**1. Introduction**

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In recent years, the application range of available soft magnetic materials has increased significantly due to the development of amorphous and nano-crystalized systems. Certain ferromagnetic alloys can be obtained as vitreous phases by rapid quenching techniques; some of them partially crystallize by certain heat treatments achieving structures composed by 10 to 40 nanometre long grains surrounded by a vitreous phase. One of these rapid quenching techniques is the melt-spinning, from which it is obtained amorphous metal strips that are, later, wound up into rolls.

The later-use of the wound rolls is the conformation of electric transformer cores showing meaningful improvement in its overall outputs, as well as an increment in the efficiency and fewer environmental impacts. In the past, these cores have been produced with grainoriented and non-grain-oriented silicon steel sheets, ferrite sheets, Ni-Fe and Co-Fe alloys sheets produced by conventional casting processes, which require several mechanical and thermal processes, which some of them, have a high cost (Gelinas, 2000). The fabrication of nano-structured magnetic packages can be done, in this particular case, by the directemployment of melt-spinning´s strips into different kinds of heat treatments, where it can also be adjusted the hysteresis cycle. Furthermore, its uses can be extended to complex geometries introducing a milling stage after the melt-spinning process, obtaining refined elemental powder particles (Nowacki, 2006; Byoung et al., 2007), which its dimensions can be modified by the control of the milling stage time (Dobrzanskia et al, 2004). The connotations of using soft magnetic alloys affect not only transformer cores but also AC motors (Pagnola et al., 2009; Pagnola, 2009). These new amorphous and nano-crystalized materials are currently sold up to 3 times the price of conventional materials (Condes, 2008).

Magnetic cores lose energy through two independent mechanisms: hysteresis (dissipated energy during the re-orientation cycle of magnetic domains) and Foucault current (eddy or parasitic current). These losses can rise up to 5% and 15% of the entire produced energy, which fluctuates over the manufacturing technique employed. Own research and other authors confirm that these losses can be reduced almost 80 % from those that appear in

Development of a Winding Mechanism for Amorphous Ribbon Used in Transformer Cores 279

Fig. 3. (a) Schematic of a melt-spinning apparatus, (b) Blow up of the contact zone. (Theisen

et al., 2010).

Fig. 2. Cooling procedure to avoid crystalline structure. (Moya, 2009).

devices built with traditional steel (De Cristofaro, 1998; Douglas, 1988; Richardson, 1990). In table 1 and figure 1, it can be seen how much smaller these losses are, and what is more important the amount of energy saved. The LSA implemented Melt-Spinning technique through the project called "Advanced technology magnetic materials production" (PICT-2007-02018), and it aims reducing energy losses to the values given. Amorphous ribbons, similar to FINEMET®, were obtained by preliminary tests, these ribbons were 1mm wide and 20µm thick, and they were quenched straight up on the copper wheel in an air atmosphere, reaching a 106 K/sec cooling rate (Muraca et al., 2009).


Table 1. Core losses in regular Fe-Si cores and Amorphous alloys cores refer to Fe-Si (100%).

Fig. 1. Core losses with different alloys (Dobrzanskia et al., 2004).

#### **2. Melt-spinning**

One of the most common rapid quenching techniques to produce amorphous metals is the one called melt-spinning. Using this technique, the molten alloy is jetted on the surface of a high speed spinning copper wheel through a nozzle. The casting wheel acts as a heat sink reaching one million degrees per second cooling rate (Praisner et al., 1995) necessary to achieve the vitreous phase instead of a crystalline structure (see figure 2). In figure 3 it is shown a diagram of the melt-spinning apparatus, where it can be seen the small and weak linkage between the ribbon and the casting wheel.

devices built with traditional steel (De Cristofaro, 1998; Douglas, 1988; Richardson, 1990). In table 1 and figure 1, it can be seen how much smaller these losses are, and what is more important the amount of energy saved. The LSA implemented Melt-Spinning technique through the project called "Advanced technology magnetic materials production" (PICT-2007-02018), and it aims reducing energy losses to the values given. Amorphous ribbons, similar to FINEMET®, were obtained by preliminary tests, these ribbons were 1mm wide and 20µm thick, and they were quenched straight up on the copper wheel in an air

Power [kVA] Core Losses [W] Saving percentage [%] Manufacturer Fe - Si Amorphous

Table 1. Core losses in regular Fe-Si cores and Amorphous alloys cores refer to Fe-Si (100%).

One of the most common rapid quenching techniques to produce amorphous metals is the one called melt-spinning. Using this technique, the molten alloy is jetted on the surface of a high speed spinning copper wheel through a nozzle. The casting wheel acts as a heat sink reaching one million degrees per second cooling rate (Praisner et al., 1995) necessary to achieve the vitreous phase instead of a crystalline structure (see figure 2). In figure 3 it is shown a diagram of the melt-spinning apparatus, where it can be seen the small and weak

10 40 13,5 66 Osaka Transformer 10 40 11 72 Westinghouse 15 50 14 72 Allied and MIT 25 85 28 67 General Electric 25 85 16 81 Prototype Allied

atmosphere, reaching a 106 K/sec cooling rate (Muraca et al., 2009).

Fig. 1. Core losses with different alloys (Dobrzanskia et al., 2004).

linkage between the ribbon and the casting wheel.

**2. Melt-spinning** 

Fig. 2. Cooling procedure to avoid crystalline structure. (Moya, 2009).

Fig. 3. (a) Schematic of a melt-spinning apparatus, (b) Blow up of the contact zone. (Theisen et al., 2010).

Development of a Winding Mechanism for Amorphous Ribbon Used in Transformer Cores 281

guides the strip towards the winding reel (5). At last, the winding reel is surrounded by a

wrapping belt that ensures the thread of the strip into the reel during the startup.

Fig. 4. Melt-spinning Equipment developed at LSA. Crucible and copper wheel.

Table 2. State of the art - Winding parameters found in different industries.

Material Winding Speed [m/s] Winding Tension [Mpa] Source Paper ≈ 8 < 10 Liu, 2009 Steel ≈ 8 15 - 75 Liu, 2009 Plastic Films ≈ 15 < 4 Lee et al., 2002 Magnetic Tape < 5 < 4 Liu, 2009 Amorphous strip 25 – 50 15 - 30 Own development

The amorphous alloy is obtained from a crystalline alloy, called mother alloy, which has the same chemical composition as the amorphous one. The way to get to the mother alloy is melting the proper quantity of the different components into an induction heater several times in order to insure a homogeneous alloy. Afterwards, the alloy is introduced into a quartz crucible with an induction coil which heats the alloy over the melting point; then, an argon over-pressure expulses the alloy through the nozzle on the high speed spinning wheel. As a result, a continuous amorphous ribbon is obtained; its thickness (≈ 20 – 100 µm) is a function of the injection pressure, the gap between the nozzle and the wheel and the cooling rate. Depending on the alloy and its corrosion susceptibility, the process should be in a controlled atmosphere, in a vacuum chamber or even in environmental conditions.
