A theoretical model for predicting the Peak Cutting Force of conical picks

In order to predict the PCF (Peak Cutting Force) of conical pick in rock cutting process, a theoretical model is established based on elastic fracture mechanics theory. The vertical fracture model of rock cutting fragment is also established based on the maximum tensile criterion. The relation between vertical fracture angle and associated parameters (cutting parameter  and ratio B of rock compressive strength to tensile strength) is obtained by numerical analysis method and polynomial regression method, and the correctness of rock vertical fracture model is verified through experiments. Linear regression coefficient between the PCF of prediction and experiments is 0.81, and significance level less than 0.05 shows that the model for predicting the PCF is correct and reliable. A comparative analysis between the PCF obtained from this model and Evans model reveals that the result of this prediction model is more reliable and accurate. The results of this work could provide some guidance for studying the rock cutting theory of conical pick and designing the cutting mechanism

Coupling vibration analysis of auger drilling system

In the process of drilling coal, the kinematics of drill-rod is quite complicated. The drill-rod not only vibrates in longitudinal, transverse and torsional direction, but also random impacts and contacts coal wall. Considering the drilling load of drill-bit and coal, contact impact of the drill-rod and coal wall, the drill-rods are dispersed into a number of finite elements. At the same time, the nonlinear dynamic model of drill-rod system coupling longitudinal, transverse and torsional vibration is set up. The simulations of the dynamic model are researched under the conditions of different hardness coal (2.7, 3.7, 4.65). In order to decrease the vibration of auger drill, the stabilizer is added onto the drilling mechanism. And the underground experiments are done at 2404 working face of Xie-Zhang Coal Mine in Shan-Dong Province of China. The results indicate that the transverse vibration radius, the longitudinal vibration frequency and amplitude all decrease with the rock hardness. The maximum transverse vibration radius shows an exponential relation with the drilling depth under the condition of the same rock. Under the same condition, the drilling depth of auger drill with stabilizer is 1.39 times that with no stabilizer, and the drilling pressure decreases about 2/3

Influence of drum motion parameters on shearer cutting properties

In order to study the influence of motionparameters of shearer drum on shearer cutting properties,an embedded system for cutting load test that can identify thecutting resistance indirectly were developed and put into test experimentunderground. The analysis results indicated that in the case of pullingspeed being constant, when pulling speed is small, the cuttingresistance nonlinearly declined and cutting specific energy consumption (CSEC)increases nonlinearly with the increase of the drum rotating speed; whenpulling speed is large, cutting resistance approximately linearly decreases andCSEC linearly increases with the increase of the drum rotating speed; in thecase of drum rotating speed being constant, the cutting resistance presentslinearly reducing form with pulling speed increasing its value in the range ofhigher speed and increases nonlinearly with pulling speed increasing its valuein the range of lower speed, and CSEC decreases nonlinearly with the increaseof the pulling speed. The consistency of the theoretical analysis and the testresults confirmed the reliability of the proposed embedded system whichprovides an effective way for the detection and analysis of mine shaft cuttingload and also provides the instruction for shearer speed-changing cutting coal. DOI : http://dx.doi.org/10.11591/telkomnika.v12i1.319

Improving the weak feature extraction by adaptive stochastic resonance in cascaded piecewise-linear system and its application in bearing fault detection

In mechanical engineering field, early fault features are extremely weak and submerged in heavy noise, and the weak feature extraction is quite challenging. In this work, we apply the adaptive stochastic resonance in cascaded piecewise-linear system to extract the weak features. The adaptive stochastic resonance is realized by the quantum particle swarm algorithm. By optimizing system parameters, the efficiency of the feature extraction is improved greatly. As a result, the weak features can be easily extracted eventually. The effectiveness and the high-performance of the proposed method are verified by the numerical simulation and experimental data of rolling element bearings. The bearing fault under different motor loads is detected effectively, consequently confirming the robustness of the proposed method

Interference model of conical pick in cutting process

The load on conical pick is affected by many factors such as pick geometry and installation angle. In order to decrease the wear and vibration of pick in the cutting process by choosing proper impact angle, the interference mathematical models of straight and revolving cutting were established according to coal cutting theory. Based on this, coal cutting experiment was carried out with different impact angles β, different head face radii of pick body R and different cutting depths d to verify the mathematical model. The results indicate that the picks cutting into coal with a certain installed angle are prone to interfere with coal in the cutting progress. There is a crsitical impact angle, and it is different under different cutting conditions. The critical impact angle decreases with the head face radius of pick body R and cutting depth d. On the condition of given pick geometry and movement parameters, the cutting force of picks or cutting torque of cutting header decreases with the impact angle. When the impact angle of the pick is larger than the critical angle, the load on pick will increase prominently

Fault diagnosis of pump valve spring based on improved singularity analysis

The fracture of pump valve springs is another typical fault of emulsion pump with high pressure and large discharge, which greatly influences the volumetric efficiency of emulsion pump. The fault diagnosis on pump valve springs of emulsion pump was analyzed based on the singularity analysis of continuous wavelet transform. The improved method for Lipschitz index was presented with better robustness and efficiency based on the Least Square Method. The criterion for the fracture of pump valve was confirmed. Diagnostic results indicate that it is accurate and effective of the improved method to locate the singularity of signals, identify the moment when the valve disc impacts on base or lift limiter and judge the fault diagnosis of pump valve

Nonlinear dynamic characteristics of load time series in rock cutting

The characteristics of the cutting load time series were investigated using chaos and fractal theories to study the information and dynamic characteristics of rock cutting. The following observations were made after analyzing the power spectrum, denoising phase reconstruction, correlation dimension and maximum Lyapunov exponent of the time series. A continuous broadband without a significant dominant frequency was found in the power spectrum. The restructured phase space presented a distinct strange attractor after wavelet denoising. The correlation dimension was saturated at an embedding dimension of 7. Lastly, and the maximum Lyapunov exponent exceeded 0 via the small data method. These findings reflected the chaotic dynamic characteristics of the cutting load time series. The box dimensions of the cutting load were further investigated under different conditions, and the difference in cutting depth, cutting velocity and assisted waterjet types were found to be ineffective in changing the fractal characteristic. As cutting depth become small, rock fragment size also decreased, whereas fractal dimension increased. Moreover, a certain range of cutting velocity increased fragment size but decreased fractal dimension. Therefore, fractal dimension could be regarded as an evaluation index to assess the extent of rock fragmentation. The rock-cutting mechanism remained unchanged under different assisted waterjet types. The waterjet front cutter impacts and damages rock, however, the waterjet behind of cutter is mainly used to clean fragments and to lubricate the cutter

Numerical simulation of rock fragmentation process by roadheader pick

A numerical model of rock fragmentation caused by a roadheader pick was established based on the particle flow code in two dimensions to study the rock fragmentation mechanism of the roadheader pick. The model simulated crack initiation, propagation and chip formation. The feasibility and reliability of the method as well as numerical model were verified by experiment. Results show that the rock fragmentation process includes three stages: crack initiation, crushing zone and radial crack formation, major tensile crack propagation and rock fragment formation. The crushing zone, number of radial cracks, specific energy consumption of rock cutting and dust level increase as the pick-tip corner radius increases. Consequently the pick-tip corner radius should range from 0 to 2 mm to obtain large rock fragments and low specific energy consumption. The damage of medium-hard and hard rock by the roadheader pick is more remarkable than that of soft rock. Furthermore, the sharp pick is suitable for the soft rock, whereas the pick tip with a proper rounding corner is perfect for the medium-hard and hard rock

Constraint optimization of shearer cutting path based on B-spline curve fitting and mayfly algorithm

In order to achieve the intelligent height adjustment control of the shearer, the key techniques are the coal-rock interface recognition, cutting path optimization, and shearer height adjustment control. Although the coal-rock interface is accurately identified, the shearer drum cannot completely follow the estimated coal-rock interface due to the flatness requirement for the roof and floor of the coal seam which guarantees the working of hydraulic supports. Therefore, the cutting trajectory should be optimized based on the coal-rock interface recognition results, which is regarded as the target trajectory of shearer height-adjusting control. To solve this issue, the cutting path optimization is required. Based on the estimated coal-rock interface and considering the limitations in practical application, the cutting path is optimized to maximize the recovery ratio. To improve the optimization results, satisfy the restricting condition, and reduce the computational complexities, this paper proposed a novel constraint optimization method of shearer cutting path based on the mayfly algorithm and B-spline curve fitting. A novel objective function is built, in which the curve node coefficients are chosen as the design variants, and the optimization target is minimizing the difference between the fitness curve and the coal-rock interface, leading to the much less designed variants and the lower computational load. The piecewise penalty function is used to deal with the constraints, which assists the exploration process in escaping from local maxima and make sure the constraints work. And then the modified mayfly algorithm is used to find the optimized cutting path to further improve the optimization effect and the convergence rate. Finally, the simulations of cutting path optimization are conducted under the condition of folds, subsidence and faults, which indicate that the proposed method can obtain the optimized smooth cutting path with the limitation of the constraints quickly, and have high real-time behavior, and good applicability