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Effect of air pressure on air covered yarn


Air covering is a process of combining two or more yarns to create unique yarns with new combination of characteristics.They are comfortable to wear and can modify their elasticity to fit different end-products. Air covered yarns can be used to produce fabrics of varying styles, hands and functions, and can be designed for woven as well as knitted fabrics according to their properties. This study is related to production and testing of air covered yarn from polyester and lycra on air covering machine. In this study yarns are produced with different level of air pressure i.e. 4, 6 & 8 kg/cm2. The results shows that denier of produced yarn, loops density and the polyester yarn content to produce air covered yarn increases with air pressure. Loop stability of air covered yarn also increases as air pressure increases.

Keywords: air covered yarn, air pressure,loop etc.


In the production of the air covered yarn two different materials are used, one is elastic and other is non-elastic. The non-elastic yarns contains filament such polyester. The non-elastic yarn is used to improve the evenness, durability, aesthetics, and functional properties of the fabrics. The yarns have the advantage of uniformity in length. Fabrics included with it are better cover and abrasion resistant.

Elastic yarn i.e. lycra is used as a core material. Elastic core yarns exhibit greater uniformity in size, strength and elongation. The higher initial modulus or resistance to stretching contributing to better loop formation, superior abrasion resistance and durability are the other advantages of the air covered yarn.

Air covered yarns have also unique properties. Generally this yarn is used in sports applications.

Material and methodology:

Two different yarns are used as raw material;Polyester textured drawn yarn of 80D and Lycra yarn of 40D to make air covered yarn.Elastic core spun yarns will be produced using air-covering machine. The air- covering machine process parameters are as follows:

Process parameters used:

  • Delivery speed       – 110 meters/min
  • Air Pressure           – 4, 6, 8 kg/cm2
  • Elastic draw ratio   – 2
  • Overfeed to jet %   -5


The air covered yarns will be tested for following characteristics:

  1. Denier of yarn

The denier of filament measured by preparing lea on hank meter and weighing on weighing pan and then denier was calculated. For this lea was prepared by 80 revolutions of wrap reel having length of 120 yards and finally the denier calculated.


  1. Loop density

Loops in the yarn is special characteristic of air covered yarn, so it is necessary to find out number of loops present in the yarn.Number of loops in the yarn is measured by taking 1m of yarn in relaxed state. After taking sample, deepen in water to measure loops by naked eye easily.

  1. Content of the components in the yarn

Lycra and polyester are the two components in the yarn produced so it is important to find out how much lycra as well as polyester present in the yarn.The yarn with 1m length taken and then its weight is taken. After taking weights the lycra separated from the yarn body and again the weights are taken gives content of polyester in the yarn, and then lycra content percentage also was calculated.

  1. Loop stability

Loops which are created by using pressured air, which may be not stable or less stable which can be easily removed. So it is important to find loop stability. Loop stability cannot be directly measured, measured indirectly. The yarn wrap is prepared on hank meter and according to denier of the yarn the weight of 0.02 gpd was loaded for 2 minutes and then length (L1) measured. Again the same lea loaded with load of 0.2gpd for 2 minutes and again length (L2) measured. And loop instability is calculated by *100

  1. Statistical analysis

As there is only one variable i.e. air pressure, one way ANOVA was used for statistical analysis of result.

 Table 1: ANOVA results:

Sr. No. Property p- value F F crit
1 Denier of Yarn 1.04E-37 7395.779 3.354131
2 Loop Density 2.96E-13 100.8839 3.354131
3 Component Content 5.28E-41 12983.91 3.354131
4 Loop Instability 4.17E-21 422.9419 3.354131

Result and discussion

  1. Denier of air covered yarn

Result shows that as pressure goes on increasing from 4 kg/cm² to 8 kg/cm², denier of the yarn increases. Increases in pressure causes increases in loop density hence yarn becomes bulkier results in increase in denier of air covered yarn.

04Figure 2: Effect of air pressure on denier of yarn

  1. Loop density in the yarn

As shown in figure 3the loop density increases as pressure increases. This is due to decrease in loop and at high pressure we get more number of loops i.e. loop density in same length. The height of loop changes as air pressure changes causingincrease in number of loops in same length of yarn. ANOVA shows that the effect of air pressure has significant effect on number of loops in yarn.

05Figure 3: Effect of air pressure on Loop Density

3. Component content in the yarn

Lycra & polyester content in the yarn is calculated by taking 1 meter of air covered yarn weight and taking again weight by removing lycra from it.


 Figure 4: Effect of air pressure on raw material content in the yarn

As pressure increases, the Lycra content in the yarn decreases due to increase in polyester content in the yarn. Lycra yarn is covered with loops of polyester and as number of loops increases the polyester content in the yarn increases. So it was found that percentage of raw material content is varied with change in air pressure after statistical analysis.

  1. Instability of loops in the yarn


Figure 5: Effect of air pressure on instability of loop

As air pressure increases, the instability decreases and it directly shows that loop stability increases. Due to increase in air pressure the binding points in yarn become stronger resulting in more loop stability. A statistical analysis is carried out which shows the loop instability differs with air pressure.


Air covering is a process of combining two or more yarns to create unique yarns with new combination of yarn characteristics. During the process, the yarns were feed into an intermingling jet which then gave desired type of intermingling quality needed in downstream process.Air covered yarnswere produced with varying air pressure i.e. 4, 6, 8 kg/cm2 and properties of yarn were tested.ANOVA showed that change in air pressure have significant effect on denier of yarn, loop density, polyester and lycra content and loop stability.As air pressure increases denier of the yarn, loop density in the yarn and polyester content in the yarn increases while instability of loops and lycra content decreases.


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