An Automated Installation for Measuring the Complex Thermal Expansion Coefficient of Polymers by the Modulation Dilatometry Technique

An installation designed for measuring the relaxation component of thermal expansion, a typical feature of polymers due to the conformational mechanism of thermal expansion inherent in them, is described. The relaxation component manifests itself as a shift in the expansion variation phase relative to the temperature variations. The installation allows variations of the temperature-oscillation frequency and amplitude in the ranges of 10^–3 to 10^–1 Hz and 1–5 K, respectively. The expansion variation amplitudes were measured using a mechanotron with a sensitivity of at least 10^–2 m. The serviceability of the installation was demonstrated in studies of the thermal expansion of a polymer (polyvinylacetate, PVA). In these studies, a shift in the expansion–temperature phase in the polymer-vitrification region and its dependence on the temperature-oscillation frequency were recorded.     

SELECTION OF GEOMETRIC PARAMETERS OF GEAR AND GRINDING WHEEL TO ENSURE MAXIMUM GEAR TOOTH PROFILE ACCURACY

An analysis of possibilities for the selection of gear and tool geometry parameters is presented to reduce tooth profile errors during the grinding of gears by double tapered wheel (Hofler or Niles method), double wheel generating (Maag method) and by worm wheel techniques (Reishauer method). The selection of gear and tool geometry parameters is based on the analysis of the grid diagram of a gear and a rack. Formulas and graphs are presented for the selection of the pressure angle, module, and addendum of the rack-tool. The experimental results of the grinding of gears confirm the theoretical analysis.     

Experimental Study and Thermodynamic Re-optimization of the FeO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> System

Phase equilibria and thermodynamic data in the FeO-Fe₂O₃-SiO₂ system were critically reviewed. New experiments were undertaken to resolve discrepancies found in previous data. The liquid oxide/slag phase was described using the modified quasichemical model. New optimized parameters of the thermodynamic models for the Gibbs energies of slag and other phases in the selected system were obtained. The new parameters reproduce all available phase equilibria and thermodynamic data within the experimental error limits from 298 K (25 °C) to above the liquidus temperatures at all compositions and oxygen partial pressures from metal saturation to 1 atm of O₂. This study was carried out as part of the development of a self-consistent thermodynamic database for the Al-Ca-Cu-Fe-Mg-Si-O-S multi-component system.