Determination of Tenacity and Percentage Elongation of Single Cotton Yarns

The tensile testing of single yarns is very important in the textile industry, as yarn coming from the spinning process has to pass through a large amount of loading, unloading, tension and tension-less mechanisms until the final product is made. Hence a yarn with good tensile strength or tenacity can bear all the forces during the textile manufacturing process and our final product will be of good quality.

Figure 1: Uster TensoRapid

In this experiment, using USTER TENSORAPID machine the tensile strength or tenacity of the yarn is calculated along its %age elongation. This machine acts on the constant rate of elongation (CRE) principle according to the ASTM committee 1997a. The constant rate of elongation or CRE is a principle used to measure tensile strength of a material i.e. fiber, yarn, fabric, paper and other other materials.

Tenacity is a term used in textile manufacturing to denote the strength of a yarn or fiber filaments of a given size. The average tenacity values of a 20S yarn are about 18-20 cN/tex. The tenacity of a yarn depends on two things:

1. No. of fibers/cross-sectional area
2. Fiber strength (GPT)

Fiber strength is calculated in grams per tex or GPT which is measured by holding a bundle of fibers in clamp jaws and calculating the required force to break that bundle one tex unit in size. A tex unit is weight in grams of 1000 meters of fiber. GPT of Pakistani cotton fibers is about 28-35. The substance utilization of the fibers in the ring-spun yarns is about 65-70% and in the rotor-spun yarns is about 50-55%. Hence the count-related tenacity (cN/tex) of rotor-spun yarn is therefore usually 10% - 20% lower than that of ring-spun yarn. That is also a reason for the ring-spun yarns to be stronger and finer.

Objectives:

• To calculate the tenacity of single cotton yarn.
• To calculate the percentage elongation of the single cotton yarn.

Materials:

• Cotton yarn package.
• USTER TENSORAPID

Procedure:

• Cotton yarn package was taken whose tenacity was needed to determined.
• It was placed on the USTER TENSORAPID machine.
• The yarn was passed through the passage of yarn.
• The test parameters and the measurement ranges were inserted in the machine.
• Now the machine was turned on.
• 15 readings were taken of that yarn.

Observations & Calculations:

English Count of Yarn = 20 Ne

Tex = 590.5/Yarn Count = 590.5/20 = 29.525

Pre-tension given to yarn = 29.525 x 0.5 = 14.7625

Machine Gauge Length = 500 mm

Speed = 5000 mm

0.70 = Substance Utilization (Yarn Area Utilization)/100 = 70/100

[Note: Remaining 30% loss due to gaps between fibers in a yarn.]

Tenacity = no. of fibers x GPT of Fibers x 0.70 = cN/tex of Fibers x 0.70

Results:

Tenacity Values for the given Yarn Package = 16.64 cN/Tex
Percentage Elongation Values for the given Yarn Package = 7.18 %

Discussion:

The tenacity values for our yarn comes out to be 16.64 cN/Tex, which is less than our desired values for the 20s yarns. This due to the thin places in the yarn. This tells us that our yarn doesn't meet the standards for the 20s yarn. If the fabric is prepared by this yarn then the fabric strength will be automatically be very low. This yarn can also cause many difficulties during the weaving process.