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.
Part of the book: Paint and Coatings Industry
Cast iron with mixed-shape graphite and controlled fractions of individual shapes, known as VM cast iron (‘Vari - Morph’), can become material for castings with special requirements. The name of the cast iron ‘Vari Morph’ (VM) was first proposed by the authors in 2018 at the World Congress of Foundries in Krakow. VM cast iron displays physical and mechanical properties, which cannot be achieved with homogeneously shaped graphite. Cast iron with (L – flake) + (V – vermicular) graphite is characterised by good thermal conductivity and better A5 (elongation) and Rm (tensile strength) (than grey cast iron. What is of particular interest is cast iron with a mixed form: (S – spheroidal) + (V – vermicular). Currently, research is being carried out to achieve cast iron with a high-quality index (QI) defined as Rm/HB. This paper presents the results of research of physical (thermal conductivity), mechanical (Rm and A5) and functional properties (thermal fatigue) of VM cast iron. The ultrasound technique was applied for assessing the graphite compactness degree (ξ): ultrasonic wave speed CL = f(ξ), damping factor α = f(ξ). The article also presents the correlations between the above-mentioned parameters, as well as describes the technology used to produce VM cast iron and possible areas of application of the material.
Part of the book: Casting Processes