Full Scale Linear Cutting Test
Linear cutting tests provide a direct measure of rock cuttability under simulated field conditions. The LCM measures the forces acting on an individual cutter while cutting actual rock. Data from this test provides input for performance prediction, machine specification, cutterhead balancing and optimization for cutting geometry. These full-scale tests eliminate the uncertainties of the rock, which may not be identified by physical property testing.
The normal force recorded by the LCM is used to calculate necessary effective mass and thrust required of the machine. This is important to ensure that the machine is able to provide the necessary thrust, so the cutters can effectively penetrate the rock. The rolling/drag force is directly related to the torque requirement of an excavator, and is used to calculate the specific energy requirement. Specific energy is defined as the amount of energy required to excavate a unit volume of rock. Using the specific energy (hp-hr/yd3), achievable production rates are calculated for a machine with a known horsepower available on the cutterhead. Lower specific energy means that a given machine will produce more material, or that a smaller/less expensive machine may be used to produce the required amount of material. The side force may be used along with normal force and rolling force to balance the cutterhead design.
The LCM features a large stiff reaction frame on which the cutter is mounted. A triaxial load cell, between the cutter and the frame, monitors forces and a linear variable displacement transducer (LVDT) monitors travel of the rock sample. The rock sample is cast in concrete within a heavy steel box to provide the necessary confinement during testing. A servo controlled hydraulic actuator forces the sample through the cutter at a preset depth of penetration, width of spacing and constant velocity. During the cut, the triaxial load cell measures the normal, rolling, and side forces acting on the cutter. After each cut the rock box is moved sideways by a preset spacing to duplicate the action of the multiple cutters on a mechanical excavator.
In field excavation, the individual cutters on the machine always operate on a rock surface damaged from the previous cutting action. This condition is duplicated in the laboratory by thoroughly conditioning the rock surface before testing began. This is accomplished by making several passes of cuts before data is collected.
LCM test equipment can be used to test different type of cutters and bits as shown in the following photos.