Sinteza, karakterizacija i primena novih vrsta vatrostalnih premaza u livarstvu

Abstract

Predmet ove doktorske disertacije je proučavanje sinteza novih vrsta vatrostalnih premaza za primenu u različitim metodama livenja, a pre svega kod livenja u pesku i livenja sa isparljivim polimernim modelima (Lost foam proces livenja). Istraživanja sinteze, karakterizacije i primene vatrostalnih premaza pokazala su da je odlučujući parametar kvaliteta sedimentaciona stabilnost suspenzije premaza. Osnovni cilj bio je da se ispita uticaj pojedinih komponenti iz sastava premaza, pre svega vrste i količine vatrostalnih punila, vezivnog sistema, vrste rastvarača, suspenzionog agensa i da se, optimizacijom sastava i izmenom postupaka izrade, postignu kontrolisana reološka svojstva premaza. Istraživane su različite vrste i količine aditiva, kao i postupci njihove aktivacije sa ciljem da se omogući laka adsorpcija aditiva na čestice vatrostalnog punioca, održavanje punioca u dispergovanom stanju u suspenziji i sprečavanje njegovog taloženja. Urađena su istraživanja sinteze premaza na bazi: talka, kordijerita, cirkona, mulita, korunda, hromita i liskuna na vodenoj i alkoholnoj osnovi i ispitivana je mogućnost njihove primene u livarstvu, a pre svega za razvoj nove metode livenja sa polimernim modelima. Za postizanje boljih efekata primene izvršeno je istraživanje uticaja mehaničke aktivacije na promenu strukture i svojstva punila, kao i svojstva dobijenih premaza. Izbor vezivnog sredstva u sastavu premaza vršen je u odnosu na veličinu i oblik čestica vatrostalnog punioca, kako bi se omogućilo povezivanje čestica i osigurala dobra adhezija vatrostalnih čestica na posmatranu površinu peščanog kalupa ili polimernog modela. Izvršena su sistematska istraživanja svojstava vatrostalnih premaza i izbor optimalne vrste premaza za konkretne metode livenja, vrste odlivaka i vrste legura. Istraživanja su pokazala da dobijena struktura i svojstva odlivaka u mnogome zavise od metode livenja i kritičnih parametara procesa (temperature livenja, vrste i sastava vatrostalnog premaza, propustljivosti premaza i kaluparske mešavine, vrste polimera za izradu modela, konstrukcije modela i ulivnog sistema) što zahteva njihovu kontrolu i optimizaciju u cilju postizanja željenih upotrebnih svojstava odlivaka. Zato je i jedan od ciljeva ove disertacije bio i izučavanje osnovnih fizičko-hemijskih i termodinamičkih pojava i procesa koji se odvijaju na granici tečan metal- vatrostalni premaz- peščani kalup u fazi ulivanja metala, hlađenja i očvšćavanja odlivaka. Posebna pažnja posvećena je proučavanju složenih pojava koje se odvijaju u sistemu: tečan metal- vatrostalni premaz -polimerni model-peščani kalup kod nove metode livenja, Lost foam procesa, u kome je proces kristalizacije odlivka praćen procesom razlaganja i isparavanja polimernog modela. Kontrola kvaliteta dobijenih odlivaka i analiza uzroka nastanka grešaka na odlivcima doprineli su boljem sagledavanju procesa livenja sa isparljivim modelima, što je značajno jer stvara mogućnost primene procesa u našim livnicama...

The subject of this PhD thesis is an examination of syntheses of new refractory coatings to be applied in different casting methods, primarily in sand casting process and in the evapourable polymer model casting process (Lost Foam Casting Process). A research concerning synthesis, characterization and aplication of refractory coatings has proven that a decisive quality parameter was sedimentation stability of coating suspension. The basic goal was to test the influence of individual coating components, primarily of the type and quantity of refractory fillers, bond systems, type of solvents and suspension agents in order to accomplish controlled reologic coating properties by both optimising the composition and changing the manufacturing procedure. Various types and quantities of additives have been examined, as well as their activation procedures, in order to facilitate additives to be easily adsorped by refractory filler particles and to retain a disperged condition of the filler in suspension, preventing its precipitation. Synthesis of coatings have been examined , with reference to the coatings based on talc, cordierite, zircon, mullite, corrund, chromite and mica. Further, the coatings used were water and alcohol based coatings and their casting applications were examined. First of all, these applications referred to development of a new casting method including polymer models. In order to attain better application effects, the influence of a mechanical activation on the change of both filler’s structure and properties were examined, as well as its influence on the properties of the coatings obtained. The choice of bond agent referred to the size and shape of refractory filler’s particles in order to enable particle connection and to ensure good adhesion of refractory particles to either the surface of a sand mold or a polymer model in subject. Refractory coating properties have been systematically examined, as well as the choice of an optimum coating type for concrete casting methods and types of mouldings and alloys.These examinations have shown that the moulding structure and properties attained mostly depend on both a casting method and critical process parameters (casting temperature, type and composition of a refractory coating, coating permeability and mold blend, type of polymer used for modelling, model design and model and inflow system design) . It implies that these parameters must be controlled and optimized in order to accomplish desirable utilization properties of mouldings. Therefore, an aim of this thesis was to examine basic physical-chemical and thermo-dynamic notions and processes carried out at the liquid metal-sand mold boundary at the stage of metal inflow and cooling and solidification of mouldings. A special attention was paid to complex notions carried out in the following system: liquid metal – refractory coating – polymer model – sand mold referring to the new casting method – Lost Foam Process. In this process, moulding crystalization is followed by degradation and evapouration of a polymer model. Quality control for the mouldings obtained and an analysis of the root cause of moulding defects contributed to a better understanding of the evapourable model casting process, which is important as it facilitates applications of this process in our foundries...