Study On Production Technology And Creep Performance Of Pure PTFE Needle-punched Filter Material

Industry is the foundation and core part of China's national economy.With the rapid expansion of industrial scale,industrial particulate matter pollution has drawing a widely attention of the government and society due to the threat to the environment.The bag-house dust removal technology is able to remove particles efficiently,and its filtering function is realized by the internal filter material.Recently,high temperature resistant filter materials adapted to high temperature,high humidity and high corrosion dust have developed rapidly.The pure polytetrafluorethylene(PTFE)needle-punched filter material as one of the representative,in the waste incineration,chemical production and other harsh dust environment shows excellent performance.However,pure PTFE needle-punched filter materials have some problems,such as difficulty in molding,low strength,and low creep resistance.Studying its preparation technology can improve the application value of the product.In this paper,using PTFE fibers and PTFE woven fabrics as raw materials,the technology of carding into mesh and needling reinforcement of pure PTFE filter materials were systematically studied,and the long-term creep behavior of the filter materials were predicted.PTFE fibers are characterized by high static electricity and difficult to comb into a web.For this reason,antistatic agent treatment and adjustment of environmental temperature and humidity were adopted to remove the charge of the fiber.A special carding machine for PTFE fibers was designed to improve the uniformity of web by means of gentle carding and enhanced transfer.In order to further improve the weight and uniformity of the fiber network,two carding machines and two cross-laying machines were used.Finally,the areal density of the prepared web was350g/m~2,the CV value was only 2.25%,and the quality of the web could meet the actual production.Then,the PTFE fiber web,PTFE woven fabric,another PTFE fiber web were stacked and needle-punched to form a"sandwich"structure of the filter material.The effects of puncture depth and puncture density on the thickness,areal density,air permeability,pore size,filtration,mechanics and other properties of the filter material were discussed,and the damage(Split,stretch and pierce)form of the base fabric is further explored.To achieve commercial applications,it is essential to maintain a balance between energy consumption and product quality.So the mathematical model of strength prediction was constructed,which provided reference for the grasp of needling process.The results showed that the puncture depth was about 9mm,the puncture density was about 400 needles cm^-2,the product quality was good and the energy consumption was the lowest.Because of the weak intermolecular force of PTFE,strain is large in macro.Controlling the creep deformation of the pure PTFE filter material within the design service life is the key to its long-term operation.In order to explore the long-term creep behavior of PTFE filter material at high temperature,the Step Isothermal Method was carried out in the range of 200??260?,and the creep curve of the filter material was obtained by the time-temperature equivalent principle,and the accuracy of the creep curve in a certain time was verified.In addition,a four-element model and a six-element model were established based on the filter material structure,and the fitted creep curve was obtained.The results show that the PTFE filter material has a variety of deformation forms in a short time(10~5s),and it meets the characteristics of typical creep in a long time.According to the time of creep failure on the curve,the service life of the filter material is predicted to be about 3 years.The four-element model is able to predict the long-term creep behavior of the filter material.The influence of post-treatment technology on creep property of PTFE filter material was also discussed.During the test period,fixed-length heat setting,immersion finishing and coating finishing reduce the creep strain of the filter material.Among them,the creep resistance of the membrane filter is the best.