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, the raw materials are in a state of change at any time. The fiber quality length in the cotton sliver is lengthened (such as increasing the combed sliver content) or the length uniformity is good, and the friction factor between the fibers in the sliver changes. When the spinning process remains unchanged, the drafting jaws cannot effectively control the fibers in the sliver, resulting in the sliver not being able to be drafted normally and drafting occurring. If the problem cannot be extended, other processes need to be adjusted.
Roving twist coefficient
When the roving twist coefficient is large, the roving strip The tightness 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 slivers cannot be effectively untwisted. , entering the main drafting area with a larger twist, and the problem of drafting failure 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 spinning yarn is drafted When the drafting force increases, under the same rubber roller state and under the condition that the draft ratio of the back zone and the roving twist coefficient are constant, the spinning holding force required for the heavy roving is greater than the holding force required for the light roving. force, so the roving weight has higher requirements on 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.
Spinning yarn guide movement
When the spun yarn guide movement When the moving direction of the whiskers is the same as the twisting direction of the yarn guide, 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 twisting direction of the whiskers is opposite to the moving direction of the yarn guide stroke, the drafting force will be the largest. The stretching force is small, which is beneficial to reducing drafting.
Spinning roller gauge
Small roller gauge is beneficial The control of floating fibers in the sliver will increase the drafting force of the sliver during the drafting process, which is prone to the problem of unable to be drafted. 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.
Spinning yarn back area drafting
Spinning yarn back area drafting multiple After the increase, the number of fibers in the cross section of the sliver entering the main drafting area 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 drafting failure. 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 gap
Smaller jaw gap The distance block is conducive to strengthening the control ability of the apron jaw on the drafted yarn, and has better control ability on the edge fibers of the yarn 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 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 draft is The jaws have weak control over the fibers, causing the fibers in the strands to not be well controlled and leading to problems with drafting. 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 glue with paint layer on the surface The surface coating of the roller is thicker, and its surface holding force 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. . Due to the lower temperature in winter, 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 fiber in the sliver The friction factor between the fibers becomes larger, and the friction resistance increases accordingly, which increases the drafting force of the whiskers. When the spinning process remains unchanged, the drafting jaws cannot effectively control the fibers in the whiskers, resulting in drafting. Can’t stretch problem. 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
