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Wilgotność mas klasycznych – czynnik determinujący skłonność do tworzenia przypaleń i wżarć na odlewach żeliwnych

Zych Jerzy S., Mocek Jan

Przegląd Odlewnictwa

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2023

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Vol. 73, nr 11-12

378--384

PL

Wady powierzchni surowej odlewów, wśród których dominują przypalenia i wżarcia, żeliwnych wykonywanych w formach piaskowych są powszechne i nie do wyeliminowania. Należą do grupy najłatwiej wykrywalnych w ocenia wizualnej, decydują o estetyce wyrobów, a to ważny marketingowo i nie tylko wskaźnik ogólnej jakości odlewów. Można jedynie dążyć do ich znaczącego ograniczania. Jakkolwiek są to wady naprawialne, jednak uciążliwość prac w ich usuwaniu. W pracy prezentowane są wyniki badań laboratoryjnych i analizy procesów przemysłowych na wpływem wilgotności mas bentonitowych na tworzenie się przypaleń i wżarć na odlewach żeliwnych. Analizowane jest oddziaływanie wilgotności mas na rodzaj atmosfery chemicznej panującej we wnęce form w powiązaniu z jej wpływem ze skłonnością do przypaleń i wżarć. Proponuje się zastosowanie nowego wskaźnika, którym można by charakteryzować podatność masy do tworzenia przypaleń chemicznych. Został on nazwany: uproszczonym wskaźnikiem potencjału tlenowego masy wilgotnej (WPT). Wskaźnik WPT jest określany jako stosunek wilgotności masy (W) do zawartości nośników węgla błyszczącego, określanej w próbie strat prażenia (S). Jego wartość oscyluje wokół liczby 1,0 i poniżej. Ogólnie im wyższa wartość tego wskaźnika, tym większa skłonność masy do tworzenia przypaleń i wżarć o charakterze chemicznym. W artykule przywoływane są dane i przykłady wad powierzchni z praktyki przemysłowej w powiązaniu z analizą wilgotności mas i wartości wskaźnika WPT.

EN

Defects of crude surfaces of iron castings produced in sand moulds, among which dominate burns-on and pitting, are universal and not to be eliminated. They belong to the group of the easiest detectable defects in visual assessments, which decide about the aesthetics of products, a very important general indicator of the casting quality. Although these defects are repairable but since their removal is very tiresome, it is only possible to limit them. The results of laboratory investigations and analysis of industrial processes concerning the influence of a moisture content of bentonite moulding sands on forming burn-on and pits on iron castings, are presented in the paper. The influence of a moisture content of sands on the chemical atmosphere inside the mould cavity in connection with its influence on the tendency for burn-on and pits, is analysed. The application of new indicator, which could characterise the sand susceptibility to form chemical burns-on, is proposed. It was called: simplified indicator of oxygen potential of sand moistness (WPT). This indicator is determined as the ratio of sand moistness (W) to the content of lustrous carbon carrier, determined in the ignition loss test (S). Its value oscillates around 1.0 and below. Generally, the higher value of this indicator the higher inclination for burns and pits of a chemical character. The data and examples of surface defects known from industrial practice in relation with the sand moistness analysis and the WPT indicator value, are also presented in the hereby publication.

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Spheroidal Cast Iron for Works at Low Temperature - Requirements, Structure, Properties, Control of the Production Process

Zych Jerzy, Jurga T., Mocek Jan, Myszka Marcin, Snopkiewicz Tomasz

Archives of Metallurgy and Materials

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2022

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Vol. 67, iss. 3

999--1005

EN

Two standardised grades of spheroidal cast iron determined in standard EN PN 1563-1997 as: EN-GJS-350-22LT (T=-40°C) and EN GJS 400-18LT (T=-20°C) are intended for work at low temperatures: -20 and -40°C. The main mechanical property of these cast iron grades is a high impact strength at a work temperature down to: -40°C. A series of controlled melts was performed to optimise the production technology of spheroidal cast iron, which in as-cast state is characterised by ferritic matrix (the best without any pearlite), fine precipitates of nodular graphite and high purity (without non-metallic inclusions). Variable structures of metal charges and various spheroidisation techniques (the modification methods) (slender ladle with a tight cover - Tundish technology as well as the technology with cored wire) were applied in the research. In order to obtain refinement of graphite precipitates and to achieve the ferritic matrix multistage inoculations of technologies were applied. Cast iron was subjected to refining to limit non-metallic inclusions since they decrease the impact strength. The production process of cast iron was controlled by the thermal derivative analysis at the stage of initial cast iron and after its secondary metallurgy (modification and inoculation). It was pointed out, that the reproducible production of cast iron for work at low temperatures was only possible when all elements of the technological process were strictly adhered to. It was pointed out, in the hereby paper, that: it should be strived to maintain Si content not higher than 2.50÷2.60%, which at producing spheroidal cast iron is sometimes difficult and requires using a lot of pig iron in the metal charge. For a fast assessment of the cast iron quality, concerning its impact strength, the proposed - in the hereby paper - index quality (IQu) can be applied. It is determined on the bases of measuring the cast iron hardness and propagation velocity of ultrasound wave.

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Thermal Conductivity of Selected Ceramic Materials at a Transient Heat Flow

Zych Jerzy, Wróbel Janusz, Mocek Jan, Myszka Maciej

Journal of Applied Materials Engineering

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2020

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Vol. 60, iss. 1

3--11

EN

In this paper, we present comparative investigations. We examined two kinds of ceramic materials used to produce bricks for isothermal cleading of the riser heads of middle and large steel castings. The ceramic materials were characterised by a low specific density (No. 1 - p = 0.854 g/cm3; No. 2 - p = 0.712 g/cm3). Thermal conductivity tests at a transient heat flow were performed by analysing the heating process of samples taken from the tested ceramic bricks, placed in a special mould in which metal was poured, and by recording the cooling process of the casting. The method proposed in this paper for the determination of samples’ thermo-physical properties is based on measuring the temperature field of the casting–sample system by means of thermocouples situated in various measuring points; it allows the direct investigation of cooling and solidification processes of metals in sand moulds. The heating process of the ceramic samples was analysed by measuring the temperature in five points situated at various distances from the heating surface (casting–sample surface). A large difference in the heating rates of samples of different materials was revealed in our comparative investigations, which indirectly indicated the materials’ heat abstraction ability from the casting surface. The ceramic material characterised by a lower density much slowly conducted heat and, therefore, appeared to be a better material for insulation cleading. At the depth of 40.0 mm, we measured differences in the heating degree corresponding to more than 190°C. The aim of this comparative study was the evaluation of the suitability of porous insulating materials as cleading of riser heads used in the production of large steel castings.