Unit 3: Warp knitted fabrics
Introduction to Knitting notes · PTU syllabus (BSTD 402-20)
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Unit summary
Warp knitting produces stable fabrics at very high speeds for lingerie, sportswear and technical uses. This unit covers categories of warp knits, loop structure and identification, tricot and Raschel fabrics, the tricot machine, yarn and fabric characteristics, and distinguishing Raschel from tricot.
After this unit you can
- Explain warp knit loop structure
- Classify tricot and Raschel fabrics
- Describe the tricot machine
- Distinguish tricot from Raschel
PTU syllabus topics
- Categories of warp knit
- loop structure and identification of warp knits
- classification into tricot and Raschel fabric
- tricot knitting machine
- yarn and fabric characteristics
- distinguishing Raschel from tricot
Needles
Bearded or compound
Latch or compound
Fabric
Fine, smooth, light
Coarser, open, lacy
Uses
Lingerie, linings
Lace, nets, curtains, power nets
Topic 1
Categories and loop structure of warp knits
- Each warp yarn is fed to its own needle and moved sideways by guide bars so it forms loops on different needles in successive courses, linking the wales together.
- Overlap
- Guide movement across the hook — forms the loop
- Underlap
- Sideways movement on the back — connects wales
- Open and closed laps
- Whether the yarn crosses itself
- Lapping diagram
- Chain notation on point paper
- Guide bars
- One to many bars; more bars = more patterns
Pillar (chain)
Yarn stays on one needle
Forms columns; used with other stitches
Tricot (1×1)
Moves one needle sideways each course
Simple tricot
Two-needle and three-needle laps
Longer underlaps
Locknit, satin, sharkskin
- Identification: warp knits show a zigzag or vertical rib on the face and horizontal underlaps on the back; they do not unravel easily and show little stretch.
Topic 2
Tricot and Raschel fabrics
Needles
Bearded or compound; one bed
Latch needles; one or two beds
Guide bars
Usually 2–4
Many (up to 70+)
Yarn
Fine filament yarns
Fine to coarse, spun and fancy yarns
Fabric
Fine, smooth, stable — face with vertical wales, back with crosswise ribs
Open, lacy or heavy, 3-D structures
Uses
Lingerie, linings, sportswear, swimwear
Lace, nets, curtains, power-net, blankets, technical spacer fabrics
- Locknit (charmeuse)
- Smooth, popular for lingerie
- Sharkskin
- Firm, crisp
- Queenscord
- Very stable
- Brushed tricot
- Napped surface — loungewear
Topic 3
The tricot knitting machine
- 1Warp beams supply many parallel ends
- 2Guide bars lap yarns over and under compound needles
- 3Sinkers hold loops; presser or closing wires close needles
- 4Fabric take-up winds the cloth
- 5Speeds over 2,000 courses per minute on modern machines
Topic 4
Yarn and fabric characteristics
- Yarns: continuous filament nylon, polyester, spandex for tricot; cotton, acrylic and fancy yarns for Raschel. Fabric characteristics: dimensional stability, run resistance, high production, little width stretch (except with elastane), cut edges do not ravel.
Key terms
- Guide bar
- Bar that laps warp yarns around needles
- Overlap
- Lapping movement across the needle hook
- Underlap
- Sideways movement forming connections between wales
- Tricot
- Fine warp knit made with bearded or compound needles
- Raschel
- Warp knit made on latch-needle machines
Quick revision
- Each end to its own needle; guide bars; overlap and underlap.
- Pillar, tricot, two- and three-needle laps; identification.
- Tricot vs Raschel; locknit, sharkskin, queenscord.
- Tricot machine; yarns; properties.
Important exam questions
Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).
Short-answer questions
- Q1.How does warp knitting differ from weft knitting?
- Q2.What is an underlap?
- Q3.Name two tricot fabrics.
- Q4.Which needles do Raschel machines use?
- Q5.Give two uses of Raschel fabrics.
- Q6.Why don't warp knits ladder easily?
Long-answer questions
- Q1.Explain the loop structure of warp-knitted fabrics.
- Q2.Compare tricot and Raschel fabrics.
- Q3.Describe the tricot knitting machine and fabric characteristics.
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