In textile machinery, roller yarn drafting devices are widely used in yarn drafting. Conventionally used pressurizing devices are divided into pneumatic pressurization and spring pressurization. Roller pressurization directly affects The smooth progress of drafting affects yarn uniformity, strength and other properties.
1. Roller drafting
Spinning frames basically consist of a feeding mechanism, drafting Mechanism, twisting and winding mechanism. The drafting mechanism of the spinning frame is composed of several pairs of drafting rollers. It is generally an apron drafting type. It can have a long bottom apron type and a short top apron type, a double short apron type, etc. The bottom roller of each pair of rollers is a steel grooved roller. , arranged along the entire length of the spinning frame and installed in the bearing seat of the roller seat. The middle and rear roller bearing seats can move along the roller seat chute to adjust the distance between the front, middle and middle and rear bottom rollers. This distance is called the roller gauge, which is one of the main process parameters of the spinning machine and can be adjusted according to conditions such as fiber length and pressure. If the middle top roller with a circumferential groove in the middle is used, the middle apron roller only plays a role in controlling but not holding the fibers, and the fibers will slip under the jaws of the middle roller. In fact, the three pairs of rollers only constitute a drafting area. The roller pressure value is also one of the main process parameters of the spinning frame. Modern drafting mechanisms often use springs or gas static weighting arms for pressure. When pressurizing, press down the handle and use the locking mechanism to pressurize the roller; when depressurizing, lift the handle to lift the entire cradle together with the top roller, upper apron and top apron pin. The use of heavy pressure, small spacing, and tight jaws can increase the draft multiple and improve the uniformity of the yarn.
The drafting roller is an important part of the drafting mechanism. It and the rubber roller form the roller jaw to hold the yarn sliver for drafting.
In the front drafting device, a curved drafting channel is formed between the upper and lower rubber rings, the jaw spacing is narrowed, and the rubber rings are heavily pressurized and shortened. The distance between the jaws and the front roller jaws can greatly improve the control of the movement of various types of fibers during the drafting process, resulting in higher drafting capacity. The rear area is a simple roller drafting, so a heavy pressure and large gap process is adopted.
Roller pressure is the most basic and positive factor in the gripping force of the nip. The rear roller pressure has little effect on the control force of the drafting process. The front roller pressure is the main factor in the control of the nip. The key to oral guidance. Roller pressure has a significant impact on the slipperiness and speed unevenness of aprons and rubber rollers.
The roller pressure in the drafting device is closely related to the yarn quality. The front roller pressure is mainly to ensure the uniformity of the yarn; the back roller pressure is mainly to ensure the yarn quality. Yarn unevenness and apron roller pressure are mainly to ensure the correct and stable running speed of the apron. Therefore, reasonable and appropriate improvement of pressure distribution is the basis for increasing draft and improving yarn quality.
Roller pressure is related to holding force and uniformity. Different roller pressures have different draft values. If the pressure is too small during the pressurization process, the evenness will be poor. If the pressure is too high, the evenness will be better, but the roller will not be able to withstand the great pressure and the roller will bend, so only uniformity will be achieved. Only when the pressure is adjusted to a moderate level can the spun yarn be of good dryness.
The holding force is determined by the friction coefficient between the upper and lower rollers and the whiskers and the pressure on the rollers. Therefore, in addition to the roller pressure, the factors that affect the holding force mainly include the hardness of the top roller, the shape and number of grooves on the surface of the roller. At the same time, due to the wear and tear of the top roller, the core of the top roller is lack of oil and is inflexible in rotation. , roller groove edge polishing, etc., also have a great impact on the holding force. In roller drafting, in order to make the drafting proceed smoothly, the roller jaws must have sufficient holding force on the sliver to overcome the drafting force during drafting of the sliver. In the spinning process, in order to ensure smooth drafting, the front roller of the spinning frame must have sufficient and reasonable holding power to overcome the drafting force of the yarn. This holding force is the maximum friction force between the yarn and the roller jaws, and its size is determined by the roller pressure and the friction coefficient between the fiber and the roller. The sliver held by the rollers is affected by the drafting force and has a tendency to slip under the jaws, causing the sliver to be defective. If the holding force of the roller is greater than the drafting force, the sliver will not slip.
The drafting force is related to factors such as the number and structure of the fed whiskers, the straightness of the fibers, the properties of the fibers, friction and drafting multiples. The traditional straight-line drafting of the rear area of the spinning frame uses simple roller drafting, and the friction in the middle is weak. It often only relies on changing the twist of the roving and adjusting the distance between the front and rear areas to control the movement of the fiber. This is very helpful for improving the performance of the spinning frame. The total draft ratio is unfavorable.
2. Experiment on the impact of pressurization on product quality
The experiment is divided into three groups, each group is Spin bobbins at different pressures and then compare the yarn quality of each set.
The experiment used 16tex carded yarn. The experimental conditions and yarn performance data are as shown in Table 1. The changes in yarn dryness and strength under different roller pressures are shown in Figures 1 and 2.
Figure 1 Different roller pressure Under the circumstances, the yarn stem changes
Figure 2 Yarn strength under different roller pressure conditions Changes
By analyzing Table 1, Figure 1, and Figure 2, it can be seen that under different roller pressures, there are differences in the quality of the yarn spun. The pressure distribution of condition 2 can Obtaining lower yarn unevenness and higher yarn strength is the optimal roller pressure.
In order to ensure smooth drafting, the roller jaws must It has enough holding power to overcome the drafting force. If the holding force of the jaws is less than the drafting force, the whiskers will slip under the roller jaws, which may cause unevenness of the product at best, or the whiskers cannot be pulled at worst. Stretch and thin. The holding force of the roller jaws is mainly determined by the roller pressure, the dynamic friction coefficient between the jaws and the whiskers, and the thickness and geometric shape of the held whiskers.
As the pressure on the rubber roller increases, the actual pressure of the rubber roller on the yarn sliver increases accordingly, and the gripping force of the jaws increases accordingly. However, the pressure on the rubber roller should not be too heavy, otherwise it will cause serious deformation of the rubber roller and bending of the roller. , torsional vibration, thus causing regular unevenness, and even causing the transmission gear of the drafting part to burst.
3. Conclusion
Through the research and optimization of different roller pressures, the optimal roller pressure was obtained. By adjusting different roller pressures, its effect on the yarn was found. Different roller pressures are related to the yarn being spun. The evenness and strength of the thread are closely related to its properties.</p
