Method to determine installing angle of conical point attack pick

In order to obtain the determining method of the installing angle and decrease the performance indices (cutting force and wearing rate) of the pick, the relationships among the installing angles (impact angle, inclination angle and the skew angle) were studied, and the static model of installing angles of the pick was built. The relationships among the impact angle, the tip angle of pick and the kinematics parameters of the pick were built, too. Moreover, the mechanic models of the maximum clearance angle and the wearing angle of the pick were set up. To research the relationships of the installing angles and the change law of the wearing angle along with the kinematics parameters, the simulation was done. In order to verify the correctness of the models, the cutting experiments were done by employing two picks with different pick tip angles. The results indicate that, the cutting force is the smallest when the direction of the resultant force of pick follows its axis, and the relationship derived among the installing angles should be satisfied. In addition, to decrease the cutting force and the wearing of the pick, the tip angle of pick should not be larger than the half of the difference between the minimum wearing angle and the impact angle of the pick, and the clearance angle must not be less than zero.

Numerical Simulation of Axial Inflow Characteristics and Aerodynamic Noise in a Large-Scale Adjustable-Blade Fan

Numerical simulation are conducted to explore the characteristics of the axial inflow and related aerodynamic noise for a large-scale adjustable fan with the installation angle changing from−12°to 12°.In such a range the maximum static(gauge)pressure at the inlet changes from−2280 Pa to 382 Pa,and the minimum static pressure decreases from−3389 Pa to−8000 Pa.As for the axial intermediate flow surface,one low pressure zone is located at the junction of the suction surface and the hub,another is located at the suction surface close to the casing position.At the outlet boundary,the low pressure is negative and decreases from−1716 Pa to−4589 Pa.The sound pressure level of the inlet and outlet noise tends to increase monotonously by 11.6 dB and 7.3 dB,respectively.The acoustic energy of discrete noise is always higher than that of broadband noise regardless of whether the inlet or outlet flow surfaces are considered.The acoustic energy ratio of discrete noise at the inlet tends to increase from 0.78 to 0.93,while at the outlet it first decreases from 0.79 to 0.73 and then increases to 0.84.

Load Characteristics and Optimal Layout of Center and Gage Cutters of Rock Formation Compound Tunnel Boring Machine

The cutter layout of a full-face tunnel boring machine(TBM)directly affects its tunneling efficiency.The revolving diameter of the center cutter is small,and the double-edged design results in its rock breaking mechanism and force characteristics being significantly different from those of the single-edged cutter.The gage cutter is installed on the transition arc of the cutterhead,and the installation inclination complicates its movement and force.In this paper,by taking sandstone as the research object,the composite rock breaking models of the center cutter group and the gage cutter group of a compound TBM are separately established based on the three-dimensional particle discrete element method.The numerical models are verified by comparing results with the full-scale rotary cutting laboratory test.From the view point of the force characteristics of a single cutter,the propagation of rock cracks between adjacent cutters,the overall mechanical properties of the cutterhead,the load characteristics and layout form of the double-edged center cutter,and the installation angle range of the gage cutter were studied.Results demonstrate that the use of a cross-shaped center cutter layout can reduce the force of a single cutter ring and the overall load of the cutterhead,which is conducive to TBM stability during tunneling.Therefore,it is recommended that a cross-shaped layout for the double-edged center cutter of a rock formation compound TBM should be used.To improve the stability and service life of the cutter,we recommend setting the installation angle of the innermost gage cutter of the rock formation compound TBM to about 9°,and the installation angle of the outermost gage cutter should not exceed 70°.