**3. Winding system**

The winding mechanism designed is capable of working at high winding speeds (an order of magnitude higher than those used in paper winding and steel-making, see table 2), it also insures the quality of the product as it´s has been solidified at the wheel without changing its surface roughness generated in the previous stage, since any aspect that has influence on its surface integrity during this stage has a direct impact on the magnetic package´s performance. This winding system is assembled next to the cylindrical sleeve by the casting wheel seen in Figure 4.

Two problems hold the design back at the first stage of the process:


Both of these issues mainly appear because of the intrinsic characteristics of the meltspinning technique. Due to the speed of the process and the fact that the strip has no fixed point at the casting wheel the solutions given are rarely similar to those found in regular winding machines. First of all, an automatic threading system was designed due to the impossibility to count on the proper time to thread the strip into the winding reel by a human (~ 5 to 10 seconds). This time implies an excessive collection of material (250 to 500m) by the casting wheel that can be wrecked by its own weight or successive folding.

With regard of the tension control, it's critical not only because of the typical problems in every wound roll, but also because an over-tension can separate the strip from the casting wheel where the material is still in a liquid state. Therefore, two zones were established in the machine, a free-tension zone and another one where it is controlled up to a set-point determined by the tension profile.

Figure 5 and 6 shows the proposed design, where it can be seen a set of guiding belts (1), that generate an air flow capable of dragging the strip from the casting wheel up to the pinch rollers (2). These rollers are powered by an asynchronous motor and variable frequency drive, where the strip purely rolls over them; the control of their speed and the winding velocity of the reel are the manipulated variables of the tension control system. Between the guiding belts and the pinch rollers, there are a set of idle rollers (8 & 9), which provide the system a stock of material in order to prevent an unwanted detachment of it at the solidification meniscus. Next to the pinch rollers there is a deflector (4) that simply

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.

The winding mechanism designed is capable of working at high winding speeds (an order of magnitude higher than those used in paper winding and steel-making, see table 2), it also insures the quality of the product as it´s has been solidified at the wheel without changing its surface roughness generated in the previous stage, since any aspect that has influence on its surface integrity during this stage has a direct impact on the magnetic package´s performance. This winding system is assembled next to the cylindrical sleeve by the casting

Both of these issues mainly appear because of the intrinsic characteristics of the meltspinning technique. Due to the speed of the process and the fact that the strip has no fixed point at the casting wheel the solutions given are rarely similar to those found in regular winding machines. First of all, an automatic threading system was designed due to the impossibility to count on the proper time to thread the strip into the winding reel by a human (~ 5 to 10 seconds). This time implies an excessive collection of material (250 to 500m) by the casting wheel that can be wrecked by its own weight or successive folding.

With regard of the tension control, it's critical not only because of the typical problems in every wound roll, but also because an over-tension can separate the strip from the casting wheel where the material is still in a liquid state. Therefore, two zones were established in the machine, a free-tension zone and another one where it is controlled up to a set-point

Figure 5 and 6 shows the proposed design, where it can be seen a set of guiding belts (1), that generate an air flow capable of dragging the strip from the casting wheel up to the pinch rollers (2). These rollers are powered by an asynchronous motor and variable frequency drive, where the strip purely rolls over them; the control of their speed and the winding velocity of the reel are the manipulated variables of the tension control system. Between the guiding belts and the pinch rollers, there are a set of idle rollers (8 & 9), which provide the system a stock of material in order to prevent an unwanted detachment of it at the solidification meniscus. Next to the pinch rollers there is a deflector (4) that simply

Two problems hold the design back at the first stage of the process:

1. Thread of the strip into the winding reel.

**3. Winding system** 

wheel seen in Figure 4.

2. Tension control of the roll.

determined by the tension profile.

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.

Development of a Winding Mechanism for Amorphous Ribbon Used in Transformer Cores 283

Fig. 7. Interlayer pressure (a) and circumferential stress (b) for the winding stress profile in

As it can be seen, the winding stress profile starts at a higher value and then it starts decreasing through a ramp towards the regime value. During this ramp the roll is setting up its linkage with the winding reel, which will determine the end of the startup stage and the beginning of the working regime stage. To insure that the threading is complete the friction force generated by the internal pressure times the surface of every wound lap must be higher than the inertial force plus the winding tension. From now on, the roll is fixed to the

*s i friction inertia winding*

Once established the tension profile, it can be calculated the power necessary for the winding reel motor and for the pinch rollers motor. On one hand, the winding reel motor

*p S dr F F T* (1)

the above figure (Liu, 2009).

winding reel and no slip between them will be found.

´ ( )

*r*

*o*

*r* 

Fig. 5. Winding machine at startup: 1. Guiding belts; 2. Pinch rollers; 3. Initial deflector; 4. Main deflector; 5. Winding reel; 6. Wrapping belts; 7.Crosslide; 8. Stocking system – dancer roller; 9. Stocking system - Fixed roller; 10. Chassis; 11. Main motor; 12. Slide guides; 13.Tension sensor.

#### **3.1 Winding tension profile**

Several winding stress models have been developed in order to find the proper winding tension profile (Li et al., 2009; Liu, 2009; Lee et al., 2002). Following the model proposed by Liu, every new wound lap is considered a collection of concentric laps of web material. In every one of them it is formulated the differential equations of internal equilibrium to find out stress, strain, displacement and pressures developed during the winding. Finally, the profiles shown in figure 7 were obtained.

Fig. 5. Winding machine at startup: 1. Guiding belts; 2. Pinch rollers; 3. Initial deflector; 4. Main deflector; 5. Winding reel; 6. Wrapping belts; 7.Crosslide; 8. Stocking system – dancer roller; 9. Stocking system - Fixed roller; 10. Chassis; 11. Main motor; 12. Slide guides;

Several winding stress models have been developed in order to find the proper winding tension profile (Li et al., 2009; Liu, 2009; Lee et al., 2002). Following the model proposed by Liu, every new wound lap is considered a collection of concentric laps of web material. In every one of them it is formulated the differential equations of internal equilibrium to find out stress, strain, displacement and pressures developed during the winding. Finally, the

13.Tension sensor.

Fig. 6. Winding machine at startup.

profiles shown in figure 7 were obtained.

**3.1 Winding tension profile** 

Fig. 7. Interlayer pressure (a) and circumferential stress (b) for the winding stress profile in the above figure (Liu, 2009).

As it can be seen, the winding stress profile starts at a higher value and then it starts decreasing through a ramp towards the regime value. During this ramp the roll is setting up its linkage with the winding reel, which will determine the end of the startup stage and the beginning of the working regime stage. To insure that the threading is complete the friction force generated by the internal pressure times the surface of every wound lap must be higher than the inertial force plus the winding tension. From now on, the roll is fixed to the winding reel and no slip between them will be found.

$$\mu\_s \cdot \prod\_{r\_o}^{r'} (p\_i \cdot S) \cdot dr = F\_{friction} > F\_{inertia} + T\_{winding} \tag{1}$$

Once established the tension profile, it can be calculated the power necessary for the winding reel motor and for the pinch rollers motor. On one hand, the winding reel motor

Development of a Winding Mechanism for Amorphous Ribbon Used in Transformer Cores 285

and electronic components. Every difference between the pinch rollers and the casting wheel speed, overcomes into an over-tension of the strip or an excessive storage of material,

Fig. 8. Wrapping belts and tension sensor at startup condition (3.1) in working regime (3.2).

The mechanism is composed by 3 idle rollers (Figure 9), two of them (9) are fixed, while the centered one (8) can move along the vertical axis forcing the strip to take a larger profile instead of the straight line from the startup. Sensing the position of this roller, it is tuned up the pinch rollers speed, only when the stock is excessive or insufficient. So, this variation will be considered as a transitory regime for the tension control system, in order to assume the pinch rollers´ speed as a constant. With this system a little stock of ribbon is created in

The winding reel (5) is provided with a mandrel for a quick demounting of the finished roll. Moreover, the reel along with the wrapping belt is mounted on a cross slide (7) which can be

which may cause a possible detachment of the solidification meniscus.

Fig. 9. Stocking system at startup and during the working regime.

order to absorb every produced over-tension.

(main motor) is going to take most of the torque necessary for the winding, on the other hand the pinch rollers motor will be working almost as a brake because upstream it is a freetension zone and downstream the tension is provided by the main motor. This is why the power of the main motor is considered to take this torque times a service factor to make up for the startup situation. Taking into account these considerations and the dimensions of the strip and the reel, it is needed a 5HP AC motor for the winding reel.
