Introduction

The ready-made garment (RMG) industry of Bangladesh started in the late 1970s and became a prominent player in the economy within a short period of time. The industry has contributed to export earnings, foreign exchange earnings, employment creation, poverty alleviation and the empowerment of women. Bangladesh exports its RMG products mainly to the United States of America and the European Union [1]. Sewing and cutting plays a vital role in garments making. Sewing thread must have good sew ability and be capable of properly joining the two materials together. After joining these materials together, the sewing thread must last for the life of the product that it is sewed in [2]. Manufacturing process of sewing thread affects on sewing thread quality. In this research study polyester thread is used. Polyester is a petroleum product. During the cracking process, crude oil is broken down into a number of components that will be a processed in to a range of product from gasoline to plastic including polyester. Xylene, a hydrocarbon compound, is generated during cracking. Nitric acid and glycol are added to modify the Xylene by a series of chemical reaction. The fluid is heated and condensed in an autoclave and molecules make parallel to form long molecules called polyester [3]. In addition to the many properties and terms, there are several other sewing thread terms one needs to know about. For some end uses, e.g. polypropylene (PP) woven bags for fertilizers, one wants a sewing thread that will stretch, or elongate. By stretching or elongation the sewing thread until it breaks, one can determine how far it will stretch until it ruptures. A ten-inch length of thread may elongate to twelve inches before breaking; therefore 12” minus 10” divided by 10” gives us a 20% elongation at break. Cotton normally has 7% elongation, spun polyester around 15%, and Duralene filament but there is often some confusion between the “yarn count” used in weaving and the “ticket number” of common sewing thread. In the weaving industry when one speaks of yarn count, it is 1 hank of 840 yards and weighting 1 pound. This is an expression of linear yield per pound. In other words, a numbering system based on length per pound [2]. In the case of sewing thread the “ticket number” is only indirectly connected with the length per pound. One is measuring the diameter of the thread in order to be able to use any ticket number, regardless of the plies or the length or weight, in the same needle size. Synthetic filament sewing threads are numbered quite differently [2]. For a particular sewing thread a convenient way of selecting proper needle size is to take a two foot piece of thread and see if the needle will slip easily from one end to the other as the opposite ends are alternately raised or lowered. If the needle does not slip easily from one end to the other by its own weight, the next larger needle should be tried [2]. At that purpose selection of needle size with the needle eye is need to be perfect. Some times it depends on count of the sewing thread significantly.

Stitch
According to ASTM (American Society for Testing and Materials) D 6193 Stitch may be defined as follow ways:

A stitch is the configuration of the interlacing of sewing thread in a specific repeated unit.
A stitching consists of a series of stitches embodied in a material for ornamental purposes or finishing an edge or both.

Principle of Lock Stitch Formation
 

EXPERIMENTAL ANALYSIS

Measurement of EPI, PPI and GSM

EPI & PPI are measured by counting glass. GSM is measured by GSM cutter. Data is given below the table:

Criteria	Plain fabric	Plain poplin fabric	Voile fabric	Gabardine fabric	Woven fabric (Shirting)
GSM	200	149	80	165	131
Warp count	21Ne	45Ne	58 Ne	27 Ne	38 Ne
Weft count	19Ne	38Ne	56 Ne	26 Ne	36 Ne
EPI	96	128	100	134	128
PPI	48	98	76	62	72

Count of the Sewing Thread

1. 45/3;

2. 50/2;

3. 24/3;

The Sewing Machine
Machine Name: Juki
Needle: Single needle lock stitch Needle size: 18

Stitch Length Dial
1.0, 2.0, 3.0, 4.0, 5.0.

Fabrics
Plain fabric; Plain poplin fabric, Voile fabric, Gabardine fabric, Woven fabric (shirting);

Experimental Details
Various counts of sewing thread and SPI have been taken to complete this paper. For this reason table shows the total condition of this paper.

Sewing Performance Rating
So far we are concerned that there is no specific scale or technique to measure sewing performance. Therefore we have thought about it and developed a techniques which are classified the sewing quality into 5 different grades e.g. Poor, Average, Good, Better and Excellent where poor represent worst and excellent represent best sewing quality. The qualities of 5 grades are further elaborated below:

Experimental Table
Experimental table shows the sewing quality in warp and weft direction, which is given bellow:

Table 4: Effect of sewing threadcount on sewingquality [Woven fabric,shirting-(38 X 36)/ (128 X72)]

Stitch Length dial	Resultant count	Thread count	Sewing quality (warp)	Sewing quality (weft)	Warp cover factor	Weft cover factor
1	8	24/3	Poor	Poor	20.76	12
	15	45/3	Good	Good
	25	50/2	Better	Better
2	8	24/3	Average	Average
	15	45/3	Good	Good
	25	50/2	Better	Better
3	8	24/3	Average	Average
	15	45/3	Better	Better
	25	50/2	Excellent	Excellent
4	8	24/3	Good	Good
	15	45/3	Better	Better
	25	50/2	Excellent	Excellent
5	8	24/3	Good	Good
	15	45/3	Better	Better
	25	50/2	Excellent	Excellent

Table 5: Effect of sewing threadcount on sewingquality [Gabardine fabric- (27 X 26)/ (134X62)]

Stitch Length dial	Resultant count	Thread count	Sewing quality (warp)	Sewing quality (weft)	Warp cover factor	Weft cover factor
1	8	24/3	Poor	Poor	25.78	12.15
	15	45/3	Good	Good
	25	50/2	Better	Better
2	8	24/3	Average	Average
	15	45/3	Better	Better
	25	50/2	Good	Good
3	8	24/3	Average	Average
	15	45/3	Excellent	Excellent
	25	50/2	Better	Better
4	8	24/3	Good	Good
	15	45/3	Excellent	Excellent
	25	50/2	Better	Better
5	8	24/3	Good	Good
	15	45/3	Excellent	Excellent
	25	50/2	Better	Better

Effect of Sewing Thread Count on Sewing Quality
The table shows that remaining all other parameters constant, if the thread counts (English Cotton) decreases i.e. sewing thread diameter increases then sewing quality decreases. There could be several reasons for this but the important reasons are as follows:

Structural jamming, -in weaving if we want to increase EPI or PPI of a woven fabric then at certain stage (EPI or PPI) it becomes difficult to insert additional yarns. This is mainly due to the fact that at higher EPI or PPI the cover of the fabric becomes very high so that insertion of additional yarn becomes difficult. Normally fabrics are produced within that limit of EPI and PPI and if that limit is crossed then various types of complicacies are observed e.g. the loom stops very frequently, problems like bumping condition or excessive yarns breaks. However in order to produce a fabric with certain GSM we need to insert certain EPI or PPI. During sewing we are inserting additional yarns in between ends or picks. If the fabrics are already produced with good cover i.e. with greater number of ends and picks then additional yarns due to sewing will definitely produce some impact on the appearance of the sewing quality.

During sewing at high speed, the thread is subjected to various types of complex and dynamic forces. The speed at which it passes through the needle eye of a lock stitch machine may reach as high as 40-45m/second. In sewing a length of thread, before being incorporated in a finished stitch, passes many times through the fabric, the needle eye and around the bobbin case. As a consequence the thread suffers from friction and stresses repeatedly during stitch formation for a prolonged period leading to deterioration of sewing quality. Thus comparatively coarser yarns lead to great amount of sewing fault.

Due to greater diameter of coarser thread in comparison with the space in the long groove the up and down movement of the sewing needle becomes difficult. Due to this problem as the needle goes upwards it draw the fabric upward but the feed dog prevents the fabric to go upwards. It may be mentioned that the needle was not changed during sewing various types of yarns. The size experimental needle was 18 is used for this experiment. In long groove position, 45/3 and 50/2 count sewing thread are easily lie and penetrating in to the needle eye because they covered lower are in the groove due to its finer count. Another side 24/3 is the lower count and coarser thread. It does not lie on properly over the groove and also not penetrating in to the needle eye. At this purpose more rigid and fluffy structure are found.
For perfect sewing the diameter of sewing thread must be lower than that of needle eye. If not then the thread will not be properly clamped on the scarf side of the needle. As a consequences there will be excessive friction between fabric & needle (including thread) leading to poor sewing quality. As the needle assembly raises, the fabric must remain friction free, if not the fabric will raise with the needle so that the widely know problem called flagging will occur,  may be mentioned that flagging is one of the most important causes of skipped stitches and thread breakage.

Effect of Cover Factor on Sewing Quality
The aspect of cover factor plays an important role in weaving as well garment sewing. A higher value of cover factor indicates a compact fabric. During sewing additional threads are inserted in between existing ends and picks so that the cover factor increases [8] [9]. Thus after sewing there will be two types of cover factors e.g. (i) Cover factor due EPI & PPI and (ii) Cover factor due to insertion of sewing thread. Therefore in a sewn fabric two types of cover factor will exist. The resultant of the both the cover factors will assure ultimate sewing quality. Resultant cover factor beyond certain limit will deteriorate the sewing quality. Therefore before sewing any fabric above mentioned both the cover
 
factors must be considered. If the cover factor of the fabric is high then certainly the cover factor of sewing thread must be low.

Conclusion
The present research implies that sewing thread count affects sewing quality. Further to that the research has given some idea about how to select a correct sewing thread count for obtaining better sewing performance. At present sewing thread count is selected according to the GSM of the fabric. Our research indicates that this approach of selecting sewing thread count is not appropriate. According to our research it must be selected giving due regards to the cover factor of both fabric as well as sewing thread. Cover factor of sewing thread is related to the count of sewing thread.


References
Mohammed Ziaul Haider “Competitiveness of the Bangladesh Ready-made Garment Industry in Major International Markets” Asia-Pacific Trade and Investment Review, Vol. 3, No. 1, June 2007.
Textile Research Journal 2010, doi:10,1177/0040517509355350.
http://www.swicofil.com/thread.html.
Geršak, Tekstil, 36, 481 (1987).
J. Geršak, Tekstilec, 29, 253 (1986).
J. O. Ukponmawn, A. Mukhopadhyay, and K. N. Chatterjee, Textile Progress, 30, (2000).
Douglas A. kerr “Stitch formation in rotary hook sewing machine” Issue 3, October 28, 2008.
Haque, Md. Mahbubul, “Importance of cover factor”, Published in a brochure published by the ITET on the event of annual general meeting held in January 2006.
Haque, Md. Mahbubul, “Sewing needle and sewing threads” Textiles & Clothing, Bangladesh- Jan,Feb & March Issue of 2007.

The author is associated with Department of Textile Engineering, Daffodil International University, Dhaka -1207