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The Segregation in Ferrous Alloys when Casting Heavy Castings
Pernica, Vítězslav ; Čech, Jan (referee) ; Vodárek, Vlastimil (referee) ; Havlíček,, František (referee) ; Šenberger, Jaroslav (advisor)
This thesis is dedicated to the field of manufacture of heavy steel castings with resulting properties which are influenced by long solidification time. During the long solidification time a segregation process of additives in the steel occurs which results in numerous metallurgical defects. The work was intended to observe the macrosegregation effects in the wall of a heavy experimental steel casting respectively a part of a real superheavy casting intended for cement furnaces (weight 210 t). The steel casting for the research was manufactured in the joint-stock company of VHM where such heavy castings are commonly produced for the market. The supplied piece of the steel casting was cut into the smaller pieces for the better examination. The examination resulted in information about the casting macrostructure and chemical heterogeneity of chosen elements in the casting wall. The heterogeneity of the chosen elements (C, Mn, Si, Cr, S, P) is clearly shown in the worked out visual concentration maps. Based on the experimental data the measured results of segregations were confronted with the results of segregation modelling with the use of the commercial simulation software ProCAST. It resulted in the conclusion that the prediction of segregations is not in accordance with the reality. Furthermore, the results from the experimental casting are shortly compared with previously manufactured castings of the same type and the results summarizing the found range of macrosegregations of the tested sample are interpreted in the work conclusion.
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Manufacture and defects of heavy castings
Vymazal, Aleš ; Čech, Jan (referee) ; Záděra, Antonín (advisor)
Objective of diploma thesis is to proceed analysis of actual technology in operational terms for concrete casting of bearing . Constructed by foundry of steel ŽĎAS a.s., Žďár nad Sázavou. After designing changes in technological process accomplish detail evaluation of mechanical properties and chemical homogenity of metal at selected parts of sample casting.
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Design of linear motor with permanent magnets
Čech, Jan ; Bulín, Tomáš (referee) ; Knebl, Ladislav (advisor)
The first part of this thesis deals with the study of linear motors. The introduction of the thesis deals with the brief description of the linear motor, including its accessories. This part explains principle of linear motors, their general advantages and disadvantages. The next section contains an overview and division of the currently used linear motors. Each type of currently used linear motors is briefly introduced and also its principle and characteristics are described, including its specific application. The second part of the thesis deals with the design of an equivalent magnetic circuit model of a linear iron-core linear motor. Hereafter, the proposed design will be used to simulate the distribution of magnetic flux in the linear motor. The evaluated flux-density distribution in the air gap is later compared with the results obtained with finite element method. The thrust is then calculated from the flux-density and the estimated value is compared with the value listed in datasheet.
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RESEARCH OF HEAVY CASTING METALLURGICAL DEFECTS
Čech, Jan ; Elbel, Tomáš (referee) ; Jelínek, Petr (referee) ; Šenberger, Jaroslav (advisor)
A massive castings defects are examined in this doctoral thesis, specialise in steels passing through peritectic transformation. There are typical types of defects at massive steel castings, as contrasted to „ordinary“ internal and surface ones. For massive steel castings are typical defects under feeders like conchoidal fractures, segregations, microporesities, reoxidation products. Combination of Al and Zr is an ordinary final deoxidation of EOP and LF steel for castings in ŽĎAS a.s. foundry. The aim of Al + Zr combination was to both deep deoxidation by Al (decrease of bubbles risk) and denitrification by Zr (decrease of conchoidal fractures). This theses refute premission mentioned above and verified persisting risk of defects under massive feeders, even though Al + Zr deoxidation is used. A final deoxidation by increased amount of Al was examinated, in combination with other deoxidation agents. Castings had 11 [cm] maximal modulus, and occurence of conchoidal fracture, reoxidation products and primary austenite grain size was evaluated. A selected optimal final deoxidations (Al, Al+Ti, Al+Zr) as a result from experiment described above, were evaluated on castings with 15 [cm] maximal modulus. The result of experiment is, that is not possible to repeatedly produce massive steel casting using EOP metallurgical equipment without defects under feeders, despite of deoxidation and pouring temperature optimalization. The defect indications look like conchoidal fracture, but there are microporesity and impurities instead. Finally, castings with maximal modulus 15 [cm] were produced using so called secondary metallurgy (LF, VD). Secondary metallurgy allowed to both significant decrease of sulfur and degassing of melted metal. Only this metallurgical procedure guarantees production of heavy steel castings without typical defects under massive feeders
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Design of synchronous linear motor thermal network
Čech, Jan ; Toman, Marek (referee) ; Knebl, Ladislav (advisor)
The first part of this thesis deals with the study of linear motors. The introduction of the thesis deals with the brief description of the linear motor, including its accessories. This part explains principle of linear motors, their general advantages and disadvantages. The next section contains an overview and division of the currently used linear motors. The second part deals with the theoretical description of forms of heat transfer. The third part of the thesis deals with the design of an equivalent thermal circuit model of a linear iron-core linear motor with permanent magnet. Hereafter, the proposed design will be used to calculate the temperatures of the individual motor units. The temperatures are later compared with the results obtained with finite element method.
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Segregation during solidification in austenitic-ferritic stainless steels
Kejha, Richard ; Čech, Jan (referee) ; Pernica, Vítězslav (advisor)
The master thesis deals with processes of segregation in austenitic-ferritic stainless steels. The introductory part consists of characteristics features of austenitic-ferritic steels and theoretical analysis of segregation processes. The second part shows practical measurements of segregation in experimental casting. Macrosegregation was measured on a spectrometric analyzer and simultaneously solved in the simulation program MAGMA. The aim of this thesis is to verify the effect of solidification time and dwell time between liquidus and solidus temperature on the chemical heterogeneity of duplex stainless steel casting of about 500 [mm]. Chemical heterogeneity was solved for selected alloying and accompanying elements such as C, Mo, Ni, Mn, Cr. The microsegregation was not addressed. Comparison of the mechanical properties of cast and heat treated duplex steel was done by tensile testing of samples cut from the center of the casting.
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Metallurgy and properties of heavy steel castings
Kubík, Jiří ; Čech, Jan (referee) ; Záděra, Antonín (advisor)
The work deals with the determination of the chemical composition and morphology of inclusions in experimental casting foundry in operating conditions as ŽĎAS in compliance with the optimum content appropriate deoxidation depending on the conditions of solidification. The introductory part is devoted to theoretical analysis of possible defects in castings. We also describe the experimental casting, sampling sites and their markings. Subsequently evaluated morphology microanalysis inclusions and the effect of inclusions on the mechanical properties and the formation of defects in the casting. The conclusion summarizes the results and proposal for further direction in the production of heavy steel castings.
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Observation of twin boundaries in Ni-Mn-Ga alloys
Čech, Jan ; Jan, Vít (referee) ; Zelený, Martin (advisor)
This bachelor’s thesis is focused on observation of twin boundaries in a magnetic shape memory alloy based on Ni2MnGa with 10M martensitic structure. Theoretical part of the thesis describes materials with shape memory effect, their response on mechanical or magnetic loading, phenomenon of twinning, which is closely connected to the shape memory effect, and various levels of twinning. Experimental part studies different types of twin boundaries in monocrystal of alloy Ni49.2Mn30.4Ga20.4 using optical and electron microscopy. The thesis also deals with detection of structural orientations in different twin variants. A holder of samples was designed and constructed for real time observation of twin-boundary movement by optical microscopy. Deformation by pressure shows, that stress necessary for movement of Type II twin boundaries is ~0.2 MPa, whereas it is ~0.6 MPa for movement of Type I.
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The Study of the Production Process Selected Technologies
Rosecká, Eva ; Čech, Jan (referee) ; Jurová, Marie (advisor)
This work is focusing on the tracking of selected orders in a company which is mainly engaged in piece production of castings. The aim is, based on the tracking of the course of the pre-production and production phases, to analyse the production process bottlenecks. This is carried out by means of the information system used in the company and through daily tracking of the selected orders. The ascertained time data are divided into the time necessary for the production and the lost time. The scheduled and the actual production times, from order receipt up to the shipment of a finished casting, are entered in the Gantt diagram. In conclusion the work deals with the evaluation of the time lost in production and the proposals for making production more effective are offered.
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