08-16-2017, 09:27 PM
INTRODUCTION
Tribology is defined as science and technology of interacting surfaces in relative motion and of related subjects and practices. However the subject Tribology generally deals with the technology of lubrication, friction control and wear prevention of surfaces having relative motion under load.
The two main constituents of Tribology are friction and wear, which controlled and reduced, automatically increases the service life of machine elements.
In past few years, wood iron and skin have been used as journal bearing materials. Later brass, bronze and white metals have also found some applications. Currently in operation to these materials, aluminum and zinc based material are used as journal bearing materials. With technical improvements, self lubricated sintered bearings and plastic materials are used where continuous lubricating is impossible. Therefore, it is essential that the bearing material be chosen depending upon area of application
Wear resistance is one of the most important properties that journal bearings should posses. There are several and investigations undergone dealing with wear resistance improvement of these materials.
Copper based alloys are widely used as journal bearing materials because they have high thermal and electrical conductivity, self lubrication property, and good corrosion and wear resistance. The effect of tin on wear in copper based materials is important. Copper based tin bronzes are used as bearing materials to have high wear resistance. Friction and wear properties of these materials can be improved by adding tin. Tin bronze (90% Cu 10% Sn) is most suitable bearing materials under corrosive conditions, at high temperatures and high loads.
Zinc based alloys were used instead of bronze during world war II as journal bearing materials to compensate for copper deficiency in Germany. Zn based alloys are used due to high strength, high hardness and good friction properties in several engineering applications. Tribological properties of Al and Cu alloys are better than those of pure Zn and Zn-Al alloys. Tribological and mechanical properties of Zn-Al alloys can be improved by heat treatment and by Mn, Si, and Cu addition. Therefore, these alloys can be used as journal bearing materials. Zn based alloys are used because of their good physical, mechanical and Tribological properties, low cost, high wear resistance as journal bearing materials. Tribological properties of ZnAlCuSi alloy were higher than those of ZnAl and bronze. ZA27 is an alloy with good Tribological properties. If 2 5% Si was added to alloys, wear resistance would increase. These alloys are important for high loading, low speed applications as journal bearing materials. Tribological properties of these alloys are higher than those of bronze materials. They are preferred to Al alloy, and cast iron due to high non-seizure, mechanical and wear resistance property for journal bearing applications. Hardness decreases, but friction coefficient and wear resistance increase by graphite addition.
Al alloys containing Cu, Mg and Mg, Si; Sn are used as bearing materials. Until the early 1940s, white metal was used and then Al alloys were used as bearing materials. Al alloys can be used in applications where corrosion is a problem. Wear resistance of Si added Al alloys is higher than that of the other Al alloys. Al Si alloys have good cast ability, thermal conductivity, and weld ability, high strength and excellent corrosion resistance. They are used in pistons and bearings due to these properties. Si particles can be distributed into structure uniformly, thus material hardness increases. In addition, Al Mg Si alloys are used in Tribology applications due to excellent sliding and mechanical properties such as high strength, high deformability and good wear resistance.
Tribo-materials used have embability and high wear resistance for crank shaft in automobiles. These bearings have lead, tin, aluminum and copper. These elements are coated to steel bearing due to their superior wear properties.
Lead and tin based white metal alloys are used due to their antifriction property as bearing materials. These alloys are produced by casting and spray deposition method. These casting alloys contain intermetallic phase. The process variables during spray forming of Babbitt bearing metal alloy strongly influence the microstructure and porosity of the spray deposits. The wear rate of the spray-formed alloy is lower than that of the as-cast alloy. Wear properties of the spray-formed alloy are attributed to the decreased intermetallic phases and modification in the microstructure of the eutectic phases. SnPbCuSb (white metal) alloys are important due to non-seizure and good wear resistance as journal bearing material.
Journal bearing materials are expected to have several properties such as low friction coefficient, high load capacity, high heat conductivity, compatibility, high wear and corrosion resistance. These properties directly affect the fatigue and wear life .White metal (babbit), cast iron, bronze, aluminum, and zinc aluminum-based materials have been widely used as journal bearings due to their superior wear properties. Some metal bearings provide these properties. In this study, friction coefficient, temperature values and wear losses of bearing-journal samples were determined by wearing. On radial journal bearing wear test rig designed especially for this purpose manufactured by CuSn10 bronze, CuZn30 brass, ZnAl zamac, AlCuMg2 duralumin, and SnPbCuSb white metal for Cu, Zn, Al, and Sn Pb based alloys. These alloys are especially used in automotive and machine element applications as journal bearing materials.
EXPERIMENTAL ANALYSIS
PREPARATION OF EXPERIMENTAL MATERIALS
In this study, CuSn10 bronze, CuZn30 brass, ZnAl zamac, AlCuMg2 duralumine, and SnPbCuSb white metal specimens were used as journal bearing and SAE 1050 was used as shaft. The chemical composition of the journal materials used in the experiments is given in table 1. The chemical composition of the bearings materials used in the experiments is given in table 2. Dimensions of bearing specimens were as follows: inner diameter 10+0 05 mm, width 10 mm, and outer diameter, 15 mm.
The specimens were worn by radial journal bearing wear test rig under lubricated condition. The wear losses were measured under lubricated conditions of 20 N loads, 1500 rpm (v = 0 785 m/s velocity) and every 30 min for 2 5 h (7065 m sliding distance). Lubricating was accomplished by using SAE 90 gear oil. The microstructures of wear surfaces were photographed using optical and scanning electron microscope.
Tensile, compressive, notch impact, three-point bending, radial fracture and hardness were performed using AL A type tensile test rig depending on TS-138, and TS- 269 (Turkish Standard) for mechanical properties. Moreover, the hardness was measured using a SADT HARTIP-3000 type.
SADT HARDNESS TESTER HARTIP 3000
DESCRIPTION
ARTIP 3000 is an advanced hand-held digital metal hardness tester with characters of high accuracy, wide measuring range and easy operation. It is suitable for testing the hardness of all metals especially on site for large structure/assembled components. Which is widely used in the industry of power, petro chemistry, air space, vehicle, machine and so on.
MEASURING METHOD
The measuring principle of HARTIP series hardness testers is defined as "the quotient of the impact body's rebound and impact velocity, multiplied by 1000." An impact body with a Tungsten Carbide test tip is propelled by spring force against the test surface and then rebounds back. A permanent magnet is contained within the impact body. When it passes through the coil on impact device, it induces an electric voltage which is proportional to the velocity of the impact body.
KEY FEATURES
High accuracy
Light weight
For all metallic materials
Wide measuring range: Rockwell B&C, Brinell, Vickers, Shore and HL
Automatic conversion to Brinell, Rockwell, Vicker and Shore
Test in any directions
Impact devices: D, DC, DL, C, D+15, E, G
All impact devices interchangeable
Menu operation
Large LCD display with backlight
RS232/USB interface to PC and micro-printer
Automatic mean, max., min. value display
Data management software
Comply to standard ASTM A956
RADIAL JOURNAL BEARING WEAR TEST RIG
Bearing materials in journal bearings were generally selected from materials which had lower wear strength than the shaft material, thereby lowering the wearing of the shaft significantly. For this reason, journal bearing wear test apparatus were designed to examine the wearing of bearing materials. In this study, a special bearing wear test apparatus has been designed to examine the
Wearing behavior of bearing material and the shaft together. Therefore, it is possible to investigate different bearing and shaft materials and the effects of heat treatments on these materials. Such a mechanism provides wear of bearings rather than using standard methods as this is more appropriate.
The system was formed by a weight applied by a rigid bar, a steel bar connected to the bearing from a distance and a comparator. Friction coefficient was determined from the friction force formed along the rotating direction of the bearing and from the movement of the steel bar connected to the bearing .Radial wear test rig is illustrated in figure 1.
In the experiments under lubricated conditions, very little movement took place for high comparator s spring coefficient and low friction. Therefore, a tensile spring of k = 0 004 N/mm was connected on the opposite side to the comparator. The movements formed by the effect of the friction force were measured by this method.
RESULTS AND DISCUSSION
Surface roughness properties
Values of surface roughness before and after wearing process are shown in table 3. These values of surface roughness, CuSn10 and CuZn30, decreased and the other bearings increased after wear tests. These tests were performed on Mitutoyo-CE surface roughness test rig.
Wear properties
Friction coefficient, bearing temperature, bearing and journal weight loss values are given in figures 2 6. The friction coefficient time variation of bearings is shown in figure 2. The temperature time variation of bearings is given in figure 3. The wear losses of bearing time variation of bearings are shown in figure 4. The wear losses of journal time variation of bearings are shown in figure 5. The wear rate values of bearings depending on materials are shown in figure 6. Friction coefficient was determined as a function of normal and friction force. The
Highest friction coefficients and bearing temperatures occurred in CuSn10 and CuZn30 bearings, whereas the lowest friction coefficients and bearing wear losses occurred in other ZnAl, AlCuMg2 and SnPbCuSb bearings. The highest journal weight loss occurred in CuZn30 and AlCuMg2 bearings, whereas the lowest journal wear loss occurred in ZnAl and SnPbCuSb bearings. The highest bearing wear rate occurred in CuSn10 and CuZn30 bearings, while the lowest bearing wear rate occurred in ZnAl bearing.
From which investigated Tribological properties of Zn Al based journal bearings. They reported that these bearings had better Tribological properties than those of bronze bearings. They determined the friction coefficient as 0 02 at zinc aluminum bearings. Rapoport determined the friction coefficient of 0 08 in bronze bearings. T rk et al (2007) determined the friction coefficient of 0 25, wear rate of 25 mg/km in SAE 660 bronze bearings at 0 5 m/s sliding speed and 30 N loads. In these studies, they reported that the wear rate increased with increasing applied load, and decreased with increasing sliding distance.
The differences in our results and those of other previous studies may be attributed to the fact that their materials were different from our materials. In addition, our results show that radial journal bearing test rig gives more accurate measurements.
Mechanical properties
Mechanical properties of copper based bronze, brass and aluminum based duralumin bearing materials generally occurred than those of zinc based zamac and tin lead based white metal bearing materials. Hardness of these bearing specimens was found to be around 100 HB. Results of mechanical tests are given in table 4.
Table 4.Mechanical properties of bearing materials
Microstructure properties
The wear surfaces in the specimens were examined using the optical and scanning electron microscope .Microstructures of wear surface of metal bearings are presented in figure 7. SEM microstructures of wear surfaces of metal bearings are shown in figure 8. Homogen and small wear tracks were present in bronze bearing, and big wear tracks occurred in brass bearing. Micro fractures occurred in zamac bearing. Huge wear tracks occurred in duralumin bearing due to different element phases. Wear tracks occurred apparently on friction orientation in white metal bearing(figures 7 8).
P r ek (1994) observed micro fractures in Zn based bearings. They have observed big wear tracks in bronze bearings. In further studied it has been observed homogen and small wear tracks in bronze bearings. In this study, similar wear tracks were observed at medium loads.
SEM microstructure of tensile fracture surfaces of metal bearing materials are shown in figure 9. As can be seen in tensile fracture surfaces, fractures in bronze, brass and duralumin bearing materials occurred as thinly grained, while zamac and white metal bearing materials had thick fractures.
Scanning Electron Microscope (SEM)
The scanning electron microscope (SEM) is a type of electron microscope that images the sample surface by scanning it with a high-energy beam of electrons in a raster scan pattern. The electrons interact with the atoms that make up the sample producing signals that contain information about the sample's surface topography, composition and other properties such as electrical conductivity.
The types of signals produced by an SEM include secondary electrons, back-scattered electrons (BSE), characteristic X-ray, light (cathodoluminescense) specimen current and transmitted electrons. Secondary electron detectors are common in all SEMs, but it is rare that a single machine would have detectors for all possible signals. The signals result from interactions of the electron beam with atoms at or near the surface of the sample. In the most common or standard detection mode, secondary electron imaging or SEI, the SEM can produce very high-resolution images of a sample surface, revealing details about less than 1 to 5 nm in size. Due to the very narrow electron beam, SEM micrographs have a large depth of field yielding a characteristic three-dimensional appearance useful for understanding the surface structure of a sample. This is exemplified by the micrograph of pollen shown to the right. A wide range of magnifications is possible, from about 10 times (about equivalent to that of a powerful hand-lens) to more than 500,000 times, about 250 times the magnification limit of the best light microscopes. Back-scattered electrons (BSE) are beam electrons that are reflected from the sample by elastic scattering. BSE are often used in analytical SEM along with the spectra made from the characteristic X-rays. Because the intensity of the BSE signal is strongly related to the atomic number (Z) of the specimen, BSE images can provide information about the distribution of different elements in the sample. For the same reason, BSE imaging can image colloidol gold immune-labels of 5 or 10 nm diameter which would otherwise be difficult or impossible to detect in secondary electron images in biological specimens. Characteristic X-rays are emitted when the electron beam removes an inner shell electron from the sample, causing a higher energy electron to fill the shell and release energy. These characteristic X-rays are used to identify the composition and measure the abundance of elements in the sample.
History
The first SEM image was obtained by Max Knoll, who in 1935 obtained an image of silicon steel showing electron channeling contrast. Further pioneering work on the physical principles of the SEM and beam specimen interactions was performed by Manfred Von Ardenne in 1937, who produced a British patent but never made a practical instrument. The SEM was further developed by Professor Sir Charles Oatley and his postgraduate student Gary Stewart and was first marketed in 1965 by the Cambridge Instrument Company as the "Stereoscan". The first instrument was delivered to DuPont.
Magnification
Magnification in a SEM can be controlled over a range of up to 6 orders of magnitude from about 10 to 500,000 times. Unlike optical and transmission electron microscopes, image magnification in the SEM is not a function of the power of the objective lens. SEMs may have condenser and objective lenses, but their function is to focus the beam to a spot, and not to image the specimen. Provided the electron gun can generate a beam with sufficiently small diameter, a SEM could in principle work entirely without condenser or objective lenses, although it might not be very versatile or achieve very high resolution. In a SEM, as in scanning probe microscopy magnification results from the ratio of the dimensions of the raster on the specimen and the raster on the display device. Assuming that the display screen has a fixed size, higher magnification results from reducing the size of the raster on the specimen, and vice versa. Magnification is therefore controlled by the current supplied to the x, y scanning coils, or the voltage supplied to the x, y deflector plates, and not by objective lens power.
In a typical SEM, an electron beam is thermionically emitted from an electron gun fitted with a tungsten filament cathode. Tungsten is normally used in thermionic electron guns because it has the highest melting point and lowest vapour pressure of all metals, thereby allowing it to be heated for electron emission, and because of its low cost. Other types of electron emitters include lanthalum hexaboride (LaB6) cathodes, which can be used in a standard tungsten filament SEM if the vacuum system is upgraded and field emission guns (FEG), which may be of the cold cathode type using tungsten single crystal emitters or the thermally-assisted schottoky type, using emitters of zirconium oxide.
The electron beam, which typically has an energy ranging from a few hundred eV to 40 keV, is focused by one or two condenser lenses to a spot about 0.4 nm to 5 nm in diameter. The beam passes through pairs of scanning coils or pairs of deflector plates in the electron column, typically in the final lens, which deflect the beam in the x and y axes so that it scans in a raster fashion over a rectangular area of the sample surface.
When the primary electron beam interacts with the sample, the electrons lose energy by repeated random scattering and absorption within a teardrop-shaped volume of the specimen known as the interaction volume, which extends from less than 100 nm to around 5 m into the surface. The size of the interaction volume depends on the electron's landing energy, the atomic number of the specimen and the specimen's density. The energy exchange between the electron beam and the sample results in the reflection of high-energy electrons by elastic scattering, emission of secondary electrons by inelastic scattering and the emission of electronic magnification. Each of which can be detected by specialized detectors. The beam current absorbed by the specimen can also be detected and used to create images of the distribution of specimen current. Electronic amplifiers of various types are used to amplify the signals which are displayed as variations in brightness on a cathode ray tube. The raster scanning of the CRT display is synchronized with that of the beam on the specimen in the microscope, and the resulting image is therefore a distribution map of the being emitted from the scanned area of the specimen. The image may be captured by photography from a high resolution cathode ray tube, but in modern machines is digitally captured and displayed on a computer monitor and saved to a computer's hard disc.
Conclusions
We conclude that journal bearings manufactured from metal based materials may be effectively used in the industry due to better tribological and mechanical properties. In this study, tribological and mechanical properties of journal bearings manufactured by metals were investigated.
The following conclusions can be drawn:
Post wear values of surface roughness decreased in CuSn10 and CuZn30 and increased in other bearings.
The highest friction coefficient and bearing temperature occurred in CuSn10 and CuZn30 bearings, whereas the lowest friction coefficient and bearing weight loss occurred in other ZnAl, AlCuMg2 and SnPbCuSb bearings. The highest journal weight loss occurred at CuZn30 and AlCuMg2 bearings.
The highest bearing wear rate occurred in CuSn10and CuZn30 bearings, and the lowest bearing wear rate occurred in ZnAl bearing.
The mechanical properties of CuSn10, CuZn30 and AlCuMg2 bearing materials were better than those of ZnAl, and SnPbCuSb bearing materials.
References
Effects of lubricants on the properties of copper-tin powders and compacts, Advances in P/M, Proc. Of PM conf., APMI, N. Jersey, pp 303 314
Design of radial journal bearing wear test rig, Conference of Mach. Mater. and Technol.
Guidelines for designing zinc alloy bearings a technical manual, Soc. Auto Eng., Paper no: 880289
History of Tribology (London: Profes. Eng. Pub.), p. 768
Investigation of Tribological properties Zn Al based journal bearings, Master thesis, Karadeniz Technical University, Trabzon, Turkey (in Turkish)
Powder metallurgy, Proc. mater. EPMA (Shrewsbury, UK) p. 492
[attachment=8286]
INTRODUCTION
Tribology is defined as science and technology of interacting surfaces in relative motion and of related subjects and practices. However the subject Tribology generally deals with the technology of lubrication, friction control and wear prevention of surfaces having relative motion under load.
The two main constituents of Tribology are friction and wear, which controlled and reduced, automatically increases the service life of machine elements.
In past few years, wood iron and skin have been used as journal bearing materials. Later brass, bronze and white metals have also found some applications. Currently in operation to these materials, aluminum and zinc based material are used as journal bearing materials. With technical improvements, self lubricated sintered bearings and plastic materials are used where continuous lubricating is impossible. Therefore, it is essential that the bearing material be chosen depending upon area of application
Wear resistance is one of the most important properties that journal bearings should posses. There are several and investigations undergone dealing with wear resistance improvement of these materials.
Copper based alloys are widely used as journal bearing materials because they have high thermal and electrical conductivity, self lubrication property, and good corrosion and wear resistance. The effect of tin on wear in copper based materials is important. Copper based tin bronzes are used as bearing materials to have high wear resistance. Friction and wear properties of these materials can be improved by adding tin. Tin bronze (90% Cu 10% Sn) is most suitable bearing materials under corrosive conditions, at high temperatures and high loads.
Zinc based alloys were used instead of bronze during world war II as journal bearing materials to compensate for copper deficiency in Germany. Zn based alloys are used due to high strength, high hardness and good friction properties in several engineering applications. Tribological properties of Al and Cu alloys are better than those of pure Zn and Zn-Al alloys. Tribological and mechanical properties of Zn-Al alloys can be improved by heat treatment and by Mn, Si, and Cu addition. Therefore, these alloys can be used as journal bearing materials. Zn based alloys are used because of their good physical, mechanical and Tribological properties, low cost, high wear resistance as journal bearing materials. Tribological properties of ZnAlCuSi alloy were higher than those of ZnAl and bronze. ZA27 is an alloy with good Tribological properties. If 2 5% Si was added to alloys, wear resistance would increase. These alloys are important for high loading, low speed applications as journal bearing materials. Tribological properties of these alloys are higher than those of bronze materials. They are preferred to Al alloy, and cast iron due to high non-seizure, mechanical and wear resistance property for journal bearing applications. Hardness decreases, but friction coefficient and wear resistance increase by graphite addition.
Al alloys containing Cu, Mg and Mg, Si; Sn are used as bearing materials. Until the early 1940s, white metal was used and then Al alloys were used as bearing materials. Al alloys can be used in applications where corrosion is a problem. Wear resistance of Si added Al alloys is higher than that of the other Al alloys. Al Si alloys have good cast ability, thermal conductivity, and weld ability, high strength and excellent corrosion resistance. They are used in pistons and bearings due to these properties. Si particles can be distributed into structure uniformly, thus material hardness increases. In addition, Al Mg Si alloys are used in Tribology applications due to excellent sliding and mechanical properties such as high strength, high deformability and good wear resistance.
Tribo-materials used have embability and high wear resistance for crank shaft in automobiles. These bearings have lead, tin, aluminum and copper. These elements are coated to steel bearing due to their superior wear properties.
Lead and tin based white metal alloys are used due to their antifriction property as bearing materials. These alloys are produced by casting and spray deposition method. These casting alloys contain intermetallic phase. The process variables during spray forming of Babbitt bearing metal alloy strongly influence the microstructure and porosity of the spray deposits. The wear rate of the spray-formed alloy is lower than that of the as-cast alloy. Wear properties of the spray-formed alloy are attributed to the decreased intermetallic phases and modification in the microstructure of the eutectic phases. SnPbCuSb (white metal) alloys are important due to non-seizure and good wear resistance as journal bearing material.
Journal bearing materials are expected to have several properties such as low friction coefficient, high load capacity, high heat conductivity, compatibility, high wear and corrosion resistance. These properties directly affect the fatigue and wear life .White metal (babbit), cast iron, bronze, aluminum, and zinc aluminum-based materials have been widely used as journal bearings due to their superior wear properties. Some metal bearings provide these properties. In this study, friction coefficient, temperature values and wear losses of bearing-journal samples were determined by wearing. On radial journal bearing wear test rig designed especially for this purpose manufactured by CuSn10 bronze, CuZn30 brass, ZnAl zamac, AlCuMg2 duralumin, and SnPbCuSb white metal for Cu, Zn, Al, and Sn Pb based alloys. These alloys are especially used in automotive and machine element applications as journal bearing materials.
EXPERIMENTAL ANALYSIS
PREPARATION OF EXPERIMENTAL MATERIALS
In this study, CuSn10 bronze, CuZn30 brass, ZnAl zamac, AlCuMg2 duralumine, and SnPbCuSb white metal specimens were used as journal bearing and SAE 1050 was used as shaft. The chemical composition of the journal materials used in the experiments is given in table 1. The chemical composition of the bearings materials used in the experiments is given in table 2. Dimensions of bearing specimens were as follows: inner diameter 10+0 05 mm, width 10 mm, and outer diameter, 15 mm.
The specimens were worn by radial journal bearing wear test rig under lubricated condition. The wear losses were measured under lubricated conditions of 20 N loads, 1500 rpm (v = 0 785 m/s velocity) and every 30 min for 2 5 h (7065 m sliding distance). Lubricating was accomplished by using SAE 90 gear oil. The microstructures of wear surfaces were photographed using optical and scanning electron microscope.
Tensile, compressive, notch impact, three-point bending, radial fracture and hardness were performed using AL A type tensile test rig depending on TS-138, and TS- 269 (Turkish Standard) for mechanical properties. Moreover, the hardness was measured using a SADT HARTIP-3000 type.
SADT HARDNESS TESTER HARTIP 3000
DESCRIPTION
ARTIP 3000 is an advanced hand-held digital metal hardness tester with characters of high accuracy, wide measuring range and easy operation. It is suitable for testing the hardness of all metals especially on site for large structure/assembled components. Which is widely used in the industry of power, petro chemistry, air space, vehicle, machine and so on.
MEASURING METHOD
The measuring principle of HARTIP series hardness testers is defined as "the quotient of the impact body's rebound and impact velocity, multiplied by 1000." An impact body with a Tungsten Carbide test tip is propelled by spring force against the test surface and then rebounds back. A permanent magnet is contained within the impact body. When it passes through the coil on impact device, it induces an electric voltage which is proportional to the velocity of the impact body.
KEY FEATURES
High accuracy
Light weight
For all metallic materials
Wide measuring range: Rockwell B&C, Brinell, Vickers, Shore and HL
Automatic conversion to Brinell, Rockwell, Vicker and Shore
Test in any directions
Impact devices: D, DC, DL, C, D+15, E, G
All impact devices interchangeable
Menu operation
Large LCD display with backlight
RS232/USB interface to PC and micro-printer
Automatic mean, max., min. value display
Data management software
Comply to standard ASTM A956
RADIAL JOURNAL BEARING WEAR TEST RIG
Bearing materials in journal bearings were generally selected from materials which had lower wear strength than the shaft material, thereby lowering the wearing of the shaft significantly. For this reason, journal bearing wear test apparatus were designed to examine the wearing of bearing materials. In this study, a special bearing wear test apparatus has been designed to examine the
Wearing behavior of bearing material and the shaft together. Therefore, it is possible to investigate different bearing and shaft materials and the effects of heat treatments on these materials. Such a mechanism provides wear of bearings rather than using standard methods as this is more appropriate.
The system was formed by a weight applied by a rigid bar, a steel bar connected to the bearing from a distance and a comparator. Friction coefficient was determined from the friction force formed along the rotating direction of the bearing and from the movement of the steel bar connected to the bearing .Radial wear test rig is illustrated in figure 1.
In the experiments under lubricated conditions, very little movement took place for high comparator s spring coefficient and low friction. Therefore, a tensile spring of k = 0 004 N/mm was connected on the opposite side to the comparator. The movements formed by the effect of the friction force were measured by this method.
RESULTS AND DISCUSSION
Surface roughness properties
Values of surface roughness before and after wearing process are shown in table 3. These values of surface roughness, CuSn10 and CuZn30, decreased and the other bearings increased after wear tests. These tests were performed on Mitutoyo-CE surface roughness test rig.
Wear properties
Friction coefficient, bearing temperature, bearing and journal weight loss values are given in figures 2 6. The friction coefficient time variation of bearings is shown in figure 2. The temperature time variation of bearings is given in figure 3. The wear losses of bearing time variation of bearings are shown in figure 4. The wear losses of journal time variation of bearings are shown in figure 5. The wear rate values of bearings depending on materials are shown in figure 6. Friction coefficient was determined as a function of normal and friction force. The
Highest friction coefficients and bearing temperatures occurred in CuSn10 and CuZn30 bearings, whereas the lowest friction coefficients and bearing wear losses occurred in other ZnAl, AlCuMg2 and SnPbCuSb bearings. The highest journal weight loss occurred in CuZn30 and AlCuMg2 bearings, whereas the lowest journal wear loss occurred in ZnAl and SnPbCuSb bearings. The highest bearing wear rate occurred in CuSn10 and CuZn30 bearings, while the lowest bearing wear rate occurred in ZnAl bearing.
From which investigated Tribological properties of Zn Al based journal bearings. They reported that these bearings had better Tribological properties than those of bronze bearings. They determined the friction coefficient as 0 02 at zinc aluminum bearings. Rapoport determined the friction coefficient of 0 08 in bronze bearings. T rk et al (2007) determined the friction coefficient of 0 25, wear rate of 25 mg/km in SAE 660 bronze bearings at 0 5 m/s sliding speed and 30 N loads. In these studies, they reported that the wear rate increased with increasing applied load, and decreased with increasing sliding distance.
The differences in our results and those of other previous studies may be attributed to the fact that their materials were different from our materials. In addition, our results show that radial journal bearing test rig gives more accurate measurements.
Mechanical properties
Mechanical properties of copper based bronze, brass and aluminum based duralumin bearing materials generally occurred than those of zinc based zamac and tin lead based white metal bearing materials. Hardness of these bearing specimens was found to be around 100 HB. Results of mechanical tests are given in table 4.
Table 4.Mechanical properties of bearing materials
Microstructure properties
The wear surfaces in the specimens were examined using the optical and scanning electron microscope .Microstructures of wear surface of metal bearings are presented in figure 7. SEM microstructures of wear surfaces of metal bearings are shown in figure 8. Homogen and small wear tracks were present in bronze bearing, and big wear tracks occurred in brass bearing. Micro fractures occurred in zamac bearing. Huge wear tracks occurred in duralumin bearing due to different element phases. Wear tracks occurred apparently on friction orientation in white metal bearing(figures 7 8).
P r ek (1994) observed micro fractures in Zn based bearings. They have observed big wear tracks in bronze bearings. In further studied it has been observed homogen and small wear tracks in bronze bearings. In this study, similar wear tracks were observed at medium loads.
SEM microstructure of tensile fracture surfaces of metal bearing materials are shown in figure 9. As can be seen in tensile fracture surfaces, fractures in bronze, brass and duralumin bearing materials occurred as thinly grained, while zamac and white metal bearing materials had thick fractures.
Scanning Electron Microscope (SEM)
The scanning electron microscope (SEM) is a type of electron microscope that images the sample surface by scanning it with a high-energy beam of electrons in a raster scan pattern. The electrons interact with the atoms that make up the sample producing signals that contain information about the sample's surface topography, composition and other properties such as electrical conductivity.
The types of signals produced by an SEM include secondary electrons, back-scattered electrons (BSE), characteristic X-ray, light (cathodoluminescense) specimen current and transmitted electrons. Secondary electron detectors are common in all SEMs, but it is rare that a single machine would have detectors for all possible signals. The signals result from interactions of the electron beam with atoms at or near the surface of the sample. In the most common or standard detection mode, secondary electron imaging or SEI, the SEM can produce very high-resolution images of a sample surface, revealing details about less than 1 to 5 nm in size. Due to the very narrow electron beam, SEM micrographs have a large depth of field yielding a characteristic three-dimensional appearance useful for understanding the surface structure of a sample. This is exemplified by the micrograph of pollen shown to the right. A wide range of magnifications is possible, from about 10 times (about equivalent to that of a powerful hand-lens) to more than 500,000 times, about 250 times the magnification limit of the best light microscopes. Back-scattered electrons (BSE) are beam electrons that are reflected from the sample by elastic scattering. BSE are often used in analytical SEM along with the spectra made from the characteristic X-rays. Because the intensity of the BSE signal is strongly related to the atomic number (Z) of the specimen, BSE images can provide information about the distribution of different elements in the sample. For the same reason, BSE imaging can image colloidol gold immune-labels of 5 or 10 nm diameter which would otherwise be difficult or impossible to detect in secondary electron images in biological specimens. Characteristic X-rays are emitted when the electron beam removes an inner shell electron from the sample, causing a higher energy electron to fill the shell and release energy. These characteristic X-rays are used to identify the composition and measure the abundance of elements in the sample.
History
The first SEM image was obtained by Max Knoll, who in 1935 obtained an image of silicon steel showing electron channeling contrast. Further pioneering work on the physical principles of the SEM and beam specimen interactions was performed by Manfred Von Ardenne in 1937, who produced a British patent but never made a practical instrument. The SEM was further developed by Professor Sir Charles Oatley and his postgraduate student Gary Stewart and was first marketed in 1965 by the Cambridge Instrument Company as the "Stereoscan". The first instrument was delivered to DuPont.
Magnification
Magnification in a SEM can be controlled over a range of up to 6 orders of magnitude from about 10 to 500,000 times. Unlike optical and transmission electron microscopes, image magnification in the SEM is not a function of the power of the objective lens. SEMs may have condenser and objective lenses, but their function is to focus the beam to a spot, and not to image the specimen. Provided the electron gun can generate a beam with sufficiently small diameter, a SEM could in principle work entirely without condenser or objective lenses, although it might not be very versatile or achieve very high resolution. In a SEM, as in scanning probe microscopy magnification results from the ratio of the dimensions of the raster on the specimen and the raster on the display device. Assuming that the display screen has a fixed size, higher magnification results from reducing the size of the raster on the specimen, and vice versa. Magnification is therefore controlled by the current supplied to the x, y scanning coils, or the voltage supplied to the x, y deflector plates, and not by objective lens power.
In a typical SEM, an electron beam is thermionically emitted from an electron gun fitted with a tungsten filament cathode. Tungsten is normally used in thermionic electron guns because it has the highest melting point and lowest vapour pressure of all metals, thereby allowing it to be heated for electron emission, and because of its low cost. Other types of electron emitters include lanthalum hexaboride (LaB6) cathodes, which can be used in a standard tungsten filament SEM if the vacuum system is upgraded and field emission guns (FEG), which may be of the cold cathode type using tungsten single crystal emitters or the thermally-assisted schottoky type, using emitters of zirconium oxide.
The electron beam, which typically has an energy ranging from a few hundred eV to 40 keV, is focused by one or two condenser lenses to a spot about 0.4 nm to 5 nm in diameter. The beam passes through pairs of scanning coils or pairs of deflector plates in the electron column, typically in the final lens, which deflect the beam in the x and y axes so that it scans in a raster fashion over a rectangular area of the sample surface.
When the primary electron beam interacts with the sample, the electrons lose energy by repeated random scattering and absorption within a teardrop-shaped volume of the specimen known as the interaction volume, which extends from less than 100 nm to around 5 m into the surface. The size of the interaction volume depends on the electron's landing energy, the atomic number of the specimen and the specimen's density. The energy exchange between the electron beam and the sample results in the reflection of high-energy electrons by elastic scattering, emission of secondary electrons by inelastic scattering and the emission of electronic magnification. Each of which can be detected by specialized detectors. The beam current absorbed by the specimen can also be detected and used to create images of the distribution of specimen current. Electronic amplifiers of various types are used to amplify the signals which are displayed as variations in brightness on a cathode ray tube. The raster scanning of the CRT display is synchronized with that of the beam on the specimen in the microscope, and the resulting image is therefore a distribution map of the being emitted from the scanned area of the specimen. The image may be captured by photography from a high resolution cathode ray tube, but in modern machines is digitally captured and displayed on a computer monitor and saved to a computer's hard disc.
Conclusions
We conclude that journal bearings manufactured from metal based materials may be effectively used in the industry due to better tribological and mechanical properties. In this study, tribological and mechanical properties of journal bearings manufactured by metals were investigated.
The following conclusions can be drawn:
Post wear values of surface roughness decreased in CuSn10 and CuZn30 and increased in other bearings.
The highest friction coefficient and bearing temperature occurred in CuSn10 and CuZn30 bearings, whereas the lowest friction coefficient and bearing weight loss occurred in other ZnAl, AlCuMg2 and SnPbCuSb bearings. The highest journal weight loss occurred at CuZn30 and AlCuMg2 bearings.
The highest bearing wear rate occurred in CuSn10and CuZn30 bearings, and the lowest bearing wear rate occurred in ZnAl bearing.
The mechanical properties of CuSn10, CuZn30 and AlCuMg2 bearing materials were better than those of ZnAl, and SnPbCuSb bearing materials.
References
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