The effect of stitch length on abrasion resistance of grey knitted fabric

Md.Azmeri Latif BegMSc.Engr (Textile)

INTRODUCTION

Knitting is a method by which thread or yarn is turned into cloth or other fine crafts. Knitted fabric consists of consecutive rows of loops, called stitches. As each row  progresses, a new loop is pulled through an existing loop. The active stitches are held on a needle until another loop can be passed through them. This process eventually results in a final product, often a garment. The art of knitting has been rapidly progressing in the world. In our country knit sector already holds the highest position if compared with weaving or other small sectors related to textile. Knit RMG is the highest foreign currency earning sector of Bangladesh. The industry is also growing very fast due to strong backward linkage, less capital investment requirement and higher profitable. Abrasion is just one aspect of wear and is the rubbing away of the component fibers and yarns of the fabric.

Knitted loop is a knit of yarn that is intermeshed at its base i.e. when intermeshed two kink of yarn is called a knitted loop. A knitted loop is a basic part of knitted fabric. Technically a knitted loop consists of a needle loop & a sinker loop. The length of yarn knitted into one stitch in a weft knitted fabric. Stitch length is theoretically a single length of yarn which includes one needle loop & half the length if yarn (half a sinker loop) between that needle loop & the adjacent needle loops on either side of it. Generally larger the stitch length more elastic & lighter the fabric also it’s poorer its cover opacity & bursting strength. Generally stitch length is expressed in mm (millimeter). In the fabrics, loop lengths combine in the form of course lengths & it is there that influences fabric dimensions & other properties like weight, density, shrinkage, spirality etc. Variations in course length between one garment & another can produce horizontal bareness & impair the appearance of the fabric. In the modern knitting machine, it needs to maintain a constant loop length at one feed & another on same machine is mandatory for continuing the constant loop length. Although a machine may be set to knit a specific stitch length, fluctuations in yarn or machine variable can affect yarn surface friction or yarn tension at the knitting point. As a result, the ratio of ‘robbed back’ to newly-drown yarn changes & alters the size of the knitted loop.

So abrasion resistance is the resistance against the wear to rubbing.Now-a-days abrasion resistance is an important quality parameter of knit fabric.  The measurement of the resistance to abrasion of textile and other materials is very complex. The abrasion resistance best measure the serviceability of any fabric or garment during end use. Though pilling test is preferred for knit fabric, abrasion resistance is also important for knit fabric which is made from combed or compact yarn.

ORGANIZATION OF THE RESEARCH: Testing lab- The experiments were executed at the Fabric

Manufacturing Lab of DIU with the Hand Driven Hosiery Knitting Machine & HATRA Course Length Tester as well as the Textile Testing and Quality Control Lab of DIU with the Martindale Abrasion and Pilling Tester – M235 and also with the help of BENGAL NFK for providing the required yarn packages.

 Test method- In this research work it was used the ASTM D 4966 -- 98 Standard Test Method for Abrasion Resistance of Textile Fabrics (Martindale Abrasion Tester Method) with the help of DIU lab facilities.

The M235- Martindale Abrasion and Pilling Tester is also known as M235 Abrasion and pilling Tester. Samples are rubbed against abradant at a certain pressure and the amount of weight loss is determined or rubbed samples are compared against standard swatch for calculating abrasion resistance.

METHODOLOGY: At first the yarns of three different counts (24 Ne, 32 Ne and

34 Ne) of same lot number were collected from the BENGAL NFK spinning mill, Dewhata, Tangail. Because of the same lot number it can be said that the raw materials have constant effect on bursting as changing the count of yarn. The each yarn was fed into the hosiery machine and cam was set to three position- bottom, mid and upper. Take down tension was similar for each case. After production courses were unrobed from the fabric and were set to HATRA course length tester with mentioned tension thus determined stitch length.

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Total needle was 132. Then fabrics were cut with the cutter of the machine; weight was taken and set to M235. After applying proper load machine was run for 100 cycles because of more loop length. After completing required cycles specimen were observed for any hole or breakage and in all cases that was discovered. Again weight of rubbed fabric was taken and weight loss ratio was calculated which refers the abrasion resistance. More weight loss ratio indicates less abrasion resistance.  

Properties of yarns used in the research.  Specimen and abradant

Stitch length determination:

When cam is in the bottom position for 24Ne when cam is in the mid position for 24 Ne

When cam is in the upper position for 24 Ne When cam is in the bottom position for 32 Ne

When cam is in the mid position for 32Ne When cam is in the upper position for 32 Ne

When cam is in the bottom position for 34 Ne When cam is in the mid position for 34 Ne

When cam is in the upper position for 34 Ne

Graph 1

Obs no.Weight (a)

(before abrasion)Weight (b)

(after abrasion)

Weight loss% Average weight loss%

1 0.1139 0.1117 1.93%  

1.572 0.0733 0.0722 1.50%3 0.0853 0.0841 1.41%4 0.0895 0.0882 1.45%

When cam is in the mid position for 24 Ne1 0.1250 0.1230 1.60%  

1.762 0.1123 0.1104 1.69%3 0.1190 0.1168 1.85%4 0.1173 0.1151 1.88%

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Results of the abrasion test:When cam is in the bottom position for 24 Ne

When cam is in the bottom position for 32 Ne

0.0834 0.0821 1.56%  

1.660.0964 0.0945 1.97%

0.0945 0.0933 1.26%

0.0912 0.0895 1.86%

When cam is in the mid position for 32 Ne

0.0712 0.0693 2.66%  

2.650.0770 0.0750 2.59%

0.0766 0.0743 3.00%

0.0854 0.0834 2.34%

When cam is in the upper position for 32 Ne

0.0544 0.0520 4.41%  

4.600.0483 0.0459 4.96%

0.0448 0.0427 4.69%

0.0507 0.0485 4.33%

When cam is in the bottom position for 34 Ne

0.0820 0.080 2.40%  

2.190.0828 0.0810 2.17%

0.0862 0.0844 2.08%

0.0940 0.0920 2.12%

When cam is in the mid position for 34 Ne

0.0728 0.0701 3.70%  

3.710.0756 0.0726 3.96%

0.0801 0.0772 3.62%

0.0783 0.0755 3.57%

When cam is in the upper position for 34 Ne

0.0526 0.050 4.94%  

4.760.0493 0.0469 4.87%

0.0524 0.0501 4.38%

Change in Abrasion Resistance The abrasive wear of a material depends on the construction of the yarn & the structure of the fabric. It was established that abrasion was less for higher density fabrics. This was because of the fact, when the density was more, more loops contributed to the wear & so its abrasion resistance increased.

Discussion:

From figure 5 it is seen that, Single jersey fabric showed higher abrasion loss% due to its soft nature on the surface. Graph 1 shows that abrasion resistance decreases slightly as stitch length increases but after few interval it decreases rapidly for 24 Ne. According to graph no. 2 and 3 abrasion resistance also decreases as stitch length increases but these are not also linear and show opposite curves. The bubble graph (graph4) indicates the variable fluctuation of abrasion at different cam position.

Following the linear regression obtained regression equation for the fabric made from 24 Ne yarn is y=0.475256x - 1.06543 and coefficient of determination R2= 0.989127.Regression equation for the fabric made from 32 Ne yarn is y= 0.270613x + 0.527763 and R2= 0.661096Regression equation for the fabric made from 32 Ne yarn is y= 0.552834x -0.39372 and R2= 0.795248

Conclusion:

Though hand driven small diameter hosiery machines (socks machines) are not in use in export oriented factory in Bangladesh but in cottage industries and in local factories these machines are used. So this research is helpful for that concerning people because in most cases they have no abrasion testing machine. Abrasion resistance can be predicted by using different regression equation for different type of yarns.

MSC. TTQC AZMIR PRESENTATION