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Recent 30

Vol. 11 (2010), No. 3 (30), November 2010

The 30th issue of RECENT journal was edited and multiplied with support of:

  • Transilvania University of Brasov, Romania

  • Romanian Association for Nonconventional Technologies

  • Brasov County Council (by Scientific Activities, Education, Culture, Cults Committee), Romania


CONTENTS


  • Sorin Adrian BARABAŞ, Eugen Cornel ŞERBAN

Stress Analysis with Finite Element Method of Large Bearings with Hollow Rollers Used in Wind Turbine System

» Abstract

In this paper is presented a method for increase the large bearings durability using hollow rollers, demonstrated through computer modelling. Implementation of large bearings with hollow rollers in wind turbine system lead to significant gains in constant power plant operation simplifying management of inertial forces. The mathematical model has been implemented in an algorithm, by which it is possible to study stress distribution for various models of hollow rollers. The analysis with finite element method (FEM) is developed with MD Nastran software.

» Keywords

large bearings, von Misses stress, hollow rollers, FEM

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  • Lucian BÂRSAN, Anca BÂRSAN

Conceptual Ecodesign for the Product Using Stage

» Abstract

Usually, the environmental impact of a product should be assessed during all the stages of its life cycle. In this paper, the evaluation will focus on the useful life of a product. Some products consume significant resources when used and others consume small amounts, even none. Designers should assess the products and establish the weight of energy and materials consumption during this stage from the total. Usually, this evaluation is performed using assessment instruments like LCA. The results of such analyse can be applied to the new products even in the conceptual stage during the design process. New solutions can be proposed and evaluated including the environmental impact criteria.

» Keywords

ecodesign, lifecycle, concept, function

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  • Nicolae BOIAN

Economic Performance of Small and Medium Enterprises (SMEs)

» Abstract

Our research in the field of SMEs include the concept of performance, problem that is different in comparison with large enterprises. Defining the concept is more importing in SMEs diagnose analysis because results should be judged in terms others than of efficiency and profit. This paper analyses the concept of “economic performance” in terms of diagnose analysis in small and medium enterprises. Theoretical considerations are presented by defining the concept of dual representation in the form of economical results and personalized expectations of the owners. Paper present a specific mode of performance evaluation of SMEs, the main factors and the main indicators used in the evaluation process of these enterprises. Also are detailed the main evaluation criteria of the factors and some key aspects of their interpretation. Conclusions refers to the need of differential treatment of diagnostic analyses to small and medium enterprises compared to large enterprises and expanding research toward other areas such as sociological, political or administrative.

» Keywords

performance, diagnose analysis, resources, organization, relationship system

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  • Rachid CHAĎB, Ion VERZEA, Mohamed BENIDIR

Contribution to the Performances Improvement of a Machine Boring Mill Operation

» Abstract

The performances requested from the production equipment and the associated economic issues bring the originators and the users of production means to be interested in the failures of the materials, with their consequences and the organizations which result from it. Among the tools used for the evaluation as of these performances, one finds the history file. Today, its exploitation became a technique of rigorous analysis consisting in exploiting the experience feedback. It is an approach of maintenance aiming providing the function and at maximizing the availability of the credit at the best possible cost, while proceeding to the good maintenance and the good moment. This approach enables us to know, to evaluate, envisage, measure and control the failures, to even accompany the operating condition of the machines. These concerns are expressed and treated through the concepts and the methods of RMAS (reliability, maintainability/maintenance, availability, safety). These files contain the failures types and their chronologies as well as the maintenance actions recorded in the form of the costs of maintenance, from duration and nature of failure. By exploiting these types of files, one can evaluate the operation parameters and the health condition of the machines, thus managed to apprehend the plans of maintenance to the needs for the production in real-time and for each machine, objective of this work. For better characterizing the breakdown and well evaluating its consequences, a coefficient called proportionality factor of the breakdowns “Fp” has been introduced. This coefficient enables us to determine the relationship between the breakdown and the duration lost to cure this breakdown. In this work, one is interested in a series of boring mill.

» Keywords

proportionality factor of the breakdowns, Ishikawa diagram, availability, maintainability, history file, failure

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  • Romeo CIOARĂ, Ovidiu SÎRBU

Transmission with Self-Adjustable Rotative Speed, for Bicycles

» Abstract

Different bicyclists have various objectives: some use it for performance, others for relaxation, others simply for traveling. Consequently, the maximal value of the power that the bicyclist is capable or is disposed to develop at the pedal shaft differs from case to case. Therefore, the bicycle gearings should be personalized. Conceiving and using a transmission with self-adjustable rotative speed, innovative and simple, easy to personalize for the various bicyclists’ requirements and performances, would be particularly advantageous from the bicyclist’s standpoint, who will no longer be preoccupied with periodically effecting the necessary adjustments for the bicycle advancement to adapt to the road and environmental conditions, which are frequently changing. Several principle solutions were studied, even some which conserve the chain gearing. The most adequate transmission with self-adjustable rotative speed for the purpose aimed at proved to be one with trapezoidal belt and speed variator with cone pulleys, only disposed on the pedal shaft. The target group for bicycles provided with self-adjustable rotative speed transmission are middle-aged bicyclists, frequent users of this transport means, non-pretentious as regards the special provision of the bicycle, relatively easy-going, little interested in frequently regulating the gearing ratio or even annoyed by the necessity of effecting this adjustment. This group of bicyclists is numerous and stable, representing a great potential for the market success of the bicycles provided with self-adjustable rotative speed transmission. The paper presents the structure and the functioning of a transmission with self-adjustable rotative speed, destined for equipping bicycles and makes considerations as regards the potential users of such equipped bicycles.

» Keywords

belt gearing, self-adjustable, bicycle

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  • Ioan CRISTIAN

An Analysis of the Dynamic Behaviour of the Linear Hydraulic Motor – Non-Linear/Liniarized Cutting Force System

» Abstract

The work is intended as a numerical simulation analysis of the dynamic behaviour of the linear hydraulic motor under cutting force strain. The case analysed is that of a linear hydraulic motor ensuring the longitudinal advance motion during cutting operation. The analysis focuses on two distinct situations: the non-linear expression of the cutting force and the linear expression of the cutting force, respectively. In conclusion, the conditions for acceptance of the errors resulting from the linear expression of the cutting force are highlighted.

» Keywords

dynamics, simulation, hydraulic motor, cutting force

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  • Konstantin D. DIMITROV

Evaluation of Operational Reliability in Industrial Sensors Control Systems via Stochastic Petri Nets (SPN)

» Abstract

The present paper describes the application of Stochastic Petri Nets (SPN) for analysis, modelling and evaluation of the operational reliability in industrial control systems. The SPN are applied for reliability modelling and reliability assessment in an industrial extruded polystyrene (XPS) grinding device. Some specific Petri net-based models of normal and abnormal control systems behaviour are developed and respectively applied under real operational control of an XPS-grinding device.

» Keywords

operational reliability, industrial control systems, stochastic Petri Nets

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  • Cătălin GHEORGHE

Insolvency - Solution for the Activity Continuation of the Companies Seriously Affected by the Crisis

» Abstract

The economic crisis began to render itself visible in the number of companies having entered under the incidence of the law concerning insolvency. The financial blockage and the impossibility of paying one’s obligations to the partners and also to the State budget led many companies towards bankruptcy. Does the explanation come only from the worsening of the economic conditions? They have determined many company owners to decide winding up their affairs, after having no longer been able to pay their debts. In the case of a company that has debts to recover, what is recommended: to start the approaches of enforcement or to open the insolvency procedure against the debtor? Substantiating the decision to enter juridical reorganization and its consequences make the content of the article herein.

» Keywords

insolvency, judicial reorganisation, enterprise, bankruptcy

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  • Vasile JIMAN, Ioan CIOBANU, Ciprian Andrei SZABO, Daniel FERARU

Research on the Influence of Thermoinsulating Cores on the Functioning of Feeders (II)

» Abstract

The paper presents the results of a study on the influence of heat insulation of feeders on the solidification of castings in silica sand moulds. The study was conducted by computer simulation of casting. The study concerned the influence of feeder thickness and heat insulation on the solidification of the casting-feeder system. Further observation focused on the influence of the thermoinsulating cores applied to feeders on the directing of the casting-feeder system solidification and on feeder efficiency.

» Keywords

casting, solidification, feeder, thermoinsulating core

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  • Aurel LUNGULEASA

Wooden Briquettes versus Pellets

» Abstract

The paper presents a comparison between wooden briquettes and pellets used for combustion, in order to promote ecological briquettes obtained from wooden biomass. Firstly there are specified the general advantages of woody biomass use, as renewable source of energy, time when the ecological problems at the world level are sharper. It is continued with a large presentation of the technical features of wooden briquettes and pellets, some elements about the use of wooden briquettes versus wooden pellets. Conclusions of paper raise one again that the wooden briquettes can become anytime a viable alternative to pellets.

» Keywords

wooden biomass, briquettes, pellets, ecological combustion

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  • Răzvan RĂCEU, Cosmina PÖLLNER

About Kinematic Parameters of the Spatial Hypocycloidal Automatic Machine for Cold Forming

» Abstract

Plane hypocycloidal automatic machines, forming an entire family, are a Romanian original concept developed at Transilvania University of Brasov. Recent researches emphasize the possibility of developing this group of automatic machines for cold forming by a new subgroup, potentially very diverse, the spatial hypocycloidal automatic machines. Although the slide blocks of these automatic machines realize a linear motion, the element which drives it describes a spatial hypocycloid, hence the name given to automatic machines in question. In the main cinematic chain of the automatic machine, there is present a sun-and-planet gear with conic gears that generate spatial hypocycloidal trajectories, used as a mechanism for transforming rotary motion into linear-alternative one. This paper presents, with adequate demonstrations, the law of motion of the driving element, the law of motion characterizing the slide blocks of these automatic machines, and its cinematic parameters.

» Keywords

hypocycloids, spatial spherical hypocycloids, automatic machines for cold forming, cinematic parameters

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  • Dorin-Mircea ROŞCA

Technical and Economic Analysis of a New Type of Cutting Tool Implementation

» Abstract

In the first part of this writing, a critical analysis is being presented, regarding the actual methodology concerning the implementation of the effectiveness of a new type of more advanced splinting tool. Considering the fact that the implementation of this new type of splinting tool does not require supplementary investment in other technological equipment or materials with deficient properties, a new algorithm is being designed, in order to determine the opportunity of the new tool adaptation. In this context are taken into account a number of specific costs such as effectively cutting time cost, new tool cost, cost of tool change time for its resharpening / replacement, waste plate cutting, etc.

» Keywords

cutting tools, optimization, computer

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  • Lyudmila STOYANOVA

Students Allocation for Practicum

» Abstract

The goal of this paper is to propose criteria for students’ assessment for allocation of students for the practicum at the cooperating companies. Analysis of the up to now used way of allocation has shown that simple arrangement of students according their results during the educational process gives not satisfying final classification. To perform more precise way of classifying students in competition for a definite company the specific activities of the company should be taken into consideration. An experiment for allocation taking into consideration the students wishes and their results in disciplines that are connected to the activities of the company has been satisfying. The connection between each company and the studied disciplines has been proposed to be measured in two levels. The experiment has been successful. Additionally the influence of the students’ performance at a practicum in a company from the abilities for group work and communication has been tested. The conclusion has been made that the performance of a group of students at the practicum has been influenced also by the presence of students with abilities to communicate and perform group work.

» Keywords

group work, allocation for practicum, criteria

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