Convective heat transfer modelling in dry-running polymer spur gears

Heat convection is an important phenomenon in the process of cooling polymer spur gears running in dry conditions, which ultimately affects the strength of the gears. In order to gain some insight into this phenomenon, a numerical heat convection model for polymer spur gears is proposed in this work, which is based on a detailed CFD simulation of the gears in operating conditions and it allows us to investigate the heat convection through their external surfaces. The performance of this numerical model is illustrated with several examples, in which a parametric study has been conducted to observe the variation of the heat transfer coefficients with the face width and the angular speed of the gears. The results obtained from this parametric study are compared to those obtained from a representative classical heat convection model, observing that the relative differences between them in terms of heat transfer coefficients can be as high as 125%. Finally, a new optimized heat convection model for polymer spur gears running in dry conditions is proposed, in which the convective heat transfer coefficients for the external surfaces of the gears are calculated from empirical equations based on the Newton’s law of cooling. This optimized model has lower computational cost than the numerical one, while it provides an important increase of the accuracy of the classical heat convection models, reducing the maximum relative differences to 10%.Funding for open access charge: CRUE-Universitat Jaume

The Tribological Properties of PEEK Machine Elements

This research reports on the relative dynamic performances of laser-sintered and injection-moulded poly-ether-ether-ketone (EOS PEEK HP3) gears and discusses the possibility of producing high performance polymer gears, manufactured by laser-sintering. Recent developments in laser-sintering of EOS PEEK HP3 have substantially improved its mechanical properties, and these are now comparable with injection-moulded PEEK. Here the wear rates and failure mechanisms, including contact fatigue and surface melting of laser-sintered and injection-moulded EOS PEEK HP3 were tested under conditions of relatively high loads and high slip-ratios through Twin Disc test rig and TE77 EP-GEAR DYNAMICS test rig high frequency reciprocating tribometer to simulate polymer gears contact unlubricated and lubricated in addition to gears direct testing. It was observed that the coefficient of friction and wear rates were significantly below that of injection moulded PEEK. However, when using of laser sintered EOS PEEK HP3 for gears for transmission of power, the predominant failure mechanism was bending fatigue, and this meant using this material limited power transmission to low levels. The use of a laser-sintered EOS PEEK HP3 in gears power transmission effects by the improving the tribological performance of gear teeth with surface lubricated conditions. Despite the advances made in laser-sintering of EOS PEEK HP3 further advances are required before it can be used for gears in power transmission

Dynamic Simulation of Gear System Based on 2D Space Multibody Physics: A Sustainable Gear Design Approach

The study employed a two-dimensional (2D) space with multibody dynamics as the physics to simulate the dynamic behaviour of intermeshing gears. Both the gear teeth and the gear body were employed to simulate the principal stress and strain as well as the Von Mises stress of the gear system. A pair of meshing teeth were examined from the pinion and the other from the gear for accurate contact stress-strain simulation. The validity of the proposed gear simulation was verified from principal surface stress, Von Mises stress, principal surface strain, elastic strain and total displacement. The results show that the dynamic behaviour of the gear could be attributed to the critical meshing characteristics of the single and double teeth. The peak-to-peak pattern of the Von Mises stress indicates the essential points of stress, which could cause the occurrence of the failure modes. The research of the gear motion study is profoundly enriched and served as a critical reference for gear design

An investigation into the effects of mould temperature on injection moulded HDPE gear performance

Polymers and polymer composite materials are emerging as viable front runner alternatives to metallic gears as they offer distinct advantages, such as good weight to strength ratios, the ability to run without external lubrication, less noise when running, and a lower coefficient of friction. Polymer gears undergo complex microstructural changes such as hysteresis, viscous flow, and elastic deformation which affect their performance capabilities to a greater extent compared to those of metallic gears. These differences mean that the failure of these gears differ to those made from metals. The wear behaviour and performance of polymetric gears has generated much interest from researchers over the past few decades, but to date there has been little focus on understanding the link between the input parameters used during the manufacturing process, and their corresponding physical and performance characteristics. This approach seems peculiar to polymer gears, as metal gears tend to be tested and graded not only by their material type, but also according to their mode of manufacture. Of particular importance during the manufacturing process for both metallic and polymetric gears, is the mould temperature (cooling temperature) of the molten material. Techniques such as quenching, annealing, or tempering, are used in metallic gear production to alter the cooling rate, which in turn alters the internal microstructure of the gear. The main objective in altering the cooling rates in metals is to increase strength, hardness, toughness, machinability, and ductility. Unlike metals, the effects of cooling rates on polymer composites are not well understood and documented. The complex microstructural changes which they undergo right from the manufacturing process to the point of operation, mean that better understanding as to how the input parameters employed during the manufacturing process determine their microstructural construct, and hence physical and performance characteristics. During this study, HDPE gears were injection moulded using optimised input parameters which were obtained using a robust design of experiments based on the Taguchi method. These parameters were then held constant, while gears were produced at 22°C, 34°C, 50°C, and 65°C. The gears were grouped according to the mould temperature setting at which they were produced. Differential scanning calorimetry (DSC) analysis was carried out for the different temperature settings to ascertain how crystallisation was affected. The results showed lower crystallisation levels for the lower mould temperatures, and higher levels for the higher mould temperatures. Gears produced at the same mould temperature were then meshed in a uniquely designed gear test rig. Torque loadings of 0.5 Nm, 1 Nm, 2 Nm, 3 Nm, and 4 Nm were applied at 500 and 1000 rpm, and were run until they failed. A bespoke data logging system was used to record rotational cycles verses wear, and corresponding wear curves were produced. SEM analysis was then carried out to ascertain the topological mode of failure for gears produced at different mould temperatures. The presented results show a direct relationship between the different mould temperatures and the resultant microstructural changes, gear characteristics, and performance. Based on these wear rate responses to the application of varying torque loadings, a Mould to Torque Reference Chart for HDPE is presented

Some Critical Issues for Injection Molding

This book is composed of different chapters which are related to the subject of injection molding and written by leading international academic experts in the field. It contains introduction on polymer PVT measurements and two main application areas of polymer PVT data in injection molding, optimization for injection molding process, Powder Injection Molding which comprises Ceramic Injection Molding and Metal Injection Molding, ans some special techniques or applications in injection molding. It provides some clear presentation of injection molding process and equipment to direct people in plastics manufacturing to solve problems and avoid costly errors. With useful, fundamental information for knowing and optimizing the injection molding operation, the readers could gain some working knowledge of the injection molding

Lubrication handbook for the space industry. Part A: Solid lubricants. Part B: Liquid lubricants

This handbook is intended to provide a ready reference for many of the solid and liquid lubricants used in the space industry. Lubricants and lubricant properties are arranged systematically so that designers, engineers, and maintenance personnel can conveniently locate data needed for their work. This handbook is divided into two major parts (A and B). Part A is a compilation of solid lubricant suppliers information on chemical and physical property of data of more than 250 solid lubricants, bonded solid lubricants, dispersions, and composites. Part B is a compilation of chemical and physical porperty data of more then 250 liquid lubricants, greases, oils, compounds, and fluids. The listed materials cover a broad spectrum from manufacturing and ground support to hardware applications of spacecraft

Mechanical Engineering

The book substantially offers the latest progresses about the important topics of the "Mechanical Engineering" to readers. It includes twenty-eight excellent studies prepared using state-of-art methodologies by professional researchers from different countries. The sections in the book comprise of the following titles: power transmission system, manufacturing processes and system analysis, thermo-fluid systems, simulations and computer applications, and new approaches in mechanical engineering education and organization systems