## 3 Investigation of the Rock-Breaking Mechanism of Potash Ore with a Single Cutter  
The employees of the Department of Mechanical Engineering of the Saint Petersburg Mining University designed and manufactured a bench (Figure 2) in order to experimentally study the rock-breaking mechanism of a potash mass with a single cutter [16; 22]. The bench includes a base \(\delta\) on which a welded frame 4 is located (connected by welded seams and jibs). Hydraulic double-sided power cylinder 5 connected to a measuring hydraulic cylinder 3, where a cutter 11 is located, is rigidly fixed on the frame 4. The supply of an actuating fluid (I-20A oil) in the cavities of the hydraulic cylinder 5 is carried out by a pumping station 1. A pressure indicator is connected to the measuring hydraulic cylinder 3 to measure the cutting force \(P_{z}\) on the cutter 11. Three vertical guide rails 6, along which rollers 7 of the measuring hydraulic cylinder 3 can move, are provided in the design of the bench in order to ensure the rectilinear motion of the cutter 11. A potash ore block 10 is installed on the base \(\delta\) and fixed in a stationary position with clamps 2 and 9. The step and deepening of the cutting are set by moving the block 10 [16; 22]. The bench hydraulic system (Figure 3) consists of two gear-type pumps 3 and 16 driven by a three-phase asynchronous motor 1 through a gearbox 2. The actuating fluid is supplied from an oil tank 12 into the cavities of the power hydraulic cylinder 13, the rod of which is connected to the measuring hydraulic cylinder 14 and the cutter 15. The piston diameter of the measuring hydraulic cylinder is 40 mm. The direction of movement of the cutter is determined by switching a spool 11, and the speed of the translational motion is controlled by a flow regulator 9. Figure 2: Laboratory bench for potash ore cutting by cutting. Expansion of the range of feed rate of the cutter _15_ during the penetration into the destroyed block is possible through the operation of one or two gear-type pumps. The gear-type pump _16_ is controlled by a spool 7. A safety valve 4 is provided in order to protect the system from overloads. The pressure is controlled by a pressure gauge 5 connected to the pressure pipe through a spool 6. Moreover, there are reverse-flow valves \(8\) and filters _10_ for cleaning the actuating fluid in the hydraulic system. The general view of the bench is shown in Figure 4.  
A pressure indicator is connected to the cylinder _14_ (see Figure 3), where the pressure is proportional to the cutting force \(P_{z}\). The feed rate of the cutter _15_ is controlled by a displacement indicator--an encoder. The sampling rate of the indicators is 0.5 kHz. Data from the measuring indicators is recorded and converted by a multi-channel AD/DA encoder and processed on a personal computer by specialized software using well-known methods of mathematical statistics, correlation, and spectral analysis. The parameters of the samples taken for the experimental studies:  
* shape: cuboid with dimensions 300 \(\times\) 300 \(\times\) 600 mm;
* origin: Uralkali PJSC, Verkhnekamskoye deposit of potassium and magnesium salts, Krasny-II seam;
* cutting resistance \(A_{c}=400\dots\) 430 N/mm [23]. Figure 4: General view of the bench (**a**) and (**b**) the measuring hydraulic cylinder **14** with the cutter **15**, pressure and displacement indicators. Figure 3: Hydraulic system of the bench. The rock cutting tool is a cutter with a flat front face and a rectangular cutting edge. The width of the cutting edge is \(b_{c}=10\) mm, cutting angle is \(\alpha_{c}=50^{\circ}\), clearance angle is \(\beta_{c}=5^{\circ}\). The hydraulic drive of the cutter provides an average speed \(V_{c}=0.1\) m/s. Types of cuttings: from a leveled surface, staggered and cross. The ore separated from the block was collected using dust exhaustion, and then it was weighed and screened in order to determine the grain-size distribution. Large ore cleavages were selected manually.