Fig. 61

Stitches of Variable Symmetry.—These defects are illustrated in various forms in Fig. 61, which gives a diagrammatic view of the chief variations which are met with in single stitch formation in the knitted texture. During knitting the yarn usually forms itself into curved loops, but various conditions have to be met if this curving has to be perfect. Should the knitting yarn be lacking in yielding property curves will not eventuate, but will be replaced by various distorted formations. Very often the mechanical structure of the yarn makes it impossible for the thread to fall out in nicely-shaped curves, this taking place when the constituent fibres are tightly arranged in the yarn or when they are composed of long fibres drawn with meticulous precision in parallel order side by side. A much more suitable thread is worked from shorter materials which gives a freer scope of direction. This renders the thread less rigid and makes it more amenable to loop formation, whilst the beneficial effects of lubrication or damping of dry yarn have already been referred to. Several typical examples of these deficiencies are illustrated in Fig. 61 by means of the stitches marked 1 to 4. Stitches 1 and 2 show a mal-formation of loop due to a straightening of the yarn, the fibres are too long and do not yield in loop formation. With hard yarns which are thick for the gauge of the frame, these straightened loops may occur six or eight together and have the effect of tightening the fabric at that point, at other times they take up a direction leaning to the right or the left which greatly impoverishes the goods. The more usual type of mal-formation is given in loops 3 and 4 where the stitch, unable to content itself with the length of yarn allotted to it, takes up an enlarged area. These are termed "pinholes," and when scattered all over a fabric seriously undermine its value.

Manufacturers are often baffled by a plain fabric issuing from the frame of the rotary type using bearded needles which shows an effect like 2 and 1 rib, that is, there is a minute opening after every second stitch which, by its general appearance, resembles 2 and 1 rib, the space giving the impression of the open part formed by the vertical row of loops which go to the back of the texture. Wherever this is detected attention should be given to the dividing of the loops in the machine. In stitch formation for an average bearded needle machine the loops are first sunk over alternate needles, and thereafter equalized or divided over all the needles. When the equalization is not accurately performed, as is the case when the divider sinkers are not pushed sufficiently between the needle or are pushed too far, then the ribbed effect will be produced. Another common defect occurs at the selvedge consisting of a variable tension of the end loops, some being large and others constricted. This may be due to the yarn having too much play at the edge, so that the end two sinkers are permitted to draw more than their quota of yarn for stitch formation, which makes the edge raw and unsightly and gives trouble in seaming when the quality of the seam is variable owing to the different size of loop. The remedy for this imperfection lies in an adjustment of the snappers which exercise a drag on the thread just when the end sinkers show a tendency to take more than their share of yarn.

INDEX

Printed by Sir Isaac Pitman & Sons, Ltd., Bath, England

TRANSCRIBER'S NOTES

  1. Silently corrected simple spelling, grammar, and typographical errors.
  2. Retained anachronistic and non-standard spellings as printed.