GB/T 14345-2008Testing method for twist of man-made filament (English PDF)

6.2 Standard atmospheres for preconditioning, conditioning and testing

USE standard atmospheres for conditioning and testing of textiles specified in

GB/T 6529.

6.2.1 Preconditioning

When the moisture regain of the sample is greater than the conventional moisture regain, preconditioning is required:

- Temperature does not exceed 50 °C;

- Relative humidity is 5%~25%;

- Time is greater than 30 min.

6.2.2 Standard atmospheres for conditioning and testing

Standard atmosphere for conditioning used by polyester and polypropylene filaments:

- Temperature is (20±2)°C;

- Relative humidity is (65±5)%;

- Conditioning time is 4 h.

Standard atmosphere for conditioning and testing used by other man-made fibre filaments:

- Temperature is (20±2)°C;

- Relative humidity is (65±2)%;

- Recommended conditioning time is 16 h.

See Appendix A for the conditioning time agreed by both parties.

6.3 Pretension

6.3.1 The pretension of the sample is calculated according to formula (1):

7.1 Determination of direction of twist

TAKE a sample with a length of about 100 mm; HOLD one end to hang it;

observe the inclined direction of the vertical helix. Those that are consistent with the middle part of the letter "S" are "S" twists. Those that are consistent with the middle part of the letter "Z" are "Z" twists.

7.2 Multifilament testing

Before the test, pull off the filament that may be injured on the surface for several meters. CLAMP one end of the sample into the fixed gripper; USE the tensioning device to apply the specified pretension. After clamping the other end of the sample into the rotating gripper, remove the twist of the sample, until the components of the multifilament are parallel to each other. Or use an analysis needle to pass from the sample at one end of the fixed gripper to the sample end of the rotating gripper; determine the twist; verify the direction of twist.

7.3 Strand testing

7.3.1 The strand testing shall be carried out according to the method for multifilament of 7.2.

7.3.2 To determine the twist of each component of the strand, each component

can be used as a new sample to be determined according to 7.2.

For each component to be determined, the pretension shall be calculated according to the nominal linear density of each component. Before measuring the number of turns, reset the initial length.

7.3.2.1 Same components

If the components of the strands are the same, for the multifilament that has been separated by the first untwisting operation, except for leaving one multifilament, cut off other separated components near the gripper. The remaining one is used to determine the twist.

7.3.2.2 Different components

After the strands are untwisted according to the method described in 7.2, use adhesive tape to fix the ends of each component. Each component is marked so that it can be distinguished during the next determination. Then cut them from between the grippers. Since this result will not maintain the original length,