Study On Continuous Carbon Fiber Vibration Blowing Spreading Device And Process Parameters

Continuous carbon fiber reinforced thermoplastic composites(CFRTP)have the advantages of high specific strength,good impact toughness,recyclability,chemical corrosion resistance,easy transportation and storage,and no harmful substances in the processing process.CFRTP composites have broad application prospects in the fields of aerospace,new energy vehicles,rail transit,wind power generation and so on,which pursue high strength and lightweight.During the preparation of prepreg by melt impregnation,there are some problems,such as the difficulty of fiber bundle spreading,the uneven distribution of fiber monofilament,the insufficient impregnation of thermoplastic resin,and the fiber cracking caused by resin enrichment.Due to the poor fracture toughness and small monofilament diameter of carbon fibers(CFs),the above problems are particularly prominent in the prepreg preparation process.The traditional mechanical fiber spreading method has the advantages of low upper limit of spreading and high fiber breaking rate.Compared with the mechanical fiber spreading,the vibration fiber spreading method can improve the fiber spreading width,but the fracture rate is higher and the fiber spreading uniformity is worse.The single internal suction type airflow fiber spreading method performs nondestructive fiber spreading on the fiber bundle through the pressure difference between the internal pressure and the external pressure of the fiber bundle,but the equipment cost is high,the fiber spreading stability is poor,and the cavity size of a fiber spreader is limited,so that the wide fiber belt is difficult to spread.At present,there is insufficient research on the bonding performance between different fiber spreading modes.In this paper,the fiber spreading mechanism and impregnation process of CFRTP prepreg preparation process were studied.Firstly,the feasibility of the combination of vibration fiber spreading and air blowing fiber spreading was explored,and the vibration blowing fiber spreading device was set up,and the mathematical models of fiber broadening and breaking rate were established.Secondly,the process parameters of fiber spreading with vibration blowing were optimized by on-line fiber spreading experiments and prepreg preparation experiments.On the basis of the best fiber spreading process parameters,the melt impregnation process parameters were optimized.Finally,the effects of different types and contents of compatibilizers on the properties of CFRTP prepreg were studied.The main work contents are:(1)Through the mechanical analysis of the process of fiber spreading by vibration and airflow,the feasibility of introducing blowing airflow during the vertical vibration of fiber spreading was determined,and the vibration blowing fiber spreading device was built.Based on the stress analysis of carbon fiber bundles in the process of fiber spreading,Newton’s law of motion and Bernoulli’s equation were used to establish the mathematical model of fiber spreading width by vibration blowing with the parameters of airflow velocity,vibration amplitude,vibration frequency and traction velocity;The Weibull distribution function was used to describe the fiber fracture in the process of fiber spreading by vibrating blowing,and the mathematical model of fiber fracture rate was established.The variation trend of the predicted value of the mathematical model is consistent with that of the experimental value,which is verified by the on-line fiber unfolding experiment.(2)DOE experiments were carried out to study the process parameters of vibration fiber spreading and vibration blowing fiber spreading,which were characterized by the width of fiber spreading,the rate of fiber breaking and the degree of fiber dispersion.The experimental results show that the single vertical vibration fiber spreading can effectively improve the broadening under a larger tension,but the impact force of the vibration roller on the fiber bundle is increased,so the fiber fracture rate is not improved,and the uniformity fluctuates greatly.Vibration blowing fiber spreading method can improve the fiber bundle broadening and fiber monofilament dispersion uniformity,and reduce the fiber fracture rate under the condition of smaller fiber tension.The optimal fiber spreading process parameters are as follows: fiber tension = 2 N,vibration frequency = 5 Hz,vibration amplitude = 22 mm,and airflow velocity = 9 m/s.(3)CFRTP prepreg preparation experiments were carried out to optimize the melt impregnation process parameters under the optimal fiber spreading process parameters.The optimal process parameters of CFs/PP prepreg prepared by melt impregnation process were obtained by optimizing the process parameters with the die temperature,die gap and traction speed as the experimental factors and the fiber impregnation degree and fiber fracture rate as the response,so that the impregnation degree reached 98.9% and the fracture rate decreased to 0.725%.(4)The mechanical properties of CFs/PP composites with different contents of CFs and compatibilizer were studied.For the long fiber injection molding composites with 20% CFs,the tensile strength and impact strength increased with the increase of the content of compatibilizer PP-g-MAH;POE-g-MAH can effectively improve the impact toughness of CFRTP composites,but the tensile strength decreases when the mass content is about 4%.