Scope of Seam Engineering to Increase the Seam Strength by Controlling Different Parameters

Scope of Seam Engineering to Increase the Seam Strength by Controlling Different Parameters

Authors: MD. Momenur Rahman,
Kazi Mustafijur Rahman
Rabeya Siddiqua
Atish Dipankar University of Science and Technology
Dhaka, Bangladesh

Abstract

1. Stitches and seams are two important elements of apparel construction.
2. Stitches are used to join the materials and hold the apparel together, and seams give the shape/contour and detail of the apparel.
3. These two elements together with the material properties contribute to the quality of the apparel.
4. Change in parameters in terms of Sewing Thread Size/Ticket Number, GSM, Stitch Per Inch (SPI) & Stitch Per Minute (SPM) are necessary parameters to calculate different types of variation and variable on which the whole fabric construction depends.
5. The purpose of this study is to investigate the performance of seam quality in terms of seam appearance and strength constructed with different sewing parameters.

Research Aims and Objectives

A. Investigating the performance of seams constructed with different sewing parameters.

• The seam quality is defined by appearance and strength.
• Seams are constructed with different sewing parameters which include the types and sizes of threads, needle sizes and stitch densities for five fabric weight categories.

B. To validate the predictive equation using new fabrics for each category of fabric weight.

• A comparison between the experimental and predictive evaluation of seam quality is done in order to measure the effectiveness and limitations of the equations.

Literature Review

Seam – joining of pieces of fabric together with stitching

Properties of Seam

• Seam Performance (Functional Properties)
• Seam Appearances (Aesthetic Properties)

Functional Properties of Seam

• Seam Strength
• Seam Elasticity
• Seam Durability
• Seam Comfort
• Seam Security

Seam Engineering
The mechanism through which the strength or seam is controlled by improving its different aspects.

Factors that Effect Seam Strength

• Fabric type and weight.
• Thread fiber type, construction, and size.
• Stitch type.
• Stitches density (SPI).
• Stitch balance.

According to Eberle, Hermeling et al. 1996 following table summarizes different types of thread with the description and applications for each thread:

Typical properties of thread
(Ukponmwan, Mukhopadhyay et al. 2000)

The size of sewing thread is usually denoted using the ticket number

• A few different systems are available for producing the ticket number but the systems are mostly based on the weight and thickness of the sewing thread.
• The two most common systems are Tex and Metric.
• Thicker and heavier sewing threads have a higher value of Tex and smaller value of Metric number.

The selection of thread size depends on a few factors which include fabric weight and thickness, stitch and seam types, and needle size (Ukponmwan, Mukhopadhyay et al. 2000).

Examples of end product with suggestions of suitable ticket number of threads to be used during production (Carr and Latham 2000)

Needles:
The way the needle penetrates the fabric during sewing will give different effects in respect of seam strength (Stjepanovic and Strah 1998)

Needle size for different thread size

Determination of Seam Strength
In a lab CRE type tensile testing machines such as INSTRON is used before testing the samples are prepared. The method is called Grab Test.

• If the specimens are from manufactured items such as garment then five specimens are cut having a length of 270 mm on either side of the stitch line and a width of 100 mm parallel to the stitch line.
• If the specimens are prepared from fabric then seam strength is measured in warp, weft and bias directions. In such cases, swatches are cut in these three directions.

The effect of needle temperature on different size needle influence machine speed or SPM (Stitch per Minute). That effect the strength of seam.

Methodology

Considering Factors

Main

• Seam class
• GSM
• Sewing thread
• Stitch type (301 Lockstitch or 401 Chainstitch)
• Thread size
• Stitch Per Inch
• Stitch Per Minute

Partial

• breaking strength
• breaking elongation
• deformation energy.

Estimating Seam Strength
Below are two formulas that were developed for estimating the seam strength on woven fabrics.

To do the calculations, you need to know the following:

• Stitch type (301 Lockstitch or 401 Chainstitch)
• Thread Strength (Single-end breaking strength of the thread, measured in pounds)
• Stitches per inch

Determination of seam strength in Laboratory
(ASTM 1683-04 Standard Procedure)

Significance of the test

• Determines the seam efficiency of a specified seam assembly with each fabric.
• If a determination cannot be made as to which seam is the best suited for a particular fabric, all should be evaluated.
• Used to determine either the sewn seam strength of textiles or the efficiency of a seam assembly with any given fabric.
• Additionally, the seam strengths of different fabrics can be compared directly by using one of the standard seam assemblies specified because current information about laboratory precision is incomplete, comparative tests may be advisable.

Relevant field of test application

• This test method is applicable whenever a determination of effective sewn seam strengths, that is, the optimum seam interaction, is required.
• The breaking force of the seam and fabric will permit the determination of seam efficiency.
• This test method can aid in determining optimum seam interaction for any given fabric by comparing the properties of the fabric with and without seams.
• Seam engineering techniques for specific fabric types can also be determined by utilizing this test method.

Prospected use of the test

• This test method can be used to determine when the sewn seam is affected by seam slippage.
• While the ultimate consequence of this phenomenon is rupture, seam slippage greater than either the values stated in customer specifications or as agreed upon by the purchaser/supplier may severely reduce the integrity such that the product cannot be used for its intended purpose.
• (An example of a commonly used seam slippage value is 6 ± 1 mm [0.25 ± 0.04 in.]).

Result Overview

• From the experimental work, it’s concluded that the usage of thicker threads did not always give better strength and the seam appearance was also poor.
• A combination of finer thread with moderate strength and a medium level of stitch density according to fabric weight category provided an effective result for both seam appearance and strength.
• Sewing Thread Size/Ticket Number, GSM, SPI & SPM is the main considerable point of the thesis. Change in those parameters seam strength is changed.
• The use of low and medium stitch density gave better results in terms of seam strengths.
• In the prediction, thread tensile strength, extensibility and size were selected in most of the equations.
• Thread properties play an important role in determining the quality of seam.
• The equations have not been tested with other types of sewing threads since threads used for this study are commonly used in the apparel industry.
• Other types of stitches and seams could be used to sew the fabrics and analysis on their seam performance could be done.
• For this research, only single stitching was used; another possible research area is to use double stitching.

Effect of sewing thread on seam strength
There are various parameters of sewing thread including its fiber type, construction, finish, size, ply & TPI, which affect the seam quality.

These parameters will be discuss following:

• Thread Fiber Type (seam strength highest for 100% spun polyester, average for cotton/polyester blend & lowest for 100% cotton).
• Thread Construction (seam strength highest for core spun yarn; 100% synthetic fiber shows more seam strengths).
• Thread Finish (mercerized threads shows more seam strength than any soft cotton threads of the same fiber type and size ).
• Thread Ply (the more the thread ply, the more the seam strengths)
• TPI (the more the TPI, the more the seam strengths).

Effect of Thread size (Ticket Number) on seam strength

Graphical Expression

• The numerical expression of sewing thread fineness or coarseness is “Ticket number”. It is equal to three times the metric count of the thread.
• The more the ticket number, the high the seam strengths.

Effect of fabric properties on seam strength
Various fabric properties like Cover factor, GSM, Thickness, Strength, Extensibility etc.

In the following sections these fabric properties are discussed in brief:

• Cover Factor (the more the cover factor, the less the seam strength is, the less the cover factor, the more the seam strength is).
• Fabric Weight (light fabric shows less seam strength than heavy fabrics).
• Fabric Thickness (the more the fabric thickness, the more the seam)
• Strength is & less seam efficiency)
• Fabric Strength (the more the fabric strength, the more the seam strength is & less seam efficiency)
• Fabric extensibility (the more the fabric extensibility, the more the seam strength is & less seam efficiency).

Effect of GSM on seam strength

Graphical Expression 

• GSM means “Gram Per Square Meter”.
• It is the weight of fabric in gram per one square meter.
• By this we can compare the fabrics in unit area which is heavier and which is lighter.
• In a certain point, when GSM increases seam strengths increase & over time seam strengths decreases though GSM increase.

Effect of Stitch Density (SPI) on seam strength

Graphical Expression

• Stitch density is specified as the number of stitches per inch (SPI).
• Higher stitches per inch (SPI) means short stitches, and lower SPI means long stitches.
• The greater the SPI in a seam, the greater the seam strengths are & the lower the SPI in a seam, the lower the seam strengths.

Effect of stitch per minute (SPM) on seam strength

Graphical Expression

• Modern sewing machine speed can reach up to 5,500 stitches a minute.
• The fact is that in a high-speed sewing machine the movement of the sewing needle is higher that generates heat.
• This creates seam damage problem that causes of poor seam efficiency and appearance in a garment.

Effect of other factors on seam strength

Human Factor:

• If the operator is lacking in skill, seam problems will be generated during sewing.
• Excessive or improper handling and positioning of the fabric parts during sewing lead to seam puckering.
• If the operator is unable to handle the sewing machine properly, there is a chance of seam damage due to frequent needle breakage.

Environmental Factor:

• All environmental problems reduce the concentration and skill of the operator to work.
• Due to poor concentration and reduction of the skill, the operator cannot properly handle the garment parts during stitching.
• High humidity and temperature also reduced the strength of sewing thread during sewing that produces poor seam strengths.

Recommendations

• For the analysis of the seam strengths, transverse loading was used for this study where the loading was across the seam and the effect of thread strength was analyzed. For future work, the seam strength test could also be done on longitudinal loading where the load is parallel to the seam.
• The performance of the seam can also be widened for weft and bias directions of sewing for both seam appearance and strength analysis. For the current study, only the warp direction of sewn fabrics was analyzed since this is the most common practice in the industry.
• Other types of stitches and seams could be used to sew the fabrics and analysis on their seam performance could be done. For this research, only single stitching was used; another possible research area is to use double stitching.