The “loop effect” of the draw frame is a common and recurring problem in the pre-spinning draw frame process. It is a problem that has plagued the draw frame process of Chinese spinning enterprises for many years.
The loop effect wave can be naturally eliminated in the tension drafting of the subsequent process, although it It will not affect the quality of the yarn, but it will distort the calculation value of the draw evenness. It may also overlap and confuse with the real mechanical wave wavelength, causing the fake to be ignored or misjudged. Therefore, it is necessary to find out the cause and eliminate it in time.
The “loop effect” often occurs when the vehicle speed is low, such as FA302, FA306A, etc., which may occur below 270 m/min, and the wavelength of the sliver can is appears in multiples of diameter. Taking the barrel diameter of 400mm as an example, when the vehicle speed is below 270 m/min, the “loop effect” wave at around 760-800mm will often be displayed on the spectrum.
01 Judgment method and causes
Put in the evenness meter If the “mechanical wave” disappears after walking over the strip that has been passed, this wave is the circle strip effect wave.
Why does the draw frame appear a loop effect at low speed? This is because most of the spinning mills currently use high-speed draw frames, and the speed corresponding to the coiling disc design is mostly above 320 m/min. The coiling disc design outlet position is at the intersection of the spiral curve duct and the bottom plane of the coiling disc. The pointed top of the elliptical outlet formed at . When the drawing speed is below 270 m/min, the coiling tension formed by the coiling disk and the spatial spiral curve duct is significantly reduced. Not only does the sliver running trajectory in the coiling disk duct change, but also the position of the sliver at the exit changes. A large displacement also occurs to form a deviation, that is, it breaks away from the top of the original elliptical outlet tip and comes out from the elliptical outlet of the coil plate at a position about 1/3-1/4 retracted from the inner side. However, the manufacturer has no chamfering at all on the inner side of this outlet or the chamfering of the process corner is very small. The cotton sliver is suddenly and strongly folded and squeezed regularly at this corner, and the cross section of the sliver is instantly deformed sharply, which is reflected on the spectrum. It is a “mechanical wave” with periodicity, regularity, and even “chimney rush”.
The wave generated by the “deformation” of the cross-sectional shape of the sliver is only that the cross-sectional shape becomes flatter, but the sliver is uneven and the fiber movement does not change or only changes slightly. , it is not a mechanical wave caused by a defect in any rotating part that causes regular changes in fiber motion. The “waves” of the two are essentially different.
02 Solution
1. Start by improving the process and increase the speed of the draw frame by at least 330 Use m/min or above.
The main problem in the current domestic cotton drawing process design is that emphasis is placed on the main area and the back area is underestimated, and there is insufficient understanding of the importance of optimizing the back area distance and draft multiple in the design of the back area. We quote a product promotion statement from a world-famous draw frame: “Draft depends on the setting of the back draft that is closely related to the factory’s spinning plan and raw material selection. If it is not set correctly, the impact of bad indicators will be amplified in the yarn”. The importance and depth of understanding that international brands attach to the key role of the back zone in drawing process design can be seen. According to personal experience, when spinning 38mm chemical fiber, the back space should be selected within 22-30mm according to the fiber fineness. Under the constraints of small pitch conditions, the drafting multiple of the rear area can only be very small, and it is impossible to enlarge it to the ideal state. This directly causes the drafting multiple of the main area to be too large. Not only are various technical indicators difficult to guarantee, but the actual use speed can only be reduced. , and one of the direct consequences of low speed is the emergence of “loop effect” waves.
2. It is also possible to leave the process unchanged, not increase the speed, and only eliminate the “loop effect”.
This is a solution for special varieties and special circumstances that require the use of draw frames at low speed. Use a small file to file the inner surface of the exit of the coiling disk (the current actual strip exit position, which has obvious friction marks) into a larger fillet (especially be careful not to “leak” the joint between the inclined tube and the lower surface of the coiling disk) , then welding repair is required) and polished with “0” metallographic sandpaper or toothpaste.
If a new type of aluminum alloy is used for one-piece casting and forming of coil bars, it not only has many advantages such as light weight, smoothness, durability, good molding, smooth strip removal, etc., but also because of its casting The thick wall of the aluminum chassis will not cause “filing leakage”. After filing, the coiling disc can be adapted to high, medium and low speeds, which is another way to solve the coiling effect. </p
