The spinning fluid is continuously, quantitatively and evenly extruded from the capillary holes of the spinneret or spinneret with a spinning pump (or metering pump) to form a liquid stream, and then in air, water or The process of solidification into filaments in a coagulation bath is called spinning or fiber forming.
The newly spun filament is called virgin fiber. Spinning is a key process in the production of chemical fibers. Changing the spinning process conditions can adjust the structure of the fiber within a wide range, thereby correspondingly changing the physical and mechanical properties of the resulting fiber.
According to the different properties of fiber-forming polymers, the spinning methods of chemical fibers mainly include melt spinning and melt spinning. In addition, there are Special or unconventional spinning methods. Among them, according to the different coagulation methods, the melt spinning method is divided into two types: wet spinning and dry spinning. In the production of chemical fibers, most of them are produced by melt spinning, followed by wet spinning, and only a small amount are produced by dry or other unconventional spinning methods.
01
Melt spinning method
also known as Melt spinning, referred to as melt spinning. It is a chemical fiber spinning method in which the polymer is heated and melted, extruded through a spinneret, and cooled and solidified in the air to form fibers. Polymers used for melt spinning must be able to melt into a viscous flow state without significant decomposition. Polyester fibers, polyamide fibers and polypropylene fibers can all be produced by melt spinning.
Features:
The main features of the melt spinning method are high spinning speed (1000~7000m/min), no need for solvents and precipitants and their recovery and circulation systems, simple equipment, and short process flow. It is a An economical, convenient and efficient forming method. However, the number of spinneret holes is relatively small.
Process flow:
1. Preparation of spinning melt – continuous polymerization worthy of award-winning melt. After pre-crystallization and drying, the fiber-forming polymer slices are added from the polymer hopper and heated in sections as required. The screw extruder successively carries out melting, mixing, metering and extrusion, and is sent to the melt metering pump through the elbow between the extruder and spinning boxes.
2. The melt is quantitatively extruded through the small hole of the spinneret through the metering pump in the spinning box to form a thin stream of melt.
3. After the thin stream of melt is used, it is cooled, solidified and formed into primary fibers at a lower temperature and cooling blowing environment.
4. The virgin fiber is then oiled, networked and wound into a cylinder.
5. This winding yarn is then subjected to subsequent secondary molding processes such as drawing and heat setting to produce a finished fiber with applicability.
Classification:
Themeltspinningmethodisdividedintodirectspinningandslicespinningaccordingtothemeltpreparationprocess.Theprocessofdirectlyfeedingthepolymerizedpolymermeltintoameteringpumpformetering,extrusionandspinningbecomesthedirectspinningmethod;whilethepolymerpelletsundergopre-crystallization,dryingandothernecessarypre-spinningpreparations,andthentheMatsuriscrewThetechnologyofextrudermeltspinningiscalledchipspinning.Directspinningtechnologyisoftenusedinlarge-scaleindustrialproduction,whichisbeneficialtoreducingproductioncosts.However,itisdifficulttoproducedifferentiatedfibervarieties,andonlyslightchangescanbemadeinlineardensityandfibercross-sectionalshape.Thechipspinningmethodismoreflexible,easytochangevarieties,andproducessmallbatchesofdifferentiatedfiberswithhighaddedvalue.
02Solutionspinningmethod
Solutionspinningistodissolvefiber-formingpolymersinacertainsolventtoprepareaspinningsolutionwithanappropriateconcentration,andthenspitthespinningsolutionthroughtinyholesintotheInthecoagulationbathorhotgas,thepolymerprecipitatesintosolidfilaments,andafterstretching,shaping,washing,anddrying,thefinishedfibercanbeobtained.
Obviously,thesolutionspinningproductionprocessismorecomplicatedthanmeltspinning.However,forsomepolymersthathavedecomposedbeforemelting,thisspinningformingtechnologycanonlybechosen.SolutionspinningTherearealsowetspinning,dryspinning,anddryandwetspinning.
01Wetspinning
Wetspinningisreferredtoaswetspinning.Achemicalfiberspinningmethodinwhichapolymerisdissolvedinasolventandathinstreamisejectedthroughaspinneretintoacoagulationbathtoformfibers.Fiber-formingpolymerssuitableforwetspinninghaveadecompositiontemperaturelowerthanthemeltingpointorareeasilydiscoloredwhenheated,andcanbedissolvedinappropriatesolvents.Syntheticfiberssuchaspolyacrylonitrilefiberandpolyvinylalcoholfiberandman-madefiberssuchasviscosefiberandcuprofiberareproducedbywetspinning.Mostofthefibercross-sectionsobtainedbywetspinningarenon-circularandhaveanobvioussheath-corestructure,whichismainlycausedbythesolidificationofthecoagulationliquid.
Features:
Thespeedofwetspinningislower,andthespinnerethasmoreholesthanmeltspinning.Theprocessiscomplex,theinvestmenttimesarelarge,andtheproductioncostishigh.Generally,intheproductionofshortfibers,multi-holespinneretsorsteppedspinneretholescanbeusedtoimproveproductioncapacity,thusmakingupfortheshortcomingsoflowspinningspeed.
Processflow:
1.Preparespinningsolution.2.Presstherawsolutionoutofthespinnerettoformathinstream.3.Thethinstreamoforiginalsolutionsolidifiesintoprimaryfibers.4.Thevirginfiberispackagedordirectlyprocessed.
02Dryspinning
Dryspinningisatypeofsolutionspinning.Iffiber-formingpolymerscanfindasolventwithalowerboilingpointandgoodsolubilitytomakeaspinningsolution,Atthistime,thespinningsolutioncanbedrawnthroughthefineholes.Out,intotheheatedgas,thesolventinthespinningliquidevaporates,thepolymerfilamentsgraduallysolidify,andthefinishedfibercanbeobtainedthroughpost-processingprocessessuchasstretching,shaping,washing,anddrying.Acrylic,spandex,vinylonandvinylonallusedryspinningtechnology.
Features:
Dryspinninghastheadvantagesofcontinuousproduction,highspinningspeed,largeoutput,andlesspollution;thefiberquality,chemicalresistance,anddyeingperformancearebetterthanwet-spunfibers.However,dryfiberhaspoorchlorineresistance,istechnicallydifficult,requiressolventrecovery,andhasrelativelyhighproductioncosts.
DrySpinning&WetSpinning
Theconcentrationofspinningsolutionishigherthanthatofwetspinning,generallyupto18%~45%,andthecorrespondingviscosityisalsohigh,whichcanwithstandgreaterspinneretstretchingthanwetspinning(2~7times),itiseasiertoproducefinerfibersthanwetspinning.Themechanicalresistanceoftheyarnonthespinninglineismuchsmallerthanthatofwetspinning,andthespinningspeedishigherthanthatofwetspinning.However,duetothelimitationofthesolventevaporationspeed,thedryspinningspeedislowerthanthatofmeltspinning.Thenumberofspinneretholesismuchlessthanthatofwetspinning.Thisisbecausedrycuringisslowandthethreadstendtostickbeforecuring.Generally,thenumberofspinneretholesfordry-spunshortfibersisabout1,200,whilethenumberofspinneretholesforwet-spunshortfibersisashighastensofthousands.Therefore,theproductioncapacityofasinglespinningpositionofdryspinningismuchlowerthanthatofwetspinning.Dryspinningisgenerallysuitablefortheproductionoflongfibers.Silk.
Processflow:
03 Dry and wet spinning
Dry and wet spinning is a type of solution spinning, also known as dry-jet wet spinning. It combines wet spinning with dry spinning. Combining the characteristics of method spinning, it is particularly suitable for the molding and processing of liquid crystal polymers, so it is often called liquid crystal spinning.
That is, the fiber-forming polymer is dissolved in a certain solvent to prepare a spinning solution with a suitable concentration, and then the spinning solution is spit out from a tiny hole, and first passes through a short air sandwich, where Since the resistance of the filament is small, the polymer in the liquid crystal state is conducive to high orientation under high-strength stretching conditions, and then the filament enters the low-temperature coagulation bath to complete solidification and molding, and the liquid crystal macromolecules are frozen in a highly orderly manner. In the liquid crystal state, the finished fiber has high strength and high modulus mechanical properties.
At present, dry and wet spinning has been used in polyacrylonitrile fiber, polylactic acid fiber, chitosan fiber, dibutyryl chitin, polyvinyl chloride fiber, aromatic polyamide fiber, polybenzimidazole fiber and other fibers. used in its preparation.
Features:
Dryandwetspinningcanspinhigh-viscosityspinningsolution,therebyreducingsolventrecoveryandunitconsumption,andatthesametime,itsformingspeedishigh,theresultingfiberhasauniformstructure,ametalliccircularcross-section,improvedstrengthandelasticity,andbetterdyeabilityandcolor.Amajordisadvantageofwetanddryspinningisthatafterthethinstreamofspinningdopebreaks,thedopecaneasilyflowalongthespinneret.Thismeansthatifasinglefilamentbreaksduringporousspinning,itislikelythatthedopewilloverflowandthedopewillflow.Causesotherfilamentstobreak,therebydestroyingthecontinuityofthespinningprocess.
Processflow:
Dry and wet spinning is , after the spinning solution is pressed out from the spinneret, it first passes through a gas (usually air) layer (air gap), and then enters the coagulation bath, so some people call this method air gap spinning. The post-processing process of the nascent fiber derived from the coagulation bath is the same as that of ordinary wet spinning. </p
