Dry Bearings Research Articles

Transforming municipal cotton waste into a multilayer fibre biocomposite with high strength

We analyzed the problematic textile fiber waste as potential precursor material to produce multilayer cotton fiber biocomposite. The properties of the products were better than the current dry bearing type particleboards and ordinary dry medium-density fiberboard in terms of the static bending strength (67.86 MPa), internal bonding strength (1.52 MPa) and water expansion rate (9.57%). The three-layer, four-layer and five-layer waste cotton fiber composite (WCFC) were tried in the experiment, the mechanical properties of the three-layer WCFC are insufficient, the five-layer WCFC is too thick and the four-layer WCFC had the best comprehensive performance. The cross-section morphology of the four-layer WCFC shows a dense structure with a high number of adhesives attached to the fiber. The hardness and stiffness of the four-layer cotton fiber composite enhanced by the high crystallinity of cellulose content, and several chemical bondings were presence in the composites. Minimum mass loss (30%) and thermal weight loss rate (0.70%/°C) was found for the four-layer WCFC. Overall, our findings suggested that the use of waste cotton fiber (WCF) to prepare biocomposite with desirable physical and chemical properties is feasible, and which can potentially be used as building material, furniture and automotive applications.

Study of bearing strength for injection molded GFRPP composites under dry and wet conditions

Thermoplastics and fiber-reinforced thermoplastics represent great deals in nowadays industries and applications where some of these applications are projected to wet environment. The present study investigates the effect of water moisture on the bearing strength (BS) of Polypropylene (PP) and glass fiber (GF) reinforced Polypropylene (GFRPP) composites. PP and GFRPP are produced by injection molding using different GF weight fractions (wt%), 10, 20, and 30 wt%, and two different initial fiber lengths 12 and 24 mm. A burnout test indicated that produced specimens with 12 mm long fibers have higher final fiber lengths than those made of 24 mm long fibers. More water was absorbed for higher GF weight fractions. The results of the dry bearing test showed higher bearing strengths for specimens with higher GF wt% and longer fibers. The same observation was obtained from wet tests, while, wet-tested specimens of all compositions have higher strengths than their dry counterparts. Strain-at-break seemed to be significantly reduced by water absorption for all specimens. Specimens tested in wet conditions have different fracture morphology than dry ones due to the change in the mechanical behavior of the materials after water immersion.

Gleitlagerprüfstand mit erweiterter Sensorik zur Bestimmung der tribologischen Verschleißcharakteristik von Werkstoffen

Friction and wear as important tribological parameters in dry running plastic plain bearings are largely determined by pressure, sliding speed and contact temperature. This paper presents a methodology for evaluating and comparing different thermoplastic materials and their filler packages for use in plain bearings considering these parameters. Bearing manufacturing, test rig setup and test program, as well as the detailed analysis of data and specimens are explained. Various calculation methods are used to remove external influences from the raw sensor data, and to determine characteristic values for temperature and wear directly in the contact zone.

High performance polymer composites - Influence of processing technique on the fiber length and performance properties

High performance polymer composites, (especially short fiber reinforced) have gained immense importance in the field of tribo-materials, especially for dry bearings. Among various key parameters controlling the final performance, the processing technique is the one, which is least investigated. Injection molding leads to a uniform dispersion and distribution of fibers but at the cost of an excessive reduction in the aspect ratio of fibers. Compression molding of short fibers retains their aspect ratio to a greater extent, but at the cost of inefficient dispersion of fibre strands. Interestingly, both the factors viz. High aspect ratio of fibers and excellent dispersion are important for deciding the performance of composites.In this work, two composites (Poly aryl ether ketone - 50 wt%, short glass fibres (length – 3 mm)– 30 wt % and synthetic graphite - 20 wt%) were molded by injection (I) and compression (C) molding. These were tribo-investigated in adhesive and abrasive wear modes in identical conditions. Based on thermal degradation of composites at 600 °C, the final fibre length was observed as 200–300 μm and 1.5 mm for I and C composites respectively. Both the composites showed low specific wear rate (K0) (~10-16 m3/Nm) and coefficient of friction (μ) (~0.03–0.05). Similarly, for abrasive wear, K0 and μ were observed ~10-10 m3/Nm and ~0.5–0.7 respectively. μ of I composite was lower in all conditions. The composite C was superior to the I in wear performance in adhesive wear, but not in abrasive wear. Worn surface analysis was done to understand the wear mechanisms.

On the significant tribo-potential of PAEK based composites and their dry bearings

Abstract The current work focusses on the designing and manufacturing process followed by tribo-evaluation of high-performance polymeric bearings based on tribo-optimized composition in earlier work on pin on disc configuration. A series of bearings was developed by a combination of graphite (10 wt%) as a primary lubricant and particles of metal chalcogenides (MoS2 and WS2) in micro and nano-form as secondary lubricants (10%) into Polyaryl ether ketone (PAEK) matrix (50%) reinforced by 30% glass fibers (GF). Tribo-performance assessment of bearings against shaft was critically done and performance of the product (bearing) and material (pin against disc) was critically compared to understand the difference in performance, from material to the product.

Diagnosing simultaneous faults using the local regularity of vibration signals

The regularity of the vibration signals measured from a rotating machine is often affected by the condition of the machine. The fractional order of regularity can be measured using the definition of Hölder continuity. In this paper, we review the connection between the pointwise Hölder regularity of a signal and its wavelet transform. We calculate the wavelet transform modulus of acceleration measurements from a test rig. The effects of different faults were recorded, such as unbalance, the coupling misalignment of a claw clutch, the absence of lubrication in a ball bearing, the absence of the bearing’s cage, and their combinations. An analysis of the estimated isolated pointwise regularities from the wavelet transform modulus maxima ridges shows that the faults often cause irregularities in the signals and that their locations and frequencies can be used in diagnosing the faults. Coupling misalignment and the absence of lubrication in a ball bearing both cause impact-like vibrations, but these impacts have positive and negative regularities in the case of a coupling misalignment and mainly negative in the case of a dry bearing. Unbalance is best diagnosed from the integrals of the acceleration signals using traditional methods. In diagnosing the misalignment, bearing problems and simultaneous faults, the local regularity analysis outperforms the use of high order norms of differentiated acceleration measurements (i.e. jerk and snap signals). Using just three features (the number of local irregularities in an acceleration signal, their mean Hölder regularity and the arithmetic mean of the absolute values of a velocity signal), a quadratic classifier can be constructed whose estimated classification error is only 0.3%.

CHALLENGES AND METHODS IN ANALYZES OF THE HEAT TRANSFER IN POLYMER DRY BEARINGS

Heat generation and dissipation in dry polymer bearings are important aspects in their design and operation, because the overheating may lead to fast wear or product damage. The estimation of the maximum temperature under defined load conditions is crucial, but it is also a challenging task. Firstly, it is difficult to measure temperature directly at the contact surface between the bearing and the shaft. Secondly, thermocouples that are commonly used as the temperature sensors might create measurement errors. The work presented in this paper utilizes the numerical model of a polymer bearing for the analysis of the internal temperature field. The model is validated with use of experimental data; and, in order to mitigate the measurement errors of the thermocouple sensor, their geometry and properties are included in the simulation model. The achieved agreement between simulation and experimental temperatures is 10% on average, and it is judged that the numerical model may be applied for thermal analysis of the polymer bearing. The obtained results confirm the influence of the thermocouples with metallic sheaths on the temperature distribution inside the tested polymer bearing. It is shown that the value of the measurement errors depends on the layout of thermocouples and might be significantly reduced by their proper arrangement. It is believed that the presented approach for the analysis of thermal performance of dry polymer bearings might be applied to similar cases, which are characterized by large temperature gradients and require temperature sensors, that are made of the materials of high thermal conductivity.

Static Ball Bearing Thermal Conductance in Air and Vacuum: Review and Correlation

A literature review of static ball bearing thermal conductance in both air and vacuum was performed, with an emphasis on understanding the conductance that would be expected across ball bearings of various sizes. Although a large number of variables can affect bearing thermal conductance, the review and survey of 353 data points from previous studies indicates that a reasonable relationship between the bearing size and thermal conductance exists. Correlations of bearing conductance as a function of the bearing outside diameter were developed for dry, marginally lubricated, and flooded bearings in vacuum. The correlation for dry bearings is a less accurate, but more convenient, order-of-magnitude estimate than the analytical expressions widely available in the literature for dry bearings. However, the marginally lubricated and flooded correlations have -squared values of 0.87 and 0.89, and 95% of the data points for these bearings fall within 50% of the value given by the proposed correlations. This work is of practical use to engineers who seek to estimate the static bearing thermal conductance in vacuum and atmospheric environments.

Attaining high tribo-performance of PAEK composites by selecting right combination of solid lubricants in right proportions

In the present study, tribo-potential of a combination of two solid lubricants (SLs) viz. a special graphite i.e. thermographite (TG) and hexa boron nitride (hBN) in a series of composites with fixed amount of short glass fibers (GF 30 wt %) and Polyaryletherketone (PAEK- 50 wt%) was investigated under severe operating condition (Load 900 N (Pressure-28 MPa), speed >1.6 m/s) against mild steel disc till the composites failed. All the composites showed excellent performance under very high PV (pressure and velocity) values and the performance depended mainly on operating parameters and amount of two SLs in the composites. It was observed that 20% of a single SL (either TG or hBN) did not show very good results, although TG inclusion proved better than hBN. When these two SLs (20%) were used in combination, synergistic effect was observed and best performance was exhibited by a composite containing 5% hBN and 15% TG with the highest PV limits of 102.2 MPa m/s (900 N, 3.65 m/s) along with very low μ (0.04) and specific wear rate (5.68 × 10−16 m3/Nm), followed by composite with 10% TG and 10% hBN. Combination of 15% hBN and 5% TG stood next in performance. Synergism in tribo-performance due to combination of two SLs was reported for oils and friction materials but not for high performance anti-friction materials. Such composites have excellent potential as materials for dry bearings, gears etc. The Scanning electron microscopy (SEM) and Energy Dispersive X-ray analysis (EDAX) studies on worn surfaces proved beneficial to understand how the fiber-matrix bonding was affected due to different combinations of SLs and how it affected wear performance.

Validation of horizontal auger drilling string assembly design based on dry bearings

The authors identify some factors that govern energy input of borings removal from hole bottom to an unloading point using auger drilling string assembly. Of specific significance appears to be the factor of insufficient reliability of anchor gears and centering devices of the drilling string assembly, which makes continuous drilling impossible without permanent servicing. The article gives the analysis of bench testing data of bearings with antifriction filler for drilling string mounting groups to be serviced outside the areas of drill holes. The design solutions based on the investigation results and aimed to improve reliability of anchor gears and centering devices of an auger drilling string assembly are described.

AN ATTEMPT AT IDENTIFYING THE INFLUENCE OF TEST HEAD ASSEMBLY STIFFNESS ON THE RESULTS OF A TRIBOLOGICAL EXPERIMENT CONDUCTED UNDER MICRO-OSCILLATION CONDITIONS

The outcome of experimental research on a group of dry bearing materials carried out under small oscillation conditions and using a test rig designed and made at Gdansk University of Technology inspired the decision to find out if the stiffness of test head elements influenced the generated results. Therefore, a computer model utilising finite elements was devised and used to simulate the workings of the test head. The model enabled full control of the head’s geometry, and loading and boundary conditions at every stage of simulation. Moreover, the simulation includes the preparation of test head elements, fixings, and the specimen loading, and executes the displacement of the counter-face during full-cycle reciprocating motion. Finally, the results of computer simulation are compared with those produced by experimental testing.

Role of treatment to graphite particles to increase the thermal conductivity in controlling tribo-performance of polymer composites

A novel type of graphite (thermographite) having higher thermal conductivity (TC) due to a patented treatment is commercialized recently. It was anticipated that such particles would be more effective in conducting away frictional heat generated on the tribo-surfaces leading to the enhanced performance. Hence two composites were developed based on high performance Polyarylether ketone (PAEK) (50% by wt) containing 30% short glass fibers (GF) and hexa-boron nitride (hBN) 10% apart from 10% graphite. First composite designated as CNG contained 10% natural graphite (NG) while the other designated as CTG contained 10% thermographite (TG). These were processed by identical method (twin screw extrusion followed by injection molding). The tribo-performance was evaluated in a pin on disc (mild steel) configuration under very high load and speeds. It was observed that both the composites exhibited excellent tribo-performance. However, CNG performed better than the CTG in all respects only under severe operating conditions. Under low PV conditions, difference was not clear. It showed lower friction coefficient, and wear rate as compared to CTG. CNG showed PVlimit value 96.6MPa-m/s which was decisively superior to CTG (91MPa-m/s). CNG could sustain higher speed (3.45m/s) than the CTG (3.25m/s) under 900N in spite of slightly lower TC. It was concluded that during treatment (patented by the company) TG has slightly distorted layer-lattice structure as compared to the natural graphite, which could be responsible for transferring less beneficial film under severe operating conditions. SEM and EDAX studies were conducted to understand wear mechanisms. Such composites with such high PVlimit values low, µ (0.04) and low wear rates (1×10−16m3/Nm) are not reported in the literature and may prove as ideal materials for dry bearings in harsh operative conditions.

A Study on the Rolling of a Multilayer Plate Composed of Teflon-Cu-SPCC Steel

This work is concerned with rolling of a Teflon-Cu-SPCC steel plate, which has been used as a base material for an oilless bearing or dry bearing. Materials for an oilless bearing require special characteristics such as high wear resistance, low friction, fast heat loss, as well as structural strength. Such superior mechanical properties could be obtained by rolling the multilayer plate composed of a mixture of Teflon-Cu powder and a SPCC steel. The main objective of this research is to investigate the deformation characteristics of a Teflon-Cu-SPCC steel plate during rolling process. Especially, focus is given to the thickness changes of the Teflon-Cu powder mixture layer. An Eulerian finite element method coupled with a contact profile correction algorithm is adopted for the simulation of rolling. Validity of the proposed finite element analysis is given. The important parameters chosen in this work are the reduction ratio, roll size, and the Cu content in a Teflon-Cu mixture. Effects of the above important parameters on the deformation behavior and on the final thickness of a Teflon-Cu mixture layer are carefully studied.

New deep groove ball bearings high frequencies vibration testing

The rolling bearing is a multi-body rotating system with rolling elements, inner, outer rings and cage transmitting motion and load from rotor to the bearing supports and machine body. The existence in the new bearing elements of micro-defects (surface roughness Rz, Rzmax, waviness Ws and of size rolling elements) generate stochastic high frequency vibration. It is important for manufacturing technology to examine quality of new bearings elements. This paper considers a new deep groove ball bearings single row 6205 2RSL C3/P6 experimental vibration testing method for quality assessment of new bearing separating micro-defects in inner raceway from micro-defects in outer races. This method is based on high frequency vibration measurements of lubricated and dry bearings with varied loads. DOI: http://dx.doi.org/10.5755/j01.mech.20.3.6740

PROPOSING A NEW ACOUSTIC EMISSION PARAMETER FOR BEARING CONDITION MONITORING IN ROTATING MACHINES

Bearings are important machine parts and their condition is often critical to success of an operation or process, hence there is a great need for periodic knowledge of their performance. According to reported research works in the past several years, it is believed that the extracted information from acoustic emission (AE) signals can be used for bearing condition monitoring. In this work, a novel parameter based on using the ratio of AE mean (μ) and AE standard deviation (σ), formulated as μ/σ is proposed to distinguish between lubricated and dry bearings. A heavy duty test rig was used in experimental work. Various levels of radial loads and rotational speed (ω) were applied to rotating shaft, which is connected to rolling element bearings. It was found that, except few cases, regardless of various levels of radial loads used, at higher levels of rotational speed, dry and lubricated bearings can be clearly distinguished when using proposed parameter.

The use of acoustic emission information to distinguish between dry and lubricated rolling element bearings in low-speed rotating machines

Bearings are known as the vital parts of machines, and their condition is often critical to the success of an operation or process. Presence of a film of lubricant such as grease between the bearing surfaces minimizes the friction and surface wear. Contaminated grease or lack of lubricant may lead to an ineffective bearing performance or malfunction of the machinery parts. Therefore, in order to avoid unexpected breakdowns, reliable and robust bearing condition monitoring techniques are demanded. According to previous studies, acoustic emission (AE) signals contain valuable information that can be used for bearing condition monitoring and fault detection. The main objective of this study is to evaluate the effectiveness of AE signal parameters to distinguish between lubricated and dry bearings under similar operating conditions. To this end, a low-speed rotating test rig is manufactured and used. Eight levels of rotational speeds and four levels of radial loads were applied to the test rig shaft end, which is connected to the testing bearing. In each test, seven time domain AE parameters were computed. The statistical tools were also used to present the dominant experimental variables on AE signal parameters. According to experimental results, it was found that four AE parameters can be used to distinguish between dry and lubricated bearings.

Planar positioning stage for micro machining

The following article presents an approach for a novel positioning stage as basic component of a small machine tool. It is a parallelkinematic machine (BiGlide mechanism), which converts the linear motion of two linear axes into a planar motion. The novel features, which were identified to be crucial for the transition from conventional machine tools to small ones, are: compact and precise feed axes, backlash free motion transmission, and direct measurement of the tool-center-point position and the ability of additional fine positioning. The proposed implementations are: hydraulic feed units, dry slide bearings as rotational joints, highly precise radar sensors and active variable-length struts of the parallelkinematic machine. Some of the simulation results are presented along with measurements of a currently designed prototype.

Pavement Subgrade Improvement by Lime

The subgrade soil of western by Pass Road Mardan, Pakistan consists of silty clay belonging to A-6(14) group of the AASHTO soil classification system. The average natural moisture content of the soil is more than 18% which makes it susceptible to water logging and problematic for pavement construction. The aim of this research is to improve the supporting power of the existing subgrade material to carry the proposed traffic safely. For this purpose, lime was incorporated into the soil. Soil samples were prepared containing 0, 4, 6, 8, 10 and 12% lime by weight of the soil. Laboratory tests were conducted for determining particle size distribution, Atterberg limits, optimum moisture contents and maximum dry density and California Bearing Ratio (CBR). From this study it was found that the CBR initially increased with increase in lime content, reaching to a maximum value (35.50 %) at 6% lime content and then decreased with further increase in lime content. The optimum lime content for CBR was found as 6.50% (w/w), which enhanced CBR value by 337% compared to control. A consistent decrease from 1.92 at 0 to 1.763 (g/cm3) at 12% lime was observed suggesting compaction in the material. Results suggested that liming subgrade material is a viable option for improving pavement.

Mix design with low bearing capacity materials

The roadway construction requirements for soils are generally fixed by standards. The most common constraints involving materials are Optimum Moisture Content (OMC), Max Dry Density (MDD) and bearing capacity predictable by using Proctor test and CBR test. These traditional tests are combined with other simple field tests to gain the max density. However, the use of low bearing materials such as clay and silt, and local resources is an important means of simplifying and economizing the road building still further. The main purpose of this experimental analysis is a procedure to characterize some road materials by its bearing capacity (CBR and MDD) from two simple standard tests (sieve analysis and Atterberg limits), and then a method to employ silt and/or clay in road mixture. The planned method suggests the minimal volume of high quality material in the roadway mixture added to silt and clay that must be available in the analyzed location, obtaining an ideal bearing capacity. Different soil types from various quarries and digs located in Southern Italy were used. The classic laboratory tests to assess the soil properties of all amassed study soils were carried out, i.e., the Atterberg limits and Grain Size Distribution (GSD). Correlations based on linear regression were then performed to determine the optimal combination of the properties measured with dependent CBR variables and Max Dry Density (MDD) to be predicted for low-volume roads. These equations were then validated by using four material types from outside the calibration sample.

A comparison of methods of modelling the bearing surfaces in an internal combustion engine

An existing model for the dynamic analysis of the piston motion in an internal combustion engine has been modified to incorporate a simpler representation of the piston–cylinder interaction, and to represent the main and big-end bearings as lubricated rather than dry journal bearings. The results demonstrate that the differences in calculated bearing forces and output torques are negligible, indicating that the simple dry journal bearing model is sufficient, but show that the modelling of the interaction between piston and cylinder is considerably improved.