Longwall machinery

Longwall machinery

Longwall machinery

The equipment used in longwall mining includesCutting MachinesArmoured Face conveyors(AFC)Powered Face SupportsStage loadersCUTTING MACHINES:Longwall shearers

Coal plough

Longwall shearersThe coal is cut from the coal face by a machine called theshearer(power loader). This machine can weigh 75120tonnes typically and comprises a main body, housing the electrical functions, the tractive motive units to move the shearer along the coalface and pumping units (to power both hydraulic and water functions). At either end of the main body are fitted the ranging arms which can be ranged vertically up down by means of hydraulic rams, and onto which are mounted the shearer cutting drums which are fitted 4060 cutting picks. These are known as "Double Ended Ranging Drum Shearers or DERDS" but being almost the only type of shearer now used, the term "shearer" is generally understood to refer to this configurationThe double ended ranging drum arrangement also allows smaller drums to be fitted while still cutting the required height, either cutting part of the seam with each drum in one pass or as two separate passes. The ranging arms allow much easier grading or changes in cutting height where required.The shearer is carried along the length of the face on the armoured face conveyor (AFC); using a chain-less haulage system, which resembles a ruggedized rack and pinion system especially developed for mining. Prior to the chainless haulage systems, haulage systems with Chain were popular, where a heavy duty chain was run along the length of the coal face for the shearer to pull itself along. The shearer moves at a speed of 1030 m/min depending on cutting conditionsMost shearers use radio control for normal operations although they are also fitted with manual and/or pendant controls for use in emergency conditions

COAL PLOUGHS:Coal Ploughs have had little application in Australia, and their main use has been in Europe, particularly in Germany where they were first developed. Essentially a plough is a large mass of steel, usually of a more or less triangular shape when viewed from the coal face or goaf sides, fitted with large "picks" (more like small agricultural plough blade tips) angled from the steel body towards the coal face.The plough height is the working height in the seam being mined (possibly a bit lower if the coal tops can be guaranteed to fall once the coal below is cut. These "picks" act in a fashion similar to chisels and break a narrow web of coal off the face (of the order of 300-400mm thick).In most cases there are no moving parts on a coal plough.The plough itself is mounted on the front of the AFC and is pushed into the face by push cylinders mounted in the supports. The plough has an endless chain haulage attached to the rear, and is driven through sprockets on electric drive(s) at the face end(s).The main advantages of ploughs compared to shearers are:CheapSimple (no moving parts on the cutting machine itself)Relatively low dust makeAble to keep exposed roof area very small (but a large number of chock movements would be required to maintain this)Though only a small web is taken, in the right conditions production rates can be comparable to a shearer as the plough is operated at a relatively fast speed along the face.Some disadvantages are:Cutting height is fixedAbility to cut stone is limitedWith increasing cutting height, machine stability becomes more problematicGrading can only be done using the AFC angleThere are safety implications with an exposed chain haulage.Armoured Face ConveyorTo maintain a safe working environment powered supports have to be advanced sequentially. This is achieved by utilising an articulating Armoured Face Conveyor(AFC) which runs along the face with the shearer mounted on it. The AFC is made up of short sections, called pans, which allows it to "snake" along the face as the supports are progressively advanced. Each powered support is pinned into a pan. Pans are normally 1.5 metres long and in recent years 2 m long pans are made to accommodate the increased width of larger powered supports. The AFC is powered by drive units located either at the maingate or tailgate ends or at both ends. The chain is driven along the face by the use of a gear and sprocket arrangement that transports the coal at a speed in excess of 1 metre/second. However some face conveyors are running at speeds as high as 1.6 m/s. Generally, the power and capacity of AFC are reflected by the motor size, pan width and chain size.

Shearers are mounted onto AFC's using either steel rollers or sliders running on the two edges of the AFC structure, either trapped or sufficiently guided by flanges to ensure derailing will not occur. The clearance between the bottom of the shearer body and the AFC base is an important design consideration as all coal cut on the tailgate side of the shearer has to pass under the shearer body on its way to the maingate. Any severe restriction at this point can cause problems, either causing coal to build up and spill over the AFC back plate or causing the AFC to jam. This is particularly the case where coal frequently comes off the face as large blocks or where roof stone has fallen on the AFC. In some instances a small coal breaker is fitted under the shearer at the low point to prevent blockages occurring.Powered SupportsHydraulic powered roof supports are self advancing structures which are interconnected along the length of the longwall face. Each unit along the line is also connected to each pan of the AFC.

The function of the powered supports are to:To control strata deformation, fracture and movement around the coal face,

To maintain a safe and coal producing working environment,

To limit the amount of roof to floor convergence,

To prevent broken rock from entering the work area, and

To secure and advance all plant on the coal face including the roof supports.

Each support structure consist of a roof canopy connected to a base via a shield and leminscate linkages. Side shields mounted to the canopy prevents excessive debris falling into the work space during support advancement. The hydraulic legs of a each type of support are inclined or splayed at an angle. This is to prevent the legs from buckling under the immense loads that they supportBeam Stage LoaderWhen the coal is transported by the AFC along the longwall face it reaches the beam stage loader at the end of the face. The beam stage loader is simply a chain conveyor that transport coal from the AFC to the main belt conveyor. Also incorporated into the beam stage loader is a small crusher to reduce the particle size of the coal for easier transportation. There are two discharge configurations for the beam stage loader

End discharge : This configuration allows the AFC to overlap the beam stage loader so that coal falls down onto it. This configuration is used for coal that is very slabby.

Side Discharge : Most modern design AFC utilises a side discharge arrangement to push the coal directly onto the beam stage loader. This design is most suited to coal with large lumps. This design can also transport a higher capacity of coal. Click to edit Master title style

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Engineering

Longwall machinery