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GEA Niro Method No. A 8 a |
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Revised: September 2005 |
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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 &n
bsp; Rewet agglomerated milk
powder
m &nb
sp;
; U.S.
Mesh &nbs
p;
m &
nbsp; &nb
sp;
U.S. Mesh
500 &nb
sp;
35
&n
bsp;
2000 &nbs
p;
10
355 &nb
sp;
45
&n
bsp;
1000 &nbs
p;
18
250 &nb
sp;
60
&n
bsp;
710
; &
nbsp; 25
212 &nb
sp;
70
&n
bsp;
500
; &
nbsp; 35
180 &nb
sp; &am
p;nb sp;
80
&n
bsp;
355
; &
nbsp; 45
150 &nb
sp;
100
; &
nbsp;
250
; &
nbsp; 60
125 &nb
sp;
120
; &
nbsp;
150
; &
nbsp; 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 &nb
sp;
; >500
5.2 &nb
sp;
>355 - ≤500
0.4
&n
bsp; >250 - ≤355
23.1 &n
bsp; >212
- ≤250
30.4 &n
bsp; >180
- ≤212
16.4 &n
bsp; >150
- ≤180
10.2 &n
bsp; >125
- ≤150
3.2 &nb
sp;
; >90 - ≤125
1.0 &nb
sp;
; ≤ 90
2. Accumulation of the numbers found
on i ndividual sieves:
%
powder sieve size,
m ; %
powder
sieve size, m
0.1 &nb
sp; >
500
;
1.0
; < 90
5.3 &nb
sp; >
355
; 4.2 &nbs
p;
<125
15.7 &n
bsp; >
250
; 14.2 &nb
sp;
; < 150
38.8 &n
bsp; >
212
; 30.8 &nb
sp;
; < 180
69.2 &n
bsp; >
180
;
61.2 &nbs
p; < 212
85.6 &n
bsp; >
150
; 84.3 &nb
sp;
; < 250
95.8 &n
bsp; >
125
;
94.7 &nbs
p; < 355
99.0 &n
bsp; >
90
99.9 &nbs
p;
< 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.