A GEAR COUPLING WITH TAPERED EXCESS LOAD ABSORPTION

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 12, December 2018, pp , Article ID: IJMET_09_12_093 Available online at aeme.com/ijmet/issues.asp?jtype=ijmet&vtype= =9&IType=12 ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed A GEAR COUPLING WITH TAPERED SHRINK SLIP PAD FOR EXCESS LOAD ABSORPTION JunWoo Bae, JongSigKwon, JinHo Seo JAC Coupling Co., Ltd., South Korea HyoungWoo Lee Department of Aero Mechanical Engineering, Jungwon University, South Korea KeunHyo Lee, Sookeun Park Korea Institute of Industrial Technology, South Korea Faculty of Technology and Engineering, The Maharaja Sayajirao University of Baroda, Vadodaraa ABSTRACT Existing gear coupling systems lack a power cutoff function or rely on shear pins for power cutoff. New types of gear coupling must be developed that can absorb excess loads or abnormal power and resume normal operations. This study developed a gear coupling system capable of absorbing excess loads when a certain amount of torque is exceeded, to prevent damage to the motor and gearbox during abnormal power supply conditions. The torque delivered was estimated based on the friction coefficient of members in relative sliding movement and the contact pressure occurring between two members. To determine the reliability of the derived stress and the sliding distance of each component, a finite element analysis was performed using the commercial software ANSYS. The results showed that the equivalent stress of the shrink clamp was of a safe level at MPa. In addition, a structural analysis was conducted to optimize the overalll gear coupling system by considering the stress acting on each component. Keywords: Gear coupling, Taper shrink, Slip pad, Excess load absorption, Element analysis. Cite this Article: JunWoo Bae, JongSigKwon, JinHo Seo, HyoungWoo Lee, KeunHyo Lee and Sookeun Park, A Gear Coupling with Tapered Shrink Slip Pad For Excess Load Absorption, International Journal of Mechanical Engineering and Technology, 9(12), 2018, pp et/issues.asp?jtype=ijmet&vtype=9&itype e=12 IJMET/index.asp 928 editor@iaeme.com

2 JunWoo Bae, JongSigKwon, JinHo Seo, HyoungWoo Lee, KeunHyo Lee and Sookeun Park 1. INTRODUCTION The main function of a coupling is to deliver power by connecting the driving shaft and driven shaft. The couplings of industrial mechanical devices are subjected to loads due to various factors such as setup conditions, thermal expansion of equipment, and surrounding support. To minimize these loads, coupling systems must compensate for misalignment and deliver power from the driving shaft to the driven shaft with minimal losses [1-3]. In particular, coupling systems used in steel mills, power plants, and shipyards have to deliver power while in high-speed rotation, and prevent damage to the gearbox and motor even when placed under excess loads. Overloading is one factor that can cause the deterioration or failure of surrounding devices, including the gearbox and motor. In manufacturing facilities this type of breakdown interferes with manufacturing operations, eventually resulting in higher maintenance and production costs [6-7]. Among the various types of coupling, gear coupling offers a number of advantages including ease of installation, and capacity for greater power transmission relative to its size [4-5]. In the event of overloading, many existing gear coupling systems either lack a power cutoff function, or rely on shear pins for power cutoff. Systems that do not come with a power cutoff function are risky since they can allow damage to the coupling components, thus endangering the safety of facilities, disrupting manufacturing, and leading to higher maintenance costs. Figure 1 Shear pin gear coupling As shown in Figure 1, a gear coupling system with a shear pin cuts off power by damaging the shear pin when the power delivered exceeds a certain level. This makes it difficult for facilities to resume normal operations, and the rotating shear pin may damage the gear coupling system or increase the likelihood of secondary failure due to flying objects or fragments. Moreover, adding a shear pin increases the size of the gear coupling system, which translates to higher manufacturing costs. To avoid these problems, new types of gear coupling must be developed that are capable of absorbing excess loads or abnormal power, and then resume normal operations. IJMET/index.asp 929 editor@iaeme.com

A Gear Coupling with Tapered Shrink Slip Pad For Excess Load Absorption This study developed a gear coupling system capable of absorbing excess loads when a certain amount of torque was exceeded, so

3 A Gear Coupling with Tapered Shrink Slip Pad For Excess Load Absorption This study developed a gear coupling system capable of absorbing excess loads when a certain amount of torque was exceeded, so as to prevent damage to the motor and gearbox during abnormal power supply conditions. In addition, the gear coupling system with excess load absorption can be integrated using a slip pad, fixed in place to support sliding, and designed with a tapered shrink fit to adjust frictional force. 2. STRUCTURE OF GEAR COUPLING WITH EXCESS LOAD ABSORPTION The proposed gear coupling with excess load absorption is small and lightweight relative to the amount of power transmission, and causes little noise or vibration during high-speed rotations. It was designed to provide long service life and minimize any loss in power transmission. Figure 2 Structure of gear coupling with excess load absorption The external crown gear of the gear coupling system is capable of self-adjustment and displacement absorption, which allows normal power transmission in the event of shaft error. The internal lubrication enhances its wear resistance. As shown in Figure 2, the integrated gear coupling system keeps the slip pad and other components fixed using the contact pressure produced by the tapered fitting. Sliding is induced when the delivered power exceeds the force of friction. The gear hub was designed as a crown gear capable of self-adjustment and displacement absorption, enabling normal power transmission in the event of shaft error. Like the external crown gear, wear resistance was enhanced with internal lubrication. The tapered slip sleeve and slip clamp were secured with reamer bolts, producing friction by creating contact pressure in the radial direction of the shaft during relative sliding movement. A copper cylindrical slip pad was placed between the slip sleeve and slip hub to produce friction from contact pressure, such that sliding occurs when the power delivered exceeds the force of friction. That is, the system was designed to deliver power through contact pressure and friction derived from the tapered fitting, and to absorb excess loads by sliding movement Design of Displacement Absorption Structure Gear coupling requires a high capacity for displacement (misalignment) absorption and low stress stiffness, and these are determined by the structure of the tooth form. As shown in Figure 3, the gear coupling system has better performance using a flexible coupling with a larger range of axial misalignment, radial misalignment, and angular misalignment. IJMET/index.asp 930 editor@iaeme.com

JunWoo Bae, JongSigKwon, JinHo Seo, HyoungWoo Lee, KeunHyo Lee and Sookeun Park Figure 3 Compensation for shaft misalignment in flexible coupling The crowned gear hub allows the tooth top to mesh in

4 JunWoo Bae, JongSigKwon, JinHo Seo, HyoungWoo Lee, KeunHyo Lee and Sookeun Park Figure 3 Compensation for shaft misalignment in flexible coupling The crowned gear hub allows the tooth top to mesh in the shaft direction, minimizing interference even when there is a slight inclination between the sleeve and hub. Power is delivered smoothly under radial, angular or axial misalignment. However, the system should be designed to prevent deformation or damage to the tooth form when the tooth face is subjected to high stress while compensating for misalignment. Specifically, in the design objective, the gear coupling system must continue functioning normally, without deformation or damage to the tooth form, while satisfying a full load misalignment angle of 2 under a torque of 70 knm. The required conditions of the gear coupling, with absorption of excess loads, include a maximum torque of 70,000 Nm, a full load misalignment angle of 2, 75 teeth, and a maximum speed of 2,150 RPM. The design parameters of the proposed gear coupling are presented in Table 1. Table 1 Design parameters Abb. Description Input Unit Value Unit T Torque 70,000 Nm 619,549 lb-in PD Pitch Circle Dia. Gear tooth mm in h active tooth height 9.75 mm in R C Radius of tooth face curvature 221 mm in DP diameter pitch of gear tooth /in N Maximum speed, RPM 2,150 RPM 2,150 RPM α Full load misalignment angle 2 degree rad FW gear tooth face width 42 mm in R Pitch radius, PD/ mm in n number of teeth C percentage of teeth in contact 90 % 90 % u friction coefficient In accordance with MIL-C-23233, compressive stress can be calculated as follows. = / h (1) Here, Sc is the compressive stress, T is the torque, Rc is the radius of the tooth face curvature, C is the percentage of teeth in contact, h is the active tooth height, DP is the diameter pitch of gear tooth. Based on Eq. 1, compressive stress in relation to the gear tooth form was calculated, as given in Table 2. Design safety was assured with a safety factor greater than IJMET/index.asp 931 editor@iaeme.com

5 A Gear Coupling with Tapered Shrink Slip Pad For Excess Load Absorption Table 2 Calculation of compressive stress in relation to gear tooth form Sc 54,664.5 Psi MPa Material S45C Heat Treatment Q&T Yield Stress 490 Safety Factor Development of Structure for Excess Load Absorption The gear coupling with excess load absorption prevents damage to the motor and gear box by absorbing excess loads when the power delivered exceeds a certain amount of torque. This study designed an integrated gear coupling system with tapered fitting to produce friction from contact pressure. In designing a friction-based power cutoff structure, the torque can be estimated based on the friction coefficient and contact pressure between members in relative sliding movement. The design objective is for the gear coupling to maintain normal operations without damage by inducing slipping under a torque of 60 to 70kNm. The tapered structure generates contact pressure in the radial direction of each ring when the tapered surface and clamp ring engage in relative sliding under the clamping force of bolts. When this contact pressure is used, the structural shape can be simplified as shown in Figure 4 and 5 to calculate the stress of the tapered ring under plane strain conditions. The contact pressure acting on the tapered ring is determined by the axial force resulting from the bolt assembly. Figure 6 shows the load distribution on the tapered surface under the axial force Fa. Figure 4 Structural shape of the tapered joint and simplified shrinkage fit Figure 5 Force diagram of tapered surface IJMET/index.asp 932 editor@iaeme.com

6 JunWoo Bae, JongSigKwon, JinHo Seo, HyoungWoo Lee, KeunHyo Lee and Sookeun Park The contact pressure acting on the surface needed to obtain the desired torque T, and the load in the shaft direction ( Fa ) needed to produce such contact pressure are calculated by Eq. 2 and Eq. 3, respectively. = 2 (2) = (+ ) (3) Here, μ is the friction coefficient, and ρ is the angle of friction. The two are related by μ = tan(ρ). When the bolt applies an axial force, the stress acting on each member is assumed to be superposed as shown in Figure 4. Stress in the radial and circumferential directions can be calculated under axisymmetric plane strain conditions. The stress acting on each ring in the radial and circumferential directions can be calculated using Eq. 4 and Eq. 5, with P0 to P4 being the contact pressure as shown in Figure 6. " # = $ $ & & + $ ' ( & $ ) 1 & $ & $ (4) Figure 6 Force diagram on tapered surface " ) = $ $ & & $ & ( & $ ) 1 & $ & $ (5) When the internal and external diameters are subjected to pressure, the respective displacements can be calculated as follows. + $ = $ (1+,) [ - $ /(1,) & + $ & +,0 1(1,)1 2 & & $ & 2](6) $ + & = & - 52 $(1, ) $ & & (1+,)((1,) & + $ $ &,)6(7) $ Based on Eq. 6 and Eq. 7, the pressure loss due to the assembly tolerance of the shaft and hub 89 : and the assembly pressure of the hub and tapered ring 89 can be expressed as Eq. 8 and Eq. 9, respectively. IJMET/index.asp 933 editor@iaeme.com

7 A Gear Coupling with Tapered Shrink Slip Pad For Excess Load Absorption = +/ 9 - <1 = > 0/4 = (8) = = +/ 9 = - > (9) To obtain the contact pressure needed for power transmission, the sum of the relative sliding distance in the internal radial direction of Ring 4, the displacement in the external radial direction of Ring 3, and the assembly tolerance 89 : and Δd are divided by the tapered angle. The displacement in the internal radial direction of Ring 4 is calculated from Eq. 6 as follows. + (1+,) /(1,) C - C The displacement in the external radial direction of Ring 3 is calculated from Eq. 7 as follows. + #=' - 52 (1, ) = + = From Eq. 10 and Eq. 11, the displacement in the radial direction and relative sliding distance are as follows. + # = + #@$ ++ #=' D/2 (12) E = + # /tan(13) Figure 7 shows the stress distribution of the slipping disk, obtained using the above equations. Figure 7 Stress distribution graph of the slipping disc IJMET/index.asp 934 editor@iaeme.com

each component. A model of 1/15 scale was obtained using 3D modeling, and the analysis was carried out under symmetric conditions.

8 JunWoo Bae, JongSigKwon, JinHo Seo, HyoungWoo Lee, KeunHyo Lee and Sookeun Park 2.3. Finite Element Analysis of Taper Fitting Finite element analysis was performed using the commercial software ANSYS 18 to determine the reliability of the calculated stress and sliding distance of each component. A model of 1/15 scale was obtained using 3D modeling, and the analysis was carried out under symmetric conditions. The contact pressure arising from the bolt assembly was used to move the shrink clamp by 5 mm, as obtained from the above equations. The friction coefficient of the hub and shaft was set at The tapered surface was given a surface roughness of Ra0.8 to facilitate transport and disassembly, and treated with an anticorrosion spray to achieve a friction coefficient of The physical properties of each component were the same as the values used in the calculations. Figure 8 gives the mesh information, and Figure 9 presents the boundary conditions. Figure 10 shows the total deformation, Figure 11 the radial normal stress, Figure 12 the hoop normal stress, and Figure 13 the equivalent stress. Figure 8 Mesh of 1/15 model of shrink disc Figure 9 Boundary conditions IJMET/index.asp 935 editor@iaeme.com

Figure 11 Radial normal stress Figure 12 Hoop normal

9 A Gear Coupling with Tapered Shrink Slip Pad For Excess Load Absorption Figure 10 Total deformation Figure 11 Radial normal stress Figure 12 Hoop normal stress IJMET/index.asp 936

10 JunWoo Bae, JongSigKwon, JinHo Seo, HyoungWoo Lee, KeunHyo Lee and Sookeun Park Figure 13 Equivalent stress Table 3 Results of shrink disc analysis No. Stress Type Shaft Slip Hub Slip Pad Shrink Hub Radial Normal Stress [Mpa] Hoop Normal Stress [Mpa] Equivalent Stress [Mpa] Shrink Clamp As presented in Figures 11 to 13 and Table 3, the axial stress values obtained using finite element analysis are the same from the center to the surface, but compressive stress tends to increase towards the surface. The finite element analysis showed that the equivalent stress of the shrink clamp was of a safe level at MPa. 3. STABILITY VERIFICATION THROUGH FINITE ELEMENT ANALYSIS OF FULL MODEL A finite element analysis was conducted using ANSYS R18 to assess the structural stability of the proposed gear coupling with excess load absorption. The stress acting on each component was determined through structural analysis, and the optimal shapes were derived accordingly. Figure 14 shows the geometry of the proposed gear coupling with power cutoff. Figure 15 shows the mesh of the model used in the gear coupling analysis. Figure 16 and 17 are the closeups of the gear hub and gear sleeve, which are the parts subjected to relatively higher stress. Table 4 provides information on the materials used in the proposed gear coupling. IJMET/index.asp 937 editor@iaeme.com

11 A Gear Coupling with Tapered Shrink Slip Pad For Excess Load Absorption Figure 14 Geometry of gear coupling with power cutoff Figure 15 Mesh densification of gear hub teeth Figure 16 Mesh densification of gear sleeve teeth IJMET/index.asp 938

JunWoo Bae, JongSigKwon, JinHo Seo, HyoungWoo Lee, KeunHyo Lee and Sookeun Park Figure 17 Mesh densification of gear sleeve teeth Table 4 Gear coupling materials Tensile S. Yield S.

the boundary conditions used in the gear coupling analysis. Structural analysis was performed on a full model for an in-depth analysis of equivalent stress on each component.

12 JunWoo Bae, JongSigKwon, JinHo Seo, HyoungWoo Lee, KeunHyo Lee and Sookeun Park Figure 17 Mesh densification of gear sleeve teeth Table 4 Gear coupling materials Tensile S. Yield S. Part Material Heat treatment Hardness [MPa] [MPa] Normalizing ~ 229 S45C QT ~ 269 C2680-H Figure 18 Boundary conditions for gear coupling analysis Figure 18 shows the boundary conditions used in the gear coupling analysis. Structural analysis was performed on a full model for an in-depth analysis of equivalent stress on each component. In Figure 19 and Table 5, the gear hub and gear sleeve were found to be under higher stress, while other components attained a highly satisfying safety factor of at least 3. The gear hub and gear sleeve were also considered safe with a safety factor greater than IJMET/index.asp 939 editor@iaeme.com

13 A Gear Coupling with Tapered Shrink Slip Pad For Excess Load Absorption Gear Hub : MPa Side Cover : 81.10MPa Gear Sleeve : MPa Shrink Clamp : 18.58MPa Shrink Hub : 60.30MPa Slip Pad : 72.17MPa Slip Hub : MPa IJMET/index.asp 940 editor@iaeme.com

14 JunWoo Bae, JongSigKwon, JinHo Seo, HyoungWoo Lee, KeunHyo Lee and Sookeun Park Figure 19 Equivalent stress of components in gear coupling with excess load absorption Table 5Safety factor of components in gear coupling with excess load absorption Component Gear Side Gear Shrink Shrink Slip Slip Hub Cover Sleeve Clamp Hub Pad Hub Material S45C S45C S45C S45C S45C C2680H S45C Heat Treatment Q.T Normal Q.T Q.T Q.T - Q.T Yield Strength [ MPa ] Equivalent Stress [ MPa ] Safety Factor CONCLUSIONS This study developed a gear coupling system capable of absorbing excess loads when the power delivered exceeds the maximum torque, so as to prevent damage to the motor and gear box. As a result, the following conclusions were derived. 1) The system was designed so that excess loads induce sliding, by delivering power through the contact pressure and friction of a tapered fitting. The delivered torque was estimated based on the friction coefficient of members in relative sliding movement and the contact pressure occurring between two members. 2) Finite element analysis was performed using commercial software ANSYS 18 to determine the reliability of the calculated stress and the sliding distance of each component. The axial stress values obtained using finite element analysis were the same from the center to the surface, but compressive stress increased towards the surface. The finite element analysis showed that the equivalent stress of the shrink clamp was of a safe level at MPa. 3) Structural analysis was conducted to determine the stress acting on each component and to derive their optimal shapes. The gear hub and gear sleeve, which deliver power through the interlocking of gears, were found to be under higher stress but considered safe with a safety factor greater than 1.1. The other components attained a highly satisfying safety factor of at least 3. A CKNOWLEDGEMENT This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No ). REFERENCES [1] J.R. Mancuso, 1986, "Coupling and Joints", Marcel Dekker. New York, pp. 234~318. [2] P.C Renzo, 1968, "Gear Coupling", J. Eng. Indust., Trans. ASME, Vol. 90, No. 3, pp. 467~474. [3] J. Piotrowski, 1995, "Shaft Alignment Handbook", Marcel Dekker. New York, pp. 90~94. [4] M. Xu and R.D. Marangoni, 1991, "Flexible Couplings: study and application ", Shock and Vibration Digest, Vol. 22, No. 9, pp. 3 ~ IJMET/index.asp 941 editor@iaeme.com

15 A Gear Coupling with Tapered Shrink Slip Pad For Excess Load Absorption [5] Neale, M. Needham and R. Horrell, 1991, "Couplings and Shaft Alignment ", Mechanical Engineering Publications. [6] D.L Dewell and L.D. Michell, 1984, "Detection of a misaligned disk coupling using spectrum analysis", Journal of Vibration, Acoustics, Stress, and Reliability in Design, Vol. 106, pp. 9 ~16. [7] B.O Kim, C.G. Park and Y.C. Kim, 1999, "A Study on the Dynamic Characteristics of a Rotor System with a Misaligned Gear Coupling", Journal of Korea Society of Mechanical Engineers, Vol. A 23, No. 8, pp ~ IJMET/index.asp 942 editor@iaeme.com

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