Knitting Technology: Warp Knit Structures

Knitting Technology: Warp Knit Structures

• Warp knitting involves loops ('laps') formed as warp yarns wrap around needles.
• Loops can be open or closed, depending on overlaps.
• A warp knitted structure is composed of two parts: the stitch (formed by wrapping yarn around a needle and pulling it through the previous loop) represented as an 'overlap'; and the yarn linking the stitches, called the 'underlap'.
• Underlap length is measured in needle spaces.
• A longer underlap results in greater lateral fabric stability and fabric weight. Conversely, a shorter underlap leads to reduced width-wise stability/strength, but increases length-wise stability.
• Yarn consumption during 480 knitted courses is called 'run-in'. A 'rack' is a cycle of 480 knitted courses. Run-in represents yarn consumption for one rack.
• For a given machine and warp: longer run-in produces larger, looser stitches; shorter run-in produces smaller, tighter stitches; the run-in ratio is the ratio of yarn from each warp thread if multiple guide bars are used.
• Stitches can be open or closed, distinguished by the direction of underlap and overlap motions.
  • Opposite directions create closed stitches.
  • Same direction creates open stitches.
• Closed laps are heavier, more compact, less extensible, and more opaque than open laps constructed from the same yarn and under similar knitting conditions.

Basic Warp Knit Structure Variations

• Five basic lapping variations compose all guide bar movements.

  • Overlap followed by an underlap is a closed lap.
  • Overlap followed by an underlap in the same direction is an open lap.
  • Only overlaps and no underlaps are open-only laps.
  • Only underlaps and no overlaps are laying-in laps.
  • Neither overlaps nor underlaps are miss-lapping.

• A pillar stitch (chain stitch) involves lapping yarn guides over the same needle.

  • These stitches lack lateral connections between wales.
  • The stitches are interconnected only in the direction of the wales.

• A fabric is not created with a pillar lap; only chains of disconnected wales occur.

• The 1&1 lap (Tricot lap) involves alternating overlap and underlap motions on two defined needles.

  • Underlaps connect courses and wales.
  • Simplest structures are formed between adjacent needles.

• Atlas lap differs in that laps continue over two or more courses in one direction, then return in the opposite direction to the starting point.

Single- or Double-needle Overlaps

• Overlap movements are typically across one needle space to avert strain on warp thread and needles from simultaneous knock-off actions.
• Varying tensions on loops negatively influence their appearance.
• Underlap between double overlaps has the appearance of a sinker loop.

Single Bar Structures

• Plain warp knitted structures are produced on a single needle bar.
• Resulting structures are called single-face fabrics.
• Rib and interlock knit structures are made on double needle bars, creating double-face fabrics.
• In single-face structures, stitches are visible on one side (technical face); the other side (technical back) only displays underlaps.

Other Key Concepts

• Underlaps alone cannot form a fabric. They are often combined with other movements.