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What it's like to go down a modern mechanised mine. No two mines are exactly alike - but what they all have is a high degree of mechanisation.

The most important consideration is that of safety. So first, pick up your personal protective equipment before going underground. This includes your helmet, ear defenders, kneepads, gloves, safety glasses, battery lamp and self rescuer - a device you are most unlikely to need but must be carried and would allow you to breathe if there was a fire causing carbon monoxide in the mine air. Swipe your pass card at the shaft side safety barriers, so that the safety department knows you are going underground. Before entering the cage to descend into the mine, you will be searched for 'contraband' (cigarettes, matches or aluminium foil), as these items are not allowed underground. Into the two-deck cage, and descend down the mineshaft, very quickly to the pit bottom.

At the pit bottom, up to 1,000 metres below the surface, you board a diesel or, battery powered locomotive train, which will take you to the outbye end of the coalface district. You may have to walk or ride on a conveyor belt to a point nearby to the actual coalface.

At the coalface itself, notice the bank of powered roof supports, the armoured face conveyor, and the coal-cutting machine. These are the three main components that make up a coalface.

The coal-cutting machine 'the power loader' comprises a main machine body, which houses the electrical switchgear, traction units and hydraulic pumps. At each end of the machine there is a ranging arm, each fitted with a vaned drum with steel picks. These drums rotate at between 30 to 40 rev/min and cut the coal out of the coalface. The power loader is mounted on the armoured face conveyor and moves backwards and forwards along this conveyor cutting the coal from the coalface and loading it onto the conveyor. Once the coal has been loaded onto the armoured face conveyor, the twin chains fitted with scraper bars, which run inside the conveyor, carry the coal along the coalface, discharging the coal onto the 'stage loader'.

As the power loader reaches one end of the 250-metre coalface. The conveyor and powered roof supports are individually 'advanced' forward ready for the power loader to make another cutting run along the coalface.

Time for us to leave the coalface and follow the coal. As already described, the coal is delivered from the armoured face conveyor onto a much shorter armoured conveyor called the 'stage loader', which delivers the coal onto a belt conveyor, which takes the coal away from the coal production district, and along several other belt conveyors to the pit bottom.

On its journey to the pit bottom, dust is kept to a minimum by the use of water sprays. The coal from our coalface, and other districts under development at the mine, is transported by conveyor belt to the pit bottom. The coal is loaded into bunkers, with a capacity of 600 to 900 tonnes. The coal is then discharged from the bunkers into coal winding skips, which carry payloads of up to 22.5 tonnes of coal, and are raised though the mine shaft from the pit bottom to the surface of the mine.

Drivages

To be able to cut the coal from a coalface, roadway's firstly have to be driven through the strata to 'block out' a parcel of coal. This parcel of coal some 1,000 - 2,000 metres in length, and 250 - 300 metres in width, becomes, the next coalface to enter into production.

The machines used to cut these roadways are called drivage machines. There are two types of drivage machines normally employed in roadway developments.

The first type is a 'Boom' type machine which has a rotating head fitted with picks at the end of a boom. The boom is positioned by means of hydraulic cylinders, up or down, left or right, to cut out the profile required for the roadway. This type of machine is usually used to drive the arched roadways, used as the main colliery roadways and transportation routes.

The second type of machine is a 'Continuous Miner'; this has an elongated cutting drum, the same width as the machine, and is pivoted at the opposite end on a support arm. The support arm is raised up or down by means of hydraulic cylinders, and cuts out a rectangular shaped profile, which is normally supported by roofbolting. This type of machine is usually employed to undertake the coalface development drivages.

Mining transformed

What you see on your underground visit is the result of mining's own Industrial Revolution of recent years, which continues with the extension of remote and automatic controls.

In 1947 the average output for each man employed in the coal industry was little over 1 tonne each shift. Today the figure is more than ten times as much. Mechanisation has made a great difference.

Look at the mining methods of a few years ago. To get the coal, miners used explosives, picks and shovels and wooden pit props were used. The explosives broke open the coalface, the pick and shovel hacked the coal out and loaded it on a crude mechanical conveyor and the props kept the roof and walls from collapsing.

Compare with today's method. Instead of large groups of miners, now one or two miners operate machines like the power loader, which cuts a clean, geometrical coalface and loads the coal it has cut onto the armoured face conveyor. This can articulate forward into the newly exposed area behind the power loader with no pause in the flow of coal.

And the pit props? Now there is a line of self-advancing powered roof supports in the modern mine. They consist of banks of steel beams carried on hydraulic legs, which are electronically operated and work at hydraulic pressures of upto 340 bar. The powered roof supports in turn are attached to the armoured face conveyor by hydraulic rams. The coalface is cut by the power loader, which moves along the armoured face conveyor and the powered roof supports 'advance', automatically adjusting themselves to the correct height and the load they must bear to support the newly exposed roof. This provides an envelope of steel to protect men and machines.

To experience what it looks like on a coalface please click here to view a short video clip of a coalface in operation (.mpeg, 2.81Mb)

Push button mining

Today's control systems have been integrated, by incorporating the position of the power loader on the coalface, into the powered roof support control computer system. This enables the automatic operation of the power roof supports determined by the position of the power loader, this is commonly known as 'Chock Initiation' ('Chock' being an alternative term for a powered roof support).

Further more recent developments that have taken place in underground coal mining are:

• 2 leg powered roof supports, which are electro-hydraulically controlled.
• Power roof support high-pressure hydraulic pumping systems.
• Radio control of power loaders.
• Power loader on board health monitoring / diagnostic packages.
• Data transmission of coalface information to the colliery surface offices.
• Electrical variable speed drive systems for armoured face conveyors and belt conveyors.

All these developments are gradually being integrated into the coalface engineering package, to give safer, higher but more consistent output from the coalface.

Remote control, automation and monitoring, are widely throughout the mine, with all information about a mine at work, being fed into the computer network system, and can be monitored at the control room on the surface, and also the relevant engineering departments and managers. Mining engineers call this system 'MINOS' - short for Mine Operating System. These systems, which improve efficiency and safety, already control transport systems and monitor temperature, mine gas concentrations and ventilation underground. Similar systems are also being deployed to monitor, and in time, to control mining operations at the coalface.

In addition other computer packages such as 'JDE' are used for stores ordering and planned maintenance systems, 'COMPASS' for time and wages management.