Optimum Drafting Conditions of Polyester and Viscose Blend Yarns

Introduction

The ring spinning machine was invented in 1828 and it has been developed frequently. In spite of the advent of modern spinning systems and their advantages, the ring spinning system is pioneer among spinning systems, because of its capability for spinning of any material to any required fineness, produce of yarn with high structural properties, simplicity of operation and flexibility for spinning any blend ratio from various fbers[1]. Therefore, the ring spinning machine is considerable for researchers in the field of spinning for enhancing of yarn quality. In the ring spinning, drafting is roller drafting.

For spinning the yarn with high quality, the draft has to be applied on the roving under the certain conditions. These conditions determine the yarn quality.

In 1945 Grishin developed a theoretical equation for calculation of sectional drafts in the roller drafting system based on the total draft, break draft, back roller gauge setting and fibre length and its variations in order to produce a drafted production with high quality [2].

In 1947, Martindale set up a utensil to measure the drafting force of cotton slivers in roller drafting system [3]. Then, some of the researchers used this tool and technique to choose a suitable break draft in roller drafting system to obtain a drafted production with promoted quality [4-6].

In 2000, for high-quality fine denier polyester spun yarn in ring frame, Ching-Iuan Su et al, investigated the effect of break draft, back roller gauge and roller pressure on the quality of yarn [7]. In another research in 2003, Ching-Iuan Su et. al, investigated the influence of the roller gauge, break draft and roving spacing on quality of Lyocell yarn from twin roving [8].In 2004, Ching-Iuan Su et al, examine the influence of roller gauge and break draft on the drafting force to determine the drafting behaviour of cotton roving in two systems of single and two aprons in order to obtain the highest quality of yarn[9]. In continuation, in 2005, Ching-Iuan Su et al studied the effect of back roller gauge, break draft and roving twist factor on the drafting force to realize the drafting behaviour during roller drafting of Polypropylene (PP) roving to approach the highest yarn quality [10]. Then, in 2006, Ching-Iuan Su et al,examined the drafting behavior of non-circular fibre (cross-shape profile polyester) to obtain the optimum drafting conditions for spinning polyester/cotton (PES/CO) blend yarn where the effect of break draft and (PES/CO) blend ratio on the drafting force were examined [11]. Drafting force to draft a sliver depends on a few factors such as fineness of the fibres, used, the friction between the fibres, spin finishing agent and the crimp of the fibres. Thus these factors determine the proper break draft [11]. The distance between the aprons in the main draft zone and the pressure of the production top roller is proportional to yarn count and the crimps of the fibres.

The purpose of this research is to achieve optimum drafting conditions that are led to spin a yarn with the highest quality. In this study, to optimize drafting conditions, we evaluated the influence of the factors of the total draft, break draft, the distance between the aprons (that is not investigated in previous researches) and the pressure of production top roller on the yarn quality. Then, we obtained a combination of factors as an optimum drafting condition of (PES/CV) blend yarn by statistical analysis and proper experimental designs in order to produce the yarn with the highest quality.

Materials and Methods

We used PES and CV fibres to spin the 20 Tex blend yarn ofPES/CV (70%-30%) blend ratio on a lab ring spinning frame. The steps that fibres are passed is shown in Figure 1. The specification of the fibres, the roving, the yarn and the setting of the ring frame are given in Table1.

We fed slivers of 4.16, 4.94, 5.59 g/m to the roving machine to produce roving counts of 640, 760 and 860 tex respectively. To avoid undesirable effects on the produced rovings quality due to a different orientation of fibres for different drafts in the roving machine, the same total draft of 6.5 were applied. The yarn qualitative properties were tested on a Uster TesterIV and tensile tester Tensorapid IV. The IPI index was defined as follows: thin places (sensitivity degree: -50%) + thick places (sensitivity degree: +50%) + neps (sensitivity degree:200%) per 1000m. The number of tests per sample for the tensile test was 30 and for Uster Tester was 2(for each test was1000m length of yarn). In the tensile tester, the gauge length was50cm and speed clamp was 5m/min. All tests were carried out under similar conditions of 65±5%RH and 20±2°C.

First of all, to identify the effective factors on the yarn quality, primarily, the factorial design of 2f was applied as the experimental design. In this design, instead of many states, we have to choose a low level and high level from each factor of the total draft, break draft, the pressure of production top roller and distance between the aprons (Clips) according to Table 2. There are 16(24 = 16) states which should be evaluated if these factors are effective on the yarn quality or not [12].

We analyzed the results of the factorial design of 2f experiments using statistical software, SPSS 22. After the identification of effective factors, we investigated the influence of the variations of these factors on the yarn quality by statistical analysis. At next step, we set the distance between the aprons on 2.5 mm(Lilac Clips) and the pressure of the roller on maximum on the base of normal setting in actual spinning. Then we changed the break draft from 1.1 to 1.9 and then we analyzed the data to obtain the most suitable break draft. Afterwards, the break draft was set on the optimum draft and other factors were changed according to the illustrated method. Finally, optimum drafting conditions for (PES/CV) blend yarns in the ring spinning frame obtained using statistical analysis.

Results and Discussion

Table 3 illustrates analyses of the factorial design of 2f experiments. Column Sig. in table 3 depicts significant of the influence of factors on quality parameters of yarn. If a factor is effective on the quality parameters of yarn at a level of 5%, its Sig. is less than 0.05. Results and statistical analysis reveal that four factors of the total draft, break draft, the pressure of the production top roller and the distance between the aprons are effective on the quality parameters of the yarn according to table 3. At the next step, for more precise investigation, we limited the factors to three factors including the break draft, the pressure of the production top roller and the distance between the aprons. Therefore, on the base of the normal setting in actual spinning, we set the total draft on 38 with roving of 760 tex and we carried out another step according to the illustrated recipe as mentioned in Methods.

According to Table 4, results and statistical analysis show that the variation of break draft is effective on CV% and Elongation of the yarn in the level of 7%, on Tenacity of yarn in the level of 5%. Figure 2 shows the relationship between the break draft andCV% of yarn. Break draft was applied on roving to the overcome on the static friction of roving. When the break draft is low, drafting force cannot overcome inter-fibres friction, resulting in thin and thick places in the yarn. When the break draft is too high, because of the lack of any apron and leader in the break draft zone, a drafting wave in the yarn would occur and CV% of the yarn would be observed. Therefore inappropriate break draft leads to critical draft and yarn mass irregularity. Suitable break draft depends on the fibres fineness, fibres cross-sectional shapes, friction between fibres and linear density of the roving. Optimumdraft takes place in 1.2 and resulting in higher Tenacity and Elongation of the yarn, shown in Figure 3. Thus according to to the results, break draft of 1.2 was selected as optimum break draft.

In the subsequent stage, we set the break draft on 1.2, the pressure of the production top roller on the maximum (18 daN) and investigated the effect of the distance between two aprons on the yarn quality. The distance between two aprons in the main draft zone will be adjusted by the clips. This distance was changed in 6 states: 1. Red clips (2mm), 2. Yellow clips (2.2mm), 3.Lilacclips (2.5mm), 4. White clips (2.8mm), 5.Grey clips (3.3mm)and 6. Black clips (3.8mm). Table 5 shows that the distance between two aprons influences on the elongation and tenacity of the yarn. This distance will be adjusted according to yarn count and crimp of the fibres. If the distance is small, the fibres cannot move easily and if the distance is large, there is not adequate control to lead the fibres towards production roller, which results in a disorder of the fibres in the yarn structure and reduce the quality parameters. Figure 4 shows that optimum distance between aprons takes places in White clips (2.8mm). Therefore, in the last step, the total draft was set on 38, the break draft on 1.2, the distance between two aprons on 2.8 mm(white clips) and the effect of the pressure of production top roller on yarn quality was investigated.

To study the effect of the pressure of production top roller on the yarn quality, we set break draft and distance between aprons according to previous optimum results and the pressure was altered in three pressures: 1. High pressure (18 daN), 2.Medium pressure (14 daN) and 3. Low pressure (10 daN).Statistical analyses in table 6 indicate that the pressure of production top roller is effective on the elongation and the tenacity of the yarn in a significant level of 5%. The pressure of production top roller depends on the number of fibres and softness of top roller. When the pressure is low, catching the fibres will be weak and resulting in escaping the fibres and no orientation in a suitable structural direction in yarn and decline of yarn quality. Optimum pressure of top roller is in maximum pressure (18 daN). Figure 5 confirms this fact.

CONCLUSIONS

On basis of the obtained results from this work, we found out for (PES/CV) blend yarns in the ring spinning frame for PES(1.4 dtex × 38 mm long) and CV fibres (1.6 dtex × 38 mm long)to spin a 20 Tex blend yarn of PES (70%)/CV (30%) blend ratio:

1. The total draft influences on the all of yarn qualitative properties such that with increasing total draft the qualitative properties of the yarn will decline.
2. The break draft is effective on the CV%, tenacity and elongation of the yarn. In comparison with other research works, fibres showed similar behaviour against the break draft.
3. The distance between aprons in the main draft zone is effective on the tenacity and elongation of the yarn.
4. The pressure of the production top roller is effective on the tenacity and elongation of the yarn.

According to this research work, the best quality of the yarn for illustrated materials would obtain under drafting conditions of38 total drafts, 1.2 break draft, 2.8 mm distance between of the aprons (white clips) and a maximum pressure of the top roller(18 daN).

In a spinning mill, in order to the promotion of yarn quality in ring frame, before manufacturing of yarn in a high volume of production, obtaining the optimum drafting conditions is vital. It seems we will be able to obtain optimum drafting conditions for different fibres to spin a yarn in ring frame using suitable experimental design and statistical analysis.

Authors

• Mohammad Hatamvand1, Seyed Abbas Mirjalili, Saeid Fattahi, Tariq Bashir, Mikael Skrifvars
• Department of Textile Engineering, Yazd University, Yazd, Iran
• Swedish Center for Resource Recovery, University of Borås, 50190 Borås, Sweden
• Corresponding author e-mail: m.hatamvand@stu.yazd.ac.ir

Republished-article

This article, published elsewhere is re-published here with the permission of the authors. All rights belong to the authors.

ACKNOWLEDGEMENTS

Authors would like to appreciate Bahar Ris Spinning Co. for their facilities and technical support during this research work.

References

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