Coal and rock excavation is typically carried out using an array of picks deployed at intervals on a continuous miner or a shearer having a rotating cutting drum. The picks cut the coal face as they come into contact with it during rotation of the drum.
Most currently available picks have a conical tool shape with a pointed tool tip. Conical picks do not actually cut, but rather crush the coal face, resulting in low coarseness of the product and the generation of a large amount of airborne dust particles. In fact, the resultant action generates dust and small fragments (fines) which require the use of continuous water sprays to meet Occupational Health and Safety conditions. These fine dust particles are a common health hazard to underground miners. As the particle size may fall into the carcinogenic and/or respiratory hazard ranges, miners subject to prolonged exposure can become susceptible to lung cancer, chronic bronchitis and pneumoconiosis. The large volumes of dust generated can also have an adverse effect on equipment reliability, resulting in increased equipment maintenance costs.
The conical picks are only loosely held in their respective holders so they are free to rotate about their longitudinal axis. Studies showed that these picks do indeed fail after locking up in their holders due to fine dust generation and therefore rotation was prevented. This action splinters the coal and rock, generating fines and frictional ignition.
Australian Patent Application No. 2672/97 published on 4 Sep. 1997, which is incorporated herein by reference, discloses a coal and rock cutting pick of chiseled shaped comprising a straight cutting edge which delimits substantially planar front and bottom faces of the cutting pick, the plane of the bottom face being inclined at an acute back clearance angle to a cutting plane and the front face being inclined at an acute front rake angle to an axis perpendicular to the cutting plane such that the front bottom faces define an acute angle at the cutting edge. However, the picks disclosed in this document are mounted to the drum with the shank of the pick extending radially from the drum. This causes the pick to be subject to large shear forces as the pick contacts the cutting surface. The pick also includes a rotating cutting head.
The above statements regarding prior discloses are not to be taken to be admissions of what was well known in the field of coal mining