Singeing process in textile pretreament- Textile Engineering
- 1. 1 SINGEING
- 2. What does Singe mean? The word “Singe” literally means “to burn superficially”. 2
- 3. 3 What is Singeing? “ Singeing is the burning of loose fibers that are not firmly bound into the yarn and/or fabric structure” Singeing is a part of the pretreatment processes carried out in textile processing, and is usually the first step carried out after weaving. SINGEING BURNER
- 4. 4 Why Singeing? Singeing is often carried out on cotton fabrics, or fabrics with cotton blends and results in: Increased wettability (better dyeing characteristics, improved reflection, no "frosty" appearance) A smoother surface Improved visibility of the fabric structure Less pilling Decreased contamination through removal of fluff and lint
- 6. 6 Necessity of Singeing Cotton materials are valued for their smooth appearance. After the formation of fabric it has a fuzzy or hairy appearance due to projecting fibers, thus affecting the lustre and smoothness cotton is known for. Unsinged fabrics are soiled easily The protruding fibers obstruct the subsequent dyeing and printing process Goods which are to be mercerized are singed to maximize the lustre In fabrics of polyester and cellulosic fiber blends singeing is the best method to control pilling, sometimes double singeing is done to minimize the pilling.
- 7. 7 Precaution During Singeing o The fabric to be singed should be dry as wet fabric tend to scorch more readily than dry. o Uneven singeing may cause streaks on fabric or bubbles when the fabric is finished. o Improper singeing may lead to loss of 75% loss in tensile strength loss in warp direction. o The fabric should not contain any acid releasing salt, which may release acid on heating and tender the fabric. o Stopping the machines may cause bars on the fabrics.
- 8. 8 Precaution During Singeing o Possibility of thermal damage to temperature sensitive fabrics. o The burning characteristics of fibers must be taken into account when this process is applied, as heat- sensitive fibers melt, forming tiny balls on the surface of the fabric. These balls interfere with dye absorption, so that, as a general rule, heat sensitive fibers would be singed after dyeing or printing.
- 9. 9 Flow chart of hairy fibre removal system
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- 11. 11 The action of burning away the protruding ends of the fibers is brought about by the direct action of the flame ensuing from the gas burners. Direct Singeing Includes: • Gas singeing • Cylinder singeing • Blade singeing • Gas singeing • Plate singeing • Roller singeing
- 12. 12 In this system, the heat, in the forms of diffused infra-red radiations, produces a more even singeing effect. • Infra-red ray burning system(both for woven & knit fabric)
- 13. 13 Types of Singeing Three main type of singeing machine are 1. Plate singeing machine 2. Rotary-cylinder singeing machine 3. Gas singeing machine
- 14. 14 1. Plate Singeing In this type of singeing machine, plates are heated to bright redness by a suitable burning arrangement of gas mixed with air and then cloth passes over and in contact with these plates at a speed ranging from 150 to 250 yards per minute. Thickness of these plates ranges from 1-2 inches. The passage of the cloth can be arranged in such a manner that one or both sides of the fabric may pass over and in contact with the heated plate(s) In order to avoid local cooling of a certain part of the plate(s) by constant passage of cloth over it, an automatic traversing mechanism is fitted to the machine. This mechanism brings the cloth into contact with a constantly changing part of the plate(s), not only to avoid local cooling but also local wearing of the plate(s)
- 16. 16 2. Rotary-Cylinder Singeing Machine ⚫ In this type of singeing machine, the cloth passes over and in contact with a heated rotary cylinder made of copper or cast iron. The rotary cylinder has internal firing and revolves slowly so that constantly a fresh surface of the roller comes in contact with the cloth. The direction of rotation of the cylinder is opposite to the direction of the fabric so that the protruding fibers or nap of the fabric is raised. ⚫ This type of machine is particularly suitable for the singeing of velvets and other pile fabrics. ⚫ If the singeing of both sides of the fabric is required, then two cylinder are employed, one for each side of the fabric.
- 18. 18 3. Gas Singeing Machine In this type of 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.
- 20. 20 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 1300C), 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. Fundamentals of Gas Singeing
- 21. 21 Main Components of Gas Singeing Machine
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- 23. 23 At the start, the fabric passes through a tension unit with guide rollers and bars, which ensure crease-free entry of the fabric into the machine. Then, there are (optional) pre-drying cylinders which even out any variations in the fabric moisture-content and temperature. Next, the fabric passes through pre-brushing unit which, in addition to removing dirt/dust, lint and loose fibers from the fabric, causes the fibers sticking to the fabric surface to stand out for easy subsequent burning. A dust collection system, provided just below the brush rollers, is connected to a powerful suction unit. PROCESS OF GAS SINGEING
- 24. 24 ROLLERS TYPES
- 25. 25 After pre-brushing, the fabric enters into the singeing chamber, where it passes over the burning flames, which are positioned on both sides of the fabric. HOW DO BURNERS WORK? The burner body is specially designed to provide gas flow at uniform pressure/velocity throughout the fabric width. Burner is termed as the “heart of singeing” and should generate homogenous, stable, uniform , and highly concentrated flame rich in energy by ideal combustion of the gas: air mixture. The gas outlet section of the burner is provided with water jacket to keep the burner cool. Adjustable water-cooled rollers are used to obtain different fabric/flame positions, which permit desired degree of singeing effect on different quality of fabrics by adjusting the guide roller position with respect to the flame
- 26. 26 A Carburetor or air/gas mixer allows automatic mixing of gas with air to control the intensity of the singeing flame. After passing over the flames, the fabric passes through (optional) steam quenching unit to put off any sparks and/or through post- brushing section for clean-up/removal of burnt fibers. The after-brushing keeps the subsequent impregnation-liquor cleaner and reduces the amount of dust entering in the following process steps. Then, the fabric passes though a saturator, which contains the desizing agent along with the auxiliary chemicals. After saturation with the desizing liquor, the fabric is squeezed by squeezing mangles and is wound on a batcher.
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- 28. 28 ⚫ FLAME INTENSITY ⚫ FABRIC SPEED ⚫ SINGEING POSITION ⚫ DISTANCE BETWEEN FLAME BURNER AND FABRIC ⚫ FLAME WIDTH GAS SINGEING PARAMETERS
- 29. 29 FLAME INTENSITY: The flame intensity of the singeing burners is based on the amount and the outlet speed of the gas-air mixture. The high thermal energy of the burner flames, which can reach temperatures up to 1300°C, is sufficient to rapidly heat synthetic fibers to their melting point. FABRIC SPEED: The fabric speed in the singeing machine is usually in the range of 50-160 m/min depending on fabric (gram per square meter) weight and fiber blend. For heavier fabrics, the speed is kept slower as compared to lighter weight fabrics.. GAS SINGEING PARAMETERS
- 30. 30 SINGEING POSITION: SINGEING ONTO FREE-GUIDED ROLLERS This is the most intensive singeing position with highest efficiency. In this position, the flame bounces onto the free-guided fabric at right angles. This position is usually recommended for singeing of fabrics with all natural fibers (e.g. cotton), regenerated fibers and blended fabrics, which have been tightly woven and heavyweights over 125 g/m2 GAS SINGEING PARAMETERS
- 31. 31 SINGEING ON TO WATER-COOLED ROLLERS In this position, the flame bounces at right angles onto the fabric while the fabric passes onto water- cooled guide roller. This position avoids the penetration of the flame into the fabric. The flame does not pass-through the fabric, and because of the fabric passing onto water-cooled roller, any thermal damage of temperature-sensitive synthetic fabrics is avoided. This position is usually recommended for all blended and synthetic fabrics as well as for fabrics having weights less than 125 g/m2 and fabrics with open structure. GAS SINGEING PARAMETERS SINGEING POSITION:
- 32. 32 GAS SINGEING PARAMETERS SINGEING POSITION: TANGENTIAL SINGEING In this position, the singeing flame falls on the fabric tangentially. The flame touches only the protruding fibers without having any significant contact with the main fabric body. This position is usually recommended for very light weight and sensitive fabrics as well as fabrics with broken filaments.
- 33. 33 DISTANCE BETWEEN FLAME BURNER AND FABRIC The Burner can be shifted in such way that for heavy weight fabric it can reach very near to fabric surface about 15 mm so that natural fabrics can be singed efficiently & perfectly. For light weight fabrics or those that are particularly sensitive to heat the burner can be shifted away 25 to 35 mm and light weight fabric can be singed easily FLAME WIDTH Each burner has manual controls to match the width of the flame to the width of fabric being processed, so that energy is not wasted outside the fabric width. GAS SINGEING PARAMETERS
- 34. 34 Following are three essential conditions for good singeing: 1. A flame with high mechanical & thermal energy to quickly burn thermoplastic protruding fibers (e.g. polyester) without any molten beads formation 2. A homogeneous flame with uniform mechanical & thermal energy to result in uniform singeing 3. An optimal flame/fabric contact time to neither result in incomplete not over- singeing ESSENTIAL CONDITION FOR GOOD GAS SINGEING
- 35. 35 ⚫ The fabric temperature can be continuously monitored by a radiation pyrometer and indicated by a thermometer. When the fabric temperature increases to a pre-set value, the machine intensity would automatically reduce, while when the fabric temperature goes down, the flame intensity would automatically increase. ⚫ Hairiness Tester provides another possibility to control the singeing effect objectively. The fabric surface is monitored by means of a laser beam and the hairiness of the fabric is displayed on a computer screen. The measured information can be used as a set value for the control of the singer in order to achieve the programmed effect PROCESS MONITORING
- 36. 36 ⚫ 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 width of the flame is set to cover just a little more than the fabric width. This will ensure conservation of energy. IMPORTANT CONSIDERATIONS DURING GAS SINGEING
- 37. 37 ⚫ Make sure that the fabric 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 exhaust blowers over the burners are in proper operation. If not, it can lead to re-deposition of the burnt out fibres on the fabric causing black specks.
- 38. 38 ⚫ 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
- 39. 39 The effectiveness of singeing process can be checked by one or more of the following: ⚫ By looking at the singed fabric with magnifying glass and comparing its hairiness with that of the un-singed fabric. A well-singed fabric shows less hairiness. ⚫ By testing the singed fabric for pilling performance and comparing it with that of the un-singed fabric. A well-singed fabric gives less pilling. ⚫ By sticking and removing a sticking tape on the singed fabric and observing the number of fibres attached to the sticking side of the tape. A well-singed fabric results in less number of fibers sticking on the tape. ⚫ Noticing the feel or handle of the singed fabric. An over-singed fabric may give a harsher feeling. TESTING SINGEING EFFECTIVENESS
- 40. 40 In complete singeing Uneven singeing across the fabric width Uneven singeing along the fabric length Horizontal singeing stripes Vertical singeing stripes Over singeing or thermal damage of the fabric Formation of small beads of molten material. PROBLEMS IN GAS SINGEING
- 41. 41 What is an Enzyme? • Each enzyme is a made of a sequence of amino acids (like pearl on a string, picture 1)folded into a unique three-dimensional structure that determines the function of the enzyme. • Only a small part of the enzyme participates in the catalysis of biochemical reactions: the active site (picture 2). Enzymes are therefore very specific (e.g. cellulose can only degrade cellulose).
- 42. 42 • Proteases act on soils and stains containing proteins. Examples are collar & cuff soil- lines, grass, blood. • Amylases remove starch-based soils and stains, e.g. sauces, ice-creams • Lipases are effective in removing oil / greasy body and food stains • Cellulases provide general cleaning benefits, especially on dust and mud, and also work on garments made from cellulosic fibers, minimizing pilling to restore color and softness • Active at very low levels (1 to 2 ppm, and sometime even below 1 ppm) • Highly specific, • Active at low temperatures, from 60°C to as low as the "30-40°C range" • Highly biodegradable • Wash at varying pH levels, from mild to high alkalinity; • Retain laundering performance in the presence of chemicals such as bleach; builder, surfactant, etc…. • Soften fabrics; • Brighten their colors; • Improve whiteness; • Remove fatty stains at low wash temperatures;
- 43. 43 Enzyme Washing • This is a bio-catalytic method where in an ultrasoft handle effect can be produced on denim. • The hydrolytic effect of enzymes causes the loss of surface fibre, which improves surface smoothness and softness of the fabric. • Cellulase enzymes are natural proteins, which are used in denim garment processing to get stone wash look on to the denim garments without using stones or by reducing the use of pumice stone. • Cellulase attacks primarily on the surface of the cellulose fibre, leaving the interior of the fibre as it is, by removing the indigo present in the surface layer of fibre.
- 44. 44 • Loading of denim Garments (addition of Stones is optional) • Desizing with- alpha-amylase Enzyme, or- Oxidative desize • Rinsing • Adjusting pH to 4.5 to 5.0 with- acetic acid, or- buffer system • Heating to 50 to 60 C • Addition of cellulose enzyme • Tumbling for 30 to 60 minutes • Hot rinsing at > 65 C • Cold washing • Softening • Dry tumbling ENZYME WASH CYCLE
- 45. 45 Advantages • Prevents tendency of pilling after relatively short period of wear. • Can be applied on cellulose and its blend. • Fancy colour-flenced surface can be obtained without or a partial use of stone. • Soft handle • More reproducible results • Increased luster • Less corrosive • Less damage to seams
- 46. 46 Advantages • Less wear & tear of machinery • Most economical due to more water saving • Reduction in pollution, waste, quality variation • Enzymes can be recycled unlike pumice stones or acids • Reduce labour engagement Limitations • Garment load size of the machine is limited. • Post treatment required.
- 47. 47 THANK YOU