Research Article  Open Access
Vibration and Deflection Behavior of a Coal Auger Working Mechanism
Abstract
Because coal auger working mechanism faces problems such as excessive vibration, serious deflection, and low drilling efficiency, a new fivebit coal auger working mechanism test model was established to explore the influence factor on vibration and deflection under different conditions. Additionally, a simulation model was built to further research the effect of partial load and stabilizer arrangement, the correctness of which was proved by experiments. The results show that the vibration and deflection increase with drilling depth in the direction, and they first increase and then gradually become stable in the direction. In addition, the vibration, deflection, and deflection force increase with the partial load. By arranging the stabilizer every five drillrod section intervals, the vibration and deflection can be decreased by 30% and 40% in the direction and by 14.3% and 65.7% in direction, respectively.
1. Introduction
The coal auger is a new type of thin seam mining equipment that has good prospects in unmanned and nonsupported coalface mining. Recently, a new type of coal auger working mechanism with five bits was used to improve coal mining efficiency [1, 2]. The fivebit coal auger is shown in Figure 1. Due to the constraint reaction force of coal wall, gravity, cutting resistance, and friction, the vibration of the working mechanism is relatively excessive, which can cause serious drilling deflection [3]. To solve this issue, simulations and experimental research were conducted to study the vibration and deflection behavior of the working mechanism. Meanwhile, a new stabilizer was deployed to reduce the vibration and deflection.
(a)
(b)
The working mechanism of coal auger consists of a drillrod and a venttube. As an important component of the working mechanism, the deflection and vibration characteristics of various shapes of drillrods were studied. A threedimensional dynamic model of drillrod was built for studying the influence of drilling pressure, torque, rotating speed, and other parameters of the drilling process, which indicated that the intermittent contact, dynamic torque, and friction have an important influence on the vibration characteristics [4–7]. Considering the gyroscopic effect, the torsional/bending inertia coupling, and the effect of the gravitational force field, a dynamic model of the drillrod including the drill collars was established [8–10]. The transient dynamic model between the drill string and the wall was established for analyzing the interaction among bits, stabilizer, and borehole walls [11]. In the same year, through analyzing the contact model between the drilling mechanism and the borehole walls, the contact model was divided into continuous contact and continuous collisions. The main reason for the drilling deflection was the increase of the borehole diameter [12]. By analyzing vibration characteristics of the drillrod under different nonNewtonian flow velocities and densities, a piecewise smooth model with three degrees of freedom, which exhibits frictioninduced stickslip oscillations, was considered, which can be used to describe the bitsticking phenomena [13, 14]. The drillrod vibrations with differential quadrature method were analyzed, which indicated the method was efficient and accurate in dealing with the drillrod vibration problems [15]. To analyze the dynamic stability, critical length, and the vibration characteristics with different boundary conditions and sizes, some relevant measures such as perturbation techniques and extended Lagrange multiplier method were adopted to reduce the drillrod vibration [16–19]. Considering the collision conditions of the drillrod and rock, the interacted system coupling dynamics model of multidrilling mechanism and rock was built, and vibration was acquired under different compression strength rocks and different rotary speeds of drill [20]. A nonlinear model of axial and torsional coupled vibration of the rotary drillrod was established. It suggests that adjusting the processing parameter properly contributes to reduce the drillrod stickslip vibration and bit bouncing [21]. The stress distribution of the drillrod worked in soft coal seam was simulated, which shows that the drillrod joint causes stress concentration [22].
Influence of different boundary conditions, drilling parameters, and drilling load conditions on the working mechanism vibration has been studied in the above articles. However, the vibration characteristics and the deflection behavior of fivebit coal auger under different conditions have not been studied. This restricts the effective vibration and deflection prediction and impedes the application of coal auger. Based on this, a rigidflexible coupling simulation model of a fivebit working mechanism was established in this paper. Vibration and deflection behavior of the working mechanism under different drilling depths, partial loads, and stabilizer arrangements were studied both by simulation and by experiments to determine the deviation law of the working mechanism. This can provide a reference for controlling the deflection and vibration of the working mechanism effectively.
The deflection and vibration along the vertical direction of the coal wall cross are very small compared with the deflection and vibration in other directions based on many field experiments. This difference is because the stiffness of the working mechanism along the drilling direction is significantly larger than that in other directions. This paper primarily focuses on researching the deflection and vibration characteristics of the coal auger working mechanism and present effective control measures for directional drilling, where the deflection and vibration along the drilling direction have little influence. Based on the above analysis, this paper does not focus much research on the deflection and vibration along the vertical direction.
2. Experiment Study
2.1. Experiment Method
The fivedrillbit coal auger working mechanism mainly consists of three rows of drillrods, two rows of venttubes, a transmission box, and five drillbits. Due to the space and condition limitations in the laboratory, the drilling experiment cannot reach the size and drilling depth as in an actual application. Therefore, drilling depth was set at one, two, three, and four drillrod sections in the experiment. The drilling test bed of the working mechanism is shown in Figure 2.
The drilling test was conducted on artificial coal and rock, which was constructed based on the main mechanical properties of coal. Frequency conversion motor was used to drive the gear reducer to provide drilling torque for the working mechanism. Propulsion resistance was supplied by a hydraulic motor through a pinionandrack mechanism. Drilling torque, propulsion resistance, and deflection displacement were measured by GBDTS200 digital torque sensor, JNBP10 MPa pressure sensor, and HZ891 electric eddy current displacement sensor, respectively. Hardness of the artificial coal and rock was and the rotation speed of the working mechanism was r/min.
2.2. Experiment Results
The displacements of the measuring points with different drill depths for one, two, three, and four drillrod sections were obtained. Figure 3 shows the measuring points displacements of the auger with four drillrod sections. It shows that the displacements have changed significantly when the drillbit drills into the coal seam after s. The statistics of deflection displacements at each measuring point are shown in Table 1, and the statistic laws are shown in Figure 4.

(a) Displacement of measuring point 1
(b) Displacement of measuring point 2
(c) Displacement of measuring point 3
(d) Displacement of measuring point 4
(a)
(b)
As shown in Figure 4, the working mechanism deflects to the right side slightly in the direction and both the maximum deflection and vibration occur in the middle of the working mechanism. In the direction, the drillrod slants downwards, whereas the drillbit tilts slightly upwards. The deflection of the drillrod close to the drillbit is larger, and the maximum vibration also appears in the middle of the working mechanism.
To illustrate the relationship between deflection and different drilling depths, the test load data statistics at the drillrod are conducted. The average and maximum displacement curves are obtained as shown in Figure 5. Figure 5 shows that the deflection displacement of the working mechanism increases with the drilling depth in the direction but increases first and then becomes stable in the direction.
(a)
(b)
(c)
(d)
The drilling depth increases with the drillrod and venttube section by section in the process of drilling which leads the overall stiffness of the working mechanism to decrease continuously. In the direction, the left and right drillrods deflect to the opposite direction under the effect of the friction force by the coal wall hole. The effect of the friction force increases with the drilling depth, leading to the drillrod deviation increase obviously as well as the drillrod vibration. The maximum vibration occurred in the central position of the drillrods. In the direction, the central position of the drillrods gradually closed on to coal wall hole with an increase in the drilling depth under the combined action of the drillrod weight and hole constraints. As the drilling depth reached a certain value, the number of drillrods that made contact with the coal wall hole gradually increased due to gravity, which tends to make the whole working mechanism stable. The vibration of drillrods in the direction increases with the drilling depth at first because of the collision between the drillrods and the coal wall hole and the maximum vibration occurs in the middle of the whole drillrods. Finally, the vibration reaches a balance as well as the deflection.
Table 2 shows the statistics of propulsion resistance and drilling torque of the working mechanism under different drilling depths. Influence of drilling depth on the propulsion resistance and drilling torque was obtained from Table 2, shown in Figure 6. It can be seen from Table 2 and Figure 6 that the propulsion resistance and drilling torque of the working mechanism increase with an increase in the drilling depth. In contrast, little fluctuation of propulsion resistance and drilling torque was changed during the process.

3. Simulation Model Establishment
The vibration and deflection of the working mechanism are affected by many different factors that cannot be investigated by the overall test. Therefore, a simulation was put forward for further studies.
3.1. Basic Hypotheses
The coal auger working mechanism is mainly composed of the drillbit, segmented drillrod, and venttube, which is pushed forward by adding the segmented drillrod and venttube. With increasing drilling depths, the axial size of the working mechanism increases at a far greater rate than its radial size. At the same time, affected by gravity, drilling load, friction, and collision force between the working mechanism and the coal wall, the working mechanism is prone to violent vibrations and serious deflections in the drilling process. To study the vibration and deflection behavior of the working mechanism, the following hypotheses were put forward:(1)The cross section of the coal wall hole is a circle, and the drilling direction is horizontal.(2)The drillbit is set as a rigid body, and the drillrod is an elastomer. Initially, drillrod is coincident with the horizontal axis of the coal wall.(3)The contact and collision between the drillrod and coal wall occur randomly because the drillrod is constrained by the bore wall.(4)The frictional resistance between coal particles and drillrod during transportation is ignored.(5)The vibration and deflection of the working mechanism are divided into and components (the component is the horizontal direction of the coal wall cross section, and the component is the vertical direction).
3.2. Simulation Model
Based on the above hypotheses, a threedimensional entity model of the working mechanism was established and imported into software ADAMS. Simulation model was obtained after quality property definition, drillrod flexibility, constraints addition, contacts addition, drives, and loads addition. Virtual prototype of fivebit coal auger working mechanism is shown in Figure 7.
The vibration and deflection behavior of the fivebit coal auger working mechanism were analyzed in the context of the drilling depth, partial load form, and stabilizer arrangement according to the actual usage in the underground coalmine. The drilling depths were set at 8.3 m, 10.7 m, 13.1 m, and 17.1 m. Partial load for single bit (A), two bits (A and C), and three bits (A, C, and E) was subjected to complex coal seam load, shown in Figure 8. Simple coal seam hardness in the simulation model is , and complex coal seam hardness is . The corresponding torque and propulsion force were obtained from cutting simulation, as shown in Figure 6. Stabilizer was arranged every three, four, five, and six drillrods. In addition, propulsion speed of the working mechanism is 1 m/min and the rotation speed is 60 r/min.
4. Simulation Results
Figure 9 shows the arrangement of different measuring points in the simulation. From displacement and force statistical analyses at different measuring points, the vibration, deflection, and collision force can be obtained.
4.1. Influence of Different Drilling Depths
Figure 10 shows the relationship between drilling depth, vibration, and deflection behaviors of the working mechanism. It can be seen from Figure 10 that the deflection and vibration of the left, middle, and right drillrods in the direction increase with an increase in the drilling depth, but left and right venttubes show no significant change. With an increase in the drilling depth, the deflection of drillrods along the direction gradually increases and tends to be steady when the drilling depth reaches 15 drillrod sections. However, the vibration of the drillrods in the direction reaches the maximum at a drilling depth of 12 drillrod sections and gradually tends to be stable as the drilling depth further increases. Because spacing between the venttube and the coal wall is greater than that of the drillrod and coal wall, the deflection and vibration of the left and right venttubes gradually increase with an increase in the drilling depth in the direction. According to the deflection and vibration characteristics of the left and right drillrods, it is speculated that the deflection and vibration of the left and right venttubes will also gradually tend to be a stable value after reaching a certain drilling depth. Compared with Figure 5, the experimental results coincide with the simulation results and then verify the correctness of the simulation.
While the drilling depth is 10.7 m (12section drillrod), the timedisplacement curves of the different measuring points in the and directions are shown in Figures 11 and 12, respectively. It can be seen that the vibration of the working mechanism is larger in its infancy and gradually tends to be more stable with time; the vibration and deflection at the middle drillrod are larger but relatively small at both ends; the vibration and deflection of the drillrod and the venttube are greatly different from each other in the and direction at the same measure point. The drillrod vibration is considerably larger than the venttube and consistent at measuring point 1 because of the fix of transmission box.
The contact force that was generated by the collision between the coal wall and each row of the drillrods of the working mechanism and venttubes is shown in Figure 13. We can see that the collision mainly occurs at the left and right drillrods on both sides and the collision force orientation is opposite in the direction and the same in the direction. Comparing Figures 13(a) and 13(b), the collision force of onesided drillrod of working mechanism in the direction is five times as great as that in the direction.
(a)
(b)
Figure 14 shows the changing trends of the collision force with drilling depth. It is observed that the collision force of working mechanism in both the and directions tends to increase nearly linearly, along with the mean square error. This suggests that the overall force of working mechanism increases after drilling into the coal seam, which results in the aggravation of the deflection and vibration degree and the approximately linear relationship with the drilling depth.
4.2. Influence on Different Partial Load Modes
Large mining width of the working mechanism during the drilling process would cause a partial load. For a different working condition, the partial load form is different. Hence, a simulation of the vibration and deflection behavior under the following different partial load forms was carried out: (I) nonpartial load; (II) only drillbit A bearing a complex coal seam load; (III) both drillbits A and C bearing a complex coal seam load; and (IV) drillbits A, C, and E bearing a complex coal seam load simultaneously, as shown in Figures 15–18.
(a)
(b)
(a)
(b)
(a)
(b)
(a)
(b)
Comparing Figures 16(a), 17(a), and 18(a) shows that the working mechanism overall deflects to the right side when only the drillbit A bears the partial load, and the maximum deflection position is near the fourth to fifth drillrod sections. When the drillbits A and C simultaneously bear partial load, working mechanism would deflect to the right side, but the magnitudes of the deflection and vibration are both less than the magnitude when only the drillbit A bears the partial load. When the left, middle, and right three drillbits simultaneously bear complicated seam load, various drillrods will have a slight deflection deformation which is consistent with their own rotation direction, but the working mechanism overall drills along the straight direction.
Comparing Figure 15(a) with Figure 18(a), the deflection and the vibration of work mechanism are basically similar under different load forms, but the amplitudes under a complex coal seam load are greater than nonpartial load. The above analysis shows that the working mechanism would deflect to the opposite side under a unilateral partial load, while remaining unchanged basically under an equalizing load. The amplitude changes are a positive correlation with the size of the partial load.
It can be seen from Figures 16(b), 17(b), and 18(b) that the deflection mode of the working mechanism has a little change in the direction; the maximum deflection location is near fifth drillrod. Meanwhile, the vibration range of the working mechanism reduces with a decrease in the partial load, which is more stable under a relatively balanced drilling load. Considering Figure 15(b), the total load of the working mechanism gradually increases under the four proposed partial load conditions as well as the deflection and the relative deflection between each row of drilling tools.
4.3. Influence of Different Stabilizer Arrangements
Drillrod stabilizer is used to control and weaken the deflection and vibration of the working mechanism for long distance drilling, whose arrangements have an important influence on the drilling efficiency. To arrange the stabilizer more intuitively and effectively and find the relationship with deflection and vibration, different stabilizer arrangements were researched as shown in Figures 19 and 20. The stabilizer was arranged along the working mechanism, every six, five, four, and three drillrod section intervals, in four ways. Meanwhile, the arrangement 0 represents the drilling process without a stabilizer placement.
(a)
(b)
(a)
(b)
As seen from Figure 19, the maximum deflection and vibration in the and directions gradually decrease with the order number of stabilizer. After the stabilizer is arranged every five drillrod section intervals, the increase in the order number of stabilizer has less influence on the maximum deflection and vibration in the direction. From this, it can be concluded that the stabilizer arrangement modes 2, 3, and 4 can effectively control the deflection and vibration.
Figure 20 shows that the mean deflection force of the working mechanism would appear positive and have negative alternation with the number of stabilizers increasing in the direction. However, the mean deflection force in the direction increases gradually with the number of stabilizers because the stabilizer arrangement directly affects the overall weight of the working mechanism. Meanwhile, the mean square error of the deflection force in the and directions gradually decreases with the number of stabilizers and reaches a minimum value under arrangement mode 2. This concluded that stabilizer arrangement mode 2 is the best to control the deflection force effectively.
According to the abovementioned analysis, considering deflection, vibration, and deflection force synthetically, the stabilizer that was arranged every five drillrod section intervals can restrain the inconsistent movement between the drillrods and venttubes effectively. This can improve the overall deflection resistance performance and stability significantly.
5. Conclusion
(1)A drilling test bed of the working mechanism was built, and vibration, drilling torque, and propulsion resistance were measured. Experiment results show that the vibration and deflection increase with drilling depth in the direction but increase first and then gradually become stable in the direction, which makes the coal and rock become more difficult to be cut. Similarly, the vibration and deflection are greater under partial load. Reasonable stabilizer arrangement can effectively reduce deflection and vibration of the working mechanism.(2)A rigidflexible coupling simulation model of a fivedrillbit coal auger working mechanism was established, and vibration and deflection under different conditions were researched. The results show that the vibration and deflection under different conditions change in the same manner as the simulation results. This means that the simulation results are agreeable. Moreover, the vibration and deflection also increase with partial load. By arranging the stabilizer at every five drillrod section intervals, the vibration and deflection can be decreased by 30% and 40% in the direction and 14.3% and 65.7% in the direction, respectively.(3)Increasing drilling depth blindly not only decreases the drilling efficiency but also increases the vibration of the working mechanism and energy loss. Power equilibrium of drillbit is good for enhancing antipartial performance of the working mechanism.
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper.
Acknowledgments
The authors acknowledge Special Foundation for the Fundamental Research Funds for the Central Universities, China (Grant no. 2014ZDPY12), and the Priority Academic Program Development of Jiangsu High Education Institute of China.
References
 J. P. Li, C. L. Du, and Y. Z. Zhang, “Present status and development tendency of mining equipment for thin and ultrathin seam in China,” Coal Science and Technology, vol. 33, no. 6, pp. 65–67, 2005. View at: Google Scholar
 X. X. Cui, H. F. Ji, M. X. Lin, and Z. A. Dong, “Vibration characteristic analysis of the multidrilling mechanism,” Journal of Vibroengineering, vol. 16, no. 6, pp. 2722–2734, 2014. View at: Google Scholar
 L. Fu, C. L. Du, and H. X. Jiang, “Simulation study of arrangement modes of stabilizers in auger miners,” Mining & Processing Equipment, vol. 40, no. 9, pp. 20–24, 2012. View at: Google Scholar
 K. K. Millheim and M. C. Apostal, “The effect of bottomhole assembly dynamics on the trajectory of a bit,” Journal of Petroleum Technology, vol. 33, no. 12, pp. 2323–2338, 1981. View at: Publisher Site  Google Scholar
 K. A. Macdonald and J. V. Bjune, “Failure analysis of drillstrings,” Engineering Failure Analysis, vol. 14, no. 8, pp. 1641–1666, 2007. View at: Publisher Site  Google Scholar
 C.Y. Kuang, Z.B. Wu, and D.K. Ma, “Lateral vibration dynamic simulation model of cone bit,” China Petroleum Machinery, vol. 27, no. 12, pp. 7–8, 1999. View at: Google Scholar
 C.Y. Kuang, D.K. Ma, Q. Y. Liu, and Z.B. Wu, “The drill stringbitrock system dynamic behavior simulation,” Acta Petrolei Sinica, vol. 22, no. 3, pp. 81–85, 2001. View at: Google Scholar
 Y. A. Khulief and H. AlNaser, “Finite element dynamic analysis of drillstrings,” Finite Elements in Analysis and Design, vol. 41, no. 13, pp. 1270–1288, 2005. View at: Publisher Site  Google Scholar
 Y. A. Khulief, F. A. AlSulaiman, and S. Bashmal, “Vibration analysis of drillstrings with selfexcited stickslip oscillations,” Journal of Sound and Vibration, vol. 299, no. 3, pp. 540–558, 2007. View at: Publisher Site  Google Scholar
 X.X. Cui and C.J. Tan, “Coupling vibration of a drilling system with interaction between drilling mechanism and coal rock,” Journal of Vibration and Shock, vol. 33, no. 16, pp. 97–104, 2014. View at: Publisher Site  Google Scholar
 G. C. Downton, “Directional drilling system response and stability,” in Proceedings of the 16th IEEE International Conference on Control Applications (CCA '07), pp. 1543–1550, IEEE, Singapore, October 2007. View at: Publisher Site  Google Scholar
 M. Bairdes, “Static and dynamic tridimensional BHA computer models,” in Proceedings of the 16th IEEE International Conference on Control Applications, vol. 3, pp. 1569–1576, Singapore, 2007. View at: Google Scholar
 E. M. NavarroLópez and D. Cortés, “Avoiding harmful oscillations in a drillstring through dynamical analysis,” Journal of Sound and Vibration, vol. 307, no. 12, pp. 152–171, 2007. View at: Publisher Site  Google Scholar
 E. M. NavarroLópez, “An alternative characterization of bitsticking phenomena in a multidegreeoffreedom controlled drillstring,” Nonlinear Analysis: Real World Applications, vol. 10, no. 5, pp. 3162–3174, 2009. View at: Publisher Site  Google Scholar  MathSciNet
 H. Hakimi and S. Moradi, “Drillstring vibration analysis using differential quadrature method,” Journal of Petroleum Science and Engineering, vol. 70, no. 34, pp. 235–242, 2010. View at: Publisher Site  Google Scholar
 S. M. Sahebkar, M. R. Ghazavi, S. E. Khadem, and M. H. Ghayesh, “Nonlinear vibration analysis of an axially moving drillstring system with time dependent axial load and axial velocity in inclined well,” Mechanism and Machine Theory, vol. 46, no. 5, pp. 743–760, 2011. View at: Publisher Site  Google Scholar  Zentralblatt MATH
 M. Z. Jiang, K. X. Dong, and M. Xin, “Dynamic instability of slender sucker rod string vibration characteristic research,” Advanced Materials Research, vol. 5, no. 50, pp. 3173–3179, 2012. View at: Google Scholar
 Q. Sun and C.C. Guan, “A method of determine dynamic stability critical length of construction member,” Applied Mechanics and Materials, vol. 16, no. 6, pp. 3306–3310, 2012. View at: Google Scholar
 Y. Kovalyshen, “A simple model of bit whirl for deep drilling applications,” Journal of Sound and Vibration, vol. 332, no. 24, pp. 6321–6334, 2013. View at: Publisher Site  Google Scholar
 S. Y. Liu, X. X. Cui, and X. H. Liu, “Coupling vibration analysis of auger drilling system,” Journal of Vibroengineering, vol. 15, no. 3, pp. 1442–1453, 2013. View at: Google Scholar
 J. M. Kamel and A. Yigit, “Modeling and analysis of axial and torsional vibrations of drill strings with drag bits,” in Proceedings of the International Petroleum Technology Conference, vol. 12, pp. 549–560, Society of Petroleum Engineers, Doha, Qatar, January 2014. View at: Publisher Site  Google Scholar
 J. Xu, Y. Xu, and J. C. Li, “Fatigue life analysis of auger stem in soft coal seam,” Applied Mechanics and Materials, vol. 472, no. 2, pp. 111–114, 2014. View at: Publisher Site  Google Scholar
Copyright
Copyright © 2016 Songyong Liu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.