냉각탑 구동계 CFRP 커플링 구조설계 및 성능특성

Abstract

Owing to the light weight, the high strength and stiffness, as well as high corrosion resistance, fiber reinforced plastic composites are widely used in the area of aerospace, marine, automobile, chemical plant, civil construction, wind power plant. The cooling tower drive system is another area that composite materials are actively applied recently. In cooling tower a long shaft coupling is located between the drive motor and a gear box which is connected to the fans. To reduce the concentrated load in the middle, the long metal shaft coupling usually employs a bearing for the load distribution. The metal shaft causes noise when rotating in high speed due to the vibration or resonance caused by the deflection of the long shaft. Another problem of the metal shaft is the corrosion weakness in the saturated wet air condition inside the cooling tower. The above mentioned problems of metal coupling can be solved by replacing with carbon fiber reinforced composites. Moreover the excellent fatigue resistance can greatly improve the fatigue life of the composite coupling. In order to develop composites coupling for cooling towers, a light-weight tube of carbon/epoxy composites was manufactured by filament winding process. When used for a rotating part, the composites tube should have straightness in the axial direction, because a small deflection in the tube will cause noise and vibration-induced structural failure. The straightness of a composites tube depends on the mandrel deflection, therefore, the effect of mandrel size was identified to minimize the deflection. The structural analysis was carried out to determine the optimal fiber direction and stacking sequence. For the accurate finite element analysis the basic material property as an input data was obtained by mechanical testing of the specimens which was manufactured by the same process of the pipe manufacturing. The disc pack is an important component in couplings because it transfers torsional moment of the drive motor to the coupling and then to the shaft of the gear. Based on the requirement of flexible material property and high strength of carrying torsional moment, the disc pack of 6 bolting holes and 3 sheets of composites with [0/0/90/0/0] lamination stacking sequence has been designed and manufactured by RTM process. Torsional testing and finite element analysis based on the failure criteria of laminated composites have been carried out to identify the effect of stacking sequence of glass fiber/epoxy prepregs on the torsional moment and stiffness of a disc pack. Torsional testing results showed that at torsional moment of 1500Nm, the 90˚ ply failed by tension, which initiated the failure of the disc pack. The experimental results were agreed favorably well with those of finite element analysis. The structural analysis of four cases of stacking sequences revealed that the highest torsional moment was the case of [0/90/0/90/0] sequence, and the sequence of [0/0/90/0/0] showed the highest torsional stiffness. One of the most important parameters determining the static and dynamic mechanical behavior of a coupling under torsional loading is the torsional stiffness. In this study, torsional characteristics of the composites tube such as torsional stiffness, strength and maximum twist angle were identified for [±θ/90/±θ/±θ/90] stacking sequence with the variation of winding angle (θ) and the tube diameter and length. The structural analysis was carried out to compare the predictions of torsional stiffness with that of the experimental results. From FEM analysis the optimal winding angle that gave the maximum torsional moment and minimum twisting angle of the composite tube was 45˚. Although the maximum torsional moment was achieved in the case of stacking sequence involving the 45˚ winding angle, [±15/90/±15/±15/90] will be the optimal stacking sequence when considering the improvement of longitudinal stiffness of the composite tube.