ASHRAE HVAC APPLICATIONS SI CH 21-2015 TEXTILE PROCESSING PLANTS.pdf

1、21.1CHAPTER 21TEXTILE PROCESSING PLANTSTerminology 21.1Fiber Making. 21.1Yarn Making 21.2Fabric Making. 21.3Air-Conditioning Design. 21.4Energy Conservation. 21.7HIS chapter covers (1) basic processes for making syntheticTfibers, (2) fabricating synthetic fibers into yarn and fabric, (3)relevant typ

2、es of HVAC and refrigerating equipment, (4) healthconsiderations, and (5) energy conservation procedures.Most textile manufacturing processes may be placed into one ofthree general classifications: synthetic fiber making, yarn making, orfabric making. Synthetic fiber manufacturing is divided into st

3、apleprocessing, tow-to-top conversion, and continuous fiber processing;yarn making is divided into spinning and twisting; and fabric makingis divided into weaving and knitting. Although these processes vary,their descriptions reveal the principles on which air-conditioningdesign for these facilities

4、 is based.1. TERMINOLOGYThe following is only a partial glossary of terms used in the textileindustry. For more complete terminology, consult the sources in theBibliography or the Internet search engine of your choice.Air permeability. Porosity, or ease with which air passes throughmaterial. Air per

5、meability affects factors such as the wind resistanceof sailcloth, air resistance of parachute cloth, and efficiency of vari-ous types of air filtration media. It is also a measure of a fabricswarmness or coolness.Bidirectional fabric. A fabric with reinforcing fibers in twodirections: in the warp (

6、machine) direction and filling (cross-machine) direction.Calender. A machine used in finishing to impart various surfaceeffects to fabrics. It essentially consists of two or more heavy rollers,sometimes heated, through which the fabric is passed under heavypressure.Denier. The mass, in grams, of 900

7、0 m of yarn. Denier is a directnumbering system in which lower numbers represent finer sizes andhigher numbers the coarser sizes. Outside the United States, the Texsystem is used instead.Heddle. A cord, round steel wire, or thin flat steel strip with aloop or eye near the center, through which one o

8、r more warp threadspass on the loom, so that thread movement may be controlled inweaving. Heddles are held at both ends by the harness frame. Theycontrol the weave pattern and shed as the harnesses are raised andlowered during weaving. Lubricant. An oil or emulsion finish applied to fibers to preven

9、tdamage during textile processing, or to knitting yarns to make themmore pliable.Machine direction. The long direction within the plane of thefabric (i.e., the direction in which the fabric is being produced by themachine).Pick. A single filling thread carried by one trip of the weft inser-tion devi

10、ce across the loom. Picks interface with the warp ends toform a woven fabric.Reed. A comblike device on a loom that separates the warp yarnsand also beats each succeeding filling thread against those alreadywoven. The space between two adjacent wires of the reed is called adent. The fineness of the

11、reed is calculated by the number of dentsper inch (per 25.4 mm): the more dents, the finer the reed.Selvage. The narrow edge of woven fabric that runs parallel to thewarp. It is made with stronger yarns in a tighter construction than thebody of the fabric, to prevent raveling. A fast selvage enclose

12、s all orpart of the picks; a selvage is not fast when the filling threads are cutat the fabric edge after each pick.Shuttle. A boat-shaped device usually made of wood with ametal tip that carries filling yarns through the shed in the weavingprocess.Tex. The mass, in grams, of 1000 m of fabric. Used

13、primarily out-side the United States. See also Denier.Warp. The set of yarn in all woven fabrics, running lengthwiseand parallel to the selvage, interwoven with the filling.2. FIBER MAKINGProcesses preceding fiber extrusion have diverse ventilating andair-conditioning requirements based on principle

14、s similar to thosethat apply to chemical plants.Synthetic fibers are extruded from metallic spinnerets and solid-ified as continuous parallel filaments. This process, called continu-ous spinning, differs from the mechanical spinning of fibers or towinto yarn, which is generally referred to as spinni

15、ng.Synthetic fibers may be formed by melt-spinning, dry-spinning, orwet-spinning. Melt-spun fibers are solidified by cooling the moltenpolymer; dry-spun fibers by evaporating a solvent, leaving the poly-mer in fiber form; and wet-spun fibers by hardening the extruded fil-aments in a liquid bath. The

16、 selection of a spinning method is affectedby economic and chemical considerations. Generally, nylons, polyes-ters, and glass fibers are melt-spun; acetates dry-spun; rayons andaramids wet-spun; and acrylics dry- or wet-spun.For melt- and dry-spun fibers, the filaments of each spinneret areusually d

17、rawn through a long vertical tube called a chimney orquench stack, within which solidification occurs. For wet-spunfibers, the spinneret is suspended in a chemical bath where coagula-tion of the fibers takes place. Wet-spinning is followed by washing,applying a finish, and drying.Synthetic continuou

18、s fibers are extruded as a heavy denier tow forcutting into short lengths called staple or somewhat longer lengthsfor tow-to-top conversion, or they are extruded as light denier fila-ments for processing as continuous fibers. Oil is then applied tolubricate, give antistatic properties, and control f

19、iber cohesion. Theextruded filaments are usually drawn (stretched) both to align themolecules along the axis of the fiber and to improve the crystallineThe preparation of this chapter is assigned to TC 9.2, Industrial AirConditioning.21.2 2015 ASHRAE HandbookHVAC Applications (SI)structure of the mo

20、lecules, thereby increasing the fibers strengthand resistance to stretching.Heat applied to the fiber when drawing heavy denier or high-strength synthetics releases a troublesome oil mist. In addition, themechanical work of drawing generates a high localized heat load. Ifthe draw is accompanied by t

21、wist, it is called draw-twist; if not, itis called draw-wind. After draw-twisting, continuous fibers may begiven additional twist or may be sent directly to warping.When tow is cut to make staple, the short fibers are allowed toassume random orientation. The staple, alone or in a blend, is thenusual

22、ly processed as described in the Cotton System section. How-ever, tow-to-top conversion, a more efficient process, has becomemore popular. The longer tow is broken or cut to maintain parallel ori-entation. Most of the steps of the cotton system are bypassed; the par-allel fibers are ready for blendi

23、ng and mechanical spinning into yarn.In the manufacture of glass fiber yarn, light denier multifilamentsare formed by attenuating molten glass through platinum bushingsat high temperatures and speeds. The filaments are then drawntogether while being cooled with a water spray, and a chemical sizeis a

24、pplied to protect the fiber. This is all accomplished in a singleprocess prior to winding the fiber for further processing.3. YARN MAKINGThe fiber length determines whether spinning or twisting must beused. Spun yarns are produced by loosely gathering synthetic staple,natural fibers, or blends into

25、rope-like form; drawing them out toincrease fiber parallelism, if required; and then twisting. Twisted(continuous filament) yarns are made by twisting long mono-filaments or multifilaments. Ply yarns are made in a similar mannerfrom spun or twisted yarns.The principles of mechanical spinning are app

26、lied in three dif-ferent systems: cotton, woolen, and worsted. The cotton system isused for all cotton, most synthetic staple, and many blends. Woolenand worsted systems are used to spin most wool yarns, some woolblends, and synthetic fibers such as acrylics.Cotton SystemThe cotton system was origin

27、ally developed for spinning cottonyarn, but now its basic machinery is used to spin all varieties of sta-ple, including wool, polyester, and blends. Most of the steps fromraw materials to fabrics, along with the ranges of frequently usedhumidities, are outlined in Figure 1.Opening, Blending, and Pic

28、king. The compressed tufts arepartly opened, most foreign matter and some short fibers areremoved, and the mass is put in an organized form. Some blendingis desired to average the irregularities between bales or to mix dif-ferent kinds of fiber. Synthetic staple, which is cleaner and moreuniform, us

29、ually requires less preparation. The product of the pickeris pneumatically conveyed to the feed rolls of the card.Carding. This process lengthens the lap into a thin web, whichis gathered into a rope-like form called a sliver. Further opening andfiber separation follows, as well as partial removal o

30、f short fiber andtrash. The sliver is laid in an ascending spiral in cans of variousdiameters.For heavy, low-count (length per unit of mass) yarns of averageor lower quality, the card sliver goes directly to drawing. For lighter,high-count yarns requiring fineness, smoothness, and strength, thecard

31、sliver must first be combed.Lapping. In sliver lapping, several slivers are placed side by sideand drafted. In ribbon lapping, the resulting ribbons are laid one onanother and drafted again. The doubling and redoubling averagesout sliver irregularities; drafting improves fiber parallelism. Somerecen

32、t processes lap only once before combing.Combing. After lapping, the fibers are combed with fine metalteeth to substantially remove all fibers below a predeterminedlength, to remove any remaining foreign matter, and to improvefiber arrangement. The combed lap is then attenuated by drawingrolls and a

33、gain condensed into a single sliver.Drawing. Drawing follows either carding or combing andimproves uniformity and fiber parallelism by doubling and draftingseveral individual slivers into a single composite strand. Doublingaverages the thick and thin portions; drafting further attenuates themass and

34、 improves parallelism.Roving. Roving continues the processes of drafting and parallel-ing until the strand is a size suitable for spinning. A slight twist isinserted, and the strand is wound on large bobbins used for the nextroving step or for spinning.Spinning. Mechanical spinning simultaneously ap

35、plies draft andtwist. The packages (any form into or on which one or more endscan be wound) of roving are creeled at the top of the frame. Theunwinding strand passes progressively through gear-driven draftingrolls, a yarn guide, the C-shaped traveler, and then to the bobbin.The vertical traverse of

36、the ring causes the yarn to be placed in pre-determined layers.The difference in peripheral speed between the back and frontrolls determines the draft. Twist is determined by the rate of front rollfeed, spindle speed, and drag, which is related to the traveler mass.The space between the nip or bite

37、of the rolls is adjustable andmust be slightly greater than the longest fiber. The speeds of frontFig. 1 Textile Process Flowchart and Ranges of HumidityTextile Processing Plants 21.3and back rolls are independently adjustable. Cotton spindles nor-mally run at 8000 to 9000 rpm but may exceed 14 000

38、rpm. In ringtwisting, drawing rolls are omitted, and a few spindles run as high as18 000 rpm.Open-end or turbine spinning combines drawing, roving, lap-ping, and spinning. Staple fibers are fragmented as they are drawnfrom a sliver and fed into a small, fast-spinning centrifugal device.In this devic

39、e, the fibers are oriented and discharged as yarn; twistis imparted by the rotating turbine. This system is faster, quieter, andless dusty than ring spinning.Spinning is the final step in the cotton system; the feature thatdistinguishes it from twisting is the application of draft. The amountand poi

40、nt of draft application accounts for many of the subtle dif-ferences that require different humidities for apparently identicalprocesses.Atmospheric Conditions. From carding to roving, the looselybound fibers are vulnerable to static electricity. In most instances,static can be adequately suppressed

41、 with humidity, which should notbe so high as to cause other problems. In other instances, it is nec-essary to suppress electrostatic properties with antistatic agents.Wherever draft is applied, constant humidity is needed to maintainoptimum frictional uniformity between adjacent fibers and, hence,c

42、ross-sectional uniformity.Woolen and Worsted SystemsThe woolen system generally makes coarser yarns, whereas theworsted system makes finer ones of a somewhat harder twist. Bothmay be used for lighter blends of wool, as well as for synthetic fiberswith the characteristics of wool. The machinery used

43、in both sys-tems applies the same principles of draft and twist but differs greatlyin detail and is more complex than that used for cotton.Compared to cotton, wool fibers are dirtier, greasier, and moreirregular. They are scoured to remove grease and are then usuallyreimpregnated with controlled amo

44、unts of oil to make them lesshydrophilic and to provide better interfiber behavior. Wool fibersare scaly and curly, so they are more cohesive and require differenttreatment. Wool, in contrast to cotton and synthetic fibers, requireshigher humidities in the processes prior to and including spinningth

45、an it does in the processes that follow. Approximate humidities aregiven in Kirk and Othmer (1993).Twisting Filaments and YarnsTwisting was originally applied to silk filaments; several fila-ments were doubled and then twisted to improve strength, unifor-mity, and elasticity. Essentially the same pr

46、ocess is used today, butit is now extended to spun yarns, as well as to single or multiple fil-aments of synthetic fibers. Twisting is widely used in the manufac-ture of sewing thread, twine, tire cord, tufting yarn, rug yarn, plyyarn, and some knitting yarns.Twisting and doubling is done on a down-

47、 or ring-twister, whichdraws in two or more ends from packages on an elevated creel,twists them together, and winds them into a package. Except for theomission of drafting, down-twisters are similar to conventionalring-spinning frames.When yarns are to be twisted without doubling, an up-twister isus

48、ed. Up-twisters are primarily used for throwing synthetic mono-filaments and multifilaments to add to or vary elasticity, light reflec-tion, and abrasion resistance. As with spinning, yarn characteristicsare controlled by making the twist hard or soft, right (S) or left (Z).Quality is determined lar

49、gely by the uniformity of twist, which, inturn, depends primarily on the tension and stability of the atmo-spheric conditions (Figure 1). Because the frame may be double- ortriple-decked, twisting requires concentrations of power. Theframes are otherwise similar to those used in spinning, and theypresent the same air distribution problems. In twisting, lint is not aserious problem.4. FABRIC MAKINGPreparatory ProcessesWhen spinning or twisting is complete, the yarn may be preparedfor weaving or knitting by processes that include winding, spooling,creeling, beaming, slashing, sizing, and dye