Research On Carbon Fiber Tow Pneumatic Spreading Technology

Pneumatic spreading technology is an effective method to spread fibers widely in width and maintain fibers in parallel with little damage, which can improve the invasion of resin into fiber tow and make CFRP(Carbon Fiber Reinforced Plastics) with better mechanical properties. Thus,it becomes a hotspot in spreading technology. Key technologies were studied in pneumatic spreading method based on pneumatic spreading theory such as the effects of related factors on spreading process, tension and optimization of the structure of the spreader.Effects of flow patterns in the spreader and tension on fibers were analyzed in first. Effects of sizing on fibers and false twists on spreading quality were analyzed and methods of how to improve the spreading quality were proposed. Pnematic spreading technical plan was determined and the spreading system was designed.Flow field model was established based on Navier-Stokes equations and flow field was simulated and analyzed by FLUENT software to optimize the structure of the spreader. Flow patterns were compared under different tilt angels of lateral plate, different open widths of spreaders and different heights of windshielts. Influence laws of flow patterns to spreading prograss were obtained and the strcture of spreader was determined which can be used to spread carbon fiber tow in high effient.A closed-loop tension control system was designed to control tension in precision and quick through the study of effects of tension on spreading. PID with variable integral was used in single stage tenson control and output compensation strategy was used in four spreading stages to improve the capacity of resisting disturbance.A four stages spreading apparatus was set up by above studies. A series of experiments were conducted. The effects of the strcture of spreader on spreading were studied which were in accordence with the simulations. The experimental results show that bigger lateral velocity contributes to wider carbon fiber tow. Besides, the effects of air velocity, tension and carbon fiber feeding velocity were studied by experiments and the range of these parameters were determined with tension from 10 to 30 g and inlet air velocity from 10 to 16 m/s in spreading process,which was a guidence to the regulation of parameters. Optimization of the spreader and regulation of air velocity, tension and fiber feeding velocity reduced and removed the flaws of twists and colapse in spreading and fibers can be spread in good uniformity. The spreading magnification of width can reach 3 to 5 and the maximum length can be more than 1250 m. The study has a great guiding significance in the development of a pneumatic spreading apparatus.