Spun yarn cannot be drafted, commonly known as hard ends. The fundamental reason is that the drafting force is greater than the holding force. Any factors that affect the drafting force and holding force may cause drafting. The main reasons for the inability to stretch are as follows.
1. Roving twist coefficient
When the twist coefficient of the roving is large, the tightness of the roving strips increases, the cohesion force is good, the friction resistance between fibers increases, and the drafting force increases accordingly. Under the condition that the spacing distance of the back zone of the spun yarn and the draft multiple of the back zone remain unchanged. The result is that the sliver cannot be effectively untwisted and enters the main drafting area with a larger twist, resulting in the phenomenon of unable to be drafted. However, the twist coefficient of the roving should not be too small. If it is too small, accidental drafting may occur when feeding the spinning machine, resulting in details and affecting product quality.
2. Spinning yarn guide motion
When the moving direction of the spun yarn guide stroke is the same as the twist direction of the sliver, the drafting force is large, and the holding force is less than the drafting force, resulting in a draft failure. When the twist direction of the sliver is different from that of the guide yarn When the stroke movement direction is opposite, the drafting force is smaller, which is beneficial to reducing drafting failure.
3. Roving ration
The increase in the roving basis weight means that the drafting force of the spun yarn increases. Under the same rubber roller state and under the condition of certain back zone draft multiple and roving twist coefficient, the spun yarn holding required for the heavy basis weight roving The force is greater than the holding force required for light weight roving, so the roving weight has higher requirements for the holding force of spinning yarn drafting. The ration of the roving should be adapted to the nip spacing to avoid drastic fluctuations in the drafting force of the yarn at the nip during the spinning process, which would affect the normal drafting of the spun yarn.
4. Spinning roller spacing
Small roller spacing The distance is conducive to the control of floating fibers in the whiskers, so that the drafting force of the whiskers increases during the drafting process, and the phenomenon of drafting failure is prone to occur. After the roller gauge is increased, the ability to control the floating fibers in the whiskers is weakened, so that the fibers can be well controlled and drafted normally, avoiding the phenomenon of unable to be drafted.
5. Drafting in the rear area of spun yarn
After the drafting ratio in the rear area of the spun yarn increases, the number of fibers in the cross-section of the sliver entering the main drafting area decreases, and the drafting force Reducing it is beneficial to the control of the fibers in the slivers by the drafting jaws and reduces the phenomenon of draft failure, but in general, it is not conducive to the improvement of yarn quality. Nowadays, most production enterprises use a larger center distance between the back rollers of the spinning yarn, a smaller draft multiple in the back area, and a larger twist coefficient of the roving.
6. Spinning yarn nip spacing
Small The jaw spacing block is conducive to strengthening the control ability of the apron jaws on the drafted yarn, and has better control over the edge fibers of the sliver when the fiber speed is changed, thereby improving the yarn dryness. After the distance block is increased, the control force of the apron jaws on the whiskers is weakened, which can reduce the phenomenon of draft failure, but it will have a certain impact on the quality of the yarn.
7. Spun yarn roller pressurization
Roller pressurization If it is small, the drafting jaws have weak control over the fibers, resulting in the fibers in the slivers not being well controlled and unable to be drafted. After the roller pressure increases, the friction force of the drafting jaw increases, so that the fibers in the sliver can be well controlled and drafted normally. The pressure of the front, middle and rear gears of the cradle should be distributed reasonably to avoid drafting failure in the rear area and resulting in failure to open.
8. Spinning yarn roller
For surfaces with paint The surface coating of the new rubber roller is thicker, and the gripping force on the surface of the rubber roller is greatly weakened. During the drafting process, the slippage rate of the rubber roller is high, so that the yarn cannot be effectively controlled and hard ends are easy to occur. The paint layer on the surface of the old rubber roller is thin, and the friction factor on the surface of the rubber roller is large. The holding force of the rubber roller on the yarn sliver is greater than the drafting force of the yarn sliver, and the sliver can be stretched normally. If the rubber roller is not treated, there is no chemical treatment on the surface. The surface of the rubber roller can be in direct contact with the whiskers. The friction coefficient is large and the larger holding force can overcome the larger drafting force. It is an effective measure to solve the problem of unable to stretch. . In winter, due to the low temperature, the top roller will become hard if not treated, the slipperiness rate will increase, and hard heads will easily occur.
9. Raw material status
In daily production, raw materials is in a state of change at any time,When the fiber quality length in the cotton sliver is lengthened (such as increasing the combed sliver content) or the length uniformity is good, the friction coefficient between the fibers in the sliver becomes larger, and the drafting force response increases during the drafting process. When the spinning process remains unchanged, In this case, the drafting jaws cannot effectively control the fibers in the sliver, resulting in the sliver not being able to be drafted normally and the phenomenon of inability to be drafted, and other processes need to be adjusted.
10. Temperature and humidity
When the workshop humidity increases, The friction coefficient between the fibers in the sliver becomes larger, and the frictional resistance response increases, which increases the drafting force of the sliver. When the spinning process remains unchanged, the drafting jaws cannot effectively exert an effective force on the fibers in the sliver. Control, there is a phenomenon of inability to stretch. The workshop should reasonably control temperature and humidity according to seasonal changes, raw material conditions and other factors to ensure normal production and avoid drafting failure.
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