Journal of Mechanical Engineering 56 (2010) 4

SV-JME-4-2010 in digital form »

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Editorial

 

Special issue

This special issue of Strojniški vestnik - Journal of Mechanical Engineering contains selected papers from the 2nd European Conference on Tribology - ECOTRIB 2009, held in Pisa, Italy on June 7-10, 2009. ECOTRIB 2009 was organized by Prof. Enrico Ciulli from the
University of Pisa in co-organization with the Italian Tribology Association, the Austrian Tribology Society, the Slovenian Society for Tribology and Swiss Tribology. Almost 180 delegates from 33 countries took part in the conference, which comprised 189 presentations, including three invited lectures, 4 society presentations, 141 oral presentations and 41 posters. ECOTRIB 2009 represents the second biennial conference primarily focused on the economy and industrial landscape of central and southern Europe, which alternates between Austria, Italy, Slovenia and Switzerland. The privilige to arrange the next ECOTRIB in June 2011 has been given to ...

Guest editors:
Bojan Podgornik
Giuseppe Palombarini

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A Model for Scuffing Prediction

Corresponding author - Enrico Ciulli

Authors - Ida Bartilotta - Alessandro Polacco - Salvatore Manconi - Dagoberto Vela - Francesco Saverio Guerrieri Paleotti

Abstract

A correct prediction of scuffing failures is not easy. Several models have been developed by a number of authors but none can be applied with a certain degree of reliability in every conditions.
In this work a simplified model for scuffing prediction is proposed. The model takes into account the presence of various lubrication regimes during the machine running.
Experimental tests are being carried out at Pisa University in order to validate the model, under a cooperation agreement between AVIO Propulsione Aerospaziale S.p.A. and AM testing s.r.l.. The procedures used and first results are presented.

Keywords - scuffing, friction, gear, Stribeck curves, thermal effects, non-conformal contacts

Paper's information

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)4 
UDC 621.833.01

 A Model for Scuffing Prediction (pdf)

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Logarithmical Crowning for Spur Gears

Corresponding author - Ellen Bergseth
Authors - Stefan Björklund

Abstract

Gear tooth modifications, such as lead crowning, are often recommended to compensate for misalignment (e.g. assembly deviations). Lead crowning means that the tooth centre is slightly thicker than the tooth edges and is usually described as a circular arc profile. The use of crowning shifts the peak load from the tooth flank edges and therefore reduces the risk for high contact pressures at the edges, which can otherwise result in a shortened service life.
In this study a logarithmical lead profile was compared with traditional lead profile modifications for gears. The profiles were applied on a spur gear pair and a numerical method for contact analysis was used to calculate the contact pressure distribution at the pitch diameter. All lead profiles were optimised with respect to low contact pressure at a specific normal load, a specified maximum misalignment in the plane of action and a tooth flank edge contact criteria.
The results show that the logarithmical profile responds differently to misalignments compared to the traditional lead profile modifications. The logarithmical profile resulted in lower maximum contact pressures for small misalignments and is therefore of further interest in terms of achieving a robust gear design.

Keywords - spur gear, lead crowning, misalignment, contact pressure

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)4 
UDC 519.6:621.83.052

 Logarithmical Crowning for Spur Gears (pdf)

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Influence of the Oil Churning, the Bearing and the Tooth Friction Losses on the Efficiency of Planetary Gears 

Corresponding author - Attila Csobán

Authors - Mihály Kozma

Abstract

The efficiency of a planetary gear depends on many factors: mainly on the tooth- and bearing friction losses, but beside them, in certain circumstances, also the oil churning losses have to be taken into consideration. This theoretical investigation was made to determine the oil churning, the bearing and the tooth friction losses of planetary gears and evaluate the influence of these types of friction losses on their efficiency. Optimization of the design of the planetary gear drives can result the best parameters leading to their highest efficiency even in the case of compound planetary gears.

Keywords - tooth friction loss, bearing friction loss, oil churning loss, loss of expel, efficiency

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)4 
UDC 621.839:621.892

 Influence of the Oil Churning, the Bearing and the Tooth Friction Losses on the Efficiency of Planetary Gears (pdf)

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EHL-Squeeze in High Loaded Contacts: The Case of Chain CVT Transmissions

Corresponding author - Michele Scaraggi

Authors - Leonardo De Novellis - Giuseppe Carbone

Abstract

We analyze the lubrication conditions at the pin-pulley interface in a Gear Chain Industrial chain CVT. In particular, we focus on the squeeze of oil which occurs as soon as the pin enters the pulley groove. The duration time to complete the squeeze process compared with the running time the pin takes to cover the entire arc of contact is fundamental to determine what actually is the lubrication regime at the interface. Taking into account that for normal CVT operations the time the pin spends in contact with the pulley groove is of about 0.01 s (traveling time), we show that rms surface roughness less than 0.1 μm and squeezing load of about 1kN acting on the pin, corresponding to values adopted in such systems, guarantee a fully lubricated EHL regime at the interface. We also show that during low-velocity CVT operations, the lubrication regime at the interface is determined by a succession of hydrodynamic and mixed lubrication stages in an order strictly related to the squeezing load history.

Keywords - continuously variable transmission, elasto-hydrodynamic lubrication, squeeze motion, multibody

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)4 
UDC 621.822.176

 EHL-Squeeze in High Loaded Contacts: The Case of Chain CVT Transmissions (pdf)

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Static Behaviour of Air Plane Pads: Comparison between Different Feeding Solutions

Corresponding author - Guido Belforte

Authors - Federico Colombo - Terenziano Raparelli - Andrea Trivella* - Vladimir Viktorov

Abstract

Air bearings are used among the others to support and guide coordinate measuring machines and instruments. There are different feeding solutions adopted to obtain the required stiffness and damping, often it is also important to minimize the air consumption.
The purpose of this paper is to evaluate the effects of supply orifice number on the static characteristics of plane pad circular air bearings. Two solutions are experimentally investigated, with six and three supply inherent orifices of same dimensions.
A test bench is used to obtain the static characteristics (load capacity and mass flow rate) of the pads. Then the static pressure distribution under the pads are experimentally determined in different directions.
A numerical model is developed to simulate the behaviour of the pads; a comparisons between experimental and numerical results is presented.

Keywords - gas thrust bearing, discharge coefficients, inherent orifices feeding system, circular pad

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)4 
UDC 531.2:621.822

 Static Behaviour of Air Plane Pads: Comparison between Different Feeding Solutions (pdf)

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Influence of Heat Treatment and Machining Parameters on Residual Stress Field and Wear of Double-Layer Cast Rolls

Corresponding author - Luis Vilhena

Authors - Bojan Podgornik - Slobodan Milanović - Jože Vižintin

Abstract

In practice, wear resistance, lifetime and capability of components and tools to resist loading greatly depend on the residual stress field in the material. This is especially true for hot-rolling applications, which require rolls with hard heat and wear resistant surface, tough core and proper compressive residual stress level to resist Hertzian cyclic loading. If casting, heat treatment, cooling process and surface machining and grinding are not done properly very high and uneven tensile residual stress field may occur, causing drop in wear resistance, cracking or even fracture of the roll.
The aim of this investigation was to determine the effect of different production operations and parameters on residual stress level and wear resistance of double-layer cast rolls. Using hole drilling method, residual stress depth distribution was measured circumferentially and transversely on the double-layer cast roll surface after casting, heat treatment, turning and grinding. Furthermore, using different turning and grinding parameters (speed, feed), and heat treatment parameters (temperature, time), influence of these parameters on residual stress level and wear resistance of roll outer layer were determined.

Keywords - residual stress, hot rolling, wear, machining, heat treatment

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)4 
UDC 539.4.016:621.785

 Influence of Heat Treatment and Machining Parameters on Residual Stress Field and Wear of Double-Layer Cast Rolls (pdf)

 

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Impact of Solid Particulate on Brittle Materials

Corresponding author - Donato Aquaro

Abstract
This paper deals with the erosion of brittle materials due to the impact of solid particulate. Erosion tests are characterized by a great uncertainty in the results and high costs. These difficulties led the author to develop alternative methods based on numerical simulations for calculating the erosion rate of brittle and ductile materials. Erosion criteria, based on fracture energy, were developed and implemented as Fortran routines in a commercial FEM code. In this paper the proposed method was applied to calculate the erosion rate of glass and glass ceramics. Fracture energy was obtained using four points bending tests. The numerical results were compared with a developed theoretical model and with the experimental results, available in the literature. In spite of several simplifying assumptions, there was a good agreement between the numerical and experimental results. This method could be a powerful tool for assessing the erosion resistance of components in real operating conditions.

Keywords - erosion model, impact wear, finite element, glass, glass ceramic erosion

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)4 
UDC 620.19:666.11

 Impact of Solid Particulate on Brittle Materials (pdf)

 

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Wear Particle Classifier System Based on an Artificial Neural Network

Corresponding author - Valdeci Donizete Gonçalves

Authors - Luis Fernando de Almeida - Mauro Hugo Mathias

Abstract
This paper describes a method to identify morphological attributes that classify wear particles in relation to the wear process from which they originate and permit the automatic identification without human expertise. The method is based on the use of Multi Layer Perceptron (MLP) for analysis of specific types of microscopic wear particles. The classification of the wear particles was performed according to their morphological attributes of size and aspect ratio, among others.

Keywords - artificial neural network, wear particles analysis, expert system

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 55(2010)4 
UDC 004.032.26

 Wear Particle Classifier System Based on an Artificial Neural Network (pdf)

 

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