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2.5 pirn winders

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2. Winding 2.5 Pirn Winders Pirns are the yarn packages used within the shuttle to supply the yarns for pick insertion during weaving. The dimension of the shuttle is restricted by the shed geometry and the strain imposed on the warp yarns during shedding operation. The dimension of the pirn is governed by the dimension of the shuttle. Thus the pirn has to be a long and thin package. In contrast to cone winding, where the supply packages (ringframe bobbins) are small and the delivery packages are big, the supply packages are bigger than the delivery package (pirn) in pirn winding. As the yarns are already been cleaned from slubs and other objectionable faults, no yarn clearing operation is required in pirn winding. The winding principle of pirn is different than that of cones and cheeses. If a crosswound package is made then there will be lot of tension variation during weaving. On the other hand, the parallel would package will give the problem of instability. Therefore, pirns are made by overlapping short, conical and crosswound sections as shown inFigure 2.20. Figure 2.20: Stages of pirn winding The base of the empty pirn is generally conical. The pirn winding starts from the conical base and progressively proceeds towards the tip of the pirn. The distance travelled in one stroke of traverse is known as chase length. One layer of coils are laid on the conical base during the forward and as well as duirng the return movement of the traverse meachanism. Thus the conicity of the package is maintained and thus the tip of the cone formed by the coils of yarn slowly proceeds towrds the tip of the pirn. The process can be visualised as if one plastic cup (having cone sahpe) is placed over another and the process is continued to build a tall cylindrical column. This is depicted inFigure 2.21. For the ease of visibility, large gaps has been maintained between two cones of coils and thus it seems that the overlapping between two layers of coils is very low which is actually not true..

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  • 7/6/2015 NPTEL::TextileEngineeringFabricManufactureI

    data:text/htmlcharset=utf8,%3Ctable%20width%3D%2255%25%22%20height%3D%22585%22%20border%3D%220%22%20align%3D%22center%22%20ce 1/5

    2.Winding2.5PirnWinders

    Pirns are the yarn packages usedwithin the shuttle to supply the yarns for pick insertion duringweaving. Thedimension of the shuttle is restricted by the shed geometry and the strain imposed on thewarp yarns duringsheddingoperation.Thedimensionofthepirnisgovernedbythedimensionoftheshuttle.Thusthepirnhastobealongandthinpackage.Incontrasttoconewinding,wherethesupplypackages(ringframebobbins)aresmallandthedeliverypackagesarebig,thesupplypackagesarebiggerthanthedeliverypackage(pirn)inpirnwinding.Astheyarnsarealreadybeencleanedfromslubsandotherobjectionablefaults,noyarnclearingoperationisrequiredinpirnwinding.Thewindingprincipleofpirn isdifferentthanthatofconesandcheeses.Ifacrosswoundpackageismadethentherewillbe lotoftensionvariationduringweaving.Ontheotherhand,theparallelwouldpackagewillgivetheproblemofinstability.Therefore,pirnsaremadebyoverlappingshort,conicalandcrosswoundsectionsasshowninFigure2.20.

    Figure2.20:StagesofpirnwindingThebaseof theemptypirn isgenerally conical. Thepirnwinding starts from the conicalbaseandprogressivelyproceedstowardsthetipofthepirn.Thedistancetravelledinonestrokeoftraverseisknownaschase length.Onelayerofcoilsarelaidontheconicalbaseduringtheforwardandaswellasduirngthereturnmovementofthetraversemeachanism.Thustheconicityofthepackageismaintainedandthusthetipoftheconeformedbythecoilsofyarnslowlyproceedstowrdsthetipofthepirn.Theprocesscanbevisualisedasifoneplasticcup(havingconesahpe)isplacedoveranotherandtheprocessiscontinuedtobuildatallcylindricalcolumn.ThisisdepictedinFigure2.21.Fortheeaseofvisibility, largegapshasbeenmaintainedbetweentwoconesofcoilsandthus itseemsthattheoverlappingbetweentwolayersofcoilsisverylowwhichisactuallynottrue..

  • 7/6/2015 NPTEL::TextileEngineeringFabricManufactureI

    data:text/htmlcharset=utf8,%3Ctable%20width%3D%2255%25%22%20height%3D%22585%22%20border%3D%220%22%20align%3D%22center%22%20ce 2/5

    Figure2.21:BuildingofapirnPirnsmaygenerallybedescribedinthefollowingcategoriesortypes(Figure2.22).

    PlaintaperedpirnPirnwithpartlyformed(half)basePirnwithfullbase

    Figure2.22:Plain,halfbaseandfullbasepirns

  • 7/6/2015 NPTEL::TextileEngineeringFabricManufactureI

    data:text/htmlcharset=utf8,%3Ctable%20width%3D%2255%25%22%20height%3D%22585%22%20border%3D%220%22%20align%3D%22center%22%20ce 3/5

    IfthefullandemptypirndiameterisDanddrespectively,Listhechaselengthandisthechaseangle,thenthefollowingexpressioncanbewritten.

    Thechaseangledependsonthetypeofyarn.Forspunyarnsthechaseanglecouldbeashighas1518.However,forfilamentyarnswithlowfriction,itcouldbeaslowas610.

    ConditionsforUniformPackage(Cheese)BuildingUniformbuildingofpackageisimperativeinwindingprocess.Thepackageshouldhaveveryuniformdensity.Inthefollowingpart,theconditionsforuniformbuildingofcheesehavebeenderivedbasedonthefollowingassumption.Assumption: Length of yarn wound per unit surface area of the package should be constant foruniformbuildingofpackage.ThepathofyarnonacylindricalcheesehasbeenshowninFigure2.23.

    Figure2.23:Uniformbuildingofcheese

    So, mustbekeptconstforuniformbuildingofthecheese.

    Drumdrivenwinder

  • 7/6/2015 NPTEL::TextileEngineeringFabricManufactureI

    data:text/htmlcharset=utf8,%3Ctable%20width%3D%2255%25%22%20height%3D%22585%22%20border%3D%220%22%20align%3D%22center%22%20ce 4/5

    Fordrumdrivenwinderswithgrooveddrums,remainsconstantduringpackagebuilding.Therefore,Vtshouldbe

    reducedwiththeincreaseinpackagediameterdtoattainuniformbuilding.ThishasbeenshowninFigure2.24.

    Figure2.24:PackagediametervstraversevelocityCommentsFordrumdrivenwinder,isconstantprovided theratioofVt andVs are constant.But ifVt is reduced (keeping

    Vsconstanttheoretically,whichispossibleiftraversingmechanismisseparatefromgroovedrum),willalsoreduce

    andCoswill increase.So,Vt has to be reduced in such amanner that the product ofVt andCos is changes

    proportionatelywith1/d.

    Spindledrivenwinder

    CommentsInspindledrivenmachine,reduces(evenwhenVtisconstant)aspackagediameter(d)increases.So,Vthastobe

    reducedaccordinglyasreducingVtwillhavefurtherbearingon.

  • 7/6/2015 NPTEL::TextileEngineeringFabricManufactureI

    data:text/htmlcharset=utf8,%3Ctable%20width%3D%2255%25%22%20height%3D%22585%22%20border%3D%220%22%20align%3D%22center%22%20ce 5/5

    CopyrightIITDelhi20092011.Allrightsreserved.


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