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AN OVERVIEW OF EXPERIMENTAL INVESTIGATION OF NEAR DRY ELECTRICAL DISCHARGE MACHINING PROCESS INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING AND TECHNOLOGY (IJARET) IJARET © I A E M E
No full textABSTRACT EDM has achieved a status of being nearly indispensable in the industry because of its ability to machine any electrically conductive material which is difficult-to-machine irrespective of its mechanical strength. Out of the three EDM processes viz. wet, dry & near-dry; near-dry EDM is proved to be most environment-friendly. Further some other problems like higher discharge energy requirement in wet EDM and the reattachment of debris to the machined surface in dry EDM can be overcome in near-dry EDM. Also, it is found that near-dry EDM has the advantage in finish operation with low discharge energy considering its higher MRR than wet EDM and better surface finish quality than dry EDM. In view of these factors, near-dry EDM may prove to be the most prominent process amongst the three EDM processes in near future to finish machine the difficult to machine materials. Significant work has been done in the parametric optimization of wet EDM processes. Efforts are also on in the parametric optimization of dry EDM processes. However, irrespective of its inherent advantages over wet and dry EDM processes, not much attention has been given towards the parametric optimization of the near-dry EDM process. It is essential to have information on the optimum operating conditions to make the near dry EDM process cost effective and economically viable one. If applied as the post process of direct metal deposition (DMD), the near-dry EDM milling processes can be targeted to finish the near-net-shape parts produced by DMD. Hence the authors feel that, there is a wide scope to work in this area to optimize the vital parameters of near-dry EDM process. The experimental investigations of near dry electrical discharge machining process carried out by a handful of researchers have been overviewed in present work
No full textAbstract Mechanical failures in general can appear because of weak design, wrong handling, and problems during the manufacturing process, material problems etc. This paper is dealing with failures in lifting machinery gearboxes which appear because of material stresses and tribological problems. The study conducted is based on theoretical analysis and analysis of inspection results for failures that have appeared in cranes and other lifting machinery in southern part of Sweden. Investigation shows that besides the surface damages like abrasive and adhesive failures also cracks in the material in different parts appear. Since these types of gearboxes are made in short series, gearbox housings and sometimes also gears are made of welded steel. Hence welding process makes the weld joints brittle; cracks do start and developed until the part fails. Another problem that happens due to welding is wrapping which leads to changes in the geometrical tolerances and that does affect the parallelism of the shafts and the functionality of the gearbox. Key words: mechanical failures, material stresses, tribology, lifting machinery, failures in gearboxes INTRODUCTION Lifting equipment is any work equipment for lifting and lowering loads. Lifting operations are inherent to many occupations in the industry. They can be performed manually or using lifting machinery. Overview of the different types of lifting machinery Different types of lifting machineries are used in construction, transportation, industries, ports and other fields. Those are machines which use one or more simple mechanisms to create mechanical advantage and thus move heavy loads. Two types of material lifting equipment are defined -Hoisting Equipment and Conveying Equipment. Hoisting Equipment is a group of machines with lifting transmission intended for moving loads mainly in batches. There are three types of hoisting equipment: Hoisting machinery, Cranes, and Elevators. [allengineering-info] A hoist: is a device used for lifting or lowering a load by means of a drum or lift-wheel around which rope or chain wraps. It may be manually operated, electrically or pneumatically driven and may use chain, fibre or wire rope as its lifting medium. A crane is a machine that is capable of raising and lowering heavy object and, while holding them suspended, transporting them through limited lateral distance. Cranes are a type of machinery, generally equipped with a hoist, wire ropes or chains, and sheaves, that can be used to lift and lower heavy materials and to move them horizontally. Cranes are distinguished from hoists, which can lift objects but that cannot move them sideways. Cranes are also distinguished from conveyors that lift and move bulk materials, such as grain and coal, in a continuous process. Cranes are classified according utilization and their form. Many factors are taken into consideration while selecting a crane. These factors include lifting capacity, crane use and application and the number of work cycles that the crane is required to undergo. ISSN 1314-7269, Volume 10, 2016 Journal of International Scientific Publications www.scientific-publications.net Materials, Methods & Technologies Page 113 Gearboxes in lifting machinery Different types of gearboxes are used in lifting machinery: gearboxes for conveyor, vertical gearboxes, forward-reverse gearboxes, electric motor gearboxes, high rpm gear speed reducers and etc. The main product objectives for gearboxes used in cranes are: wide range of reduction ratio, high mechanical transmission efficiency, smooth operation, low noise, long service life, high carrying capacity, easy to overhaul, and easy to install. The most common for different types of lifting machineries is the reduction gearbox for hoisting. The range of the used gearboxes varies very much. From larger hoisting speed reducers and large crane gearboxes to medium hoist lifting gearbox reducers and small hoisting reduction gearboxes. The principal structure of a hoist contains: motor, brake pad, coupling, gear reducer, bearing house, steel cable, hook, and limitation stopper (see Failures in lifting machinery Because of working in heavy conditions, and in changing environment failures are natural to appear in lifting machineries. Failures in the sub-systems of the lifting equipment add high risks of fatal collapse, and unexpected consequences, such as economical lose and even people injuries. Any undesirable change in the size, shape or material properties of a structure, machine or machine part that affects the satisfactory performing machine´s intended function is called mechanical failure. Mechanical failures in lifting machineries could appear due to causes from different type and nature (see To analyse a mechanical failure there are four main categories to be defined: The equipment (for example gearbox in a hoist) The failure defined in time and logical sequence (for example catastrophic breakage of teeth in a gear) The failure-inducing agents are also divided in four types -Force, Temperature, Time, Reactive environment. The two failure locations could be: body type and surface type. Each specific failure mode is defined as a combination of one or more manifestation of failure with one or more failure-inducing agents and a failure location. Some typical failure mechanisms in lifting equipment are due to fatigue, wear, corrosion, and ductile or brittle fracture. Insuring the lifting equipment is not overloaded, in addition to appropriate inspections, maintenance, and repair can help eliminate many failures. The leading cause of lifting equipment failures are due to improper operation. Unfortunately, overloading of a lifting mechanism is not an uncommon practice. Wear is the most readily recognized condition by operators and maintenance personnel. Excessive wear is usually a relatively easy condition to correct. However, complete elimination of wear in components used in lifting equipment is not feasible. Fatigue is a more insidious type of failure mechanism as it is more difficult to detect. Periodic inspection by properly trained inspection and maintenance personnel can prevent fatigue failures of critical components. Mapping the content of the presented work The focus in this paper is on failure due to the material of gear transmission parts. But the material cannot be treated separately from other factors, which are part of the problem causes, like contact stresses in gears and rolling bearings. In addition to the material problems, also tribological issues, like surface texture in the contact areas, have to be treated. There are loads in all the machine elements of the gearbox and these have to be dimensioned for the type and size of the stresses. Therefor load and force analysis must be presented, when dealing with material issues. The content of the presented work is mapped in figure 1.3. MACHIN ELEMENTS AND MATERIALS IN GEAR TRANSMISSIONS In this paper only parallel gear drives or gear transmissions (transmissions with parallel shafts), containing spur or helical gears, will be treated. According to Figure 2.1. Sketch of a mechanical drive application Gears and gear materials Gears are the "heart" of the gear transmission and the parameter relation between them will decide the transmission ratio. Spur gears are the simplest gears and they make the base of other type of gears. The only difference between the spur gears and helical gears is that the direction of the gear teeth in the helical gears is not parallel with the axis of the gear. The geometry of the gears is based on the size of the module which is standardized. The parameters for spur gears are shown in Gear materials are selected depending on the required properties, lowest cost, and to satisfy other functional and technical requirements. Fatigue strength, surface hardness, and wear resistance are few of the most required material properties. Gear materials in lifting machineries are made of steel, cast iron, or cast steel. Since the gear teach will be subjected to contact stresses, the gear material must be heat-treatable, for example possible to be hardened. The best physical property with respect to the gear strength is that the gear has a hard surface and a ductile core. In many cases the gear transmission series for lifting machineries are too short; therefore, gears (and housings) are made of welded plates and parts. In this case, the material must be weld-able and heat-treatable. Shaft and shaft materials A shaft is a rotating or stationary machine part, usually with circular cross-sections. Shafts in gearboxes are usually rotating and they are prepared for having mounted on gears, pulleys, sprockets, bearings, etc. It is normally subjected to various combinations of axial, bending and torsional loads and theses loads may be static or fluctuating. Typically, a rotating shaft transmitting power is subjected to a constant torque Materials, Methods & Technologies Page 117 Many shaft-design situations include the problem of transmitting torque from one element to another on a shaft, for example from shaft to hub and in opposite. Common torque transfer elements are keys, splines, setscrews, pins, press or shrink fits, and tapered fits. Press-and shrink-fits for securing hubs to shafts are used both for torque transfer and for preserving axial locations. The resulting stressconcentration factor is quite small To minimize deflections, shaft materials are generally cold drawn or machined from hot-rolled, plain carbon steel. Cold drawing improves the physical properties, it improves the values of ultimate tensile and yield strengths of steel [Ugural, 2015]. Alloy steels are used when toughness, shock resistance or greater strength are needed. These materials can be heat treated to give the desired properties. Where wear resistance is needed rather than extreme strength, it is usual to harden only the surface of the shaft requiring it, the reminding of the shaft is left in its original conditions. All changes in the shaft cross sections are sources for stress rising, therefore stress risers in already high stressed parts of a shaft should be avoided. All the stress concentration factors must be taken into concentration in the dimensioning and design process. Keys are used to enable the remission of torque from the shaft to the hub or in opposite. There are many types of keys for different requirements, the square and flat keys are the most used in machine assemblies. To use keys, it requires corresponding keyways in the shafts as well as in the hubs. Keys are, in the most of the cases, made of low-carbon, cold-drawn steel. For example, from the American Standard, steel AISI 1020 CD having an ultimate strength of 420 MPa, yield strength of 352 MPa, and a 15% elongation Bearings Bearings used in gearboxes in lifting machineries are rolling-element bearings also known as rolling bearings. Rolling bearings are standardized machine elements with dimensions and all other important data. All the data about the bearings are published in the rolling bearings' manufacturers product catalogues and/or on their websites to be available for machine designers. Rolling bearings can carry radial, axial, or a combination of radial and axial loads. These bearings provide coefficient of friction between 0,001 and 0,002. The designer must deal with such matters as fatigue, friction, heat, lubrication, kinematic problems, material properties, machining tolerances, assembly, use, and cost [Ugural, 2015]. There are of course many different types of rolling bearings designed for different load type, size and other conditions. The rolling bearings are divided in two major groups depending on rolling element, i.e. roller bearings and ball bearings. A rolling bearing is made of an outer ring (race), rolling elements, inner ring (race), and separator (see According to To insure that the seal lip can follow the variations. The surface of the shaft should be free of burrs to protect against tearing the seal. A surface finish of 254 to 508 μm with adequate lubrication is recommended, to ensure full contact and to reduce friction between the seals and the shaft surface. Most of seal materials are resilient (elastic) to permit the sealing point to follow minor variations in the geometry of mating surface. Radial shaft seals require rigid, hard materials that can withstand constant sliding motion. Resilient seals are made from synthetic elastomers such as Neoprene, Fluorocarbon, Butadiene, Polysulfide, Polyacrylate etc. Design requirements and material properties will de will decide which of the material will suite in any case. Lubrication system It is not possible to run a gearbox without lubricant. All contact areas which are moving with respect to each other must include a type of lubricant to prevent solid surface contact (like metal to metal contact). In the case of gearboxes, lubricant is needed for the bearings, gears, and seals. Besides the separation of solid surfaces, lubricant has other advantages like heat distributing and dissipating, corrosion prevention, and transportation of broken surface peaks in the machine elements. Depending on the load, speed, and temperature requirements, bearing lubricants are either greases or oils. For high speed and/or higher load demands, oil is recommended. Closed gearboxes are usually lubricated by oils. As mentioned, no gearbox, unless it is designed for very light loads and low speeds, will manage to run without lubrication. These gearboxes must have a well-planned lubrication system to insure lubrications of all the roller bearings, gears, seals and other solid surfaces in contact, and with relative movement. The duties of lubricants are to minimize the contact friction, cooling down, and cleaning the contact surfaces. It is very important that the lubricant is fresh and clean in order to accomplish its duties to carry loads, to separate the hard surfaces for minimizing or preventing metal to metal contacts. The simplest method of oil lubrication is the oil bath. The oil, which is picked up by the rotating components of the gearbox, is distributed within the gearbox and then flows back to the sump in the housing. Figure 2.5. A) Lubrication system; B) Tolerances in relation to the shaft diameter The oils (lubricants) are classified in systems, like ISO-Grading system based on the lubricant viscosity. Viscosity is the most significant lubricant property, but the viscosity is depending on the temperature of the lubricant. Therefore, the viscosity for oils is represented in diagrams where one axis is showing the viscosity and the perpendicular axis is showing the temperature. The relation viscositytemperature is used to be expressed in the Viscosity Index (VI). ISSN 1314-7269, Volume 10, 2016 Journal of International Scientific Publications www.scientific-publications.net Page 120 Materials, Methods & Technologies Figure 2.6. A) Friction in relation to speed; B) Contact zone for different type of lubrication Lubrication is commonly classified according to degree with which the lubricant separate the sliding surfaces as shown in 2. Mixed-film lubrication: The surface peaks are intermittently in contact, and there is partial hydrodynamic support 3. Hydrodynamic lubrication: The surfaces are completely separated by the lubricant film. Lubricant additives are mainly added to the base oils to enhance the viscosity index, the lubricity under boundary lubrication conditions, and the lubricant life, which in turn enhances the lifetime performance of the machine [Van Beek, 2009]. Lubricity concerns the friction and wear in the boundary lubrication regime. To improve lubricity, anti-wear (AW), and extreme pressure (EP) additives are added to the lubricants. Other additive like anti-oxidant, rust and oxidation, detergents, anti-foam etc. are also added to extend the lubricants life resulting in longer oil change intervals. For hydrodynamic lubrication, when the solid surfaces are totally separated, there will be a minimum oil film thickness hmin (usually from 0,1 to 0,5 μm) which is very important for the function, friction and heat in the machine element. For example, in a journal bearing, the minimum oil film thickness will be in the narrow gape, see As shown in 3) The specific film thickness defines the lubrication classification according the following table. Table.2.3. Lubrication classification FORCE ANALYSES AND STRESSES The materials in different structures and machine parts behave different depending on the type of loads and forces. Material behaviour in such situations cannot be treated isolated from the stresses appearing in the material due to the different types and sizes of loads. This part is showing the process of analysing the different types of forces and loads in vital parts of a simple gearbox, and then connects the forces to the different types of stresses which appear in the material. A gearbox is usually connected to driving machinery through an ingoing shaft, and to driven machinery through an outgoing shaft, as is shown in Gear forces and stresses When the ingoing shaft is rotating, the pinion which is connected to that shaft will also rotate and it will force the gear and the outgoing shaft to rotate with opposite direction. The gear is rotating because of the pressure on its flank from the contact with the pinion flank. The torque of the ingoing shaft T1 in combination with the pitch diameter of the pinion d1 will produce a contact force between the gear flanks; this force is called normal force F. Because of the geometry of helical gears with helix angle β and pressure angle α, the normal force is nor perpendicular with the gear pitch diameter. To make the force analysing easier, the gear normal force is divided in three force components; i.e. radial force Fr, axial force Fa, and tangential force Ft, as shown in figure 3.1.B). The latest force component can easily be calculated by the equation below. is showing the relation between the normal force and its components together with the pressure and helix angles. The loads together with the geometry of the gears will produce different types of stresses. As shown in Figure 3.1. A) Helical gear pair with forces in the contact area; B) Force components in the contact point of helical gears The teeth roots of the gears are subjected to bending stresses, where one side is subjected to tension and the other side to compression stresses. This situation can be compared with a beam with a free end loaded by a perpendicular load to the bean length. The bending stress in the gears is calculated in the same way as for a beam when modification factors are taken into consideration. The gear teeth are loaded during a short period of each cycle (rotation), therefore the loads and the stresses are cyclic. In this case both the contact stress and the bending stress are repeated from zero to the maximum values during each rotation. Shaft forces and stresses Gearbox shafts are usually designed in that way that it is prepared to be connected to different hubs like gears, sprockets, pulleys etc. These preparations include keyways, grooves, holes, shoulders etc., as shown in figure 3.3. The power and the torque are transmitted from one hub to another through a shaft at same time as the shaft must be supported by bearings. Therefore, the shafts in gearboxes are usually loaded by a combination of loads producing a combination of stresses. When the shear force and bending diagrams for the both planes are made, the maximum bending moment and its position along x-axis will be calculated. The bending moment is static (constant), but because the shaft is rotating, it will produce "rotating bending" fatigue (or cyclic stress) in the shaft. The bending stresses are normal stresses (σ). The torque is normally constant which leads to static shear stresses in the "torque" loaded parts of the shaft. The "static" axial loads will produce axial "normal" stresses in the loaded parts of the shaft. Materials, Methods & Technologies . Ingoing Shaft force analysis These three different types of stresses will be used to find the equivalent Alternating bending stress σea and the equivalent mean bending stress σem : Stress concentration factors must also be taken into the account to find the most stressed area, or the weakest point of the shaft. The size of the "static" stress concentration factors is depending of the type and the size of changes in the cross section area. Where q is a notch sensitivity factor. Rolling bearing forces and bearing life length The force analyses of the shaft are including forces and loads on bearings which are carrying the shafts. Figure 3.7. Hertz contact stress in roller bearings Forces and stresses in seals The radial seals are usually pressed in the gearbox housing and placed in correct position with the "soft" lips in contact with the shaft. There must be a certain pressure between the seal lips and the shaft surface to prevent leakage of lubricant, and penetration of contaminations, water, etc. from outside. In this case, the only force acting on the seal will be the friction force between the lips and the shaft. This force is of course a product of the normal force (because of the pressure between the lips and the shaft) and the friction coefficient. The size of friction coefficient is depending on material combinations and surface finish. Lubricants has also huge impact on the friction coefficients, it will act like a slide bearing with separated surfaces by an oil film thickness when right conditions are fulfilled. ISSN 1314-7269, Volume 10, 2016 Journal of International Scientific Pub
Self-assembly of three-dimensional nanoporous containers
Get PDFWe describe a strategy to construct three-dimensional (3D) containers with nanoporous walls by the self-assembly of lithographically patterned two-dimensional cruciforms with solder hinges. The first step involves fabricating two-dimensional (2D) cruciforms composed of six unlinked patterns: each pattern has an open window. The second step entails photolithographic patterning of solder hinges that connect the cruciform. The third step involves the deposition of polystyrene particles within the windows and the subsequent electrodeposition of metal in the voids between the polystyrene particles. Following the dissolution of the particles, the cruciforms are released from the substrate and heated above the melting point of the solder causing the cruciforms to spontaneously fold up into 3D cubic containers with nanoporous walls. We believe these 3D containers with nanoporous side walls are promising for molecular separations and cell-based therapies
The P-L relation in the BVRI bands for Cepheids in IC 1613
Get PDFAbstract. A set of six BVRI observations collected with the WFI at the ESO 2.2 m telescope have been used to derive multicolor data of Cepheids in IC 1613 identified in previous surveys. The method of Freedman has been applied to get reliable mean intensity values of Cepheid magnitudes in the various bands. The resulting slopes of the relations in the BV I bands are similar, within the uncertainties, to those previously obtained by other authors for the LMC
A Novel Hybrid Fuzzy Multi-Criteria Decision-Making Model for Supplier Selection Problem (A Case Study in Advertising industry)
Get PDFAbstract Choosing the proper supplier has a critical role in designing of a supply chain. This problem is complex because each supplier may fulfill some of the manufacturer criteria and choosing the best supplier is a multi criteria problem. This paper proposes a novel hybrid approach to rank suppliers in advertising industry and considers two new criteria to evaluate the suppliers. The proposed approach combines Modified Digital Logic (MDL) and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) using fuzzy theory. At the end, the results of the proposed approach are compared with a hybrid method using Fuzzy Analytical Hierarchy Process (FAHP) and Fuzzy TOPSIS on a real case study
2011 Designing a virtual keyboard with multi-modal access for people with disabilities 2011
No full textAbstract-Virtual keyboards or on-screen keyboards are commonly used as a means of augmentative communication by people with severe speech and motion disability. Any such virtual keyboard is characterized by keys' layout design and method of access. In this paper we present a virtual keyboard that can support multiple modes of access and has an optimum layout based on the frequency of occurrence of alphabet in English text. We have compared our proposed layout against commonly used alphabetical layout, which demonstrates a superior performance of our design
Mechanisms of geometrical seismic attenuation
Get PDFAbstract In several recent papers, we explained the frequency dependence of the apparent seismic quality-factor (Q) observed in many studies by the effects of geometrical attenuation (GA), which was defined as the zero-frequency limit of the temporal attenuation coefficient. In particular, GA was found to be positive for most waves traveling within the lithosphere. Here, we present three theoretical models illustrating the origin of such GA, and investigate the causes of its preferential positive values. In addition, we discuss the physical basis and limitations of both the conventional and new attenuation models. For waves in media with slowly varying properties, GA is caused by variations of wavefront curvatures, which can be both positive (for defocusing) and negative (for focusing). In media with velocity/density contrasts, incoherent reflectivity leads to GA coefficients which are proportional to the mean squared reflectivity and always positive. For "coherent" reflectivity, the GA is approximately zero, and the attenuation process can be described by the concept of "scattering Q." However, the true meaning of this parameter is in describing the mean reflectivity within the medium and not that of the traditional resonator quality factor known in mechanics. The general conclusion from these models is that non-zero and often positive levels of GA are common in realistic, heterogeneous media both observationally and theoretically. When transformed into the conventional Q-factor form, such positive GA leads to Q values quickly increasing with frequency. These predictions show that the positive frequency dependent Q observed in many datasets may represent artifacts of the transformations of the attenuation coefficients into Q
No full textWe argue that an understanding of the faculty of language requires substantial interdisciplinary cooperation. We suggest how current developments in linguistics can be profitably wedded to work in evolutionary biology, anthropology, psychology, and neuroscience. We submit that a distinction should be made between the faculty of language in the broad sense (FLB) and in the narrow sense (FLN). FLB includes a sensory-motor system, a conceptual-intentional system, and the computational mechanisms for recursion, providing the capacity to generate an infinite range of expressions from a finite set of elements. We hypothesize that FLN only includes recursion and is the only uniquely human component of the faculty of language. We further argue that FLN may have evolved for reasons other than language, hence comparative studies might look for evidence of such computations outside of the domain of communication (for example, number, navigation, and social relations)
Trends in corrected lung cancer mortality rates in Brazil and regions
Get PDFABSTRACT OBJECTIVE: To describe the trend in cancer mortality rates in Brazil and regions before and after correction for underreporting of deaths and redistribution of ill-defined and nonspecific causes. METHODS: The study used data of deaths from lung cancer among the population aged from 30 to 69 years, notified to the Mortality Information System between 1996 and 2011, corrected for underreporting of deaths, non-registered sex and age , and causes with ill-defined or garbage codes according to sex, age, and region. Standardized rates were calculated by age for raw and corrected data. An analysis of time trend in lung cancer mortality was carried out using the regression model with autoregressive errors. RESULTS: Lung cancer in Brazil presented higher rates among men compared to women, and the South region showed the highest death risk in 1996 and 2011. Mortality showed a trend of reduction for males and increase for women. CONCLUSIONS: Lung cancer in Brazil presented different distribution patterns according to sex, with higher rates among men and a reduction in the mortality trend for men and increase for women
AN INNOVATIVE METHOD OF PREPARATION OF HEALTHY GRAIN SPAWN
Get PDFABSTRACT Mushroom spawn is prepared on cereal grain media by inoculating them with pure cultures of selected mushroom species under sterile conditions, yet the problem of contamination of spawn is a major bottle-neck in the growth and spread of mushroom farming in developing countries. Species of Trichoderma, Aspergillus, Penicillium, Rhizopus, etc. besides wet spot causing bacteria are known to be major contaminants of mushroom spawn in eastern India, including Jharkhand affecting commonly grown mushrooms viz., Pleurotus spp, Hypsizygus ulmarius and Volvariella volvacea, which need urgent action for their management. In view of reports of appearance of fungicide-resistant strains of Trichoderma, therefore, a Neem-based herbal formulation, viz., Mahaneem containing 0.15% Azadirachtin was tried as a prophylactic pretreatment of the wheat grains used for the spawn medium together with some empirical changes in the current method of preparation of the grain spawn medium. The modified method tried successfully for raising healthy, contamination-free and productive master and planting spawns of oyster and paddy straw mushrooms has been discussed