Study on strength and breaking elongation for yarns and knitted fabrics used to make socks.

Vlad, Dorin ; Floca, Alina Mihaela ; Dinu, Milena 等

1. INTRODUCTION

Strength and elongation at break values are influenced both by the test samples on the device, such as specimen length, speed and rate of extension, and environmental conditions: temperature, humidity, air flow speed.(Budulan, 2009).

If the thread tension is too high during processing, the thread may break and if too small, in this case can be defective products--spool too soft (at winding), irregular knitted eye (at knitting).

It is important to know the physical-mechanical properties of the yarns, because they depend heavily on properties of knitted fabrics, both in terms of processing and their exploitation.

2. EXPERIMENTAL

This study used cotton yarns with different yarn counts and knitwear obtained from these yarns--socks--with different structures (table 2).

Focused characteristics are tensile strength and extension at break. These characteristics have been measured throughtesting method according to specific standard (Vladet all, 2009). The conditioned samples are employed before the preparation stage technology.

Tensile strength and extension at break of the yarns and knitwear were determined using a dynamometer type Titan2--Universal Strength Tester, based on two standards:

--For yarns: EN ISO 2062--Yarns from packages. Determination of single-end breaking force and elongation at break. Jaw separation: 250 mm, pretension: 0.500cN/tex, break detection: 50.00%, specimens 20, rate of extension: 250mm/min.(Technical book of [Titan.sup.2]).

--Forknitted fabrics: SR EN ISO 13934-1:2002--Textiles Tensile properties of fabrics--Determination of maximum force and elongation at maximum force using the strip method. Jaw separation: 100 mm, pretension: 100gf, break detection: 50.00%, specimens 20, specimen dimensions: 50mm x 300mm. Titan's software has been pre-programmed with British (BS), European (EN), International (ISO), American (ASTM) and Retailers' Standards (e.g. Next, M&S), the instrument's software is easy to follow and makes testing both quick and easy.(Technical book of [Titan.sup.2]).

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[FIGURE 2 OMITTED]

Based on table 1 we graphically represented the breaking load (figure 1) and elongation at break (figure 2) for cotton yarns. Figure 1 is observed that the higher number is yarn count, the breaking load is less. Also, elongations at break values are inversely proportional to the yarn counts.

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3. RESULTS AND DISCUSSION

Also from Table 1, we conclude that, if twisted, breaking load is twice the breaking load of yarn. Yarn elongation is lower than that of twisted yarn.

After the dyeing process, the tensile strength of cotton yarn decreased. This is explained because the painting is done at high temperatures, which weaken the intermolecular forces.

Whatever yarn count and finishing, tensile strength is higher by 5.5% in case of double jersey and lynx compared with single jersey structure.

For the same yarn count, tensile strength for the finished knits is 10% lower than the unfinished knits.

Whatever yarn count and finishing, elongation at break is higher by 5% in case of double jersey and lynx compared with single jersey structure.

For the same yarn count, elongation at break for finished knits is 10.8% lower than the unfinished knits.

4. CONCLUSIONS

Comparing results from tables 1 and 2 shows that the properties of yarns are reflected in the properties of knitted fabrics used to make socks. For knitted fabrics made from thinner yarns, the breaking load and elongation were lower than thicker yarns.

During finishing, yarns and knits so reduces its strength and elongation at break. This can be improved by treatment with substances to increase their tensile strength--for example mercerization of cotton yarn.

Using thin yarns for knitting are obtained socks with low tensile strength, which means a shorter wearing time. It is recommended to use plain plating knits--for example cotton + polyamide.

5. REFERENCES

Budulan R. (2009), Basics of knitting, Publisher University "Lucian Blaga", Sibiu, Roumanie

VladD., Floca A., Budulan C. (2009), Methods for testing the seams for making knitted fabrics, The Second International Proficiency Testing Conference, pp 311-321, Sibiu, Romania (15)16th--18th September, 2009, http://www.pt-conf.ro/0809/conference- proceeding.php, (10.09.2010)

EN ISO 2062--Yarns from packages. Determination of single end breaking force and elongation at break.

SR EN ISO 13934-1:2002--Textiles--Tensile properties of fabrics--Determination of maximum force and elongation at maximum force using the strip method

Technical book of [Titan.sup.2]--Universal Strength Tester, Model 710

Tab. 1. Results of tests for cotton yarns

 Yarn Mean Mean
Type of count Force Elongation
Yarn [Nm] [gf] [%]

single 20 425 4.73
 27 320 4.66
 40 268 4.56
 54 240 4.54
 70 186 4.40
 100 93 4.16
 140 84 3.72
 170 68 3.54
twisted 40/2 435 4.22
 70/2 280 4.20
 100/2 206 4.06
 140/2 179 3.94
 170/2 151 4.00
dyeing 40/2 318 4.21
 70/2 266 4.14
 100/2 200 4.04
 140/2 171 4.00
 170/2 132 3.96

Tab.2. Results of tests for knitted structures

 Yarn Mean Mean
Tipe of count Knitted Force Elongation
knits [Nm] structures [gf] [%]

unfinished 70/2 single jersey 44.2 56
 70/2 double jersey 2:2 46.8 58
 100/2 single jersey 36.6 46
 100/2 links-links 37.2 50
 140/2 double jersey 1:1 30.2 43

finished 70/2 single jersey 39.8 50
(dyeing) 70/2 double jersey 1:10 41 53
 100/2 single jersey 32.5 47.8
 140/2 single jersey 26.7 45.1
 140/2 double jersey 2:8 28 46.8