Evaluation of additive manufacturing of sand cores in terms of the resulting surface roughness

Obtaining a good surface finish on casting is challenging and depends on the dimension of the sand particles and the processing method of the mold. Evolving modern trends in mould and core production as a binder jetting technology is an option and it is more than desirable to evaluate and remove any possible negative effects. The aim of this study is to compare the influence of furan no-bake technology and 3D printing method on the surface quality of cores and cavities formed in aluminium alloy castings. In addition to the sieve analysis and mechanical properties of the moulding mixtures, the roughness (Ra, Rz) of the cores and resulting casting surfaces of indi-vidual samples were compared in this study.Web of Science810art. no. e1075

Ivanov’s Theorem for Admissible Pairs Applicable to Impulsive Differential Equations and Inclusions on Tori

The main aim of this article is two-fold: (i) to generalize into a multivalued setting the classical Ivanov theorem about the lower estimate of a topological entropy in terms of the asymptotic Nielsen numbers, and (ii) to apply the related inequality for admissible pairs to impulsive differential equations and inclusions on tori. In case of a positive topological entropy, the obtained result can be regarded as a nontrivial contribution to deterministic chaos for multivalued impulsive dynamics

Optimizing the Gating System for Steel Castings

The article presents the attempt to optimize a gating system to produce cast steel castings. It is based on John Campbell’s theory and presents the original results of computer modelling of typical and optimized gating systems for cast steel castings. The current state-of-the-art in cast steel casting foundry was compared with several proposals of optimization. The aim was to find a compromise between the best, theoretically proven gating system version, and a version that would be affordable in industrial conditions. The results show that it is possible to achieve a uniform and slow pouring process even for heavy castings to preserve their internal quality

The Importance of the Geometry of the Down Sprue in the Gravity Casting Process

This article presents the results of experiments on the optimization of down sprue geometry in the process of pouring sand molds. Theoretical assumptions and computer simulation tests are presented. The starting point was the theory and experience of gas entrapment caused mainly by a poorly designed gating system and the down sprue. Simulations were performed using Magmasoft software. First, initial studies were carried out to determine how the geometry (mainly the channel cross-section) of the sprue affects the problem, and then a detailed experiment was carried out on the so-called ‘short sprue’ version. The air entrapment process was analyzed, as were the parameters of the liquid alloy flow that passes through the analyzed channels. Nine geometric versions of the sprue were proposed and analyzed, and the results allowed us to conclude which sprue geometry is the best from the point of view of minimization of the gas entrapment problem

Method for Resistivity Measurement of Grainy Carbon and Graphite Materials

The article presents the issue of electrical resistivity measurement of carbon materials. The device that was developed by the authors is described and is the subject of a Polish patent. The innovative approach of the setup is based on the possibility of measuring the resistivity of grainy (powdered, dusty) materials without having to conduct their preliminary pressing. The material that is to be analyzed is placed inside the chamber made of electrically non-conducting material. The sample is then compacted with pneumatically driven pistons and the compaction force can be controlled by the air pressure. The device as proposed by the authors works at a pressure of 900 kPa, which is equal to the compaction force of 1.2 kN. Resistivity is calculated on the basis of the voltage drop recorded on the sample length. The research covers the analysis of the influence of carbon material grade and compaction force on the resistivity value. It was stated that the resistivity of the graphite materials that were analyzed here changed within the range of 43⁻172 µm: petroleum coke—360⁻780 µm; the anthracite—1900⁻3900 µm. The experimental method presented here can be used whenever carbon materials are present in the form of grains

Relative versions of the multivalued Lefschetz and Nielsen theorems and their application to admissible semi-flows

The relative Lefschetz and Nielsen fixed-point theorems are generalized for compact absorbing contractions on ANR-spaces and nilmanifolds. The nontrivial Lefschetz number implies the existence of a fixed-point in the closure of the complementary domain. The relative Nielsen numbers improve the lower estimate of the number of coincidences on the total space or indicate the location of fixed-points on the complement. Nontrivial applications of these topological invariants (under homotopy) are given to admissible semi-flows and differential inclusions