Papers by Keyword: Powder Milling

Abstract: Mixtures of WC-Co containing 6% and 9%wt cobalt and having variable particles size of 8nm, 50nm and 3.5mm were selected for sintering by spark plasma sintering (SPS). The starting powder of WC with a particle size of ~3.5mm was ball milled for intervals of 3 hours for up to 72 hours yielding WC with 8nm average crystallite size. Later, pre-milled WC powders were ball mixed for 18 hours with cobalt. All sizes of powders, 8nm, 50nm and 3.5mm were sintered in SPS at the temperature of 1150°C and 1250°C for 10 minutes by applying uniaxial pressures of 50 and 75 MPa. Sintering parameters were optimized by examining densification and microstructural observations. Sintered samples were studied by XRD, SEM, and hardness testing. It was observed that optimizing the parameters of SPS has a crucial role in increasing the densification percentage of the final product and slightly affects the hardness values.

Abstract: This work develops a mathematical model that explains the ball mills operational speed. The scope of the model is defined by the powder as the number of particles per cm3 and the Relevance defined as the ratio between different forces. In this study, the Relevance is defined as the ratio between superficial tension and inertial forces. The conditions for a free flowing powder and a single particle are differenced and non-dimensional numbers are found. The model proposed use the friction force between mill walls and the powder mass is related by a friction coefficient that can be calculated from angle repose. An experimental approach proves that the suppositions made in order to develop the model were adequate in this way the existence of the non-dimensional numbers is confirmed. It is also discussed the use of non-dimensional numbers to increase processing speeds with by increasing gravity clarifying that a given Relevancy, it is not dependent of the non-dimensional numbers. Thus, the model can help in the design process of ball mills with a deeper understanding of the phenomena.