Preparation And Properties Of The Biaxial Weft-knitted Seamless Air Filter Material

In front of the crisis in global environmental,with the vigorous promotion of the national heavy industry and the further improvement of emission,the development of high-performance filter materials with high filtration efficiency and long service life become the research focus of the air filtration industry.Traditional filter bags are sewn from air filter materials.There are two problems at present.Firstly,the filter bag is prone to rupture due to the impact of pulsed air flow during the use of the filter bag.Secondly,dust accumulation caused by overlaps of sewing material and excessive needle traces reduces the effective filtration area of the air filter material.Therefore,the filtration efficiency of the entire filter bag reduces.In this subject,an electrostatically enhanced polytetrafluoroethylene monofilament was prepared.With this monofilament used as the structural reinforcement raw material,a biaxial weft-knitted seamless air filter material was developed to effectively solve the above two problems.In view of the above new biaxial weft-knitted structure,this subject developed a special biaxial circular weft machine and a cylindrical needle punching machine to achieve the successful preparation of the noval biaxial weft-knitted seamless air filter material.Aiming at the various performances involved in the use of air filter materials,the biaxial weft-knitted seamless air filter materials were compared with the traditional air filter materials.Finally,through the numerical simulation,the advantages of the biaxial weft-knitted seamless air filter materials in mechanical properties and filtration efficiency were revealed.(1)In this project,a new type of polytetrafluoroethylene monofilament was prepared by extrusion spinning.The advantages of its mechanical properties and electrostatic properties were used to improve the mechanical properties and filtration efficiency of seamless filter materials.In the pretreatment,tourmaline particles with different particle sizes and contents were added to mix before spun.The change of the tourmaline particle had a greater impact on the surface morphology,mechanical properties and electrical properties of the polytetrafluoroethylene monofilament.Studies have shown that with the increase of content and particle size of tourmaline particles,the more and deeper the number of grooves were appeared on the surface of the monofilament,which resulted the decrease in mechanical properties.However,due to the static electricity of tourmaline particles,the static voltage on the surface of the monofilament significantly increased and appears exponential distribution.Considering the improvement of the mechanical properties and electrical properties of monofilaments on the mechanical properties and filtration efficiency of seamless structural materials,the optimal content of tourmaline was 5 wt% and the optimal particle size was 5 μm.The above research provided material support for the research and development of biaxial weftknitted seamless air filtration material.(2)A new biaxial weft-knitted seamless structure was designed.The interlock stitch structure was used as the ground structure,and warp and weft-lined yarns were laid in the basic structure.In response to this new fabric structure,a novel biaxial circular weft-knitted machine and cylinder needling machinewas designed and developed.Among them,the new biaxial circular weft machine was equipped with a special loop forming mechanism,yarn feeding mechanism and transmission mechanism.By continuously adjusting the relative position of the yarn feeder,the tension of the yarn and the fabric pulling force,and the cooperation between the mechanisms,the weaving of biaxial weft-knitted seamless fabric was realized.Based on the structural characteristics of seamless tubes,this subject developed a needle punching machine for cylindrical fabrics with different diameters to further enhance the fabric structure and improve its porosity,and finally obtained a weft-knitted seamless biaxial air filter material.The research and development of new structures and equipment brought opportunities for the development of new products in the textile field and the expansion of new applications,and also provided design ideas for the development of new products of air filter materials.(3)Six kinds of samples composed of weft-knitted seamless air filter materials with different structures and traditional air filter materials were tested for tensile strength,burst strength,static voltage,air permeability,pore size distribution,filtration efficiency and filtration resistance.The performance index was analyzed by fuzzy synthesis.In the process of stretching and bursting,the transverse and longitudinal reinforcing structure of the biaxial weft-knitted seamless air filter material was conducive to the improvement of the tensile and bursting strength of the material.From the stretching and bursting curves,the tensile and bursting performance of the biaxial seamless air filter material was relatively stable.In the filtration performance,the air permeability and average pore size of the biaxial weft-knitted seamless air filter material were lower than the traditional materials.However,due to the application of enhanced static electricity materials and seamless structures,the filtration efficiency improved effectively.Finally,through the fuzzy comprehensive analysis of the mechanical properties,electrical properties and filtration performance of the six air filtration materials,the final results show that due to the application of electrostatically enhanced PTFE and seamless structure,the mechanical properties and filtration performance of the biaxial weft-knitted seamless air filtration developed in this paper have been significantly improved,which provided a performance reference for its application in the filtration industry.(4)The physical model of air filter material was established by ANSYS.The advantages of weft-knitted seamless air filtration material in filtration performance were theoretically analyzed.The seamless filter material with different PTFE monofilament content,the seamless structure material and the slit filter material were formed into two groups of contrasts.From the three aspects of filtration process,filtration mechanism and filtration efficiency,the filter material had an obvious adsorption effect on the fine particles,and the seamless structure can improve the filtration efficiency of the fiter material obviously.It matched the experimental data,confirming the effectiveness of the model.(5)A general model of the dust removal system was established by MATLAB.Through the improvement of the mechanical properties and filtration efficiency of the seamless filter material,the corresponding parameters in the model were changed.The results show that the application of the seamless filter material significantly improved the stability of the dust removal system.Using the analysis of various factors of the bag-type dust removal system,the differential equations of the system were obtained to establish the generalized system model of the dust removal system model.Using the analysis of the stability of the generalized system,it was obtained that the dust removal model can reach stability when the relevant parameters meet certain conditions.The time it takes for the dust removal model to reach stability was used as the standard to measure the stability performance of the system.The shorter the time for the dust removal model to reach stability meant the higher the system stability.By changing the parameter values of the mechanical properties and initial dust removal efficiency in the system,the change of the system stability was calculated.The results show that with the improvement of the mechanical properties and filtration efficiency of the filter material,the stability of the dust removal system was significantly improved.The establishment and stability analysis of the generalized system model of the bag filter would provide a basis for selecting filter bags with different specifications.The above five aspects all aimed at the deficiency of mechanical properties and filtration efficiency of traditional filtration materials.Starting from the four aspects of raw materials,structure,equipment,performance and simulation,the structure and equipment were the focus of this research,and the comparison of the performance was the ultimate goal.Combined with numerical simulation,a new type of seamless air filter material with superior mechanical properties and filtration performance is finally obtained,which lays a theoretical foundation for the application of this type of new seamless air filter material with excellent mechanical and filtration performance.