The impact of winding and twisting processes on yarn quality
Multiple sets of tests were conducted using Uster evenness testers under different process conditions to analyze the effects of winding and twisting processes on yarn evenness, thick places, details, and neps. It was pointed out that: from the tube The fundamental reasons for the deterioration of evenness from yarn to package are friction damage and changes in yarn linear density and twist redistribution due to tension. The evenness of single yarns can be improved through the twisting process, and different twisting process routes have different effects on the yarn. Evenness CV values have different effects.
0 Foreword
Yarn quality has always attracted people’s attention, and an important indicator to measure yarn quality – yarn evenness , is more valued. People have discussed more about the influence of spinning and pre-processes on yarn evenness, but less research has been done on the changes in yarn evenness after winding and twisting. The following is a discussion on the effects of winding and twisting on yarn evenness.
1 The influence of the winding process on the yarn dryness
From the bobbin to the package is achieved by the grooved drum frictionally driving the bobbin to wind up the yarn at a certain speed. In order to obtain a package that meets quality requirements, the yarn must have a certain winding tension. While winding increases the package capacity, the yarn clearer removes some occasional (harmful) yarn defects in the yarn, such as thick spots. , details, neps and impurities. However, during the winding process of the yarn, affected by the friction of the machine parts and the winding tension, the uniformity of the yarn stem changes. Next, the USTER evenness tester is used to test the CV value of the yarn evenness, and count the details, thick places, and neps. A group of 10 spun yarn bobbins was used to wind the bobbin yarn under different winding process conditions, and the changes in the CV value, details, thick places and neps of the bobbins were compared one by one with the bobbins.
1.1 Statistics and analysis of test data
There are 48 sets of Uster evenness CV value test data corresponding one-to-one from bobbins to cones, and 14 sets of data are collected, totaling 62 sets. , the winding uses different bobbins, different processes and equipment conditions.
1.1.1 Statistical analysis of evenness CV values from bobbins to cones
In the comparison of evenness CV values from bobbins to cones, 58 groups increased. , accounting for 93.5% of the total statistical groups, of which 84% increased by no more than 0.4 percentage points. Only 4 groups decreased, accounting for 6.5% of the total statistical groups. Among these 4 groups, 2 groups were tested on automatic winding machines with low line speeds, 1 group was tested on the metal trough of the 1332M winding machine, and the other group was tested because there was a tube in it. It is caused by the influence of too high evenness CV value in the yarn test. Statistics show that the evenness CV value of spun bobbin warp cone and cone yarn generally shows an increasing trend.
1.1.2 Statistical comparison of thick places and neps from bobbin to cone yarn
According to statistics, the proportion of increased details and neps from bobbin to cone yarn It reaches about 65%, and the thick places are reduced. It is worth noting that among the 21 groups where neps were reduced, the thick places were also reduced at the same time. Among them, 7 groups were tested on the automatic winding machine. There are 8 groups tested on the metal trough of the 1332M type rolling machine.
1.2 The influence of winding technology and equipment on the CV value of evenness
1.2.1 Comparison between automatic winding machine and 1332M type winding machine
It can be seen from Table 1. The impact of winding on the CV value of the yarn with the 1332M type winding machine using a lower linear speed is less than that of the automatic winding machine using a higher linear speed. This is because as the speed of the trough drum increases, the trough drum has a greater impact on the yarn. The increased friction will have a negative impact on the CV value of the evenness.
1.2.2 The impact of the gap-type anti-overlapping device of the 1332M type winding machine on the CV value of the evenness (see Table 2)
As can be seen from Table 2, the 1332M type winding machine When the gap-type anti-overlap device is used correctly, the impact on the CV value of the evenness is equivalent to that of the non-gap anti-overlap device.
1.2.3 The influence of winding tension and speed on the yarn backbone CV value
With the increase of winding tension and speed, the yarn backbone CV value shows a worsening trend, and the relevant data have been There are analysis and statistics, which will not be elaborated here.
1.3 Analysis of the causes of changes in evenness CV value caused by webbing
1.3.1 Evenness fluctuations caused by friction
Transmission mode and channel components to the yarn Damage to the line stem causes the stem to fluctuate. In the winding process, in order to ensure the normal unwinding of the subsequent processes, the bobbin yarn needs to be wound into a conical bobbin yarn. When winding cone yarn, there is only one point on the simple yarn whose linear speed is equal to the linear speed of the grooved drum. This point is called the transmission point. When the cone yarn rotates, the large end of the linear speed is greater than the transmission point and the small end is less than the transmission point. Therefore, sliding and friction will occur between the big end and small end of the package yarn and the grooved drum. The friction will cause damage to the yarn wound on the surface of the package yarn. At the same time, due to the relative sliding and friction of the yarn in the groove of the trough, the damage to the yarn is even greater, especially at the corners. The friction and damage to the yarn by the trough, the yarn guide, the tension device and other channel components cause the fiber to fail. Details, slugs and neps are created as they break free from the yarn structure. By performing a correlation analysis on the +50%, -50%, +200% defects and evenness CV values recorded in the evenness tester, we can get: The correlation coefficient r between the +50% thick spot defects and the evenness CV value is: The correlation coefficient r between -50% detail defects and evenness CV value is 0.7465, and the correlation coefficient r between +200% nep defects and evenness CV value is 0.The twist angle tends to be a constant value everywhere above. Since the twist at the details is greater than the average twist of the yarn, the density at the details also increases due to the increase in twist, while the opposite is true at the neps and thick places.
Since yarns with different twists have different twist elongation and twist contraction, it directly affects the density of the yarn and changes the evenness CV value.
During the twisting process of the yarn, affected by the tension, the yarn is stretched by traction and the friction damage of the machine parts causes the yarn density and fiber structure to change, thereby changing the yarn dryness CV value. There are also changes.
3 Conclusion
(1) From bobbin to package, evenness CV value shows an upward trend. Details and overall neps are also increased, but the use of metal grooves is beneficial to the improvement of neps.
(2) The fundamental reasons for the deterioration of evenness from bobbin to package are friction damage, changes in yarn density, and redistribution of fibers and twists due to tension.
(3) Reduce details below -50% and +50%, and thick spots above are beneficial to the improvement of yarn texture.
(4) The 1332M winding machine with a lower linear speed has less impact on the CV value of the slivers than the automatic winding machine with a higher linear speed; it is reasonable on the 1332M winding machine The use of gap-type anti-overlap devices does not have much impact on the CV value of the strips.
(5) Twisting a single yarn can improve the evenness. Single yarns with different twists have a certain impact on the evenness CV value of the strands when twisted. Different process routes during yarn twisting have different effects on the CV value of the yarn stem.
(6) The CV value of the strands has a certain curvilinear relationship with the twist of the strands. During twisting and stretching, the CV value of the strands shows an upward trend as the twist increases, but as the twist increases, the CV value of the strands shows an upward trend. When the strands are twisted and shrunk, the CV value of the strands shows a downward trend. Since twist expansion or contraction occurs during the twisting process, the structure of the strands undergoes fundamental changes. Therefore, the merger theory cannot be used to simply deduce the CV value of the strands.
(7) The influence of different twisting elements, ordinary yarn guide hooks and twist-resistant yarn guide hooks on the CV value of the yarn line is not obvious. Depending on the yarn number and twist, the reasonable selection of travellers can improve the yarn dryness.
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