The manufacturing process of denim is unique in that it is a product that is first warp dyed and sized with indigo and then woven. The production process of denim is also quite complex, with the following main steps.

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(1) Dyeing and sizing. The indigo dyeing of denim warp yarns is done in three ways: rope dyeing, piece yarn dyeing and hanging ring dyeing. The first two are connected to the sizing, and the latter is dyed and then sized.　

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Rope dyeing and sizing On a spherical warping machine, 350 to 400 warp yarns are sorted into multi-stranded ropes with a length of 10,000 to 15,000 m. Then 12 to 36 strands of ropes are fed side by side into a continuous dyeing machine, where they are dyed and then dried and wound into a barrel. In the long chain beam warping machine, the ropes are then dispersed and wound into individual warp yarns. These warp yarns are then fed into the sizing machine and wound into beams according to the total number of warp strands required.　　

 

The disadvantage of rope dyeing is that the dyeing, oxidation and washing are not sufficient, and the equipment is huge, generally covering an area of about 1000m2 , with a height of about 8m.②Sheet dyeing and sizing: Sheet dyeing is commonly known as warp dyeing. The warp yarn is warped into a piece of yarn rather than into a multi-strand rope into the dyeing machine. This type of dyeing is characterized by a uniform arrangement of the warp yarns, fast and even colouring, sufficient oxidation and easy washing. The colour is pure, homogeneous and vivid after dyeing. In addition, the investment is low and the area occupied is about half that of a rope dyeing machine.

 

The disadvantage is that the cotton yarns are arranged in single ropes and are prone to tangled shafts, which are not easily detected, especially under the liquid surface. Due to the slow dyeing speed, it is also possible to produce two dyeing machines in combination with a sizing machine, which doubles the efficiency, i.e. a double warp beam piece yarn dyeing machine.　

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The current production plants for piece yarn dyeing machines include the Swiss company Sulzer and the German company Zell. Suspension ring dyeing: This method uses a single dyeing trough in which the warp yarn is repeatedly dyed in several cycles until the required depth is reached.

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The dyeing and sizing process is: Alkali cooking (or wetting): sodium hydroxide 2 to 3g alkali-resistant penetrant 1g / L temperature 95 to 100 degrees time 20 to 30S indigo dyeing: indigo (2 + χ) g sodium hydroxide 2 . 5g insurance powder (85%) 2g/L bath volume approx. 1000L temperature room temperature time 20S Because of the low colouring rate of indigo on cotton fibers, the poor fastness when dyeing at high temperatures, the high consumption of insurance powder and the dark red colouring, it is dyed several times at room temperature. This is the colouring characteristic of denim. In order to obtain a pure colour, indigo dyeing is done without oxidizing agents and with natural oxidation by air. As indigo has the property of being easily reduced and not easily oxidized, it is also oxidized repeatedly. The temperature of the water is room temperature. During the washing process, the floating colour, residual alkali and impurities are removed on the one hand, and the oxidation can be continued on the other hand, so that it is fully oxidized.　　

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In order to save indigo dye, Sulphur black can be used as a base without the alkali cooking process, first dyed as a light grey and then dyed indigo. After dyeing, if the finished product is red, the amount of sodium hydroxide can be reduced, and the amount of greenish colour is reduced by the amount of insurance powder, which in general does not destroy the state of indigo's hidden colour body.　　

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(2) Weaving. At present, the world's denim weaving is widely used shuttle less loom, accounting for about 80% or more. Shuttleless loom in the most for the piece of shuttle loom, followed by rapier loom, the least for the air jet loom. The heavy denim fabric processed by the slice shuttle loom can reach 551g/㎡, while that woven by the air-jet loom can only reach 407g/㎡.

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As the warp and weft yarns of denim are of different colours, faults such as uneven weft streaks are clearly exposed on the fabric. In addition, sometimes raw yarns are used for the weft, which can also cause weft stalls due to the yellow and white yarns. To prevent this, we can use a weft mixing device or dye the weft yarns in a light grey colour.　　

 

Weaving with large warp beams and large take-ups. This is due to the coarse yarn count, the high turnover and the fast machine cycle, so large warp beams must be used, generally 800 mm in diameter, the fabric roll usually 560 mm. if rolled off the body, using large rolls up to 1500 mm (about 600 m of denim can be accommodated), but special carriers and verification equipment are required.　　

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Variations in weft tension during weaving can also produce transverse stalls on the fabric surface. Although a single weft guide on a shuttle less weaving machine can avoid the difference in tension between shuttles on a shuttle weaving machine, additional yarn storage is required to eliminate the difference in tension between the size of the cylinder yarn and the quality of the cylinder yarn winding. The yarn tension provided to the weft clamp by the weft storage device should be consistent, which is particularly important for stretch fabrics.　　

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Denim has coarse yarn counts, wide widths and high warp tensions. In order to have a clear opening, the healed frame movement must be positive. Some shuttle less weaving machines still use spring return heralds, which are not suitable for coarse and thick fabrics. This is why an external treadle device is available. The treadle opening movement is controlled precisely by means of a compound treadle. The movement of the treadle is driven by means of a rotor bar, a treadle healed bar and a healed frame drive linkage, and is equipped with a shed opening levelling device which allows all healed frames to be adjusted to the same height.　　Variations in warp tension during weaving can also cause weft faults (especially weft breaks).

 

This problem can be solved by using an external treadle device. This is because the warp feed, winding and weft beating do not move when weft breaks are looking for the weaving opening. The pedals can be moved independently and the warp tension does not change. This device is available as a separate motor drive on the picaro 174 PGWMA rapier weaving machine and as a handwheel drive on the Toyoda - Sulzer PU130 MWE10D,R shuttle weaving machine, both patented.　　

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(3) Finishing. The shrinkage of denim blanks is above 10% and can only be reduced to less than 3% by pre-shrinking treatment. The general requirement is that the shrinkage is within 1. 5% to 2 %.　

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Process: which desizing with BF --- 7658 enzyme effect is good, soft to the touch and no damage to the colour. After the garment is made and then washed with volcanic stone, sodium hypochlorite, acid, rubbing and other treatments, made of stone wash, snow wash (also known as marble wash), rubbing and other varieties. There are now new products such as bio-wash with cellulase.

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