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

Identification of Gas Products from Pyrolysis Process of Waxes Used in Lost-Wax Casting Technology

Foundry waxes currently used in lost-wax casting technology are composed of paraffin, stearin, and – to a lesser extent – ceresin, polyethylene wax, and other natural and synthetic waxes. Most of these compounds are non-toxic; however, they may release aromatic hydrocarbons as a result of exposure to high temperatures. Based on a chromatographic analysis (pyrolysis gas chromatography-mass spectrometry, Py-GC/MS), the compounds that are separated from the popular wax mixtures used in foundries were evaluated (as well as the impact they may have on foundry workers). For this purpose, the three main stages of the process (wax, burnout, and pouring) were analyzed, and the appropriate test temperature was chosen (similar to the actual conditions during the process)

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

Dependence of tensile wet strength from regeneration time and grain size of the matrix ceramic moulds

Tyt. z nagłówka.Bibliogr. s. [61].Technologia wytwarzania precyzyjnych odlewów polega na nadawaniu elementom kształtu, wymiarów i odpowiednich własności poprzez wypełnienie ciekłym metalem formy ceramicznej odtworzonej przez model wykonany z wosku, usuwany z niej metodą wytapiania. Proces wytwarzania odlewów precyzyjnych w technologii wytapianych modeli składa się z szeregu operacji technologicznych obejmujących: wykonanie modeli woskowych i ich łączenie w zespoły modelowe, przygotowanie masy ceramicznej, nanoszenie kolejnych warstw, wytopienie wosku w autoklawie, suszenie próbek w temperaturze 100 °C, wygrzewanie próbek w zakresie temperatury od 400 do 700 °C. Dotychczasowa technologia oparta była na stosowaniu mas ceramicznych, w których spoiwem był zhydrolizowany krzemian etylu. Aktualnie, ze względu na ochronę środowiska i poprawę warunków pracy, coraz częściej spoiwo z alkoholem zastępowane jest wodnym roztworem krzemionki koloidalnej. W badaniach do tworzenia warstw formy ceramicznej stosowano osnowy pochodzące ze zużytych form z odlewni precyzyjnej poddanych regeneracji oraz osnowę świeżą. Czas regeneracji wynosił odpowiednio 5 i 15 minut. Masę po regeneracji mechanicznej poddano analizie sitowej w celu określenia wielkości ziarna dL. Ziarna o wielkości 0,2; 0,4 i 0,63 mm użyto do wykonywania warstw form ceramicznych. W artykule przedstawiono wyniki badań ukierunkowanych na wyznaczeniu zależności pomiędzy wytrzymałością na rozciąganie w stanie na wilgotno i wielkością ziarna osnowy formy ceramicznej: Rm =f(dL). Badania zostały przeprowadzone na próbkach w kształcie walca o powierzchni dzielonej, na które nanoszono warstwy z wykorzystaniem osnowy pochodzącej z regeneracji, jak również ze świeżej osnowy.Production technology of nwestment casting involves transmitting the elements of shape, dimensions and properties by filling in the appropriate liquid metal ceramic forms reproduced by a model made of wax removed by melting it. The manufacturing process of inwestment casting in the lost wax technology consists of a number of technological operations: preparing of wax models and their assembling in the model units, the preparation of ceramic mixture, successive layers of debris, wax melting in an autoclave, drying the samples at 100 °C, heating the samples at temperatures ranging from 400 to 700 °C. So far, the technology was based on the use of ceramic mixture, which the bond was hydrolysed ethyl silicate. Currently, due to environmental protection and improvement of working conditions, more and more binders with alcohol is replaced with an aqueous solution of colloidal silica. In the study, to create the individual layers a ceramic form, used regenerated ceramic mixture derived from foundry and green ingredients. The regeneration time was respectively 5 and 15 minutes. Used ceramic moulds after mechanical reclamation was given to sieve analysis to determine the grain size (di). Grain sizes 0.2, 0.4 and 0.63 mm were used for the coating of ceramic moulds. The paper presents results of research aimed at the determination of the relationship between tensile wet strength and grain size of ceramic mould: Rm = f[dL). Tests were conducted on cylindrical samples, which deposited the layers of reclaimed ceramic material.Dostępny również w formie drukowanej.SŁOWA KLUCZOWE: odlewnictwo, forma ceramiczna, osnowa, temperatura. KEYWORDS: foundry, ceramic mould, matrix, temperature

EFFECT OF GRAIN SIZE OF THE RECLAIMED MATRIX CERAMIC MOULDS USED IN THE LOST WAX TECHNOLOGY ON THE STRENGTH AT HIGH TEMPERATURE

Production technology of investment casting involves transmitting the elements of shape, dimensions and properties by filling in the appropriate liquid metal ceramic forms reproduccd by a model made of wax removed by melting it. The manufacturing process of investment casting in the lost wax technology consists of a number of technological operations: preparing of wax models and their assembling in the model units, the preparation of ceramic mixture, successive layers of debris, wax melting in an autoclave, drying the samples at 100 °C, heating the samples at temperatures ranging from 400 to 700 °C. So far, the technology was based on the use of ceramic mixture, which the bond was hydrolysed ethyl silicate. Currently, due to environmental protection and improvement of working conditions, more and more binders with alcohol is replaced with an aqueous solution of colloidal silica. In the study, as the basic of individual layers a ceramic form, used regenerated ceramic mixture derived from foundry and green ingredients. Used ceramic moulds after mechanical reclamation was given to sieve analysis to determine the grain size (dL). Grain sizes 0.2, 0.4 and 0.63 mm were used for the coating of ceramic moulds. The paper presents results of research aimed at the determination of the relationship between tensile wet strength and grain size of ceramic mould: Rm =f(dL). Tests were conducted on cylindrical samples, which deposited a layer of reclaimed ceramic material

RECLAMATION OF SPEND MOULDING SANDS WITH THE CARBOPHEN 8178 RESIN

The aim of investigations was to collect the experimental data allowing the quality assessment of the reclaimed material obtained by means of the mechanical reclamation from spent sands with the Carbophen 8178 resin. The investigation program was as follows: •   making the moulding sand with the Carbophen 8178 resin and its preparation for the primary reclamation, •   carrying out the secondary reclamation of the spent sand in the experimental mechanical reclaimer, at several variable parameters (inclination, reclamation time, rotor rotational speed), •   necessary instrumental tests of the reclaimed spent sand and the analysis of the obtained reclaimed materials. Investigations were carried our for three positions of the apparatus: α = 0o, 3o, 6o. The reclamation was performed for each position at three rotational speeds of impact-abrasive elements. The reclamation process effects were checked after 5, 10, 15 and 20 minutes. The reclamation results for the average rotational speed of the rotor, being 700 rpm, are presented in the paper

STRENGTH PARAMETERS AND A MECHANICAL RECLAMATION TOGETHER WITH THE MANAGEMENT OF ITS BY-PRODUCTS

Selfsetting sands with furan resins are still the largest use of SMS with synthetic resins. They can be used to prepare such forms and cores - of different sizes and shapes, for casting all type alloys [1-3]. A reclamation of spent moulding sands, as a recycling method of waste foundry materials, originated from the casting production cycle, constitutes a very serious problem of each foundry plant, related first of all to the environment protection and also to the rational material management. The results of furan resin sands strength tests from the matrix of pure quartz sand reclaimed was performed on the test apparatus AT-2. Sand sieve analysis was made of fresh and reclaimed material, and loss on ignition tests conducted on reclaimed material, obtained at different times of reclamation treedment. Granulation tests of post out reclamation dust, obtained from the sand were also carried of furan resin