Showing 15 results for Lubricant
H. Binaie, R. Sarraf-Mamoory, M. Zahir-Mirdamadi,
Volume 6, Issue 1 (9-2006)
Abstract
The friction materials are generally consisted of homogeneous dispersed friction materials in a metallic based which produced via a process of compaction and sintering of metallic powders, hard materials, and if necessary lubricant. The role of these materials in the components is transferring kinetic energy to heat and generating torque (brakes and clutches). This research is a property investigation of effected parameters in manufacturing of bronze based friction materials which is used in heavy automotive clutch plates, helicopter brakes, and etc. Four compositions were selected for bronze friction materials and different parameters such as compaction pressure, sintering time and temperature on density, porosity, and hardness were studied. The nearest results to imported samples are: compaction pressure of 5 t/cm2, sintering time and temperature of 30 min. and 820 DC respectively. The wear resistant in [mal sample containing 2% of hardened additives was determined by ASTM G-I05 standard and compared with foreign samples. The sample containing WC had the closest property and microstructure with imported samples.
Saleh Akbarzadeh, Abolfazl Ebrahimi Serest,
Volume 14, Issue 10 (1-2015)
Abstract
Gears are one of the most important elements of any power transmission system. Among all types of gears, helical gears are more common due to their high capacity in power transmission as well as lower level of noise. The aim of this study is to present a model for analyzing the contact of teeth of helical gears considering thermal effects and surface roughness. In the present model, each helical gear is divided to several narrow spur gears in which each of the spur gears have a small rotation angle relative to the previous one. Also each contact point of gears is replaced with contact of two equivalent cylinders. Considering the fact that the governing regime for gears lubrication is the mixed-elastohydrodynamic regime, the total load is carried by lubricant and asperities' contact. Meshing and lubrication analysis of a pair of helical gears is conducted based on the load-sharing concept and parameters such as film thickness, friction coefficient and temperature rise are predicted. The predictions based on the load-sharing concept are compared to other published results Acceptable accuracy, short execution time along with considering thermal and roughness effects are some of the major characteristics of this study.
Hamed Hassanpour, Amir Rasti, Mohammad Hossein Sadeghi, Mohamad Hossein Saadatbakhsh, Ahmadreza Omiddodman,
Volume 14, Issue 14 (3-2015)
Abstract
AISI4340 hardened steel have a vast functionality in industries. Hard machining of this steel have several benefits such as, higher productivity, lower production cost and improved workpiece properties. In machining operation, ultimate surface roughness is the most important characteristic of machined surface and plays an important role in workpiece life. One of the effective factors on surface integrity is cutting fluid used in machining operation, which have health and environmental problems is spite of positive effects. As a result, using minimum quantity lubrication is considered as an alternative method. In present study, relations between milling parameters and final surface quality in milling of AISI4340 hardened steel, in the presence of lubrication systems including; dry, wet and minimum quantity lubrication have been investigated. Cutting speed, feed rate, axial and radial depth of cut have been considered as main parameters of milling operation. Totally, 90 experiments have been done using response surface method to analyze the effects of process parameters on surface roughness. Results revealed that feed rate and cutting speed have the most Influences on surface roughness. Also higher values of cutting speed and lower values of feed rate are necessary to reduce surface roughness. In addition, compared to other lubrication methods, minimum quantity lubrication have the best performance in surface quality, especially in high cutting speed and depth of cut.
Sasan Rahmanian, Mohamad-Reza Ghazavi,
Volume 14, Issue 15 (3-2015)
Abstract
In general, in dynamic analysis of mechanical systems, joints are assumed to be ideal. However, due to errors in fabrication and assembly of components, existence of joints clearances is an inevitable issue that caused frequent collisions between the journal and bearing and stable periodic behavior of system becomes chaotic. Degradation the dynamic performance of the system, reduction in fatigue life of components and produce undesirable vibrations are all of the factors resulted from impact- contact forces due to joint clearance. First, different contact force models for two surfaces has been introduced and dynamical models of revolute joint with clearance for two modes, namely, dry contact model and lubricated joint model is then presented. In this paper, the dynamic behavior of a slider- crank mechanism with a revolute joint clearance between the slider and connecting rod, using the Lankarani-Nikravesh contact force model is studied and compared to the ideal case. Considering the effect of friction between journal and bearing, governing equations of motion of the system for two phase, contact and non-contact modes are extracted and it is shown that system exhibits chaotic behavior under specified size of clearance. A fluid lubricant is used in clearance between journal and bearing for stabilizing an unstable periodic orbit embedded in the chaotic attractor.
Mohammad Mahdi Jalili, Mahdi Zare Mehrjardi, Reza Rashidi,
Volume 14, Issue 16 (3-2015)
Abstract
In this article, using finite element method the effects of the preload on the nonlinear dynamic behavior of the noncircular two lobe aerodynamic journal bearing have been investigated. Assuming that the rotor is solid, the governing Rynolds equations for both the gas lubricant and rotor equation of motion in static and dynamic conditions have been derived and performance of the noncircular aerodynamic journal bearing in different conditions has been evaluated. Rung Kutta method has been used to solve the time dependent equations of motions of noncircular aerodynamic journal bearing and its gas lubricant. Using the numerical results, to investigate the motion of the center of the rotor in dynamic conditions, the graphs of frequency response, power spectrum, dynamic trajectory, Poincare map and bifurcation diagram have been plotted. The results show periodic, quasi periodic and chaotic rotor behavior for different bearing preload. It is concluded that appropriate selection of rotor parameters like its preload and suitable design and fabrication of rotor and its bearing can prevent any undesirable perturbed motions of the shaft and both the collision and wear of the rotor and bearing.
Behrooz Zareh-Dsari, Mohammad Abaszadeh, Behnam Davoodi,
Volume 15, Issue 1 (3-2015)
Abstract
Lubrication is an essential factor in sheet metal forming processes such as deep drawing in order to reduce friction at contact surfaces, forming load, tool wear rate and increasing of sheet formability. Various metal oxide nanoparticles can be used as additives to create desirable tribological properties in base lubricants because of their unique properties such as specific surface area. In the present study, the conventional lubricant enhanced by alumina nanoparticles (Al2O3) is utilized in deep drawing process in order to improve frictional conditions. The forming load, surface roughness (Ra) and thickness distribution values of the formed cups were assessed to evaluate the performance of the enhanced conventional lubricant with alumina nanoparticles (Al2O3) in comparison to the conventional lubricant and dry forming condition. The obtained results from experimental tests revealed that adding 0.5 wt.% Al2O3 nanoparticles to the conventional lubricant improves lubrication property significantly and reduces forming load by 16.39% and surface roughness by 19.33% compared to the conventional lubricant. Furthermore, it is observed that using lubricant containing nanoparticle additives results in 23.94% improvement in maximum thickness reduction in critical zone.
Amir Torabi, Saleh Akbarzadeh, Mohammadreza Salimpour,
Volume 15, Issue 4 (6-2015)
Abstract
One of the challenging problems of tribology is cam and follower elastohydrodynamic lubrication due to the simultaneous effect of various lubrication mechanisms. These mechanisms are transient, squeeze film, elastic deformation of contacting surfaces and variation of lubricant properties with pressure. In this paper, besides studying the mentioned factors, the effect of using a non-Newtonian lubricant such as grease is numerically investigated. The lubrication governing equations and Oswald’s grease behavior equation have been discretized using finite difference technique. The system of equation has been solved via Multi-Grid method which is an advanced iterative method in solving system of partial differential equations. The results are showed for Newtonian oil comparing to grease for different cam rotational speed. Also different grease behaviors are investigated. The results are verified by a comparison to the results obtained using the famous Newton-Raphson method. Finding shows that the minimum lubricant thickness as well as the maximum pressures is lower when using grease compared to the case that a Newtonian lubricant is used. In the case of Newtonian lubricant, increasing the speed results in an increase in the lubricant film thickness but it is shown that the speed does not affect the lubricant thickness in the case of non-Newtonian lubricant.
Mahdi Zare Mehrjardi, Asghar Dashti Rahmatabadi, Reza Rashidi Meybodi,
Volume 15, Issue 7 (9-2015)
Abstract
Oil journal bearings are one of the most common parts of high load carrying rotating machine. Stability of these bearings can be affected by various stimulus such as changes in loading and lubrication conditions. Therefore, identification of the dynamic response of journal bearings can improve the control and fault detection process of rotor-bearings systems and prevent them from placing in critical operation condition. Since past, the mass unbalance of rotor is proposed as an effective factor on the dynamic behavior and long life of bearings. For this reason, in this research the effects of this parameter on the stability of hydrodynamic two lobe noncircular journal bearing with micropolar lubricant is investigated based on the nonlinear dynamic model. To achieve this goal, the governing Reynolds equation is modified with respect to micropolar fluid theory and the equations of rotor motion are derived considering the mass unbalance parameter. The static and dynamic pressure distributions of the lubricant film and the components of displacement, velocity and acceleration of the rotor are obtained by simultaneous solution of the Reynolds equation and the equations of rotor motion. Investigation of results in terms of dynamic trajectory, power spectrum, bifurcation diagram and Poincare map show that the dynamic behavior of two lobe bearings appears in different manner with variation of mass unbalance of rotor. The response of analyzed dynamic system include converge oscillations to the equilibrium point, periodic, KT periodic and quasi periodic behavior and also divergent disturbances which leads to collision between the rotor and bearing.
Majid Elyasi, Farzad Ahmadi, Morteza Hosseinzadeh,
Volume 15, Issue 12 (2-2016)
Abstract
Rubber pad forming is a practical and low-cost method of producing metal bi-polar plates with complicated multi- array contours since it only needs a rigid die and a flexible rubber. In this study, 316 stainless steel sheets with the thickness of 0.1 mm were used. To form the plates, a polyurethane rubber was used with the hardness shore of A 85 with the thickness of 25 mm. In order to increase the depth of the channel flow and form filling plates with a high depth-to-width ratio, firstly, the effects of lubricants on shaping metal plates were ignored. Subsequently, by implementing lubricants, their effects on achieving a higher filling depth and a more uniform thickness distribution were investigated. The results showed that in rubber pad forming process, lubricants could be used to further enhance the depth of filling and have a uniform thickness distribution in the channels of generated plates. Moreover, among available lubricants, polypropylene nylon will be the best alternative for the production of bipolar plates due to its high tensile strength and low thickness.
Mojtaba Mehrabi, Mehdi Mohammadimehr, Mohammad Reza Fatehi, Ali Ghorbanpour Arani,
Volume 17, Issue 8 (10-2017)
Abstract
In the present paper, thermal analysis of used spiral bevel gears in main gearbox of helicopter- belong to Iran Aircraft Manufacturing- is investigated. Firstly, with introducing the geometry properties of gears, basic lubrication and thermal analyses are considered based on standards of gear design such as AGMA. Then, in order to create the finite element model, initial and boundary conditions with considering the oil viscosity and calculating the friction coefficient, convection and heat conduction coefficients are determined based on experimental and analytical models in spiral bevel gear. It is noted that, the goal of finite element model is considered to reduce the complex calculation errors and increase the speed of problem solving. Effects of various parameters such as increasing the FLASH temperature and influences of initial temperature on it, contact stresses and heat fluxes, comparison of different mineral oils on the decreasing of temperature and fatigue life are examined. The obtained results of present work show that the FLASH temperature of main gearbox is linear function of initial temperature, so that FLASH temperature increases 56 centigrade in comparison of initial temperature. Also, it is demonstrated that the presence of various mineral oils in this system lead to reduce the solid-solid surface contact and friction coefficient. Moreover, these lubricants cause the cooling in the gearbox and enhancing more temperature, thus the employing these lubricants lead to exceed the system temperature to 90 centigrade.
Mohammad Zamansani, Asghar Dashti Rahmatabadi, Reza Rashidi Meybodi, Mahdi Zare Mehrjardi,
Volume 17, Issue 12 (2-2018)
Abstract
Today, oil journal bearings are widely used as an efficient support for rotary systems in various industries. When these bearings are used by loading in high speed conditions, whirling disturbances in the rotor motion status leading to collisions and abrasion is probable. Designing specific geometric shapes or applying industrial lubricants with different new combinations can affect the journal bearings ability to maintain their dynamic stability in critical situations. From this view, the use of non-circular bearings and non-Newtonian fluids in the field of lubrication has recently been heavily taken into consideration. In the present study by choosing non-Newtonian lubricant simulated by power law fluid model, the effects of design parameters such as eccentricity ratio, aspect ratio and power law index on dynamic stability of noncircular two, three and four lobe bearings are investigated. For this purpose, assuming the limited cycle oscillations of the rotor around the equilibrium point after damping the effects of initial imposed disturbances and using finite element numerical method to solve the governing equations, stability range of the system in form of linear dynamic analysis characteristics is determined based on the whirl frequency ratio and critical mass parameter. The results indicate that by increasing the power law index and decreasing aspect ratio, the dynamic range of bearing support will be developed. Also, by increasing the number of noncircular bearings lobes with power law lubricant and providing the system's positioning conditions in high values of eccentricity ratio, more ability to damping dynamic disturbances can be achieved.
M. Maleki Varnoosfaderani, A. Dashti Rahmatabadi, A.a. Dehghan,
Volume 19, Issue 1 (1-2019)
Abstract
In recent years, due to the increase in the speed of rotary machineries, demands for enhanced lubrication and bearing design to overcome this challenge has increased. To satisfy these need, researchers have proposed additive contained lubricants such as Nano-lubricants and bearings with different designs such as noncircular lobed bearings. In this article, effects of preload and aspect ratio on static performance of noncircular lobed journal bearings of finite length lubricated with lubricant containing TiO2 Nano-particles for particle volume fraction of 0.01 are studied. Using finite element method, the steady-state film pressure is obtained by solving the modified Reynolds equation based on the Nano-lubricants and Couple Stress model theories. With the help of film pressure, attitude angle, friction coefficient, friction force, and side leakage of noncircular lobed journal bearings are obtained. The results show that using lubricants containing TiO2 Nano-particles can enhance the performance of static characteristics of two, three, and four lobed journal bearings. According to results, increase in preload and bearing length will increase load carrying capacity noncircular lobed bearings. Based on results, choosing proper design parameters can have great impact on static performance of noncircular lobed journal bearings.
M. Zare Mehrjardi, A. Dashti Rahmatabadi, A. Rasoolizadeh Shooroki,
Volume 20, Issue 5 (5-2020)
Abstract
The lubricant's ability to maintain the dynamic stability of rotor particularly in special conditions such as operating at critical speeds and instantaneous turbulences in loading or lubricant properties is always one of the most prominent characteristics of the journal bearings. Aspect or length to diameter ratio of bearing is an important factor that in different loading conditions will have an obvious effect on the performance of the trapped lubricant film between the rotor surface and bearings shell. So, the effects of aspect ratio on the damping of rotor disturbances with linear and nonlinear dynamic analysis approaches are studied in this research. Initially, the static equilibrium point of the rotor center in noncircular two, three and four lobe bearings space is obtained using the governing Reynolds equation of micropolar lubrication for different values of aspect ratio. Later, assuming the rotor perturbation as the limit cycle oscillations around the equilibrium point, critical mass and whirl frequency ratio are determined as the linear dynamic stability indexes for recognizing the converging disturbances. In nonlinear analysis model, the simultaneous solving of the lubrication and the rotor motion equations in successive time steps with Runge-Kutta method is done to differentiate the converging or diverging rotor perturbations. Results show that decreasing the aspect ratio improves the stability and the chance of controlling disturbances and returning the rotor center to static equilibrium position. Comparison of linear and nonlinear dynamic analysis results also indicates more cautious behavior and limited stability range of linear model in most of investigated cases.
Sh. Darzi, M.j. Mirnia, M. Elyasi,
Volume 20, Issue 8 (8-2020)
Abstract
Single point incremental forming is a cost-effective process with high flexibility and as a result, would be a proper selection for low-batch and high-customized production compared to traditional processes such as pressing. The target market of this process usually consists of medical, automotive, and aerospace industries in which metals with high strength to weight are highly in demand. These materials are usually formed at elevated temperatures due to their low formability at room temperature. In this study, the AA6061 aluminum sheet was homogeneously heated at 25-400°C. In addition, the effects of important process variables of heat-assisted SPIF including temperature, vertical pitch, feed rate, and three types of lubricants were investigated on formability of truncated cones with various wall angles. According to the results, despite the inability of local heating in enhancing the formability of the AA6061 sheet (37% improvement of formability under optimal conditions), the homogenous heating approach which was used in this article leads to a significant improvement in formability (528%). Temperature is the most important parameters effective on the formability, while lubricant and vertical pitch are ranked as the second and third parameters, respectively and the effect of feed rate is negligible. The critical wall angle increases from 60 to 65 degrees with increasing the temperature from 25 to 400°C. In order to choose a suitable set of parameters, the surface roughness should be taken into account, which may alter the results from 1.18 to 4µm as the best and worst surface conditions, respectively. Furthermore, a truncated cone with a wall angle of 65 degrees was successfully formed to 44mm depth using an appropriate combination of process parameters. This demonstrates an outstanding improvement in formability.
Amirhosein Abasi, Rasoul Safdarian,
Volume 23, Issue 6 (5-2023)
Abstract
Single point incremental forming (SPIF) is a cost-effective process with high flexibility and as a result, it is a suitable choice for low-batch production compared to traditional metal forming methods. In the present experimental research, the warm SPIF with ball nose tool was used in the forming of aluminum tailor welded blanks (TWB) that were joined together by the argon welding process. Aluminum sheets of 6061 and 5083 with an equal thickness of 1.5 mm were used as base metals and joined together using the butt welding method. In this research, the effect of four parameters of temperature, lubricant, step down, and feedrate were investigated on the formability and appearance of aluminum. The temperature range is between room temperature and 290 degrees Celsius, and three types of lubricants are used in the experimental tests. The Taguchi method was used for the design of the experiment. The results of the tests indicated that an increase in the temperature as the most effective parameter led to an increase in the formability of TWB by 79%. The lubrication, step down, and the feedrate was in the next ranks of effectiveness in the formability of aluminum TWB.
