Common defects in the dyeing of denim warp yarn are mainly colored files, streaks, chromatic aberrations in the edges, color aberrations in the head and tail (or fragment color aberration), stains, and tank aberrations.

1. Color file

Color profile refers to the color difference between the latitude segments, which presents a straight strip of uneven color, which is also called horizontal profile. The probability of the ball being broken after dyeing and going around the guide roller is small. The dyeing and sizing are carried out separately, and the color file defect is few. Therefore, the color file defect mostly occurs in the dyeing of the dyeing and sizing machine. The main reason is that the dyeing process stops in the middle of the dyeing process, and the yarn fragments staying in the dyeing tank dyeing liquid absorb excessively, resulting in color stalls. Generally, if the parking time exceeds 30s, it will cause defects in the cloth surface.

1. The main reason for parking

(1) Broken ends and winding guide rollers occurred during the dyeing process, but the turner failed to find out in time, resulting in more serious broken ends and yarn entanglement, and was forced to stop for treatment;

(2) Shutdown caused by power outage or mechanical failure;

(3) Due to high impurity content in dyeing materials and slurry or high cotton yarn short lint, or poor chemical and sizing operations, the dye liquid supply pipeline is blocked and forced to stop;

(4) The dyeing and sizing of the dyeing and sizing combined machine is carried out on the same machine, and the two influences each other, such as the threading of the splitting rod, the operation error of the upper and lower shafts, etc., will cause the automatic stop of the dyeing unit.

2. Methods to prevent color shading

(1) Reduce end breaks and winding guide rollers, do a good job of cleaning the machine, especially the guide rollers, keep the surface of the guide rollers smooth and clean, and at the same time do a patrol inspection, and find that the broken ends of the winding guide rollers are dealt with in time;

(2) Reduce power outages and mechanical failures. Strengthen the contact with the power supply department, avoid the planned power outage time as much as possible; strengthen the preventive maintenance and lubrication of the machine to ensure that the machine is always in good condition;

(3) Improve the quality of dyeing and chemical materials, reduce the rate of raw cotton linters, do a good job in the inspection of dyeing and chemical materials and sizing materials, and carefully implement the chemical materials and sizing operation process. The prepared dyes and slurry should be filtered before being put into use, and the infusion and slurry pipeline system should be cleaned regularly;

(4) Efforts to improve the operating technical level of the car workers on duty;

(5) The warp yarn section that has caused the parking color stop can be discarded.

Second, the warp stripe

Warp streaks refer to dark and light color streaks in the warp direction of dyed fabrics.

1. The main reason

(1) Mixed use of warp yarns with different cotton composition or different twists, with cotton color, the maturity difference is too large, and the dyeing is uneven.

(2) The cotton yarn has uneven dryness, uneven weight, and uneven twist, resulting in the formation of streaks due to the difference in dyeing rate;

(3) Warp yarn tension is not scooped, the arrangement is uneven, and the yarn pieces overlap, resulting in different oxidation-reduction degrees and the formation of streaks.

2. Prevention method

(1) The original yarn is used in batches;

(2) Improve the quality of raw yarn;

(3) The warp yarns are evenly tensioned and arranged uniformly, increasing the number of twisting, improving the ventilation of the workshop, and facilitating the progress of oxidation and reduction.

3. Dispersive streaks

1. Cause

(1) The dyed yarn of the dyeing and sizing machine enters the sizing tank before it is dried, resulting in uneven sizing;

(2) When the ball warp dyeing machine is stopped and the color block warp is re-warped, the position of the color block is staggered to form short-segment color block-like streaks due to the inconsistent warp tension of each ball shaft;

(3) The ball warp dyeing has a color difference in a certain district, and the color difference shifts due to the difference of the ball warp and the unwinding tension of the sizing, forming streaks.

2. Prevention methods

(1) The yarn should be dried during the pre-drying of the sizing;

(2) Reduce the color scale and keep the tension of each ball axis consistent;

(3) Reduce chromatic aberration and ensure consistent unwinding tension.

Fourth, the chromatic aberration in the edge

1. Reasons

(1) The surface of the dyeing roller is worn and the pressure of the dyeing roller is uneven;

(2) The yarn surface is uneven and the degree of drying is different when drying after washing.

2. Prevention methods

(1) Regularly test and grind the roll to ensure that the surface of the roll is round and the left and right pressures are consistent.

(2) Humidify and twist before drying to separate the yarn layers.

Five, head and tail color difference

There are two reasons for the formation of the color difference between the head and the tail: one is that a certain guide roller yarn needs to be driven at a slow speed, and the other is that the liquid level changes and the circulation pipeline of the dye solution is blocked, which makes the dye solution unable to be replenished in time.

Solution: It is necessary to dredge the pipeline regularly to replenish it normally. Therefore, three points must be taken to control the color difference between the front and rear, namely, fixed vehicle speed, fixed liquid level, and fixed flow.

Six, stains

The stains appear more scattered and generally irregular.

1. The main reason

(1) In the process of raw yarn blending with cotton, the mixing of heterosexual fibers causes uneven dyeing, and whitish spots appear on the cloth surface;

(2) The uneven twist of the original yarn causes uneven dyeing;

(3) When the warping tension is set too high, the yarn will be twisted into a "braid knot" when it is loose. The "braid" is not opened during dyeing and cannot be dyed evenly. "It is pulled apart to form a white spot;

(4) Uneven dyestuff materials, impure dye liquor, and accumulation of color particles;

(5) The white yarn is stained with oil stains.

2. Prevention methods

(1) Improve the quality of raw yarn and cotton;

(2) Control the warping tension, appropriately extend the warping shutdown time, and stabilize the driving speed;

(3) Ensure uniform chemical materials and pure dye liquor;

(4) Prevent the occurrence of oil stains on the original yarn.

Seven, cylinder difference

1. Cause

(1) There is a small amount of residual liquid after dyeing in the previous vat, and there are various dyes in the residual liquid. Because the dye uptake rate of each dye is different, the dyeing process of the continuous vat has more times of adding dyes, which causes large errors. Lead to cylinder difference;

(2) The influence of dyeing time and temperature: long time is easy to color, and the color will be darker; the dyeing percentage will increase as the temperature drops under the condition that the dyeing can reach the process balance. Therefore, the length of the dyeing control time and the dyeing temperature will affect the dye uptake rate and cause the tank difference;

(3) The influence of alkali agent: The amount of alkali agent used will affect the combination of dye and fiber:

(4) The influence of rolling margin. The inconsistent rolling-over rate of equipment will affect the dyeing quantity of dyes. Therefore, it is necessary to ensure the same rolling-over rate.

(5) The effect of soaping: Indigo dyeing, except for individual cases where soaping is not required, generally must be washed in post-treatment, otherwise it will affect the washing fastness and rubbing fastness of the dyed material, resulting in different colors;

(6) Different dye batch manufacturers (that is, they do not use the same batch of dyeing materials) cause tank difference:

(7) The difference of yarn pretreatment; the difference of yarn pretreatment quality caused by the deviation of operation causes the cylinder difference.

2. Prevention methods

Test before dyeing to keep the raw material properties consistent.

(1) Strengthen the monitoring of the hardness of dyeing and finishing water:

(2) The dye must be fully dissolved before it can be dyed;

(3) Strictly operate in accordance with the process, strictly control the addition of residual rate, time, temperature, alkali agent and other related additives, and maintain the specified amount of dyeing mother liquor and replenishing liquor;

(4) After fixing the color, it must be fully washed and soaped to remove the floating color to obtain normal color light and fastness.