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There are various forms of clearance at the connection of various parts of the hydraulic support. However, the influence of clearance has been ignored in various related research studies of the hydraulic support. In order to clearly grasp the accurate impact contact response law between coal gangue and the hydraulic support, the radial clearance in the pin shaft connection structure of the tail beam is considered for the first time in this paper. By constructing the theoretical contact model of the pin shaft connection, the difficulty of studying the interaction between coal gangue and the hydraulic support through theoretical solution is proved. On this basis, the finite element contact simulation analysis method is proposed to study the impact contact behavior between coal gangue and the tail beam. This paper constructed the finite element impacting simulation model between coal gangue and the radial clearance-contained tail beam structure and carried out impact contact simulation between coal gangue and the multiple clearance-contained tail beam structure as well as the changing clearance-contained tail beam structure, respectively, and contact responses of the tail beam structure such as the spring stress, the pin shaft test point stress, acceleration, and velocity of the tail beam test point under different working conditions are obtained. The influence law of clearance on different contact responses is studied, and the differences of contact responses after coal gangue impact between two clearance-contained tail beam structures and three clearance-contained tail beam structures are compared and analyzed. Research results show that, in the condition of multiclearance, the amplitude of each contact response when gangue is impacted is greater than that of coal. When the radial clearance of the connection unit increases from 0 to 0.25 mm, the overall fluctuation amplitude of the contact responses decreases. In 3-clearance state, increase of the radial clearance size of the connection unit will lead to the increase of the spring stress, the stress of the pin shaft test point, and the velocity of the tail beam test point gradually and the decrease of the acceleration of the tail beam test point. Throughout the research, the vibration response of the pin shaft can be taken as coal gangue recognition parameter. The work provides a theoretical basis for the study of the influence law of clearance on hydraulic support and provides a reference for the study of contact behavior between coal gangue and the hydraulic support. [ABSTRACT FROM AUTHOR]

The new method of rock breaking based on the combination of circular sawblade and conical pick was proposed to improve the effectiveness of hard rock breaking. The numerical simulation method was applied to research the conical pick cutting arc rock plate by ANSYS/LS-DYNA. The conical pick cutting arc rock plate numerical simulation model was established to research the influence of arc rock plate structural parameters and cutting parameters on cracks formation and propagation of the arc rock plate and the cutting force in the process of conical pick cutting arc rock plate. The amount of cracks is positively correlated with arc rock plate thickness, the cutting speed, and distance of cutting point to arc rock plate central axis and negatively correlated with the cutting angle. The mean peak cutting force is positively correlated with the thickness of arc rock plate and the distance of cutting point to arc rock plate central axis; however, it is negatively correlated with the arc rock plate height and width and cutting angle of conical pick. The simulation results can be used to predict the conical pick work performance with various cutting parameters and structural parameters. [ABSTRACT FROM AUTHOR]

Conical pick wear is an urgent problem in the roadway excavation caused by hard rock difficult to break. The traditional method of increasing cutting power to improve cutting performance of conical pick significantly increases pick wear. In the paper, a saw blade and conical pick combined cutting method is proposed based on increased free surface. To research the fracture morphology and cutting force of rock plate, theoretical, numerical, and experimental methods are used. By theoretical research, the bending mechanical model of rock plate bending is established. The cutting position and the junction between the free sides and fixed sides are preferentially broken. A numerical model combining the erosion and damage constitutive model is built, and the cutting process of rock plate was presented. According to rock plate experiment, the peak cutting force increases with the increasing uniaxial compressive strength, thickness of rock plate, and cutting depth of conical pick and decreases with the increasing width and height of rock plate. Exponential relationships exist between peak cutting force and thickness, width and height of rock plate, and cutting depth of conical pick. Linear relationship exists between peak cutting force and uniaxial compressive strength. The size of rock fragments increases with uniaxial compressive strength, width, and height of rock plate. [ABSTRACT FROM AUTHOR]

Conical pick is a rock cutting tool that is commonly used in roadway driving. Pick wear frequently happens in the course of breaking hard rock. The current paper shows a new method to solve the problem of pick wear. The rock is preslit with the saw blade and then broken by the conical pick. In order to study the cutting force and features of rock fragment, the numerical model is built between rock plate and conical pick. And element erosion is added in the code to obtain the fracture result. The rock plate cutting testbed is made to testify the correctness of numerical simulation. The width, height, and thickness of the rock plate, as well as cutting angle and cutting position, which influence cutting force and rock fracture are studied. According to the results, there exist exponential relationships between cutting force and width and thickness of rock plate. In addition, a linear relationship is found between the cutting force and the height of rock plate. Furthermore, both the cutting angle and cutting depth have an influence on cutting force. In particular, the factors of thickness and height or rock plate have the most obvious influence on cutting force. It is proven that what is beneficial to rock fracture is higher height and lower thickness of rock plate. [ABSTRACT FROM AUTHOR]

There are some issues that should be solved like load shock, vibration, and uneven load distribution during transmission of involute spur gears. However, common modification methods such as axial modification as well as profile modification could not solve these problems once for all. Hence, a novel method of comprehensive modification was proposed, and the evaluation methodology of transmission performance was drawn up too. Changing modification parameters can control transmission performance of gear unit, which can generate many different modification ways. Besides, based on the orthogonal experiment method and evaluation methodology, optimal modification ways can be chosen for gear pairs working in different conditions. Taking a set of spur gear pair as an example, an ideal modification way was obtained. In addition, analysis results verified that conducting comprehensive modification could enhance the meshing performance once for all. [ABSTRACT FROM AUTHOR]

In order to overcome conical pick wear in the traditional rock cutting method, a new cutting method was proposed on account of increasing free surface of the rock. The mechanical model of rock plate bending under concentrated force was established, and the first fracture position was given. The comparison between experimental and numerical results indicated that the numerical method is effective. A computer code LS-DYNA (3D) was employed to study the cutting performance of a conical pick. To study the rock size influenced on the cutting performance, the numerical simulations with different thickness, width, and height of a rock plate was carried out. The numerical simulation with the different cutting parameters of cutting speed, cutting angle, and cutting position influenced on cutting performance was also carried out. The numerical results indicated that the peak force increased with the increasing thickness of rock plate. With the increasing width and height of the rock plate, the peak force decreased and then became stable. Besides, the peak force decreased with the increasing of cutting position lxp/lx. Moreover, the peak force increased and then decreased with the increasing of cutting angle. The cutting speed has nonsignificant influence on the peak force. The strong exponential relationship was obtained between the peak force and cutting position, thickness, height, and width of the rock plate at a confidence level of 0.95. A binomial relationship was observed between the peak force and cutting angel. The cutting force comparison between traditional rock cutting and rock plate cutting indicated that the new cutting method can effectively reduce peak cutting force. [ABSTRACT FROM AUTHOR]

To predict fragment separation during rock cutting, previous studies on rock cutting interactions using simulation approaches, experimental tests, and theoretical methods were considered in detail. This study used the numerical code LS-DYNA (3D) to numerically simulate fragment separation. In the simulations, a damage material model and erosion criteria were used for the base rock, and the conical pick was designated a rigid material. The conical pick moved at varying linear speeds to cut the fixed base rock. For a given linear speed of the conical pick, numerical studies were performed for various cutting depths and mechanical properties of rock. The numerical simulation results demonstrated that the cutting forces and sizes of the separated fragments increased significantly with increasing cutting depth, compressive strength, and elastic modulus of the base rock. A strong linear relationship was observed between the mean peak cutting forces obtained from the numerical, theoretical, and experimental studies with correlation coefficients of 0.698, 0.8111, 0.868, and 0.768. The simulation results also showed an exponential relationship between the specific energy and cutting depth and a linear relationship between the specific energy and compressive strength. Overall, LS-DYNA (3D) is effective and reliable for predicting the cutting performance of a conical pick. [ABSTRACT FROM AUTHOR]

Fused deposition modeling (FDM) has been one of the most widely used rapid prototyping (RP) technologies leading to the increase in market attention. Obviously it is desirable to print 3D objects; however, existing FDM printers are restricted to printing only monochrome objects because of the entry-level nozzle structure, and literature on the topic is also sparse. In this paper, the CAD model of the nozzle is established first by UG (Unigraphics NX) software to show the structure of fused deposition modeling 3D printer nozzle for color mixing. Second, the flow channel model of the nozzle is extracted and simplified. Then, the CAD and finite element model are established by UG and ICEM CFD software, respectively, to prepare for the simulation. The flow field is simulated by Fluent software. The nozzle’s suitable temperature at different extrusion speeds is obtained, and the reason for the blockage at the intersection of the heating block is revealed. Finally, test verification of the nozzle is performed, which can produce mixed-color artifacts stably. [ABSTRACT FROM AUTHOR]