Research On Multi-Strands O.C.C Equipment And Technology For Production Of Cu-Base Shape Memory Alloys

In recent years, shape memory alloys (SMAs) have got increasingly wide applications because of their good mechanical properties, shape memory effect, superelastic and damping characteristics. Especially Cu-based SMAs have great potential for mass production due to their low production cost. The heated-mold continuous casting process (Ohno continuous casting process, O.C.C) can obtain longitudinal columnar structure or single crystal in producing SMA wires. This new technology can produce alloy wires with desirable size and shape and smooth surface in one step. Moreover, the mechanical properties of such alloy wires are equivalent to those with single crystals. But the production of Cu-based SMA wires is limited to the laboratory with singlestrand and very low production efficiency. Based on the single-strand O.C.C equipment, this study is to design and test a complete set of multi-strands O.C.C equipment for industrial mass production of SMAs.The Control of solid-liquid(S-L) interface location is the key to the success of O.C.C. The S-L interface location is determined by the cooling distance, mold temperature, and casting speed. In addition, the stability of drawing affects the surface quality of the SMA wires; the metal pressure head affects the diameter. According to the calculation and the experimental results, the mold temperature, casting speed, metal pressure head and cooling distance can be fixed in an appropriate range and adjusted.The alloys is melt in a melting furnace, then poured into a holding furnace with temperature control system. The volume of crucible should ensure melt temperature stability and the continuity of production. The cast mold has 10 cavities parallel arranged for 10 strands and an induction coil around for heating. The metal head is detected by a buoy and automatically controlled by a motor-screw system.Cooling-support device is used for obtaining an unidirectional cooling and a hightemperature gradient to achieve unidirectional solidification and supporting the wires to increase the motion stability. To each wire, the cooling position can be adjusted independently.The drawing type, speed and stability directly affect the quality of the wires. Synchronous belts and gears are used to transmit power and draw wires. To each wire, the drawing speed can be adjusted smoothly and independently. The encoder and PLC control system is adopted to measure the speed.In the Cu-Al-Be heated mold continuous casting tests, the wires produced show straight and smooth appearance, without apparent bamboo-shaped defects, and show very good super-elasticity, good cold-forming and fatigue properties. As long as we can control the process parameters well, we can produce desirable SMA wires in large scale.But in tests, a few problems occur: Induction furnace is easy to be over loading; Driving machine gears present a little jumping, Break out of one strand will affect other strands, Belts are easy to wear, Belt tension adjustment and replacement are difficult; Melt pouring is troublesome to operate. With further testing and improvement, it can be sure that this equipment will promote SMAs production industrialization, and create considerable economic benefits.