Problems and Limitations of Circular Knitted Structures

Introduction:
Circular knitting machines have been designed and manufactured for mass production of knitted fabrics. The special properties of knitted fabrics, especially fine fabrics made by the circular knitting process, makes these types of fabric suitable for application in clothing, industrial textiles, medical and orthopaedic garments, automotive textiles, hosiery, agro and geotextiles, etc. Among them huge positive this knitting machine also has some problems and limitations. These are given below.
High-speed circular knitting machines
Problems and Limitations of Circular Knitted Structures
  1. Problems in high-speed circular knitting machines
  2. Limitation of pattern in jacquard circular machines
  3. Production limits of seamless knitting machines
Problems in high-speed circular knitting machines
The most important problems in high-speed knitting machines are classified as the limitation of friction occurrence in knitting elements and tension control in the yarn feeding system.

Some research has been done about the influence of different parameters and factors among yarn, needles and knitting elements during the knitting operations. Important factors in the contact between yarn and knitting elements during the knitting process are friction, flexural rigidity, the mechanical properties of the yarn and the velocity of knitting elements and yarn in the knitting zone.

The tension on the yarn during knitting is influenced by the number and the angles of yarn wrap between yarn and machine elements, and the fact that robbing back can reduce tension in the yarn.

An increase of input tension makes the position of maximum knitting tension move towards the yarn supply side, and with lower input tension the point of maximum knitting tension lies closer to the knitting point. These factors and the fact that many parameters cooperate and influence each other between yarn and machine elements make knitting a rather complex process. When it comes to producing knitted structures of yarns or monofilament fibres with high stiffness such as carbon, aramid or polyester mono-filament, parameters such as friction and the flexural rigidity of the yarn are of considerable importance for the knit-ability of the structure.

However, a significant problem is that some of these stiff yarns are almost inextensible, which causes tension peaks with breakage of the yarn or single filament in the yarn bundle, especially in high speed knitting operations.

Limitation of pattern in jacquard circular machines
The creation of patterns in jacquard machines is limited to a number of knit elements: the yarn feeder system, the needle selection system and the dial needle bar gauge. Mini-jack circular knitting machines are suited to the production of jacquard fabrics. Some models are equipped with selection systems that have 39 levels, 37 of which are for jacquard selection and two for set selections, but more selection elements are limited by the diameter of the dial.

Production limits of seamless knitting machines
The most important limitation of seamless knitting machines in circular form is the poor flexibility of these types of machine for producing fabrics in different diameters. In the commonly used method of apparel making in flat fabrics the cutting operation is important. In seamless technology the fabric cannot be cut, and therefore the various diameters should be prepared in the knitting process. This applies to different types of seamless machine of varying cylinder diameters.

The short, thin fabrics are knitted in small diameter cylinders and therefore the production rate is lower. This leads to increasing costs and may be a serious problem for seamless, circular knitting technology.

Seamless fabric is knitted in simple structures and there is no advanced jacquard machine to prepare a mixed pattern fabric for this purpose. Seamless circular knitting machines have lately been manufactured to apply a fine gauge as well. These machines are suitable if the benefit of selling price of fabric is justified by the cost of production at a limited rate of production.

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