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    CC-E - Best Practice Design, Maintenance and Troubleshooting of Conveyors and Chutes

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    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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    Table of Contents

    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:

    • Lump size: This refers to the quantitative distribution of the particles of a particular bulk material according to their sizes and is also known as granulometric composition of the material. It is characterized by the particle size denoted by diagonal a(Figure 1.1) in mm. A number of parameters related to conveyors and auxiliary equipment are determined by this characteristic:

     

    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, amaxamin < 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

    • Bulk density:It is the weight of the material per unit of volume in bulk (the volume including the voids or air pockets present in the heap) and is generally denoted by with the units of measurement being tons/cubic meter and pounds/cubic inch. The bulk density of some of the most frequently used materials is mentioned in Table 1.2. It is an important consideration particularly when the capacity of a conveyor and the pressure on the walls and outlet of a hopper is to be calculated. The loose bulk density of a material can be determined by weighing samples of a known volume of uncompacted material. Most ores have varying bulk densities based on the amount of impurities present and the particle size. It is therefore essential to evaluate a reasonable number of samples in order to determine the likely range in the bulk density values.
    • Specific weight:It is the weight of the material particles dried at a temperature of 100 to 105°C, with respect to the volume of water displaced by them. The specific weight of materials must be taken into account in order to calculate the capacity of pneumatic and hydraulic material handling equipment.
    • Particle size and shape: The size of the lumps and the lump to fines ratio can influence the burden surcharge angle, while the particle shape can affect material flow in the chute and also the amount of belt wear.
    • Maximum lump size: This is, in turn, dependent on the material characteristics and the crusher type employed. Large lumps tend to occur on conveyors handling mining products and primary ores. It is important for the maximum lump size to be established, as large slabs of material can pass through crushers.
    • Angle of repose:This defines the mobility or flowability of material and is defined as the angle between the surface of a freely formed pile of the material and the horizontal. When a loose material spills unobstructed on a horizontal plane it assumes a slope. The angle of this slope with respect to the horizontal plane is its angle of repose: j. (Refer Figure 1.2). The Angle of Repose is used as the base value for determining the burden surcharge angle.
    • Angle of surcharge:This is the angle to the horizontal which the surface of the material assumes when the material is at rest on a horizontal supporting surface vibrating vertically. This feature also defines the mobility or flowability of the material. Angle of surcharge is approximately 5 to 15° less than the angle of repose:

     

    Figure 1.2

    Angle of repose

    • Internal friction angle: Materials with high internal friction angles will normally give higher burden surcharge angles and are less likely to slump when the belt flattens out at the discharge pulley. The internal friction angle can be determined by a material shear test, which in turn gives an indication of the behavior of different materials on a troughed belt conveyor.
    • Coefficient of friction: This factor is taken into account for bulk material  in contact with steel, wood, concrete, rubber and so forth when designing conveying machines and auxiliary equipment. The friction factor determines the angle of inclination of walls and ribs of hoppers, chutes and also the maximum inclination of certain conveyors.
    • Abrasivity: The tendency of the particles of bulk materials to wear away the surface they are in contact with, when in motion, is known as the abrasivity of the material. The extent of abrasion depends on the hardness, surface condition, shape and size of the particles. Some bulk materials such as bauxite, iron ore, sand and coke are highly abrasive.
    • Specific properties: These include moisture content, stickiness, fragility, hygroscopy, toxicity, corrosiveness etc. All these properties need to be considered when designing conveying machines and auxiliary equipment, and effective measures are taken to neutralize their harmful influence. Let us briefly discuss some of these properties:
    • Moisture Content: Tends to have a marked influence on the burden surcharge angle as well as slumping of the conveyed material at the discharge pulley.
    • Cohesion:This property is based on the angle of repose, the method of classifying the cohesive properties of a material is provided by ISO 3435.
    • Temperature:Is a very important consideration. Any material temperature that is significantly higher than the ambient temperature may prove detrimental to the belt cover, necessitating the use of a special heat-resistant rubber (see Table 1.3 and Table 1.4).

    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:

    • Belt velocity and angle of inclination at the loading point
    • Material properties
    • Special allowance for trippers

    The nominal surcharge angle in degrees is given by the equation,

    Surcharge angle = X - K- K- 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

    K in degrees

    Fine material having 5% moisture or interlocking material

    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

    • Cyclic operation is a characteristic feature of these machines
    • They operate on an alternately reciprocal principle; they run loaded in one direction and idle in the other
    • Examples of intermittent action machines include cars, trucks, rail mounted cars, cable cars and tractors
    • Loading and unloading are generally accompanied by stoppages
    • They possess great flexibility in the path of transport, with the path being provided with a number of branches at times
    • They are suitable for small and medium capacity work
    • They are difficult to put into automatic operation

    1.4.2          Continuous action machines

    • A feature specific to continuous action machines is that their load carrying member conveys the load in a practically uninterrupted stream or in small successions (buckets, tubs etc)
    • They move along a precisely determined path
    • Examples of this type include various types of conveyors and pneumatic and hydraulic transport installations
    • They are suitable for all capacity ranges, from small to very high
    • They are most suited for automatic operation

    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:

    • Required capacity of the equipment – If the capacity is high, economic considerations will dictate selection of the equipment that is compact and low in cost.
    • Direction and length of conveying run –This is of prime importance in selecting the equipment type. Certain types of machines easily permit change of direction in one or both planes; others operate in a straight path and in one direction. While some are adopted to convey materials a considerable distance, others are limited by their length.
    • Storage of material at the head and tail end –The method of loading and unloading of material also has an important bearing in the selection of a conveying machine. While some of them are self loaders, others may require certain additional loading devices. Loose material can be stored in heaps, from which they are loaded on to the conveying machines with the help of buckets, scrapers or by other means. The material stored in a bin is discharged on to the conveying machine by gravity.
    • Processing steps and the movement of loads –In most cases, conveying machines are related to the overall manufacturing cycle, depend on it and serve to carry a load processed en route.
    • Specific local conditions – These include the area of the site at disposal, its topography, type and design of the building, mutual layout of handling machines and processing equipment, humidity, ambient temperature, environment protection etc. It is also important to know whether the machine will be installed outdoors or indoors.

    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:

    • Reduction in the amount of movement of bulk load to a minimum. This means that load is to be handled from the initial to the final point of conveyance, with minimum number of transfers, for example, by using a single or minimum number of machines. It must be ensured that the shortest path is always taken. On the other hand, there is a trend towards bringing the process plant closer to the source of material.
    • Increase in handling capacity.
    • More reliable operation, improvement in working condition and minimum maintenance requirement. Which is an essential prerequisite for automation of the manufacturing process.
    • Automatic control of individual conveying machines and group of installations, automatic loading/ unloading operations and distribution of loads.
    • Light weight machines of small size.

     

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