Screening analysis

Screening analysis is generally performed in the laboratory and is a method of analyzing the particle size composition of the material for the purpose of testing. A test conducted on a fine material of less than 0.5 mm is usually referred to as a sieve analysis. For tests greater than 0.5 mm, the screening test is called.
(1) Tools for screening test 1. Standard sieve Standard sieve is a sieve made of a certain size of mesh size, mesh width and wire diameter according to standard processing. The sieve surface is usually woven square hole. , sometimes bigger perforated plate mesh, very small holes (20 ~ 90μm) method employed to obtain the metal electrowinning. The screen surface is mounted on the cylindrical frame, and the upper and lower frames of each frame can be superposed on each other, from top to bottom, arranged from large to small, and each set of sieve has an upper cover and a bottom plate to form a sieve. In each set of sieves, the order in which the individual sieves are arranged from top to bottom is called a sieve sequence. In the same sieve sequence, the ratio of the mesh size on the adjacent sieve surface is usually a certain value, which is called the sieve ratio of the sieve. Some standard sieves have a sieve as a reference called a base sieve.
The standard sieves commonly used internationally are listed in Table 1. The standard sieve series used in China is similar to the Taylor standard sieve. The Taylor standard sieve series is marked by the mesh, that is, the number of sieve openings opened in the length of the lin. The sieve mesh of Taylor sieve is 0.075mm, the diameter of the sieve is 0.052mm, the diameter of the wire and the mesh are 0.127mm, so there are 200 mesh holes per inch length, so 200 mesh is called the base of the sieve. screen. Adjacent screen ratio is An additional sequence made for Taylor.

Table 1   Common standard sieve
American Taylor Screening 1
British National Standard 1
Sieve
(mm)
International Organization for Standardization 5
Screen number
(net)
Screen size (mm)
Main sequence R20/3
(mm)
Auxiliary sequence
Current standard
Old standard
(net)
Sieve
(mm)
R20
(mm)
R40/3
(mm)
2.5
3
3.5
4
5
6
7
8
9
10
12
14
16
20
twenty four
28
32
35
42
48
60
65
80
100
115
150
170
200
250
270
325
400
8.00
6.70
5.60
4.75
4.00
3.35
2.80
2.36
2.00
1.70
1.40
1.18
1.00
0.850
0.710
0.600
0.500
0.425
0.355
0.300
0.250
0.212
0.180
0.150
0.125
0.106
0.090
0.075
0.063
0.053
0.045
0.033
7.925
6.680
5.613
4.699
3.962
3.327
2.794
2.362
1.981
1.651
1.397
1.168
0.991
0.833
0.701
0.589
0.495
0.417
0.351
0.295
0.246
0.208
0.175
0.147
0.124
0.104
0.088
0.074
0.063
0.053
0.044
0.037
5/16 inch
1/4 inch
3.5
4
5
6
7
8
10
12
14
16
18
20
25
30
35
40
45
50
60
70
80
100
120
140
170
200
230
270
325
400
8.00
6.70
5.60
4.75
4.00
3.35
2.80
2.36
2.00
1.7
1.4
1.18
1.00
0.850
0.710
0.600
0.500
0.425
0.355
0.300
0.250
0.212
0.180
0.150
0.125
0.106
0.090
0.075
0.063
0.053
0.045
0.038
8.00
6.70
5.60
4.75
4.00
3.35
2.80
2.36
2.00
1.7
1.4
1.18
1.00
0.850
0.710
0.600
0.500
0.425
0.355
0.300
0.250
0.212
0.180
0.150
0.125
0.106
0.090
0.075
0.063
0.053
0.045
8.00
5.6
4.00
2.80
2.00
1.40
1.00
0.710
0.500
0.355
0.250
0.180
0.125
0.090
0.063
0.045
8.00
6.30
5.60
4.50
4.00
3.35
2.80
2.24
2.00
1.60
1.40
1.12
1.00
0.800
0.710
0.560
0.500
0.400
0.355
0.280
0.250
0.200
0.180
0.140
0.125
0.100
0.090
0.71
0.063
0.050
0.045
0.036
8.00
6.70
5.60
4.75
4.00
3.35
2.80
2.36
2.00
1.7
1.4
1.18
1.00
0.850
0.710
0.600
0.500
0.425
0.355
0.300
0.250
0.212
0.180
0.150
0.125
0.106
0.090
0.075
0.063
0.053
0.045
0.038
Note: These screens meet international standards recommended by the International Organization for Standardization (ISO). The international standardization series below 0.045 and above 8.00mm are not listed, and the finest part of R20 auxiliary series and R40/3 auxiliary series and above 8.00mm are not listed. The above list is for comparison of these sieves.
1—The sieve order of Taylor's standard sieve.
2—American Screening—ASTM (American Material Testing Standard), Specification E-11-1970 (77).
3—Canada standard sieve order.
4 - British National Standard BS410-1976.
5 — International Standard ISO 565-1972.
Since countries have standard screens for various countries and are not convenient for international exchanges, the International Organization for Standardization has comprehensively summarized several internationally important standard sieves to propose a compromise scheme that coexists and coexists. It is proposed to use sieves with a side length of 1 mm. , main sequence sieve ratio: Same as the national standard screening of the United States, Canada, and the United Kingdom. This has led to the harmonization of national standards.
2. Non-standard sieve
When sieving coarser materials (>0.5 mm), a woven non-standard sieve may be used, and the sieve openings are generally: 150, 100, 80, 50, 25, 13, 6, 3, 1, 0.5 mm, and the like. It is also possible to increase or decrease the size of one (or some) of the mesh as needed.
(2) Samples of the screening test
Screening test is to determine the size distribution of materials, and components required for certain items of various size according to the test object (e.g., the coal ash, sulfur, moisture, volatile matter, calorific value, etc.) measured.
Specimens for screening tests must be representative. Therefore, the sample must be taken in accordance with national or industrial standards.
The quality of the coal sample required for the screening test is related to the particle size of the material. The minimum representative test volume required for a typical screening test can be selected as follows:
Maximum blockiness (mm): 0.1 0.3 0.5 1 3 5 10 20
Minimum amount of sample (kg): 0.025 0.05 0.1 0.2 0.5 2 5 20
The coal sample quality of coal screening test shall be carried out according to the national standard GB477-87, and the pulverized coal screening of less than 0.5mm shall be carried out according to the standard MT58-81. The amount of screening test sample is not only related to particle size but also to its use. Screening coal samples for different purposes can be determined by reference to the following values:
(1) The design is not less than 10t.
(2) The coal sample used in mine production is not less than 5t.
(3) The coal sample selected from the coal preparation plant and its product coal sample shall be determined according to the upper limit of the selected particle size: 300mm is not less than 4t; 100mm is not less than 2t; 50mm is not less than 1t.
(4) The coal sample of 13~0mm grade can be reduced to not less than 100kg, and the coal sample of 3~0mm is reduced to not less than 20kg.
(5) The mass of coal samples less than 0.5mm shall not be less than 200g.
(6) The coal sample for coal screening test must be a sample taken under air dry conditions. [next]
(3) Method of screening test
The method of screening tests is also related to particle size. Generally, the material of 6mm or less can be used as a standard sieve, and the sieve of 6mm or more (0.5mm or more of coal) is used.
Screening experiments greater than 0.5mm shall be carried out in accordance with international or industry standards, and the samples shall be sequentially passed through sieves of: 100mm, 50mm, 25mm, 13mm, 6mm, 3mm and 0.5mm, if large sample content in the sample If it is small, it can be sieved with a sieve of 13mm or 23mm mesh, and then sieved and sieved, and sieved from the large sieve to the small sieve. However, it should be noted that the discarded samples are over-weighed and their mass is recorded so that the fractions can be converted for the yield of the total sample.
When the coal is subjected to the screening test, the size of the grain is larger than 50mm, and the coal is selected by hand, and the four products of coal, vermiculite and iron sulfide are sandwiched. Then, the quality of each fraction is determined separately, and then the coal samples for testing are extracted from each fraction and each product according to the provisions of GB 474-83. The amount of coal required should meet the requirements of Table 2.
Table 2   Preparation of sample size for each grade test
Maximum particle size (mm)
Minimum mass (kg)
>100
100
50
25
13
6
3
0.5
150
100
30
15
7.5
4
2
1

For the screening test of materials less than 6mm (coal less than 0.5mm), standard sieves can be used. At this point, it can be divided into dry sieve and dry and wet combined screening. When the sample is easily muddy or the requirements are not strict, the dry method is used for screening. When the material bonding is serious and strict, the dry and wet combined screening should be used. Dry screening, first arrange the sieve according to the order of the sieve holes from large to small, put the sieve bottom, pour the sample into the top sieve, and cover the sieve cover. Place the sieve on the vibrating screen machine, start the machine, stop every 5~10min, remove each layer of sieve in turn, and check the sieve on the enamel plate or tape by hand. If the hand is sieved for 1min, the quality of the sieve. No more than 1% of the mass of the sieve, which is sieved. Otherwise, re-screen on the vibrating screen until it is screened.
Dry and wet combined sieving, first use the finest sieve hole in the test (such as 0.045mm) to carry out wet sieving in water. After the fine sieving is finished, the sieve and the sifted material are separately baked. After baking in an oven not exceeding 75 ° C, the sieve is placed in a top sieve of a sieve for dry screening. The bottom layer of finely sieved undersize is still incorporated into the washed sieve and combined for calculation. After the sieving is finished, weigh it step by step. The difference between the sum of the masses of each granule and the total amount of the original sample before sieving shall not exceed 1% of the original sample. Otherwise, it should be redone.
When the coal is sieved small, it is necessary to reduce the size of each grade product into a test coal sample and determine the ash content.
(4) Test results and data compilation
The results of the screening test should be filled in the experimental report, usually in the form of a table, and the coal screening test report is shown in Table 3.
Table 3   Screening test report form

Production of coal sample number:
Screening test number: Test date: Year Month Day
Screening total sample extension test results: Mining Bureau Mine layer Working surface Sampling instructions:

Laboratory project

Coal sample
M ad
A d
V daf
S td
Q gr,d
Colloidal layer
Cohesive index
X(mm)
Y(mm)
Wool coal
Floating coal (<1.4)
5.56
5.48
19.50
10.73
37.73
37.28
0.64
0.62
25.686
71
Total weight of coal before screening: 19459.5kg Maximum grain size: 730 × 380 × 220mm
Granular grade
(mm)
Product name
Yield
quality
Q gr,d
(MJ/kg)
Weight (kg)
Accounted for the whole sample (%)
Cumulative on the sieve (%)
M ad (%)
A d (%)
S t,d (%)
>100
Hand selection
coal
Clam coal
Meteorite
Pyrite
Subtotal
2616.5
102.6
162.9
2882.0
13.497
0.528
0.839
14.846
14.846
3.57
2.86
0.85
3.39
11.41
31.21
80.93
16.04
1.10
1.43
0.11
1.06
28.680
20.871
100~50
Hand selection
coal
Clam coal
Meteorite
Pyrite
Subtotal
2870.4
80.6
348.7
3299.7
14.787
0.415
1.796
16.998
31.844
4.08
3.09
0.92
3.72
13.72
34.47
80.81
21.32
0.78
0.95
0.13
0.72
28.119
19.674
50~25
25~13
13~6
6~3
3~0.5
0.5~0
>50 total
coal
coal
coal
coal
coal
6181.7
2467.1
3556.7
2624.2
2399.4
1320.5
862.6
31.844
12.709
18.322
13.518
12.360
6.803
4.444
31.844
44.553
62.875
76.393
88.753
95.556
100.00
3.57
3.73
2.56
2.40
4.04
2.94
2.98
18.86
24.08
22.42
23.85
19.51
16.74
17.82
0.88
0.54
0.61
0.55
0.74
0.74
0.89
23.781
24.133
23.484
24.803
26.289
25.447
50~0 total
Total coal
Total raw coal (excluding vermiculite and pyrite above 50mm)
13230.5
19412.2
18900.6
68.156
100.00
97.365
3.08
3.24
3.30
21.62
20.74
19.11
0.64
0.72
0.74
In Table 3, the cumulative on the sieve (also called positive accumulation) indicates the sum of the yields of the respective grades larger than a certain sieve hole, that is, the percentage of the material larger than a certain sieve hole in the total amount of the material, and the same as the accumulation under the sieve. (also known as negative accumulation), which is the sum of the yields of the individual fractions smaller than a certain hole.
See Table 4 for small screening test reports for grades less than 6 mm (or less than 0.5 mm).
Table 4 Pulverized coal screening test report form
Coal sample name: Raw coal sample size: 0~0.5mm coal sample quantity: 500g
Test number:        Coal mining location:          Coal ash: 25.49%
Test date:       
granularity
(mm)
quality
(g)
Yield
(%)
Ash
(%)
Grand total(%)
Yield
Ash
>0.500
0.500~0.250
0.250~0.125
0.125~0.075
0.075~0.045
<0.045
total
107.55
106.50
43.60
38.10
204.25
500.00
21.51
21.30
8.72
7.62
40.85
100.00
24.00
25.03
25.95
25.90
26.34
25.49
21.51
42.81
51.53
59.15
100.00
24.00
24.51
24.76
24.90
25.49
Test leader: Check: Calculate:

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