Tasks and processes of the drawing process
1. Tasks of the Drawing Process
Although the raw cotton (or chemical fiber) has been made into raw cotton slivers after going through the blowroom and carding processes, the unevenness of the long segments of the raw cotton sliver is relatively high, and the fibers in it are They are mostly in a hooked and buckled state, with poor straightening and parallelism, and there are also some small fiber bundles in the raw slivers. Therefore, it is necessary to improve the quality of slivers through the drawing process. The main tasks of the drawing process are as follows:
Merging: randomly combine 6-8 raw slivers to reduce the uneven weight of the cooked slivers.
Drafting uses drafting to improve the sliver structure and improve the straightening, parallelism and separation of the fibers.
Mixing: With the help of combining and drafting, the fibers of different properties in the cotton sliver are fully mixed and evenly distributed.
Sliver making: Make cotton sliver with uniform dryness and place it regularly in the sliver can for easy transportation and use in the next process.
2. The process flow of the draw frame
1. Feeding part: sliver can, sliver guide roller, and cotton feed roller.
2. Drafting part: drafting roller, drafting top roller, pressure mechanism, etc. The surface of the draft roller has grooves, and the top roller is also called the top roller. The top roller is driven by the rotation and friction of the bottom roller. Spring cradle pressurization, air pressure pressurization, etc.
3. Strip forming part: bundler, strip coiler, etc.
The feeding types of the draw frame include platform type and elevated type: the platform type sliver guide table is V-shaped, which can hold the slivers and arrange them in parallel, and enter the drafting device through the platform, which requires the table to be The height of the platform should not be too low if it is completely smooth, otherwise it will easily produce folding strips and breakage. There is a guide column on the platform to change the advancing direction of the cotton sliver. However, this type is neat and beautiful, has bright finished lines, and is easy to clean. However, the distance between the sliver can and the cotton feed roller is large, and the friction force is large, and the sliver is also subject to greater friction resistance when turning, so it limits the draw frame. further increase in speed. Elevated type, short circuit route, because the cotton sliver is vertically and actively pulled up and has less discount, which can reduce accidental elongation. However, after long-term parking, the sliver is easy to sag, causing accidental elongation, so it is suitable for fine combed cotton with good fiber straightness. It is generally not advisable to adopt this type of article.
At present, the more advanced draw frames abroad include Swiss Standa, German Truetzschler, Japanese Toyota, etc.
3. Merging and drafting
1. Merging function
The so-called merging is to stack two or more cotton slivers in parallel to form a whole. During the merging process, if the thick section and the thin section are merged, an obvious uniform effect can be obtained; if the thick section (or thin section) is merged with the segments of moderate thickness, due to the relative difference in weight or thickness of the sliver segments, is smaller, so the uniformity effect still exists; when thick segments and thick segments or thin segments and thin segments in the corresponding segments are combined, the uniformity of the segments is not improved, but it is not worsened either. Therefore, after the tampons are merged, the unevenness of long segments is improved.
In fact, the more cotton slivers are merged, the more opportunities there are for thick and thin segments to merge, and the chances for thick segments and thick segments (or thin segments and thin segments) to merge. The less it is, the more obvious the union and uniform effect will be.
2. Basic principles of roller drafting
Drafting is to lengthen and thin the whiskers. The function of the drafting process is to lighten the weight of the unit length of the strand and reduce the number of fibers in its cross section. Drafting also increases the degree of parallel straightening of the fibers within the strands. The essence of drafting is the relative relaxation between fibers in the strands.
Generally speaking, the ratio of the actual linear density or the actual basis weight of the beard before and after drafting is called the actual drafting multiple.
4. Quality control
1. Control of evenness
Evenness is an indicator of the uniformity of cotton sliver thickness, expressed as evenness. Evenness is an important factor that directly affects the quality of subsequent processes and even the quality indicators of cotton yarn and cotton cloth.
Irregularity includes two categories, namely regular unevenness (also called mechanical wave) and irregular unevenness (also called draft wave). The former is the periodic roughness and fineness caused by the failure of the rotating parts in the drafting part, and the latter is the roughness and fineness caused by the irregular relaxation of floating fibers in the yarn during the drafting process.
2. Quantitative control
Controlling the quantitative control of cooked slivers is an important means to ensure yarn quality, stabilize the end-break rate, and reasonably control the amount of cotton used. It is also one of the tasks of drawing.
Quantitative control is to control the difference between the average dry weight of spun cooked strips and the designed standard dry weight within a certain range. There are two adjustment ranges for the cotton sliver quantitative control box, namely, controlling the quantitative control of cotton sliver in each eye of a single machine and controlling the average quantitative control of all machines of the same variety. The former affects the uneven weight of slivers and spun yarns and the weight deviation of spun yarns, while the latter affects the amount of cotton used in each piece of yarn. Under normal circumstances, the average dry weight of a single machine shall not exceed ±1%, and the average dry weight of the entire machine shall not exceed ±0.5%. The quantitative control of cooked strips is mainly the control of a single machine.
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