Published in the August 2006 American Longwall Magazine
Many decades after the longwall method was first applied to underground coal mining, the shearer and the automated plow system are the prevailing cutting and loading machines today.
The objective is to extract coal with a seam thickness from as little as 23.5 inches to as high as 19.7 feet as productively, efficiently and safely as possible while minimizing the amount of rock extracted for any given seam height. Operators use both DBT’s powerful shearers and automated plow systems for many years and experiences on both technologies can be shared.
The DBT shearer
The DBT Electra range of high-powered shearers comprises a solid mainframe that encapsulates the major units of the shearer and absorbs all cutting and haulage forces.
AC haulage with frequency controlled drives is standard on all new DBT shearers, with typical cutting speeds ranging from 10 meters per minute to 30m/min as standard and the ability to operate at 60m/min in applications such as half-web cutting. The actual web depth is determined by the armored face conveyor push over and varies from 0.8m to 1.2m. Installed cutting power is an essential element of any shearer performance.
The EL3000 shearer, designed to operate in medium and thick-seam applications, has an installed cutting power of up to 2 x 850kW at 50Hz (2 x 900 kW at 60Hz). The EL2000 shearer with a machine body height of 480mm is designed to operate in medium-high seams and is equipped with cutting power of up to 2 x 500kW at 50Hz (2 x 600kW at 60Hz). A new powerful model with a cutting power of up to 2 x 750kW (machine body height 540mm) is now available. The maximum haulage power is currently up to 2 x 125kW.
DBT has made significant advances of late in shearers. Currently an operator typically travels through the longwall face with the shearer, however, with the application of the automated systems the operator’s role is changing to that of an observer rather than a hands-on operator. Further developments by DBT in the field of shearer automation will increasingly eliminate the role of the shearer operator as defined today.
The Automated DBT Plow System
Today’s modern, automated plow system is a totally different animal than the manually operated plows used around the world until the late 1980’s. Whilst the early plows enjoyed quite some success, today they would be deemed uneconomic due to a number of inherent operational weaknesses associated with the manual operation. The need for personnel to be on the face working in extremely restricted and confined conditions limited the potential of the plow. In addition, the limited level of installed horsepower did not allow for the effective cutting of hard coal or rock.
However, the introduction of incremental plowing in the late 1980’s facilitated automation of plow movement, face conveyor push and shield advance without operators being required on the face. This system quickly became widely used in Germany and on two longwall installations in the USA.
With the introduction of DBT’s PM4 electronic shield control system, the reliability of this system resulted in very high availability from plow installations. The increase in installed horsepower implemented during the 1990’s has resulted in the successful application for plows even when cutting very hard coal or rock. This improved performance lead to a renewed demand for the DBT integrated automated plow systems from markets around the world.
The plow uses a “scraping” type method of applying the cutting force to the coal face and deflects the cut coal towards the conveyor by employing the “snow plow” effect.
It is attached to an endless chain with its overload protection drives situated at each end of the longwall face. The plow body itself is a simple piece of high-strength steel pulled over a steel plow guide normally located at the face side of the AFC with high speeds of up to 3.6m/s.
The cutting depth is achieved by pushing the face conveyor towards the coal face in accurately controlled increments that are preset into DBT’s PM4, or the PMC-R series shield control units. It is dependent on the installed power of the plow system and the prevailing coal or rock hardness and typically ranges from 50-150mm.
The shields advance automatically to maintain optimum roof support throughout the face. The overall face alignment is automatically controlled from a central computer located in the head gate entry or on the surface; operators are removed from the operating face environment.
DBT currently offers the “Reisshakenhobel” or base plate plow (max. 2 x 400kW cutting power) with a gob-side chain for very thin seams from 0.6-1.6m height and the more common Gleithobel plow GH 38 (2 x 400kW cutting power) with a face-side chain for thin and medium high seams from 0.9-2.2m. In 2003, DBT introduced the new Gleithobel plow system GH 42 with 2 x 800kW cutting power designed to provide vastly increased productivity in hard coal cutting conditions and with the ability to negotiate faulted conditions without any need for drilling and blasting.
The GH 42 plow (cutting range 1-2.5m) was put to the test operating in very arduous cutting conditions on its maiden panel and performed beyond expectations already resulting in a number of repeat orders. In some applications, the installation of a single 800kW head gate drive will allow for the elimination of the tailgate drive and the associated requirement to cut into the tailgate.
Cutting and loading: Shearer versus Plow
Installed cutting power is a critical element in the design of high-performance mining equipment. In low height shearer applications, this factor becomes increasingly critical as the physical size of cutter motors can obstruct and limit coal clearance capability.
The EL2000 shearer can be provided with a machine body (mainframe) thickness of 480mm with smooth contours to maximize coal clearance capability. This model has a realistic minimum cutting height of 1.6m; while the bigger model with a body height of 540mm may be used in seam heights above 1.9m. A balance of shearer height to the top of the mainframe combined with cutting speed and cutting drum diameter can maximize the productivity from any given application where under-machine clearance becomes a critical factor.
In low-seam applications, cutting drum design and...click here to read on.
