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Singeing Process

Singeing Process

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Introduction:

The term "singe" refers to the act of superficially burning a material. In the textile industry, singeing is used to remove:

  • Loose fibers that are not firmly bound to the yarn or fabric structure.
  • Loose yarns that are not firmly bound to the fabric structure.
  • Protruding fiber ends that stick out of the textile yarns or fabrics.
Fig: Fabric Before and After Singeing
Textile materials are commonly singed in the form of woven or knitted fabrics, as well as in yarn form.

Objectives and Advantages of Singeing:

  1. Singeing fabric helps to achieve a clean fabric surface, which allows for the fabric's structure to be clearly visible.
  2. Singed fabrics are less prone to soiling compared to unsinged fabrics.
  3. Pilling, especially with synthetic fabrics and blends, is reduced with singed fabrics.
  4. Singed fabrics allow for printing of intricate patterns with high clarity and detail.
  5. Singeing removes randomly protruding fibers that could cause diffused reflection of light, thus reducing the risk of skittery dyeing with singed articles dyed in dark shades. 

Types of Singeing Machines


There are three main types of singeing machines:

  1. Plate Singeing Machine
  2. Rotary-Cylinder Singeing Machine
  3. Gas Singeing Machine

1. Plate Singeing Machine

Fig: Plate Singeing Machine

Plate singeing is a type of textile finishing process used to remove the protruding fibers from the surface of the fabric. In this process, the fabric is passed over two heated curved plates at a fixed speed (usually between 135 to 225 meters per minute) to singe the fibers on one side of the fabric. The plates are heated using a combination of air and gas, and when they are heated, they turn reddish in color.
The thickness of the plates used in plate singeing is typically between 1 to 2 inches, and they are made of materials that can withstand high temperatures, such as cast iron, stainless steel, or ceramic.

Advantages of Plate Singeing include:
  1. Provides a small amount of luster due to the friction of the heated surface and the fabric.
  2. Offers uniform singeing, resulting in a consistent appearance and texture of the fabric.
  3. Particularly suitable for velvet and pile fabrics, as it helps to remove loose fibers and create a smooth surface.
Disadvantages of Plate Singeing include:
  1. Difficult to control the temperature of the plate, which can affect the singeing quality and potentially damage the fabric.
  2. Only one side of the fabric is singed, which can result in uneven singeing if the fabric is not of uniform thickness.
  3. Takes more time compared to other singeing processes due to the need to pass the fabric over the heated plates twice to singe both sides.
  4. Uniform singeing is not achieved in the stitch part of the fabric, which can result in uneven appearance and texture in those areas.

2. Rotary-Cylinder Singeing Machine

Fig: Rotary-Cylinder Singeing Machine

Rotary cylinder singeing is a type of singeing machine commonly used in the textile industry. It is a process in which the cloth passes over a heated rotary cylinder made of copper or cast iron. The cylinder is internally fired and rotates slowly, allowing a fresh surface of the roller to constantly come in contact with the fabric. The cylinder rotates in the opposite direction of the fabric, causing the protruding fibers or nap of the fabric to rise and be removed.

Advantages of rotary cylinder singeing include:

  1. It produces a uniform singeing of the fabric, creating a consistent appearance and texture.
  2. This method is particularly suitable for velvet and pile fabrics.
  3. It increases the luster of the fabric, giving it a shiny and smooth appearance.

Disadvantages of rotary cylinder singeing include:

  1. Only one side of the fabric can be singed at a time, which may result in uneven singeing if the fabric is not of uniform thickness.
  2. Local cooling may occur on the cylinder’s surface due to contact with cold fabric, which can affect the quality of singeing.
  3. Uniform singeing is not achieved for very wide fabrics.

If the singeing of both sides of the fabric is required, two cylinders are employed, one for each side of the fabric. Rotary cylinder singeing is a popular choice for textile manufacturers looking to improve the appearance and quality of their fabrics.

3. Gas Singeing Machine

Fig: Gas Singeing Machine
Gas singeing is a widely used process for singeing woven fabrics. This process allows both sides of the fabric to be singed simultaneously, typically with two burners used for singeing. The fabric is guided over the gas burner in open width and at a speed of 200-400 yards per minute. The length of the burner can be adjusted according to the fabric width. 
After singeing, a brush is used to remove any remaining singed fibers. The fabric is then immersed in water or a desizing tank for the next process. The gas singeing machine may be either horizontal or vertical.
Advantages of gas singeing include:
  1. Uniform temperature control ensures proper singeing
  2. Both sides of the fabric can be singed at once
  3. Continuous process with no hamper in production
  4. Sparks can be easily removed
  5. Standard process that ensures ideal singeing
  6. Inter-stitches of warp and weft are singed
Disadvantages of gas singeing include:
  1. A dirty burner can cause spots on the fabric
  2. Not suitable for synthetic fabrics
  3. Fabric speed inconsistencies can result in burnt fabric.
Parameters for Gas Singeing Machines
The following are the important parameters for gas singeing machines and their descriptions:
  1. Flame Intensity
    2. The burners and gas-air supply and control units are the most crucial parts of any singeing machine. Flame intensity depends on the amount and outlet speed of the gas-air mixture from the burner slots. In addition to high thermal energy, the flame also has significant mechanical energy, which is directed onto the fabric during singeing. The temperature at the mouth of the burner is typically between 1250°C and 1300°C, and the flame speed at the outlet can range from 15 to 35 meters per second. Generally, flame intensity ranges from 5 to 20 mbars.

  2. Fabric Speed
    3. The fabric speed in the singeing machine typically ranges from 50 to 160 m/min and depends on the fabric weight (in grams per square meter) and fiber blend. For heavier fabrics, the speed is usually slower than for lighter fabrics.

  3. Singeing Position
  1. Singeing onto free-guided fabric
    2. Fig. Singeing on free-guided fabric
    This position involves bouncing the flame onto the free-guided fabric at right angles. It is the most intensive singeing position with the highest efficiency and is recommended for fabrics with all-natural fibers (such as cotton), regenerated fibers, and tightly woven blended fabrics with weights over 125 g/m2.
  2. Singeing onto water-cooled roller
    3. Fig. Singeing onto water cooled roller
    In this position, the flame bounces at right angles onto the fabric while the fabric passes onto a water-cooled guide roller. This position avoids flame penetration into the fabric and thermal damage to temperature-sensitive synthetic fabrics. It is recommended for all blended and synthetic fabrics, fabrics with weights less than 125 g/m2, and fabrics with an open structure.
  3. Tangential Singeing
    4. Fig. Tangential Singeing
    In this position, the singeing flame falls tangentially on the fabric, touching only the protruding fibers without significant contact with the main fabric body. It is usually recommended for very light-weight and sensitive fabrics as well as fabrics with broken filaments.
  4. Distance between Flame Burner and Fabric
    5. Increasing the distance between the burner and the fabric reduces the energy content of the flame, and consequently, the singeing efficiency. The distance between the burner and the fabric is typically in the range of 6-8mm but can be adjusted between 6-20mm.
        
  5. Flame Width
Adjusting the flame width according to the fabric width is essential for optimizing gas economy. All good singeing machines come with a provision for flame width adjustment.

To ensure good quality GAS singeing, there are three essential conditions that must be met:

  1. The flame must have high mechanical and thermal energy to quickly burn protruding thermoplastic fibers (such as polyester) without forming molten beads.
  2. The flame must be homogeneous with uniform mechanical and thermal energy to result in uniform singeing.
  3. The flame/fabric contact time must be optimal to avoid incomplete or over-singeing.

Monitoring and controlling the singeing process is crucial for achieving consistent results. One indicator of singeing effectiveness is the fabric temperature just after passing over the singeing flame. This can be continuously monitored using a radiation pyrometer and thermometer. The fabric temperature can then be used to control and regulate the intensity of the machine. 
Another way to control the singeing effect is by using a Hairiness Tester. The fabric surface is monitored using a laser beam, and the hairiness of the fabric is displayed on a computer screen. The measured information can be used to achieve the desired effect.

During GAS singeing, there are several important considerations to keep in mind:

  • Ensure that the flame is more bluish than yellowish to achieve maximum temperature.
  • Control and maintain the recommended flame length and angle of contact based on fabric construction, thickness, weight, and heat sensitivity.
  • Regulate the fabric speed according to fabric construction, thickness, weight, etc.
  • Ensure that all burner nozzles are free from choking, as this may result in haziness, patchy appearance, or faint lines after dyeing.
  • Ensure that the machine is threaded correctly to avoid rubbing marks or defects.
  • Singe both sides of the fabric to avoid face-to-back shade variation after dyeing.
  • Set the width of the flame to cover slightly more than the fabric width for energy conservation.
  • Ensure that exhaust blowers over the burners are working correctly to prevent re-deposition of burnt-out fibers on the fabric.
  • Quench the fabric appropriately into water or a desize bath after singeing to avoid entrapped smoldering particles from causing holes in the fabric.
  • Cool guide rollers next to the flames or guide rollers on which the flame is directed in case of heat-sensitive fabrics.
  • Interlink the stop button, flame switch-off mechanism, and quenching system effectively to avoid fabric burning and fire incidents.

To test the effectiveness of the singeing process, you can:


  1. Look at the singed fabric with a magnifying glass and compare its hairiness with that of the unsinged fabric. A well-singed fabric shows less hairiness.
  2. Test the singed fabric for pilling performance and compare it with that of the unsinged fabric. A well-singed fabric gives less pilling.
  3. Stick and remove tape on the singed fabric and observe the number of fibers attached to the tape's sticking side. A well-singed fabric results in fewer fibers sticking to the tape.
  4. Notice the feel or handle of the singed fabric. An over-singed fabric may give a harsher feeling.

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