Fabric defect · Knit fabric - Dropped stitches in knit fabric: causes and how they count

ConductVision Textile is designed to flag each defect with its place on the roll, its size, its points and a still image. Your inspector names the defect and confirms or dismisses it.

On the defect map in the roll report, a dropped stitch is a spot, and dropped stitches down one wale are a line along the roll.

Cotton Incorporated's textile glossary describes the moment a drop stitch happens: "When a knitting needle clears the old stitch and does not receive a yarn to form a new stitch, a drop stitch is made" ¹. Its fabric defect glossary traces its dropped stitch examples to "a malfunctioning needle or jack" ².

A U.S. military glossary of knitting imperfections defines a drop stitch as "an unknitted stitch," and a split stitch as one where "one end of yarn of a stitch is knit and the other end dropped" ³. Where the yarn is not knitted by several needles side by side, the drop stitches lie together in a patch, which a university module on knit defects calls cloth fall-out ⁴.

Dropped stitches recur "in one or more wales within a length of a knitted fabric" ³, and a wale is the "vertical column of loops produced by the same needle knitting at successive knitting cycles" ¹. Cotton Incorporated lists its dropped stitch examples as warp lines, or vertical lines ². So one dropped stitch is a spot, and dropped stitches that repeat run along the roll, not across it.

Cotton Incorporated's defect glossary rates its dropped stitch examples as major defects ². Its grading guide defines a major defect as one severe enough, if exposed, to make the end item a second ⁶.

A dropped stitch that leaves an opening falls under the rule for holes and openings: in the 4-point table one trade guide sets out, 1 inch or less scores 2 points and over 1 inch scores 4 ⁷. A missing stitch with no opening is scored by its length: 1 point up to 3 inches, 2 points over 3 up to 6 inches, 3 points over 6 up to 9 inches and 4 points over 9 inches ⁷.

Dropped stitches that continue along the roll are a running defect. One buyer manual, which follows the 4-point system of ASTM D5430, gives up to 4 points to each linear yard or metre in which a continuous running defect exceeds 9 inches, and no linear yard gets more than 4 points ⁸.

A 2020 trial knitted single jersey from 30 Ne cotton yarn on one 24-gauge circular knitting machine and changed the yarn input tension three ways: through the yarn delivery rate, and through the stitch cam setting, changed at all the cams together or at one cam. Each way, higher tension brought drop stitches. Of the four defects the trial found (drop stitches, holes, runs and press-offs), drop stitches and holes were "the prominent ones" ⁹.

On that yarn and machine, when the cams were changed together, drop stitches became significantly more frequent once yarn tension passed about 10 cN (centinewtons), measured just before the yarn entered the knitting zone. When the delivery rate was changed instead, the number of defects rose significantly once tension passed 8 cN ⁹.