DESIGN CONSIDERATIONS OF PLATFORMS FOR TRAPEZOIDAL FRAME PENDULUM STYLE FUGALS

MOST SUGAR mills today utilise pendulum style fugals for batch operations. This type of centrifuge minimises forces transmitted to the factory platform, which is especially important for poorly purging massecuite. The newer trapezoidal frame ‘stand-alone’ fugal has installation advantages and more open access for easier maintenance. Thus, it has found favor over older designs. However, troublesome platform vibration can still be problematic for the ‘stand-alone’ fugal as the heavy motor is positioned well above the platform floor in contrast to older designs where building beams are directly beneath the motor. In some cases the ‘stand-alone’ fugal rocks on the platform at a vibration resonance far in excess of the allowable vibration severity. Accordingly, traditional platform beam sizing methodologies must be re-evaluated for the ‘stand-alone’ fugal platform. The traditional platform design method has worked well dating back at least 50 years. This involves specifying empirical dynamic loads to assure the platform floor-beams are rigid enough. Even if the platform designer only uses simple beam equations without taking into account vibration or natural frequency, a specification in terms of allowable beam deflection will assure the natural frequency of the combined platform-fugal structure will be high enough to avoid operational problems. This traditional ‘static’ platform design method is only a starting point with today’s modern trapezoidal frame fugals. These ‘dynamic’ machines require more in-depth analysis involving more sophisticated vibration considerations. For example, to achieve a high natural frequency, factors such as: platform size, weight, bolted versus welded construction, and symmetric versus non-symmetric layout must be considered. In our discussion, we offer an example of proper floor beam layout in which a crisscross floor beam pattern is used to achieve the actual calculated beam rigidity. A primary goal in modern platform design is to make the natural frequency 50% above the top spin speed. This is not always possible or practical due to the multiple natural frequencies of the platform-fugal structure itself. This paper discusses the allowable resonant modes within the fugal operational speed range.