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Vasile Bratu and Ileana Nicoleta Popescu

Abstract

In order to determine the optimum geometry of the ingot mold format (the format of ingot mold with a diameter per height ratio H / D <3 and the conicity of minimum 7%) was analyzed by mathematical modeling of solidification and segregation of the carbon and sulfur in it.

It was considered 205Cr115 steel type (according with , STAS 3611 - Romanian stardandization) and known also as X210Cr12 steel type (according with European standard). It has been considered an element of volume of coordinates x, y, z in the solidifying ingot and have made the following assumptions: (i) the equilibrium distribution ratio K, is applied to the solid-liquid interface; (ii) solid diffusion is negligible during solidification; and (iii) the solid density is constant during solidification. In carrying out the simulation of segregation mechanisms are resolved heat transfer equation, that simulating the solidification process and are are solved the interdendritic fluid equation of motion.

Open access

Polidor Bratu and Ovidiu Vasile

Rezumat

Lucrarea abordează comportarea unui model de solid-rigid cu anumite simetrii structurale. Aceste simetrii permit simplificarea calculelor (ecuaţii de mişcare) şi, deci, a modelelor matematice. Dacă solidul rigid este conectat la structură prin patru legături elastice, modelul rămâne încă simplu şi uşor de rezolvat, vibraţiile putând fi decuplate în patru subsisteme de mişcare.

În final, se prezintă un studiu de caz pentru analiza modală a unui viaduct, modelat precum un corp solid-rigid, rezemat elastic, de pe autostrada Transilvania (km 29+602.75 m).

Open access

Elena Valentina Stoian, Vasile Bratu, Cristiana Maria Enescu and Carmen Otilia Rusanescu

Abstract

The paper presents the study of internal defects resulting from the continuous casting of steels. The 50 samples were taken from a total of 20 continuously cast bits of different steel grades. The investigation of the causes of internal defects, shown on the analyzed samples, started from the assumption that the secondary metallurgy was performed correctly. The following internal defects have been evident: internal cracks (axial cracks, section cracks), central porosity and marginal punctuation impurities.

Open access

Nicolae Angelescu, Cristina Stancu, Sofiane Amziane, Vasile Bratu and Elena Valentina Stoian

Abstract

Refractory concretes based on aluminous cements are used with great success in areas where high temperatures are required. The mineralogical composition of the high alumina cement is the main factor which gives the physical and mechanical properties at high temperatures of refractory monolithic materials.

It is therefore desirable to use high alumina cements based on mineralogical compounds with high refractoriness, because in the end those beneficial properties can be found in the final product - refractory concrete.

The aim of this paper is to design, realize and characterize different compositions of high alumina cements based on mineralogical compounds with the highest refractory from the CaO-Al2O3 binary system (i.e. CA, CA2, and CA6), and to find ways of hydraulic activation of calcium hexa aluminate, also.

Open access

Ileana Nicoleta Popescu, Ruxandra Vidu and Vasile Bratu

Abstract

Over the last few decades, researchers has been focused on the study of processing using different methods of new biocompatible and/or biodegradable materials such as permanent or temporary medical implants in reconstructive surgery. The advantages of obtaining biomedical implants by Powder Metallurgy (P/M) techniques are (i) obtaining the near-net-shaped with complex forms, (ii) making materials with controlled porosity or (iii) making mechanically resistant sintered metallic materials used as reinforcing elements for ceramic/polymeric biocompatible materials. In this first part of the 2-part review, the most used and newest metallic biomaterials obtained by P/M methods are presented, along with their compaction and sintering behavior and the properties of the porous biomaterials studied in correlation with the biomedical domain of application.

Open access

Nicolae Angelescu, Dan Nicolae Ungureanu and Vasile Bratu

Abstract

The current work is intended to explain the role of some organic admixtures on the hardened structure of refractory concretes with aluminous cement. The influences on the mechanical-structural properties in the normal hardening but in the heating conditions at different temperatures are emphasized, also. These are due to the influence on the hydration process (i.e. the kind of the neoformations and degree of hydration) and implicitly on the size and distribution of structural pores.

Open access

Elena Valentina Stoian, Vasile Bratu, Cristiana Maria Enescu and Dan Nicolae Ungureanu

Abstract

Aim of the study is to present the technological process of obtaining cast iron with lamellar graphite for use in the manufacture of cylinder liners, and to identify the main alloying elements and track their influence on the mechanical properties of cast iron with lamellar graphite.

Also paper presents analysis of 20 batches of cast iron with lamellar graphite, which are made of cylinder liners, in terms of chemical composition and the mechanical properties.

After the analysis of the 20 castings of cast iron Fc 250 it is observed that: the increase in the carbon content shows a decrease of the tensile strength and hardness of the gray cast iron; the increase in silicon content shows a decrease in hardness and tensile strength. Decreasing the amount of graphite and especially the alloy of silicon iron lead to hardness increase 1% Si increases hardness by 50 HB). A statistical analysis has been performed on the data obtained that accounts for changes in alloying additions. A modeling and optimization of mechanical properties (tensile strength and hardness) was performed according to the percentages of carbon, silicon and manganese. Mathematical modeling found that the hardness and traction resistance of the cast iron decreased with the increase in carbon, silicon and manganese content.

Open access

Vasile Bratu, Aurel Gaba, Elena Valentina Stoian and Florina Violeta Anghelina

Abstract

This article presents different solutions to reduce natural gas consumptions of the aluminum melting furnaces, through recovery of the heat from flue gases. In order to be able to analyze the recovery solutions, a mathematical model for energy balance of these furnaces was adapted. This mathematical model allows drawing up energy balances together with the main working technique and economical parameters of these types of furnaces, in actual conditions, and the same, under optimizing conditions, by applying recovery solutions.

The mathematical model which can elaborate energy balances for aluminum melting furnaces, was transposed in M. Excel based software, where the quantification of different solutions for natural gas consumption saving is possible. One of the applications of this computer software for an aluminum melting furnace, either for actual working conditions or per upgraded furnace by use an air pre-heater, materials pre-heater, or a regenerative burner system, is presented in this article.

Open access

Nicolae Angelescu, Vasile Bratu, Elena Valentina Stoian, Dan Nicolae Ungureanu and Ana-Maria Gurban

Abstract

Calcium-phosphate cements is one of the most popular types of biomaterials, both due to their specific properties of self - setting and of their superior biocompatibility.

Although in general the phosphocalcic cements, which are the subject of the present paper, have somewhat lower mechanical properties than other biomaterials based on calcium and phosphorus, or even other dental cements of the same nature. The ceramic compositions presented in the present paper constitute a special category of biomaterials due to other notable advantages that characterize them. Thus, this category of materials is defined by a near-perfect adaptation to the surface of the biological tissue, as well as by a convenient resorption rate, processes followed by the generation of optimal bone formation. In this paper are presented principles of realization of the calcium-phosphate cements (raw materials and conditions of production), as well as the properties of these biomaterials, insisting, in particular, on the chemistry of the setting reactions. At the same time, informations regarding the possibilities of clinical use, such as implants are presented.

Open access

Elena Valentina Stoian, Maria Cristiana Enescu, Vasile Bratu, Carmen Otilia Rusanescu and Florina Violeta Anghelina

Abstract

Non/oriented electrical sheets are sheets tailored to produce specific properties and are produced from Fe-Si or Fe-Si-Al alloys. Non-oriented electrical steel sheets are incorporated into a wide range of equipment, from the simplest domestic appliances to hybrid and pure electric vehicles. In studying about the magnetic, there have a lot of method can be used for the different experiment requirement such as measuring magnetic flux, nominal loss and other objectives.

During electrical steel processing, there are usually small variations in both chemical composition and thickness in the hot-rolled material that may lead to different magnetic properties for the same steel grade. Therefore, it is of great importance to know the effects of such variations on the final microstructure and magnetic properties of these steels. The purpose of this work was to study microstructural changes of the bands investigated during processing occurring siliceous strips with non-oriented grains. The second aim was to study the influence of grain size on the total magnetic losses at 1.0 T and 1.5 T. Materials 10 rolls intended to be processed into quality electrical steel M400-50A (according to EN 100027-1) were analyzed with metallographic microscope Neophet 32 and the magnetic characteristics was made with Epstein frame according IEC 6040/4-2, with an exiting current frequency of 50Hz at 1.5T and 1.0T induction after aging treatment of 225°C for 24 hours. Sample for light microscopy observation were prepared by polishing and etching in 5% Nital.