International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Ultrasonic testing (UT) of castings is common foundary practice. For the correct calibration of UT, it is necessary to measure the velocity propagation of the ultrasound waves in the castings. It is inverse ultrasonic problem. A method for velocity measurement, according to ASTM E 494: 2015, with one-sided access to the casting, is being considered.
In this article the equations for determined of transversal and longitudinal velocities propagation – ( Vt;Vl ) V ;V , through measurement: distance between transducers (source-reflector) – 2.W X and the time of propagation – ( X ) T/t are obtained.

Cobalt-chromium based alloys are widely used in dental applications due to their excellent mechanical properties, high corrosion resistance and good biocompatibility. Although they are generally fabricated by casting for dental restorations, recently selective laser melting (SLM) has become an attractive production method since it allows complex geometries. Recent studies revealed that Co-Cr alloys formed by SLM, provided better corrosion resistance as well.

In this study, tribo-corrosion behavior of a Co-Cr-Mo alloy produced by casting (Biosil-Degudent) was compared with the one (Co212-f ASTM F75) produced by SLM. The wear properties were investigated by tribo-corrosion tests in a Fusayama-Meyer artificial saliva solution using a “ball-on-disc” type tribometer. Polished surfaces were tested against zirconia balls at the same sliding speed, distance and load. Friction coefficient values were determined and the worn surfaces were evaluated using microscopes to compare the wear and tribo- corrosion resistance through wear tracks. SLM proved to be a promising manufacturing method for dental applications.

Contemporary production of castings is inevitably associated with improvement of foundry mixtures, and in particular with quartz sands as a basic moulding material. The interest is motivated by opportunity of reaching mixture’s appropriate parameters at different combinations between sands and binding compositions. One option of particular importance in obtaining mixtures’ physical and mechanical, and technological properties is to get a greater number of contact points among individual grains of quartz sands.

The report examines the impact of dispersive mineral particles for increasing contact points of interaction between individual sand particles in the process of solidification. A theoretical basis for the possibility of applying such reinforcement in the preparation of mixtures is presented. An attempt for optimization has been done by some criteria – porosity, morphology, gas permeability and other properties.

Results and conclusions from the conducted tests have been graphically presented.

As a whole, the contemporary self-hardening foundry moulds and cores represent a result of chemical reactions between quartz sands and binders at mould formation after good homogenization in mixers. Mixtures are hardened, obtaing the necessary physico-chemical characteristics; thus they realize the geometry of the future cast. One of the most important characteristics is the strength of mixtures, especially the adhesion strength that is formed on the border between sand and binding composition.

In this report, an improved method on adhesive strength determination of foundry mixtures is presented. Some theoretical protection aspects of the shown method are considered. A technological sequence of the method work and way of measurement are given. In figures, practical results from measurements of adhesion strength according to “No Bake”are shown.

At the contemporary conditions of cast production there has been a permanent interest in economically more profitable technologies for obtaining moulds and cores of controlled properties. A part of this interest is related to quartz sands as a basic and the most common component in the practice of foundry mixture productions. State of sand surface and its influence in formation of foundry mould and core physico-chemical properties are of particular importance.
In this report, various conditions of mechanical activation on the surface of quartz sand in “a fluidized bed” are discussed. The theory of such activation necessity has been partly explained. The “time” factor in preserving the activated layer potential is noticed. The efficiency of the activated layer in producing foundry mixtures strength by the method “No Bake is shown.

Studying the fracture characteristics of porcelain coatings plays a main role in selection of materials for metal-ceramic restorations. The aim of this work is to study the effect of the substrate manufacturing process on the adherence of the porcelain. The coatings of porcelain IPS.Inline (Ivoclar Vivadent) are fused onto dental Co-Cr alloys fabricated via casting (Biosil F) and Selective Laser Melting (SLM) (Co212-f). The adhesion strength of the ceramic coatings is studied under tensile load of flat specimens. The interfacial shear strength is determined using experimental results. The shear stress distributions in the metal-ceramic interface at the critical load are evaluated by analytical approach. It is established that the interfacial shear strength values of ceramic coating are 67.5 MPa for cast Biosil F alloy and 83.8 MPa for SLM Co212-f alloy. The higher shear strength of the porcelain to the SLM samples is due to the nearly two times higher surface roughness, which is reason for increasing both the mechanical and the chemical adhesion. The nature of the fracture of the ceramic coating on the Co-Cr alloys, produced by casting and SLM, is similar and is mixed adhesive–cohesive mode. The higher adhesion strength of the porcelain coating to the SLM dental alloy is a good precondition for the SLM application in production of metal-ceramic fixed partial dentures for areas with heavy loads.

The aim of the present paper is to investigate the mechanical properties (hardness and tensile strength) of dental Co-Cr alloys fabricated via casting and selective laser melting (SLM). Two groups of metallic specimens (four-part dental bridges and standard tensile test specimens) made of Co–Cr dental alloys were produced by lost-wax casting and SLM processes. Vickers hardness distribution along the depth of the dental bridges as well as the Rockwell hardness and tensile strength of the samples were studied out. The hardness of Co–Cr dental alloys are dependent on the manufacturing technique employed. It was established that the average Vickers hardness of the samples, produced by SLM, was higher than that of the cast samples 382 HV and 335 HV respectively. The nearly even hardness distribution in the bridges, produced by SLM, and fluctuations of the hardness values along the depth of the cast bridges were observed. The Rockwell measurements confirmed the higher hardness of the SLM samples – 39 HRC in comparison with that of the cast ones – 33 HRC. The tensile strength is in good agreement with the hardness values. Due to the unique microstructure, the yield strength and tensile strength for the SLM samples were higher than those of the as-cast alloy.