Knitting, Nonwovens and Braiding: Constructions and Processes

This chapter answers the second part of Section XE9.3, Fabric Manufacture, Structure and Properties, of XE9 Textile Engineering and Fibre Science, one of the nine optional sections of the Engineering Sciences (XE) paper. The syllabus lines covered are: “Fundamentals of weft knitting; Classification of weft knitting technologies; Weft knitted constructions such as plain, rib, interlock, purl and others; Different knit stitches such as loop, tuck, float and others; Principle of warp knitting; Classification of warp knitting technologies; Swinging and shogging motion of guide bar; Basic warp knit constructions such as pillar, tricot, atlas, inlay nets and others; Fibre preparation processes for nonwovens; Web formation and bonding processes; Spun-bonding and melt-blowing technologies; Applications of nonwoven fabrics; Principles of braiding; Type of braids; Maypole braiding technology.” It teaches loop, tuck and float stitches, the weft-knit structures, the guide-bar motions and warp-knit laps, nonwoven web formation and bonding, and the maypole braider. The numericals are needle count from gauge, knitting-machine output, warp-knitting delivery, needle-punch density and spunbond basis weight.

1. Weft knitting: loop structure, needle action and stitches

In weft knitting one yarn runs across the fabric and forms a horizontal row of loops, a course; the vertical column of loops is a wale. Each loop has a head, two legs and a foot, and is held by the loop it was drawn through (intermeshing). Fabric is produced as a flat or circular (tubular) body. The latch needle forms a loop in a cycle of rising so that the old loop slides off the opened latch (clearing), receiving fresh yarn in the hook, and descending so that the old loop closes the latch and is knocked over the new loop, which is drawn through it. Needles act individually, controlled by cams (or electronic selection), so patterns can be made course by course.

The three basic stitches
StitchWhat the needle doesEffect on fabric
Knit (loop)Rises fully, clears, takes yarn and knocks over the old loopNormal intermeshed loop
TuckRises only far enough to take the new yarn above the old loop, which is not clearedTwo loops in one hook; the fabric becomes wider and shorter and the surface is textured
Float (miss)Stays down and takes no yarn; the yarn floats behind the loopsFabric becomes narrower and less extensible

Machine gauge is the number of needles per inch (25.4 mm) of needle bed. A circular machine of diameter d inches and gauge G has about π d G needles, so a finer gauge takes finer yarn and gives a denser, lighter fabric. Output is set by the speed in rev/min, the number of feeders (yarn feed points, each knitting one course per revolution), the needle count and the loop length: courses per minute = rev/min × feeders, and yarn used per course = needles × stitch length.

Worked example. A single-jersey machine has 2400 needles and 90 feeders, runs at 25 rev/min, with stitch length 3.0 mm, yarn 20 tex, and 85% running efficiency. Courses per minute = 25 × 90 = 2250. Yarn per course = 2400 × 3.0 mm = 7.2 m. Yarn per minute = 2250 × 7.2 = 16,200 m = 16,200 × 20 mg = 324 g. Per hour = 324 × 60 = 19.44 kg; at 85%, 16.52 kg/h.

2. Weft-knitted constructions: plain, rib, interlock, purl

Principal weft-knit structures
StructureNeedle bed(s) and loopsProperties
Plain (single jersey)One needle bed; all loops pulled the same way, so the face shows wale-wise V’s and the back shows coursesLight, extensible, curls at the edges, unravels from the end where the last course was knitted
Rib (1×1)Two needle beds in rib gating; face and back wales alternateVery extensible and elastic widthways, lies flat, same appearance on both sides
InterlockTwo 1×1 ribs knitted into each other, using alternating long and short needles so that a wale on each face is directly opposite the otherSmooth on both faces, thicker, stable, less extensible than rib, does not curl
PurlDouble-ended latch needles slide between two beds, so face and back loops appear in the same waleVery extensible lengthways as well as widthways, bulky, shows rows of loops on both sides

Why they differ. Plain fabric is unbalanced, because all the loops lie to one side, so it curls to relieve the stored bending energy. In rib the face and back wales balance each other, so the fabric does not curl, and the sideways pull of the two sets of loops makes the width spring back. Interlock is dimensionally steadier because the two rib courses lock each other. Other structures come by combining stitches: tuck stitches give lace, pique and cardigan effects, floats give stability or jacquard patterns, and plating knits two yarns with one always on the face.

⚠️ Rib gives stretch, interlock gives stability
Do not confuse them: both use two needle beds, but 1×1 rib has face and back wales offset (so it is springy widthways), while interlock has them aligned and interlocked (so it is smooth, thick and stable). Purl is the only one of the four with face and back loops in the same wale, and it needs double-ended needles.

3. Warp knitting: guide bars, swinging and shogging, basic constructions

In warp knitting every needle in the bed has its own warp end, fed from one or more beams, and all needles form loops at the same time, so a whole course is made per machine cycle. Loops in a course are made from different yarns, and the yarn zig-zags up the fabric along the wales. The yarns are laid on the needles by guide bars, each carrying one guide per needle. In each cycle a guide bar makes two motions. Swinging carries the guides between the needles to the hook side and back again (through the needle gaps). Shogging moves the whole bar sideways by a stated number of needle spaces, controlled by a pattern chain, cam or electronic drive. Swinging round the needle hook makes the overlap; shogging behind the needles between loops makes the underlap.

Basic warp-knit constructions
ConstructionGuide-bar lappingCharacter
Pillar (chain)Overlap only, no underlap: the guide laps the same needle each cycleVertical chains with no sideways connection; needs inlay or another bar to hold the wales together
TricotUnderlap of one needle space, alternating directionSmooth and fine; used for lingerie and linings
AtlasUnderlaps over several needle spaces in the same direction for several courses, then reverseZig-zag diagonal wales, used with other bars for patterns
InlayA yarn is laid in between the overlaps and underlaps, held by the loops but not looped itselfGives stability and stiffness in the laid-in direction; fancy yarns are used because they need not bend
NetsSeveral bars with long, opposing shogs create open meshOpen, stable structures for laces, nets and technical meshes

Classification. Warp-knitting machines divide into tricot machines (typically fine gauges, two or a few guide bars, for fine filament yarns) and raschel machines (typically coarser gauges, many guide bars, for nets, laces and technical fabrics). Tricot machines use bearded or compound needles, and raschel machines use latch or compound needles. Delivery. Courses per minute equal the machine cycles per minute, so cloth delivered per minute (cm) = cycles per minute ÷ courses per cm.

4. Nonwovens: fibre preparation, web formation and bonding

A nonwoven is a sheet of fibres or filaments held together by entanglement, by cohesion or by adhesion, not by weaving or knitting. Production runs in four steps: fibre preparation (opening, blending, and cleaning staple fibres, or melting polymer), web formation, bonding, and finishing. Because no yarn is made, output per machine is high, and the web’s mass per unit area (basis weight, g/m²) is a first design variable.

Web formation and bonding routes
StageMethodPrinciple
Web formation (dry)Dry-laid: carded parallel or cross-lapped, or air-laid randomCards align fibres; a cross-lapper folds the web to build weight and strength across the web
Web formation (wet)Wet-laidShort fibres in a dilute water suspension are filtered on a screen, as in papermaking
Web formation (polymer)Polymer-laid: spunbond, meltblownThe web is made directly from extruded polymer, with no staple fibre stage
Mechanical bondingNeedle-punching; hydroentanglement (spunlace); stitch-bondingBarbed needles or fine high-pressure water jets entangle fibres; stitching knits through the web
Thermal bondingCalender (point) bonding; through-air bondingHeat softens thermoplastic fibres or a low-melting component so that they fuse at contacts
Chemical bondingSaturation, spray, foam or print binderA latex or resin binder glues the fibres at crossings and is cured

Needle-punching pushes barbed needles through the web, carrying fibres through its thickness. The punch density (punches per cm²) governs strength and compaction. If the needle board carries n needles per metre of width and the web advances a mm per stroke, then punches per cm² = n ÷ (10 a). The web advance per stroke is the line speed divided by the strokes per minute, so doubling stroke frequency at the same line speed halves a and doubles the punch density. For a cross-lapped web the final basis weight is roughly the card-web basis weight × the number of layers laid, after any draft.

⚠️ Bonding type decides the properties
Needle-punched fabric is bulky and drapes; thermal point-bonded fabric is flat and strong in the bonded points; spunlace is soft and cloth-like; chemically bonded fabric depends on the binder. Thermal bonding needs a thermoplastic component, so it cannot bond 100% cotton or other non-melting fibre.

5. Spun-bonding, melt-blowing and applications

In spunbonding, polymer chips are melted in an extruder and the melt is spun through a spinneret into many continuous filaments. The filaments are quenched with cool air, drawn (attenuated) by high-velocity air or an air-slot, and laid randomly on a moving belt to form a web that is then bonded, usually thermally by a calender. The filaments are continuous, of a diameter of several to a few tens of micrometres, and give a strong web with good tear resistance and low cost per square metre.

In melt-blowing, the molten polymer is extruded through a row of very fine die orifices into converging streams of hot, high-velocity air that stretch the melt into microfibres (often only a few micrometres) which are collected on a drum or belt, partly self-bonded by their own warmth. The web is fine-pored and soft but weak, so it is used for filtration and barrier layers, often in a spunbond–meltblown–spunbond (SMS) laminate in which the spunbond skins give strength and the meltblown core gives the barrier. Basis weight follows from the mass flow: g/m² = (polymer throughput per metre width in g/min) ÷ (line speed in m/min).

Worked example. A spunbond line extrudes 90 kg/h of polymer per metre of width and runs at 100 m/min. Throughput = 90,000 g/h ÷ 60 = 1500 g/min per metre width. Basis weight = 1500 ÷ 100 = 15 g/m².

  • Applications. Hygiene products (diaper and napkin cover stock, backsheets), medical and surgical drapes, gowns and masks, wipes and filtration media, geotextiles for road, drainage and erosion control, automotive carpets and headliners, roofing and house-wrap, agricultural covers, and apparel interlinings. Choose the route by the need: strong and cheap sheet (spunbond), barrier and fine filtration (meltblown), bulk and resilience (needle-punched), softness and absorbency (spunlace).

6. Braiding: principles, types and the maypole braider

Braiding intertwines three or more yarns diagonally to form a rope, a cord or a tubular or flat fabric. All yarns run at an angle to the braid axis, and the yarns are carried by bobbin carriers in two sets, half moving clockwise and half anticlockwise. In maypole braiding the carriers run on a track plate with intersecting serpentine paths cut by horn gears that pass carriers from one gear to the next, so the carriers weave in and out of each other like dancers round a maypole. A machine with N carriers makes N/2 yarns in each direction, and the braid is drawn off at a take-up speed that sets the braid angle.

  • Types of braid. A tubular (circular) braid is a hollow cylinder, a flat braid is a narrow tape, and a solid braid has a core. A biaxial braid has only the two diagonal sets, while a triaxial braid adds axial (longitudinal) yarns that do not move round, giving much more stiffness along the axis. The interlacing pattern may be diamond (each yarn over one and under one, 1/1), regular (over two and under two, 2/2) or Hercules (over three and under three, 3/3). Braids are used for ropes, hoses and cable sheaths, sutures, shoe laces and the preforms of fibre-reinforced composites.

Key takeaways

  • A course is a row and a wale a column of loops. The latch needle clears, feeds and knocks over. Knit makes a loop, tuck makes a wider, shorter fabric and float a narrower, less extensible one. Needles ≈ π d G, and output follows from rev/min × feeders × needles × stitch length × tex.
  • Plain curls and is unbalanced. 1×1 rib is elastic widthways and flat. Interlock is smooth, thick and stable. Purl has face and back loops in one wale and needs double-ended needles.
  • Warp knitting: one end per needle, all needles loop together. Swinging passes the guides through the needle gaps; shogging moves the bar sideways. Overlap is formed round the hook, underlap behind. Pillar has no underlap, tricot one space, atlas several, and inlay is trapped, not looped.
  • A nonwoven is made by fibre preparation, web formation (dry, wet or polymer-laid), bonding (mechanical, thermal, chemical) and finishing. Punch density = n ÷ (10 a) punches/cm²; basis weight of a polymer-laid web = throughput per metre ÷ line speed.
  • Spunbond gives strong continuous-filament webs. Meltblown gives weak microfibre webs with fine pores for filtration and barrier, and SMS combines the two. Thermal bonding needs a thermoplastic component.
  • A maypole braider with N carriers has N/2 yarns each way; the braid angle is set by the take-up speed. Biaxial braids have two diagonal sets, triaxial braids add axial yarns. Patterns are 1/1 diamond, 2/2 regular and 3/3 Hercules.

Practice questions (16)

Attempt each one before opening the answer. Every explanation names the tempting wrong option as well as the right one, because that is where marks are lost.

  1. Which statement correctly distinguishes warp knitting from weft knitting?

    1. In warp knitting one yarn runs across the fabric and forms an entire course by itself, as it does on a flat bed
    2. In warp knitting every needle has its own warp end and all needles form loops in the same machine cycle
    3. In weft knitting guide bars swing and shog to lap the yarns round the needles of the whole bed
    4. In weft knitting the loops of one course are all made from different yarns fed from separate beams
    Show answer

    Answer: B — In warp knitting every needle has its own warp end and all needles form loops in the same machine cycle

    A warp knitting machine feeds each needle from a beam end and loops all needles together, so the loops of a course come from different yarns. Weft knitting does the opposite: one yarn per feeder makes a course, and needles knit in turn. The guide-bar motions belong to warp knitting only.

  2. A plain (single-jersey) fabric and a 1×1 rib fabric are knitted from the same yarn at the same stitch length. Which comparison is correct?

    1. Plain fabric curls at its edges, whereas rib balances face and back wales, lies flat and recovers well widthways
    2. Rib fabric curls more than plain because it has two sets of needles pulling the loops in opposite directions at once
    3. Both are made on one needle bed, but rib uses a much finer yarn count to keep the same weight
    4. Plain fabric is the more extensible widthways because it has fewer loops in each course than rib
    Show answer

    Answer: A — Plain fabric curls at its edges, whereas rib balances face and back wales, lies flat and recovers well widthways

    In rib the wales alternate between face and back, which balances the loop-bending forces so the fabric lies flat, and the loops can spring back sideways. Plain has all loops on one side and curls. Rib needs two needle beds and the yarn is the same in this comparison, and the stated reasons for rib curling or for plain stretching are not true.

  3. On a weft-knitting machine, one needle in every few courses is set to tuck instead of knit. Compared with a plain fabric of the same needle count, what is the effect?

    1. The fabric becomes narrower and longer because the held loop pulls yarn from the sides
    2. The fabric becomes narrower and less extensible because the yarn floats behind the loops
    3. The fabric becomes wider and shorter, and the surface becomes textured
    4. The fabric is unchanged, because a tuck loop adds no yarn to the course
    Show answer

    Answer: C — The fabric becomes wider and shorter, and the surface becomes textured

    A tuck holds the old loop and adds a new one in the same hook, so the loops are distorted, the fabric spreads sideways and shortens, and a textured surface results. Floating the yarn behind is the float stitch, which narrows the fabric, and it is the tempting alternative. A tuck loop does take yarn from its neighbours.

  4. In warp knitting, which pair correctly describes the two guide-bar motions?

    1. Shogging carries the guides between the needles to the hook side and back, while swinging moves the bar sideways
    2. Swinging moves the bar sideways by a number of needle spaces, and shogging moves the needles up and down in their bed
    3. Swinging carries the guides between the needles to the hook side and back, and shogging moves the bar sideways
    4. Both motions are lateral, differing only in the number of needle spaces moved
    Show answer

    Answer: C — Swinging carries the guides between the needles to the hook side and back, and shogging moves the bar sideways

    Swinging passes the guides through the needle gaps to lap the yarn over the hooks, which forms the overlap, and shogging moves the whole bar laterally between laps, which forms the underlap. Giving shogging the through-the-gaps motion swaps the names, and saying shogging moves the needles up and down is wrong because the needles are moved by the needle bar, not by shogging.

  5. A guide bar on a warp-knitting machine overlaps the same needle in every cycle and is never shogged between overlaps. What does the resulting fabric look like?

    1. Separate vertical chains (pillar stitch) with no sideways linking, needing another bar or inlay to form a fabric
    2. A zig-zag tricot structure, because the guide still travels one needle space each course before it laps
    3. An atlas structure, whose long continued shogs lock the neighbouring wales together
    4. A weft-inlay fabric, because the bar lays its yarn straight across the whole fabric width
    Show answer

    Answer: A — Separate vertical chains (pillar stitch) with no sideways linking, needing another bar or inlay to form a fabric

    No shog means no underlap, which is the definition of a pillar (chain) stitch: each wale is an isolated chain of loops. Tricot needs a one-space underlap and atlas needs several spaces of continued shogging. An inlay bar lays yarn without looping it and does not describe a bar that overlaps every cycle.

  6. Compared with a spunbond web of the same polymer, a meltblown web is characterised by which of the following?

    1. Much coarser continuous filaments, higher tear strength and larger pores
    2. Much finer, short microfibres, a fine pore structure and low strength
    3. Fibres made by drawing cold filaments on rollers before laydown
    4. Fibres that always need a chemical binder because they cannot bond thermally
    Show answer

    Answer: B — Much finer, short microfibres, a fine pore structure and low strength

    In melt-blowing the hot, high-velocity air attenuates the melt into very fine, relatively short microfibres, giving fine pores for filtration and barrier but a weak web. Coarse strong continuous filaments describe spunbond. The microfibres are partly self-bonded by heat and do not always need binder.

  7. A needle-punching line is run at a fixed line speed with a given needle board. The stroke frequency is doubled and nothing else is changed. What happens to the punch density (punches per cm²)?

    1. It halves, because each stroke now has less time to penetrate the web
    2. It doubles, because the web advance per stroke is halved
    3. It is unchanged, because punch density depends only on the number of needles
    4. It quadruples, because the needle speed through the web also doubles
    Show answer

    Answer: B — It doubles, because the web advance per stroke is halved

    Punch density = n ÷ (10 a) with a the advance per stroke. At fixed line speed a = speed ÷ frequency, so doubling the frequency halves a and doubles the density. It depends on the advance per stroke as well as on the needles, so it is not independent of frequency, and there is no further factor of two from needle speed.

  8. A maypole braiding machine has 24 carriers. How many yarns travel in each rotational direction in a biaxial tubular braid made on it?

    1. 24 in each direction
    2. 6 in each direction
    3. 48 in each direction
    4. 12 in each direction
    Show answer

    Answer: D — 12 in each direction

    The carriers divide equally into a clockwise set and an anticlockwise set, so 24 carriers give 12 yarns in each direction. Counting all 24 in each direction double-counts the carriers.

  9. Which of the following statements about weft-knitted structures are correct?

    1. A tuck stitch holds the old loop while adding a new one in the same needle hook
    2. Interlock consists of two 1×1 ribs knitted into each other with opposing long and short needles
    3. Purl fabric is knitted with ordinary single-ended latch needles on one needle bed only
    4. In plain fabric the face and back wales alternate across each course
    Show answer

    Answer: A — A tuck stitch holds the old loop while adding a new one in the same needle hook; B — Interlock consists of two 1×1 ribs knitted into each other with opposing long and short needles

    A tuck loop sits in the hook with the old loop, and interlock is defined by its interlocked pair of ribs. Purl needs double-ended needles that slide between two beds so that one wale can carry face and back loops. In plain fabric all loops are pulled the same way, whereas alternating face and back wales is the rib structure.

  10. Which of the following are correct statements about bonding of nonwoven webs?

    1. Needle-punching bonds a web by carrying fibres through its thickness with barbed needles
    2. Hydroentanglement (spunlace) entangles fibres with fine high-pressure water jets
    3. Thermal bonding needs a thermoplastic fibre or binder component that softens and fuses at the contacts
    4. Calender point-bonding is a chemical bonding method that uses a latex binder
    Show answer

    Answer: A — Needle-punching bonds a web by carrying fibres through its thickness with barbed needles; B — Hydroentanglement (spunlace) entangles fibres with fine high-pressure water jets; C — Thermal bonding needs a thermoplastic fibre or binder component that softens and fuses at the contacts

    The needle-punching, hydroentanglement and thermal-bonding statements describe the mechanical and thermal routes correctly. Calender point-bonding is a thermal method, using heat and pressure on a heated, engraved roll, not a latex binder, which is the saturation or spray route of chemical bonding.

  11. Which of the following statements about braiding are correct?

    1. A maypole braider with N carriers puts N/2 yarns into each of the two helical directions
    2. A triaxial braid contains axial yarns in addition to the two diagonal sets
    3. For a given machine the braid angle is independent of the take-up speed
    4. A diamond braid has each yarn passing over two and under two yarns
    Show answer

    Answer: A — A maypole braider with N carriers puts N/2 yarns into each of the two helical directions; B — A triaxial braid contains axial yarns in addition to the two diagonal sets

    The carriers split evenly into two sets, and axial yarns are what make a braid triaxial. The braid angle is set by the ratio of carrier speed to take-up speed, so it does change with take-up. Over one and under one is the diamond (1/1) braid; over two and under two is the regular (2/2) braid.

  12. A circular weft-knitting machine has a cylinder of diameter 34 inches and a gauge of 28 needles per inch. Taking the number of needles as π d G, the needle count, to the nearest whole number, is ____.

    Numerical answer — type the value.

    Show answer

    Answer: 2991

    Needles = π × 34 × 28 = π × 952 = 2990.8, which is 2991 to the nearest whole number. Using the radius, or forgetting that gauge is per inch of circumference, would give half or a very different value.

  13. A single-jersey machine has 2000 needles and 72 feeders and runs at 30 rev/min. The stitch length is 2.8 mm, the yarn is 25 tex (mg per m) and the running efficiency is 90%. Each feeder knits one course per revolution. The output of fabric (equal to yarn consumed) in kg per hour, to two decimal places, is ____.

    Numerical answer — type the value.

    Show answer

    Answer: 16.33

    Courses per minute = 30 × 72 = 2160. Yarn per course = 2000 × 2.8 mm = 5.6 m. Yarn per minute = 2160 × 5.6 = 12,096 m = 12,096 × 25 mg = 302.4 g. Per hour = 302.4 × 60 = 18.144 kg. At 90% efficiency = 16.33 kg/h. Omitting the efficiency gives 18.14.

  14. A warp-knitting machine runs at 1200 cycles per minute and produces fabric with 12 courses per cm. The fabric is 2.4 m wide and the machine runs at 85% efficiency. One course is formed per cycle. The area of fabric produced, in m² per hour, to one decimal place, is ____.

    Numerical answer — type the value.

    Show answer

    Answer: 122.4

    Length per minute = 1200 ÷ 12 = 100 cm = 1.0 m. Per hour at full speed = 60 m. Area = 60 × 2.4 = 144 m². At 85% efficiency = 144 × 0.85 = 122.4 m²/h. Forgetting the efficiency gives 144.

  15. A needle loom has 3000 needles per metre of board width and runs at 800 strokes per minute. The web is fed at 4.8 m/min. Using punches per cm² = n ÷ (10 a), where n is needles per metre of width and a is the web advance per stroke in mm, the punch density in punches per cm² is ____.

    Numerical answer — type the value.

    Show answer

    Answer: 50

    Advance per stroke a = 4.8 m/min = 4800 mm/min ÷ 800 strokes/min = 6.0 mm. Punch density = 3000 ÷ (10 × 6.0) = 50 punches per cm². Using 4.8 as a in mm directly, instead of dividing by the stroke rate, gives 62.5.

  16. A spunbond line 3.2 m wide extrudes 288 kg of polymer per hour in total and runs at 200 m/min. Assuming all the polymer ends up in the web, the basis weight of the web, in g/m² to one decimal place, is ____.

    Numerical answer — type the value.

    Show answer

    Answer: 7.5

    Polymer per minute = 288,000 g ÷ 60 = 4800 g/min. Web area made per minute = 3.2 m × 200 m/min = 640 m²/min. Basis weight = 4800 ÷ 640 = 7.5 g/m². Dividing 4800 g/min by the line speed alone gives 24, which ignores the 3.2 m width.