames and setup are suitable for liquid flow.
- Sample stability: whether contact with liquid changes the sample.
- Cleaning and drying: how the sieve will be cleaned and returned to service after testing.
Do not switch methods just to get a nicer result
Wet and dry results are not automatically interchangeable. Changing preparation or separation conditions can change the measured distribution. If results are used for compliance or acceptance, follow the specified procedure and document any approved deviation.
What to tell a sieve supplier
State that the sieves will be used for wet testing, identify the material and liquid if relevant, provide the required apertures and frame dimensions, and reference the test method. That gives the supplier enough context to recommend an appropriate format.
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