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Minimizing Thread Breakage & Skipped Stitches |
Introduction
Thread breakage and
skipped stitches are common aggravations on any sewing floor because it
interrupts production, affects quality, and reduces the earnings and
efficiency of production operators. Thread breakage and skipped stitches
can be caused by many factors including the following listed below.
As you can see then there are many variables that impact thread breakage
and skipped stitches. Initially, we will focus on the characteristics in
thread that impact thread breakage, but later we will also discuss a
logical approach used for trouble-shooting thread breakage.
Factors that Cause
Skipped Stitches
Wrong thread for the application.
Quality defects in
the thread.
Improper needle /
thread size relationship.
Worn or defective
thread guides or eyelets.
Improper threading.
Excessive machine
thread tension.
Defective needle or
improper positioning of the needle.
Needle heat.
Worn or defective
machine parts (burrs or sharp surfaces on thread handling or stitch
forming devices).
Machines out of
adjustment.
Improper feeding. Improper operator
handling. Flagging.
The key product
characteristics in thread that have the greatest impact on thread breakage
and skipped stitches include:
- Proper loop
formation.
- Absence of yarn
imperfections.
- Proper lubrication.
- Ply security or ply
adhesion.
Proper Loop Formation
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Every sewing machine uses a needle to pass thread through the seam
to form a stitch. Most sewing machines begin their stitch forming
cycle when the needle starts to rise from the bottom of its
stroke. |
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(1)
The upward motion of the needle, (2) the clamping action of the thread
between the needle blade and the fabric, and (3) the holding of the
seam in a stationary position all play an important role in proper
loop formation.
Loop Formation refers
to the forming of a loop for the stitch-forming device (e.g., hook, looper,
spreader) to enter. When the needle thread loop is formed, three things
can happen and two of them are bad. Ideally, the stitch forming device
will enter the loop and continue to form the stitch; however, if an
improper thread loop is formed, the stitch forming device can strike the
thread causing the thread to break or miss the loop causing a skipped
stitch. The thread
characteristics that impact loop formation include:
- Elongation or
stretchiness of the thread.
- Initial modulus or
initial resistance to stretching.
- Twist direction &
twist level.
- Liveliness of the
thread.
- Frictional
characteristics needed to set a balanced stitch
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If the needle size - thread size relationship is improper, the
thread will not be properly clamped on the scarf side of the
needle and poor loop formation will occur. If the seam is not held
in a stationary position when the needle is rising, the seam will
rise with the needle and not form a proper needle loop. This
condition, called flagging, is one of the most common causes of
skipped stitches and thread breakage. |
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Many times a skipped
stitch or thread break will occur when crossing another seam. This problem
could occur due to the additional thickness that the needle has to
penetrate. This could apply additional tension to the thread or cause the
needle to deflect away from the stitch-forming device. However, many times
the skip or break occurs right after the thickness has been crossed and
usually the result of flagging. This happens when the back portion of the
presser foot is still on the seam and the front portion of the foot is no
longer clamping the fabric securely. Therefore, as the needle begins to
rise, the fabric moves up with the needle and a poor needle loop is
formed.
Thread Elongation
and Initial Modulus The inherent
stretchiness or elongation of the thread is generally determined by the
fiber type. For example, both nylon and polyester threads have a much
higher elongation than 100% cotton threads. On the following graph, you
can see the relationship between tension and elongation. The cotton thread
stretches approximately 3 to 4% before it breaks. Polyester thread, on the
other hand, stretches approximately 17 to 20% before it breaks. The
polyester thread has a higher elongation at break that contributes to
greater seam elasticity and seam strength.
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A key product
characteristic developed in our synthetic threads to enhance loop formation
is a high initial modulus or initial resistance to stretching. A thread with
a higher initial modulus will minimize the amount that the thread stretches
as the needle approaches the bottom of its travel. Therefore, when the
needle begins to rise, the thread will be relaxed so a proper needle loop
will be formed. |
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When the thread is
stretched as the needle reaches the bottom of its travel in the stitch
formation cycle, the thread will recover to its original un-stretched length
as the needle begins to rise. The more the thread is stretched, the later a
needle loop will be formed and the smaller the target the stitch forming
device has to enter to form a proper stitch. The end result may be a skipped
stitch or thread breakage.
The physical properties in thread that impact how much the thread is
stretched during the sewing process include:
- Elongation
properties of the fiber being used.
- Initial modulus -
the thread's initial resistance to stretching.
- Frictional
characteristics of the thread needed to set a balanced stitch.
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Note:
Regardless of the type of thread being used, as more and more tension is
applied to the thread, the thread will stretch more, affecting loop
formation. Improper loop formation will result in a higher frequency of
sewing interruptions. This is why it is recommended to always adjust the
sewing machines thread handling system to sew with minimum thread tension.
Below is a recommended
procedure for balancing the stitch on a any sewing machine:
- Set the bottom
tension (bobbin or looper) to a minimum that still forms a consistent
stitch.
- Reduce the needle
thread tension until the stitch appears to be loose on the bottom side
of the seam then tighten the top tension until a balanced stitch is
achieved.
Thread Lubricant
The thread lubricant
is another important variable in the loop formation equation. Ideally, the
thread lubricant will give the thread a consistent dynamic tension as it
passes through the sewing machine's thread guides and tension devices and
also allow the thread to form a balanced stitch with minimum thread
tension. This will minimize the amount that the thread stretches allowing
a proper needle loop to form. Later in this bulletin, we will look at some
of the variables that impact the frictional characteristics of sewing
thread.
Many thread lubricants
include an antistat to minimize the static electrical attraction of the
thread to metal surfaces. This attraction can cause the thread to leave
its proper thread path impacting loop formation and thread breakage.
Synthetic threads made from polyester and nylon are more susceptible to
static than threads made from cotton or rayon.
Uniformity - Consistency of Physical Properties
Many factors affect
the uniformity of the thread. By uniformity, we are referring to the
consistency in physical properties regarding:
- Yarn Construction.
- Yarn Diameter
(absence of yarn imperfections like knots and slubs, etc.).
- Strength.
- Elongation and
modulus.
- Lubrication.
- Cone build or wind.
These are the primary
thread properties that have an impact on sewability. Other factors that
affect seam integrity and seam appearance include:
- Color.
- Color Fastness.
- Resistance to seam
degradation (chemicals, abrasion, UV, etc.).
- Loop strength.
For the sake of this
technical bulletin, we will focus on the factors that affect thread
breakage.
Yarn Construction
Continuous filament
thread constructions are more consistent in physical properties and
diameter and generally have a higher tenacity or strength per size than
spun constructions made with staple fibers. Below is a ranking of thread
constructions regarding consistency of construction:
- Monofilament.
- Monocord.
- Twisted
Multifilament.
- Textured Air
Entangled.
- Corespun.
- Spun.
Many factors affect
the uniformity of the thread. By uniformity, we are referring to the
consistency in physical properties regarding:
- Yarn Construction.
- Yarn Diameter
(absence of yarn imperfections like knots and slubs, etc.).
- Strength.
- Elongation and
modulus.
- Lubrication.
- Cone build or wind.
These are the primary
thread properties that have an impact on sewability. Other factors that
affect seam integrity and seam appearance include:
- Color.
- Color Fastness.
- Resistance to seam
degradation (chemicals, abrasion, UV, etc.).
- Loop strength.
For the sake of this
technical bulletin, we will focus on the factors that affect thread
breakage.
Uniformity -
Absence of Yarn Imperfections
Yarn imperfections
like knots and slubs will generally cause thread breakage; that is why
A&E has reengineered many of its processes to eliminate major
imperfections. This includes the use of Air Splices where knots used to
be used. We believe that "no knot is a good knot".
Payoff the Cone
Due to the Build or the Wind
To minimize thread
breakage, it is imperative that the thread feed off the cone with the
least amount of resistance. This is why it is important that the
thread-stand eyelet is located directly over the center of the cone.
Proper Frictional Characteristics
The frictional
characteristics of a sewing thread can be affected by:
- Fiber Type (e.g.,
Cotton, Polyester).
- Thread Construction
(e.g., Spun, Textured, Air Entangled).
- Dye Types and Cycle
times (e.g., Disperse, Acid) ?/font>
- Thread Finish
(Soft, Bond, Glace).
- Thread Lubricant
(e.g., Silicone, Wax based).
- Cone type and wind.
A&E is working hard to
reduce the variation in all these characteristics to allow our threads to
be sewn with minimum machine tension adjustments.
Thread Lubricant
One purpose of a
thread lubricant applied to the surface of the thread is to allow the
thread to pass through the sewing machine's thread guides and tension
devices with uniform tension and to also allow the stitch to be set with
minimum thread tension.
Good Ply Security or Ply Adhesion
If you look at the end
of the thread that has broken, it usually is not a clean break but an
unraveled group of fibers. These unraveled thread breaks are caused by a
breakdown in the ply adhesion of the fibers in the thread. If there was a
clean cut or break it could be caused by a weak spot in the thread or a
sharp surface in the machine that cuts the thread. However, most breaks
appear to have been unraveled.
A number of factors
affect the ply security of the thread. They include:
- Thread construction
(e.g., spun, core, textured).
- Uniformity of
construction.
- Twist level (TPI).
- Fiber cohesion
characteristics.
- Thread finish
(e.g., soft, bonded, glaced).
- Frictional
characteristics of the thread.
Most manufacturers
have learned by experience that core spun threads give better sewing
performance on automated multi-directional sewing machines than spun
constructed threads.
Thread Selection Summary
As you can see from
the preceding remarks, there are many causes of thread breakage and
skipped stitches so it is important to observe and evaluate the problem to
determine what might be the primary cause. Usually, more than one of the
factors listed contributes to excessive thread breakage.
If you need technical
assistance in evaluating your thread breakage problem, you can contact
A&E's Technical Service Department for assistance. We look forward to
serving you.
Other Causes of Thread
Breakage and Skipped Stitches
In the following
comments, we will outline a trouble-shooting guide from three
perspectives:
- Is the thread
breakage or skipping occurring on all operations and on most types of
machines?
- Is the thread
breakage or skipping occurring primarily on one operation or type of
machine?
- Is the thread
breakage or skipping occurring on one or two machines only?
The reason for this
analysis is to help you differentiate between thread related problems and
machine related problems. Common sense should tell you that if a sewing
problem is occurring on only one or two machines, the problem is most
likely NOT a thread related problem unless a noticeable defect is visible.
On the other hand, if the problem is occurring on one color and on all
sewing operations, the thread should be investigated first.
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Is
Thread Breakage Occurring on All Operations and on Most Types of Machines? |
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Check the following:
a) Has there been a
thread change:
- From one type to
another?
- From one size to
another?
- From one supplier
to another?
b) Check the quality
of the thread for obvious defects:
- Knots, slubs, neps,
improper twist, etc.
- Does the thread
feel weak?
- Does the thread
feel dry or pull through the sewing machine with a rough drag?
c) Check the quality
of the piece goods being sewn:
- Has there been a
change from one supplier to another?
- From one type to
another?
- In the weight or
stiffness of the fabric?
d) Is thread breakage
occurring on all colors and patterns, or on one color or style?
Recommendations
- Try sewing with
thread from a different case or shipment.
- Make sure the
correct thread type and size is being used.
- Send cones that are
breaking to your thread supplier for evaluation. Ask for technical
assistance if available.
- If the fabric
appears to be different, see if fabric from a different shipment
causes the same problem.
- Ask your piece
goods supplier to check the fabric for proper finishing, etc.
- Check for signs of
needle heat.
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Is
Thread Breakage or Skipping Occurring Primarily on One Operation or Type
of Machine? |
a) Has there been a
thread change:
- From one type to
another?
- From one size to
another?
- From one supplier
to another?
b) Is the correct type
and size needle being used?
c) Is the proper
machine and attachment being used for the operation?
d) Are the machines
adjusted correctly for the operation?
e) Have the sewing
operators made any changes in their method of operation?
Recommendations:
- Observe the
operation to see if the thread is breaking at the same location most
of the time. Depending on the fabric and operation, a special thread
might be required.
- Make sure the
correct needle and thread sizes are being used for the operation.
- The machines should
be set up correctly for the operation with the correct presser foot,
feed, needle plate and attachments.
- Check to make sure
the mechanics are familiar with the particular type of machines being
used on this operation. If not, try to find a training program on the
equipment. Check with your machine supplier.
- Check for signs of
needle heat. Try reducing the size of the needle or use a special
coated needle. Use needle coolers on the machines if needed.
- Make sure the
sewing operators are properly trained on the operation and are using
the correct material handling techniques.
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