The Influence of Stitch Density and of the Type of Sewing Thread on Seam Strength
Daniela Barbulov – Popov1, Nenad Cirkovic2, Jovan Stepanović2 1Technical faculty “Mihajlo Pupin”, Zrenjanin, University in Novi Sad, Serbia
2Technological faculty, Leskovac, University in Nis, Serbia
Abstract – Having in mind the complex problems of technological process of sewing, as well as general demands for seams produced in garment production, this research should contribute the development of sewed seams breaking forces. Thus, many measurements of seam breaking forces have been conducted. These measurements enable us to define optimal strength of seam strength that improves the compliance of sewed seams parameters. This paper deals with the influence of the thread type and stitch density on the seam strength. The breaking forces and elongations at break were determined by the standardized method (SRPS 2062) and fabric (tape method) according to SRPS EN ISO 13934-1. Fabric samples used for seam testing were sewed by seam (1.01.01) and stitch type 301 with stitch densities 3, 4 and 5 cm-1. Optimal seam strength (130.9 Ncm-1) on the fabric T71, and at the same time the highest strength, has been noticed at the samples with seam line in weft direction with stitch density 5 cm-1, sewed with polyester thread 20x2 tex count, while on fabric T71 that value is 115.9 Ncm-1. According to obtained results, it can be concluded that stitch density (3 cm-1 ÷ 5 cm-1) and the type of sewing thread (cotton and polyester,K1 ÷ K5) have great influence on defining seam sttrength, their inconsistency may lead to great differences in seam behavior.
Keywords – Seam Strength, Seam Breaking Force
The seam characteristics include: strength, elasticity, durability, safety, and appearance. Inconsistency of these characteristics can lead to significant differences in seam behavior and it also affects their deformation characteristics. During the process of clothes exploitation, sewed seams and materials are subjected to different loads, which are usually very variable, leading to different deformations. Seam strength should correspond to material strength in order to obtain product uniformity which will be capable to endure all forces which is that product subjected to [1,2]. During wearing, stitch bonded parts of clothing are subjected to different stresses. In order to improve seam endurance, seam elasticity should be a little stronger than material elasticity. Thus, the material would also mitigate the effect of the forces that affect clothing product during wearing. The seam elasticity depends on material that is stitch bonded, stitch type, seam type, stitch density, etc. Seam durability depends on its strength and on relationship between seam and material elasticity [3,4]. Seam safety depends mainly on sewing width, slippage of fabric wires as well as on stitch type. It is crucial to prevent its slitting and breaking during the wearing process.
Defining seam strength
One of the most important indicators of the sewed products quality is seam strength, which depends on different technical-technological parameters, such as: fabric type, type and sewing thread count, sewing needle count, stitch type, stitch density, seam type, etc. According to definition, strength and elasticity of sewed seam should be made in such a way that they do not allow seam breakage upon normal stresses of garment products, but also it cannot allow the fabric deformation [1,4]. The seam strength can be determined experimentally (by defining the force which the seam can withstand). Defining breaking force, the point when deformation, seam breakage and elongation at break occur, i.e. when the sewed sample changes its length, is based on measurements related to force and elongations under constant direct stress.
On the dynamometer, during the testing fabric samples with seam in transverse direction in relation to the seam, the stress (loading) q at mobile pirn clamp is evenly applied (Figure 1a). Furthermore, we can notice q reaction at fixed pirn clamp which is also evenly applied stress even to q (N/cm), i.e. q = q.
Figure 1. Seam stress at transverse tension a) sample on dynamometer, b) and c) application of the stress in a stitch For the value of the applied force on the lower mobile pirn clamp, the loading q will be:
q – stress of the sample at mobile clamp (N/cm),
q' – the reaction to the stress q (N/cm),
F – drawing off force of lower mobile clamp (N),
b - the sample’s width on the dynamometer(cm).
If we observe the application of the force in one stitch, 301 type, (Figure 1b), it is obvious that, ideally, threads will be stressed at elongation in each stitch. Due to the fact that q = q, stitch stress will not cause the thread migration at entangle points. Because of that, we must define reactions that occur at side stitches (Figure 1c). In that case, if we apply the force of lower clamp movement and the theory of material resistance, we can find values of reaction forces A(N) and B(N), which would refer to the strength of thread built in the seam:
Where: d-stitch length (cm).
If we change the values for the stitch length that is d= b/n, in the last formula, the seam breaking force F, which is bonded with stitch type 301, can be expressed as follows:
FP – thread breaking force (N),
n – number of stitches in sewed material sample
If we know the initial thread breaking force and the coefficient of strength loss of thread in the process of stitch making , the previous formula is changed into:
Where: FP1 - initial thread breaking force (N),
- Coefficient of strength loss of thread.
If we want to use this formula, it is necessary to determine the value of coefficient of strength loss of thread experimentally under the different conditions of stitch formation. On the basis of these experimental data relating to different fabrics sewed by lockstitch of different densities, the value of this coefficient is between 0,8 and 1,2.
Methods used for testing seam strength are based on testing thread slippage or thread breakage in the seam area. According to tt.Coats method, the seam breaking force is defined at one cm of seam length, i.e. by defining relative breaking force, in transverse direction in relation to seam line. The relative seam breaking force is calculated on the basis of average value of breaking force and seam length (the width of test tube used for testing) according to the expression [3,5]:
Where: Fr – relative seam breaking force (Ncm-1)
F – breaking force of test tube seam (N),
b – the width of sewed sample test tube (cm).
As the stitch density and breaking force of used thread have great influence on breaking characteristics if seams, it is necessary for this paper to introduce parameter called “seam strength factor”, which is calculated according to the following equation:
Where: fk – seam strength factor (Ncm-1)
FP – thread breaking force (N)
gu – stitch density (cm-1)
Havin in mind the analysis of seam breaking forces testing and the instability of wire system of the fabric and thread system in the seam (due to the stress), it is necessary, for projecting sewed seams breeaking forces, introduce appropriate correction coefficients that would take this fact into consideration. In this case, correction coefficient k is defined throug the relationship between seam breaking force (Fr) and seam strength factor (fk).
Two types of fabrics were used for sample seam bonding (Figure 1), which were bonded by sewing machine (PFAFF company), class 461 (sewing speed 2500 min-1), stitch type 301 (Figure 2) .
Figure 2. The shape of seam sample used for testing breaking characteristics The machine is equiped with upper and lower transport, pedal and needle positioning and automatic thread cutting. Fabric samples, tape shape (two pieces), dimensions 185 mm x 50 mm, were sewed by the seam mark 1.01.01 (Figure 3) , at the distance of 10mm from the edge, with the needle 90 (normal needle point), and stitch density 3 cm-1, 4 cm-1 and 5 cm-1.
Breaking characteristics of threads were tested on dynamometer USTER TENSORAPID 4, according to standardized method SRPS 2062 , while breaking characteristics of fabrics were tested on dynamometer ZWICK, according to SRPS EN ISO 13934-1 . The processing of research data was carried out by mathematical statistics.
Results and discussion
Table 1 presents basic fabric characteristics that were used for making seam samples, while table 2 presents the characteristics of used sewing threads.
Table 1. Basic characteristics of fabrics used for making seam sample.
Five wired sateen weave
Five wired sateen weave
Raw material content (%)
Surface mass (gm-2)
Warp yarn count (tex)
Weft yarn count (tex)
Warp density (cm-1)
Weft density (cm-1)
Breaking force in warp direction (N)
Breaking force in weft direction (N)
Elongation at break in warp direction (%)
Elongation at break in weft direction (%)
Table 2. Characteristics of used threads for sample seams sewing.
Raw material content (%)
Number of twists for single wired yarn (m-1)
Number of twists at plying (m-1)
Breaking force (cN)
Elongation at break (%)
Breaking force at loop (cN)
Table 3 shows the results of testing breaking characteristics of sewed seams.
Table 3. Results of testing seam breaking forces on fabric T21:
Table 4. Results of testing seam breaking forces on fabricT71:
Seam line in warp direction
Seam line in weft direction
Seam breaking force
Relative seam breaking force
Seam strength factor
Seam breaking force
Relative seam breaking force
Seam strength factor
The graph shows the results of testing seam breaking forces according tables 3 and 4. These results are presented in figure 5.
Statistical data of correlation and regression analysis
( Y = A + B · X)
In warp direction of fabric T21
In weft direction of fabric T21
In warp direction of fabric T71
In weft direction of fabric T71
Figure 5. Changes of seam breaking forces depending on thread type and stitch density, a) for fabric T21 and b) for fabric T71 (O – seam line in warp direction,
P – seam line in weft direction) The analysis of obtained results of breaking forces shows:
Increased stitch number improves the strength of analyzed seams, i.e. their breaking and relative breaking force. This improvement can be noticed for all samples, regardless to the type of used thread.
Comparing fabrics T71 and T21, the bigger breaking force can be noticed at fabric T71, which is caused by fabric construction itself. As these fabrics are in the same weave and of the same raw material content, the seam breaking force is influenced by the density of weft and warp wires in the fabric (Table 1). The seams in weft direction have bigger breaking force comparing to seams in warp direction, which can be explained as a result of structural solution of woven fabric and its bigger breaking force in warp direction.
Seam samples were sewed by PES threads (K2, K4) that, thanks to better mechanical characteristics, have bigger values of breaking forces in relation to samples sewed by cotton threads (K1, K3).
Statistic data processing proves the validity of results obtained by the influence of stitch density and sewing thread type on seam strength. This also confirms mutual dependance of seam relative breaking force, as dependance variable, and stitch density and sewing thread type, as independant variable, during which correlation coefficient R is determined.
Table 5 shows correlative and regression analysis of results, which are obtained by testing relative breaking force of seam and stitch density for seam samples with used stitch 301 type.
Table 5. Correlation and regression analysis of results obtained by testing the influence of seam strength factors on relative seam breakin force.
Note:Fr –average value of relative breaking force of seam force, R – correlative coefficient, A and B – coefficients of regression (linear) equation, fk –seam strength factor (Ncm-1)
Linear regression of dependence between relative breaking force and seam strength factor is shown in figures 6 and 7. These regressions are valid for stitch density interval from 3 cm-1 to 5 cm-1.
(a) seam in warp direction
(b) seam in weft direction Figure 6. Linear regression between relative breaking force and seam strength factor for samples used on fabric T21, a) seam in warp direction and b) seam in weft direction.
(a) seam in warp direction
b) seam in weft direction Figure 7. Linear regression between relative breaking force and seam strength factor used for samples on fabric T71, a) seam in warp direction and b) seam in weft direction On the basis of results shown in tables and graphs, it can be noticed that optimal seam strength on fabric T71 with 4 cm-1 has the value 70.8 Ncm-1 for the seam in the warp direction, and 75.5 Ncm-1 for seam in weft direction, with 5 cm-1 , it is 114 Ncm-1 for the seam in warp direction and 130.9 Ncm-1 for the seam in weft direction.
It acan also be concluded that change of seam breaking force (results referring to stitch densities in itnterval from 3-5 cm-1) gains aproximative functional dependance. Higher values of stitch density cause damaging of above mention dependance.
Dependence correlation between parameters, in an interval, besides information on the type of dependence, can also be used for calculating values of one parameter for appropriate value of other one. Understanding dependence between some parameters of sewing process is of great importance in quality control and in the process of textile processing.
According to the results from this experiment, it can be concluded that seam strength depends on used fabric (structural and construction parameters), type of used thread (raw material content, count), as well as on stitch density per cm of the seam. Optimal seam strength (130.9 Ncm-1) on fabric T71, which is at the same time the highest strength value, was seen at samples with seam line in weft direction with stitch density 5 cm-1, sewed by poliester thread 20x2 tex count, while, for fabric T21, that value is 115.9 Ncm-1.
Having analyzed dependency of relative breaking force and seam strength factor on stitch density, as well as having applied given correlative relationships, it can be concluded that there is connectivity between parameters. It is approved by the values of correlation coefficient. On the basis of this analysis, it is possible to predict seam-breaking force for stitch density interval from 3 cm-1 to 5 cm-1 for all above mentioned sewing threads.
Taking into consideration numerous parameters influencing the seam quality (type of material, type and thread count, seam type, stitch type, stitch denstiy, etc.) , there are many possibilities for combining them with different final characteristics of seams. The main purpose of these combinations is defining the appropriate technical-technological parameters of sewing process in order to improve productivity and seam quality.
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Corresponding author: Daniela Barbulov – Popov
Institution: Technical faculty “Mihajlo Pupin”, Zrenjanin, University in Novi Sad, Serbia.