Papers by Keyword: Hot Strength

Abstract: Hot strength and fracture mechanisms in high quality cast irons were studied, comparing the standard gray iron Grade 300, alloyed with Mo, typically used for cylinder heads in high power engines, with other two materials: one gray iron Grade 300, obtained through graphite refinement and one compacted graphite iron, Grade 450. In these last two materials, the strength increase was obtained by changing the graphite structure, not by hardening the matrix. The experimental results with tensile tests carried out up to 500 °C show that the different strengthening mechanisms, use of Mo or modification of the graphite structure, are both efficient for increasing the strength at room temperature as well as at high temperatures. The CGI has a lower strength reduction with temperature than the gray irons, which shows the significant impact of the compacted graphite shape in reducing the notch effect. These results show the enormous potential of CGI in cylinder heads for high-performance engines.

Abstract: The phosphate bond generally provides a lower modulus of elasticity compared to more brittle conventional cement and ceramic bonded materials. The flexible bonding mechanism results in higher impact resistance. Moreover, phosphate bonded materials show excellent resistance to aluminium metal penetration and corundum growth. In addition, phosphate bonded bricks with low alkali content possess high hot strengths at elevated temperatures which can significantly increase their performance against mechanical abuse. Based on this information a project was started to develop phosphate bonded monolithic materials with similar or better physical and chemical properties than phosphate bonded bricks but with the advantage of installation characteristics of conventional cement bonded materials. Additional goals were to use a water based system and minimize restrictions on installations techniques. Flow and working time should be similar to conventional monolithic materials, making this material as versatile as possible. In order to achieve these goals extensive tests were carried out in collaboration with independent research laboratories and as a secondary step, some of the new formulations were installed in severe environment applications with high mechanical abuse and chemical attack. The development process and the physical and chemical properties of a new phosphate bonded monolithic material will be shown in context with available literature and in comparison with test data of phosphate bonded bricks and conventional cement bonded materials. The results of field tests and potential new applications will also be presented.

Abstract: The influence of silicon addition on the microstructure and properties of corundum-mullite refractory was studied. Results show that Si addition as raw material of the matrix can accelerate mullite crystal formation. The oxidation of Si leads to nucleation of mullite via liquid phase and gas phase. The network microstructure is formed by tiny mullite crystals with few glass phase. So it enhances obviously the high temperature strength of sintered corundum-mullite refractory.