Theoretical and experimental study of color-alternation fancy yarns produced by a double-channel compact spinning machine

Abstract

The aim of this work is to explore a new method for producing color-alternation fancy yarn on a modified compact spinning machine. Color-alternation fancy yarn is a new kind of fancy yarn with varying color effects along the yarn axis. The modified compact spinning machine produces double-channel compact spinning, which has two coaxial back rollers in a drafting unit. In this spinning process, two different colored rovings are alternately fed into each back roller to produce alternant color effects along the yarn axis. The mean length of the connecting piece between of two different solid color pieces of this yarn is the key research subject. Mathematical equations have been derived to describe the relationship between the mean length of the connecting pieces, the mean length of the wedged broken end of roving, the mean overfeeding length of the roving and the total draft ratio. The effect of the total draft ratio and overfeeding length on yarn properties, such as tenacity, elongation and yarn evenness, was studied. The results indicate that a relatively small total draft ratio is beneficial to shorten the mean length of the connecting pieces, enhance the tensile property and improve yarn evenness.

Keywords

color-alternation fancy yarn double-channel compact spinning connecting piece total draft ratio overfeeding length

Fancy yarns are considered as fashionable products with a bright future due to their special aesthetic and highly decorative additions to fabrics and clothing. The search for new textile products in terms of fashion and appearance has continuously led to the design of new types of fancy yarns with an impression of varying color effect.

Researches relating to fancy yarns have mainly focused on three aspects: (1) the manufacturing techniques and properties of these yarns^1–3 and factors affecting their properties;^4,5 (2) the classification and application of fancy yarns;^6,7 (3) modeling studies based on yarn structures and properties.^8,9 Ring spinning techniques have attracted both researchers’ and manufacturers’ attention in developing various fancy yarn products from the relatively good yarn quality of the ring spinning process. The representative ring spinning fancy yarn, such as slub yarn^10,11 and section-color yarn,¹² have been studied by many textile researchers. Slub yarn is manufactured by altering the yarn count along the yarn axis in the spinning process. In addition, section-color yarn is produced by feeding two different rovings simultaneously, with one roving feeding continuously as the basic yarn and another roving feeding discontinuously as the decorative yarn. However, none of the above fancy yarns realize the equivalent rotation of two rovings. There are few studies that focus on color-alternation fancy yarn produced by feeding two rovings alternately.

Therefore, this study presents a novel color-alternation fancy yarn that is based on a newly designed double-channel compact spinning machine. The color of the fancy yarns can gradually vary from one color to another, and several fabrics with gradated zigzag line patterns and ornamental effects of the color-alternation fancy yarn were produced conventionally. An example of the weft knitted fabric made of the color-alternation fancy yarn is shown in Figure 1. This fabric contrasts with the smoothness of dyed or printing patterns, building up shapes of immense complexity in three areas, that is, white, black and mixed areas. The white and black areas are respectively formed by the white and black solid color pieces of the fancy yarn, and the mixed areas are formed by the connecting pieces. The artistic characteristic of this pattern depends on the length of each kind of solid color piece and the connecting piece of the color-alternation fancy yarn, and the parameters of the fabric. Among them, the length of the solid color piece is relatively easy to control by merely adjusting each roving feeding time, but the length of each connecting piece is influenced by a number of factors. As the sharpness of the pattern edge is significantly dependent on the length of the connecting piece, the factors affecting the length of the connecting piece should be found out immediately.

Figure 1.

Color-alternation fancy yarn and fabric.

In this paper, the spinning mechanism of the color-alternation fancy yarn is detailed, and the relationship between the connecting piece length, the wedge shape length of the broken roving end, the total draft ratio and the overfeeding length is theoretically analyzed. The effects of the total draft ratio and the overfeeding length of roving on the yarn properties are also investigated by experimental studies.

Introduction of the double-channel compact spinning for color-alternation fancy yarns

Spinning mechanism of color-alternation fancy yarn

The schematic of the newly developed double-channel compact spinning method is shown in Figure 2. In this spinning system, two coaxial back rollers, namely back roller 1 and back roller 2, are installed in a drafting unit, where back roller 1 is fixed in the shaft and driven by the shaft, and back roller 2, attached with a drive gear, is rotatably fitted on the shaft close to back roller 1; the two back rollers can be controlled individually by a servomotor. Meanwhile, a roving guide converges the two rovings, which are independently fed by two back rollers in one drafting unit, into a suitable space. The feeding speed of the two rovings can be changed on-line by varying the speed of the two back rollers to regulate the blend ratio of the two rovings, showing a different appearance along the lengthwise direction of the yarns. In addition, a compact spinning device with a triangular suction slot is added to further reduce the width of the fiber band between the nip of the front rollers and the nip of delivery rollers, and the compact device can effectively reduce the rate of yarn breakage.

Figure 2.

Schematic of double-channel compact spinning.

In the spinning of the color-alternation fancy yarn, it is necessary for the fancy yarn to feed two rovings in turn, so that the color can change along the yarn axial direction. According to experimental observation of the roving breaking motion in the break draft zone, it was found that the break point of the roving is closer to the middle roller when the back roller stops running, while the roving end rest on the break draft zone could be successfully fed into the nip of the middle rollers when the back roller starts to run again. Figure 3 shows two typical moments of the spinning process, when the roving fed from the left-hand back roller is being drafted in the draft zone, another roving end stays at the break draft zone and is held by the right back roller; then the left-hand back roller stops running, and the roving fed by this roller breaks in the break draft zone; at the same time, the right-hand back roller starts running and the resting roving is feeding into the nip of the middle rollers, and the ends of the two running rovings connect to each other. After passing the draft zone, the drafted fiber band converges at the suction slot of the compact device; then, the converged fiber band is twisted at the output point. This process is repeated (see Figure 3) and a color-alternation fancy yarn will be produced. The numbers from 1 to n mean that the two rovings rotate from the beginning to the end in a doffing cycle.

Figure 3.

Feeding order of color-alternation fancy yarn spinning: (a) spinning process with the left-hand back roller running; (b) spinning process with the right-hand back roller running.

Ideal connecting piece length model

As is known to all spinners, the fracture of the head of the broken roving is not even, but is more like a wedge shape. The schematic diagram of roving breaking can be described by Figure 4. In the break draft zone, roving A breaks in the wake of the feeding of roving B (see moment 1 in Figure 4), and the fibers of roving A in front of the black line keep on moving ahead and the resting roving B in the last break starts running, and thus they are both fed into main draft zone and joined together at moment 2, forming a consecutive yarn with two color sections. It is assumed that the roving breaks along an oblique line (see Figure 4) and the distance from the back roller nip to each line is assumed to be constant, and the shape and size of the head of each broken roving are invariable. Then, $L = L^{'}$ and $L_{0} = L_{0}^{'}$ , where L is the length of the wedge shape head of roving A, L₀ is the distance between the initial point of the wedge shape head to the nip of back rollers, $L^{'}$ is the length of the wedge shape head of roving B and $L_{0}^{'}$ is the distance between the initial point of the wedge shape to the nip of the back rollers.

Figure 4.

Schematic diagram of roving running.

To obtain the ideal structure of the color-alternation fancy yarn, a color-alternation fancy yarn was captured continuously by an image acquisition set-up, and a set of stitched images of a yellow/black color-alternation yarn is shown in Figure 5. Figure 5 shows that there is a blending piece between the yellow and black piece. The blending piece is named the connecting piece. The vertical short red line is the boundary between the connecting and the solid piece. As the yarn cycles between the solid and the connecting piece, the simplified ideal structure of a fancy yarn in Figure 6 is abstracted from the yarn structure in Figure 5.

Figure 5.

Image of the color-alternation fancy yarn. (Color online only.)

Figure 6.

Simplified ideal structure of the color-alternation fancy yarn.

The ideal structure of the color-alternation fancy yarn is shown in Figure 6. Here, M_i is the length of one solid color piece of yarn, N_i is the length of another solid color piece of yarn and K_i is the length of the connecting piece between two adjacent solid color pieces.

On the assumption that $L = L^{'}$ , K_i would be a constant value according to the roller drafting rule and it can be deduced as follows

K_{i} = L \times E

(1)

where E is the total draft ratio.

Roving break line distribution

In color-alternation fancy yarn spinning, when the back roller stops running, the roving breaks immediately. Although it is hoped that the roving will break at the same place each time, the distribution of the break line is actually in a certain range in practical spinning. This random distribution is due to the fact that fibers arrange randomly along the axis of the roving and each weakest point of roving in the break draft zone is not in the same place. Figure 7 shows a sketch map of the possible roving break line distribution. It is assumed that line-A and line-a are the edge of the breaking position of roving A, and line-B and line-b are the edge of the breaking position of roving B. As a result, W is the width of the roving break line distribution. Therefore, the most representative example of the break line is listed in Figure 8 to describe the roving breaks. In addition, roving A runs on ahead, and it is easy to find out that an end break will occur in the spinning process when the broken rovings A and B are in A-b state. If rovings A and B randomly break at the aforementioned four places in the practical spinning process, there will be eight possible connecting states for rovings A and B.

Figure 7.

Schematic of roving break line distribution.

Figure 8.

Possible situations of the roving breaks.

In general, twists have an effect on the position of the roving breaks in the break draft zone. In roller drafting, the roving twist multiplier and the fiber length influence the draft behavior. The twists of the roving in the break draft zone are redistributing, namely, more twists are concentrating on the roving near the nip of the middle rollers. This could lead to a retroposition of the roving break.

Therefore, to eliminate this situation (A-b state) caused by the fluctuation of the roving break line, it is necessary to feed the back roving earlier before the running roving breaks. Figure 9 shows the modified roving connecting state with overfeeding. The roving B rest on the break draft zone should start running before roving A breaks, and T is the overfeeding length and should be satisfied with Equation (2), In this yarn spinning, the overfeeding roving start running from rest, so the overfeeding length T depends on the average linear velocity $\bar{v}$ of the back roller at the launch phase and the overfeeding time t. The overfeeding length T can be expressed as Equation (3)

T \geq W

(2)

T = \bar{v} t

(3)

Figure 9.

Modified roving connecting state with overfeeding.

Connecting piece length model considering roving break line distribution and overfeeding

There are many limitations of the aforementioned ideal connecting piece length model, so a connecting piece length model considering the roving break line distribution and overfeeding length is closer to the truth. Figure 10 shows a schematic diagram of the roving break in the back draft zone. For roving A, L is the length of the wedge shape of the broken roving, c_i represents the roving length between the nip of the middle rollers and the end of the wedge shape and is the roving length between the nip of the back rollers and the end of the wedge shape. Similarly, for roving B, $L^{'}$ is the length of the wedge shape of the broken roving, e_i is the roving length between the nip of the middle rollers and the end of the wedge shape and f_i is the roving length between the nip of the back rollers and the end of the wedge shape. G is the gauge of the back draft zone.

Figure 10.

Schematic diagram of roving break in the back draft zone.

From Figure 10, two relations can be described as

c_{i} + d_{i} + L = G

(4)

e_{i} + f_{i} + L^{'} = G

(5)

To describe the connecting piece length of this yarn, i represents the ith break of rovings A and B and K_i represents the length of the ith connecting piece. To simplify the issue, it is assumed that $L = L^{'}$ . The length of connecting pieces can be listed as follows

\begin{matrix} (c_{1} + f_{1} + 2 L - G + T) \times E = K_{1} \\ (e_{2} + d_{1} + 2 L - G + T) \times E = K_{2} \\ (c_{2} + f_{2} + 2 L - G + T) \times E = K_{3} \\ (e_{3} + d_{2} + 2 L - G + T) \times E = K_{4} \\ \dots \\ \dots \\ (c_{n} + f_{n} + 2 L - G + T) \times E = K_{2 n - 1} \\ (e_{n + 1} + d_{n} + 2 L - G + T) \times E = K_{2 n} \end{matrix}

Equation (6) can be derived by summing the above equations

\begin{matrix} [\sum_{i = 1}^{n} (c_{i} + d_{i}) + 2 nL - nG + nT + \sum_{i = 2}^{n} (e_{i} + f_{i}) + 2 nL - nG + f_{1} + e_{n + 1} + nT] \times E \\ = \sum_{i = 1}^{2 n} K_{i} \end{matrix}

(6)

where n is the occurrence number of roving A or roving B.

Substituting Equations (4) and (5) into Equation (6), we obtain Equation (7)

[e_{n + 1} + f_{1} + L - G + 2 nL + 2 nT] \times E = \sum_{i = 1}^{2 n} K_{i}

(7)

Because W is the width of the roving break line distribution, Equation (8) can be obtained as follows

| e_{n + 1} - e_{1} | \leq W

(8)

From Equation (5), we know that $e_{1} + f_{1} + L = G$ ; substituting this equation into Equation (8) meets

| e_{n + 1} - e_{1} + (e_{1} + f_{1} + L - G) | \leq W

(9)

Substituting Equation (7) into Equation (9), we obtain

| (\sum_{i = 1}^{2 n} K_{i}) - (2 nL + 2 nT) \times E | \leq WE

(10)

Then, both sides of Equation (10) are divided by 2 n, and Equation (11) can be deduced as follows

| \bar{K_{i}} - (L + T) \times E | \leq \frac{WE}{2 n}

(11)

Taking the limits of n→∞ yields

{lim}_{n \to \infty} \frac{WE}{2 n} = 0

Thus

{lim}_{n \to \infty} \bar{K_{i}} = (L + T) \times E

(12)

Substituting Equation (3) into Equation (12), Equation (13) can be obtained as follows

{lim}_{n \to \infty} \bar{K_{i}} = (L + \bar{v} t) \times E

(13)

From Equation (13), when a roving was chosen, that is to say L is a constant value, it can be concluded that factors having influence on the average connecting piece length $\bar{K_{i}}$ are total draft ratio E, back roller average linear velocity $\bar{v}$ and overfeeding time t.

Experimental details

Materials

Rovings produced from a batch of cotton silvers into 300, 350, 400, 450 and 500 tex in white (roving A) and black (roving B) were used to produce 19.4 tex color-alternation fancy yarns at a twist factor α_tex = 360, with corresponding total draft ratios of 15.46, 18.04, 20.62, 23.20 and 25.77, respectively. The overfeeding length for each total draft ratio was set at 5, 7 and 9 mm, respectively. The overfeeding time was calculated according to the overfeeding length under each total draft ratio and the control precision is 0.01 seconds. The necessary spinning parameters are as follows: spindle speed 8000 rpm, roller diameter 27 mm × 27 mm × 27 mm, roller gauge 18 mm × 38 mm, back draft ratio 1.2 and linear velocity of the front roller 9.80 m/min. Detailed feeding parameters are shown in Table 1.

Table 1.

Parameters of roving feeding time

Total draft ratio		15.46		18.04		20.62		23.20		25.77
Overfeeding length/mm	Feeding order	Feeding time/s
Overfeeding length/mm	Feeding order	A	B	A	B	A	B	A	B	A	B
5	Piece A	8	–	8	–	8	–	8	–	8	–
	Overfeeding	0.47	0.47	0.55	0.55	0.63	0.63	0.71	0.71	0.79	0.79
	Piece B	–	8	–	8	–	8	–	8	–	8
	Overfeeding	0.47	0.47	0.55	0.55	0.63	0.63	0.71	0.71	0.79	0.79
7	Piece A	8	–	8	–	8	–	8	–	8	–
	Overfeeding	0.66	0.66	0.77	0.77	0.88	0.88	0.99	0.99	1.10	1.10
	Piece B	–	8	–	8	–	8	–	8	–	8
	Overfeeding	0.66	0.66	0.77	0.77	0.88	0.88	0.99	0.99	1.10	1.10
9	Piece A	8	–	8	–	8	–	8	–	8	–
	Overfeeding	0.85	0.85	0.99	0.99	1.14	1.14	1.28	1.28	1.42	1.42
	Piece B	8	–	8	–	8	–	8	–	8	–
	Overfeeding	0.85	0.85	0.99	0.99	1.14	1.14	1.28	1.28	1.42	1.42

‘–’: no roving feeding.

Measurements

In this study, the lengths of the connecting pieces of the color-alternation fancy yarns were measured manually, and 100 sequential connecting pieces of each yarn samples were collected to study the effect of the total draft ratio and the overfeeding length on the connecting piece length. The method is shown in Figure 11. In the measurement, a long ruler is placed on a laboratory table, and a tension plate is situated on the left-hand side of the ruler and a guide is situated on the right-hand side of the ruler. The color-alternation yarn passes through the tension plate and guide, and a weight hangs on the end of the yarn to provide tension to ensure that there is the same elongation of yarn in each measurement.

Figure 11.

Method of the connecting piece length by manual measurement.

In this manuscript, the tenacity of the connecting and the solid pieces were separately measured by a YG020B tensile tester (Changzhou Second Textile Machinery Co. Ltd, Changzhou, China), and the tenacity of yarn was tested by a YG068C tensile tester (Suzhou Changfeng Textile Electromechanical Technology Co. Ltd, Suzhou, China). The tensile testers are shown in Figure 12.

Figure 12.

Tensile tester: (a) YG020B; (b) YG068C.

Method 1 for testing the connecting pieces

The tenacity of the connecting pieces was tested by the YG020B tensile tester. The test length was 50% of the mean length of the connecting pieces of each sample, and 30 measurements were taken of each sample. The test lengths of each sample are shown in Table 2. The test position of each connecting piece is manually selected.

Table 2.

Test length of the connecting pieces

Test length/mm
Overfeeding length/mm	Total draft
Overfeeding length/mm	15.46	18.04	20.62	23.20	25.77
5	197.0	229.5	254.5	292.5	322.5
7	213.0	248.5	275.5	314.5	351.5
9	221.5	266.5	304.5	340.5	374.0

Method 2 for testing the solid pieces

The tenacity of yarn was tested by the YG020B tensile tester. The test length was 500 mm of the solid pieces of each sample (the test length was shorter than the mean length of the solid pieces), and 30 measurements were taken of each sample. The test position of each connecting piece is manually selected.

Method 3 for testing the yarn (consisting of both the connecting and the solid pieces)

The tenacity of yarn was tested by the YG068C tensile tester in automatic mode. The yarn was continuously tested. The test length was 500 mm and the space length was 500 mm, and test was carried out 60 times.

Yarn evenness and imperfection were tested by an USTER TESTER 5 (Uster Technologies AG, Uster, Switzerland) and 10 bobbin yarns of each sample were tested. The test speed was 400 m/min and the test time was 2.5 minutes. All yarn samples were conditioned for at least 24 hours under standard conditions (20 ± 2℃ and 65 ± 2% relative humidity) prior to testing.

Results and discussion

Effect of the total draft ratio and overfeeding length on the mean length of the connecting piece

The length of the connecting piece of color-alternation fancy yarn determines the pattern of the corresponding fabrics. Finding the affecting factors of the length of the connecting piece is extremely valuable for this type of yarn. The relationship between the mean length of the connecting piece and the total draft ratio is shown in Figure 13. The results of the mean length of the connecting pieces were assessed statistically at the significance level of 0.05 for the effects of overfeeding length and total draft ratio. The two-way analysis of variance (ANOVA) in Table 3 shows a significant impact for both overfeeding length and total draft ratio on the mean length of connecting pieces. The linear fitting equations are shown in Table 4. The coefficients of determination R² of the above three fitting equations are 0.96, 0.90 and 0.94, respectively. The results indicate the good reliability of the forecast and goodness of fit. Compared with Equation (12), each linear fitting equation has a constant term; however, it can be seen from Figure 13 that all the constant terms are much less than the mean length $\bar{K}$ of the connecting piece. From Table 5, it can be seen that the maximum evaluation parameter is 0.54% of the linear fitting equation at overfeeding length 5 mm and total draft ratio 15.46. This means that the constant term accounting for the largest proportion of the mean length of the connecting piece is 0.54%. Therefore, the linear fitting equation can almost be revised to the format of Equation (13), that is, ignore the constant term. The possible wedge shape length L of the used roving could be calculated by the revised fitting equation and overfeeding length. Three calculated values of L, that is, 20.0, 20.1 and 20.3, are shown in Table 4. It was found that the three values were very similar to each other, and the mean value of the above three calculated L values are 20.1. Obviously, the derived equation (12) could reflect the influence of the total draft ratio and overfeeding length on the mean length of the connecting piece.

Figure 13.

The relationship between the length of the connecting piece and the total draft ratio.

Table 3.

Two-way analysis of variance results for the effects on the mean length of the connecting pieces

Source of variation	SS	df	MS	F	P-value
Overfeeding length	17,809.6	2	8904.8	61.35599	0.000
Total draft ratio	143,247.7	4	35,811.93	246.752	0.000
Error	1161.067	8	145.1333
Total	162,218.4	14

Figure 14.

Knitted fabrics with color-alternation yarn at overfeeding length 9 mm: (a) total draft 15.46; (b) total draft 20.62; (c) total draft 25.77.

Table 4.

Linear fitting equation

Overfeeding length T/mm	Linear fitting equation	R ²	Revised fitting equation (ignored constant term)	Calculated L/ mm
5	$\bar{K} = 25.0 \times E + 2.1$	0.964	$\bar{K} = 25.0 \times E$	20.0
7	$\bar{K} = 27.1 \times E + 1.7$	0.989	$\bar{K} = 27.1 \times E$	20.1
9	$\bar{K} = 29.3 \times E - 0.5$	0.941	$\bar{K} = 29.3 \times E$	20.3

Table 5.

Evaluation parameter of the ignored constant term of the fitting equation

Evaluation parameter	Linear fitting equation	Total draft ratio
Evaluation parameter	Linear fitting equation	15.46	18.04	20.62	23.20	25.77
100 × (Constant term)/ $\bar{K}$ (%)	$\bar{K} = 25.0 \times E + 2.1$	0.54	0.46	0.40	0.36	0.32
	$\bar{K} = 27.1 \times E + 1.7$	0.40	0.35	0.30	0.26	0.24
	$\bar{K} = 29.3 \times E - 0.5$	0.11	0.09	0.08	0.07	0.07

As shown in Figure 13, the mean length of the connecting piece increases with the increase of the total draft ratio, and the amplification of mean length from a total draft ratio to a higher total draft ratio with a certain overfeeding length is comparatively stable. According to the above analysis, when the wedge shape length L and overfeeding length T are invariable, the mean length $\bar{K}$ of the connecting piece only depends on the total draft ratio E, and $\bar{K}$ is proportional to E. Therefore, the amplification of $\bar{K}$ does not vary with the increase of the total draft ratio. Meanwhile, the mean length of the connecting piece also increases with the increase of overfeeding length, and the amplification of the mean length of the connecting piece between two overfeeding length levels increases with the increase of the total draft ratio. Obviously, when the wedge shape length L and total draft ratio E are both constant, a linear correlation is found between the mean length $\bar{K}$ of the connecting piece and the overfeeding length T, so the mean length of the connecting piece increases with increasing the overfeeding length; if setting the wedge shape length L as a constant, the dependent variable $\bar{K}$ depends on two arguments, T and E. Then, the amplification of the mean length of the connecting piece with the increase of overfeeding length under a small total draft ratio is lower than that under a larger total draft ratio.

As Equation (12) shows, the mean length of the connecting pieces is mainly determined by the total draft ratio. To compare the color-alternation yarns with different mean length of the connecting pieces, three typical yarn samples with different total draft ratios of 15.46, 20.62 and 25.77 at overfeeding length 9 mm were knitted into rib stitch fabrics. The rib stitch fabric was produced with 264 loops in each row, and the loop length is 0.53 cm. As can be seen, the black area and white area decrease with the increase of the total draft ratio; in other words, the mixed area increases with the increase of the total draft ratio. Correspondingly, from Figure 13, the results show that the mean length of the connecting pieces increases with the increase of the total draft ratio. Therefore, the pattern effect of the knitted fabric is consistent with the results shown in Figure 14. Meanwhile, it also can be seen that the connecting piece length of the color-alternation yarn has a great influence on the pattern of its knitted fabric.

Effect of total draft ratio and overfeeding length on the tenacity and elongation

Yarn tenacity is one of the most important properties in the yarn spinning and fabric manufacturing process, as the color-alternation fancy yarn consists of two components: the solid color piece and the connecting piece. To an extent, the tenacity of the solid color piece is similar to that of traditional single yarn because they have an identical single yarn structure. Therefore, the tenacity of the connecting piece is a critical point for color-alternation fancy yarn due to its special structure characteristics. To compare the tenacity and elongation of yarns, the two-way ANOVA method was conducted, and the results are presented in Table 6. In this table, the P-value is a measure of how much evidence we have against the null hypothesis at the 5% level. The results show that there is no remarkable influence of total draft ratio on the tenacity and elongation of the connecting piece; however, the overfeeding length greatly affects the tenacity and elongation of the connecting piece. For the solid color piece, the total draft ratio and overfeeding length have no effect on the tenacity and elongation.

Table 6.

Two-way analysis of variance for tenacity, elongation and evenness versus total draft ratio and overfeeding length

	Parameter	Source	P-value
Connecting piece	Tenacity	Total draft ratio	0.617
	Tenacity	Overfeeding length	0.000
	Elongation	Total draft ratio	0.555
	Elongation	Overfeeding length	0.000
Solid color piece	Tenacity	Total draft ratio	0.547
	Tenacity	Overfeeding length	0.425
	Elongation	Total draft ratio	0.528
	Elongation	Overfeeding length	0.764
Yarn	CV_m	Total draft ratio	0.000
Yarn	CV_m	Overfeeding length	0.000

The tenacity of the connecting piece and solid color piece are shown in Figure 15. As Figure 15(a) shows, the connecting piece has the lowest value of tenacity at the lowest overfeeding length in all five groups, and an increasing overfeeding length is associated with an increase in the tenacity. Compared with the solid color piece in Figure 15(b), the tenacity of the connecting piece at overfeeding lengths 7 and 9 mm is very close to that of the solid color piece. The possible reason is that, in the connecting piece, the overlap region of two roving ends become longer with the increase of overfeeding length, and the linear density of the overlap region also increases with the increase of overfeeding length. It is well known that thicker yarn is more likely to have higher tenacity.

Figure 15.

Tenacity values: (a) tenacity values of the connecting pieces tested by Method 1; (b) tenacity values of the solid pieces tested by Method 2.

Figure 16(a) shows the breaking elongations of the connecting piece and the solid color piece. The results show that, along with the overfeeding length increasing, the elongation of the connecting piece will go up to a peak value; the change law is similar to that of the tenacity of the connecting piece. For a certain structural yarn, the larger extension would have the higher tension during the tensile process. This is the possible reason that the elongation of the connecting piece increases with the increase of the tenacity of the connecting piece. Figure 16(b) shows that the total draft ratio and overfeeding length have almost no effect on the elongation of the solid color piece. This is because the structure of the solid color piece is almost free from the overfeeding length.

Figure 16.

Breaking elongation values: (a) break elongation values of the connecting pieces tested by Method 1; (b) break elongation values of the solid pieces tested by Method 2.

Figure 17 shows the tenacity and elongation of the color-alternation yarns. The results show that, along with the overfeeding length increasing, the tenacity of the yarn increases at each total draft ratio. As is known, the color-alternation yarn consists of the connecting piece and the solid color piece. The tenacity of the connecting piece increases with the increase of the overfeeding length, so the tenacity of the color-alternation yarn also increases. However, with the increase of the total draft ratio, the tenacity of the yarn slightly decreases. The reason may be that thin places (+50%/km) increase with the total draft ratio increase (see Figure 19). The elongation of yarn slightly decreases with the increase of the total draft ratio, as the tenacity of the yarn decreases.

Figure 17.

Tenacity and elongation values tested by Method 3: (a) tenacity; (b) elongation.

Effect of the total draft ratio and overfeeding length on yarn evenness

The results of the two-way ANOVA analysis in Table 4 indicate that the total draft ratio and overfeeding length have a significant impact on yarn evenness. As noted in Figure 18, it was easy to conclude that the coefficient of variation of mass (CV_m) shows an increasing trend with the increase of overfeeding length. As the overfeeding length increases, the increase in the CV_m value is due to the increase of the overlap region of the connecting piece. From Figures 19 –21, although increasing the overlap region can vastly decrease the possible thin places of the connecting piece, this action also surely brings on numerous thick places (see Figure 20), which can distinctly lead to a worse yarn evenness. However, the neps have no obvious change in each overfeeding length (see Figure 21). Figure 18 also shows that the CV_m of yarn increases as the total draft ratio increases. The possible reasons could be divided into two parts: the solid color piece and the connecting piece. The drafting behavior of the solid color piece is essentially the same as that of the traditional single roving drafting. It is well known that the effect of drafting behavior on yarn evenness mainly depends on the fiber accelerated point distribution in the main draft zone of the two-zone roller drafting system.^13,14 Since we used five count rovings spun with the same grade of raw cotton and the twist factor of roving decreases with the increase of the roving count, the fiber accelerated point distributions in the spinning solid color piece of yarn with different count rovings are close to each other. This is due to the fact that the fiber accelerated point distribution was primarily influenced by the fiber length and roller gauge. Therefore, the higher draft ratio will lead to the worst yarn evenness with the same fiber accelerated point distribution. In addition, the length of the connecting piece shows an increasing trend with the increase of the total draft ratio, so a longer connecting piece will be a negative factor against yarn evenness.

Figure 18.

Coefficient of mass variation.

Figure 19.

Thin places of color-alternation yarn.

Figure 20.

Thick places of color-alternation yarn.

Figure 21.

Neps of color-alternation yarn.

As is known, in ring spinning, the general relationship between the irregularity of a drafted roving and draft behavior involves an optimum range of drafts for a given roving. This effect is reflected in an optimum draft range of break draft for the best yarn quality in spinning. In color-alternation fancy yarn spinning, the break draft is also important to the yarn irregularity, despite the roving being intermittently broken in the break draft zone. The length of the wedged roving end is related to the break draft ratio and roller gauge, as well as the roving twist. The effects of these factors will be studied in the following work.

Conclusion

A new method of producing color-alternation fancy yarns was developed by a modified compact spinning machine, namely the double-channel compact spinning system. In this yarn spinning system, two different colored rovings were alternately fed into each back roller and alternant color effects on the yarn axis could be produced. The mean length of the connecting piece between two solid color pieces of this yarn was investigated, and a mathematical equation was derived to describe the relationship between the mean length of the connecting pieces, the wedge shape length of the broken roving, the overfeeding length and the total draft ratio. The effect of the total draft ratio and overfeeding length on yarn properties, such as tenacity, elongation and yarn evenness, was studied. The results show that the mean length of the connecting piece increased with the increase of the total draft ratio and overfeeding length; the connecting piece had the lowest value of tenacity at the lowest overfeeding length, and an increasing overfeeding length was associated with an increase in the tenacity; the tenacity of yarn increased with the increase of the overfeeding length and decreased with the increase of the total draft ratio. Yarn evenness deteriorated with the increase of the total draft ratio and overfeeding length. These results would be helpful for fancy yarn manufacturers to fully understand the manufacturing processes of the color-alternation yarn and thus improve the yarn quality.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was supported by the Fundamental Research Funds for the Central Universities (JUSRP51631A); Basic Research Fund of China National Textile and Apparel Council (J201506).

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