Shield extension

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Shield extension
Individual shield extension

As a shield support one is hydraulic system to face support in underground coal mines referred. In longwall mining, the shield support supports the mining site against the pressure of the otherwise collapsing hanging wall and moves an integrated chain conveyor with a coal plow or shearer loader working on it in progressive mining through suitable coal seams .

history

Before the longwall mining was automated , punches weighing 40–80 kg were used, which were laboriously moved manually following the mining process. Today hydraulic expansion replaces physical labor, whereby in Germany in 1971 only 1%, but in 1975 80% of the coal was extracted with the aid of hydraulic shield expansion. This principle has been used exclusively since 1990.

Basics

Underground coal mining creates cavities that have to be supported against the hanging wall above to prevent break-ins. The shield extension serves the protection and safety of miners and conveyor systems. Due to its construction, a complete shielding of the face area from the hanging wall, the lying and the fracture area is achieved. At the same time, the shield extension enables a stamp-free dismantling front, like all step-on extensions . This enables mining machines to be used in longwall mining. Removing a shield for a longwall costs several million euros, depending on the design, and is up to ten times more expensive than expanding with individual stamps. However, with the shield support, high face rates and high construction speeds can be achieved. The world's leading suppliers of shield support technology are Caterpillar and Joy Global .

construction

Hydraulic shields with a shearer loader on a chain conveyor
Shields with coal plow and chain conveyor

The shield support consists of hydraulically operated shields, i.e. hydraulically adjustable support and protection devices, on skids, the upper part of which is closed like a shield and supports the hanging wall. A typical sign is around 1.5 meters wide, weighs between 30 and 60 tons and can be adjusted in height between 0.65 and 4 meters. Thicker seams require larger types of shields that can be raised further. So that the shield can be moved, it has a walking mechanism and a lifting cylinder which lifts the tip of the runner. This walking gear is connected to the faceplate and pulls forward with the help of the walking gear cylinder. So that the gap between shields can be sealed, each shield has a gap cover, this is a hydraulically operated sheet metal. The cap in the area of ​​the working face is matched to the respective type of extraction. The design of the shield cap is decisive here. Shields with sliding caps are used for peeling extraction using a coal plow. In the case of cutting extraction using a shearer loader, shields with hinged caps are used.

Several shields in a row follow the mining machine and thus secure the exposed space. The length of a so-called shield pillar can be between 250 and 400 meters , depending on the length of the face . It is controlled hydraulically, electrohydraulically or electrically. While the mining machines mine the coal layer by layer in front of the shields, the shields advance automatically. Just as the mining conditions vary in hard coal mining, the shield support must also be adapted to the respective conditions in order to achieve maximum performance of the plant. The spectrum of shield support controls ranges from manual hydraulic controls to highly developed face automation, monitoring and remote diagnosis. Optimally coordinated electro-hydraulic control systems achieve minimal repositioning and return times.

function

The face conveyor is used as an abutment to move the shields , with the shields individually lowering and pulling towards the chain conveyor, only to then lock themselves back to the ceiling after a step forward . Pressures of up to 400 bar are required for the setting process . The shields introduce a weight of 850 tons into the rock. As soon as an appropriate group of shields has carried out this operation, the chain conveyor is pushed against the coal face and the next coal layer can be mined. Behind the shields the mountains give way and collapse in a controlled manner. The process is repeated until the seam is broken down.

Advantages over other longwall mining

The shield extension has been continuously developed since its introduction. Among other things, the support force was increased and the hydraulics improved. The protection against breakage has also been optimized by means of appropriate shield caps and dust control on the shield support has been improved. The advantages of shield support over other types of longwall construction are first and foremost the very good control of overhangs and fractures . This is particularly noticeable with used hanging walls. Further advantages are the low need for repairs and the simple construction of the shield support. This also has an advantage over the other types of expansion when installing and robbing the shield extension.

Types

Shield extension with two hydraulic rams

Over the years several different types of shield support have been developed and used. For the longwall area, the following types were developed: the circular arc shield extension, the lemniscata shield extension, the articulated shield extension and the bracket shield extension. The circular arc shield extension represents the first stage of development in the shield extension. As a special design feature of this shield extension type, the horizontal runner and the breakage shield are connected by a fixed hinge point. Due to this design, the tip of the hanging shield describes an arc of a circle when the punch is inserted through load absorption and when the thickness changes. There are circular arc shield extensions with and without conveyor support frames. The circular arc shield extension was largely replaced by the lemniscate shield extension developed from it. With this type of shield, a movable double rocker is mounted between the horizontal runner and the breakage shield. As a result, when the stamp is loaded by the tip of the hanging shield, an almost bench-like movement is carried out on part of an imaginary lemniscate. There are two types: Lemniskatenschildausbau with diving cap and Lemniskatenschildausbau with hinged cap. The fixed shield extension is a shield extension with four hydraulic rams. All four punches direct their supporting force into the hanging wall. There are special face shields for the face burn area. These shields are designed in such a way that they allow embankments to be installed.

Individual evidence

  1. ↑ a b c d e f g Heinz M. Hiersig (Ed.): VDI-Lexikon Maschinenbau . VDI, Düsseldorf 1995, ISBN 3-540-62133-4 .
  2. ^ A b Hermann Irresberger: The hydraulic shield extension . In: Peter Frieß, Peter M. Steiner (Ed.): Raw material security . 1995, p. 414 ( deutsches-museum.de [PDF; 2.3 MB ; accessed on December 8, 2013]).
  3. ↑ Ernst-Ulrich Reuther: Introduction to mining . 1st edition. Glückauf, Essen 1982, ISBN 3-7739-0390-1 .
  4. ↑ Horst Roschlau, Wolfram Heinze, SDAG Wismut (Hrsg.): Knowledge storage mining technology. 1st edition. German publishing house for basic industry, Leipzig 1974, p. 89.
  5. ^ A b c d e f g Heinrich Otto Buja: Engineering handbook mining technology, deposits and extraction technology. 1st edition, Beuth Verlag GmbH Berlin-Vienna-Zurich, Berlin 2013, ISBN 978-3-410-22618-5 , pp. 337–339.
  6. ^ A b c d e Heinz Kundel: coal production . 6th edition. Glückauf, Essen 1983, ISBN 3-7739-0389-8 .
  7. ↑ a b P. Migenda, F. Gräwe, B.-W. Ratz: Shield extension, simpler, lighter, more effective. In: Commission of the European Communities (Ed.): Technical research coal. Contract No. 7220-AC-114 Final Report. Luxembourg 1986.
  8. ↑ P. Migenda, F. Graewe, B.-W. Ratz: Striding extension for longwall and striving in great depth. In: Commission of the European Communities (Ed.): Technical research coal. Research project No. 7220-AD / 133 final report. Luxembourg 1990.
  9. ^ A b c Walter Bischoff , Heinz Bramann, Westfälische Berggewerkschaftskasse Bochum: Das kleine Bergbaulexikon 7th edition, Verlag Glückauf GmbH, Essen 1988, ISBN 3-7739-0501-7 .

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