
Designed for engineers and technicians from a wide range of abilities and backgrounds, this manual covers basic conveyors, selection, safety, legal obligations, terminology and background. It is an excellent introduction to troubleshooting and maintenance of conveyors and chutes.
It is intended to cover the fundamentals of belt conveying and would be useful for those with little experience in this area. Also featuring numerous tips and case studies throughout, this manual is a collection of important information in one place.
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Introduction - Best Practice Design, Maintenance and Troubleshooting of Conveyors and Chutes
1 Introduction
1.1 Introduction
Material handling plays an important part in the modern economy. No modern industrial plant: be it a coal mine, power plant, cement plant or a metallurgical plant, would be conceivable without an efficient transport system. Conveying equipment, of one or several types, is usually employed to mechanize material handling, loading and unloading operations. Conveying equipment works in conjunction with process equipment, such as that used for crushing, screening, blending etc. Overall mechanization of the processes becomes effective with appropriate selection of material handling equipment. This equipment not only substitutes manual labor, but also helps in the rational matching with all equipment responsible for the manufacturing processes, thereby enhancing the overall mechanization. Nowadays the operation and control of an entire plant is done from a properly networked centralized control room. Even the troubleshooting is carried out from there for detecting problem areas and initiating maintenance activities.
The boiler stoking system in a thermal power plant requiring supply of coal round the clock, materials transported in blast furnaces and materials conveyed from underground and open pit mines are some of the important areas where material handling plays a vital role.
1.2 Classification and characteristics of materials
The type of material handled and its physical as well as mechanical properties are the principal factors determining the type and design of conveying equipment and its accessories. Bulk materials include various heap-loaded, granular and powdered materials such as coal, ore, molding sand, saw dust, food grains and so on.
Bulk materials are characterized by their physical and mechanical properties, such as:
Figure 1.1
Particle size
Lump size is determined through a consecutive screening of the material through meshes of different sizes. According to the uniformity of lumps in its composition, a bulk material is classified as sized or graded and unsized or non-graded.
A material, in which the ratio between the largest characteristic particle amax and the smallest characteristic particle amin is above 2.5, is considered to be unsized.
In sized materials, i.e. more or less homogeneous ones, amax: amin < 2.5. Sized materials are characterized by their average lump-size, for example:
In the unsized material, if the weight of a group of particles of lump size ranging between 0.8 amax and amax is greater than 10% of the total weight of the sample, then the material is characterized by lump-size amax and if it is otherwise, the characterization is done as 0.8 amax.
Tables 1.1 and 1.2 below show sizekWise classification of bulk materials and the recommended maximum lump size for different belt widths.
Table 1.1
Material characteristics
Material Characteristic |
Size (mm) |
Large-Lumped |
Over 160 |
Medium-Lumped |
60 to 160 |
Small-Lumped |
10 to 60 |
Granular |
3 to 10 |
Fine |
0.5 to 3 |
Very Fine |
Below 0.5 |
Table 1.2
Maximum lump size for different belt widths
Belt width in mm |
Uniform lumps (mm) |
Mixed with roughly 80% fines (mm) |
300 |
- |
- |
350 |
50 |
100 |
400 |
75 |
125 |
450 |
100 |
150 |
500 |
100 |
175 |
600 |
125 |
200 |
650 |
125 |
250 |
750 |
150 |
300 |
800 |
150 |
300 |
900 |
175 |
325 |
1000 |
200 |
375 |
1050 |
200 |
375 |
1200 |
300 |
450 |
1350 |
300 |
500 |
1400 |
300 |
600 |
1500 |
350 |
600 |
1600 |
375 |
600 |
1800 |
450 |
600 |
2000 |
450 |
600 |
1.3 Properties of the conveyed material
Figure 1.2
Angle of repose
Table 1.3
Properties of most commonly used bulk material (approximate values)
Material |
Bulk Density, g Tons per cu.m |
Angle of Repose, j degree |
Anthracite, fine, dry |
0.8 to 0.95 |
45 |
Gypsum, small-lumped |
1.2 to 1.4 |
40 |
Clay, dry, small-lumped |
1.0 to 1.5 |
50 |
Gravel |
1.5 to 1.9 |
45 |
Foundry sand, shake-out |
1.25 to 1.30 |
45 |
Ash, dry |
0.4 to 0.6 |
50 |
Limestone, small lumped |
1.1 to 1.5 |
38 |
Coke |
0.36 to 0.53 |
50 |
Wheat |
0.65 to 0.83 |
35 |
Saw dust |
0.16 to 0.32 |
39 |
Sand, dry |
1.4 to 1.65 |
45 |
Iron ore |
2.1 to 2.4 |
50 |
Coal, run of mine |
0.8 to 1.0 |
38 |
Cement, dry |
1.0 to 1.3 |
40 |
Crushed stone, dry |
1.8 |
45 |
Slag, blast furnace, crushed |
1.3 to 1.4 |
25 |
Table 1.4
Bulk material characteristics
Material
|
Material bulk/density (kg/m3) |
Surcharge angle degrees
|
Recommended maximum inclination degrees |
Code
|
Alum, fine |
721-802 |
|
|
B35 |
Alum, lumpy |
802-962 |
|
|
D35 |
Alumina |
802-1042 |
10 |
10-12 |
B27M |
Ammonium nitrate |
721 |
|
|
•C36NUS |
Asbestos shred |
320-401 |
|
|
E46XY |
Ash, black, ground |
1683 |
15 |
17 |
•B35 |
Ashes, coal, dry, 13mm and under |
561-641 |
20 |
20-25 |
C46TY |
Ashes, coal, dry, 76mm and under |
561-641
|
|
|
D46T
|
Ashes, coal, wet 13mm and under |
721-802
|
25
|
23-27
|
C46T
|
Ashes, coal, wet 76mm and under |
721-802
|
|
|
C46T
|
Ashes, fly |
641-721 |
20 |
20-25 |
A47 |
Ashes, gas-producer, wet |
1250 |
|
|
D47T |
Asphalt, binder for paving |
1283-1363
|
|
|
C45
|
Asphalt, crushed, 13mm and under |
721
|
|
|
C35
|
Bagasse |
112-160 |
|
|
E45Y |
Bark, wood, refuse |
160-320 |
20 |
27 |
E46Y |
Barley |
609 |
10 |
10-15 |
B15N |
Barytes, powdered |
1924-2245 |
|
|
B26 |
Bauxite, ground, dry |
1090 |
15 |
20 |
B26 |
Bauxite, mine run |
1283-1443 |
15 |
17 |
037 |
Bauxite, crushed 76mm and under |
1202-1363
|
|
20
|
D37
|
Bentonite, crude |
561-641 |
|
|
D46X |
Bentonite, 100 mesh and under |
802-962
|
|
20
|
A26XY
|
Bones |
545-641 |
|
|
* |
Bonemeal |
882-962 |
|
|
B36 |
Borax, 50mm to 100mm lumps |
962-1042
|
|
|
D36
|
Borax, 40 to 50 mm lumps |
882-962
|
|
|
D36
|
Brewer's grain, spent, dry |
401-480 |
|
|
C45 |
Brewer's grain, spent, wet |
882-962 |
|
|
C45T |
Brick, hard |
2004 |
|
|
D47Z |
Brick, soft |
1603 |
|
|
D47 |
BuckWheat |
641-673 |
10 |
11-13 |
B25N |
Carbon, black, pefletised |
320-401 |
|
|
B15Q |
Cardon, black, powder |
64-112 |
|
|
•A35Y |
Carborundum, 61mm and under |
1603
|
|
|
D27
|
Cement, Portland |
1507 |
20 |
20-23 |
A26M |
Cement, Portland, aerated |
962-1202 |
|
|
A16M |
Cement rock (see limestone) |
1603-1764
|
|
|
D36
|
Cement clinker |
1202-1523 |
15-20 |
18-20 |
D37 |
Cement mortar |
2132 |
|
|
37Q |
Chalk, lumpy |
1202-1363 |
|
|
D26 |
Chalk, 100 mesh and under |
1042-1202
|
|
|
A46MXY
|
Charcoal |
289-401 |
15 |
20-25 |
D36Q |
Chips, paper mill |
320-401 |
|
|
E45 |
Chips, paper mill, softwood |
192-480
|
|
|
E45
|
Clay (see also bentorite, diatomaceous earth, fullers earth, kaolin and Marl) |
||||
Clay, calcined |
1283-1603 |
|
|
B37 |
Clay, dry, fines |
1603-1924 |
15 |
20-22 |
C37 |
Clay, dry, lumpy |
962-1202 |
15 |
18-20 |
D36 |
Coal, anthracite, river or culm, 32mm and under |
962 |
15 |
18
|
B35TY
|
Coal, anthracite, sized |
882-962 |
15 |
16 |
C26
|
Coal, bituminous, mined 50 mesh and under |
802-866 |
20 |
24 |
B45T |
Coal, bituminous, mined and sized |
721-882
|
15
|
16
|
|
Coal, bituminous, mined, run of mine |
721-882 |
20 |
18 |
D35T |
Coal, bituminous, mined slack, 13 mm and under |
689-802 |
20 |
22 |
C45T |
Coal, bituminous, stripping, not cleaned |
802-962 |
|
|
D36T |
Coal, Lignite |
641-72 |
20 |
22 |
D35T |
Coke, loose |
369-561 |
|
18 |
D47QVT |
Coke, petroleum calcined |
561-721 |
|
20 |
D36Y |
Coke, breeze. 64mm and under |
401-561 |
15-20
|
20-22
|
C37Y
|
Concrete, 51mm slump |
1764-2405 |
|
24-26 |
D26 |
Concrete, 102mm slump |
1764-2405 |
|
20-22 |
D26 |
Concrete, 152mm slump |
1764-2405 |
|
12 |
D26 |
Copper ore |
1924-2405 |
|
20 |
•D27 |
Copper ore, crushed |
1603-2405 |
|
|
D27 |
Copra, lumpy |
353 |
10 |
9 |
D25 |
Com grits |
641-721 |
|
|
B25W |
Cryolite, dust |
1202-1443 |
|
|
A36 |
Cryolite, lumpy |
1443-1603 |
|
|
D35 |
Diatomaceous earth |
176-224 |
|
|
A36MY |
Dolomite, lumpy |
1443-1603 |
|
22 |
D26 |
Earth, as excavated - dry |
1122-1283 |
15 |
20 |
B36 |
Earth, wet, containing clay |
1603-1734
|
20
|
23
|
B46 |
Feldspar, 13mm screenings |
1122-1363
|
20
|
18
|
B36
|
Feldspar, 38mm to 76mm lumps |
1443-1734
|
15
|
17
|
D36
|
Feldspar, 200 Mesh |
1603 |
|
|
|
Fish, meal |
561-641 |
|
|
B45W |
Flour, wheat |
561-641 |
|
21 |
A45PN |
Flue dust, boiler house, dry |
561-641
|
|
|
A17MTY
|
Fluorspar, 13mm screenings |
1363-1683
|
|
|
C46
|
Fluorspar, 38mm to 76mm lumps |
1734-1924
|
|
|
046
|
Flay ash, dry (see flue dust) |
|
|
|
|
Foundry sand, loose (see sand) |
1283-1443
|
|
|
B47
|
Foundry refuse, old sand cores, etc |
1122-1603
|
|
|
D37Z
|
Fullers earth, dry |
481-561 |
10 |
|
B26 |
Fullers earth, oily |
962-1042 |
|
|
B26 |
Fullers earth, oil filter, burned |
641
|
|
|
B26
|
Fullers earth, oil filter, raw |
561-641
|
15
|
20
|
•B26
|
Garbage, household |
802 |
|
|
•E45VW |
Glass batch |
1283-1603 |
|
20-22 |
D27Z |
Granite, 13mm screenings |
1283-1443
|
|
|
C27
|
Granite, 38mm to 76mm lumps |
1363-1443
|
|
|
D27
|
Granite, broken |
1523-1603 |
|
|
027 |
Gravel, bank run |
1443-1603 |
20 |
20 |
|
Gravel, dry, sharp |
1443-1603 |
|
15-17 |
D27 |
Gravel, pebbles |
1443-1603 |
15 |
12 |
Q36 |
Gypsum dust, non-aerated |
1491
|
|
|
|
Gypsum dust, aerated |
962-1122 |
20 |
23 |
A36Y |
Gypsum, 13mm screenings |
1122-1283
|
20
|
21
|
C36
|
Gypsum, 38mm to 76mm lumps |
1122-1283
|
15
|
15
|
D26
|
Ice, crushed |
561-721 |
|
|
D16 |
llmenite ore |
2245-2565 |
|
|
B27 |
Iron ore |
1603-3206 |
15 |
18-20 |
•D36 |
Iron ore, crushed |
2164-2405 |
|
20-22 |
•C26 |
Iron oxide, pigment |
401 |
20 |
25 |
A45 |
Kaolin clay 76mm and under |
1010
|
15
|
19
|
036
|
Kaolin talc, 100 mesh |
673-898 |
20 |
23 |
A46Y |
Lead ores |
3206-4329 |
15 |
15 |
'B36RT |
Limestone, agricultural 3mm and under |
1090 |
|
20 |
B26 |
Limestone, crushed |
1363-1443 |
20 |
18 |
C26X |
Limestone, dust |
1283-1363 |
|
20 |
A46MY |
Malt, meal |
577-641 |
|
E25 |
|
Manganese ore |
2004-2245 |
20 |
20 |
'D37 |
Nickel-cobalt, sulphate ore |
1282-2405
|
|
|
•D27T
|
Oats |
417 |
10 |
10 |
C25M |
Paper pulp stock |
641-962 |
|
|
•E15MV |
Phosphate, acid fertilizer |
962 |
15 |
13 |
B25T |
Phosphate, triple super ground fertilizer |
801-882 |
20 |
30 |
B45T |
Phosphate rock, broken, dry |
1202-1363
|
15
|
12-15
|
026
|
Phosphate rock, pulverized |
962
|
20
|
25
|
B36
|
Pyrites, iron 52mm to 76mm lumps |
2164-2325
|
|
|
D26T
|
Pyrites, pellets |
1924-208 |
|
|
C26T |
Quartz, dust |
1122-1283 |
|
|
A27Y
|
Quartz, 13mm screenings |
1283-1443
|
|
|
C27Z
|
Quartz 38mm to 76mm lumps |
1363-1523
|
|
|
027Z
|
1.3.1 Estimation of surcharge angle
In the absence of reliable information on the surcharge angle, the following method may be employed to serve as a guide in the selection of a suitable value. The process is based on reducing the angle of repose and allows for:
The nominal surcharge angle in degrees is given by the equation,
Surcharge angle = X - Kv - Km - Ks
Where:
X is the angle of repose in degrees
Kv is the velocity or slope reduction allowance in degrees
Km is the material reduction allowance in degrees and
Ks is the special reduction allowance in degrees
Velocity/ slope reduction allowance - Kv
This factor takes into consideration both the belt velocity as well as the angle of the conveyor at the loading point. Values of Kv for a wide range of belt velocities and loading angles are given in the table below. These values are, in turn, proportional to the time taken for accelerating the material at the loading point, assuming the coefficient of friction between the belt and the material as 0.5. These values are for typical transfers in which some amount of material is redirected at the loading point. These values could reduce further in the event of there being effective material redirection. On the other hand, they could increase in the event of the feed chute not providing any material redirection (see Table 1.5).
Table 1.5
Typical Kv values in degrees
Conveyor angle at loading point |
Belt velocity in m/sec |
|||||
1 |
2 |
3 |
4 |
5 |
6 |
|
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 |
2 2 2 2 2 2 3 3 3 3 3 3 4 4 4 4 5 |
4 4 4 4 5 5 5 5 6 6 6 7 7 8 8 9 10 |
6 6 6 7 7 7 8 8 8 9 9 10 11 11 12 13 15 |
8 8 9 9 9 1 1 1 1 1 1 1 1 1 1 1 2 |
10 10 11 11 12 12 13 13 14 15 16 17 18 19 21 22 24 |
1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 |
Material reduction allowance - Km
Table 1.6 gives the values of Km for different materials as described.
Table 1.6
Material reduction allowance - Km
Material |
Km in degrees |
Fine material having 5% moisture or interlocking material |
5° |
Dry material with low fines content such as crushed rock |
10°
|
Dry, free flowing fine material |
15°
|
Special reduction allowance - Ks
The value of Ks for belt sag, trippers and horizontal curves will depend partly on the design features of the conveyor and also the nominal surcharge angle obtained from other factors. In case the nominal surcharge angle is high, say more than 15°; there must be some additional reduction in the surcharge angle to account for these special features.
Typical values of Ks
For conveyors with tripper – 5 to 10°
For high belt sags exceeding 1% of the idler centers - 5°
Refer to Appendix C for surcharge angles
1.4 Classification of conveying machines
Owing to the wide range of conveying machines available, such as those differing in the principle of operation, design features, direction and means of conveyance, a general classification of material handling equipment is almost impossible.
According to their principle of operation, conveying machines can be categorized as those based on intermittent action and continuous action, the salient features of which are mentioned below.
1.4.1 Intermittent action machines
1.4.2 Continuous action machines
1.4.3 Auxiliary equipment
Auxiliary equipment forms a special group and is designed for operation in conjunction with conveying machines. They are not an independent means of conveyance. Auxiliary equipment comprise chutes, troughs, hoppers, gates, feeders and so on.
1.5 Selection of conveying machines
Following are the technical factors to be considered when selecting a conveying machine:
Nature and properties of the material to be conveyed:
After selecting the machine on the basis of the technical factors discussed above, a detailed review also has to be carried out from the economic point of view. An optimum solution would be the type of conveying machine that meets all the processing requirements while ensuring a high degree of mechanization and favorable working condition. Such equipment will, in the long run, ensure minimum per unit handling cost and will recoup the initial outlay in the shortest possible time.
1.6 Trends
Following are the most visible modern trends in bulk material handling:
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