What is Gas Singeing?
Gas singeing is normally practiced in majority of the mills as flames can penetrate the gaps in the fabric and singeing can be more effective. Gas singeing is more convenient, more economical and more effective than other methods and is well accepted commercially.
The main purpose of singeing is to burn the protruding fibers from the yarn and/or fabric surface. In order to burn the protruding fibers, energy must be supplied. The supplied energy must be just enough to burn only the protruding fibers, while keeping the firmly bound fibers in tact. This is achieved by allowing time of contact between the singeing flame and the fabric to practically a fraction of a second. As the temperature of the flame is too high (around 1300°C), any regulation of this temperature is out of the question. However, metering and control of thermal energy of the flame is essential for the safe but effective burning off process.
Gas Singeing Machine: Old singeing machines are often used which in their time worked acceptably when only pure cotton materials were singed, but which, however are no longer suitable for singeing of newer fibers and their blends. New technologies and techniques have been developed to suit the modem requirements.
Besides, from the problems facing with the plate and roller singeing machines it was understood that the fabric should not be touching a hot surface during singeing. Hence the gas singeing machines were designed, where a width wise flame was created and the fabric is passed through the flame where by the fibers are burned-off to get a clean surface.
In gas singeing machine, the fabric passes over a burning gas flame at such a speed that only the protruding fibers burn and the main body of the fabric is not damaged by the flame. This is the most common type of machine used for singeing fabrics as well yarns. The gas-singeing machine is typically equipped with four burners, and is capable of singeing one or both surfaces of the fabrics. A water-cooled roller is provided at a location opposite to the burners, thereby enabling singeing to be performed without undermining the strength of even thin fabrics. It is important to set a drain temperature of the water-cooled roller in a range of 50 to 55°C. Cautions are required because a dew-point is generated when the water-cooled roller is cooled down too much, and results in increased amount of remaining fuzz or adhered carbon. The fabric feed speed is preferably set at around 100 to 150m/minute.
Line Diagram of Gas Singeing Machine for Woven Fabrics:
Fig: Schematic diagram of Gas Singeing Machine
Working Principle of Gas Singeing Machine: Operation of gas singeing machine are described below.
a) The fabrics to be singed are opened and prepared so that they can be fed to singeing machine without any hindrances. Normally the fabrics are batched and rolled.
Fig: Gas singeing of fabric
b) The fabrics are fed in open width without any slackness or wrinkles. Singeing cannot be done in rope form.
c) The cloth is exposed to flame from a twin gas burner where the gas comes through the filter at a pressure of 100–140 mbar.
d) The ratio of gas to air mixture is maintained at 1:4. The fabric is brushed using special brush roller. Different types of brush rollers are developed for different type of fabrics.
e) As the cloth runs at a high speed, only protruding fibers are burnt out. The cloth passes in water after burning to avoid chances of fire.
There are three different positions to get varied effect of singeing:
The singeing flame meets the free-guided fabric at right angles as the fabric passes between two guide rollers. This position is recommended for materials made of 100% natural fibres and for blended fabrics which have been thoroughly beaten, with weights over 125 g/m2.
The singeing flame meets the fabric at right angles as it is bent over a water-cooled roller. The choice of this position is recommended for qualities of fabric composed of temperature sensitive fibers, open-weave blended fabrics and those with weights of less than 125 g/m2.
The singeing flame passes close to the fabric with the jet direction being at a tangent to the fabric surface. This singeing process is recommended for all materials which cannot tolerate direct exposure to flame. Tangential singeing can also equalize protruding fibres and repair filament breaks. However, at present, this facility is not available on our machines.
Fig: Different positions of flame to get different singeing effect
Important GAS Singeing Parameters:
Following are the important gas singeing parameters:
Flame intensity
Fabric speed
Singeing position
Distance between flame burner and fabric
Flame width
Essential Conditions for Good GAS Singeing:
Following are three essential conditions for good singeing:
A flame with high mechanical and thermal energy to quickly burn thermoplastic protruding fibres (e.g. polyester) without any molten beads formation.
A homogeneous flame with uniform mechanical and thermal energy to result in uniform singeing.
An optimal flame/fabric contact time to neither result in incomplete not over-singeing.
Important Considerations During GAS Singeing:
Make sure that the flame is more bluish (less yellowish) to give the maximum temperature.
Control and maintain the recommended flame length and angle of contact, depending on the fabric construction, thickness, weight, heat sensitivity, etc.
Regulate the fabric speed according to the fabric construction/thickness/weight etc.
Make sure that all the burner nozzles are free from choking. Choking of nozzles may result in the appearance of haziness, patchy appearance or faint lines, which become apparent after dyeing.
Make sure that the machine is threaded through the machine correctly. Rubbing marks may show up if the fabric is threaded wrongly over defective stationery bars and/or if the fabric rubs against the burners. (As the guide rollers are very close to the burners, any problems due to loose brackets supporting the rollers will guide the fabric to touch the burner block/nozzle). Invariably such defects only show up after dyeing or finishing, at which stage it is difficult to attribute the cause to the singeing machine operation.
Make sure that the threading is as per specification drawing so that both sides of the fabric are singed. Singeing on only one side of the fabric may result in face to back shade variation after dyeing.
Make sure that the width of the flame is set to cover just a little more than the fabric width. This will ensure conservation of energy.
Make sure that the exhaust blowers over the burners are in proper operation. If not, it can lead to redeposition of the burnt out fibres on the fabric causing black specks.
Ensure appropriate quenching into water/desize bath after singeing. Otherwise, the entrapped smouldering particles may lead to fabric getting burnt (holes).
Guide rolls next to the flames or the guide rollers on which flame is directed in case of heat-sensitive fabrics should be cooled, generally by cold water circulating through the guide rollers. Otherwise they could become red hot and scorch the fabric.
Interlinking of stop button/flame switch-off mechanism/ quenching system should be effective to avoid burning of the fabric and any incident of fire.
References:
Handbook of Value Addition Processes for Fabrics By B. Purushothama
Chemical Technology in the Pre-Treatment Processes of Textiles by S. R. Karmakar
Pretreatment of Textile Substrates by Mathews Kolanjikombil
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.
