DTY – Drawn Textured Yarn

Properties of Drawn Textured Yarn

Drawn textured yarn (DTY) can also come in a variety of colors, including semi-dull, raw white, dope-dyed black, and dope-dyed hues.

Drawn textured yarn has good insulation properties, so it is helpful for insulated and warm clothing.

Lightweight with good covering properties and good extensibility.

Due to drawn textured yarn it gives a woolly and mat appearance.

Drawn textured yarn has high wear and tear resistance.

DTY yarn has a very low moisture content.

Quality metrics for Drawn Textured Yarn

Strength and Elongation

For the strength of fibers, the higher the better, for drawn textured yarn (DTY), the strength of 2.5cN/dtex and the elongation of 12% to 30% can meet the requirements of weaving and wearing. The higher its toughness (strength x elongation/2), the better. Fibers with high toughness not only have good internal quality, but are also wear-resistant and fold-resistant. In actual production, different weaving methods have different requirements for tenacity. For example, weft knitting machines require DTY yarn to have a much lower strength than warp knitting and weaving. The elongation range of DTY yarn for weft yarns is wider, but the elongation of warp yarns cannot too high. In DTY yarn production, the strength and elongation are generally controlled by adjusting the draw ratio of the filament. As the draw ratio increases, the strength of the filament increases and the elongation decreases. However, when the stretching ratio is too large, the strength and elongation of the filaments will decrease.

Crimp Performance

The crimp properties include crimp rate KE, crimp stability KB and boiling water shrinkage. High shrinkage rate, DTY yarn has a plump feel, beautiful appearance and good elasticity. Crimp stability indicates the degree of gradual loss of crimp during weaving and wearing, and is inversely proportional to crimp. Therefore, these two indicators must be taken into account in actual production. DTY yarn with a higher shrinkage rate can cover up part of the uneven dyeing, so the shrinkage rate is often controlled to be slightly higher during the production process. However, if DTY yarn is dyed with a bobbin in post-processing, the bobbin shrinkage of DTY yarn with a high shrinkage rate is large, making it difficult to unwind the bobbin after dyeing. If DTY filaments are used for dyeing or dyeing after weaving into fabrics, there is no limit, and the shrinkage rate can be controlled to be higher at this time.

Evenly Dyeing

For DTY yarn with high physical properties such as strength, elongation, crimping rate, evenness unevenness and fiber structure unevenness, there will be disadvantages such as horizontal stripes and color difference after weaving into fabrics. Therefore, it must be controlled during the DTY yarn production process and detected in time after the finished product inspection, so as to avoid the DTY yarn with poor dyeing uniformity from being mixed into the normal products, resulting in a large amount of degradation of the final fabric.

Broken Filament

One of the main quality problems of drawn textured yarn at present is the broken filament, which will affect the smooth progress of the post-weaving process and the quality of the fabric. Different weaving processes have different requirements for broken filament. The drawn textured yarn for weaving needs to be woven after twisting, sizing or networking, so the requirements for fluffing are not strict. The drawn textured yarn used by the water jet loom does not want broken filament. In the knitting process, the weft knitting yarn has a short weaving process and low speed, so the requirements for broken filament are not strict; while the production speed of the warp knitting yarn is high, each DTY yarn must pass through the needle eye, and the broken filament is easy to cause end breakage , should be strictly controlled.

Ossified Filament and Tight Spot Filament

Ossified filament refers to the segmented, continuous and non-fluffy tightly twisted filaments that appear on DTY yarn. Tight spot filament refers to the unserious ossified filament, that is, the continuous length of the ossified filament is very short, almost point-like. Ossified filament and tight spot filament can be judged by visual inspection and appearance classification. The ossified filament can also be identified on dyed stockings. It is darker than the normal filament and has a strip shape. Tight spot filament has dark spots on the sock shaft, which is generally difficult to distinguish.

Principle of False Twist Deformation

False Twist

If one end of the filament is fixed, hold the other end to make it rotate by itself. Every time it rotates, a twist is added to the filament. Turn counterclockwise to get S twist, and turn clockwise to get Z twist. If both ends of the filament are fixed, and the middle part is held and rotated, with the holding point as the boundary, the upper and lower parts will respectively have the same number of twists and opposite twists.

If the filament passes through the fixed points at both ends in a moving manner and rotates the holding point, the twist will change. Along the moving direction of the filament, before the holding point, the filament is twisted (assuming Z twist) ; After passing the holding point, add S twists equal to the number of Z twists. Since the upper and lower twist directions of the holding point are opposite, in fact all the Z twists added before the holding point are untied. This process of twisting first and then untwisting is called false twisting.

On the false twist texturing machine, the small rotor is a rotating holder, and the feeding roller and the intermediate roller not only fix the two ends of the filament, but also continuously transport the filament forward. The filament is twisted before entering the small rotor, untwisted after exiting the small rotor, and finally the filament is untwisted.

Heating and Cooling

Heating and cooling are necessary to exploit the thermoplastic properties of synthetic fibers to obtain false twist effects. Heating is carried out in the twisting stage of the false twisting process, the purpose of which is to use the thermal movement of molecules to eliminate the internal stress caused by twisting and to fix the twisting deformation. In addition, the plasticity of the filament increases after heating, and the rigidity is weakened, which can reduce the twisting tension and facilitate twisting.

The purpose of cooling is to fix the plastic deformation obtained by twisting deformation. If the filament in its thermoplastic state passes immediately through the rotating holder (small rotor), untwisting will not work, resulting in a stiff filament with very poor bulk. When cooled to below the secondary transition temperature (glass transition temperature, 81°C), the deformation after twisting has been solidified. Although untwisted, each single filament still retains its original curled shape, which appears fluffy and elastic.

To sum up, the false twist deformation is to use the thermoplasticity of the filament, heat and shape after twisting, then cool, and untwist all the added twist after cooling. Due to heating and cooling after twisting, the curved shape of the filament is fixed, and the filament still maintains the curved shape after untwisting.

Notes on DTY Yarn Production

The so-called good product is to meet the specified needs and potential features. In simple terms, it is able to bring a good sense of experience to users. For example, in our texturing industry, texturing workers are users of raw material POY, and are very sensitive to the quality of raw materials. Bad tails, fluff, uneven tension, broken wires for no reason, etc. If the user experience is not satisfactory, it is generally because the quality of the raw materials is not good.

Then, most people don’t know how our own product DTY yarn will give downstream users the experience, so the texturing process lacks a little awareness of product quality. From the process point of view, if you can understand the use characteristics of the next process, it is the key to do a good job in the quality of this process.

Understand the Customer’s Process Characteristics

When working in a nylon DTY yarn processing factory, even though I have worked in workshop management and production positions for many years, sometimes I still don’t know what kind of DTY filament the customer needs. We only know that according to our consistent experience, we can make conventional standard DTY filaments, and take “not stiff or fluffy, and all indicators are balanced and sufficient” as the process standard, and it is good for customers to buy it back without any problems. Even if a customer complains, it is only a partial solution to a certain problem, and there is no systematic overall quality management. In fact, to be precise, in order to subdivide customer complaints, at the very least, we need to understand which link has the problem and what is the root cause of the problem? However, these post-event remedies have caused losses to customers after all. Therefore, quality management must focus on “goals”, refine each link, and have a complete understanding of the requirements and characteristics of each process. Taking blanket enterprise customers as an example, there are processes such as weaving, pre-finishing, brushing, ironing, shaping, printing and dyeing, post-finishing, and finished product packaging. The following briefly describes the processes that are directly related to DTY yarn and the quality management key control points in .

The first is the weaving process. Good weaving can increase the weaving output and ensure that the loom can produce the proper number of meters of cloth in one shift. When DTY yarn adjusts the process, it is necessary to know which loom will be used to weave these batches of DTY yarn. The characteristics of warp knitting and weft knitting are different, and the process must be targeted. According to experience, if the product satisfies the weaving process, it can meet 60%/70% of the needs. The first requirement of weaving is that it should be easy to do and not easy to break. This requires DTY yarn to have good strength, good bundling, good shaping, and good unwinding.

The use of warp knitting upper creel also requires small residual torque and no excessive looping. When using warp knitting upper warping machine, it is especially required that the fixed length of DTY yarn is consistent, while weft knitting also requires the standard tail of DTY yarn, which not only reduces Reduce the labor intensity of weaving workers, promote work efficiency without wasting raw materials.

Secondly, there should be no horizontal bars for circular knitting machines, and no vertical bars for warp knitting machines. This requirement is reflected in the texturing machine to check the differences between each spindle position to ensure the quality consistency of each DTY yarn.

Thirdly, the weight of the cloth is up to the standard, and there are precise requirements for the fineness of the facing filament under the condition of a certain bottom thread. If weaving is still a preliminary judgment on the condition of the cloth surface, then the pre-trimming, brushing, and ironing processes are another exact test of the smoothness of the cloth surface and the consistency of the stripes.