Development of a Small, Covered Yarn Prototype

The small prototype of the front unwinding of the covered yarn tube refers to the idea that the wrapping of the outer yarn cover to the core yarn is formed at the front end of the hollow spindle. Its mechanical structure sketch is as follows:

The wrapping process of the small, covered yarn prototype with front unwinding of the covered yarn tube is as follows: due to the drafting action of motor 2, the core yarn is slowly unwound from the bobbin, and the core yarn is always passively unwound by constant tension due to the action of the front and rear yarn guides and the drafting action of the uniform motion of motor 2, which participates in the work of the subsequent process. When the core yarn is at the front end of the hollow spindle, the hollow spindle driven by motor 1 rotates rapidly, and the rotation of the hollow spindle drives the rotation of the fixed covered yarn tube. The rotation of the bobbin causes the wound outer cover yarn to rotate and unwind, and each time the hollow spindle rotates, the outer cover yarn is covered around the core yarn. By the functioning of the friction tensioner, the outer cover yarn will not be unwound or sloughed off because of the centrifugal force produced by the rapid rotation of the yarn bobbin. It will be actively fed only into the outer cover yarn according to the amount of outer cover yarn necessary to cover the core yarn, and the outer cover yarn will be fed evenly and actively^[6]. Finally, the fancy yarn is formed by the wrapping passes through the hollow spindle and enters the winding system by way of the yarn guide. Then motor 2 drives the rotation of the grooved drum. The groove on the grooved drum enables the fancy yarn to be regularly covered on the fancy yarn tube and provides anti-overlapping functionality to facilitate the subsequent transportation, storage, and processing. The fancy yarn tube is fixed on the frame of the yarn because the tension provided by the spring attached to the frame forces the fancy yarn tube close to the groove and evenly rotates, ensuring a good package effect. In addition, it ensures that the core yarn can maintain a uniform speed and constant drafting force when it is unwound, which will enable a more uniform covering.

The small prototype of back unwinding of the covered yarn tube is the idea that the wrapping of the outer cover yarn to the core yarn is formed at the back end of the hollow spindle. Its mechanical sketch is as follows:

The drawing system and winding system of the small covered yarn prototype with back unwinding of the covered yarn tube are the same as that with front unwinding of the covered yarn tube, but the wrapping systems are different. When the core yarn passes through the hollow spindle, motor 1 drives the hollow spindle to rotate by the conveyor belt, and the hollow spindle drives the rotation of the fixed, covered yarn tube, so that the outer cover yarn of the core yarn is rotated and unwound. Then, every time the hollow spindle rotates, the outer cover yarn is also covered around the core yarn. The functionality of the friction tensioner leads us to believe that the outer cover yarn will not be unwound and sloughed off because of the centrifugal force of the rotation of the covered yarn tube but will be actively unwound according to the needs of the core yarn covering so that the outer cover yarn can be evenly covered on the core yarn^[7–8].

Figure 1

Figure 2

The effects and performance of the covered yarn formed by different assembly methods are also different. After the debugging and testing have been done, the two different types of small covered yarn prototypes can form a good covered yarn when motor 1 rotates at 360 r/min and motor 2 rotates at 6 r/min. The different effects and properties of the covered yarn formed under these conditions are shown in Tables 1 and 2.

Yarn twist is one of the main performance indicators of covered yarn. It can be seen from Table 1 that under the same speed conditions, the twist of the covered yarn with front unwinding of the covered yarn tube is larger than that of the covered yarn with back unwinding of the covered yarn tube. It can also be seen that the twisting efficiency of the front unwinding of the covered yarn tube is higher, the covered yarn is tighter, and the tension between yarns is larger. From the standard deviation in Table 1, it can be seen that the twist fluctuation of covered yarn of the small prototype with front unwinding of the covered yarn tube is greater than that of the small prototype with back unwinding of the covered yarn tube. It can be seen that the wrapping work of the small prototype is more stable and the covered yarn is more uniform with front unwinding of the covered yarn tube. The average number of the covered yarn with front unwinding of the covered yarn tube is 92.5 tex, and the average number of the covered yarn with back unwinding of the covered yarn tube is 85.8 tex.

Yarn strength is a key performance indicator of covered yarn. The test results of the covered yarn formed by the electronic single-yarn strength tester for the two assembly methods of small prototypes are shown in Table 2.

It can be seen from Table 2 that the strength of the covered yarn with front unwinding of the covered yarn tube is slightly higher than the strength of the covered yarn with back unwinding of the covered yarn tube. The strength fluctuation of the covered yarn of the small prototype with front unwinding of the covered yarn tube is greater than that of the small prototype with the back covered hollow spindle. Furthermore, it shows that the wrapping mode of the small prototype of the back unwinding of the covered yarn tube is more stable, and the wrapping effect of covered yarn products is better.

When the core yarn is stretched and deformed, the tensile force of the outer cover yarn will gradually increase until the core yarn is broken, so the presence of the outer yarn will enhance the breaking strength of the core yarn. As the stretching continues and the core yarn is pulled off, the outer cover yarn will begin to be individually stressed, the pulling force will become abrupt, and the outer cover yarn will continue to be stretched and straightened until it breaks. When the core yarn breaks under the action of external force, the external force will abruptly change to zero, but the outer yarn will not break. At this time, the outer cover yarn will be separately stressed, and as the stretching is continued, the tension will gradually become larger and the outer yarn will continue to elongate and deform. The outer cover yarn will not be broken after the core yarn is broken but will only experience untwisting elongation. Under the same conditions, the larger the core yarn fineness, the higher the breaking strength of the core yarn and the wrapped yarn. When the core yarn is broken, the outer cover yarn untwists and elongates and then bears the tension alone. Therefore, the more the core yarn and the outer cover yarn, the higher the breaking strength of the wrapped yarn.