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Modern Technological Developments in the Storage and Handling of Bulk Solid
A. W. Roberts
Director, School of Engineering, Director TUNRA Ltd,
The University of Newcastle, NSW, Australia
Acknowledgements : Bionic Research Institute ‐ Chute Design Conference 1992
SUMMARY
This paper presents an overview of some modern developments in the technology of bulk solids handling. An overv
of storage system design including bins and gravity reclaim stockpiles is presented and aspects of feeder performanc
given. The importance of wall or boundary friction in hopper and chute design is discussed and the associated adhes
and wear characteristics are outlined in relation to the selection of appropriate lining materials. Problems due to f
instabilities during discharge from coal bins are reviewed; these flow pulsations may give rise to severe dynamic loads
the bin structure.
1. INTRODUCTION
Throughout the world bulk materials handling operations perform a key function in a great number and variety
industries. While the nature of the handling tasks and scale of operation vary from one industry to another and, on
international scene, from one country to another according to the industrial and economic base, the relative cost
storing, handling and transporting bulk materials are, in the majority of cases, very significant. It is important, theref
that handling systems be designed and operated with a view to achieving maximum efficiency and reliability .Dire
related to these objectives is the ongoing need for engineers and those involved in the operation of handling plant
be kept informed of the latest research and technological developments relevant to their industry and, at the sa
time, contributing to these developments and to the dissemination of information in the light of their own experience
The theme embodied in the foregoing remarks is of particularly relevance to Australia in view of the heavy depende
on bulk handling operations. While these operations range across the broad spectrum of industries, of prime importa
are the mining and mineral processing industries which handle coal and mineral ores in large tonnages. These indust
make a major contribution to Australia's export earnings and economic growth.
Over the past three decades much progress has been made in the theory and practice of bulk solids handling. Relia
test procedures for determining the strength and flow properties of bulk solids have been developed and analyt
methods have been established to aid the design of bulk solids storage and discharge equipment. There has been w
acceptance by industry of these tests and design procedures and, as a result, there are numerous examples through
Australia of modem industrial bulk solids handling installations which reflect the technological developments that h
taken place.
Notwithstanding the current situation, the level of sophistication required by industry demands, in many cases, a be
understanding of the behaviour of bulk solids and the associated performance criteria for handling plant des
Experience indicates that the solution one problem which leads to an improvement in plant performance often expo
other problems which need to be solved. It becomes progressively clearer that there are many gaps in the present st
of knowledge where further research is necessary.
The purpose of this paper is to briefly highlight the present state of knowledge associated with bulk handling
indicate where further work is necessary. The material presented is based on the research conducted by Tunra B
Solids Handling Research Associates of the University of Newcastle. This research group has been involved in b
handling research and industrial consulting for some considerable time and in recent years has been .supported
research grants obtained from AMIRA.
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2. HANDLING PLANT DESIGN ‐ BASIC CONCEPTS
2. 1 General Remarks
The design of handling plant, such as storage bins, gravity reclaim stockpiles, feeders and chutes is basically a four s
process:
i. Determination of the strength and flow properties of the bulk solids for the worst likely flow conditi
expected to occur in practice.
ii. Determination of the bin, stockpile, feeder or chute geometry to give the desired capacity, to provide a f
pattern with acceptable characteristics and to ensure that discharge is reliable and predictable.
iii. Estimation of the loading on the bin and hopper walls and on the feeders and chutes under opera
conditions.
iv. Design and detailing of the handling plant including the structure and equipment.
The general theory pertaining to gravity flow of bulk solids and associated design procedures are fully documented [1
For the purpose of the present discussion, the salient aspects of the general philosophy are briefly reviewed.
2.2 Modes of Flow in Bins of Symmetrical Geometry
As is now well established, there are two basic modes of flow, namely, mass‐flow and funnel‐flow. These are illustra
in Figure 1.
In mass‐flow, the bulk solid is in motion at every point within the bin whenever material is drawn from the outlet. Th
is flow of bulk solid long the walls of the cylinder (the upper parallel section of the bin) and the hopper (the lo
tapered section of the bin). Mass‐flow guarantees complete discharge of the bin contents at predictable flow rates.
as a first‐in, first‐out flow pattern; when properly designed, a mass‐flow bin can re‐mix the bulk solid during discha
should the solid become segregated upon filing of the bin. Mass‐flow requires steep, smooth hopper surfaces and
abrupt transitions or in‐flowing valleys.
Mass‐flow bins are classified according to the hopper shape and associated flow pattern. The two main hopper types
conical hoppers which operate with axi‐symrnetric flow and wedged‐shaped or chisel‐shaped hoppers in which plaflow occurs. In plane‐flow bins, the hopper half ‐angle a will usually be, on average, approximately 8 to 10 larger than
corresponding value for axi‐symmetric bins with conical hoppers.
Figure 1. Modes of Flow
Therefore, they offer larger storage capacity for the same head room than the axi‐symmetric bin, but this advantag
somewhat offset by the long slotted opening which can give rise to feeding problems. The transition hopper, which
plane‐flow sides and conical ends, offers a more acceptable opening slot length. Pyramid shaped hoppers, while sim
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to manufacture, are undesirable in view of build‐up of material that is likely to occur in the sharp corners or in‐flow
valleys. This may be overcome by fitting triangular‐shaped gusset plates in the valleys.
Funnel‐flow occurs when the hopper is not steeply sloped and the walls of the hopper are not smooth enough. In
case, the bulk solid sloughs off the top surface and falls through the vertical flow channel that forms above the open
Flow is generally erratic and gives rise to segregation problems. Flow will continue until the level of the bulk solid in
bin drops an amount HD equal to the draw‐down. At this level, the bulk strength of the contained material is suffic
to sustain a stable rat‐hole of diameter Df as illustrated in Figure 1(b). Once the level defined by HD is reached, ther
no further flow and the material below this level represents 'dead' storage. This is a major disadvantage of funnel‐fl
For complete discharge, the bin opening needs to be at least equal to the critical rathole dimension determined at
bottom of the bin corresponding to the bulk strength at this level. However, for many cohesive bulk solids and for
normal consolidation heads occurring in practice, rat‐holes measuring several meters are often determined. This ma
funnel‐flow impracticable. Funnel‐flow has the advantage of providing wear protection of the bin walls, since
material flows against stationary material. However it is a 'first‐in last‐out' flow pattern which is unsatisfactory for b
solids that degrade with time. It is also unsatisfactory for fine bulk solids of low permeability. Such materials may aer
during discharge through the flow channel and this can give rise to flooding problems or uncontrolled discharge.
The disadvantages of funnel‐flow are overcome by the use of expanded‐flow, as illustrated in Figure 2. This combi
the wall protection of funnel‐flow with the reliable discharge of mass‐flow. Expanded‐flow is ideal where large tonna
of bulk solid are to be stored. For complete discharge, the dimension at the transition of the funnel‐flow and mass‐f
sections must be at least equal to the critical rathole dimension at that level. Expanded‐flow bins are particulsuitable for storing large quantities of bulk solids while maintaining acceptable head heights. The concept of expand
flow may be used to advantage in the case of bins or bunkers with multiple outlets.
Figure 2. Expanded Flow
Generally speaking, symmetric bin shapes provide the best performance. Asymmetric shapes often lead to segregat
problems with free flowing materials of different particle sizes and makes the prediction of wall loads very much m
difficult.
2.3 Mass‐Flow and Funnel‐Flow Limits for Symmetrical Bins
(a) Established Theory due to Jenike
The mass‐flow and funnel‐flow limits have been defined by Jenike on the assumption that a radial stress field exist
the hopper [1,2]. These limits are well known and have been used extensively and successfully in bin design. The lim
for axi‐symmetric or conical hoppers and hoppers of plane‐symmetry depend on the hopper half ‐angle α, the effec
angle of internal friction 8 and the wall friction angle Φ. Once the wall friction angle and effective angle of inte
friction δ have been determined by laboratory tests, the hopper half ‐angle may be determined. In functional form
α = ( Φ,δ ) ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ (1)
The bounds for conical and plane‐flow hoppers are plotted for three values of δ in Figure 3. In the case of conical or
symmetric hoppers, it is recommended that the half ‐angle be chosen to be 3 less than the limiting value. For plane‐fl
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the bounds between mass and funnel‐flow are much less critical than for conical hoppers. In plane‐flow hoppers, m
larger hopper half angles are possible which means that the discharging bulk solid will undergo a significant chang
direction as it moves from the cylinder to the hopper.
For plane‐flow, the design limit may be selected; if the transition of the hopper and cylinder is sufficiently radiused
that the possibility for material to build‐up by adhesion is significantly reduced, then a half ‐angle 3 to 4 larger than
limit may be chosen.
Figure 3. Limits for Mass‐flow for Conical and Plane‐Flow Channels
(b) Modification to Mass‐Flow Limits ‐More Recent Research
Since in the work of Jenike, flow in a hopper is based on the radial stress field theory, no account is taken of
influence of the surcharge head due to the cylinder on the flow pattern developed, particularly in the region of
transition. It is been known for some time that complete mass‐flow in a hopper is influenced by the cylinder surcha
head. For instance, there is a minimum level Hcr which is required to enforce mass‐flow in the hopper [5]. For the m
flow bin of Figure 1(a), this height ranges from approximately O.75D to 1.0 D.
More recent research has shown that the mass‐flow and funnel‐flow limits require further explanation and refinem
For instance, Jenike [6] published a new theory to improve the prediction of funnel‐flow; this led to new limits
funnel‐flow which give rise to larger values of the hopper half ‐angle than previously predicted, particularly for hvalues of the wall friction angle. In the earlier theory, the boundary between mass‐flow and funnel‐flow was based
the condition that the stresses along the centre line of the hopper became zero. In the revised theory the flow bound
is based on the condition that the velocity becomes zero at the wall.
In a comprehensive study of flow in silos, Benink [7] has identified three flow regimes, mass‐flow, funnel‐flow and
intermediate flow as illustrated in Figure 4. Whereas the radial stress theory ignores the surcharge head, Benink
shown that the surcharge head has a significant influence on the flow pattern generated. He derived a fundame
relationship for Hcr in terms of the various bulk solid and hopper geometrical parameters, notably the H/D ratio of
cylinder and the effective angle of internal friction δ. Benink developed a new theory, namely the arc theory, to quan
the boundaries for the three flow regimes. This theory predicts the critical height Hcr at which the flow changes.
Figure 4. Flow Regimes for Plane‐Flow Hopper defined by Benink [7]
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2.4 Bin Geometry for Mass‐Flow
(a) Basic Considerations
Basically the aim in mass‐flow design is to determine the hopper geometry to give reliable flow at all times at
required discharge rate. Primarily, the requirement is to determine the hopper half angle α, which defines the slope w
respect to the vertical, and opening dimension B.
Undisturbed storage time and changes in moisture content can significantly influence the unconfined yield strength
the bulk solids. By way of illustration, the critical hopper opening dimension B for three Hunter Valley coals plotted
function of moisture content are shown in Figure 5. This figure shows three coal samples, Sample (1) being a Raw O
Cut Coal, Sample (2) a washed version of (1) and Sample (3), a blend of (2). The high strength of the raw, unwashed c
is clearly evident. Experience has shown that the peak bulk strength of coal may occur at a moisture content somewh
between 70% and 90% of the saturation limit.
(b) Influence of Wall Friction
Since an increase in both the normal wall pressure and consolidation pressure accompany an increase in hopper sp
then the corresponding decrease in wall friction angle will permit the hopper half angles to be increased. Hence
possible to calculate a hopper half angle α as a function of hopper span or opening dimension as indicated in Figure 6
shown, the half hopper angles for both wedge and conical hoppers tend towards limiting values as the opendimension increases.
2.5 FUNNEL‐FLOW AND EXPANDED‐FLOW GEOMETRY
As previously discussed, it is necessary to compute the critical or minimum diameter Df for an unstable pipe or "
hole" from which the minimum bin opening for funnel‐flow or the transition dimension for expanded‐flow
determined. The transition dimension for expanded‐flow refers to the transition of the mass‐flow hopper with the up
funnel‐flow section of the bin.
Figure 5 Critical Opening Dimension BCR as a Function of Moisture Content for Three Coal Samples ‐Stainless Stee1304‐2B Linin
Figure 6 Variation of Hopper Half ‐Angle with Span for Coal on 304‐2B Stainless Steel
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3. BIN WALL LOADS
In bin design, the prediction of bin wall loads continues to be a subject of some considerable complexity. In view o
obvious importance it is a subject that has, in recent years, attracted a good deal of research effort. Currently, there
several research groups in various countries of the world directing their attention to the study of bin wall loads usin
range of analytical and numerical techniques such as those involving finite element analysis. Despite the widely vary
approaches to the analysis of bin wall loads, it is clear that the loads are directly related to the flow pattern develope
the bin.
The flow pattern which a mass‐flow bin exhibits is reasonably easy to predict and is reproducible. However, in fun
flow bins the flow pattern is more difficult to ascertain, especially if the bin has multiple outlet points, the loading of
bin is not central and/or the bulk solid is prone to segregation. Unless there are compelling reasons to do otherwise,
shapes should be kept simple and symmetric.
3.1 Wall Pressures in Mass‐Flow Bins
In mass‐ flow bins, the pressures acting normal to bin walls vary from the static or filling conditions to the dynami
flow conditions. The pressure distributions are well defined and, using current theories [3‐4], may be predicted w
confidence.
It is to be noted that in the flow situation a high switch stress occurs at the transition. The magnitude of this sw
stress is several times the corresponding static value. Further, it may also be noted that the wall pressures acting in
cylindrical section during flow may be higher than the static values. For a perfectly parallel cylinder, the wall pressu
during flow would be the same as the static values. However, when imperfections such as weld projections or p
shrinkage give rise to flow convergences, peak stresses occur. The stresses are taken into account by computing
locus of all such possible peak pressures.
3.2 Wall Pressures in Funnel Flow Bins
While for design purposes wall pressures in symmetrical funnel‐flow bins may be determined with a high degree
confidence, the wall loading in bins with multiple outlets and eccentric discharge points are far more difficult
estimate. Under eccentric discharge, the walls are subject to bending moments and hence, bending stresses in additto hoop stresses [8]. In the case of tall grain silos, the use of anti‐dynamic tubes offers significant advantage
controlling the wall pressures, both in the case of symmetrical funnel‐flow silos as well as silos with eccentric load
points [9‐10].
3.3 Australian Standard for Loads in Bulk Solid Containers
In recent years there has been considerable activity in several countries of the world in the development of new
revised codes for bin wall loads. Of particular note is the preparation of the new Australian Standard "AS‐89138 Lo
for Bulk Solids Containers " [11], which represents a major milestone. This publication presents a very comprehen
review of the loads acting in bin and silo walls under a the full range of operating conditions likely to occur in practice
an example, Figure 7 shows the wall loadings determined on the basis of this new Standard for a large coal bin havseven outlets; the pressure profiles correspond to one possible mode of discharge involving the operation one eccen
outlet only.
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Figure 7. Circumferential Pressure Variation due to Operation of One Eccentric Outlet
4. FEEDING OF BULK SOLIDS
4.1 Use of Feeders to Control Discharge
In general, a feeder is a device used to control the flow of bulk solids from a bin. While there are several types of feed
commonly used, it is essential that they be selected to suit the particular bulk solid and the range of feed rates requi
It is particularly important that the hopper and feeder be designed as an integral unit so as to ensure that the flow fr
the hopper is fully developed with uniform draw of material from the entire hopper outlet. For example, in the case screw feeder, this is achieved by using selected combinations of variable pitch, variable diameter and variable core
shaft diameter.
In the case of a belt or apron feeder, a tapered opening is required as illustrated in Figure 8. The use of vert
triangular plates in the hopper bottom are an effective way to achieve the required taper. The gate on the front of
feeder is used only for flow trimming and not for controlling the flow rate. The height of the gate is adjusted to give
required release angle Ψ to achieve uniform draw along the slot. Once correctly adjusted, the gate is then fixed
position and the feed rate is controlled by varying the speed of the feeder.
Figure 8. Belt and Apron Feeder
In the case of vibratory feeders, there is a tendency for feed to occur preferentially from the front. To overcome
problem, it is recommended that the slope angle of the front face of the hopper be increased by 5 to 8 as illustrate
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Figure 9. Alternatively, the lining surface of the front face in the region of the outlet may selected so as to have a hig
friction angle than the other faces.
Figure 9. Vibratory Feeder
4.2 Determination of Feeder Loads and Power
The determination of feeder loads and drive powers requires a knowledge of the stress fields generated in the hop
during the initial filling condition and during discharge. Under filling conditions, a peaked stress field is generathroughout the entire bin as illustrated in Figure 10. Once flow is initiated, an arched stress field is generated in
hopper and a much greater proportion of the bin load is supported by the hopper walls. Consequently, the load ac
on the feeder substantially reduces as shown in Figure 10.
Figure 10. Load Variations on a Feeder
It is quite common for the load acting on the feeder under flow conditions to be in the order of 20% of the initial lo
The arched stress field is quite stable and is maintained even if the flow is stopped. This means that once flow is initia
and then the feeder is stopped while the bin is still full, the arched stress field is retained and the load on the fee
remains at the reduced value. The subject of feeder loads is discussed in some detail in Refs. [12‐15]. The loads
feeders and the torque during start‐up may be controlled by ensuring that an arched stress field fully or partially ex
in the hopper just I prior to starting. This may be achieved by such procedures as:
Cushioning in the hopper, that is leaving a quantity of material in the hopper as buffer storage.
Starting the feeder under the empty hopper before filling commences.
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Raising the feeder up against the hopper bottom during filling and then lowering the feeder to the operating condit
prior to starting. In this way an arched stress field may be partially established.
5. GRAVITY RECLAIM STOCKPILES
5.1 Draw‐Down Performance Considerations
Gravity reclaim stockpiles when properly designed, operate under expanded‐flow, as illustrated in Figure 11. This sho
discharge through a single opening in a stockpile. Discharge will take place by funnel‐flow in the main body of
stockpile, with the flow expanded through the mass‐flow hopper. In this way, reliable flow to the feeder is assured. F
will continue until the draw‐down head hD is reached; flow then ceases as a stable pipe or rathole is formed. The dr
down is consistent with critical rathole dimension Df which forms at that level. The shape of the rathole depends on
consolidation conditions within the stockpile, the particle or lump size range of the stored bulk solid and the moist
content.
Figure 11. Draw‐Down in Stockpile
Complete draw‐down, as illustrated in Figure 11, corresponds to the critical rathole dimension Dfm at the base of
stockpile. For complete draw‐down to occur, it is necessary for the diagonal dimension of the hopper transition to b
least equal to Dfm Since values of Dfm may be several meters, often it is not practical or economical to employ a la
enough hopper to achieve complete draw‐down. For this reason, the design of stockpile reclaim hopper and fee
systems requires a full consideration of the various options available with a view to optimizing the reclaim performa
within specified practical and economic limits.
5.2 Use of Multiple Hoppers
The use of multiple hopper systems which allows for intersection of the flow channels to occur, as illustrated in Fig
12, provides for good reclaim performance to be achieved. By varying the separation distance X, an optimum spac
can be established as illustrated in Figure 13.
5.3 Live Capacity versus Moisture Content
In a programme of research conducted at the University of Newcastle 16,17], studies have been performed usin
conical stockpile model which allowed different feeder configurations to be examined. Although the scale of the mo
relative to actual stockpiles is very small (a factor of 1/50 in one case of an iron ore stockpile), the predic
performance base on the model studies were surprisingly good. The modeling process involves scaling the particle
and adjusting the moisture content of the bulk solid to reproduce, as close as possible, the same arching characteris
in the model feed hoppers as would occur in the full scale stockpile.
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Figure 12. Improved Reclaim Performance using Double Reclaim System
Figure 13. Live Capacity versus Feeder Separation
By way of illustration, Figure 14 shows the reclaim performance for a double hopper system for five different c
moisture contents. Several tests were conducted over a range of hopper separation lengths. The separation of
hopper is measured by the distance S between the inner edges of the two hoppers which are equi‐distant on each s
of the stockpile centreline.
The data in Figure 14 show the reduction in live capacity with increase in moisture. This is to be expected because
strength of the bulk solid increases with moisture content. The results also show that there is an optimal separat
length for the two‐hopper system where maximum reclaim of material can be expected. This optimal distance be
dependent on the moisture content of the bulk material.
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Figure 14. Double Hopper Stockpile Live Capacity for Model Stockpile using Coal. Hopper length at transition = 12Omm, width
100mm
5.4 Loads on Reclaim Hoppers and Feeders
The loads on reclaim hoppers and feeders and the corresponding power to drive the feeders varies from the "initial
the flow condition as discussed in Section 4. The loads are illustrated in Figure 15. The initial load will correspond to
case when the stockpile or crater above the feeder is filled. The surcharge load Qs will depend on the consolidat
condition of the bulk solid in the stockpile. The worst case corresponds to the hydrostatic pressure. However, if a rath
has been pre‐formed, then the surcharge load will be reduced. When an arched or flow stressed field has been formwithin the mass‐flow reclaim hopper, the load on the feeder will be greatly reduced. Confirmation of the load conditi
acting on reclaim hoppers has been obtained from the model stockpile tests.
Figure 15. Loads on Stockpile Feeders
6. SURFACE OR WALL FRICTION
6. 1 Selection of Lining Materials
Of the various parameters affecting the performance of hoppers, feeders and chutes, the friction at the bound
surface has, in most cases, the major influence. Judicious choice of lining material to achieve low friction and wear is
important consideration.
There are a great many lining materials and surface coatings on the market, some common linings being illustrate
Table III. Also shown are the bulk materials for which the lining material is commonly used.
TABLE III ‐ SOME COMMON LINING MATERIALS
Lining Material Remarks
Carbon Steel Cheap ‐ suitable for most bulk materials ‐ corrosion a problem. High friction often a limiting
factor.
Stainless Steel
304
‐
2B
Excellent material for bulk materials which are not too abrasive. Very suitable for black
coal. Very poor performance for brown coal. Low friction.
Stainless Steel
3Cr12
Similar application to 304‐2B stainless. Is cheaper and lower chrome content than 304‐2B.
Low friction.
Ultra High
Polyethylene
Excellent for bulk materials which are not too abrasive. Fixing must be by mechanical
fasteners. Very good performance for both black and brown coal.
Bisalloy 360
Domite Ni Hard
For more arduous applications with Domite being quite expensive. Suitable for such bulk
material as Bauxite, Iron Ore, Copper Ore, Copper Ore, Lead Ore, Zinc Ore. Generally high
friction.
Epoxy Coated
Surfaces
Good performance for bulk materials such as coal where abrasive wear is not a major
problem. Relatively low friction.
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While cost is a significant consideration, it is most important that the lining material be selected on the basis of serv
life and performance. Factors to be considered include:
Surface friction and adhesion
Resistance to impact, if appropriate
Method of attachment
Installation cost and maintenance
Resistance to abrasive wear
Resistance to corrosion
Initial cost
It is recommended that appropriate tests be conducted to determine the relevant flow properties of the bulk solid
the proposed lining surface. In view of the importance of surface or wall friction, some salient aspects are now review
6.2 Surface Friction and Adhesion
The adhesion of bulk solid particles to hoppers and chutes is a result of the interaction between the bulk solid and
boundary or wall surface[18‐21]. While adhesion and/or cohesion are difficult to measure directly, an indication of th
parameters may be gleaned from bulk solid and wall surface friction measurements using a direct shear test appara
The parameters of interest are defined in Figure 16. 1.
Figure 16. Wall or Surface Yield Locus (WYL)
The surface friction characteristics are displayed by the wall yield locus W .Y .L.; the surface friction angle Φ is define
follows:
Φ = tan‐1
/ ح) σw) ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ (2)
where ح = shear stress at the wall
σw = corresponding normal stress at the surface.
As indicated by Figure 16, the friction angle Φ between the bulk solid and boundary surface decreases as the nor
pressure increases. This effect is illustrated in Figure 17.
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Figure 17. Characteristic Surface or Wall Friction Variation with Normal Pressure
6.3 Interaction Characteristics
Bulk solid/boundary surface friction and adhesion depend on the interaction between three groups of variables, th
relating to the bulk solid, those relating to the wall or boundary surface and those which arise from loading
environmental conditions. This interaction is shown, diagrammatically in Figure 18.
Figure 18. Bulk Solid/Boundary Surface Friction Interactions
The relevant properties in each of the three groups are summarized as follows :
(i) Bulk Solid Characteristics ‐
Particle size and size distribution
Panicle shape, hardness and density
Moisture content
Bulk density
Chemical composition
(ii) Wall Surface Characteristics ‐
Surface roughness
Hardness
Chemical composition
(iii) Loading and Environmental Factors ‐
Pressure between bulk solid and wall surface
Relative rubbing or sliding velocity
Temperature and humidity or moisture conditions
Wall vibrations
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Undisturbed contact time
6.4 Wall Friction versus Normal Pressure Characteristics
As an illustration of some of the factors influencing wall or surface friction, a set of wall yield loci graphs are shown in Figure 19 [
The bulk solid in this case is coal. Figure 19(a) shows the variation of wall friction for black coal at 10% moisture cont
on three surfaces, namely, stainless steel type 304 with 2B finish, mild steel polished and mild steel rusted all at
instantaneous or zero storage time condition. In the case of the 120 polished mild steel surface the wall friction was a
determined after 72 hours undisturbed contact or storage time is also shown; the high friction in this case is q
considerable with corrosion and adhesion or bonding of coal particles to the steel surface.
Figure 19(b) compares the Wall Yield Loci for black coal at 19.7% moisture content and brown coal at 65% moist
content on two surfaces, stainless steel type 304 with 2B finish and Tivar 88, an ultra high molecular we
polyethylene material. While in absolute terms the moisture contents of the two coals are significantly different
relative terms, taking account of their composition and saturated moisture conditions, they are comparable. For
black coal the wall friction angle for stainless steel and Tivar are similar, both exhibiting low friction. This is also the c
for brown coal on the Tivar surface. However, the brown coal has abnormally high friction on the stainless steel, des
the smoothness of the surface; the stainless steel is entirely unsuitable for brown coal.
(a) Wall Yield Loci for Black Coal (b) Wall Yield Loci for Black and Coals
Figure 19. Typical Wall Yield Loci
6.5 Surface Roughness
(a) Roughness Parameters and Effect on Wall Friction
Surface roughness is an important factor in terms of its influence on wall friction. Yet the specification of surf
roughness in terms of appropriate parameters which adequately describe the surface is a complex matter requi
careful and detailed consideration.
It is common to simplify surface characteristics in terms of height parameters, such as the centre line arithmetic aver
roughness (CLA or Ra Number) or RMS roughness. Such parameters are useful for comparison purposes but do
adequately provide an assessment of the interaction between panicle size and surface profile. For this reason, Ooms
Robens [18] have found it useful to specify the surface characteristics in terms of Surface Spectoral Density. This disp
the RMS roughness amplitude as a function of frequency where the frequency is the inverse of the roughness w
length.
(b) Roughness Classification of Surfaces used in Bulk Solids Handling
The new Australian Standard on Loads in Bulk Solids Containers [11] designates four surface roughness characteristic
to D4. In order that these surface classifications may be quantified in some way, Ooms (Ref. [21]) proposed that the f
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categories of surfaces be grouped in terms of roughness bands based on the Mean Centreline Roughness or Ra num
Surfaces commonly used have been classified according to this procedure and presented in Figure 20.
Figure 20. Ooms Chan for Lining Surface Roughness Classification
From the discussion in the previous Section, it is apparent that the proposed form of classification is somew
restrictive in terms of the limited information conveyed by the Ra number. Also the wall roughness may not necessa
remain constant and should be considered as a variable. For instance, a polished or lightly rusted carbon steel surf
may become deeply pitted and change from group D2 to group D3. An aluminum surface is easily scored and m
change from group Dl to group D2. On the other hand, some stainless steel surfaces will polish during service and m
change from group D2 to D 1.
6.5 Influence of Vibrations
Roberts et al [22‐24], have shown that the application of vibrations to a wall surface can significantly reduce wall frictand therefore promote flow. Vibrations can also reduce bulk strength, further assisting in promoting gravity flow.
evidence indicates that the best results are achieved by using frequencies of 100 Hertz or higher, and low amplitude.
7. ADHESION OF BULK SOLIDS ON WALLS OR SURFACES
7. 1 Adhesion of Bulk Solids in Chutes
The characteristics of surface or wall friction discussed in the previous section indicate that, for most bulk solids
lining materials, the Wall Yield Loci (WYL) tend to be convex upward in shape. Furthermore the WYL often intersect
shear stress axis corresponding to zero normal pressure indicating an adhesion/cohesion effect as depicted in Figure
Problems due to high wall friction, cohesion and adhesion, which are associated with low pressure conditions, of
occur in chutes and standpipes. Cohesion and adhesion can cause serious flow blockage problems when corro
bonding occurs, such as when moist coal is in contact with carbon steel surfaces. The bonding action can occur a
relatively short contact times. Impurities such as clay in coal can also seriously aggravate the behaviour due to adhes
and cohesion.
Transfer chutes should be designed to ensure that satisfactory flow is obtained without flow blockages. Yet despite t
apparent simplicity, the flow patterns developed in chutes often not fully appreciated. Occasions have arisen in prac
where costly flow interruptions have occurred due to incorrect chute design arising from a lack of understanding of
bulk solid and chute surface friction characteristics.
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The design of transfer chutes is discussed in References [25‐28]. Consideration should be given to the flow propertie
the bulk solid and the characteristics of the chute lining material. Moist coal can adhere to vertical, as well as incli
faces of steel chutes eventually causing blockages. This has been found to occur in practice after only a few hour
operation. Problems of this type have occurred, for example, in conveyor feed chutes in coal screening operation
illustrated in Figure 21. The momentum of the coal particles falling from the screen is usually not sufficient to ca
scouring of the chute surfaces and, as a result, build‐up and complete blockages have been known to occur.
Figure 21. Build‐Up of Cohesive Bulk Solid such as Coal on Screen House Conveyor Feed Chute
When determining chute slope angles, account must be taken of the variation of friction angle with change
consolidation pressure, or more particularly, with change in bed depth. Figure 22 shows, for a typical coal, the variat
of wall friction angle with bed depth. As indicated, high friction angles can occur at low bed depths, the decreas
friction angle being significant as the bed depth increases.
Figure 22 Wall friction angle versus bed depth for bulk solid on chute
The slope θ of the chute should be at least 5 larger than angle of equivalent friction [4].
That is :
θmin = tan‐1 [tanΦ (1 + Kv Ho / B)] + 5o
where Φ = Wall friction angle corresponding to HO
Ho = Bed depth
B = Chute width
Kv = Ratio lateral to normal pressure
Kv will depend on bulk solid properties Normally Kv = 0.5 to 1.0. In the absence of information Kv may be taken to be 0
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Often moist bulk solids will adhere initially to a chute surface, but as the bed depth increases, the correspond
decrease in friction angle will cause flow to be initiated. In some cases flow commences with a block‐like motion of
bulk solid as depicted in Figure 23.
Figure 23 Block‐like Flow Down Chute
7.2 Adhesion in Vertical Chutes or Standpipes
Bulk solids, such as coal with high clay contents and at high moisture contents, may adhere to walls of vertical pipechutes leading to progressive build‐up and flow choking. Problems of this type have been known to occur in the c
handling plant of power stations, as depicted schematically in Figure 24.
Figure 24 Schematic Arrangement of Coal Handling Plant of Typical Power Station
When blockages occur in feed‐pipes to the feeder and mill, a boiler may "flame out" in the space of a few minuBlockages are initiated by the coal adhering to the pipe wall and then growing inwardly, this action often occurring a
only a few tonnes of coal have passed through the system. Often such problems occur when unwashed coal is store
open stockpiles prior to use. The weathering process can cause the clays to be dispersed, rendering them more likel
adhere to chute and pipe walls. The adhesion process may be aggravated in this case due to the temperature of the
and standpipe above the mill.
It is important that the pipe or chute diameter be sufficiently large to cause the bulk solid to fall away from the wall
proposed simplified methodology is presented. Referring to Figure 25, assuming the weight of bulk solid is just suffic
to cause slip along the wall, the required pipe or chute diameter D is given by
D ≥ 4ţ / ŷ (1 ‐ C2
) ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ (4)
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where :
C = d / D such that C ≥ 0.8
ţ = shear stress at wall corresponding to normal pressure σ
ŷ = ρ g = bulk specific weight.
Figure 25 Build‐Up of Bulk Solid in Vertical Chute or Standpipe
It is also wise to check whether the pipe diameter is sufficient to prevent a cohesive arch forming. For this analysis,
methods presented in Refs. [3,4] may be used.
8. WEAR IN BULK HANDLING PLANT
Wear in bulk handling plant may result from impact or abrasion or, as is often the case, a combination of both
addition, deterioration of metal surfaces can occur as a result of corrosion.
8.1 Impact
Erosive type wear due to impact consists of a combination of plastic deformation and cutting wear. Such wear,
example, occurs in pipe bends of pneumatic conveying systems where impact velocities are normally relatively high
where several impacts and rebounds may take place. Normally the particle size is small in this case.
Impact wear also occurs at discharge points of belt conveyors and at entry points to transfer chutes. Velocities of imp
are normally relatively low whereas particle size range can be quite wide with large lumps being present.
Impact wear depends on several factors, the relative hardness of the particles and the surface having a signific
influence. For impact on hard, brittle materials, the greatest amount of damage occurs when particles impringe at an
of approximately 90. On the other hand, for ductile materials, the greatest amount of erosive wear occurs wparticles strike the surface at low angles of attack, usually in the range 15 to 30. Erosive wear due to impact is norm
composed of two types, deformation wear and cutting wear.
8.2 Abrasive or Rubbing Wear
This occurs in storage bins and silos particularly in hoppers under mass‐flow conditions. Under mass‐flow the pressu
in a hopper will vary significantly over the hopper surface, with the maximum pressure occurring at the transition,
pressure decreasing towards the outlet. The velocity of the bulk solid adjacent to the wall increases non‐linearly fr
the transition to the hopper outlet. While the magnitude of the velocity at particular point on the hopper wall depe
on the bin discharge rate, normally the bulk solid velocities are quite low with pure sliding taking place.
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Abrasive wear also occurs in transfer chutes, the flow being characterised by lower pressures and higher velocities t
those occurring in hoppers. There are several other areas where abrasive wear is experienced such as in feeders,
conveyors, vibratory conveyors and screw conveyors. Any mechanical device which involves the motion of bulk so
relative to surfaces will experience wear problems.
8.3 Abrasive Wear Parameters
The concepts of a non‐dimensional Relative Wear Number NWR has been introduced [20] in order to per
comparisons to be made between different bin and chute geometries, is defined as :
NWR = [(σw / ŷB) (Vs / Vo) tan Φ
Where :
σw = Normal pressure at boundary
ŷ = Bulk specific weight
B = Characteristic dimension, B = outlet dimension in case of hopper; B = chute width in case of chute
Vs = Velocity of sliding at wall
Vo = Sliding velocity at reference location.
For hopper, Vo is defined at transition of cylinder and hopper
For chute, Vo is normally defined at point of entry to chute
Φ = Wall friction angle
8.4 Wear in Mass‐Flow Bins
The application of the foregoing to the assessment of relative wear in mass‐flow bins has been discussed in Ref. [20]
way of illustration, the relative wear profiles for axi‐symmetric (or conical) and plane‐flow bins having the same open
dimension and hopper half angle respectively are illustrated in Figure 26. In the case of the axi‐symmetric bins,
maximum relative wear occurs at the outlet, while for the plane‐flow bins the maximum relative wear occurs at
transition. In the latter case the wear at the transition is likely to be less than as indicated in Figure 26 owing to
possible build‐up of material at the transition. Also, the normal wall pressure occurring at the transition is difficul
predict precisely and is likely to be lower than as indicated.
Some bins are constructed with a variable hopper slope and with the hopper section having different surface textu
Such a bin is discussed in Ref. [29]. The bin in question is axi‐symmetric with a capacity of 2400 tonnes. The hopper
lined with 3 mm type 304‐2B stainless steel. Examination of the lining after approximately 5 million tonnes of coal passed through the bin showed that the maximum wear of the stainless steel was around 1mm.
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Figure 26 Relative wear profiles for axi‐symmetric and plane‐flow mass‐flow bins
B = 1.0 m, α = 22, Ф (cylinder) = 30, Ф (hopper) = 20
8.5 Avoidance of Wear Problems due to Eccentric Funnel‐Flow
Serious wear problems will occur during funnel‐flow where the flow channel or pipe is not fully contained in the b
solid itself but may incorporate part of the hopper or bin wall. Problems of this nature may occur when bins w
eccentric discharge are used, particularly when the bin opening is located near aside wall. On other occasions a ba
designed feeder may cause material to pipe adjacent to the hopper wall. Flow channels of this nature give rise to hvelocity flow against the wall resulting in accelerated wear.
Often side delivery chutes are incorporated in bins for the purpose of off ‐loading bulk materials. Side delivery chu
create undesirable flow patterns in bins, leading to accelerated wear of the bin wall in the region of the chute intake
well as in the plates above the chute. This wear is caused by both abrasion and impact Abrasive wear results from
high velocity of the materials during chute discharge, the flow velocity of the materials during chute discharge, the f
following a funnel‐flow pattern, as Indicated in Figure 27. The eccentric discharge induces a non‐uniform press
distribution, as shown; bending is induced and the bin shell is deformed as indicated by the dotted curve.
Figure 27 Eccentric discharge due to use of side delivery chutes
Impact wear can occur on filling the bin after discharging from the side delivery chute. The surface is left in a ri
condition as indicated in Figure 27. When filling commences, lumps of bulk material may bounce off the rilled surf
and impact the wall in the weakened area above the chute.
It should be noted that despite the fact that side delivery chutes may only be used intermittently, the wear rate du
operation is considerable. It is therefore most desirable that side delivery chutes be avoided and incorporate any
loading via a transfer conveyor operating from the main bin discharge. If side delivery chutes are used, such as
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existing installation, it is essential that the bins be lined with wear plates in the region of the chute intakes as wel
above the chutes.
8.6 Wear in Transfer Chutes
Abrasive wear in transfer chutes has been discussed in Ref. [18‐21]. In the case of straight inclined chutes of const
cross‐sectional geometry, the wear is constant along the chute. For chutes of constant curvature, it has been shown t
the wear varies along the chute as depicted in Figure 28 reaching a maximum at a particular chute angle and t
decreasing. However, the wear is virtually independent of chute radius.
Figure 28. Wear factor for circular curve chutes [20]
Q = 30 tonnes/hr, Vo = 0.2 m/s, ρ= 1000 kg/m3, b = 0.5 m, E = 0.6, Ф = 30.
8.8 Abrasive Wear Tests
In order to evaluate lining materials for wear resistance, a linear wear tester, as proposed by Roberts [30,31], has b
developed jointly at The University of Twente, The Netherlands, and The University of Newcastle, Australia. The tes
which is shown in Figure 29, incorporates the following features:
i.
Provision for a continuous supply of "fresh" bulk solid. ii. Provision for the bulk solid normal pressure on the test surface to be varied over the specific range.
iii. Provision for the sliding or rubbing velocity to be varied over the specific range.
Figure 29. Abrasive Wear Tester
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During tests, the friction coefficient, surface roughness, weight and thickness loss are progressively monitored. The t
samples used in the linear wear tests are of similar size to those used in the Jenike Direct Shear Test. This allows cr
checking of the wall or boundary friction at various stages throughout the tests. A typical set of test results
illustrated in figure 30.
Figure 30. Comparative Wear Rates for Three Common Lining Materials
9. PULSATING LOADS IN BINS ‐'SILO QUAKING'
9.1 General Discussion
As is often the case, the solution of one problem which leads to an improvement in plant performance exposes ot
problems which require further research and development, This applies particularly to gravity flow in storage bins
silos where the application of known theories for reliable discharge, such as by mass‐flow, can give rise to dynami
pulsating flow effects. These effects are normally imperceptible as far as bin discharge is concerned having
detrimental effect on the plant operation. However, the pulsating flow can have a significant influence on the lo
acting on bin walls by imposing severe dynamic loads. The phenomenon is often described as 'silo quaking'; it may
linked with the critical head Hcr for mass‐flow as discussed in Section 2.
The discussion that follows provides a qualitative view of the 'silo quaking' problem as it r relates to mass‐flow, fun
flow and expanded‐flow bins.
(a) Velocity Profiles and Pressure Distribution (b) Variable Density and Dilation
Figure 31 Mass‐Flow Bin
Referring to the mass‐flow bin depicted in Figure 31; as the material flows, it dilates leading to variations in density fr
the static condition. This is depicted pictorially in Figure 31(b). With H > Hcr, the flow in the cylinder is uniform or 'p
like' over the cross‐section, with flow along the walls. In the region of the transition, the flow starts to converge due
the influence of the hopper and the velocity profile is no longer uniform. The velocity profile is further developed in
hopper as shown. As the flow pressures generate in the hopper the further dilation of the bulk solid occurs. As a re
of the dilation, it is possible that the vertical supporting pressures decrease slightly reducing the support given to
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plug of bulk solid in the cylinder. This causes the plug to drop momentarily giving rise to a load pulse. The cycle is t
repeated.
Studies of the phenomenon of pulsating loads in bins and silos are presently in progress at the University of Newcas
Australia. In this work, a pilot scale mass‐flow, steel silo 1.2m diameter by 3.5 m high and fitted with a stainless s
hopper is being used. The silo is fitted with 14 load cells designed by Prof. V. Askegaard of the Technical Universit
Denmark; these cells are capable of measuring both normal pressure and wall shear stress. An example of a w
pressure and shear stress records depicting the pulsating load in the cylinder are shown in Figure 32.
Figure 32. Load Cell Records depicting Pulsating Loads in Mass‐Flow Bin
A similar action to that described above for mass‐flow bins may occur in tall funnel‐flow bins or silos where the effec
transition intersects the wall in the lower region of the silo. As a result, there is flow along the walls of a substantial m
of bulk solid above the effective transition.
During funnel‐flow in bins of squat proportions, where there is no flow along the walls, as depicted in Figure 33, dilat
of the bulk solid occurs as it expands in the flow channel. As a result some reduction in the radial support given to
stationary material may occur. If the hopper is fairly steeply sloped, say [θ ≥ δ], then the stationary mass may
momentarily causing the pressure in the flow channel to increase as a result of the 'squeezing' action. The cycle t
repeats.
Figure 33 Funnel Flow Bin
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A similar behaviour may occur in expanded flow bins, such as the bin depicted in Figure 2 .Pulsating loads can occu
such bins, particularly if the slope angle e of the transition is too steep. Owing to segregation on filling, larger
particles are more likely to be located adjacent to the sloping surface at the lower end of the funnel‐flow section. S
particles tend to roll as well as slide, aggravating the load slipping problem and giving rise to load pulsations. Proble
of this type have been experienced in large coal bins.
7.2 Multi‐Outlet Coal Bins
Silo‐quaking problems have been known to occur in bins with multiple outlets. By way of illustration, consider the la
coal bin shown in Figure 34. The bin has seven outlets, six around an outer pitch circle and one located centrally.
hopper geometries provide for reliable flow permitting complete discharge of the bin contents. Coal was discharged
means of seven vibratory feeders onto a centrally located conveyor belt. When the bin was full or near full, severe sh
loads were observed at approximately 3 second intervals during discharge. The discharge rate from each feeder wa
the order of 300 t/h. When the level in the bin had dropped to approximately half the height, the shock loads
diminished significantly. With all the outlets operating, the effective transition was well
Figure 34 Multi‐Outlet Coal Bin
down towards the bottom of the bin walls and the critical head Hm was of the same order as the bin diameter
greater than DF. Substantial flow occurred along the walls, and since the reclaim hoppers were at a critical slope for m
and funnel‐flow as determined by flow property tests, the conditions were right for severe 'silo quaking' to occur.
Confirmation of the mechanism of silo quaking was obtained in field trials conducted on the bin. In one series of te
the three feeders along the centre line parallel with the reclaim conveyor were operated, while the four outer feed
were not operated. This induced funnel‐flow in a wedged‐shaped pattern as indicated in Figure 34, with the effec
transition occurring well up the bin walls, that is Hm < Hcr (= DF ) or Hm << D. The same was true when only the cen
feeder (Fdr. 1) was operated; in this case the stationary material in the bin formed a conical shape. Under th
conditions, the motion down the walls was greatly restricted and, as a result, the load pulsations were ba
perceptible.
In a second set of trials, the three central feeders were left stationary, while the four outer feeders were operated. T
gave rise to the triangular prism shaped dead region in the central region, with substantial mass‐flow along the wThe load pulsations were just as severe in this case as was the case with all feeders operating. Dynamic st
measurements were made using strain gauges mounted on selected support columns. When the bin was full (or n
full), the measured dynamic strains with Hm Hcr were in the order of 4 times the strains measured when the f
pattern was controlled so that Hm < Hcr.
10. CONCLUDING REMARKS
In this paper an overview of some salient aspects of the storage, flow and handling of bulk solids has been presente
is quite clear that, in recent years, significant advances have been made in research and development associated w
bulk handling systems. It is gratifying to acknowledge the increasing industrial awareness and acceptance through
the world and particularly in Australia of modern bulk materials handling testing and plant design procedures. Th
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procedures are now well proven, and while much of the industrial development has, and still is, centred aro
remedial action to correct unsatisfactory design features of existing systems, it is heartening that in many new indust
operations the appropriate design analysis and assessment is being performed prior to plant construction
installation. It is most important that this trend continues.
The paper has indicated, by way of example, the ongoing need for research and development which is necessary
industrial plant and processes become more sophisticated, the demands for better quality control become m
stringent and both national and international competition requires more efficient and cost‐effective performance.
11. ACKNOWLEDGEMENTS
Much of the work presented in this paper is based on a current research grant from AMIRA. The support of AMIRA
the sponsoring companies is gratefully acknowledged.
REFERENCES
1. Jenike, A.W. "Gravity Flow of Bulk Solids". Bul. 108, The Univ. of Utah, Engn Exp. Station, USA 1961.
2. Jenike, A.W. "Storage and Flow of Solids". Bul. 123, The Univ. of Utah, Engn Exp. Station, USA 1964.
3. Arnold, P.C., McLean, A.G. and Roberts, A.W. "Bulk Solids: Storage, Flow and Handling". The Univer
of Newcastie Research Associates (TUNRA), Australia, 1982.
4. Roberts, A. W ."Modern Concepts in the Design and Engineering of Bulk Solids Handling System
TUNRA Bulk Solids Research, The University of Newcastle, Australia, 1988.
5. Thomson F.M. "Storage of Particulate Solids". Chapter 9, Handbook on Powder Science & Technolo
(1984) Van Nostrand.
6. Jenike, A.W. "A Theory of Flow of Particulate Solids in Converging and Diverging Channels Based o
Conical Yield Function". Powder Tech., Vol.50. (pp. 229‐236).
7. Benink, E.J. "Flow and Stress Analysis of Cohesionless Bulk Materials in Silos Related to Codes". Doct
Thesis, The University of Twente, Enschede, The Netherlands. 1989.
8. Roberts, A.W. and Ooms, M. "Wall Loads in Large Steel and Concrete Bins and Silos due to Eccen
Draw‐Down and Other Factors". Proc. 2nd Inti. Conference on 'Design of Silos for Strength and Flo
Powder Advisory Centre, U.K., 1983, (ppI51‐170).
9. Ooms, M. and Roberts, A. W ."The Reduction and Control of Flow Pressures in Cracked Grain Silos". BSolids Handling, Vol. 5, No.5, Oct. 1985. (pp.1009‐1016).
10. Roberts, A. W. "Some Aspects of Grain Silo Wall Pressure Research ‐Influence of Moisture Content
Loads Generated and Control of Pressures in Tall Multi‐Outiet Silos". Proc. 13th Inti. Powder and B
Solids Conf., Chicago, USA, May 1988. (pp.II‐24).
11. Australian Standard AS89138 "Loads on Bulk Solids Containers"
12. Roberts A. W ., Ooms M and Manjunath K.S., "Feeder Loads‐ and Power Requirements in the Contro
Gravity Flow of Bulk Solids from Mass‐Flow Bins" Trans. I.E.Aust., Mechanical Engineering, V.ME9, N
April 1984.
13. Manjunath,K.S. and Roberts, A.W., 'tWall Pressure‐Feeder Load Interactions in Mass‐F
Hopper/Feeder Combinations". Part I. IntI. Jnl. of Bulk Solids Handling, Vol. 6, No.4, Aug. 1986.
14. Manjunath, K.S. and Roberts, A.W., "Wall Pressure‐Feeder Load Interactions in Mass‐FHopper/Feeder Combinations". Part II. Inti. Jnl. of Bulk Solids Handling, Vol. 6, No.5, Oct. 1986.
15. Rademacher, F.J.C., "Reclaim Power and Geometry of Bin Interfaces in Belt and Apron Feeders". IntI.
of Bulk Solids Handling, Vol. 2, No.2, June 1982.
16. Roberts, A. W. and Teo, L.H., "Performance Characteristics of Gravity Reclaim Stockpiles of Con
Form", Trans. of Mechanical Engineering, The Instn. of Engrs. Australia, Vol. ME 14, No.2, 1989, pp
102.
17. Roberts, A. W .and Teo, L.H., "Design Considerations for Maximum Reclaim Capacity of Con
Stockpiles", IntI. Journal of Bulk Solids Handling, Vol. 10, No. 1, 1990.
18. Ooms, M. and Robens, A.W. "Significant Influence of Wall Friction in the Gravity Flow of Bulk Soli
IntI. Jnl. of Bulk Solids Handling, Vol. 5, No.6, 1985 (pp.1271‐1277)
5/13/2018 Modern Technological Developments in the Storage and Handling of Bulk Solids_Edit - slidepdf.com
http://slidepdf.com/reader/full/modern-technological-developments-in-the-storage-and-handling-of-bulk-solidsedit 26/26
19. Robens, A.W., Ooms, M. and Scott, O.J. "Surface Friction and Wear in the Storage, Gravity Flow
Handling of Bulk Solids". Proc. Conf. 'War on Wear', Wear in the Mining and Mineral Extraction Indus
Instn. of Mech. Engnrs, Nottingham U.K., 1984. (pp.123‐134).
20. Robens, A. W. "Friction, Adhesion and Wear in Bulk Materials Handling". Proc., AntiWear 88, The Ro
Soc. London. 1988. Inst. of Metals, I.Mech. E. .
21. Roberts. A.W., Ooms, M. and Wiche, S.J. "Concepts of Boundary Friction, Adhesion and Wear in B
Solids Handling Operations". IntI. Jnl. of Bulk Solids Handling, Vol.10, No.2, May 1988. :
22. Robens, A.W."Vibrations of Powders and Bulk Solids". Chapter 6, Handbook on Powder Science
Technology. (1984) Van Nostrand.
23. Robens, A.W., Ooms, M. and Scott, O.1. "Influence of Vibrations on the Strength and Boundary FrictCharacteristics of Bulk Solids and the Effect on Bin Design". Inti. Jnl. of Bulk Solids Handling, Vol.6, N
1986. (pp.161‐169).
24. Robens, A.W. and Rademacher, F.J.C. "Induced Gravity Flow by Mechanical Vibrations". To appea
Inti. Jnl. of Bulk Solids Storage in Silos, UK.
25. Robens A. W. "An Investigation into the Gravity Flow of Non‐Cohesive Granular Materials Thro
Discharge Chutes". Trans. A.S.M.E., Jnl. for Engng. in ,Industry, Vol. 91, Series B, No.2, May 1969.
373‐381). ,
26. Robens A. W. and Scott O.1. "Flow of Bulk Solids Through Transfer Chutes of J Variable Geometry
Profile". Bulk Solids Handling, Vol. 1, No.4, December 1 1981. (pp. 715‐727).
27. Parbery , R.D. and Robens, A. W ."On Equivalent Friction for Accelerated Gravity 1 Flow of Gran
Materials in Chutes". Powder Technology, Vol. 48. 1986. (pp. 75‐79). ; 28. Savage, S.B. "Gravity Flow of Cohesionless Granular Materials in Chute and Channels". J.Fluid Me
Vol.92, Pan 1, 1979. (pp.53‐96).
29. Andrews, B.R., Boundy, B .1. and Roberts, A. W ., "Flow Property Analysis, Design and Construct
Details for a 2400 tonne Mass‐Flow Bin". IntI. 1nl. of Bulk Solids Handling, Vol. 3, No.4, November 19
(pp.781‐786).
30. Roberts, A. W., " Abrasive Wear Testing and Analysis in Bulk Solids Handling", Report of Bulk So
Research Group (Sectie Stort‐geotechnologie), Dept. of Mechanical Engineering, University of Twe
The Netherlands, 1986.
31. Roberts, A.W., "Hopper and Chute Performance and Wear", AMIRA Project No. 245, Handling of B
Solids, The University of Newcastle, 1989.
32. Roberts, A. W., Ooms, M., Askegaard, V. and Wiche, S.1. "Investigation of Flow Instabilities and Bea
in Silos'. Paper for Presentation at the cmsA 90 Congress, Prague, Czechoslovakia. August 1990.