Test methods
Test methods for industrial multifilament yarns
1 Test room conditions
The standard conditions according to BISFA are:
- temperature: 20 ± 2°C
- relative humidity: 65 ± 2%
All tests must be carried out in conditioned state.
2 Linear density
The linear density decitex [dtex] corresponds to the yarn weight in grams of 10’000 m length.
In order to determine the linear density, a sample of 25 or 100 metres length is wound on a standard reel under a pretension of 0.5 cN/tex and weighed on an analytical scale. The grams per 10’000 m yarn length are then calculated.
3 Breaking force and elongation at break
The breaking force leads to the rupture of the thread or yarn. The corresponding unit is the 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 initial length. The test is carried out on a dynamometer 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
Yarns with zero twist (0-00) are measured with Z 60 for technical reasons.
4 Tenacity (yarn count tenacity)
This is calculated from the breaking force and linear density
and is expressed in centinewton per tex [cN/tex].
| breaking Force [N] | |
| Tenacity (cN/tex) = | ———————————— |
| linear density [dtex] x 0,001 |
5 Force at specified elongation (FASE)
This is the force resulting from a defined extension (usually at 2% and 5%).
6 Hot air shrinkage
This is the reduction in length caused by treatment with hot air, expressed as a percentage of the initial length. We distinguish between free shrinkage and shrinkage under pretension.
a) 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 a defined temperature (between 100-200°C)
for 15 min.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:
(L1 - L2) x 100
L1b) Shrinkage under pretension
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: 15min at 180°C Polyamide 6.6: 10min at 180°C <dtex 940 15min at 180°C >dtex 940 c) Shrinkage curve
The shrinkage curves shown were 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.
7 Hot air shrinkage force
This is the shrinkage force in cN resulting from hot air treatment (180°C). Pretension 0.1 cN/tex
8 Hot water shrinkage (95°C)
This is the reduction in length caused by hot water, expressed as a percentage of the initial length.
It is calculated as follows:
- On a standard reel, skeins of 1 m circumference and 5’000 dtex approx. are prepared and measured at a pretension 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 (L2) is determined again with 1 cN/tex pretension.
- The hot water shrinkage in percent is calculated according to the following formula:
| (L1 - L2) x 100 | |
| Hot water shrinkage in % = | ———————————— |
| L1 |