Thermal Volumetric Analysis (TVA): A New Test Method of the Kinetics of Gas Emissions from Moulding Sands and Protective Coatings Heated by Liquid Alloy

Production of medium-sized and large castings is carried out in the sand moulds. The sand moulds, which components are made of moulding sand, the binder are different kinds of materials, the most common: moulding resins (furan, alkyd, phenolic, etc.). Internal surfaces of moulds, for increased thermal resistance, are usually covered by protective coatings. Liquid foundry alloys filling sand moulds produce intense heat, especially in layers adjacent to the cast. Under such conditions, the organic binders are burned or gasified. The resulting gases can penetrate the liquid causing the formation of defects such as blow-holes, pinholes, pitted skin, etc. The greater the intensity of the secretion of gases and the greater their volume (number), the more likely defects are created in castings. An important quality criterion of foundry resins is their tendency to emit gas. The authors developed the new test method, which allows to monitor the kinetics of gas emissions from the moulding sand and foundry coatings as a function of time and temperature (thermal volumetric analysis (TVA)). A number of studies were made for moulding sand with organic binders. Description of the research methodology and the presentation of results are the subject of the article

Investigations Concerning Improvements of the Knock Out Property of Ceramic Moulds Applied in the Investment Casting Technology

In lost wax technology, self-supporting ceramic moulds are made, which must have adequate strength after being filled with liquid metal. The final structural strength is determined by such factors as the thickness of the individual layers applied to the wax model resulting from the viscosity of the liquid mass, the specific strength of the layers formed, and the heat treatment of the moulds. The development of technology and materials is moving in the direction of increasing the specific strength of self-supporting ceramic moulds. The consequence of this is that the final strength of these moulds is too high, making it difficult to knock castings out of the moulds. Removing mould remnants from holes, closed spaces of the casting, corners, sharp edges, variable cross sections and etc. is cumbersome. In order to remove mould remnants from the casting, a method is used to dissolve them in heated solutions of suitable chemical composition and reaction. The paper presents the results of research on a new solution, the essence of which is the production of layers in a ceramic mould, in the middle zone of the mould, characterized by a significantly reduced final strength, achieved after firing. These layers are produced using a different liquid ceramic mass than the base one, based on an organic binder. As a result, thanks to the embedded layer, very good knock-out of castings is achieved and separation of residual ceramic mass. Special layers can be incorporated over the entire surface or only in those places where the bonding of the casting surface and ceramic mass occurs

CASTING OF Al-Si ALLOYS IN THE FULL-MOULD TECHNOLOGY. PROCESS CONDITIONS

A review of various technologies using expendable casting patterns made of expanded polystyrene is given in the paper. The results of our own investigations on implementing this technology at the pilot-plant scale – for the art castings series – were presented. The results of tests of materials and moulds applied in the full-mould technology were shown. Gas evolution tendencies of expanded polystyrenes and protective coatings were estimated. Gas evolutions were described as functions of the polystyrene heating temperature. The tests of protective coatings used in this technology were performed and strength (Rm), permeability (P), and gas evolution tendency of these coatings assessed. New solutions developed by the team of researchers were applied in testing coating strength, permeability, and the gas evolution tendency of expanded polystyrene. A good correlation between the results of coating properties and the obtained casting quality was found. Coatings, which were characterised by higher strengths and better permeability, allowedus to produce castings without surface or inner faults

COMPARATIVE ASSESSMENT OF Al-Si ALLOY GASSING DEGREE WITH THE APPLICATION OF THE ‘FIRST BUBBLE’ AND ‘SOLIDIFICATION UNDER DECREASED PRESSURE’ METHODS

All aluminum alloys in a liquid state are characterised by easy oxidation and absorption of hydrogen from the surroundings (which are the main reasons for casting defects). The amount of hydrogen adsorbed by a liquid alloy depends mainly on temperature and melting time. The performed investigations were aimed at comparing two known methods of measuring a metal gassing degree; the first bubble method and sample solidification under decreased pressure. Liquid metal melting and holding processes were performed under different conditions that caused variability of its gassing degree, resulting in a variability of purity and quality of the liquid metal. The investigations were carried out with using the hypoeutectic aluminum-silica AK7 alloy

METALLOSTATIC PRESSURE FUNCTION IN THE QUALITY OF Al-Si ALLOY CASTINGS MADE IN SAND MOULDS

The paper presents results of the studies regarding influence of metallostatic pressure of AlSi7Mg alloy on surface roughness of castings prepared in sand moulds as well as on alloy’s density. Castings in a cylindrical shape with a diameter of 15.0; 25.0 or 3.5 mm and height of 700 mm that were cast in a vertical orientation are investigated. The melted alloy was poured into moulds in two ways: bottom up, and top down. Higher pressure and larger diameter of castings favors increaseof surface roughness. In the analyzed range of height of a metal column, density increases linearly: for instance, in case of castings with diameter of ø25 mm, the density increases from ρ = 2.60 g/cm3 to ρ = 2.68 g/cm3, what is about 0.10 g/cm3. In the roller with larger diameter, the density is slightly smaller, however the range of changes along the longer axis is similar to that in the cylinder with diameter of ø25 mm. Additional, ultrasonic studies were performed, which prove that with small changes of the alloy density, velocity of a longitudinal wave changes only slightly. Thus, it is difficult to control small variations (Δρ < 0,10 g/cm3) in density of AlSi7Mg alloy with ultrasonic technique

The Importance of TDA Thermal Analysis in an Automated Metallurgical Process

The article presents the results of research and work related to the implementation of the research and development project POIR.01.01.01-00-0120/17 co-financed by the EU, through the NCBR, entitled: Innovative technology using thermal analysis, TDA, of self-feeding manufacturing of high-quality cast iron to produce new generation, enhanced performance casts. In many foundries, thermal derivative analysis (TDA) is used in addition to chemical analysis to evaluate the physical and chemical properties of an alloy while it is still in the melting furnace or ladle and before it is poured into the mold. This fact makes it possible to improve the metallurgical quality of the alloy by introducing alloying additives, carburizers or modifiers into the furnace as part of the pre-modification or primary or secondary modification in the ladle or when pouring into molds. Foundry machinery (modifier dosing systems and spheroidizing station) is very important in these operations. Only the full synergy of modern equipment with modern technology ensures high quality and repeatability of the casting process. The article mainly discusses the obtained parameters of TDA analysis (with the use of the ITACA system) at different stages of melting and how to improve them by using modern and fully automated dosing systems (Itaca OptiDose, ItacaWire and ItacaStream). Special attention was paid to the minimum temperature of the eutectoid. The change of its value after the modification process, its influence on the quality of the melted metal, a very strong correlation with the number of nuclei and the number of graphite precipitations in the casts were shown

Effects of Polylactide Copolymer Implants and Platelet-Rich Plasma on Bone Regeneration within a Large Calvarial Defect in Sheep

The aim of this study was to verify whether L-lactide/DL-lactide copolymer 80/20 (PLDLLA) and platelet-rich plasma (PRP) trigger bone formation within critical-sized calvarial defects in adult sheep ( = 6). Two craniectomies, each ca. 3 cm in diameter, were created in each animal. The first craniectomy was protected with an inner polylactide membrane, filled with PRP-polylactide granules, and covered with outer polylactide membrane. The second control craniectomy was left untreated. The animals were euthanized at 6, 7, 17, 19, 33, and 34 weeks after surgery, and the quality and the rate of reossification were assessed histomorphometrically and microtomographically.The study demonstrated that application of implantsmade of PLDLLA 80/20 combined with an osteopromotive substance (e.g., PRP) may promote bone healing in large calvarial defect in sheep. These promising proof-of-concept studies need to be verified in the future on a larger cohort of animals and over a longer period of time in order to draw definitive conclusions

Analiza zawartości flawonoidów i kwasów fenolowych o działaniu leczniczym w koniczynie inkarnatce (Trifolium incarnatumL.)

Koniczyna inkarnatka (Trifolium incarnatum L.) jest rośliną należącą do rodziny bobowa-tych (Fabaceae), do której zalicza się również inne gatunki Trifolium, takie jak koniczyna czerwona (Trifolium pratense L.) i koniczyna biała (Trifolium repens L.). W medycynie stosowana jest przede wszystkim kończyna czerwona, gdyż zawiera m.in. flawonoidy i kwasy fenolowe, którym zawdzięcza swoją aktywność biologiczną. Koniczyna inkarnatka jest obecnie wczesnym źródłem nektaru do produkcji miodu przez pszczoły, zielonym na-wozem oraz rośliną pastewną. Ponieważ wiele roślin z rodziny bobowatych stosowanych jest w medycynie, można podejrzewać, że koniczyna inkarnatka również może zawierać cenne związki farmakologicznie czynne, które mogą znaleźć zastosowanie w terapii róż-nych schorzeń. Celem niniejszej pracy była optymalizacja metod izolacji, analizy chromatograficznej oraz wstępna identyfikacja flawonoidów i kwasów fenolowych obecnych w zielu i nasionach Trifolium incarnatum L. Ilościowe oznaczanie zawartości flawonoidów przeprowadzono metodą spektrofotometryczną, natomiast identyfikacji związków doko-nano przy użyciu jednokierunkowej i dwukierunkowej chromatografii cienkowarstwowej. W wyniku przeprowadzonych analiz stwierdzono, że ziele koniczyny inkarnatki zawie-ra więcej związków flawonoidowych niż jej nasiona. Dzięki analizie chromatograficznej w zielu stwierdzono obecność wielu farmakologicznie czynnych flawonoidów oraz fenolokwasów. Nasiona badanej rośliny okazały się o wiele bardziej ubogie w związki farmakologicznie czynne. Powyższe wyniki wskazują, że koniczyna inkarnatka, po bardziej dokładnych analizach fitochemicznych, może stać się cennym źródłem surowca zielarskiego i farmaceutycznego