YARN TEST METHODS

1. Test room conditions
2. Linear density
3. Breaking force and elongation at break
4. Tenacity
5. Force at specified elongation
6. Hot air shrinkage
7. Hot air shrinkage force
8. Hot water shrinkage

The standard according to BISFA is:
 

• room temperature: 20 ± 2°C
• relative humidity: 65 ± 2%

All tests must be carried out in a conditioned state.

The linear density decitex [dtex] corresponds to the yarn weight in grams of 10'000 meters lengths.

In order to determinde the linear density, a yarn sample of 25 or 100 meters length is wound on a standard reel under a pretension of 0.5 cN/tex and weighed on an analytical scale. Hereafter, the grams per 10'000m yarn are calculated.

The breaking force leads to the rupture of the thread or yarn. The corresponding value is Newton [N].

The elongation at break is the increase in length produced by stretching a test specimen to the breaking point, expressed as a percentage of the inital length. The test is carried out on a dynmometer with a constant increase in elongation, according to the following conditions:
 

• length between clamps: 500 mm (or 250 mm)
   
• test velocity; if elongation at break
  • ≤ 8%:     50 mm/min (25 mm/min)
  • 8-50%:   500 mm/min (250 mm/min)
  • > 50%:   1000 mm/min (500 mm/min)
     
• pretension: 0.5 cN/tex

This is calculated from the breaking force as well as linear density and is expressed in centi Newton per tex [cN/tex]:

This is the force resulting from a defined extension (usually at 2% and 5%).

This is the shrinkage in length in percent caued by treatment with hot air. We distinguish between free shrinkage and shrinkage under pretension.
 

FREE SHRINKAGE

This value defines the change of length after the influence of heat. 

Method: After the measurement of length (L1) under 1 cN/tex pretension the samples will be treated without pretension at the defined temperature (between 100°C and 200°C) during 15 minutes. After a cooling time of 1 hour under standard atmospheric conditions, the shrunken length (L2) will be determined again with 1 cN/tex pretension. The residual shrinkage is then calculated according to the following formula:  

SHRINKAGE UNDER PRESSION

This value defines the change of length during the influence of heat.

Method: The sample is introduced into the heating channel with a pretension of 0.1 cN/tex at 180°C. The shrinkage will be read in percent directly from a scale.
 

• Polyamide 6:             15 min at 180°C
   
• Polyamide 6.6
  • < dtex 940:        10 min at 180°C
  • ≥ dtex 940:        15 min at 180°C
     
• Polyester:                    15 min at 180°C

 

SHRINKAGE CURVE

The shrinkage curve in our brochure "Product information" was obtained by continuous heating under pretension of 0.1 cN/tex. Due to this, there can be differences to the indicated value in the table.

 

This is the shrinkage force in cN resulting by hot air treatment (180°C).
Pretension: 0.1 cN/tex.

This is the shrinkage in length which is caued by hot water. It is calculated as follows:
 

• On a standard reel, skeins of 1m circumference and approximately 5'000 dtex are prepared and measured at a prention of 1 cN/tex lengthwise = L1
   
• The skeins are then treated without tension during 15 minutes in hot water (95°C), dried and conditioned at standard conditions.
   
• The shrunk length is determined again with 1 cN/tex pretension = L2
   
• The hot water shrinakge in percent is calculated according to the following formula: