What is silver formation in yarn formation?
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Fibers can be wound in spirals around other fibers only by increasing their length through exploitation of fiber elongation.
When a fiber is extended, its elasticity tries to draw it back. This constant tendency to return to the unextended condition results in a high tension directed towards the core and thus to increase pressure continually towards the yarn interior.
These tensions cause the strong compression, and hence great density of the yarn body. The compression leads to a reduction in the diameter of the yarn.
Diameter is thus inversely proportional to twist. However, the tendency to relax also leads to shortening of the yarn (twisting-in, spinning-in).

Fig.3 : Influence of Yarn Twist on the Degree of Shortening
The same effect is produced by the inclined disposition of the fibers relative to the yarn axis. Hence, the length of the spun yarn never corresponds to the delivered length measured at the front roller.
The degree of shortening is also dependent upon the raw material and especially upon the number of turns. Fig.3 shows how the degree of shortening depends upon the yarn linear density and the twist .
Twist formulas
To elucidate several relationships involved in twisting, two yarns are considered below in a theoretical model. One yarn is assumed to be double the thickness of the other. Consider for each case a single fiber f and f', respectively (Fig.4). Prior to twisting, these fibers lie at the periphery on the lines AC, A'C', respectively.
Assume that the yarns are clamped at the lines AG (A'G') and CD ( C'D') and are each turned once through 360°. Then the fibers take up new positions indicated by the lines AEC and A'E'C', respectively. Each fiber can adopt this helical disposition only if its length is increased. However, owing to the greater diameter of yarn II, the extension of fiber f' must be significantly higher than that of fiber f.
The difference becomes clear if the yarns are rolled on a plane, whereupon two triangles ( ABC and AB'C') are derived, each with the same height H. Fiber f has extended from H to l , while fiber f' has extended from H to L. The greater extension in yarn II also implies greater tension and thus more pressure towards the interior. The strength of yarn II is considerably greater than that of yarn I.
Fiber extensions in the yarn can be measured only with difficulty, so that they cannot be used as a scale of assessment of the strength to be expected. Such a scale could, however, probably be provided by an angle, for example, the angle γ of inclination to the axis. From the above considerations, it follows that yarn II has a higher strength than yarn I. Yarn II also has a greater inclination angle γ than yarn I.
The strengths ( F) are proportional to the inclination angles:

In other words, the greater the angle of inclination, the higher the strength. If the two yarns are to have the same strength, then the inclination angles must be the same, so that  (all other influencing factors being ignored here). This is only possible if the height of each turns in yarn I is reduced from H to h.
In the given example, yarn I must therefore have twice as much twist as yarn II (Fig.5).
When a fiber is extended, its elasticity tries to draw it back. This constant tendency to return to the unextended condition results in a high tension directed towards the core and thus to increase pressure continually towards the yarn interior.
These tensions cause the strong compression, and hence great density of the yarn body. The compression leads to a reduction in the diameter of the yarn.
Diameter is thus inversely proportional to twist. However, the tendency to relax also leads to shortening of the yarn (twisting-in, spinning-in).

Fig.3 : Influence of Yarn Twist on the Degree of Shortening
The same effect is produced by the inclined disposition of the fibers relative to the yarn axis. Hence, the length of the spun yarn never corresponds to the delivered length measured at the front roller.
The degree of shortening is also dependent upon the raw material and especially upon the number of turns. Fig.3 shows how the degree of shortening depends upon the yarn linear density and the twist .
Twist formulas
To elucidate several relationships involved in twisting, two yarns are considered below in a theoretical model. One yarn is assumed to be double the thickness of the other. Consider for each case a single fiber f and f', respectively (Fig.4). Prior to twisting, these fibers lie at the periphery on the lines AC, A'C', respectively.
Assume that the yarns are clamped at the lines AG (A'G') and CD ( C'D') and are each turned once through 360°. Then the fibers take up new positions indicated by the lines AEC and A'E'C', respectively. Each fiber can adopt this helical disposition only if its length is increased. However, owing to the greater diameter of yarn II, the extension of fiber f' must be significantly higher than that of fiber f.
The difference becomes clear if the yarns are rolled on a plane, whereupon two triangles ( ABC and AB'C') are derived, each with the same height H. Fiber f has extended from H to l , while fiber f' has extended from H to L. The greater extension in yarn II also implies greater tension and thus more pressure towards the interior. The strength of yarn II is considerably greater than that of yarn I.
Fiber extensions in the yarn can be measured only with difficulty, so that they cannot be used as a scale of assessment of the strength to be expected. Such a scale could, however, probably be provided by an angle, for example, the angle γ of inclination to the axis. From the above considerations, it follows that yarn II has a higher strength than yarn I. Yarn II also has a greater inclination angle γ than yarn I.
The strengths ( F) are proportional to the inclination angles:

In other words, the greater the angle of inclination, the higher the strength. If the two yarns are to have the same strength, then the inclination angles must be the same, so that  (all other influencing factors being ignored here). This is only possible if the height of each turns in yarn I is reduced from H to h.
In the given example, yarn I must therefore have twice as much twist as yarn II (Fig.5).
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Answer:
- A sliver (/ˈslaɪvər/) is a long bundle of fibre that is generally used to spin yarn. A sliver is created by carding or combing the fibre, which is then drawn into long strips where the fibre is parallel. When sliver is drawn further and given a slight twist, it becomes roving.
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