The production of high quality fabric is gaining importance because of increasing consumer consciousness and tough competition in the global market. On circular weft knitting machines yarn feeding devices play a major role in controlling the size and the regularity of the stitches formed. In fact the yarn- feeding device has become one of the most important elements of a modern multi-feeder circular knitting machine as it draws yarn from the package and delivers it to the needle to form stitches during a defined interval. Currently in Circular weft knitting machines, positive feeding is generally used and the stitch length is altered by manually adjusting the diameter of the quality pulley, sometimes termed as QAP (Quality Adjusting Pulley) or VDQ (Variable Diameter Quality) pulley or Quality wheel. QAP is adjusted to match the drive belt speed to the required yarn delivery rate. Even if the QAP diameter is adjusted to the correct speed, stitch length on the fabric may be quite different.
As the knitter has to work with quick production process of present days he should have the knowledge to adjust the VDQ pulley to get the required stitch length value in a short time. In this project work such an attempt has been taken to establish a relation between the QAP diameter and stitch length of the fabric produced on the large diameter single jersey circular weft knitting machine of AUST laboratory.
To discover the maximum and minimum limits for QAP diameter settings in the circular weft knitting machine of AUST laboratory.
To find out the range for stitch length that can be achieved practically on the produced fabric in the mentioned machine.
To calculate the amount of deviation between calculated and actual course length during different stages of knitting.
To establish a relation between VDQ pulley diameter and fabric stitch length for common prediction purpose.
To build up a knowledge base for applying the outcome of this work in the professional life.
1.3. Literature Review:
Some of the relevant research works are mentioned below :
Dias and Lanarolle (2002) made an analysis of the tension build-up of the yarn on its way from the package to the storage yarn feed wheel. They also did some experimental works related with yarn tension. They observed that the yarn tension at immediately before the positive storage feed wheel very linearly with the yarn unwinding tension from the package for a given yarn. They also found that course length in the fabric becomes shorter when the yarn is wound onto the storage yarn feed wheel at higher winding tension despite delivered positively at the same rate and the same input tension to the needles at same cam setting.
Mohammed showed that yarn unwinding tension from a conical package is almost inversely proportional to the yarn count(Ne).With the help of experimental works he also showed the unwinding tension is almost proportional to yarn speed(m/min).
2. THEORETICAL BACKGROUND:
2.1. Principles of yarn feeding:
For continuous knitting, yarn is to be supplied or fed to the needles or to the knitting zone continuously. In weft knitting, yarn is generally supplied or fed from cones or other suitable yarn packages positioned in a creel. The principles involved in supplying or feeding of yarn may be summarized as follows:
2.1.1. Negative feeding – Yarn is pulled by the needles directly from the package through guides, tensioner etc. This is a very simple technique of yarn feeding. It does not require any extra attachment as yarn is drawn automatically due to the knitting process. This technique does not maintain uniform yarn tension. But it can easily adjust and take care of difference in stitch cam setting in different feeds.
2.1.2. Positive feeding – In case of positive feeding, yarn is first...
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