In ceramic forming techniques high particles packing can provide better properties of the final ceramic products. The high quality of the material coupled with the shape complexity of the ceramic product is still challenging. The aim of this work was the optimization and preparation of the ceramic samples based on two alumina powders of different particle size (AA05: 0.5 μm and TM-DAR: 0.15 μm). Firstly, ceramic suspensions of 50vol.% solid loading and the volumetric ratio of AA05 to TM-DAR 1:1, 2:1, 3:1, 4:1, respectively have been prepared. The 2-carboxyethyl acrylate was applied as the new monomer limiting the negative effect of oxygen inhibition. Additionally, the cold isostatic pressing (CIP) was used in order to increase relative density of green bodies. The results of presented research have shown that samples with the ratio of AA05 to TM-DAR 2:1 were characterized by the highest green density (62%). Moreover, CIP process proved to be effective and increased the density of green bodies from 62% to 67%. The pore size distribution of the green bodies has been measured. Samples were sintered at different conditions (1400°C, 1450°C and 1500°C for 1h and 1300°C, 1400°C, 1450°C and 1500°C for 5h).
This paper presents technological trials aimed at producing Ag-W, Ag-WC, Ag-W-C and Ag-WC-C composite contact materials and characterizing their properties. These materials were obtained using two methods, i.e. press-sinter-repress (PSR) at the refractory phase content of less than 30% by weight as well as press-sinter-infiltration (PSI) at the refractory phase content of ≥50% by weight). The results of research into both the physical and electrical properties of the outcome composites were shown. They include the analysis of the influence of the refractory phase content (W or WC) on arc erosion and contact resistance changes for the following current range: 6 kAmax in the case of composites with a low refractory phase content, 10 kAmax in the case of composites with the refractory phase content of ≥50% by weight.
The aim of research was the elaboration of the synthesis of new organic monomer applicable in gelcasting. The substance named 3,4-di-acryloyl-D-mannitol which contains two acryloyl groups and four hydroxyl groups in its molecule has been synthesized. The monomer has been then applied in the preparation of Al2O3-ZrO2 composites by gelcasting and subsequent sintering. Rheological properties of ceramic suspensions have been examined, as well as the properties of green and sintered bodies. SEM observations allowed to determine the distribution of zirconia grains in alumina matrix. Density, Vickers hardness and fracture toughness of ZTA composites have been measured. The new monomer, that is diacryloyl derivative of mannitol, is less sensitive to the oxygen inhibition than commonly used in gelcasting and commercially available 2-hydroxyethyl acrylate.
This paper presents novel bi-converter structure to supply the Doubly Fed Induction Machine (DFIM). Two Voltage Source Inverters (VSI) feed the stator and rotor windings. The outputs of two VSI are combined electro-mechanically in the machine and, as a result, novel features can be obtained. For example, for high power drive applications, this configuration use two inverters dimensioned for a half of the DFIM power. A new Dual-Direct Torque Control scheme is developed with flux model of DFIM. Two Switching Tables (ST) linked to VSI are defined for stator and rotor flux vector control. Experimental and simulation results confirm good dynamic behaviour in the four quadrants of the speed-torque plane. Moreover, experimental results show the correct flux vector control behaviour and speed tracking performances.