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Sample Size For Particle Sieving Analysis


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Sample Size For Particle Sieving Analysis

For a lot of experiments, the tendency is to use an excessively large sample to get more accurate test results. However, for sieving analysis, the accuracy of the result will be reduced if the sample is too large. In fact, dividing the sample into several small batches reduces the chance of errors occurring. If the samples size is too large, it will fail to permit each of the particles an opportunity to present themselves on the test sieve surface. Generally speaking, a 25-100g sample is recommended for hand sieving.

How to establish the sample size in general:

Step 1: use a sample splitter to reduce sample to different weights (25g, 50g, 100g,200g)

Step 2: test samples with the various weight range

Step 3: Evaluate the weight figures. If the test with 50gram sample shows approximately the same percentage passing the fine sieve as 25gram sample, whereas 100 gram shows a much lower percentage, this would indicate that the 50gram sample is the appropriate sample size.

How to choose sample sizes for different test sieves:

Test sample size is determined by the aperture of the test sieve and the bulk density of the sample itself. Table 2 below is an index of recommended sample volumes to be used on different aperture sizes. However, the table should be used as approximate guidance, users still need to alter the sizes depending on the attributes of the sample and the diameter of the test sieves used.

Table 2 demonstrates the volume of the sample rather than the weight. Normally sieving tests run with the measurement of sample weights. Users need to multiply sample density by recommended volume to get the recommended sample weight.

For instance, 200mm or 8” diameter test sieve with 1mm aperture size, recommended volume is 140 cm³. Recommended sample volume multiplied by the bulk density of the sample will come up with the recommended sample size weight in grams as in Table 1 below.

Recommended sample size weight (g) = Recommended sample volume (cm³) x sample density (g/cm³)

Table 1 Demonstrate how to use recommended sample volume, using 200mm diameter test sieves to test builders cement powder as example


Tips:

  • It is recommended to split sample into a couple of batches, especially when more than half volume of sample is still retained on the test sieves after sieving.

  • Overloading can cause damage on fine mesh test sieves. It is suggested to place a larger aperture size test sieve above to help remove the burden and unnecessary weight from heavy particles.

  • Care should be taken in selecting the sieve aperture size when particles are in deformed shapes (pointed, forked, tapered, flaky etc.)

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Table 2 Recommended Test Sample Volume on Test Sieve Apertures.


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