Fabric defect · Yarn - Thick and thin places in yarn and fabric

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 thick or thin place in one yarn is a streak, and a heavy or light band from the loom is a line across the width.

A U.S. federal glossary of fabric imperfections starts with two groups: thick places, "imperfections which cause places in the cloth to be thicker than normal," and thin places, which "cause places in the cloth to be thinner than normal" ¹. A coarse pick is "a yarn larger in diameter than normally being used in the cloth," and a fine pick is "a yarn smaller in diameter than normally being used in the cloth" ¹. The military glossary of knitting imperfections defines a thick place as "an area of fabric that is thicker than normal" and a thin place as "an area of fabric that is thinner than normal" ².

Goldberg's 1950 casebook puts thick places and thin places in one family of yarn faults with slubs, neps, uneven twist and fuzziness, under the word unevenness ³. A slub is the short, abrupt kind of thick place, "an abruptly thickened place in the yarn" ¹; this page covers the rest.

Thin places can show as open, weak areas. In one of Goldberg's cases, thin filling yarns were "frequently ruptured" in napping, with "open-appearing and tender areas" as the result, and the book's photograph of the thin spots was taken with light shining through the fabric ³. In another, streaks came from thick and thin places in filling yarn that varied "from as fine as 51/1 to as heavy as 37/1 within 1 yard" ³. Thickness can change the shade too: of thick-and-thin filament yarn, Goldberg notes the "tendency of the coarser filaments in the thick portions to dye much darker than the finer filaments in the thin sections" ³.

In woven cloth a coarse or fine pick is a filling yarn, so it crosses the width, and a coarse or fine end is a warp yarn, so it runs along the roll ¹. Heavy and light places made at the loom are bands "either across the full width of the cloth or a portion of it" ¹. The same glossary also gives thin place as another name for a light place, and for a crack, an open streak along the filling ¹. In filament filling, a denier variation of as little as 5 percent may show up as a filling band in some constructions ³.

Some repeat. The thick and thin places of periodic denier "will occur at regular intervals or periods," which gives the filling "a wavy or chattery appearance in a somewhat regular pattern" ³. Others are spread through the goods: thin, weak spots "scattered through several pieces," or thin places from wrapped filaments "at frequent intervals throughout the piece" ³.

Thick and thin places are scored by their 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 ⁶. A heavy or light band across the full width is longer than 9 inches, so it scores 4 points. A coarse end that continues along the roll is 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 ⁷.

For military contract cloth, U.S. specifications score coarse yarn only when it is clearly coarse: "only coarse yarns that exceed twice the normal diameter shall be scored" ^{8, 9}. For knits, a 2019 military standard scores "coarse or fine yarns resulting in noticeable difference in appearance stiffness and thickness" at 4 points for each yard in which they occur ⁹.

A 2013 study tested thin places in ring spun yarns, places with 30, 40 and 50 percent less mass than the mean mass of the yarn. As the mass fell, the local twist rose, and the breaking load and breaking extension fell ¹⁰.

A thin place has fewer fibers and more twist, which should bind them tighter, yet yarn generally breaks at a thin place: in the study, about 80 percent of the breaks came at a thin region ¹⁰. The authors argue that thin places should be kept to a minimum, for lower cost and smoother processing after spinning ¹⁰.