Method for producing profiled fibers having low broken filament rate by polyester FDY process

1 . A method for preparing profiled fibers with a low lousiness rate by a polyester fully drawn yarn (FDY) process, comprising that: when preparing the profiled fibers by the FDY process, horizontal and longitudinal positions of wire guide ceramic pieces on a pre-entangling wire guide frame are adjusted to maintain a vertical alignment of a filament bundle in a pre-entangling device having a pre-entangling yarn path and achieve an optimal jitter effect of the filament bundle in the pre-entangling yarn path, so as to prepare the profiled fibers with the low lousiness rate;

wherein the profiled fibers comprise triangular profiled fibers, trilobal profiled fibers or flat profiled fibers; when the profiled fibers are the triangular profiled fibers, a lousiness rate is 0.35-0.65%; when the profiled fibers are the trilobal profiled fibers, the lousiness rate is 0.85-1.25%;

when the profiled fibers are the flat profiled fibers, the lousiness rate is 0.5-0.85%;

wherein a jitter condition of the filament bundle in the pre-entangling device is detected by fiber optic sensors; wherein optical fibers of the fiber optic sensors are divided into two groups, located directly in front of and behind the pre-entangling yarn path respectively, both arranged in horizontal arrays along a horizontal symmetry axis of the pre-entangling device;

wherein a diameter of the optical fibers is smaller than a diameter of each monofilament in the filament bundle; wherein the fiber optic sensors detect left and right deviation distances of all monofilaments passing vertically from top to bottom through the horizontal symmetry axis relative to a longitudinal central axis of the pre-entangling yarn path; a distance value corresponding to the longitudinal central axis of the pre-entangling yarn path is set to 0, with leftward distances as positive values and rightward distances as negative values; a computer central processing unit (CPU) collects distance data, then counts and calculates a discrete distribution coefficient of variation (CV) value of the deviation distances, and generates a time-distance curve based on the distance data, at a maximum left jitter distance and a maximum right jitter distance of the monofilaments, a horizontal upper jitter limit line and a lower jitter limit line are drawn respectively, with a center line drawn exactly midway between the upper and lower jitter limit lines; using the center line as a reference, the upper jitter limit line is shifted downward by 20% of a distance between the upper jitter limit line and the lower jitter limit line and the lower jitter limit line is shifted upward by 20% of the distance between the upper jitter limit line and the lower jitter limit line to define an upper boundary line and a lower boundary line of a normal jitter range; then using the center line as the reference, the upper boundary line is shifted downward by 30% of the distance between the upper jitter limit line and the lower jitter limit line and the lower boundary line is shifted upward by 30% of the distance between the upper jitter limit line and the lower jitter limit line to define an upper offset line and a lower offset line;

when the time-distance curve appears in an area above the upper boundary line or below the lower boundary line continuously for 2 ms, the entire area where the curve appears during this period is defined as a “long segment”; when the curve appears only in an area between the upper offset line and the lower offset line continuously for 2 ms, the entire area where the curve appears during this period is defined as a “short segment”;

when the discrete distribution coefficient of variation (CV) value of the deviation distances is <3.5%, the center line coincides with the longitudinal central axis of the pre-entangling yarn path, and no “long segments” or “short segments” appear in the time-distance curve, so that the filament bundle maintains the vertical alignment and achieves the optimal jitter effect in the pre-entangling device, the optimal jitter effect being defined by the discrete distribution coefficient of variation (CV) value being <3.5%, the center line coinciding with the longitudinal central axis of the pre-entangling yarn path, and the absence of “long segments” and “short segments”.

2 . The method of claim 1 , wherein the pre-entangling wire guide frame comprises a channel frame, wire guide ceramic pieces, positioning blocks, a pressure strip and a first screw, as well as a sliding groove and a second screw located at both ends of the channel frame, wherein the wire guide ceramic pieces and the positioning blocks are installed inside the channel frame and fixed by the pressure strip and the first screw; wherein each wire guide ceramic piece is installed between two adjacent positioning blocks, in an alternating sequence of positioning blocks and wire guide ceramic pieces;

wherein the channel frame and the pre-entangling device are both horizontally arranged; wherein the pre-entangling device is fixed in a middle of a pre-entangling panel;

wherein the channel frame is divided into an upper row and a lower row, the upper row channel frame is located above the pre-entangling device while the lower row channel frame is located below the pre-entangling device;

wherein the sliding groove has an inwardly concave trapezoidal structure; wherein the pre-entangling panel has one slide rail on each side, and the slide rail has an outwardly convex trapezoidal structure matching the sliding groove; wherein the sliding groove is embedded in the slide rail and fixed with the second screw, allowing a vertical distance between upper and lower rows of the wire guide ceramic pieces to be adjusted by moving the sliding groove up and down along the slide rail.

3 . The method of claim 2 , wherein a width of the positioning blocks is 3-5 mm.

4 . The method of claim 2 , wherein the wire guide ceramic pieces installed in the upper row channel frame are U-shaped wire guide ceramic pieces, and those installed in the lower row channel frame are fishfork-shaped wire guide ceramic pieces.

5 . The method of claim 4 , wherein a width of the yarn path on all wire guide ceramic pieces is 1.5 mm.

6 . The method of claim 5 , wherein a horizontal width of both the U-shaped and the fishfork-shaped wire guide ceramic pieces is 12 mm.

7 . The method of claim 2 , wherein a surface of the slide rail is polished, and an inner surface of the sliding groove is also polished.

8 . The method of claim 2 , wherein a gap of 0.3-0.5 mm exists between the sliding groove and the slide rail on each side.

9 . The method of claim 2 , wherein an area near the slide rails on the pre-entangling panel is marked with scales.

10 . The method of claim 1 , wherein FDY process parameters are as follows: a winding speed of 3800-5300 m/min, a first godet roller speed of 2400-3980 m/min, a godet roller draw ratio of 1.1-1.6, a pre-entangling pressure of 0.025-0.055 MPa, and an oiling rate of 0.8-1.2%.

11 . The method of claim 1 , wherein a sampling frequency of the fiber optic sensor is 100 kHz.