Sino Textile Machinery

Major Problems and Solutions in Rapier Loom Weaving

Major Problems and Solutions in Rapier Loom Weaving

1. How to configure the shed opening time and weft insertion time of the rapier loom?

The weft insertion time of the rapier loom--the time of weft-sending gripper and the weft-receiving gripper entering the shed- is basically fixed. The opening time is mainly determined by the characteristics of the fabric and the clarity of the shed. Generally, plain weave fabrics should be configured with early shedding, conducive to weft beating, reducing the cloth fell movement, and improving the fabric's quality. Twill and jacquard fabrics should be configured with late shedding, which can meet the fabric's appearance and reduce the breakage rate.

2. What effect does the shed opening time have on the quality of the fabric?

The opening time is early, the shed is clear, and the weaving defects will be less. However, when the shed opening is early, and the closing is also early, the rapier squeezes the warp more severely, and the fabric and warp at the edge are easy to loosen. The shed opening time is late, and the shed's clarity will be poor, which can easily cause triple-jumping defects at the edge of the fabric, but due to the late opening and the closing, the rapier has relatively less squeeze on the warp.

3. How to set the leveling time of the small heald frame for the waste selvage?

The leveling time of the small heald frame of the waste edge of the rapier loom should be 25°~30° earlier than that of the plain weave, to ensure that the weft is gripped before the rapier gripper is released,  instead of retracting back to the cloth fell and causing weft shrinkage.

4. In the rapier loom's operation diagram, why does the rapier weft insertion time take up more degrees than the shuttle loom flying in the shed?

Shuttle looms usually start to pick the shuttle before the lower center. When the back center, the shuttle has entered the shuttle box on the opposite side. The flying time of the shuttle is about 120°. When the rapier loom is at 62°, the gripper head enters the shed. It takes about 300° to retreat the weft gripper, and the rapier moves about 240° in the shed. As the rapier loom's speed is fast, the sending and receiving grippers move towards each other and pass by in one stroke. To ensure the stable delivery of the weft, the running speed must be reduced accordingly. Therefore, the rapier takes more time in the shuttle.

5. In the entire rapier weft insertion process, what is the grip force's principle toward the weft yarn?

The weft receiving gripper's grip force> the grip force of the weft sending rapier> the clamping force of the weft feeder clamping piece.

6. What is the impact of the rapier loom's cutting time during weft insertion?

The weft cutting time is too early, the depth of the weft yarn clamped by the sending gripper is not enough, and it is easy to make mistakes during delivery. The cutting time is too late, and the weft tail is too long, which will cause two-wefts or weave the waste yarn into the cloth fell and affect the quality.

7. What effect does floating guide hook and ordinary guide hook have on weaving?

Ordinary guide hook--the gripper head, the gripper tape, and the lower warp sheet are prone to friction. The lower warp sheet and the felt pasted on the sley are easy to rub, and warp breakage will be relatively high. At the same time, it is also easy to cause the back of the cloth to fuzz. When weaving colored fabrics, the color hairiness in the horizontal direction increases, which affects the quality of the fabric and the loom's efficiency.
Floating guide hook--also call free flight weft insertion, in which the gripper belt and the gripper head traverse overhead in the shed. The friction with the warp yarn will be reduced, the warp breakage will be relatively less, the cloth surface is not easy to fluff, and the horizontal color hairiness is also less.

8. What effect do the separated sley and integrated sley have on weft insertion?

Separate sley must have a long static time in the back center to ensure the weft insertion's successful carryout. Generally, conjugate cam beating-up is used, as long as the adjustment is good, there will be no impact on weft insertion. However, when the sley is moving, the gripper head cannot stay within the reed's swing range. Thus, on the rapier loom with separate sley, the reed's remaining length is limited and should be cut off once it exceeds. And integrated sley is simple in machinery and adopts ordinary four-bar beating-up. The beating-up stroke is large, the shed height is large, and the speed is relatively low, but there is no need to worry about its impact.

9. Why do the rapier tape and the rapier head squeeze the warp yarn during the weft insertion process?

To ensure stable handover of the weft, the rapier needs a long traverse time in the shed, but the shed's opening time cannot be too long because a long stationary time means that the heald frame movement time will be shortened. In this way, the acceleration of the heald frame movement increases, the impact will be very strong, which is detrimental to the loom's stability. So when the gripper tape and the gripper head have not exited the shed, the heald frame has begun to close, and the gripper and the tape will have a severe squeeze on the closed warp.

10. What is the reason that warp on the selvage is easy to loosen? What will be the impact on the weaving? How to prevent it?

As the gripper head and the gripper tape squeeze the warp sheet seriously when they exit the shed, the warps on the exit side are easy to loosen. The consequences of this situation are unclear openings and increased defects on fabric.
Preventive measures: the first measure is to increase the height of the opening appropriately; the second measure is to move the warp-stop frame forward to shorten the length of the second half of the shed; the third measure is to keep the number of ends per reed on both sides slightly less than that in the middle. The two sides of the finished weaver's beam will bend slightly inward so that the selvage yarn tension is somewhat larger. In this way, fabric slack selvage will be improved.

11. What factors are related to the beating-up force of rapier looms?

The strength of the beating-up force is mainly related to the sley's weight and the acceleration of the sley's movement--the weight is large, the beating-up force is large; the movement's acceleration is large, the beating-up force is also large. Shuttle looms mainly rely on significant weight for beating up wefts, while new rapier looms use conjugate cams to beat up wefts, which mainly rely on increasing acceleration to increase the beating-up force.

12. Why does high-speed rapier looms use a conjugate cam beating-up mechanism?

Firstly, high-speed rapier loom adopts a separate sley to ensure that the sley has a long static time in the rear center during the weft insertion process. Secondly, the sley of the high-speed rapier loom is made of aluminum alloy, which is very light in weight. The reed is very narrow and has no reed cover, and the beating-up mechanism is very lightweight. The only way to increase the beating-up force is to design a conjugate cam beating-up mechanism to increase the acceleration.

13. Why the rapier loom shuts down for no reason in the weft direction? How to correct it?

One reason is that there are flying fluff in the weft clamp, or the clamping force is too small. The other reason is that the sensitivity of the piezoelectric ceramic sensor is too high. It can be corrected from cleaning the weft clamp, adjusting the clamping force, and adjusting lower the piezoelectric ceramic sensor's sensitivity.

14. What method of drawing-in and denting should be used when the rapier loom produces high warp density fabrics?

High warp density fabrics should adopt the fly-threading method. 3 or 4 ends should be threaded per reed. For drop wire, drawing-in can adopt the technique of 1.1.2.2.3.3.4.4.5.5.6.6, which will reduce warp breakage and increase efficiency.

15. If rapier loom adopts a cannon-type stepless weft density changing device, why is the weft density on the machine easy to change?

After the device has adjusted the weft density, the top support screw must be tightened and tightened with a nut, otherwise, the screw is prone to loosening, and the weft density on the machine will change after loosening.

16. What will happen if the rough rubber pasted on the emery roller and guide roller peels off?

When the rough rubber peels off, the emery roller, guide roller, and cloth surface will slip, which will cause the cloth fell position to be unstable, the weft beating-up is not tight, and the weft density on the loom will also change accordingly.

17. What are the reasons for the weft delivery error of the rapier loom?

(1) There are flying fluff and sundries in the sending gripper weft clamp, and the weft clamp does not hold the weft effectively.
(2) The weft cutting time is too early, the weft pick entering the weft gripper clamp not deep enough, and the gripping force of the sending gripper is too small.
(3) The weft segment tension is unreasonable, and the weft gripper's clamping force is too small.

18. What is the reason for the waste edge yarn to be woven into the fabric?

(1) The heald leveling time of the waste edge heald frame is too late.
(2) The weft yarn separate from the receiving gripper too late, causing a too long waste edge. When the gripper enters the shed again, the waste yarn is taken into the next cloth fell.
(3) The number of ends threading the waste edge heald frame is not enough, and the waste edge is not effectively grasped.

19. What is the reason for the temple mark on the rapier loom?

(1) Warp yarns are embedded between the copper rings of temples, and the copper rings are retarded, and the rotation is not flexible.
(2) The needles on the copper ring are bent or cracked.
(3) The temple ring does not conform to the weaving species, including the type of needle (thick, medium, fine, extra-fine needle), and the length of the needle (0.2mm, 0.4mm, 0.6mm, 0.8mm).
(4) Inadequate installation position of the temple.

20. What kind of temple should be used to produce fine and extra-high-density fabrics on rapier looms?

It is best to use rubber temples for fine, extra-high-density fabrics, holding the fabric surface, and reducing temple defects.

21. How is the segment tension of the weft yarn on the rapier loom controlled?

The weft cone's draw-out tension is controlled by the hairpin sensor at the back of the weft feeder. The draw-out tension of the weft on the feeder is controlled by the secondary yarn gripper. In weft sending, the weft's tension is controlled by the sending gripper's spring lamel. In weft receiving, the weft's tension is controlled by the spring lamel of the receiving gripper.

22. How does the rapier loom choose the weft feeder's brush ring according to the weft yarn's twist direction?

Under normal circumstances, the weft is Z twist, and the warp is S twist. The brush's oblique direction on the weft feeder should be the same as the twist direction of the drawn yarn; otherwise, it will cause the weft yarn to untwist and increase the chance of weft breakage.

23. How to determine the position of the backrest of the rapier loom according to the fabric structure?.

Generally speaking, in plain weaving, the backrest should be higher than the breast beam to realize plain fabric's flatness and plumpness. In twill and jacquard weaving, the backrest should be lower than the breast beam to achieve the evenness, depth, and straightness of twill fabrics.

24. How to determine the backrest's front and rear positions according to the fabric's raw material and weave pattern?

When weaving linen and wool fabrics on the rapier loom, a short warp position line should be applied, and the backrest should be moved forward to the first hole position. When weaving cotton fabrics, the backrest should be placed in the second hole position. When making silk fabrics, the warp position line should be extended, and the backrest should be placed in the third hole position.

25. What is the reason for the floating defects on the fabric produced by the rapier loom? How to prevent it?

The main reason is that the shed opening is not clear. Shuttleless looms generally weave with small openings and high tension. When the shed is fully opened, the height of the shed at the reed is only 2.8~3.2cm. To ensure stable handover of the weft yarn, the rapier grippers traverse in the shed for a long time. The rapier movement will severely squeeze the shed. At the same time, suppose the opening time and the weft insertion time are not matched well, it will lead to floating defects, especially in the weaving of high warp density fabrics and jacquard fabrics with late opening.

Precaution:

(1) In the preparatory process, try to keep an even warp sheet tension during winding, warping, and sizing sheet tension.
(2) Pay attention to the reed density when sizing. The number of threads per dent on the two sides can be slightly smaller than in the middle so that the finished beam turns out a slight inward bending structure. Hence ensuring a certain tension during warp uncoiling to compensate for the relaxation of the side warp tension caused by the warp's squeezing by the gripper head and the gripper tape.
(3) Adjust the looming plan of the rapier loom. To improve the the sheding clearness, the opening time can be set slightly early, or the warp stop frame can be moved forward to shorten the length of the second half of the shed.
(4) Strengthen the first beam's inspection and the first batch of fabric, report defects, and mend in time.
(5) Ensure the quality of the warp beam.

26. Why does the rapier loom still generates motion marks even with an automatic cloth fell matching device? And how to prevent it?

Cause:

(1) Improper selection of running mode.
(2) Let-off and take-up motion are abnormal.
(3) Some particular fabric patterns, such as basket weave and fancy basket weave, have loose and tight structures due to the organizations, and there will still be motion mark after loom stop.

Precaution:

(1) Choose the appropriate running mode according to the fabric pattern.
(2) Check whether the let-off and take-up motions are normal.
(3) Appropriately reduce the set tension.
(4) Put off the shedding time appropriately.

27. What is the reason for the weaving colored hairiness and fibers into fabric? How to prevent it?

Reasons:

(1) The dyed yarn goes through many production processes; more processes lead to more wear. So color yarn turns out to have more hairiness.
(2) The color fastness of bleached and dyed yarn is poor, and the colored yarn is decolored in the size tank and stained with white or light-colored yarn.
(3) The product process design is unreasonable, that the dark and light colors are arranged in the same slurry tank for sizing.
(4) Light sizing leads to more fluffy flyings drop on the loom.
(5) The loom configuration will affect the volume of colored hairiness. For example, the lower warp sheet of rapier loom without floating guide hooks directly abrase with the gripper head and tape, making it easy to cause horizontal colored hairiness.
(6) Poor cleaning and tidying of workshops and machines.

Precaution:

(1) In the various processes that the colored yarn passes through, the yarn channel should be smooth to keep less abrasion as possible.
(2) Use pigments with better color fastness for dyeing, soap-boiling and washing should be clear.
(3) Species with dark stripes on white or shallow backgrounds should better be sized on the double-sized slot sizing machine.
(4) Ensure proper sizing volume and eliminate light sizing.
(5) Species with dark stripes on white or shallow backgrounds should better be woven on looms with floating guide hooks.
(6) Workshop should have different production areas for dark color and shallow color species.
(7) For dark color weft yarns to be woven into white or light-colored backgrounds, if contain too much hairiness, should better go through light sizing beforehand.
(8) It is best to use thread with similar fineness as the inserted line in the white or light-colored background.
(9) Good cleaning and tidying of workshops and machines.

28. What are the requirements for the length of the reed for rapier looms with separated sley? Why?

For the rapier loom with a separate sley, the rapier stroke must be readjusted after the reed width is changed.
The reed length is generally 5.5cm plus the effective reed width, with 2cm on the inlet side and 3.5cm on the outlet side. If the reed is too long, not only the weft will be wasted, but the reed will collide with the rapier during the movement, causing a reed breaking accident.

29. How to configure the thickness of the selvedge yarn according to the fabric species?

The selvedge yarn must be firm with a good strength; furthermore, its thickness should not be thicker than the warp being used for production. Too thick selvedge yarn will cause stringy selvedge. Generally, 14.6tex warp can use 7.3tex×2 thread as selvedge yarn, and 11.7tex warp can use 5.8tex×2 thread as selvedge yarn.

30. How to determine the inner distance between the two flanges of the weaving beam according to the fabric of different reed widths?

The weaving beam flange inner distance is preferably equal to the effective reed width, which is beneficial for reducing the selvedge yarn breakage. If the weaving flange inner distance is slightly larger than the effective reed width, it is acceptable, but should not be less than the effective reed width.

31. What are the reasons for the weft-loop defect in rapier weaving? How to prevent it?

Cause:

(1) The heald leveling time of the waste edge heald frame is too late. When the weft receiving gripper opens and releases the weft, the waste edge does not effectively control the weft.
(2) The opening time of the receiving gripper is too early.
(3) The number of waste edge yarn is too insufficient to clamp the weft effectively.

Precaution:

(1) The heald leveling time of the waste edge heald frame shall be 25~30° earlier than the rest heald frames.
(2) Adjust the opening time of the weft receiving gripper. If too early, it is easy to produce a weft-loop defect; if too late, the waste edge will be too long.
(3) Check whether the number of waste yarns is sufficient and whether the broken ends have been fixed.

32. In rapier loom weaving, the cloth surface will sometimes turn out one side rough and backside smooth. What is the cause of this? How to prevent it?

Cause:

(1) This situation is easy to occur on the loom with ordinary guide hooks.
(2) The heald frame is hoisted too low, and the lower warp sheet scrapes rapier race board.
(3) The bottom of the gripper head gripper tape is worn with burrs.

Precaution:

(1) Adjust the height of the warp leveling line.
(2) Check and exchange the gripper head and tape.
(3) Try to arrange production on rapier looms with floating guide hooks.

33. When the rapier loom is weaving fine tex high-density fabric, sometimes irregular and broken defects appear on the cloth surface. The flaws may not be easily found during grey fabric inspection but will become evident after finishing. Why? How to solve it?

Rapier looms generally use equal tension sheds. If the loom tension is too high and the weft yarn is too thin, the strength is too low, or the weft yarn is uneven, the shear stress generated by the warp yarn interlacing during the weaving process may lead to damage of the weft yarn weak spot. After finishing oxygen bleaching and the mercerizing process, broken defects will occur.

Precaution:

(1) Check the strength and unevenness of the weft yarn. If the single strength is too low or strand unevenness is too severe, the weft yarn has to be changed.
(2) Reduce loom tension appropriately.
(3) Raise the backrest to keep the two layers warp sheet tension in a relatively big difference to reduce the shearing strength when interlacing.

34. How to prevent the looped weft at the shed exit when weaving fabric with elastic weft on the rapier loom?

(1) Increase the number of waste warp yarns from 14 ends to 20-24 ends.
(2) Strictly control the heald leveling time of the waste yarn heald frame, which should be 30° earlier than the ground warp leveling time.
(3) Properly postpone the time of opening the receiving gripper and releasing weft.

35. What is the reason for the double weft in the left half of the fabric? How to prevent it?

Cause:

(1) The left weft scissors' cutting time is too late, and the weft yarn is not cut successful.
(2) The weft gripper clamp's elasticity is too low, or there is flying fluff or waste yarn stuck in the gripper head, leading to the failed clamp of weft and delivery error.

Precaution:

(1) Adjust the weft cutting time.
(2) Increase the clamping force of the weft rapier head.
(3) Check whether there are flying fluff and broken ends in the receiving gripper.

36. When the rapier weaving machine weaves high weft density fabrics, it is easy to cause the unstable cloth-fell, and the weft beating-up is not tight. What is the reason?

Rapier looms are generally equipped with equal tension sheds and high tension weaving. If the warp yarn tension is high in weaving high warp-density fabrics, the weft yarn is easy to reverse in the shed, leading to unstable cloth-fell, and the weft yarn cannot be beaten up tightly. When encountering this kind of species, unequal tension shed should be configured to make one layer of warp tight and the next layer loose to reduce the weft's reverse and enable the warp tightly wrap the weft. The specific operation is to lift the backrest high to keep the upper warp sheet in low tension and the lower warp sheet in high tension.

37. When weaving a single color weft fabric, how to properly handle the weft yarn to prevent color difference?

Should use 1:1 weft mixing or 1:1:1 weft mixing. Weft mixing aims to eliminate the influence on the cloth surface caused by weft color difference or uneven weft yarn. Introduce weft yarn from two or three cones to avoid the difference between the cones and the fabric's influence.

38. What actions needed when the rapier loom is weaving colored fabrics with similar color yarns?

Try to separate the wefts of similar colors and don't put them on the adjacent color selection needles to avoid picking mistakes.

39. The change of the front and rear positions of the warp stop motion will change the length of the second half of the shed. What effect does this have on the clarity of the shed and the rate of warp breakage?

The warp stop motion moves forward, and the second half of the shed is shortened, which is beneficial to improve the clarity of the shed and reduce the fabric defects, but the warp breakage will increase.

40. What is the nominal width of a rapier loom? What is the effective reed width? What is the relationship between the two?

The nominal reed width of a rapier loom is one of the signs of the rapier loom model. If it is a four-link beating-up loom, the nominal reed width refers to the distance between the two cranks' center; if it is a conjugate cam beating-up loom, The nominal reed width refers to the distance between the centers of the conjugate cams on both sides. The effective reed width refers to the maximum reed width that can be actually used. Relationship between the two--the nominal reed width is bigger than the effective reed width, the difference between the two is around 5cm, e.g., if the loom nominal reed width is 190cm, the actual effective reed width is 185cm. If the loom nominal reed width is 230cm, the actual effective reed width is 225cm.

41. On the rapier loom with separate sley, how to calculate the on-loom reed length?

On-loom reed length = effective reed width + 5.5cm

42. What data should be applied in the calculation of the volume of weft yarn on the rapier loom?

The reed width should be the sum of the effective reed width and the waste yarn's width on both sides, which is generally 8~12cm according to each mill's situation. If the waste yarn's width is not considered, the volume of weft yarn will be insufficient.