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About the cause of stiff silk

Update:28-12-2019
Summary:

Causes of Stiffness (DTY) DTY's "stiffness" will make t […]

Causes of Stiffness (DTY)

DTY's "stiffness" will make the fabric noticeably produce "defects (details) and stains". The types and causes of formation of stiff wires are as follows: (1) Long-segment malformed silk is "long stiff silk". The external form lacks curl elasticity and fluffy, silk is stiff and shiny, and looks like raw silk. The fabric surface has obvious streaks and dark streaks after dyeing. The reasons for this are violations of operating procedures, poor equipment conditions and high unevenness of raw silk fineness.

(2) Twisted yarn. When the external form is in a relaxed state. Form overlapping twist. With branch-like protrusions, it feels hard. The surface of the fabric is stiff. After dyeing, the color points and stripes are stiff. The reasons are as follows: D / Y ratio is too large. POY fineness is uneven, or untwisting tension is reduced. Make twisted.

(3) Tightly twisted yarns are "melt tight points. The nodes are formed by fusion bonding between the filaments. It is not easy to pull apart with a certain external force or until it breaks, and the hand feels stiff. The surface of the fabric is firm, and the color points are stiff after dyeing. The reason is that the temperature of the hot box is too high, the molecular chain orientation and crystallinity are low, the heat is not stable enough, the fiber surface is softened, the viscosity is increased, and even the monofilament adhesion is formed to form a tight point.

(4) Untwisted yarn is the "tight spot". The fiber forms a tight twist node at the twist concentration point ", which makes the thread fluffy and can be pulled apart with external force. The surface of the fabric is not clear, and the surface of the dyed surface produces sesame dots. The reason is that the thread runs unstable and the tension fluctuates into: It is related to improper selection of DTY process and poor quality of POY raw silk. For example, when the POY elongation suddenly decreases, the internal stress of deformation increases, and T2 is small, the untwisting is incomplete, leaving untwisted "nodes".

Factors Influencing Stiffness

⑴tension ratio

In the processing of DTY, in order to have good processing performance and deformed silk performance, the selection of the tensile deformation process parameters should first make T1 and T2 as consistent as possible, or make the ratio slightly higher than 1. Since T1 changes less and T2 changes more, the smaller the K value, the smaller T2. When the K value is less than or equal to 0.8, the number of stiff wires is significantly increased; when the value of K is less than or equal to 1.4, the number of stiff wires is reduced. This shows that when T2 is small, it is not enough to overcome the elastic restoring force (f) and produce stiff filaments; and f is slightly smaller than T1. At this time, it is affected by the relaxation characteristics of nylon 6 and irreversible deformation occurs. If T2 is too large, the frictional resistance will increase, and it is easy to produce wool and incomplete twisting, so it forms a "tight spot".

⑵Processing speed

When producing silk of the same specification, as the processing speed increases, the residence time of the wire speed in the hot box is shortened, the crystallinity is reduced, the entropy value is large, and the elastic recovery force is also large. In the case where T2 is substantially unchanged, since T1

⑶ Stretching ratio (stretched)

In the process of tow, under the action of external force and thermal energy, the supramolecular structure changes, the degree of orientation increases, and the degree of crystallinity increases. The internal energy increases due to the effects of orientation and crystallization, and the elastic restoring force caused by the "energy" change also increases. In addition, because the stretch ratio (DR) is directly proportional to the K value, as DR increases, T1 increases less, while T2 increases more. This is due to the clamping effect of false twist for some reason. As a result, the increase in tension caused by the increase in DR results in an uneven distribution, so that the increase in untwisting tension is greater than the increase in elastic restoring force, so the larger the DR, the less stiff wires. Conversely, when DR decreases, the reduction in untwisting tension is also greater than the reduction in elastic restoring force, so when DR decreases, causing T2 to be insufficient to overcome the elastic restoring force, a stiff wire will appear.

(4) D / Y ratio

The D / Y ratio is the ratio of the linear speed of the friction disk to the linear speed of the output roller. D / Y is too small, the change of T1 is small, and T2 is greatly reduced. When the elastic restoring force is basically the same, T2 is not enough to overcome the restoring force and form a stiff wire. When the D / Y ratio is too large, because the displacement of the polymer segment in the three-dimensional space is greatly increased, and the deformation of the molecular chain is intensified in the three-dimensional space, the elastic recovery force is greatly increased, and the twist of the tow greatly exceeds the normal twist range; and The increase in untwisting tension is much smaller than the increase in elastic restoring force, resulting in insufficient T2 to overcome the elastic restoring force and appear twisted yarns.

⑸Hot box temperature

Relevant data show that the elastic recovery force is directly proportional to temperature. This temperature includes the heat energy H absorbed from the deformation heat box and the temperature rise caused by the deformation heat generated by the external force. In addition, an increase in temperature is favorable for crystallization, and at the same time, the elastic recovery force caused by the "energy" change is increased. Therefore, the higher the temperature of the deformed hot box, the greater the elastic restoring force produced by the glass transition temperature. In other process conditions, only increasing the temperature of the hot box will make T2 insufficient to overcome the restoring force and cause stiffening (melting tightness). point).

⑹Yarn quality and DTY equipment status

The relationship between the quality of raw silk, DTY equipment and the production of stiff silk

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