The inability to draft the spun yarn is 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 the inability to draft. The main factors include raw materials, technology, machinery, temperature and humidity, etc., which will seriously affect the quality of spun yarn and the production efficiency of spun yarn.
Raw material status
In daily production, raw materials are in a state of change at any time, and the fiber quality length in the cotton sliver is lengthened (such as Increase the combed sliver content) or the length uniformity is good, the friction factor between the fibers in the sliver becomes larger, and the drafting force increases accordingly during the drafting process. When the spinning process remains unchanged, the drafting jaws cannot The fibers in the sliver are effectively controlled, resulting in the sliver not being able to be drafted normally and causing the problem of inability to be drafted. Other processes need to be adjusted.
Roving twist coefficient
When the roving twist coefficient is large, the tightness of the roving strip increases, the cohesion force is good, and the friction resistance between fibers When the yarn is increased, the drafting force increases accordingly. Under the condition that the spacing of the back area of the spun yarn and the drafting multiple of the back area remain unchanged, the sliver cannot be effectively untwisted and enters the main drafting area with a larger twist. , and the problem of inability to stretch occurs. 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.
Roving basis weight
The increase in roving basis weight means that the drafting force during spinning drafting increases. In the same rubber roller state When the draft multiples of the lower and rear areas and the roving twist coefficient are constant, the holding force required for the spun yarns with heavy weight rovings is greater than the holding force required for light weight rovings, so the roving weights have a negative impact on the spinning draft. There are higher requirements for strength. 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.
Spinning yarn guide motion
When the moving direction of the spun yarn guide motion is the same as the twist direction of the whiskers, The drafting force is the largest, and the holding force is less than the drafting force, resulting in the problem of drafting failure. When the twist direction of the slivers is opposite to the direction of movement of the yarn guide, the drafting force is smaller, which is beneficial to reducing drafting failure. .
Spinning roller gauge
A small roller gauge is beneficial to the control of floating fibers in the whiskers, but it will The drafting force of the whiskers increases during the drafting process, and the problem of drafting failure is prone to occur. After the roller gauge is increased, the ability to control the floating fibers in the strands is weakened, so that the fibers can be well controlled and drafted normally, avoiding the problem of insufficient drafting.
Drafting in the back area of spun yarn
After the drafting multiple in the back area of spun yarn increases, the hair entering the main drafting area The number of fibers in the cross section of the sliver is reduced, and the drafting force is reduced, which is beneficial to the control of the fibers in the sliver by the drafting jaws and reduces the problem of unable to be drafted. But in general, it is not conducive to the improvement of yarn quality. Most current production companies 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 to solve this problem.
Spinning yarn jaw spacing
The smaller jaw spacing block is beneficial to strengthening the grip of the apron jaws The ability to control the yarn stretch has better control over the edge fibers of the sliver when the fiber speed changes, thereby improving the yarn evenness. After the distance block is increased, the control force of the apron jaws on the whiskers is weakened, which can reduce the problem of draft failure, but it will have a certain impact on the quality of the yarn.
Spin yarn roller pressure
The roller pressure is small, and the drafting nip has weak control over the fiber, resulting in strands The fibers in the machine cannot be well controlled and the problem of drafting cannot occur. After the roller pressure increases, the friction force of the drafting nip 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 draft failure in the rear area and the problem of inability to open the draft.
Spinning yarn rubber roller
For New rubber rollers with a coating layer on the surface have thicker surface coatings and their surface holding power is greatly weakened, resulting in a higher slippage rate during the drafting process, making the yarn unable to be effectively controlled and prone to hard ends. 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 factor 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 lower temperature, the rubber roller will become hard if not treated, the slipperiness rate will increase, and hard ends will easily occur.
Temperature and Humidity
When the humidity in the workshop increases, the friction factor between the fibers in the whisker becomes larger, and the friction resistance increases accordingly. This increases the drafting force of the sliver. When the spinning process remains unchanged, the drafting jaws cannot effectively control the fibers in the sliver, resulting in the problem of inability to draft. The workshop should reasonably control temperature and humidity according to seasonal changes, raw material conditions and other factors to ensure normal production and avoid problems with drafting. </p
