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Existing Technologies for Stitch Formation: Type 301 (Lockstitch) and Type 401 (Double Thread Chain Stitch) and Their «Eternal» Disadvantages.
Existing Technologies for Stitch Formation: Type 301 (Lockstitch) and Type 401 (Double Thread Chain Stitch) and Their «Eternal» Disadvantages.
Straight stitches are the most commonly used method for joining materials in the production of various sewn products, surpassing other types of stitches. The technologies responsible for creating straight stitches operate under conditions that are more complex than those applied to other seam types. This is due to the need to sew different materials with varying thicknesses, densities, rigidity, and elasticity, as well as through multilayer constructions and thick cross seams.
Currently, the primary types of stitches used for straight sewing are the lockstitch type 301 and the double thread chain stitch type 401. These stitches are formed using sewing technologies based on hook and looper mechanisms, featuring a bottom thread passing eye at the tip, an invention that dates back to the 19th century.
However, the existing technologies for forming these stitches have a number of disadvantages related to their formation process, which can be described as «eternal». No matter how advanced these technologies may become, they will never provide an ideal solution for straight stitch sewing. Their inherent limitations prevent the achievement of true perfection.
In our next videos, we will not only illustrate these «eternal» disadvantages but also demonstrate them in action, showing why these technologies, despite their advancements, cannot escape their historical roots.
Technologies may evolve, but the associated disadvantages remain «forever».
VIDEO: 1_ZARIF 2023_Revolution in sewing_Eternal disadvantages of existing sewing technologies 301_401.
The Existing Technologies for Forming the Lockstitch 301.
The Existing Technologies for Forming the Lockstitch 301.
Existing technologies for forming lockstitch type 301 using different types of hooks.
LockStitch Formation Principles.
By analysing the lockstitch type 301, we can identify the key principles that ensure its formation. The first principle is that one branch of the bottom thread is passed through the loop of the top thread formed during sewing.
The second principle involves tightening the loop of the top thread toward the middle of the material being sewn, ensuring the interlacing of the threads within the very center of the sewn material.
Manual Method for Forming LockStitch 301.
The process of passing the branch of the bottom thread through the loop of the top thread is only possible when the bobbin with the bottom thread passes through the loop of the top thread, while the end of the bottom thread is held outside of the top thread loop.
To form the top thread loop, a standard needle with an eye at the tip is used, through which the top thread is threaded. As the needle pierces the material, it pulls the top thread through it, and during the upward movement, a loop is formed near the needle’s eye.
Once the bobbin with the bottom thread passes through the loop of the top thread, we achieve the main condition – passing one branch of the bottom thread through the loop of the top thread. Next, the loop of the top thread is tightened toward the middle of the material, ensuring uniform interlacing of the top and bottom threads in the center of the sewn layer. This process is repeated in cycles until all the bottom thread on the bobbin is used.
Mechanical Method for Forming LockStitch 301.
The mechanical method of forming the lockstitch type 301 in a sewing machine differs from the manual method only in that a specialized hook is used in the machine. This hook, which has a tip and contains a bobbin with the bottom thread inside, captures the loop of the top thread formed by the needle. The hook then expands this loop and wraps it around the bobbin with the bottom thread. After the top thread loop reaches its maximum expansion, the thread take-up lever begins the process of pulling the loop of the top thread towards the center of the material.
Since the bobbin with the bottom thread is inside the hook, when the top thread loop exits the hook, it pulls along a branch of the bottom thread. The thread take-up lever then completes the tightening of the top thread loop to the center of the material, thus forming a strong interlacing of threads.
The lockstitch type 301 technology ensures the passage of one branch of the bottom thread through the loop of the top thread by utilizing various types of hooks, where the bottom thread bobbin is housed. Depending on the design, the hook can perform rotational, oscillating, or reciprocating movements to wrap the top thread loop around the bobbin with the bottom thread.
At present, hooks with reciprocating motion are practically no longer used in modern sewing machines, as they are limited to low-speed operation.
Machines with oscillating hooks also have certain speed limitations — up to 3,500 stitches per minute. This is due to increased inertia and vibration during high-speed operation, which can lead to increased noise and other performance issues.
THE «ETERNAL» DISADVANTAGES OF EXISTING TECHNOLOGIES OF LOCKSTITCH TYPE 301.
THE «ETERNAL» DISADVANTAGES OF EXISTING TECHNOLOGIES OF LOCKSTITCH TYPE 301.
1. For all types of hooks it is essential to change the bobbin with the bottom thread inside the hook regularly due to the limited amount of bottom thread available on the bobbin. All automatic bobbin changers and automatic bobbin winders and feeders are very complicated and expensive, adding to the cost of the machine.
2. When using all types of hooks, it is necessary to adjust the thread tension so that the threads are intertwined in the centre of the materials to be sewn, depending on the thickness, density, stiffness and elasticity of the materials to be sewn, as well as to obtain a tighter connection of the materials, a smoother seam on light materials and a more elastic seam on elastic materials.
3. With all types of hooks, the thread take-up has to tightening the top thread unevenly because it has to complete the tightening of the large size of the top thread and have time to feed the top thread to the needle before the needle eye is immersed in the material when the needle starts to consume the top thread. Therefore, depending on the thickness of the material to be sewn, four types of thread take-ups are used, all of which require lubrication, except for the rotary type (D), which is used for sewing light materials.
A. Cam type thread take-up lever. Sewing speed up to 1500 rpm. For sewing extra heavy thick materials.
B. Link type thread take-up lever. Sewing speed up to 5000 rpm. For sewing medium materials.
C. Slide type thread take-up lever. Sewing speed up to 3500 rpm. For sewing heavy materials.
D. Rotary thread take-up lever. Sewing speed up to 5000 rpm. For sewing lightweight materials.
4. All types of hooks have a complex design and are made up of many parts, which increases their cost.
5. All types of hooks have a sliding area, as they have both fixed and moving parts, and their sliding areas must be lubricated, which can be done manually or automatically, the automatic lubrication system for the sliding area complicates the design of the hooks, making them more complex and expensive.
6. All types of hooks have both fixed and moving parts, which can cause thread segments to be caught between them, resulting in the hook jamming and the sewing machine stopping suddenly.
7. All types of hooks have a limited life due to friction in the sliding area between the fixed and moving parts of the hook.
8. All types of hooks do not guarantee sewing without skipping a stitch, which occurs when the hook point does not enter the loop of the top thread formed by the needle when it is lifted from its lowest position.
9. All lockstitch sewing machines cannot guarantee sewing without thread breakage because the needle deflection during the downward movement may cause the needle to collide with the needle plate or hook housing, resulting in needle breakage or deformation of the needle point, resulting in thread breakage. In addition, collision with the needle may cause burrs to form on the walls of the hole of the needle plate and hook housing, which may also cause thread breakage. In addition, when the top thread tension is high, the uneven tightening of the top thread by the thread take-up device may cause the top thread to be subjected to a heavy load, which may also cause the top thread to break. In addition, if the oil supply to the hook is insufficient, the hook may become very hot at high sewing speeds, which may also cause the top thread to break.
10. For all hook types when changing from needle Nm. 130/21 to needle Nm. 60/8, it is necessary to adjust the hook in relation to the needle, as the maximum permissible distance between the hook tip and the needle is 0.1 mm.
11. All lockstitch sewing machines cannot guarantee sewing without needle breakage or deformation of the needle point. The reason for this is that as the needle moves downwards it passes very close to the hook body and the wall of the hole in the needle plate. As a result, the needle may collide with hard objects when it is deflected when sewing thick and cross seams and when sewing stiff and dense materials.
12. All types of hooks are equipped with a needle guard to increase the reliability of the entry of the hook tip into the loop of the top thread formed by the needle when it is lifted from the lower position; the deflection of the needle in its downward movement can lead to a collision with the needle guard, causing the needle to break or the needle point to be deformed.
13. Depending on the thickness, stiffness, density and elasticity of the material to be sewn, it is necessary to adjust the height of the needle lift from the lower position for forming the loop from the top thread, so that the hook tip enters more securely into the loop formed by the top thread on the needle.
14. All lockstitch sewing machines use a thread-tension spring in the top thread tensioner to keep the top thread taut at least until the needle point penetrates the material and the tension of the thread tension spring should be between 20 and 50 cN (1 cN = 1 g) depending on the material and thread.
15. In industrial lockstitch sewing machines, it is necessary to use a bobbin case opener to ensure that the loop of the top thread comes out of the hook set with high reliability, regardless of the thickness and tension of the thread, which complicates the design of the sewing machine.
16. All types of hooks consume a considerable amount of the top thread, as a result of which each part of the top thread repeatedly passes through the fabric, the needle eye and the thread guides before entering the stitch, resulting in wear and loss of strength of the top thread; as the size of the hooks and the sewing speed increase, so does the loss of strength of the top thread during the sewing process.
17. For sewing thick and heavy materials up to 8 mm thick, it is necessary to change to another model of lockstitch sewing machine with a longer needle bar stroke of more than 32 mm. The disadvantages of increasing the needle bar stroke are that inertia increases and vibration or noise may occur, mechanical load increases and it is not suitable for high speed, needle heat increases, etc.
18. If non-stretchable threads are used, a seam sewn with the lockstitch type 301 on elastic material is less stretchable than a seam sewn with the double thread chain stitch type 401. However, the use of modern elastic threads increases the elasticity of the lockstitch seam on elastic materials, but at the same time, the elasticity of the threads reduces the density of the join of elastic materials using such a seam.
The Existing Technologies for Forming the Double Thread Chain Stitch Type 401.
The Existing Technologies for Forming the Double Thread Chain Stitch Type 401.
Existing techniques for forming a double thread chain stitch type 401 using three types of looper with an eye at the tip to fill the bottom thread.
The existing technologies for forming the double thread chain stitch type 401 use three types of loopers, each with an eye at the tip for threading the bottom thread.
Double Chain Stitch Formation Principles.
By analyzing all types of chain stitches, we can understand the fundamental principles behind the technology used to create them. The core principle of all chain stitch formation is the «loop in loop» mechanism, meaning each subsequent loop must pass through the previous one. In the double thread chain stitch type 401, the bottom loop first passes through the top loop. Then the top thread loop passes through the bottom thread loop, and the top thread loop is pulled to the underside of the material to ensure the interlocking of threads on the back side of the material.
Due to this chain stitch formation principle, all chainstitch seams unravel from the end of the chainstitch seam and from the skipped stitch towards the beginning of the seam. Therefore, the primary requirement for all chain stitch seam types is the absence of any skipped stitches and the secure fastening of the end of the chainstitch seam to prevent it from unraveling if the chainstitch seam end is left open, i.e., not closed by another seam.
Types of Loopers for Double Chain Stitch 401.
The existing technologies for forming the double thread chain stitch type 401 use three different types of loopers, each equipped with an eye at the tip for threading the bottom thread:
1. A looper capable of performing complex movements.
2. A looper that only performs oscillating movements in the vertical plane in conjunction with a spreader.
3. A looper that performs oscillating movements in the horizontal plane.
Looper Movements and Functionality.
The looper that performs complex movements executes two different actions: oscillating movement perpendicular to the direction of material feed and oscillating movement parallel to the material feed direction. In contrast, the looper that only oscillates in the vertical plane moves parallel to the material feed direction, while the spreader moves perpendicular to the material feed direction. Their respective paths cross above the looper.
The looper that oscillates in the horizontal plane has a semicircular shape, with the axes of the needle and looper aligned along a line perpendicular to the material feed direction.
Three Principles of Chain Stitch Formation.
The three technologies for forming the double thread chain stitch type 401 use three different types of loopers, which also differ in the position of the eye for threading the bottom thread. Despite these differences, all three types of loopers follow the same fundamental principle for forming the double thread chain stitch type 401, consisting of three principles:
1. Pulling the bottom thread loop through the top thread loop.
2. The needle passing the top thread loop through the bottom thread loop.
3. Tightening the top thread loop on the underside of the material.
First Principle.
To implement the first principle, which involves pulling the bottom thread loop through the top thread loop, loopers threaded with the bottom thread through the eye must enter the top thread loop formed by the needle when it rises from its lowest position. As the needle continues to move upwards, it exits the material, leaving the top thread loop on the looper. The material is then fed the stitch length before the needle pierces the material again.
Second Principle.
To implement the second principle, where the top thread loop passes through the bottom thread loop, the needle threaded with the top thread makes a second puncture in the material while the top thread loop remains on the looper. The needle continues descending, pulling the top thread through the material.
Looper Types and Thread Triangle Formation.
To pass the top thread loop through the bottom thread loop, the tip of the needle must pass through the thread triangle formed by the looper body, the bottom thread exiting the looper eye, and the top thread loop on the looper as the needle approaches the looper body. The ends of the bottom thread and the top thread loop converge at the point of the previous needle puncture.
The size of the thread triangle depends on the stitch length. As the stitch length decreases, the size of the thread triangle also decreases, increasing the likelihood that the needle may not pass through the thread triangle. This can result in a skipped stitch, which is unacceptable for all types of chainstitch seams, as chainstitch seams unravel from the skipped stitch towards the beginning of the seam.
The looper capable of complex movements forms the thread triangle by oscillating in a direction parallel to the material feed. The looper that only oscillates in the vertical plane creates the thread triangle using a spreader that captures the bottom thread exiting the looper eye and extends it horizontally, allowing the needle to penetrate the thread triangle. The looper that oscillates in the horizontal plane forms the thread triangle due to its semicircular shape.
Once the needle passes through the thread triangle, the looper continues moving in the opposite direction and releases the top thread loop from its body. As a result, the needle, threaded with the top thread, passes through the bottom thread loop, thereby implementing the second principle.
Third Principle.
To implement the third principle, the top thread loop from the previous stitch must be tightened to the underside of the material being sewn. This is a complex task for the three existing technologies, as the quality of performing this third principle directly determines the quality of the seam produced for various types of materials.
Two-Stage Top Thread Loop Tightening Process.
To address this challenge, the process of tightening the top thread loop occurs in two stages. In the first stage, the top thread loop is pre- tightening, allowing the bottom thread loop to freely tighten through it.
This stage is performed by the needle, which continues moving downward, consuming the top thread until it reaches its lowest position.
For the needle to begin pre- tightening the top thread loop after it is released from the looper body, the thread take-up lever feeds the top thread into the needle until the top thread loop is released from the looper body.
As the needle descends and reduces the size of the top thread loop, friction occurs between the material and the top thread, as the top thread moves inside the sewn material. To minimize this friction, a special needle with two long grooves is used, allowing the top thread to move within the needle groove.
However, friction also occurs at the previous needle puncture point, as the top thread moves within the material, and it is impossible to reduce friction between the top thread and the sewn material at this point, which is a major problem for all three stitch formation technologies.
In the second stage, the final tightening of both the top thread loop and the bottom thread loop is carried out by the looper during material feed for the stitch length. The looper, with the top thread loop on its body during material feed, moves in the opposite direction relative to the material feed.
Limitations of Double Chain Stitch 401.
This two-stage process of tightening the top thread loop from the previous stitch does not allow for strong tightening of the top thread loop, preventing the stitch from tightly securing the joined materials.
Therefore, at present, a seam made with the double thread chain stitch type 401 cannot provide a tight join of materials. For this reason, the lockstitch type 301 is primarily used for this purpose.
Additionally, due to the insufficient tightening of the top thread loop in the stitch, the underside of the chainstitch seam becomes relatively thick, reducing the seam’s wear resistance.
Furthermore, this two-stage process of tightening the top thread loop from the previous stitch makes it difficult to sew material combinations like textile-leather or textile-plastic due to the significant increase in friction between the material and the top thread at the previous needle puncture point, which cannot be reduced. In such cases, the needle may draw the top thread from a large spool through the tensioning device, where the top thread tension is low, leaving the top thread loop in the previous stitch untightened. This untightened top thread loop cannot be fully tightened in the second stage during material feed by the looper.
As a result, the lockstitch type 301 is currently the primary stitch used for sewing such material combinations.
THE «ETERNAL» DISADVANTAGES OF EXISTING TECHNOLOGIES OF DOUBLE THREAD CHAIN STITCH TYPE 401.
THE «ETERNAL» DISADVANTAGES OF EXISTING TECHNOLOGIES OF DOUBLE THREAD CHAIN STITCH TYPE 401.
1. Existing technologies do not currently allow the tight joining of stitched materials with stitches, which limits the use of the double thread chain stitch type 401. This is because the two-stage process of tightening the top thread loop - first with a needle and then with a looper as the material is fed - does not allow for strong tightening of the top thread loop in the stitch.
2. Existing technologies are not able to combine different materials such as leather-textile, plastic-textile, etc., which limits the range of applications of the double thread chain stitch type 401. This is because when the loop of the top thread is tightened in two stages, first by the needle and then by the looper during material feed, the friction forces between the top thread and the material to be sewn increase at the point of the previous needle penetration. These forces cannot be reduced and, as a result, the needle cannot perform its function of qualitatively tightening the loop of the top thread.
3. Existing technologies use a special needle with two long grooves. This needle is less resistant to longitudinal bending than a needle with only one long groove. The reason for this is that the needle has a second long groove, which helps to reduce friction between the top thread and the material being sewn at the point of needle penetration. This groove helps to tighten the loop of the top thread in the previous stitch.
4. Existing technologies do not allow to sew qualitatively different materials with different thickness, density, stiffness and elasticity without thread tension adjustment, i.e. to set normal thread tension for all threads and sew qualitatively different materials.
5. Existing technologies are unable to reduce the thickness of the underside of the chainstitch seam, which makes the underside less resistant to wear and limits its range of applications. This is because the two-step process of tightening the top thread loop - first with a needle and then with a looper as the material is fed - does not allow for strong tightening of the top thread loop in the stitch.
6. Existing technologies cannot guarantee sewing without needle breakage or needle point deformation. This is because as the needle moves downwards it passes very close to the looper body and the deflection of the needle can cause it to collide with the looper body.
7. Existing technologies cannot guarantee stitch skipping free sewing. Stitch skipping can occur if the looper tip does not enter the loop of the top thread formed by the needle when it lifts from the lower position, or if the needle does not pass through the area of the thread triangle formed by the looper body, the bottom thread and the loop of the top thread.
8. Existing technologies does not allow the length of the double thread chain stitch to be reduced to 0.5 mm in order to tack the end of the chain stitch seam more securely with a condensed stitch. This is because when the stitch length is reduced to 0.5 mm, the triangular area of the triangular thread, consisting of the bottom thread, the looper body and the loop of the top thread, is greatly reduced and the needle may not be able to penetrate this triangular area, resulting in a skipped stitch.
9. Existing technologies require the use of movable or fixed needle guards to increase the reliability of the entry of the looper tip into the top thread loop formed by the needle as it is lifted from its lower position.
10. Existing technology, where the looper performs a complex movement, uses complicated mechanisms that complicate the design of the sewing machine.
11. Existing technologies limits the maximum allowable gap between the needle and the tip of the looper to 0.1 mm. This means that when switching between different needle sizes, from needle Nm. 130 to needle Nm. 60, it is necessary to adjust the position of the looper in relation to the needle.
12. Existing technologies are not able to sew materials up to 8 mm thick with a short needle bar stroke of 32 mm, which limits their universality in sewing a wide range of materials with different thicknesses up to 8 mm.
ADVANTAGES AND DISADVANTAGES OF A LOCKSTITCH TYPE 301 AND A DOUBLE THREAD CHAIN STITCH TYPE 401.
Advantages and disadvantages of type 301 and type 401.pdfCOMPARISON OF THE CAPABILITIES OF INDUSTRIAL SEWING MACHINES.
Comparison of technologies for forming various stitches for sewing with a straight seam.pdfPage updated
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