Fit Clearance Research Articles

Torsional vibration characteristics analysis and vibration suppression research of compressor flexible rotor system considering fit clearance

Torsional vibration characteristics analysis and vibration suppression research of compressor flexible rotor system considering fit clearance

A Multiscale Modeling and Experimental Study on the Tensile Strength of Plain-Woven Composites with Hybrid Bonded-Bolted Joints.

CFRP hybrid bonded-bolted (HBB) joints combine the advantages of traditional joining methods, namely adhesive bonding, and bolting, to achieve optimal connection performance, making them the most favored connection method. The structural parameters of CFRP HBB joints, including overlap length, bolt-hole spacing, and fit clearance relationships, have a complex impact on connection performance. To enhance the connectivity performance of joint structures, this paper develops a multiscale finite element analysis model to investigate the impact of structural parameters on the strength of CFRP HBB joint structures. Coupled with experimental validation, the study reveals how changes in structural parameters affect the unidirectional tensile failure force of the joints. Building on this, an analytical approach and inverse design methodology for the mechanical properties of CFRP HBB joints based on deep supervised learning algorithms are developed. Neural networks accurately and efficiently predict the performance of joints with unprecedented combinations of parameters, thus expediting the inverse design process. This research combines experimentation and multiscale finite element analysis to explore the unknown relationships between the mechanical properties of CFRP HBB joints and their structural parameters. Furthermore, leveraging DNN neural networks, a rapid calculation method for the mechanical properties of hybrid joints is proposed. The findings lay the groundwork for the broader application and more intricate design of composite materials and their connection structures.

Structure optimization design approach of friction pairs for low-temperature rise wet brake in hydraulic motor

Cam-lobe radial-piston hydraulic motors are widely used in large heavy-duty machinery as direct-drive components of hydraulic systems. Due to their extremely high output torque and power density, the wet brake equipped with the hydraulic motors are necessary to achieve ultra-high braking torque in a compact space. However, due to a large number of internal friction pairs and small fit clearance between multiple friction pairs in wet brake, the rotation of the friction pairs in non-braking state will cause large friction torque loss and obvious temperature rise, thereby leading to the thermal failure of wet brake. How to optimize the structure of friction pairs to reduce the temperature rise of wet brake in non-braking state is a persistent challenge. Existing structure optimization design approaches of friction pairs in brakes mainly focus on the structure of each friction pair, which ignore the effect of fit clearance between the friction pairs on the temperature rise of brakes. Nevertheless, the fit clearance between friction pairs is an important factor that affect the temperature rise. For that, this study proposes a two-step structure optimization design approach of friction pairs for low-temperature rise wet brake in hydraculic motor, which simultaneously considers the fit clearance between the friction pairs and the structure of each friction pair. In this approach, the design process could be divided into two steps: firstly, the influence of fit clearance between multiple friction pairs on the temperature rise of wet brake in non-braking state is analyzed and optimized by the temperature rise theoretical model; secondly, in order to further reduce the temperature rise of wet brake, the oil groove structure of each friction plate are introduced and optimized by fluid-solid-thermal coupling simulation method. By this approach, the low-temperature rise structure of friction pairs with the optimized fit clearance between multiple friction pairs and oil grooves of each friction plate. Finally, a series of experiments are conducted to verify the effectiveness of the design approach. The result show that the temperature rise of wet brake could be effectively reduced 12 % by optimizing the structure of wet brake, demonstrating that the structure optimization design approach could provide a theoretical guidance to design low-temperature rise wet brake for large torque hydraulic motors.

A clearance control and interference repair method for ship rib plate assembly based on reverse engineering

Due to the influence of manufacturing errors, welding deformation of ship parts and other factors, interference often occurs due to out-of-tolerance assembly clearance for ship rib plate assembly using the pull-in method. To solve the problem, a clearance control and interference repair method for ship rib plate assembly is proposed. Firstly, the factors causing ship rib assembly errors were analyzed, and an accurate model of the ship rib with manufacturing errors was built based on a 3D scanning point cloud. Secondly, the fit clearances between multiple components during the motion process were calculated based on simulation. Finally, the assembly clearances were redistributed through pose coordination technology to autonomously control the assembly clearance, allocate excess clearances to interference areas and quantitatively complete the subsequent interference processing. The case study results show that the proposed method can achieve quantitative prediction of assembly clearances and generate a precise repair scheme. The interference for ship rib plate assembly is reduced by 50%, and the efficiency is increased by 24%.

Nonlinear dynamic analysis of ceramic bearing rotor system considering temperature variation fit clearance

Nonlinear dynamic analysis of ceramic bearing rotor system considering temperature variation fit clearance

A comprehensive misalignment-rub-impact nonlinear dynamic spindle model considering contact angle and fit clearance under EHL

A comprehensive misalignment-rub-impact nonlinear dynamic spindle model considering contact angle and fit clearance under EHL

Study on the fastening property of precision locknut under simulated dynamic impact loading with consideration of interference factors

Abstract Screw thread fastening system is the category of mechanical connection utilizing both wedge and friction actions to transfer clamping force and torque. This fastening system shows the advantages of simple in structure and ease in application. However, its shortcomings include the performance limitation by dimension and precision, stress concentration induced by the notch geometry, loosening in dynamical service, susceptible to atmospheric condition, etc. Therefore, the possible interference on the anti-loosening property of the locknut by noise factors of the ambient temperature, operator characteristics, and type of torque wrench used was investigated using Taguchi method in this study beside the main control factors of type of locknut, fit clearance, and type of lubrication grease. The goal was to evaluate the anti-loosening property of the locknut, i.e. the anti-loosening ratio and axial force ratio, in a more realistic manner. The connection joint of the locknut was subjected to cyclic transverse impact and the anti-loosening property was measured after a specified number of cycles. The loading effect on the surface roughness of thread surface was examined and discussed after the test. It was found that the factor of locknut type dominated the influence over the lubrication grease and fit clearance factors. Through the analysis, the design with optimal combination of the control factors improved the axial force ratio and anti-loosening ratio by 7.8% and 47.9%, respectively.

Solid-liquid flow characteristics and sticking-force analysis of valve-core fitting clearance

Solid-liquid flow characteristics and sticking-force analysis of valve-core fitting clearance

Effect of spool posture on control valve performance considering outlet shape and large fit clearance

The control valve serves as a crucial component of the downhole integrated water distributor in water injection oilfields, enabling waterflooding into oil reservoirs. However, the control valve opening cannot be adjusted in the practical environment, resulting in ineffective injection, which means that the spool is stuck. Furthermore, it is difficult to observe the details of the spool sticking and reproduce this phenomenon during testing. To reveal the mechanism of sticking, this paper establishes a CFD model, which considers the spool posture, large fit clearance and outlet shape, to study the spool performance. Additionally, the proposed model is demonstrated experimentally and theoretically. It is found that larger fit clearances result in significant distortion of the flow characteristic curve, with a flow regulation rate of only 90.87% observed when the fit clearance is 0.25 mm. Furthermore, the lateral outlet causes a reduction of 77.27% and 69.15% in radial forces for eccentricity or inclination angles changed from 0° to 180°, respectively. Sticking is strongly correlated with radial forces, the axial force is contingent upon the spool end face area. These findings provide crucial theoretical guidance for the design of control valves.

An Inspection Technique Using Fit Clearance Based on Microscopic Vision in Precision Assembly.

Inspection is a crucial process to ensure product quality. In the precision assembly of an optic-mechanical device, a part with micro multi-section arcs needs to be inspected and assembled into another part. Actually, because of machining errors, including dimensional and geometric shapes, can lead to complex deformation modes for parts with micro multi-section arcs, posing challenges to their inspection. Furthermore, inconsistencies in feature images in microscopic vision may complicate the extraction of the Region of Interest (ROI). To address these issues, this paper proposes an ROI extraction method based on the CAD model for rough positioning of feature points and connected region detection for refinement. Subsequently, based on feature points, the CAD model is used again to obtain the ROI. For inspection purposes, this paper proposes a method suitable for micro multi-section arcs based on assembly fit requirements. Experimental testing was performed on parts with eight-section arcs and mirrors to verify the effectiveness of the proposed method. This method provides a suitable solution for the inspection of micro multi-section arcs in precision assembly with the potential to improve the accuracy of the inspection results.

Failure analysis of aviation hydraulic rotary joints

The aviation hydraulic rotary joint is an accessory of the aviation hydraulic system used to connect two pipelines in relative motion. The safety accident caused by the failure of the aviation hydraulic rotary joint occurred in engineering. The analysis of the potential failure causes of aviation hydraulic rotary joints can provide basic technical support for aircraft maintenance activities. In this study, a ground reliability experimental apparatus for an aviation hydraulic rotary joint was built, and a reliability test was conducted. The potential failure mode of an aviation hydraulic rotary joint was analyzed by observing the surface topography of each component. Finally, the failure mechanism was analyzed using the finite element method. To provide a basis for the maintenance and replacement strategy of the joints, the influence of the fit clearance on the reliability of aviation hydraulic rotary joints was analyzed. The results show that the wear of metal components and sealing components and the stress failure of sealing components are the main failure mechanisms of rotary joints; when the fit clearance increases from 0.02 mm to 0.12 mm, the maximum von Mises stress and maximum shear stress of the retaining ring were increased by 44.45% and 43.72%, respectively, and the maximum von Mises stress and maximum shear stress of the O-ring were increased by 131.89% and 123.64%, respectively. With the increase of the fit clearance, the stress damage probability of the retaining ring and O-ring will increase. The maintenance and replacement strategy of rotary joints can be made according to the size of the fit clearance.

Influence of Fir-Tree Tenon Blade Parameters on Blade Dynamic Characteristics

In this paper, based on the theory of elastic structure analysis, considering the rotational softening and centrifugal stiffening of the blade, the dynamic model of the fir-tree rotating blade and the macroslip hysteresis model of the dry friction on the contact surface of fir-tree tenon are established. Based on elastic mechanics, the pressure distribution model of fir-tree tenon is innovatively established and the relationship between fit clearance and contact pressure has been derived. After the blade is discretized by the finite element method, the dynamic equation of the blade is solved iteratively by the Newmark-β numerical integration method. According to the dynamic equation of the blade, the influence of the change of the tenon angle on the forced response and contact stress of the blade is derived. Finally, some novel conclusions are obtained by analyzing the influence of pressure distribution, tenon angle, friction coefficient, rotational speed, and aerodynamic excitation on blade vibration characteristics. It provides a scheme and relevant basis for the design and development of tenon blades with the most damping effect at different speeds in industrial practice.

Dynamic behaviors and contact characteristics of ball bearings in a multi-supported rotor system under the effects of 3D clearance fit

Clearance fit is a common assembly method for bearings in rotor systems, which leads to a certain clearance between the outer ring of the bearing and the bearing pedestal, that is, the fit clearance. The nonlinear factors caused by the fit clearance may affect the mechanical properties of the bearing and rotor system. Considering the fillet and six-degree-of-freedom (6-DOF) motion of the outer ring, a three-dimensional (3D) clearance fit model is proposed. In addition, considering the interference fit between the inner ring and spindle, an analytical stiffness model of ball bearings is developed. By coupling the clearance fit model and the analytical bearing stiffness model with a finite element (FE) model of a spindle, a dynamic model of a multi-supported rotor system is established and verified by the experiment, which fully considers the nonlinear factors of ball-raceway contact and outer ring-bearing pedestal contact. The effects of fit clearance, radial force, and axial force on the vibration behaviors and contact characteristics of the ball bearing in the system are analyzed. The results indicate that the larger fit clearance of the unilateral bearing may lead to misalignment of the bearing and reduce the bearing force. Under radial force, the bearing clearance and fit clearance are eliminated, which improves the stability of the system. At this time, further application of axial force causes the load-bearing area to become larger and weakens the variable compliance (VC) characteristics of the bearing. This investigation can provide technical support for the assembly and design of the bearing-rotor system.

Effects of Fit Clearance and Viscosity of Lubricating Oil on Shaft Center Orbit of Camshaft

In an oil-film lubricating system, fit clearance and the different types of lubricating oil can result in changes in the orbit of shaft center, thereby affecting the stability of the system. Subject of this paper is the camshaft lubricating system of airspace engine, to figure out the effects of fit clearance and the type of lubricating oil on the shaft center orbit of camshaft, in this study, a 3D model of the camshaft lubricating system was built for simulation purpose based on Reynolds equation, and the calculation results suggest that, as the fit clearance grows larger, the convergence position of shaft center gradually moves away from the starting position, and the stability of shaft center declines; in terms of the type of lubricating oil, the higher the viscosity of the lubricating oil, the closer of the position of shaft center to the starting point, and the higher the stability. Our research method can be applied to common oil-film lubricating systems and we hope it could provide a theoretical evidence for the selection of fit clearance and type of lubricating oil for such systems.

Failure analysis of auxiliary support bearing/shaft tribopair in seawater hydraulic axial piston pump

The auxiliary support structure is used to prevent the cylinder block from tilting in seawater hydraulic axial piston pump (SHAPP). The failure modes of auxiliary support bearing and shaft under different material combinations were compared. Experimental results show that improper design of radius fitting clearance in auxiliary support bearing/shaft tribopair will seriously affect the normal operation of SHAPP and even lead to its damage. Based on the inertia force, nonlinear water film force and dynamic load balance of the rotating cylinder block, the mathematical model of the nonlinear shaft centerline orbit of the auxiliary support bearing was established. The nonlinear shaft centerline orbit of auxiliary support bearing in the cylinder block bore during SHAPP operation is analyzed accurately. Simultaneously, the water film pressure field under different radius fitting clearance is simulated and the range of the optimal value is determined. The running-in experiment of SHAPP is carried out under the optimum clearance of the auxiliary support bearing/shaft tribopair. The results show that the SHAPP can run normally and the performance is obviously improved without the wear on the friction pair surfaces. Therefore, the proposed method has provided the guidance reference for the design of auxiliary support bearing in SHAPP.

Tribo-dynamic performances and vibration transmission of lubricated translational joints in marine engines

• A new tribo-dynamic model for lubricated translational joints in two-stroke marine engines is established to study its dynamic and lubrication performances. • The fit clearance and profile are investigated so as to reveal their influences on the tribo-dynamic performances. • The use of a quadratic profile is an effective way to form a stable wedge-shaped oil film and avoid unnecessary collisions. • The vibration energy of lubricated translational joints through an optimal quadratic profile is greatly reduced in each frequency band. In this paper, a new tribo-dynamic coupling model for lubricated translational joints in two-stroke marine engines is established to study its dynamic and lubrication performances. Dynamic responses of spatial rigid-flexible multi-body systems are solved by a unified absolute nodal coordinate formulation (ANCF). Mixed lubrication performances are described by the modified Reynolds equation and solved by the finite element method. According to the coupling model, the fit clearance and profile are investigated to uncover their influences on the tribo-dynamic performances. The results show that the use of a quadratic profile is an effective way to form a stable wedge-shaped oil film and avoid unnecessary collisions. An optimal quadratic profile of crosshead is suggested in the light of the above analysis, and its influence on the transmission characteristics of vibration signals in the joint is analyzed. It can be concluded that the vibration energy through the optimal profile is greatly reduced in each frequency band.

Study on significant factors of stable dynamic stiffness and advanced assembly for precision fastening system by Taguchi method

Precision assembly fastening is an indispensable part of technology. The clamping force of the precision fastening system maybe remain Table or decrease when the assembly is subjected to axial vibration. In the meantime, rotating for a long time at a very high speed will produce a very high temperature. When the temperature rises, it will greatly reduce the overall performance and accuracy of the precision fasten system. With the background of this problem, this research was started. In this study, experiments were carried out with a rotation dynamic percussion testing machine, and the Taguchi method was used to discuss the assembly of the precision fasten system with different parameters and conditions. The experimental control factors are the fitting clearance, bearing contact angles, and the viscosity of the lubricating oil. After getting the test value, the next step is a statistical analysis using the Taguchi method in stages to get the final optimal results of the experiment. The results showed that the bearing contact angle and the viscosity of the lubricating oil are important factors affecting the temperature rise of the bearing. The results of this experiment can be applied as a basis for assembling machine tools for the advanced manufacturing industry, aircraft industry, automotive light vehicles to heavy vehicles in the mining world, etc. This also aims to improve the accuracy and stability of the precision fastening system.

Optimizing the Clearance Fit of a Progressive Cavity Pump for the Thermal Recovery of Petroleum Using Fluid-Structure Thermal Coupling.

It is important to incorporate the effects of fluid–structure thermal coupling and the boundary conditions when calculating the thermal dynamics and response of progressive cavity pumps. This study develops a fluid–structure thermal coupling model of the progressive cavity pump to improve the accuracy of its measured field of deformation and the temperature field of the stator. A function for the macroscopic motion of a rigid body is written in a typical fluid domain, and the user-defined function (UDF) in FLUENT is used to load the boundary of the rotor to realize its planetary motion. Local remeshing is used to update the moving grid, and the viscoelastic hysteretic heat of the stator is treated as the internal source of heat. One-way decoupling is used based on tire slip theory, and heat flux on the surface of the stator is calculated by the ANSYS Parametric Design Language (APDL). The sequential fluid–structure thermal coupling of the progressive cavity pump is calculated by using the ANSYS workbench. A scheme for optimizing the fit clearance of the stator and rotor is given to improve the volumetric efficiency of the progressive cavity pump and prevent the stator from being stuck owing to a large deformation, and the calculations are verified by experiments on volumetric efficiency. The average deviation in the calculated volumetric efficiency was less than 5% compared with the experimental values. The proposed scheme provides a theoretical basis for the optimal design of the progressive cavity pump for the thermal production of petroleum.

The Effect of Fit Clearance between Outer Race and Housing on Vibration Characteristics of a Cylindrical Roller Bearing with Localized Defects

Due to bolt looseness or operating ambient temperature, fit clearance can often be found between the outer ring and housing. The vibration characteristics of a cylindrical roller bearing with localized defects are greatly affected by the fit clearance and the accuracy of bearing fault diagnosis may be reduced. Thus, a mathematical model for a cylindrical roller bearing was constructed and the interaction between the outer ring and housing was described. The classical localized defects were modeled, such as the inner ring defect, outer ring defect and roller defect. The relative experiments were conducted to check the constructed model. Then, it was found that the RMS (Root Mean Square) of housing acceleration decreased with increasing housing stiffness and viscous damping. When the fit clearance and friction coefficient increased, the RMS values increased. Except for housing stiffness and viscous damping, there were no uniform change rules of defect frequency amplitudes for other conditions. In the bearing with an outer ring defect or roller defect, the shock times of housing acceleration and the contact force between outer ring and housing were delayed, while fit clearance decreased. However, contrary variation trends were found for the inner ring defect. If the phase difference between defect location and rotor unbalanced force increased, the RMS and acceleration fluctuation amplitudes for the inner ring defect decreased. When the location angle of the outer ring defect increased, RMS and frequency amplitudes increased and RMSy/RMS decreased. The calculated results may provide the theoretical foundation for condition monitoring rotating machinery systems.

Influence of Fit Clearance and Tightening Torque on Contact Characteristics of Spindle–Grinding Wheel Flange Interface

The spindle and grinding wheel flange (GWF) adopt double positioning of a tapered surface and end face. Due to the processing quality, the contact state of the spindle–GWF interface cannot be determined accurately. Based on the theory of finite element and the Yoshimura integral method, an analysis method for the contact stiffness of the spindle–GWF interface was established. In addition, the effects of the spindle–GWF interface’s original clearance and tightening torque on the contact pressure, final contact state and contact stiffness of the spindle–GWF interface were investigated and experimentally verified. It was found that the final contact state of the spindle–GWF changed when the tightening torque increased, especially when the original contact state was tapered contact, and the final contact state changed significantly after assembly. The contact pressure and contact stiffness of the spindle–GWF interface are increased by increasing the tightening torque. The radial stiffness is more affected by the end clearance variation compared to the axial and angular stiffness. When the original contact state is tapered contact, the radial stiffness of the interface is at maximum in three contact states. This research provides theoretical guidance for GWF assembly on gear-grinding machines.