Influence of Steel Shots Size on Tensile Properties of Magnetic Moulded MMC

The Magnetic moulding process is an extension of lost foam process, in which an Expendable Poly Styrene (EPS) pattern is surrounded by steel shots bonded together by the action of an induced electromagnetic field. Magnetic moulding is a potential alternative for conventional sand casting, which has disadvantages like low thermal conductivity and low permeability, which affects the metallurgical and mechanical properties of the casting. In the present work Al/SiCp metal matrix composite (MMC) samples are moulded by magnetic moulding technique, using different size steel shots viz. 0.18 mm, 0.6mm, 1mm and the tensile properties of the moulded samples were evaluated. The fractured surfaces of the tensile samples were also examined using SEM. The results show that medium size steel shots gives better tensile properties.

Feeding and Cooling and Time of Thermal Treatment of a Massive Bush Made of the Complex Aluminum Bronze Cast by the Lost Foam

Small additions of Cr, Mo and W to aluminium-iron-nickel bronze are mostly located in phases κi (i=II; III; IV),and next in phase α (in the matrix) and phase γ2. They raise the temperature of the phase transformations in aluminium bronzes as well as the casts’ abrasive and adhesive wear resistance. The paper presents a selection of feeding elements and thermal treatment times which guarantees structure stability, for a cast of a massive bush working at an elevated temperature (650-750°C) made by means of the lost foam technology out of composite aluminium bronze. So far, there have been no analyses of the phenomena characteristic to the examined bronze which accompany the process of its solidification during gasification of the EPS pattern. There are also no guidelines for designing risers and steel internal chill for casts made of this bronze. The work identifies the type and location of the existing defects in the mould’s cast. It also proposes a solution to the manner of its feeding and cooling which compensates the significant volume contraction of bronze and effectively removes the formed gases from the area of mould solidification. Another important aspect of the performed research was establishing the duration time of bronze annealing at the temperature of 750°C which guarantees stabilization of the changes in the bronze microstructure - stabilization of the changes in the bronze HB hardness.

The Effects of Foam Density and Metal Velocity on the Heat and Mass Transfer in the Lost Foam Casting Process

As an innovative technique, the lost foam casting (LFC) process has drawn great attention from both academia and industry in recent years. The key feature of LFC process is that a desired shape pattern made of expandable polystyrene (EPS) foam is buried in unbonded sand and replaced by advancing molten metal. The heat and mass transfer between the molten metal front and the EPS foam pattern plays an important role in the soundness of the product in the LFC process. The present study focuses on determining the characterization of heat and mass transfer during the EPS pattern degradation process. A unique experimental system using a cylindrical quartz window and heated steel block simulating the hot molten metal front has been constructed to make measurements and visualize the process. The foam pattern is 88 mm in diameter and 254 mm long. It is coated twice with DCH Ashland refractory material and the average coating thickness is 1.2 mm. The heat flux and pressure between the moving steel block and the EPS pattern are measured. The process variables studied during this experiment include foam density and steel block speed. It was found that unlike the fluidity of the molten metal which is highly dependent on the density of the foam patterns, foam density has marginal effect on the heat flux from the steel block to the foam pattern. The heat flux increases about 37% during a one-minute process under steel block velocity of 4.4 mm/s using different EPS foam density of 24 kg/m3 and 27 kg/m3. Flow visualization shows a gaseous gap formed between the steel block and the foam pattern. The phase change and degradation of EPS foam pattern and the heat and mass transfer in the gap are crucial to characterize the mold filling process which decides the quality of casting products. The maximum pressures measured in the gap using steel block velocity of 4.4 mm/s are 1.1 kPa and 1.4 kPa for EPS foam density of 24 kg/m3 and 27 kg/m3, respectively. Under a slower steel block velocity of 3.6 mm/s the gap peak pressure using 24 kg/m3 density EPS foam pattern is 0.43 kPa. It is concluded that higher foam density and faster steel block speed give rise to larger gas pressure between the steel block and foam pattern. The measured pressure values confirm data reported in literature.