Large Gears Research Articles

A Novel RFID-Based Sensing Method for Low-Cost Bolt Loosening Monitoring.

In coal mines, bolt loosening in the cage guide is affected by the harsh environmental factors and cage hoist vibration, leading to significant threats to work safety. It is crucial, to this effect, to successfully detect the status of multipoint bolts of guide structures. This paper proposes a system to monitor bolt status in harsh environments established based on the RFID technique. A proof-of-concept model was demonstrated consisting of a bolt gearing system, passive UHF RFID tags, a reader, and monitoring software. A tinfoil metal film is fixed on the retaining plate and an RFID tag bonded to a large gear, with the bolt to be detected fixed in the center of a smaller gear. The radio-frequency signal cannot be received by the reader if the tag is completely obscured by the tinfoil, and if the bolt is loose, the tag’s antenna is exposed when the gear revolves. A radio-frequency signal that carries corresponding bolt’s information is transmitted by the RFID tag to the RFID reader due to coil coupling, identifying loose bolt location and reporting them in the software. Confirmatory test results revealed that the system indeed successfully detects bolt loosening and comparative test results (based on a reed switch multipoint bolt loosening monitor system) provided valuable information regarding the strengths and weaknesses of the proposed system.

Approach for a General Pose-dependent Model of the Dynamic Behavior of Large Lightweight Machine Tools for Vibration Reduction

Large-scale machine tools for the manufacturing of large work pieces, e.g. blades, casings or gears for wind turbines, feature pose-dependent dynamic behavior. Small structural damping coefficients lead to long decay times for structural vibrations that have negative impacts on the production process. Typically, these vibrations are handled by increasing the stiffness of the structure by adding mass. That is counterproductive to the needs of sustainable manufacturing as it leads to higher resource consumption both in material and in energy. Recent research activities have led to higher resource efficiency by radical mass reduction that rely on control-integrated active vibration avoidance and damping methods. These control methods depend on information describing the dynamic behavior of the controlled machine tools in order to tune the avoidance or reduction method parameters according to the current state of the machine.The paper describes the approach for a general pose-dependent model of the dynamic behavior of large lightweight machine tools that provides the necessary input to the aforementioned vibration avoidance and reduction methods to properly tackle machine vibrations. The paper starts with an overview of the state of the art of the pose-dependent dynamic behavior of machine tools followed by the most common methods for vibration avoidance and reduction. Based on the results of an experimental modal analysis of a lightweight machine tool structure, the relevant pose-dependency is shown and the relevant parameters to derive the dynamic behavior are deduced. Then, a general model structure to model the machine tool's dynamic behavior is introduced. After updating the model parameters to different discrete machine poses the dynamical behavior of the model and the real machine tool structure are compared. Finally, it is explained how the model contributes to the actual vibration reduction of lightweight machine tools.

Multi Objective Design Optimization of Helical Gear Pair Using Adaptive Parameter Harmony Search Algorithm

Mechanical design engineers design products by selecting the best possible materials and geometries that satisfies the specific operational requirements of the design. It involves lot of creativity and aesthetics to make better designs. A gear design makes the designer to compromise many design variables so as to arrive the best performance of a gear set. The best possible way for multi variable, Multiobjective gear design is to try design optimization. For many complex engineering optimization problems multi objective design optimization methods are used to simplify the design problem. In this paper, multiobjective design of helical gear pair transmission with objective functions namely volume of the small and large helical gear and opposite number of overlap ratio is taken into account. The design variables considered are normal module, helix angle, gear width coefficient and teeth number of small helical gear. A recent meta-heuristic algorithm namely parameter adaptive harmony search algorithm is applied to solve this problem using the weighted sum approach. It is evident from the results that the proposed approach is performing better than other algorithms.

An Effect of Laser Hardening on Contact and Bending Fatigue of a 42CrMo4 Steel

The paper deals with an investigation of surface laser hardening characteristics on contact and bending fatigue resistance of a 42CrMo4 steel, being often used for manufacture of gear wheels. The aim of the experimental programme was to simulate the complex service loading of fairly large gears by two separate investigations, namely contact fatigue performed on a special, so called analogon machine and bending fatigue performed on high cycle fatigue resonance machines using three-point-bend (3PB) fairly large specimens. It was shown that after optimising the methodology and parameters of the laser hardening technology, contact fatigue resistance is very good, comparable with very expensive and time consuming thermochemical high-depth surface treatments. Bending endurance limit can be increased. The role of residual stresses resulting from the laser treatment was shown as decisive.

Simulation Based Design for Large Module Gear Machining with Indexable Inserts

Production processes for large module gears are characterized by small batch sizes and high workpiece costs. Therefore, the production of scrap parts cannot be accepted. Manufacturing processes are often not pushed to their limits so that the limits themselves are often not clearly known. To use the potentials of modern tool and machine tool concepts, a deeper theoretical understanding of the processes is necessary. This applies especially to modern indexable insert gear cutting tools, which gain importance in these processes.In the past, gear cutting processes for large module gears have seldom been a subject of scientific research. Therefore, the design of these processes is largely based on experience. Especially, for the newer and more complex tool concepts using indexable inserts, a possibility to analyze processes theoretically is a key factor for deeper understanding of the processes and tool concepts.In this paper the two most important processes for green machining of large module gears, gear hobbing and form milling, are analyzed using simulation and machining trials. For the process simulation, major changes to existing process simulation tools for gear machining processes were implemented. For suitable machining trials, model processes were developed for milling and hobbing. These allow an analysis of the wear behavior of the tools based on a reduced number of machined parts. In this paper the bridge between simulation and machining for large module gears will be drawn in terms of chip removal and deformation, wear behavior and tool design features. As final result a first method for a simulation based process design will be given.

A Novel Simulation Approach to Determine Thermally Induced Geometric Deviations in Dry Gear Hobbing

The ability to predict temperature distributions in workpiecesduring dry gear hobbing, especially of large ring gears, enables the avoidance of lubricants. Up to now wet hobbing is state of the art in the gearing industry. The calculation and compensation of thermal deviations during dry gear hobbing is necessary to achieve high gear quality. Based on previous work, which was concentrated on chip forming, the current simulations are performed for the full hobbing process of a complete gear with the focus on thermal distributions and the following geometry deviations. A modified dexel model is presented in the paper which is able to describe modern gear geometries, to store temperature fields and to provide information for 3D visualizations at every time. Additionally a numerical simulation of the complex gear hobbing kinematic is effectively realized with the help of quaternions algebra and parallel computations. The problem of thermo-mechanical coupling is solved by using commercial FE software and a self-developed finite difference based solver. Subsequently different compensation strategies will be discussed against each other by the help of the developed simulation model to avoid thermal deviation in advance.

Approach for the Calculation of Cutting Forces in Generating Gear Grinding

One of the main challenges in generating gear grinding is the determination of cutting forces due to their significant influence on the dynamics of the grinding process. Thus, optimizing the cutting forces can lead to an increased quality of ground gears and a minimized wear behavior of the grinding worm. Currently, the knowledge of the generating grinding process is limited and research is based mostly on empirical studies. A theoretical model which help to predict the cutting forces is missing.This paper presents an initial approach for calculating the complex contact conditions in generating gear grinding as well as cutting forces and key values to characterize the process. This approach gains more and more importance especially for large module gears, to reduce manufacturing costs. By means of the calculated forces, the manufacturing process can be optimized and the quality of the manufactured gear can be increased.

Novel Configuration of Laryngeal Mask Airw

Hospital airway emergency teams are often responsible for responding to codes, emergency intubations etc. The individual provider may have to respond quickly to widely separated areas of large medical centers on a moment's notice. Further, in addition to the urgency, the distance of different sites makes it important that the airway team not have to lug a large medical gear bag with airway supplies and emergency drugs. While the importance of the LMA in emergency airway management has been well established, it is sold as a fairly bulky device that requires a disproportionate space in an airway pack. We sought to examine whether modifying the LMA packaging might reduce the amount of space taken up by the need to carry three different sizes in an airway pack. A commonly used Laryngeal Mask Size Number 3 manufactured by Ambu Company was studied. The volume displacement of the package, and then just the LMA was measured using volumetric techniques. Removing the large packaging yielded a much smaller footprint in cubic ml that was only 18% of the original packaging: 43 versus 240 cubic milliliters. This configuration of LMA transport allows for transporting more airway equipment in less space. These results have important implications for emergency airway response teams. Removing the original packaging and using this folded-over configuration allows to use 82% less volume in cubic milliliters per LMA in the airway pack. This allows emergency teams to carry more equipment in much less space.

Magnetic Gears for High Torque Applications

An analytical model for the prediction of the magnetic field distributions in the airgaps and permanent magnets of large radial-field magnetic gears equipped with radially and Halbach magnetized (HM) permanent magnets is presented. The model is compared to 2-D finite element analysis and has been employed for the design optimization of a large magnetic gear. It is shown that adopting a discrete HM distribution results in significant improvements in torque transmission capability and substantial reduction in active mass.

Improving the Hardness of a Wind Turbine Gear Surface by Nitriding Process

This paper presents a surface hardness improvement methodology of a wind turbine helical gear which is made up on EN36 alloy steel material. Now days the wind turbine gears are frequently failed due to high contact stress, due to sudden impact load, change of wind speed and wind directions. Pitting is a method of surface failure in a gear. So, to avoid the gear failures we need to improve the surface hardness of wind turbine gears by using Nitriding process. There are three modes of hardness test taken from this process to improve the hardness. They are before nitriding, after nitriding & without nitriding. By comparing the hardness test values, Gas Nitriding is the best suitable process to increase the surface hardness of a large size gear. By the method of improving surface hardness of wind turbine gear, the load withstanding capacity of the wind turbine gears are increased, pitting failure may be avoided at a desired level and the power production rate is increased.

Manufacturing the new type concave–convex profile involute gears modeled by CAD–CAM in CNC milling machines

Gears are used in the design of modern machines extensively. These gears are of various types according to their tooth profiles and tooth widths, and can be manufactured in various sizes as small as the ones in small appliances to the very large gears used in heavy industry. In addition, some of the gears have proven benefits, and universally accepted standard manufacturing methods have been developed in time for these gears. However, researchers have always made more experiments, believing that there is no end in science, and have performed research activities in order to contribute to the science a little more. And numerous researches have been carried out on the gear wheels, and many successful studies have been presented. In this study, involute profile cylindrical gears were manufactured at the CNC milling machines and the results were evaluated. The idea that these involute profile cylindrical gears can be manufactured at the CNC milling machines by two different methods, which are completely different from the present manufacturing methods, was proposed by other researchers. Although these gears were proven useful by the researchers, they were not widespread because of the previous unsuccessful methods developed for their production.

The Slow-Speed Wear Behavior of Case-Carburized Gears Lubricated with NLGI 00 Grease under Boundary Lubrication Conditions

NLGI 00 greases are often used to lubricate gears running at low pitch line velocities, such as, for example, in large open gear drives. At low pitch line velocities, sliding wear, which under these operating conditions is referred to as slow speed wear, is often the limiting factor to gear lifetime. A thorough knowledge of the effect of different grease components on the wear behavior is therefore important when selecting a grease to effectively reduce gear wear in a given gear drive. In order to systematically investigate and analyze the influence of different grease components on the slow-speed wear behavior of case-carburized gears, systematic gear tests using the Gear Research Center's (FZG) back-to-back gear test rig were conducted. Primarily, the focus of the experimental investigations is on the influence of the base oil viscosity and type, the additive type, and also the type of soap thickener on the gear wear behavior at low pitch line velocities. To experimentally determine the influence of these different grease components on the wear behavior of case-carburized gears, a modified, more stringent wear test, based on the standard DGMK slow-speed wear test for gear oils, was developed. Different NLGI 00 greases with base oil viscosities between ν40 = 70 and 1,200 mm2/s were investigated.Base oil type and base oil viscosity were shown to have only a minor effect on the wear behavior under boundary lubrication conditions. On the other hand, the thickener type and especially the additive type play an important role in determining the wear behavior.

Macropitting in Microsegregated Induction-Hardened Gear Tooth

A sample from a large gear was submitted for investigation into the cause of apparent macropitting observed around the pitch line on the loaded face of one of the teeth. A banded (light and dark etching) martensitic structure was observed, which varied significantly in hardness. Cracking was observed to be isolated to the case-hardened surface. The macropitting observed appeared to be consistent with contact fatigue. The nonhomogeneous microstructure observed may have been particularly susceptible to fatigue initiation and propagation. The microstructure observed appeared to be due to a lack of homogenous diffusion of carbon during the austenization of the part from the annealed condition.

Bending and contact fatigue strength of innovative steels for large gears

Large gears for wind turbine gearboxes require high performances and cost-effective manufacturing processes. Heat distortion in the heat treatment phase and the consequent large grinding stock are responsible for high manufacturing costs due to reduced productivity. A research project aimed at the identification of new materials, manufacturing and heat treatment processes has been performed. Air quenchable alloy steels, combined with a specifically developed case hardening and heat treatment process, have been identified as an interesting solution, both from the point of view of cost effectiveness, thanks to reduced distortions and grinding stock, and for the environmental sustainability. The research project has been completed by the manufacturing of a full-scale gear, on which the whole process has been validated. Nevertheless, in order to judge the applicability of these steels to large gears, data from specific tests on the performances against typical gear failure modes, like bending and contact fatigue, are necessary as well. Single tooth fatigue bending tests and disc-on-disc contact fatigue tests have therefore been performed on two innovative materials, respectively, a high hardenability steel and a bainitic structure steel, and on a reference traditional case hardening steel. The results of these tests, which provide useful data for gear designers, are presented and discussed in this paper.

Surface Integrity Aspects of Milled Large Hardened Gears

With the rising performance of wind turbines the requirements for large scale gears are growing. Due to the bigger loads based on the higher megawatt output per turbine gears especially at slewing bearings need to be hardened. Rising demands for better gear qualities and higher loads require a hard machining of these hardened gears. The development of special cutting materials for geometrically well-defined cutting edge processes enables the manufactures to mill these gears in hardened condition on standard milling machines. The process of milling hardened gears needs control of the surface integrity of the tooth flanks. The generation of white etching areas must be avoided and can be influenced by process parameters (e.g. cutting speed and feed rate). Preferably compressive residual stresses should be generated in the surface and sub-surface of the tooth flank. The paper describes the potentials of milling theses hardened gears instead of grinding and reveals the generated surface integrity state.

Remanufacturing the Pinion: An Application of a New Design Method for Spiral Bevel Gears

Damages of a large spiral bevel gear drive as used in heavy industry typically affect the pinion. Even if the gear still could be used, the complete pair has to be changed. This leads to long off times, high costs, and unnecessary waste. This paper applies a recent design technology for spiral bevel gears to the production of a replacement pinion for the sake of energy saving, reduction of costs and off times, and for the realization of green engineering. The process involves the following steps. First, the real tool surface of the gear is measured by a CMM. Based on the new design method, the tooth surface of the mating pinion is derived from this discrete point cloud. In order to improve the meshing performance, the resulting surface of the pinion is modified in the third step. Finally, the pinion is produced on a CNC machining center. In contrast to other approaches, none of these steps needs the parameters of the special machine tool defining the original gear pair. It is worth noting that our technology can also be profitable to gain more freedom in the design of new gear pairs.

Numerical Simulation and Experiment of Hot Roll Forming Large Module Gear

To compare with the other gear manufacturing methods, the hot roll forming process is applied in forming large module gear. The hot gear rolling theory is realized by modeling in Solidworks and Deform-3D, the finite element model (FEM) that coupled deformation and heat transfer was established, and the FE model velocity boundaries were set by converting the workpiece rotation into the revolution speed of the roller. The total displacement of metal flow, folding angel of teeth, effect strain and the temperature distribution of the part were obtained in the whole process of hot gear rolling, also the rolling force was predicted by simulation. The simulation results reveal the forming mechanism, and the rolling experiments were carried out with self-designed rolling mill, which verify that the hot roll forming large gear is feasible.

Research on Floating Moment Balancing Mechanism of a Gear Pump's Asymmetric Floating Plate with a V-Shaped Groove

Symmetrical floating plate of the high pressure and large displacement gear pump in rated conditions is inability to achieve the floating moment balance. To solve this problem, a new balancing mechanism is presented in this paper, which is asymmetric with a V-shaped groove structure on its driven side, called asymmetric balancing mechanism. Compared with traditional symmetric balancing mechanism, the floating plate with asymmetric balancing mechanism the can the coupling problem between the gear shaft and gear inner flow field through its own asymmetrical structure, so that the gear pumps internal flow field was the symmetrical distribution. According to the structural characteristics of the floating plates, Parameterized moment model based on discrete feature points was established. Theoretical analysis and experimental tests show the result , when suffered floating moment as evaluation criteria, in rated conditions, compared with the traditional symmetrical balancing mechanism one, that the balance performance of the floating plate with V-shaped groove asymmetric balancing mechanism improve by 41.42%.

Finite element analysis on the formation and distribution of residual stresses during quenching of low carbon bainitic–martensitic large gears

Applications requiring high strength and wear resistance such as in large gears are expected to benefit from using low carbon bainitic–martensitic (LCBM) steels. Unlike conventional gear steels (SAE 4140 and AISI 5130), post surface hardening treatments namely induction and flame hardening used to increase surface hardness and promote the formation of compressive residual stresses in the teeth are not necessary using LCBM steels. A thermo-mechanical FE model was developed to model the evolution of microstructure, the volumetric changes associated with the kinetics of martensitic phase transformation and the formation and distribution of residual stresses during quenching of LCBM large gears. Two cases, air-cooled and a two stage quenching process of the LCBM large gear were evaluated to determine the residual stress distribution formed in the root of the tooth which is prone to bending fatigue. The results showed that the novel two stage quenching process is most suited for LCBM gears with large root fillet radius since compressive residual stresses achieved in the fatigue prone areas of the gear were found to exceed those of conventionally induction hardened treated SAE 4140 gears. The effects of root fillet radius on the resultant bending stresses incorporating residual stresses in the root of the tooth were analysed for large LCBM gears.

Global optimization of reliability design for large ball mill gear transmission based on the Kriging model and genetic algorithm

This paper aims to improve the global optimization operation efficiency in engineering by establishing the Kriging model to simplify the calculated mathematics model. In the case of the large ball mill, this paper presents in detail the application of the stress–strength distribution interference theory to calculate the reliability of gear transmission, establishes the Kriging model for function fitting, and uses genetic algorithm to globally optimize the volume and reliability of large ball mill gear transmission. The optimal result based the Kriging model is contrasted with the Monte Carlo Method in terms of calculation accuracy, greatly improving the efficiency of calculation.