Circular weft knitting tubular structures

Both weft and warp knitting machines are able to construct tubular structures. Although circular weft knitting machines can only be used in producing single tubes, flat weft knitting machines with two needle beds and double-needle bar Raschel machines are able to produce single, bifurcated and multibranched tubes. 

The key feature of circular weft knitting is to produce fabric structures in a tubular form. Figure 6.5 shows a tubular weft-knitted fabric developed for vascular stent application on a circular weft knitting machine with a small-diameter cylinder. The diameter and stitch density of a tube can be adjusted by varying the cylinder diameter and machine gauge, respectively. 

Compared to circular weft knitting, flat weft knitting is more flexible in producing tubular structures due to the capabilities of individual needle selection, loop transfer and multiple system knitting and the use of stitch presser and holding down sinkers... 

As the name implies, yarns run horizontally across the width of the fabric. The knitting needles form the loops in horizontal courses, with one loop built on top of the other, and are generally made from a single yarn. Weft knits can be made flat on a flat bed machine, or tubular on a circular knitting machine. Weft knits are basic loop structures and can be stretched in both directions (Figure 21.16). 

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