New-Tech Europe Magazine | October 2018

a superior choice for portable devices. The reduced bearing wear also means your mean time between failures (MTBF) will typically be much higher with a ball bearing-based design rather than with a sleeve variant. While ball bearings reduce the amount of friction you must overcome to start and operate your fan motor, they are costlier, noisier, more complex and less impact- resistant than sleeve bearings. omniCOOL™ system: Bridging the gap To minimize the need for designers to make tradeoffs when specifying a fan, CUI’s omniCOOL™ system (Figure 3) seeks to bridge the cost-performance gap by incorporating two key elements into fan design: a magnetic rotor- balancing structure and an enhanced sleeve bearing. Thanks to the magnetic structure, the rotor effectively becomes a spinning top that never falls over and can work at any angle. This is because the system’s magnetic structure sits in front of the rotor and uniformly attracts it all the way round, no matter what angle the fan is operating. A supporting cap at the tip of the shaft keeps it in place, forming the point

Figure 1: Diagram of a typical sleeve bearing fan

develop, which may make the fan noisier and cause it to wobble. This bearing wear problem can be worse if your fan is required to operate at different angles, as could be the case with portable equipment. With gravity pulling the rotor’s mass in different directions, depending on the angle of use, the sleeve will wear unevenly, which can exacerbate the wobble and noise problems. Ultimately, this wear shortens the life of the bearing and, depending on your design, possibly the whole fan unit or even the product it is cooling. Furthermore, the lubricant mentioned earlier that is required to keep everything rotating is typically provided by including an oil ring and Mylar washer at both ends of the bearing bore. These components are intended to combat friction, but the reality is their presence adds to it. In addition, their positioning makes it harder for the gases generated by rotational friction to escape. If these gases cannot dissipate, they turn into solid nitride particles, which clog up the bearing, hampering rotation and shortening its life. The basics of ball bearings Fans with ball bearings (Figure 2)

typically have two rings of little steel balls surrounding the shaft, one closer to the rotor than the other. A ring of springs presses them apart. This setup helps tackle the issues of rotor tilt and uneven wear that you get with sleeve bearings. The reason for this is that the rotor’s weight rests on the ball bearing closest to the rotor itself, but the springs help offset any tilt that might occur as a result of gravity pulling down on the rotor. This means a fan with ball bearings can be used at any angle, making this design

Figure 2: Diagram of a typical ball bearing fan

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