Zagorka Aćimović-Pavlović

Implementation of the Infrared Thermography for Thermo-Mechanical Analysis of the AlSi Cast Piston

Abstract In this paper, the possibility of implementation of the infrared thermography as a technical systems’ diagnostic method is investigated. The infrared thermography as a contemporary method was used for visualization of the working conditions in the piston of an automotive engine as well as for analyzing of the thermal changes the piston sustained under exploitation. The obtained results were used to define the properties of the alloy used for production of the piston for a highly loaded diesel engine. In such way, the problems caused by erroneous choice of the material could be avoided.

Corrosion behaviour of thixoformed and heat-treated ZA27 alloys in NaCl solution

Abstract The influence of corrosion on the microstructure of thixoformed and heat-treated ZA27 alloys was investigated. The microstructure of ZA27 alloy was affected by heat treatment. The process of electrochemical corrosion occurs in both ZA27 alloys through the area of η phase. According to the results of immersion test and electrochemical measurements, the corrosion rate of the thixoformed ZA27 alloy is at least 50% lower than that of the thixoformed and thermally processed alloy. This indicates the unfavourable influence of applied heat treatment (T4 regime) on the corrosion resistance of the thixoformed ZA27 alloy.

A Kinetic Study of Micronization Grinding of Dry Mica in a Planetary Ball Mill

This paper presents results of the research of micronization grinding of dry mica in a planetary ball mill. Investigation was conducted in order to improve the quality and to obtain clearly defined properties and characteristics of mica powder. The micronization grinding of dry mica was performed in four time periods: 30, 60, 120, and 360 minutes. The micronized powder was investigated by means of differential thermal and thermogravimetric analyses, analysis of the degree of micronization, the specific surface area analysis, and X-ray diffraction analysis. The achieved results pointed out that dry mica micronization grinding which exceeds 360 minutes is recommended for this type of mill. However, it was also shown that the micronized mica produced by means of planetary ball mill after extra long periods of micronization grinding can pass into amorphous state.

Effect of Operating Parameters on the Mechanical Activation Process of Mica Powder

Mechanical activation of mica is a great technological and technical problem because of their specific crystallochemical structure. This is dependent upon the type of equipment used and the type of disintegration process. The paper presents the investigations of kinetics of operational parameters, effect on properties and structure of powder mica, etc. The mica sample was subjected to mechanical activation in ultra-centrifugal mechanoactivator with a peripheral comminution path. During the investigation, some operating parameters, viz. number of rotor revolutions (rpm), sieve mesh size (µm) and current intensity (A), and some technological parameters, viz. time of mechanical activation, t (min), circumferential rotor speed, v (m.s−1), capacity of ultra-centrifugal mechanoactivator, Q (kg.h−1) and specific energy consumption, W e (kWh.t−1) were monitored. Analyzing the results it can be concluded that the rate of mechanical activation of mica was increased with the increasing load and rotor revolution of ultra-centrifugal mechanoactivator with peripheral comminution path. Under these conditions, the powder mica was transformed into amorphous state. It was confirmed by X-ray and thermal analyses.

Ceramic Coating for Cast House Application

The coatings for moulds and cores represent an integral part of castings production. Basic role of ceramic coatings is to form an efficient refractory barrier between the sand substrate and liquid metal flow during the phase of casting, solidification and forming of the castings. This provides a smooth and clean surface of castings, with no adhered sand or defects due to metal penetration into the mould (lumps, dents, rough surface and alike). Dimension accuracy and surface appearance of castings depend both on metal and mould. In casting practice, sand casting technology is widely applied for castings production. Quartz sand mostly used in the composition of mould and core blends has a number of faults – low refractoriness, high heat expand coefficient, causing casting surface faults, especially when metals and alloys with high melting temperatures are concerned. Higher quality mould blends based on zircon, olivine, chromite, sinter magnesite containing much better thermalphysical properties than quartz sand are relatively less applied for their high pricing. Various additions to mould blend are used more frequently, as well application of ceramic coatings on moulds and cores. Application of higher quality ceramic coatings significantly influences either reduction or elimination of expensive cast house cleaning and machining operations for the castings, thus directly reducing production costs of a foundry.