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Recent 26

Vol. 10 (2009), No. 2 (26)

The 26th issue of RECENT journal was edited and multiplied with support of:

  • Romanian Association for Nonconventional Technologies

  • Transilvania University of Brasov, Romania

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


CONTENTS


  • Constantin COSOVAN

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THE COMPUTATION OF RIGIDITY FOR THE STEP PARTS, CUT ON LATHE

» Abstract. In the classical strategy of the dimensional directing of the machining processes the particular stress is laid upon the machining agent (programmer), while the adaptive management is based on the interpretation of the information collected from the process and machined through the program. For the adaptive control, the knowledge of the possible strains, which the semi-finished product may show (mainly in case of high duty), is essential. In this work, there is proposed an analytical way of computation for the possible strain of the middle fibre of the semi-finished product that is being processed, an objective less discussed in the literature. Thus, there is also met the permanent interest for the improvement of the mathematical models, which become more and more adequate for the description of these machining processes. This tendency is also supported by the occurrence of some more and more performant sensors and subassemblies for pressure, vibrations and temperature measurement.

» Keywords: adaptive, control, middle fibre, technological function, machining


  • Konstantin D. DIMITROV

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MODEL-BASED FAULT DIAGNOSIS IN A WASTE-PROCESSING INDUSTRIAL SYSTEM VIA CAUSAL GRAPHS

» Abstract. The paper describes a Casual Graph (CAG) approach to fault diagnosis of industrial systems, based on logical and qualitative methodology for modelling the diagnostic aspects of a system structure and behaviour. The main goal consists in a development of necessary algorithmic structures, which are applied in an intelligent diagnostic system, based on a deep representation of the knowledge. A specific CAG diagnostic model, representing the causal behaviour of the diagnosed waste-processing industrial system is developed and presented in the paper. The diagnostic process is developed as a multi-stage algorithm, consisting of following main stages: failure detection, search for solutions, model tests, causal relations among symptoms and faults, and validation procedures.

» Keywords: model-based fault diagnosis, causal graphs, knowledge representation, diagnostic reasoning, system’s behaviour


  • Mariana FRATU, Aurel FRATU

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SIMULATION OF THE GAS TRANSPORTATION THROUGH PIPES INSPECTED BY INTELLIGENT ROBOTS

» Rezumat. In this paper, the authors have created the visual images of transport gas nets, by using the Delphi visual programming medium, as qualitative simulation tool. The authors show that using this tool, one can obtain a priori, in the design stadium, the information about the state of the transport pipe. In a real environment these information must be confirmed using the physical measurements and by the examination of the state of transport pipe by the intelligent robots inspectors. During the inspection, the robot stays in contact with pipe’s wall and the robot motion path will be imposed by the pipe profile and the pipe route. If the robot discovers the cracks in the pipe wall, this will signalize the defect zone. In this paper, for testing the robot motion control algorithms in the environment with constraints, the authors propose the using of the behavioral simulation method.

» Keywords: qualitative simulation, virtual applications, leakage monitoring


  • Bojidar GRIGOROV, Rosen MITREV

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A NEWTON - EULER APPROACH TO THE FREELY SUSPENDED LOAD SWINGING PROBLEM

» Abstract. The present article is dedicated to the creation of a mathematical model for solving the problem of swinging of a freely suspended load, the pivot point of which moves along a known, spatial, time dependent or position dependent trajectory. The motion of the pendulum is described as rotations about two mutually perpendicular axes. Thus, the Newton – Euler dynamic formulation is utilized and the equilibrium of a spherical pendulum under influence of a set of gravity and inertia forces and moments is considered. This approach leads to a system of two straightforward ordinary differential equations which could be solved numerically using any available solver. The solution is easy to programming and could be used for dynamic investigation of the scope of different types of equipment.

» Keywords: payload, swinging, dynamics, mathematical model


  • Vasile JIMAN, Ioan CIOBANU, Sorin I. MUNTEANU

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2D MATHEMATICAL MODEL FOR THE SIMULATION OF CENTRIFUGALLY CAST PART SOLIDIFICATION

» Abstract. The paper discusses the particularities of the mathematical modelling of centrifugally cast part solidification. The principle of 2D mathematical modelling of centrifugally cast tubular part solidification is presented. The mathematical model uses cylindrical coordinates and is based on the method of finite differences. The particularisation of the equations underlying the mathematical model is achieved by type and composition of the alloy.

» Keywords: centrifugal casting, castings, simulation, mathematical modelling, solidification


  • David JOGUET, Bogdan BORCEA, Camelia OLTEANU, Alexandru MUNTEANU

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SILICON’S INFLUENCE ON TIN AND TIC THIN FILMS OBTAINED BY PVD

» Abstract. This paper aims to present the influence of the silicon on the structure and properties of thin films, type TiN and TiC, enriched by physical vapour deposition method. The studied thin films were deposited by cathodic magnetronic sputtering technique, using a classic DC generator and a high power generator (HIPIMS). The hexagonal crystallographic structure of α Ti modifies into a cubic centred crystal lattice, NaCl type, together with the nitrogen or carbon enrichment and the synthesis of TiN and respectively TiC compounds. The supplementary addition of silicon, offers the conditions for the formation of SixNy or SixCy amorphous fazes, besides the crystalline ones (TiN or TiC). The properties of such nanocomposites films, with a thickness of maximum 3 µm, depends on the ratio between the metallic phase (TiN or TiC) and the amorphous phase (SixNy or SixCy) and on the TiN or TiC columnar grains diameter.

» Keywords: nanocomposites, PVD, thin films


  • Ioan MĂRGINEANU, Lucian Mihai ITU

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GAP DETERMINATION FOR CLINKER PREPARATION KILNS

» Abstract. Cement kilns are the heart of the cement production process; they are used for the pyroprocessing stage of manufacture of Portland and other types of hydraulic cement. Their capacities usually define the capacity of the cement plant. The gaps between the kiln and the rings which support the kiln have to be constant. The gap has to be kept between two limits so that the force of friction is great enough to avoid uncontrolled sliding between the ring and the shell of the kiln. If these are not equal for all of the rings, they can twist the kiln. The measurement of the temperature of the shell and of the kiln, and the computing of the gap based on these two are difficult. The purpose of this work is to build up a measuring system for the gap, based on the measurement of the time of an entire rotation of the two entities using a programmable logic controller (PLC). The computing algorithm has been applied to determine the gap for the clinker kiln at the cement mill LAFARGE Hoghiz, Romania. The results obtained have been verified. Before the kiln was turned on, a line a line has been drawn starting on the ring and ending on the shell of the kiln. By measuring the distance between the two lines after the accomplishment of n rotations the gap has been determined manually. This gap was then compared with gap determined by the PLC and the two were nearly equal. The higher the number of rotations taken into account is, the greater the precision of the obtained gap will be. Because the gap is determined by a program, the result can then be sent to higher ranked system which can take a decision which will cause the growth or the decrease of the gap.

» Keywords: rotary kiln, furnace, tunnel kiln, cement kiln, cement breaking heater


  • George NICOLAE

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MEASUREMENT METHOD FOR DETERMINING ELECTROMAGNETIC FIELD ATTENUATION IN NANOMATERIALS USING THE TEM CELL (2nd Part)

» Abstract. This paper presents the results of experimental determinations concerning electromagnetic field attenuation in materials containing micro-particles of iron, graphite or carbon black in their structure. In order to determine the shielding effectiveness of electromagnetic absorbents to electromagnetic field, a measuring system based on the TEM cell was proposed and tested. This measurement system was used to determine the electromagnetic shielding properties of materials at frequencies ranging between 1MHz and 1000 MHz. The experimental investigations were conducted in the frame of the CNCSIS project No 429/2006 ”Study of shielding properties of materials obtained by nano-technologies and nano-processing with application in electrical and electronic equipments in order to improve the quality of the environment”.

» Keywords: shielding effectiveness, attenuation measurement system, shielding materials, nano-materials


  • Nikolay NIKOLOV, Lenin LAZOV

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NUMERICAL ANALYSES OF THE FEEDER NUMBER INFLUENCE ON THE RESIDUAL STRESS IN A STEEL CASTING

» Abstract. In the present article, the residual stresses, formed during the cooling of a steel sand casting, are achieved by computer simulation. The casting is a real industrial product - an elevator brake wheel made of low carbon steel. Calculations have been made for four different types of casting feedings - using one, two, three, and four main feeders. The distribution of the three principle stresses and the equivalent stresses in the one main feeder version have been shown. The maximum residual stress zones have been defined and the stress values in them have been specified. The formation of the stresses in these zones has been explained as well as the origin of the corresponding stress state. For two of the high value residual stress zones the formation course of the stresses during the casting cooling process has been shown. A comparison has been made between the casting residual stresses in the four considered versions. It has been shown that the feeders influence the casting residual stresses only in the zones near their necks. It has been established that the most appropriate would be to use just one main feeder.

» Keywords: feeder, finite element method, residual stress, sand casting, steel


  • Rumen NIKOLOV

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KINEMATIC ANALYSIS AND SYNTHESIS OF DIFFERENTIAL SCREW ACTUATOR

» Abstract. The paper considers structural and kinematic studies of differential screw actuators. For a distinct type of kinematic chain named Closed Differential Screw Mechanism, consisting of an ordinary gear train and a crew pair, synthesis by minimal velocity ratio is done. The main dependences and values of the mechanism parameters are obtained so the minimum of velocity of the output link to be achieved.

» Keywords: differential screw mechanism, linear actuator, kinematic synthesis


 

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