Editing Stacker (section)

{{Short description|Large machine used in bulk material handling}}
{{about|a machine used in bulk material handling applications|other uses of the term|Stacker (disambiguation)}}
{{Unreferenced|date=December 2009}}

[[File:krupp stacker rtca kestrel mine.jpg|thumb|[[ThyssenKrupp|Krupp]] coal stacker featuring tripper conveyor and non-slewing, luffing boom at [[Rio Tinto Coal Australia|RTCA]] Kestrel Mine|300px]]
[[File:Tagebau Garzweiler - Absetzer Nr. 755 in Betrieb.webm|300px|thumb|Stacker at [[Garzweiler surface mine]]]]
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A '''stacker''' is a large [[machine]] used in [[bulk material handling]]. Its function is to pile bulk material such as limestone, ores, [[coal]] and cereals onto a [[stockpile]]. A [[reclaimer]] can be used to recover the material.

[[Gold dredge]]s in Alaska had a stacker that was a fixed part of the dredge.  It carried over-size material to the [[tailings]] pile.

Stackers are nominally rated for capacity in t/h [{{cvt|1|t/h|LT/h ST/h|lk=on}}]. They normally travel on a [[Rail profile|rail]] between stockpiles in the stockyard.  A stacker can usually move in at least two directions: horizontally along the rail and vertically by luffing (raising and lowering) its boom.  Luffing of the boom minimises dust by reducing the distance that material such as coal needs to fall to the top of the stockpile.  The boom is luffed upwards as the height of the stockpile increases. Some stackers can rotate the boom.  This allows a single stacker to form two stockpiles, one on either side of the [[conveyor]].

Stackers are used to stack in different patterns, such as cone stacking and chevron stacking.  Stacking in a single cone tends to cause size segregation, with coarser material moving out towards the base.  In raw cone ply stacking, additional cones are added next to the first cone.  In chevron stacking, the stacker travels along the length of the stockpile adding layer upon layer of material.

Stackers and reclaimers were originally manually controlled, with no means of remote control.  Modern machines are typically semi-automatic or fully automated, with parameters remotely set. The control system used is typically a [[programmable logic controller]], with a [[human-machine interface]] for display, connected to a central [[control system]].

Other than stacking, a stacker has three basic movements:
* Luffing: This is vertical movement. Stackers use either a winch mechanism with metal wire, or hydraulic cylinders, generally two. Winch mechanisms are highly reliable compared to hydraulic actuators and remain widely used, particularly in large stackers.
* Travelling: The stacker moves on a [[Rail tracks|rail track]], which may be [[broad gauge|broad]] or [[narrow gauge]], enabling it to move around the stockyard as required. For this purpose, traction motors powered by direct current (DC) are connected by [[bevel gear]]s to between 12 and 22 wheels. For manual control, all the controls are in a controller's cabin above the boom conveyor or boom. Modern stackers can be controlled remotely.
* Slewing: This is rotation of the stacker around its central axis to align or place the stockpile where required. This works mostly by a slew pinion that rotates around a slew base. This type of gear assembly is called a [[sun and planet gear]]. The axles may be multiple and are driven by DC-powered axle motors which transmit the torque via bevel or [[Gear#Helical|helical]] gears.

The [[conveyor belt]]s used in stackers may be made of fabric or metal wire, depending upon the material to be handled. They are driven by pulleys, which in turn are driven by [[DC motor]]s. The motors and gear are coupled by [[fluid coupling]].

Most stackers are electrically powered by way of a trailing cable. There are basically two types of cable trailing: power cord rotating drum (PCRD) and control cable rotating drum (CCRD). Pendulum adjustments are made to ensure the proper alignment of these cables while the stacker is travelling.