GEA Niro Method No. A 8 a Revised: September 2005

1. Definition

The powder sample is divided into fractions with different particle sizes by sieving.

2. Scope

The method is to be used for agglomerated milk powders, rewet agglomerated milk powders and other free-flowing powders. When modified, the method can also be used for fatty and sticky products – see Remarks 9.1.

3. Principle

Powder samples are sieved through a number of sieves with different mesh sizes using a horizontally oscillating movement.

4. Apparatus

1. Balance - sensitivity ± 0.1 mg.

2. Shaker for sieves, e.g. as supplied by Engelsmann, Germany (Fig. 1).

3. Brush.

4. Sieves with different mesh sizes, lid and base.

5. Reagents

None.

6. Procedure

1. Select the sieves, weigh them and the base, and place them on the base in decreasing order.

Agglomerated milk powder                     Rewet agglomerated milk powder
m                           U.S. Mesh                    m                                        U.S. Mesh

500                       35                                   2000                                 10

355                       45                                   1000                                 18

250                       60                                     710                                  25

212                       70                                     500                                  35

180             &am p;nb sp;         80                                     355                                  45

150                     100                                     250                                  60

125                     120                                     150                                100

2. Weigh out 50.0 g of powder and transfer it to the upper sieve.

3. Set the lid on the upper sieve and place the stack on the base of the shaker. Secure the stack and shake for 5 minutes.

4. Weigh each sieve and the base with the powder. Make sure that no powder sticking to the bottom of the sieve.

5. If >20% powder is found on the upper sieve or on the base, an additional sieve with a larger or smaller mesh size is added for a new sieve analysis.

7. Result

The result can be found in two different ways:

1. Each fraction is indicated as a percentage of the total weight.

; a = weight of powder on the sieve

; w = total weight of powder

Results are reported with 1 decimal.

Example:

% powder              sieve size, m

0.1                          >500

5.2                          >355 - ≤500

0.4                          >250 - ≤355

23.1                        >212 - ≤250

30.4                        >180 - ≤212

16.4                        >150 - ≤180

10.2                        >125 - ≤150

3.2                          >90 - ≤125

1.0                          ≤ 90

2. Accumulation of the numbers found on i ndividual sieves:

% powder         sieve size, m    ;        % powder             sieve size, m

0.1                      > 500                        1.0                         < 90

5.3                      > 355                        4.2                       <125

15.7                    > 250                      14.2                      < 150

38.8                    > 212                      30.8                      < 180

69.2                    > 180                      61.2                      < 212

85.6                    > 150                      84.3                      < 250

95.8                    > 125                      94.7                      < 355

99.0                    > 90                        99.9                       < 500

8. Reproducibility

N/A

9. Remarks

1. Fatty and sticky products will lump together and not pass through the sieves, especially for mesh sizes <150 µ. To prevent this, a free-flowing agent (e.g sodium aluminium silicate - Tix-O-Sil or Cal-Flo) can be used. Normally, 1-2% of free-flowing agent is suitable to prevent lumping on the sieves. Before sieving, gently mix the free-flowing agent with the powder in a beaker. When the corre ct amount of free-flowing agent is used, it will disperse evenly, so that no correction is needed when calculating the particle size distribution.

The use of free-flowing agent must be noted together with the results.

2. The particle size distribution of agglomerated and brittle powder will depend on the sieving time. If any deviation from this procedure is decided , specify it together w ith the results.

10. Literature

· GEA Niro Research Laboratory

· Allen Terence, Particle Size Measurement, 2. edition 1975 by
Chapman and Hall Ltd.