Mining from A to Z

In our glossary, you will find a comprehensive list of explanations for a wide variety of mining industry terms.
We have explained all the technical terms for you in a detailed and understandable way.




Amphibolite is a metamorphic rock. The main components are amphiboles (mostly hornblende) and plagioclase. Quartz, garnet, diopside, epidote and biotite may also be present. The chemical composition of the amphibolites is metabasic. They are obtained from basic magmatites such as gabbros, basalts, andesites and their tuffs or from marls and tuffites (para-amphibolites).

Angle of repose (slope)

Bulk materials property

For cohesion-free, free-flowing, grainy materials such as grain, granulated mineral fertilizer, limestone, pellets, coke, etc., the natural angle of repose – also known as the angle of slope – is the maximum angle at which individual surface particles stop sliding down. The natural angle of repose can be easily determined by allowing the bulk material to flow from the base area of a cylinder-shaped sampler at low tipping height onto a firm horizontal support.


Bituminous coal

Anthracite is a bituminous coal with a volatile content of less than ten percent. This high-grade form of coal is extremely hard. Anthracite forms from vegetable matter under high pressure and in the absence of air. This increases the carbon content which lies at over 91.5 percent by weight. Anthracite is particularly prized as a fuel due to its high energy content, the hot flame it produces and its combustion properties which mean that it leaves almost no residue.



Cavity filling

In mining, the term backfilling refers to the filling-in of the cavity between the excavated area and the rock mass using suitable materials. Various materials (such as gravel) and a number of different technologies are used for backfilling.



Banded iron formation

Sedimentary rock

Banded iron formations are units of iron-bearing marine sedimentary rock that were primarily deposited in the Precambrian period. They possess a characteristic banded structure due to their metal-bearing layers. The layers primarily consist of ferrous minerals with a vertical cross-section reminiscent of bands. This is what gives them their name.



Igneous rock

Basalt is a basic igneous rock. It consists in particular of iron and magnesium silicates with pyroxenes and calcium-rich feldspar (plagioclase), and usually also olivine. Basalt is the volcanic equivalent of gabbro (plutonite), which has the same chemical composition. Basalt is usually dark gray to black. As the rock is formed through the action of volcanic processes, the groundmass is usually fine-grained due to the rapid cooling it undergoes.


Base metal

Base metal

Base metals are characterized by the fact that they oxidize – under normal conditions they react with oxygen in the air. For example, iron rusts. Zink and aluminum protect themselves through passivation, which is the formation of a corrosion-resistant oxide layer that prevents further oxidation. Base metals differ chemically from noble metals in that their redox pairs have a negative instead of a positive standard electrode potential (relative to the standard hydrogen electrode).



Aluminum ore

Bauxite is an aluminum ore that consists primarily of the aluminum materials gibbsite (hydrargillite) and diaspore as well as the iron oxides haematite and goethite, the clay material kaolinite and small amounts of the titanium oxide anatase. Bauxite takes its name from its place of discovery, Les Baux-de-Provence in the south of France. It was unearthed there for the first time in 1821.


Belt conveyor

A system for moving bulk material

Machine which transports bulk material on a conveyor belt. It mainly consists of a supporting structure made of steel sections, a drive station, a return station, idlers and a conveyor belt.


Belt wagons

Mining technology

Belt wagons are standalone machines built on crawlers which serve to transport and discharge the overburden or minerals. In opencast mining these machines are very important links for continuous excavating, transporting, and discharging activities especially when mining and dumping areas are spread apart over significant distances.

The belt wagons help save on overall investments and operating costs which otherwise would be substantially higher due to the need to acquire larger main equipment.


Blending bed


Numerous bulk materials handling applications require process-compatible treatment of the material. Their chemical and physical properties should be as homogeneous as possible. Since most of these materials come from quarries or opencast mines, their properties may vary enormously and so stockyards have to meet much higher standards. A stockyard designed not only as a buffer or to hold back-up stocks but also for homogenizing material properties is known as a blending bed. Such a facility ensures blending or pre-homogenization by combining a specific stacking technology with a particular type of reclaiming technology.

Generally speaking, the material is stacked in consecutive layers, and depending on the type of reclamation, individual, several or all of the layers are reclaimed at the same time. The efficiency of such a blending bed is expressed as the homogenizing effect, generally also denoted as the blending effect.


Block caving

Mining of ore

Block caving is an underground mining method in hard rock in which an ore body is undercut until it finally collapses under its own weight. This can cause the formation of large surface depressions called dolines or sinkholes. The method is an economical means of mining large ore deposits.


Bridge-type reclaimers

Stockyard machines

Bridge-type reclaimers are exclusively employed in face reclamation. A bridge girder is used for the supporting structure. The scraper chain is located underneath the bridge girder. Harrow-type carriages with harrow arms are mounted on the bridge structure on either one or both sides. Their shape is adapted to the cross-section of the stockpile. The bridge girder spanning the entire foot width of the stockpile is supported on a rail-borne undercarriage. By moving the harrow carriage in reverse, the harrow arm, which is supported on the face side of the stockpile, loosens the bulk material. As a result, the bulk solids trickle down to the foot of the stockpile on the slope surface. Here they are picked up by the scraper chain and transferred to a belt conveyor for discharging.

In circular stockyards, bridge-type reclaimers, which rotate via a slew column around a central axis, are employed. In this arrangement, the bridge girder’s outer point with the undercarriage is supported on a ring rail.

Bridge-type reclaimers are also known as blending bed installations because they produce the best homogenizing effects in bulk solids reclaiming. This homogenizing effect is produced by the work of the harrow arm traveling transversely to the stockpile, thus pre-blending the bulk solids from various layers of the stockpile. Subsequently, the bulk material is mixed again by the scraper shovels on the stockpile foot. The harrow can reach all the layers on the stockpile’s face side and remove them at uniform depth.

The use of bridge-type reclaimers with scraper chains is limited by the properties of the bulk material. Slow-flowing bulk materials can be reclaimed only very slowly (if at all). In such cases, bridge-type machinery with a bucket wheel or bucket chain are used.


Bucket elevator

Vertical transport of powdery or small-sized bulk material

A continuous conveyor for vertically elevating powdery or small-sized bulk material. The buckets are attached to a double- or single-strand chain, a pintle chain or a belt. Vertical continuous conveyor with buckets used as support elements that scoop the material to be transported or are filled and emptied in certain areas. Belts or chains are used as traction elements.


Bucket wheel reclaimers

Stockyard machines

Bucket wheel reclaimers equipped with a bucket wheel boom are used on stockyards to reclaim large mass flows of poorly flowing bulk solids or bulk materials of relative high density. The design principle and function of bucket wheel reclaimers are not essentially different from those of the bucket wheel excavators used in opencast mines. However, the cutting forces required on the bucket wheel and the mass flows to be achieved are usually somewhat higher in opencast mining. Bucket wheel reclaimers mostly consist of a slewable superstructure and a rail-mounted sub-frame. Both the bucket wheel boom and the counterweight boom are hinge-mounted on the superstructure and guyed by guy ropes or tiebacks via a pylon. The bucket wheel boom is raised or lowered with the help of cable winches or hydraulic cylinders. The bucket wheel, which is mounted eccentrically on the wheel boom head, picks up the bulk material and transfers it laterally to the boom conveyor. The belt conveyor transports the bulk solids to the central chute in the superstructure slewing axis, from where the material is transferred to a discharging stockpile conveyor running between the rails of the reclaimer. In order to achieve potentially large clearance angles and good bucket cutting, filling and emptying, the bucket wheel is mounted so that it is not only turned torsionally around a vertical axis, but also tilted around a horizontal axis arranged at right-angles to the wheel shaft.

Furthermore, crawler-mounted compact-type bucket wheel excavators are also employed as reclaimers. They are characterized by a particularly favorable unit weight. They are very flexible and can be used for many applications. Reclaimers of this type have a relatively short bucket wheel boom that can be hydraulically raised and lowered, and for reclaiming stockpiles in block operation they are equipped with slewing gear for the superstructure and a separately slewable discharge boom. The short wheel boom requires only a small counterweight outreach. This counterweight is positioned on the superstructure platform extended toward the rear such that the discharge boom can be slewed above it. The wheel boom is supported in the pylon of the superstructure above the feeding chute of the discharge belt conveyor.

Besides this design, which is typical of compact-type excavators, modified compact-type bucket wheel reclaimers on crawlers without a separate discharge boom are built for specific applications. In this case the material is transferred by a continuous belt conveyor without any intermediate transfer from the bucket wheel to the discharge point of the machine. Compact-type bucket wheel reclaimers without separate discharge booms are used solely in bench-type operation. Compared to the compact-type bucket wheel excavators with separate discharge boom, the steel structure of these machines’ superstructure is of a simpler, lighter design. There is no material transfer point in the center of the device, which is an additional benefit in connection with abrasive materials such as copper ore.


Bulk material

A granular or fragmented mixture in pourable form

Bulk materials are different kinds of lumpy, granular and powdered products, e.g. ores, coal, peat, sand, saw dust, cement. According to VDI 2411, bulk materials are “loose, pourable materials to be conveyed”.


Bulk materials handling

Engineering field centered on the design of equipment used for the handling of dry materials

Bulk materials handling denotes the change-over between the different means of transport in the transport chain from the place of extraction to the place of processing or the consumer. A wide variety of means of transport can be employed in the transport chain, including trucks, railway wagons, seagoing vessels and inland barges. The handling process comprises the loading and unloading of the means of transport. Selection of the handling equipment to be used depends primarily on the properties of the bulk materials, the volume to be handled per unit time (mass flow) and the type of transport. Furthermore, the environmental regulations in force, particularly regarding dust and noise emissions (especially at ports and freight depots), have to be met. As handling systems are often an interface in freight transport, they need to meet certain demands in connection with the testing and quantity measurement of the bulk solids shipped or supplied.


Bulk terminal

Transshipment port for bulk goods

The area of a port used for transshipment of bulk goods. The warehouse capacities, loading equipment and packaging facilities are designed for handling bulk goods.


Chevcon method

Stacking procedure

The Chevcon method has been developed for circular storage with a stacker slewing continuously back and forth over a stockpile area. With each slewing cycle, the stockpile area shifts through a defined angle that corresponds to the radial growth of the stockpile. The stacker can be lifted and lowered to deposit roof-like layers one on top of the other. The stacker can be programmed to run at a minimal distance from the crest of the stockpile to avoid dust build-up and damage to the material during stacking. As the stockpile grows higher, there is less homogenization because grain sizes tend to segregate in each layer that is stacked. However, this effect can be fully compensated for by using bridge-type reclaimers. Considerably more complicated equipment and control systems are required than for the Chevron method.


  • Stacking method: Chevcon
  • Reclaiming at the face -> Homogenization effect: good
  • Reclaiming along the side -> Homogenization effect: moderate


Chevron method

Stacking procedure

In the Chevron method, the stacker travels alongside the stockpile all the time and tips the material in a series of rooflike layers on top of each other. The stacking point can always be kept at a constant height. However, gentler stacking action is possible with height-adjustable booms that can be programmed to keep a minimal distance from the crest of a stockpile to avoid material damage and dust. In this procedure, different bulk components can easily be mixed.

As the stockpile grows, changes in layer thickness (same layer volume) can be compensated for by reducing the speed of the stacker (greater layer volume). Grain size segregation which detracts from the homogenizing effect can later be fully compensated for by using bridge-type reclaimers at the face of the stockpile.


  • Stacking method: Chevron
  • Reclaiming at the face -> Homogenization effect: good
  • Reclaiming along the side -> Homogenization effect: moderate


Ore mineral

Chromite is a mineral belonging to the oxides. Chemically it is an iron chromium oxide. It typically occurs in granular to massive aggregates. The color is usually black, but rarely also dark brown. The surface has a greasy metallic luster.


Circular stockyards


Circular stockyards are “endless” stockyards where the material is stacked in a circular stockpile by a stacker rotating around a central column. A reclaimer which also rotates around the stockpile center axis moves the material to a bottom funnel under the center column and then onto tunnel conveyors for transport underneath the circular stockyard. Due to their compact design, circular stockyards are well suited for the roofed storage of bulk materials. In contrast to longitudinal stockyards, they allow simultaneous and continuous stacking and reclaiming from the same stockpile without any restrictions.


Cone Shell method

Stacking procedure

In the Cone Shell method, stockpiles are built up by a stacker that moves at a uniformly low speed or in very small steps and tips from a constant height, or by ridge-mounted belt conveyors in a storage building. Such stockpiles are used for bulk solids of small, uniform grain sizes, i.e. materials of a comparatively homogeneous composition. The major advantage of this method is that the mechanical equipment and control systems required are kept to a minimum. Segregation only occurs within the same row of cones, and grain size distribution over the entire cross-section of a stockpile is very uniform. The number of cones built in a row will depend on the bulk material grain size, the angle of repose, and the desired blending effect.


  • Stacking method: Cone Shell
  • Reclaiming method: at the face, along the side
  • Homogenization effect: small


Continuous ship unloading with a bucket elevator

Port handling

The automatic, continuous take-up of bulk material is essential for effective application of the continuous conveying principle and utilization of scooping bucket elevators for ship unloading, including residual emptying. For the vertical transport of bulk materials by means of a bucket elevator, the buckets must be arranged so that they can take up the material by scooping in the bottom return point (bucket elevator boot). The bucket elevator of continuous ship unloaders (CONTI ship unloader) can be moved in all directions. The bucket elevator boot is designed to reach all positions inside the cargo hold.

The bucket elevator’s freedom of motion is due to its specific design typical of CONTI ship unloaders. The machine’s superstructure with unloading boom and counterweight boom is slewably mounted on a portal, which can be moved alongside the quay. The scooping bucket elevator, which rotates around the vertical axis, is located on the head of the luffing unloading boom. While the vertical and horizontal conveying paths are enclosed to prevent noise and dust emissions, the bucket elevator boot with the triangular chain guide is not enclosed. Because of this design, chip extraction is possible with the scooping buckets in a similar way to the bucket wheel or bucket ladder principle. The material is taken up on the lower horizontal section of the bucket chain strand.

At the bucket elevator head, the buckets are unloaded onto a horizontal turntable, which transfers the bulk material to the boom conveyor. Compared to the use of various chutes, this design considerably reduces the bulk material’s height of fall, which is determined by the design, the height of construction of the revolving bucket elevator, and the development of dust and noise at the bucket elevator head. The boom conveyor transports the material to the feeding hopper arranged in the ship unloader’s slewing axis from where it is transferred to the terminal’s quay conveyors by reversible bunker discharge conveyor.


Conveying and Loading

Conveying and loading of bulk materials along the entire process chain

Ores, salts, rocks, earth and other resources that have been mined must be transported over long distances. After extraction and crushing, the material must pass through stations like grinding, flotation, drying, homogenization, mixing, interim storage and loading. Conveyor systems have to ensure safe, efficient and environmentally friendly handling of these materials along the entire process chain.



Efficient and environmentally friendly handling system for bulk material along the entire process chain

Also called conveyor system, belt system or belt conveyor. Means of transporting granular or fragmented cohesive or non-cohesive material or piece goods. These systems transport all kinds of bulk material in a wide variety of industrial sectors.


Drive power

Machine calculation

Determining the drive power for each drive is particularly important when calculating handling equipment functions. Generally speaking, the drive power is the product of the resulting kinematic resistance and the rate of motion. The main types of kinematic resistance in the various handling sections include frictional resistance, lifting resistance, wind resistance, acceleration resistance.


Dynamic leach pad systems

Mining technology

Specific technological situations require stockpile reclaiming and building new stockpiles to take place at the same time or shortly after material has been reclaimed and in the same place or close by so as to make efficient use of the available equipment and storage area. This is typically the case in the chemical preparation of copper ore. The broken and crushed copper ore is stacked on large-area stockpiles and subsequently acid-leached via a piping system to dissolve the copper contained in the ore. Subsequently the acid is collected by a drainage system and conducted to an electrolysis plant for copper recovery.

After a technologically required retention period (leaching time), the leached copper ore is reclaimed again in order to dump it on a final site farther away. Parallel to the reclaiming process, the space now free is used to build up a new pile. This process of continuous reclamation of leached piles and simultaneous rebuilding of a stockpile with fresh copper ore is called the dynamic stockpile system or dynamic leach pad system.




Grain size

Bulk materials property

Most bulk materials consists of grains or particles of different size and shape. Grain size and grain distribution have a major impact on the flow properties of bulk materials. The maximum grain size is important for calculating of machine components (belt width, bucket size, troughed width, etc.) and transfer systems (discharge chutes).




Apart from mere storage, the principal function of a blending bed is to homogenize bulk materials of different qualities, grain sizes or properties. The related effect largely depends on the stockpile’s shape and stacking as well as the arrangement and type of equipment used. The effect of homogenization varies with deviations of the stacked material from its average composition and with the function of the reclaimers used (bridge-type reclaimers, portal scrapers, bucket wheel reclaimers).





Longitudinal stockyards


The most widespread type of storage for bulk materials is the longitudinal stockyard, which normally has a length-width ratio of 3:1. Longitudinal stockyards are often located outdoors. However, if the material has to be shielded from the weather or the environment has to be protected from emissions, these stockyards may be located inside buildings. Stacking is carried out from stackers traveling alongside the stockyard, roof ridge-mounted tripper cars or mobile belt conveyors. For reclamation, bridge-type reclaimers, portal and side scrapers or bucket wheel reclaimers are used.


Mining industry

Extraction of mineral resources

Extraction of useful mineral resources like ores, coal, copper, rocks or earth in compliance with special legislation (mining law). This is done in open-pit mining or underground mining with the help of special machinery and equipment.



Mobile conveyor bridges

Mining technology

Crawler-mounted mobile conveyor bridges were specifically designed for a continuous dynamic operation to streamline the technological process of piling the ore, reclaiming leached stockpiles and creating new ore stockpiles space-efficiently and in a timely manner.

When building the stockpile, a tripper car takes the copper ore supplied by a belt conveyor running alongside the pile to a crawler-mounted conveyor bridge which travels alongside the stockpile. The tripper car traveling back and forth on this conveyor bridge supplies the table-type stockpile line by line. The double crawler units of the conveyor bridges are capable of compensating for any variations in the ground profile in all directions. For this reason, no special demands are made on the subgrade. Furthermore, this helps maintain a very stable belt run.

In dynamic stockpile systems – parallel to building a stockpile – reclaiming is performed by a compact crawler-mounted bucket wheel reclaimer which in bench-type operation reclaims the pile line by line. The bucket wheel reclaimer delivers the leached ore via a mobile hopper car to a crawler-mounted conveyor bridge from where the material is transferred to a belt conveyor running alongside the pile to take the material away. Further stationary conveyor systems then transport the bulk material to a shiftable belt conveyor with mobile tripper car and discharge boom. The latter either transfers the material directly or via an intermediate belt wagon to a crawler-mounted compact-type spreader for dumping the leached ore on a final pile.

To ensure effective utilization of the stockpile equipment, the mobile conveyor bridges travel either in a semi-circle at the end of the table-type stockpile or (after the double crawlers have been turned) longitudinally to the side opposite the longitudinal conveyors to continue their work. In doing so they cross the longitudinal conveyors running in this area below ground level.



Moisture index

Bulk materials property

The properties of bulk materials are determined mainly by their water content. Rather than the bound water (structural water, adsorbed water), the ‘free’ water between the particles (pore water retained in hollow spaces due to surface tension) is important under normal temperature and pressure conditions. The water content of bulk materials is determined by drying a sample in a drying furnace at 105°C for more than six hours. Alternatively, high-speed drying with infrared emitters (DIN 18121, Part 1 and Part 2) is possible.



Overland conveyor

A belt conveyor for overland transport of bulk material

A conveyor for continuous overland (long-distance) transport of bulk material to a storage location such as a stockpile. From there the material can be taken up by railroad cars or trucks for further processing. Overland conveyors are used wherever large quantities of bulk material must be transported in an efficient and environmentally manner from A to B.


Portal scrapers

Stockyard machines

The portal of the portal scraper fully spans the stockpile. The portal is supported by two undercarriages on either side, allowing stockpiles up to 75 m wide to be spanned. The scraper boom is maneuvered by lifting gear. Once again, the bulk material is transferred to the reclaiming conveyor by a transfer trough (located outside the portal) or a feed table (inside the portal). When used in outdoor stockyards, portal scrapers often have one or two main booms arranged in parallel. In their raised position, these booms project beyond the contour of the portal.

Portal scrapers with main and auxiliary booms are deployed inside storage buildings. In this type of construction, the booms do not extend beyond the contour of the portal in any position, so that the cross section of the warehouse can be largely adapted to the dimensions of the scraper’s portal. The auxiliary boom has the task of feeding the material to the main boom, so that the entire stockpile cross section can be continuously reclaimed. This ensures a very even flow of material during longitudinal reclaiming. However, the engineering requirements for this arrangement are more sophisticated, particularly regarding the driving gear and control system of the reclaiming elements.

Portal scrapers are also employed in circular stockyards. For this version, the portal is supported on one side on the center column by a ball-bearing slewing ring and on the other side through the undercarriage on a ring rail.


Quadrant radial-type ship loaders

Port handling

Radially traveling shiploaders, also known as quadrant radial-type ship loaders, are used in seaports whose depth does not allow vessels of big draft to dock. They are located offshore and connected to the mainland via conveyor bridges. The special feature of a quadrant radial-type ship loader is its main bridge, which can be slewed at a certain angle (quadrant) around a central axis of rotation. In this case the external rail mounting of the main bridge is supported on a pile foundation in the sea and on the rail bend mounted on the foundation. A boom bridge which can be radially extended is supported on the main bridge via rail mountings. The boom can be lifted or lowered by cable control, as required. The ropes of the latter are connected to the boom bridge via a pylon. This room to maneuver allows the head of the boom to reach all the loading hatches without having to move the vessel. The bulk material is transferred to the conveyor system of the ship loader in its axis of rotation via the conveyor bridge coming from the mainland, and the vessel is loaded by the belt conveyor of the boom bridge.



Stockyard machines

Whereas some smaller stockyards that handle small material flows use high manpower (e.g. driving wheel loaders) for reclamation, larger sites may choose from a number of continuous reclaimers and blending bed equipment. The latter include various types of semi-automatic or automatic scraper reclaimers and bucket wheel reclaimers. These machines withdraw material, pick it up and transfer it to a belt conveyor, which takes it elsewhere for further processing.

Reclaimers for longitudinal stockyards run on rails laid alongside a stockpile and transfer the bulk material to a belt conveyor which also runs beside the stockpile. In circular stockyards, slewable reclaimers are used. They take the material to the center of the yard for transfer via a funnel in the ground to a belt conveyor underneath. As regards the reclamation of material from a stockpile, a fundamental distinction is drawn between reclamation along the side and at the face.


Scraper reclaimers

Stockyard machines


These days, scraper reclaimers of various designs working in continuous operation are mainly used for reclaiming bulk material stockpiles. Scraper reclaimers are basically divided into boom-type and bridge-type equipment. Their main functional assemblies comprise the reclaiming element, the load bearing unit, and the undercarriage or slewing mechanism. The reclaiming element consists of two continuously running steel pintle chains arranged in parallel. The scraper shovels are mounted on the pintle chains, which are supported via track rollers running on rails. The scraper shovels are equipped with a center guide roller, which transfers the forces generated during reclaiming to an additional guide rail at right angles to the run of the conveyor belt. In boom-type devices, the scraper boom is connected to a base frame (side scraper), a portal (portal scraper) or a slew column (slewing scraper) in an articulated manner and is held, lifted, or lowered by cable winch control.



Ship loader

Port handling

Decisive factors when selecting and sizing a ship loading system are the bulk material properties, the local conditions, the performance parameters and the environmental requirements. Taking all these aspects into consideration, the most effective and cost-efficient handling principle requiring a minimum of operation and maintenance needs to be worked out. The loading system must be adapted to the port infrastructure and must be coordinated to suit current and future ship sizes.

Ship loaders working in continuous mode to load the cargo holds of a vessel generally consist of a portal and a superstructure with a boom that can be raised or lowered. The loading device is located at the head of the boom. In the case of loose bulk solids, a telescopic chute or a loading tube is used for loading. To handle bulk materials, telescopic chutes are frequently equipped with a dust collection device. A ship loader’s superstructure can be slewable or non-slewable.

Depending on the nature of the port terminal, ship loaders are either in stationary design or are movable in longitudinal direction or radially. Stationary ship loaders have a slewable superstructure and are used primarily in inland ports. During loading, the ship to be loaded must be moved so that the ship loader can fill the entire cargo hold.

Longitudinally movable ship loaders are the most frequently used. They are employed both in inland and seaports. While a stationary ship loader is supplied directly by a belt conveyor, ship loaders moving alongside the quay have to be operated in combination with a tripper car.


Semi-portal scrapers

Stockyard machines

In the semi-portal scraper, the portal spans a stockpile with a lateral or peripheral retaining wall. In this case, one track is located at the foot of the stockpile while the opposite one is supported in a raised position on the retaining wall of the stockpile.

Semi-portal scrapers are also employed in circular stockyards. For this version, the portal is supported on one side on the center column by a ball-bearing slewing ring and on the other side through the undercarriage on a ring rail.


Side scrapers

Stockyard machines

Side scrapers are equipped with scraper booms that can be raised and lowered, a counterweighted base frame, and the rail-mounted undercarriage. The position of the scraper boom is adapted to the slope of the stockpile by a cable winch. The rail-mounted undercarriage is located on just one side of the stockpile. The unit is protected from tilting by an appropriate counterweight. The reclaimed bulk material is taken away on a belt conveyor running parallel to the stockpile.


Slewing scraper

Stockyard machines

The design of slewing scrapers resembles that of side scrapers. However, the scraper boom is connected with the slewing gear platform in an articulated manner. They are employed primarily in circular stockyards. When used in longitudinal stockyards, slewing scrapers are additionally equipped with a rail-borne or crawler-mounted undercarriage. Slewing scrapers allow reclaiming not only by means of tunnel belt conveyors, but also via gallery conveyor belts running along the side of the storage building.

Slewing scrapers on crawlers are ideally suited for longitudinal stockyards with a wide stockpile foot (e.g. for fertilizer). For the reclaiming process, the scraper boom is moved to and fro along the face side, transferring the bulk material with the help of a transfer trough to a slewable loading boom, which is connected to the gallery belt. In this case, instead of a rail-borne undercarriage, a crawler-mounted undercarriage is selected because of its lower load on the storehouse floor. Specially developed software is employed to control the crawler drives. To this end, the position of the loading boom is adjusted to the position of the feed hopper car of the gallery belt. Any required corrections of the position are made automatically by the carriage of the hopper car and by changing the slewing angle of the loading boom.

While slewing scrapers in circular stockyards are operated in automatic mode, in longitudinal stockyards they are mostly operated manually because the automation of stockpile reclaiming is very complicated and expensive.



Mining machines

To build up large stockpiles (dumps), compact-type spreaders on crawlers are used to dump bulk materials. In most cases, shiftable belt conveyors with tripper cars are required to supply and transfer the bulk materials to the spreader. As a rule, heavy-duty boom-type spreaders on crawlers are used for direct dumping in opencast mines. The maximum length of these booms can reach 200 m. However, stackers with booms up to 60 m long are satisfactory for most applications in stockyards.




Stockyard machines

The stacking of bulk materials on stockyards and the development of diverse types of blending beds in order to homogenize different material qualities are performed primarily with the help of stackers. The bulk material to be stored generally arrives directly by belt conveyor or by truck, i.e. by road, rail or barge, and is then unloaded and subsequently taken by conveyor belt to a stacker, which tips it to make a stockpile. In exceptional cases where materials extraction and processing are close to each other, the stockyard will be directly supplied by long-distance conveyors, which are also known as overland conveyors.

Rail-mounted stackers are most frequently used in longitudinal stockyards. The discharge booms of these stackers are often slewable or can be raised and lowered. A stacker with a slewable discharge boom is essential for stockyards operated according to what is known as the parallel arrangement and for stacking using the Strata or Windrow methods. For this design, the stacker belt is slewed by ball-bearing slewing ring. The height of the boom is adjustable through hydraulic lifting gear or cable-winch operated systems. If the bulk material is to be stacked from a minimal distance above the crest of the stockpile (to avoid major dust built-up or damage to the material), the boom’s height of discharge needs to be variable over a wide range.

In a longitudinal stockyard, a tripper car is used to supply the stackers with the bulk solids. The tripper car either follows the stacker or is connected to it. In circular stockyards (or circular blending beds), the stacker is positioned in the center so that it can be slewed. It is fed with the material to be conveyed by a conveyor bridge located above the stockyard directly in its axis of rotation. Stackers for circular stockyards are mounted on a central column. During slewing, the height of the discharge point can be varied by lifting or lowering the boom.



Stacker-reclaimers (combined machines)

Stockyard machines

When stockpiling operations require stacking and reclaiming to be performed at the same time, separate machines are absolutely necessary. However, in many applications simultaneous stacking and reclaiming are not required. This is when stacker-reclaimers, i.e., combined machines, become an excellent solution because their functional principle combines both types of operation. The bucket wheel reclaimer with a reversible boom conveyor has proven to be an extremely functional, versatile machine.

The stacker-reclaimer can be employed like a stacker provided the bucket wheel boom conveyor is arranged so that the bulk material is transported to the boom head where it is discharged. Similar to a stacker, a stacker-reclaimer is fed via a tripper car. As the boom’s inclination can be adjusted and the boom slewed, the various methods of building bulk material stockpiles can be applied without any restrictions. When the stockpile is being built, the bucket wheel remains in its rest position. As with the bucket wheel reclaimer, for stockpile reclaiming the material is taken up by the bucket wheel, transferred to the machine’s rotation center by the reversible belt conveyor, and discharged into the central chute. Stacker-reclaimers are designed and scaled using the same engineering principles as are applied for separate equipment.

Other types of stockyard equipment with combined functions have been developed for specific applications. For example, portal scrapers can also be equipped to work in both stacking and reclaiming mode. To this end the portal scraper’s main boom works in reversible operation while the auxiliary boom is only used for reclaiming. In stacking mode, the belt conveyor running alongside the stockpile feeds the scraper via the tripper car or receives the bulk solids from the transfer trough of the scraper chain in reclaiming mode.

Furthermore, stacker-reclaimers also exist that are equipped with both a stacker boom for stacking and a scraper boom for reclaiming at one portal.


Stacking procedure


If a stockyard is to serve not only as a buffer but also for homogenizing the bulk material properties, the first important decision when planning a blending bed is to choose a suitable stacking procedure. This decision depends on criteria such as the bulk solid properties, the desired degree of homogenization and the proposed reclaimer.




The storage and homogenization of different bulk materials are important aspects of their flow and handling processes within the overall logistics of the bulk materials handling industry. For various reasons, stockyards are needed for the processing of bulk materials. The prime reason in most cases is to create buffers between discontinuous delivery (for example by ship or train) and continuous withdrawal, which is especially useful if deliveries are delayed. As long as no process-related requirements are made on the homogeneity of the material (i.e. its chemical and physical uniformity), bulk material stockpiles are simply stockyards. The available space and the required storage capacity are the main factors when deciding on the type of stockyard. The two main types are longitudinal stockyards and circular stockyards.

Longitudinal and circular stockpiles are primarily built up by stackers. Longitudinal stockyards are equipped with rail-borne stackers that move alongside the stockpile. For circular stockyards they are centrally arranged and build up the stockpile by slewing. A stacker in a circular stockyard receives material from a belt conveyor, which transfers the bulk material to the stacker at a point above the stockpile. In the case of longitudinal stockyards, the stacker is connected by a tripper car to an incoming belt conveyor. In longitudinal stockyards located under a roof or in a building, bulk materials may alternatively be stacked from ridge-mounted belt conveyors with a tripper car or a number of mobile and reversible belt conveyors.


Strata method

Stacking procedure

In Strata stacking, the stacker travels alongside the stockpile several times. On each longitudinal run it varies the stacking point in transverse direction to produce a stratified stockpile. The stacker must be of the slewing type in order to reach all the stacking ribs. The scraper will reclaim material from the side of the stockpile at points where all strata are accessible continuously and at the same time.

Bulk materials with a wide range of grain sizes often display undesirable separation when stacked. For bulk materials which give off dust or can be easily damaged when falling from a great height, the distributing boom of the stacker is designed to lift and lower as required to adapt the stacking height to the bulk solid’s properties and the height of each rib so that segregation is reduced.


  • Stacking method: Strata
  • Reclaiming at the face -> Homogenization effect: moderate
  • Reclaiming along the side -> Homogenization effect: good



Truck loading

Loading systems

The process of loading trucks and wagons is similar. Trucks or railway wagons are often loaded with bulk solids from bunkers or silos. While bunkers of various sizes are used to store bulk materials for a short time, large silos serve to store these materials for longer periods. Bunkers are often required as a buffer between continuous and discontinuous conveying systems.

The simplest case is as follows. After opening the bunker locking gate valve, the bulk material flows down into the transportation space/cargo hold of the means of transport. However, this is only possible in the case of easy-flowing materials such as grain, lumpy coal, or certain building materials. To minimize dust emissions, a telescopic chute that can be lowered is employed to bridge the difference in height between the bin outlet and the loading space.


Tubular conveyor

Conveyor technology

Closed pipe conveyors reliably move products while protecting them from external influences and preventing the escape of dust. Bulk material can be transported downhill in closed belts. Different materials can be conveyed in the top strand and bottom strand.




Vertical transport

Conveyor technology

In vertical transport, belt bucket elevators reliably convey powdery to coarse-grained bulk materials like limestone, coal and ores to heights of 200 meters and more. The materials can be fed to the bucket elevator in a space-saving manner from below or directly via a chute. Specially designed buckets are available in different widths, depending on the application and the quantity to be conveyed. Belt bucket elevators are also suitable for conveying hot bulk materials.


Wagon unloading

Unloading systems

Depending on the design, a distinction is drawn between gravity unloading and unloading by wagon tipping in bulk material wagon unloading. Wagons with automatic gravity unloading can be emptied continuously into the bunker located underneath the track bed while the train is moving slowly. In this process the rail wagon’s side walls are opened either manually or automatically so that the bulk solids can flow out on either side of the inclined surfaces of the saddle mounted in the middle of the wagon.

Wagon tipping systems turn the entire wagon in a tipping or turning unit to the point where the bulk material is discharged by gravity through the cargo space opening. A distinction is made between end wall and side tipping systems. However, because of the side tipplers’ higher unloading capacity, they are more common in bulk materials handling.

Due to the material’s residual moisture at temperatures below zero, the bulk solids stored in the wagon can freeze and cake onto the walls, making unloading more difficult or even impossible. To overcome such difficulties, a wagon thawing station is often employed to heat the side walls or the floor of the wagon prior to unloading, thus minimizing or preventing caking completely. To this end, the trains go through a special hall where, depending on the length of the hall, one or more wagons can be thawed at the same time. Depending on the situation, electric radiators, natural gas burners or hot steam heat exchangers can be used to generate heat.



Windrow method

Stacking procedure

Windrow stacking, also known as the principle of stacking small rows, evenly spreads one or more bulk materials in a longitudinal stockpile. Since different delivery positions of the bulk material are needed with this method, the stacker should have a slewable boom which can span the width of the stockyard.

Layers form compact longitudinal strips on top of and next to one another. While in the longitudinal ones the coarse grain of a row gravitates to the bottom, stacking with a very uniform grain size distribution is possible by selecting suitable row spacing (and thus heights) and an appropriate total number of rows per cross-section of the stockpile. Grain size distribution improves with the number of rows.


  • Stacking method: Windrow
  • Reclaiming at the face -> Homogenization effect: very good
  • Reclaiming along the side -> Homogenization effect: very good