Fit Clearance Research Articles

Effect of the fit clearance between ceramic outer ring and steel pedestal on the sound radiation of full ceramic ball bearing system

Full ceramic ball bearings(FCBB) are widely applied in wide temperature ranges due to the good thermal shock resistance, but the change of fit clearance becomes a new problem affecting the sound radiation performances. A sound radiation model of FCBB system concerning the temperature-related fit clearance is built in this paper, and the sound radiation characteristics with the impact of temperature, rotation speed and radial load are studied. New geometric and force boundary conditions are set with varying fit clearances, and the change of sound radiation with the working conditions are verified by experimental investigations. Results show that the impact of fit clearance on the sound radiation is significant due to the change in the interactions between FCBB system components, and the sound radiation indicators such as peak angle and directivity also vary with working condition parameters such as rotation speed and radial loads. The results provides insights to the running performance of FCBB systems, and are of reference value for improving the overall characteristics.

Design and contact characteristics analysis of a new internal twin-screw pump

This paper designs a new internal meshing twin-screw pump (new twin-screw pump). To study the new twin-screw pump in the principle, performance parameters, and contact characteristics of the differences with the single-screw pump, the mathematical method of motion conversion is used to convert the planetary motion of the single-screw pump into the fixed-axis rotation of the internally intermeshing twin-screw pump. It is found that the movement relationship of the two pumps is similar. When the structural parameters of the two pumps are the same, the flow per revolution of the single-screw pump is N+1 times that of the new twin-screw pump. To obtain the force transmission characteristics in the internal meshing process, a numerical method was used to analyze the structure of the new twin-screw pump statically. Due to the existence of the meshing relationship, the influence of the screw meshing fit clearance, progression, and pitch on the contact stress is further explored. The results of the study show that the internal and external rotor contact stresses show a trend of small in the middle and large at the ends, the stress distribution coefficient [Formula: see text] increases with the increase of the mating clearance, and the stress distribution becomes uneven with the increase of the number of screw stages and pitch. The results of this study provide a basis for the reasonable selection of structural parameters of the new twin-screw pump.

Research on Probability Analysis Technology of Circular Section Cabin Socket Structure Based on APDL

In the strength design of sleeve joint structure, manufacturing tolerance and fit clearance are generally ignored. The load of connecting screw is usually calculated by the method of linear distribution. The contact force between screw and cabin is usually simulated by deterministic finite element method. The command flow of probability analysis for typical circular section socket structure is developed based on APDL. The uncertainty of manufacturing tolerance and fit clearance for socket structure is defined as random input variables, such as the cabin diameter, cabin hole position, and cabin aperture and so on. Monte Carlo method is used in probability analysis, and the input variables are random uniform distribution. The analysis results show that the transfer load of screws is redistributed under the probability analysis compared with the finite element analysis, and some screws bear larger load, while the nearby screws bear smaller load. At the same time, the load transferred by screw is not only affected by its own variables, but also by others. The probability analysis method can fully consider the influence of manufacturing tolerance of the structure, and evaluate the structural strength margin more accurately. It can not only prevent the harm caused by uncertainty of random manufacturing tolerance, but also prevent over design caused by conservative method.

Failure analysis of shot-piston used in squeeze casting process equipment

The failure investigation has been conducted on shot-piston used in injection system of squeeze casting equipment to clarify its failure mechanism. The macroscopic morphology of failed shot-piston showed there were many network cracks on its upper-end surface while the cylindrical surface was seriously worn. Further studies were carried out on the two surfaces respectively. Firstly, the shot-piston upper-end surface was sampled. And the crack distribution and depth were observed. Then, the crack micromorphology was investigated by scanning electron microscope (SEM), and the sampling points inside cracks were analyzed by energy dispersive spectrometer (EDS). The results show the shot-piston upper-end surface produces thermal stress cracks due to the high-temperature thermal cycle, and oxidation occurs in the cracks. The same method was also used for the cylindrical surface failure mechanism analysis. Above all, the cylindrical surface was sampled and the wear morphology was measured. Afterward, the material composition of the bulge on the cylinder surface and the micromorphology were confirmed by SEM and EDS. The results demonstrate the main failure forms are abrasive wear and adhesive wear. The inconsistent thermal deformation of the shot-piston and shot sleeve caused changes in the fit clearance and resulted in friction and wear. Simultaneously, the metal solution and oxygen erode the shot-piston matrix through the furrow, accelerating wear and failure. According to the failure mechanism of different surfaces, shot-piston service life can be extended by optimizing the squeeze casting process, controlling the temperature gradient, and selecting the appropriate fit clearance, which has important engineering significance.

Dynamic force transmissibility of flywheel rotor systems supported by angular contact ball bearings considering clearance fit

This study investigates the dynamic force transmissibility (DFT) of angular contact ball bearings (ACBB) supported flywheel rotor systems (FRS) considering the clearance fit. By introducing the influences of combined load and contact angle variation in the Jones formula, the internal load distribution and nonlinear stiffness of ACBBs are accurately solved. The rigid inner/outer ring contact model is adopted to characterize the clearance fit between the ACBB outer ring and mounting sleeve. Based on the Hertzian contact theory, the discontinuous and nonlinear support stiffness caused by the clearance fit is obtained analytically. The lateral vibration model of the FRS considering the fit clearance and ACBB nonlinear support stiffness is established. Combined with the harmonic balance method and alternative time/frequency technique, the DFT of the system is determined, and the stability of the results is proved. Numerical integration and dynamic tests are used to verify the accuracy of the analytical model and solution method. Based on these, the effects of unbalanced mass, fit clearance, axial preload, and rotor damping on the DFT are discussed. The support stiffness of the FRS is nonlinear after considering the ACBB and fit clearance. The amplitude of the unbalanced mass determines the nonlinear characteristics of the system. Increasing the fit clearance decreases the speed corresponding to the peak of the DFT curve. The resonant peak of the DFT curve shifts to the high-speed region with an increase in axial preload. In addition to increasing the peak value of the DFT curve, reducing the damping coefficient causes a soft-to-stiff alternation phenomenon in the system DFT curve. The results provide an important reference for designing a reasonable vibration isolation system to reduce the transmission of micro vibrations of the FRS to a spacecraft platform.

A Kinematic Analysis Method of Double Roller Tripod Joints Based on the Principle of Conjugate Surfaces

Abstract To systematically investigate the contact constraint relationships and the influences of fit clearances on the kinematic performances of a double roller tripod joint (DRTJ), a method for the kinematic analysis of DRTJs is proposed based on the principle of conjugate surfaces. In the proposed method, the constraint relations between rollers and tracks as well as between rollers and trunnions are first derived based on the principle of conjugate surfaces. Then, according to the constructed constraint relationships, the kinematic analysis model of a DRTJ considering the influences of fit clearances is established. Next, the effectiveness of the proposed method is validated by measuring the relative displacements and angles between rollers and tracks via experiment. Finally, kinematic analyses are carried out and the main results show that the relative pitch angle between rollers and tracks are always kept as zeroes under any working condition by designing the shapes of rollers’ outer surfaces to be semi-toroid. The fit clearances have little influence on the kinematic performances of the DRTJ, thus proper fit clearances between rollers and tracks as well as between rollers and trunnions can be designed to improve the lubricating conditions of the DRTJ.

Analysis of uncertainty relation of pin-shaft fitting in mechanical system with clearance

Pin-shaft fit is one of the most basic assembly structures for mechanical products, and the fit clearance plays a decisive role in the performance, safety and effective operation of the product. Taking the uncertainty of the shaft hole clearance fit in the positioning process as the research objective, based on the analysis of the factors affecting the uncertainty of the shaft hole clearance fit in the positioning process, an information entropy model of the shaft hole machining uncertainty is constructed to quantify describe the uncertainty of the shaft hole clearance fit. The uncertainty index of shaft hole clearance fit is proposed to comprehensively characterize the uncertainty of shaft hole clearance fit accuracy. And analyze the inherent relationship between the uncertainty index and the accuracy of shaft hole clearance fit keeping reliability. The effectiveness and feasibility of the method are verified through examples.

Influence of Fit Clearance on the Stability of “Three Oil Film-Rotor” Structure

Influence of Fit Clearance on the Stability of “Three Oil Film-Rotor” Structure

Raceway Defect Frequency Deviation of Full‐Ceramic Ball Bearing Induced by Fit Clearance in Wide Temperature Ranges

Full‐ceramic ball bearings are widely applied in wide temperature ranges due to their excellent thermal shock resistance, and the condition monitoring and fault diagnosis are mainly conducted through the spectrum analysis based on the defect frequencies. However, the outer ring has a spinning motion in the temperature‐related fit clearance, which leads to the deviation of raceway defect frequencies, and is not conducive to the fault diagnosis. In this paper, the temperature‐related fit clearance is considered in the dynamic model, and defects are added on the inner raceway and outer raceway. The motions of the rings are calculated and analyzed in the frequency domain, and the trends of peak frequencies with temperature are investigated. Simulation and experimental results show that the spinning speed of the outer ring increases with temperature, and the defect frequencies exhibit obvious deviation in wide temperature ranges. In a temperature range of 500 K, the defect frequencies exhibit deviations of over 3%, which is obvious in the defect frequency identification. The results provide insights on the full‐ceramic ball bearing dynamics and help with the fault diagnosis and status monitoring of the relevant devices.

Passive vibration reduction of a squeeze film damper for a rotor system with fit looseness between outer ring and housing

Clearances between bearing outer ring and sleeve can generally be maintained to provide a margin for the thermal expansion of the bearings. However, temperature variation, improper assembly and long-term vibration can enlarge the clearances and accelerate mechanical wear, leading to what is known as the fit looseness fault. Therefore, it is important to study a fit looseness fault model and investigate how to control the vibration coming from the fit looseness fault. In this paper, a Jeffcott rotor system with three disks was modeled as a single unit. A fit looseness model was applied in the whole rotor model to study the contact problems and response characteristics using a numerical integration method. Then, a squeeze film damper model was applied to assess the vibration reduction effects on the whole rotor system with the fit looseness fault. By comparing the results of the fit looseness fault without squeeze film damper and with squeeze film damper, it is found that the squeeze film damper can reduce nonlinear vibration responses effectively generated by the fit looseness fault for the nonlinear contact. This research work contributes to understanding the mechanism of fit looseness fault and controlling strong nonlinear vibration responses due to the fit clearances.

Qualitative research on the relationship between spindle vibration characteristics and bearing thermal load

The dynamic performance of machine tool is one of the most important factors affecting the machining accuracy. As the core part of machine tool, the dynamic performance of spindle directly determines the performance of machine tool. In this paper, the spindle of machine tool is taken as the research object, and the change of fit clearance between bearing inner and outer rings, rotating shaft and bearing seat caused by spindle bearing heat, and its influence on the stiffness of spindle system are analyzed. Based on Timoshenko beam theory and finite element method, this paper qualitatively analyzes the variation characteristics of spindle stiffness caused by bearing overheating and grease lubrication failure during high-speed machining.

Investigation of the orbit-spinning behaviors of the outer ring in a full ceramic ball bearing-steel pedestal system in wide temperature ranges

Owing to the difference in thermal deformation of the ceramic outer ring and steel pedestal, the outer ring experiences orbital and spinning motions in the fit clearance in wide temperature ranges, which has significant impacts on the bearing performance. In this paper, a dynamic model considering the temperature-related clearance is proposed, and the interactions between bearing and pedestal are calculated with a loose outer ring boundary condition. The orbit and spinning speeds are obtained, and the parameters concerning the speed ratio are used to evaluate the dynamic behaviors of the outer ring. Parametric analyses of temperature, rotation speed, and external load are conducted, and the results are verified through an experiment. The results show that changes in orbit-spinning behaviors are produced by variations in contact forces and area, and increased axial preload improves the stability of the bearing system. The results provide insights on bearing dynamics, and are useful for the design of ceramic bearing systems.

Experimental study on the failure of tangential anti-loose dowel of ship hydraulic fluid tubing in alternating torque and vibration environment

The internal hydraulic fluid tubing in central shaft is a critical part of pitch adjusting paddle in the ship propulsion system. The failure of screw pairs of internal hydraulic fluid tubing will result in a loss of propulsion. This real accident has happened on a ship. In order to determine the reason for the tangential anti-loose dowel falling out from the screw pairs, 380.5h and 147h alternating torque and vibration environment tests are completed on two samples with difference of manufacturing processing. The result shows that alternating torque and vibration combined stress is the synthesis stress for the dowel falling out from dowel hole. The basic reason is the larger fit clearance between dowel and dowel hole. This clearance is suggested to be manufactured below 0.2∽0.3mm, and the value of diameter for piercing outside the dowel hole should be greater than 1.95mm.

Influence of water-based drilling fluids on the performance of the fluidic down-the-hole hammer

Fluidic down-the-hole (DTH) hammer is a recently explored percussion drilling tool for the production of boreholes in hard rock. It has been proven efficient for exploration core drilling, geothermal drilling, and oil and gas drilling. Previous studies of this hammer have concentrated on its performance operating with clear water rather than water-based drilling fluids with additives. As the first step to filling the gap of knowledge in this area, this study was designed to explore only the performance of an SC86–H fluidic DTH hammer driven by water-based drilling fluids with various temperatures and different contents of bentonite and barite. Such performance was characterized in terms of output power, motion characteristic and operating pressure drop, and compared with that driven by water. The results showed that the output power of the SC86–H type hammer driven by drilling fluids with bentonite content <3% was better than that driven by water thanks to the lubrication effect in the fit clearance, whereas with bentonite content ≥3%, its output power was in the range or below that driven by water due to the elevation of the hydraulic losses and the frictional drag. Its operating pressure drop is only insignificantly influenced by the bentonite content. As the weighting agents in the drilling fluids, the barite particles impeded the smooth motion of the piston. However, the increased impact energy and output power can entirely offset the disadvantage mentioned above. Temperature affects the performance of the SC86–H type hammer by influencing the viscosity and density of the drilling fluids. Some optimal schemes are suggested for the rational design and application of the fluidic DTH hammer in practice. In summary, the SC86–H type hammer operated well in the drilling fluids with realistic fluid power levels. It means that the fluidic DTH hammer has good adaptation and robustness, which is favorable to practical application.

Deformation and leakage mechanisms at hydraulic clearance fit in deep-sea extreme environment

Hydraulic system is widely used as a power source in deep-sea operation equipment. The sealing performance and the relative movement of the parts in hydraulic components are significantly affected by the structural deformation at the clearance fit and the viscosity increase of the hydraulic fluid medium, which are both caused by high seawater pressure. In this paper, the deformation formula at the clearance fit in the deep-sea environment is deduced, which indicates that the deformed height of the fit clearance decreases linearly in the axial direction. A minimum clearance design criterion is proposed, and it is found that the smaller the difference between the bulk modulus of the matching parts and the fit radius are, the smaller the variation of the height of the fit clearance is under various working conditions and the smaller the required minimum initial height is. The leakage flow rate formula at the clearance fit in the deep-sea environment is deduced as well, which introduces modified factors to consider the effects of structural deformation, viscosity increase, and eccentricity. The calculation result shows that under the condition of 11 000 m deep sea, the leakage flow rate calculated by the classic formula is about five times larger than that of the modified formula. Multi-parameter fluid–solid-interaction simulations are carried out to verify the correctness of the deduced deformation and leakage flow rate formulas. The leakage flow rate of the situation with inclination involved is also analyzed through numerical simulations.

Effect of Diameter Expansion Ratio on Recovery Properties of TiNiFe Alloy Pipe Coupling

The reverse transformation temperature, recovery strain and pull-out force of TiNiFe alloy pipe couplings under different diameter expansion ratios (7%, 9%, 11%, 13%, 15%) were studied. The results show that the martensite reorientation occurs and the elastic strain energy released decreases with the increase of the expansion ratio, which leads to the increase of martensite reverse transformation temperature as’ and Af’. The recovery strain increases and the recovery rate decreases with the increase of expansion ratio. The expansion ratio of pipe couplings has a great influence on the pull-out force, which is related to the fit clearance and the diameter of the connected rod. When the fit clearance is the same, the larger the expansion ratio is, the greater the pull-out force is, and when the diameter of the connected rod is the same, the pull-out force decreases with the increase of the expansion ratio.

Research on the seawater-lubricated sliding bearing of a novel buoyancy-regulating seawater pump considering the working depth

ABSTRACT Seawater hydraulic pump is a key component in buoyancy regulation systems. In this paper, a novel full-water-lubricated three-plunger seawater pump was designed in which the plunger suction and drainage are driven by the crankshaft. For this structure, the sliding bearing that supports the crankshaft is a very important factor affecting the pump characteristics. The pressure flow model and the thermal coupling system model of the left/right sliding bearings were established, and the deformation of the left/right sliding bearings in the deep sea environment was analysed by ANSYS Workbench. The change of the fit clearance has a great influence on the work of the hydraulic pump. Different fit clearances at different seawater depths under different radius gaps are obtained. The results show that the fit clearance of the left/right sliding bearings decreases as the depth of the seawater increases. As the depth of the seawater increases, the sliding bearing is gradually changed from the frictional lubrication of the liquid to the boundary friction lubrication. With the increases of the radius gap, the working water depth of the hydraulic pump first increases and then decreases, and the optimal radius clearance and the optimal working depth are obtained.

Research and Experiment of Repairable Space Telescope Interface System

Space technology is the core competitiveness of a powerful country. Space maintenance technology has just started in our country. The biggest innovation of this article is to design a set of interface system, which is suitable for on-orbit maintenance of space science instruments. It represents that this technology from scratch in our country. A new measuring method is proposed. According to the homogeneous coordinate transformation, the mathematical models of the relationships between fit clearances of interface system and the six-degree of freedom change of the maintenance module are derived. According to the index requirements, the corresponding fit clearance and repeat positioning accuracy are determined. Set up an experimental platform, and use autocollimator and laser tracker to measure the repeated positioning accuracy of the module. Based on the theory of small displacement, the least square method is used to deduce the rotation angle and translation amount of the module through the change of the characteristic point coordinates. The experiment proves that the interface meets the requirement of on-orbit maintainable operation, and the experimental data proves that the theoretical equation is correct. Providing engineering reference for other space maintenance scientific instruments.

Nonlinear Dynamic Analysis of Rotor-Bearing-Pedestal Systems With Multiple Fit Clearances

Dynamic analysis of a rotor-bearing-pedestal system with multiple bearing clearances is conducted in this study. Firstly, Jones-Harris method is used to deduce the equivalent nonlinear support stiffness of angular contact high-speed ball bearing with preload considered. Ignoring the structural deformation, the contact model of inner and outer rings with clearance is used to describe the clearance fit between the outer ring and the sleeve, and between the sleeve and the bearing pedestal. Based on Hertz contact theory, the discontinuous and nonlinear support stiffness is then obtained. The lumped parameter model of rotor-bearing-pedestal system is established and verified based on dynamic test results. Based on this, the influence of clearance fit parameters and external excitation parameters on the vibration response amplitude of the system is analyzed. When the radial displacement is greater than the fit clearance, the radial support stiffness changes abruptly and increases rapidly. If it increases to a certain value, the increase of radial stiffness would slow down. The vibration response curve appears sub-harmonic resonances and amplitude jump. The increase of the fit clearance aggravates the vibration response level, the resonance speed of the system moves to the low speed, and the jumping phenomenon becomes more prominent, which is not conducive to the stable operation of the rotor system.

Experimental Investigation on Contaminated Friction of Hydraulic Spool Valve

This paper focuses on the contaminated friction of fit clearance between the spool and valve body to explore the influence principles of clamping stagnation phenomenon. From the perspective of surface morphology and size of particulates in the clearance, designing and manufacturing the valve body, rough spool, conical spool, and standard morphology spool, the test bench was built up and the curves of real-time contaminated friction in the movement of spools were obtained through experiments. The curves show that the contaminated frictions have a feature of pulsation; meanwhile, the stagnation-sensitive size of particulates is between 0.7 and 0.9 times that of clearance. Compared to the ideal morphology spool within the range of sensitive size, the contaminated fiction of rough spool is increased, whereas the lower limit of stagnation-sensitive size range of particulates on conical spool is decreased. The contaminated friction is gradually increased on cis-conical spool but increased first and then decreased on invert cone spool.