The extrusion components are used in many industrial fields, such as railroad vehicles, cars, heat exchangers and domestic articles. However, the demand of the component whose tube is not uniform on cross section is increasing. Circular tube of copper with spiral projections on the inside wall is used for the improvement of the heat exchange efficiency of the heat exchanger. The projections are conventionally manufactured by swaging. Some researchers tried to study the spiral projection on the tube, but nobody could make the tube. We modified the traditional extrusion machine and can successfully extruded the trial circular tube with many spiral projections. The extrusion was performed by the mandrel with set up many grooves. When the plastic flow of the billet was changed to angle of spiral direction by grooves of mandrel, the tube with the spiral projections was produced. Therefore the important extrusion condition is mandrel height which is the mandrel position in the examination. When the mandrel hangs out die, circular tube is trusted by the slot mandrel. As the mandrel height gets higher, the tube will be strongly trusted. The billet material is 1050 aluminum. We examine the extruded circular tube experimentally with the many spiral projections by using the mandrel with many spiral slots. Furthermore, we will have to make the characteristic and limit of the tube with the many spiral projections clear.

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Ocean thermal energy conversion (OTEC) has attracted attention as a technique to obtain renewable energy. OTEC systems usually use a plate heat exchanger and ammonia as a working fluid. The materials used for manufacturing the heat exchanger are generally “titanium” or “stainless steel” of which contact surface should not be corroded with ammonia. However, the thermal conductivity of these materials is very low. Consequently, the heat transfer performance of the heat exchanger deteriorates. Therefore, the author proposed an advanced plate heat exchanger material with high thermal conductivity for OTEC systems. This plate is made of an aluminum alloy and the surface is coated with a special high polymer material (PEEK^TM polymer), which has high ammonia resistance. In this study, two tolerance experiments were performed using the advanced plate at different coating thicknesses of 300 and 20 μm for approximately one month. These experiments were (1) immersion of the plate in a pressure tank containing liquid ammonia and (2) exposure of the plate in the path of a forced convective flow of liquid ammonia. As a result, although the PEEK coating aluminum plate surface deteriorated slightly, it is found that the base of the plate has not influenced by the ammonia.

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Grain refinement performance of as-cast aluminum using machining chip of aluminum was studied. For this purpose, aluminum machining chips with different shape were fabricated. Aluminum wire is also used for the aluminum cast as model material of grain refiner. It is found that the machining chips act as the grain-refiner, since the lattice disregistry towards aluminum is absolutely zero. Moreover, higher cooling rate for aluminum cast with chips also influences on the grain refining of the as-cast aluminum. Although some pore and gap were found for the as-cast aluminum with the machining chips, these defects can be reduced when the mold is preheated.

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The measurements of corrosion weight loss, rest potential–time curves and polarization curves of aluminum in 1, 3 and 5 mass% sodium hydroxide solution which are in the solution conditions of open-to-air, stagnant and room temperature are carried out. It is confirmed that corrosion weight loss increased with increasing concentration of sodium hydroxide and dipping-time in the solutions. It is shown that current densities which are converted from corrosion weight loss in 1, 3 and 5 mass% sodium hydroxide solution show 4.5, 13 and 21 mA·cm^-2, respectively. On the other hand, current densities which are calculated by using the polarization resistance method show 4.10, 12.90 and 23.10 mA·cm^-2, respectively. It was shown that the results of the calculated current densities gave good agreements with the values that have been obtained by the corrosion weight loss.

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