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SIZING PROCESS:
The sizing is a preparatory process of weaving that comes after warping. It is a very important and critical preparatory process. “The process of application of a thin film of adhesive and binder on the yarn surface to improve the weavability of yarn is called sizing process”. It is essential for weaving the fabric with single-ply spun yarn. The quality of the sizing process directly influences the performance of the loom and the quality of the fabric to be woven. "The people say that sizing is the heart of weaving". In this process, the warp sheet gets immersed in the paste of adhesive and binder, then the warp is squeezed properly to eliminate the excess amount of adhesive. Now the warp is dried and the ends are separated from each other. Now the warp ends are wound on the weaver’s beam. The strength of warp yarn is increased after the sizing process. The hairiness of yarn gets reduced too. During the sizing process, warp yarn passes under moderate tension. This tension causes some stretch in the yarn, thus elongation of yarn after sizing gets reduced. This is a negative aspect of the sizing process. Many types of sizing agents are used in the sizing process to improve various properties of the yarn. This process is carried out carefully and precisely. Improper and poor sizing results from many difficulties in weaving. An excess amount of sizing also creates difficulties. The amount of size pick-up is applied according to the yarn parameters used in warp yarn. The selection of correct sizing ingredients plays a major role in the quality performance of sizing. Better process control and quality control in sizing always result in the form of the best performance of the sizing process.
OBJECT OF SIZING PROCESS:
The main objective of the sizing process is given below:
• To improve the weavability of warp yarn.
• To improve the fibre to fibre adhesion force in the yarn.
• To prevent slippage of fibres in the yarn during weaving.
• To make the yarn twist permanent by applying adhesive film on the yarn surface. The twist in unsized yarn tends to untwist due to rolling action during weaving so that it necessitates to be fixed.
• To strengthen the warp yarn.
• To improve the abrasion resistance of warp yarn.
• To protect the yarn from being ruptured during passing through drop pin, the eye of heald wire and dent of reed.
• To reduce the hairiness of warp yarn.
• To improve the smoothness of warp yarn.
• To ensure good fabric quality in weaving.
• To ensure maximum efficiency of the weaving process.
• To prevent the development of electrostatic charges in the yarn during weaving.
BASIC REQUIREMENTS OF SIZING PROCESS:
The basic requirements of the sizing process are given below:
• The film of adhesive should be as flexible as possible.
• The loss of elongation at the break of yarn should be as minimum as possible.
• The adhesive film should not be cracked due to abrasion during weaving.
• Moisture content of warp should be properly maintained.
• There should be a minimum sticking end in the sized beam.
• It should be ensured that sizing liquor penetrates the yarn. It should not coat only the surface of the yarn.
• Stretch percentage should be minimum to control the loss of elongation at break.
• Size pick-up should be proper to reduce warp breakages in the weaving.
• Size pick-up below the required amount and excess amount is always dangerous in sizing. These factors should be controlled necessarily.
• All the beams should have equal tension during sizing to obtain uniform tension in the sized beam.
• Adhesive film should be smooth.
• There should be no yarn rupture during the process.
• Hairiness should be reduced.
• Beam winding tension should be proper.
• There should be minimum short ends in the sizing beam.
• The warp ends should be equally distributed across the beam width by using the correct denting order.
SIZING INGREDIENTS:
The chemicals to be used in the preparation of sizing liquor is called sizing ingredients. Sizing ingredients may be classified into two categories:
• Primary sizing ingredients
• Secondary sizing ingredients
Primary sizing ingredients:
the names and their roles of primary sizing ingredients are given below:
Adhesive agent:
The main role of an adhesive agent in the sizing liquor is to form a thin layer (film) on the yarn surface. It is a very important ingredient. A major portion of sizing liquor consists of adhesive agents. It penetrates inside the yarn and increases the yarn strength. The protruding fibres also bind with the yarn surface and help to increase yarn strength. The hairiness of the yarn reduces too. Film on the yarn surface improves the abrasion resistance and smoothness of warp yarn. Now, these days following types of adhesive agents are used in the sizing process.
Simple starch:
this is untreated starch powder. Mainly maize starch, sago starch, wheat starch, potato starch are used as adhesive agents in sizing. The viscosity of sizing liquor with untreated starch is always high. It gives poor penetration in the warp yarn. This starch is suitable for sizing a coarse count of yarn up to 20s count.
The viscosity of untreated starch can be improved by adding potassium persulphate in it and improved viscosity of liquor allows to use it in the sizing of a medium count of yarn. It gives the best performance in weaving with the medium speed of loom. This is cost-effective. It helps to control the sizing cost per kilogram of warp.
Thin boiling starch:
it is chemically treated starch. It has a lower viscosity than untreated starch. It easily penetrates the yarn. When warp count increases, the size pick-up percentage is also increased thus the concentration of liquor is also increases but the viscosity of liquor is kept almost the same by using thin boiling starch. It may be successfully used in the sizing of the medium count of warp yarn. It is a little expensive than untreated starch.
Modified starch:
it chemically modified starch. It has a very low viscosity. It gives the best penetration effect in the yarn. It is suitable for all types of yarn count. It can be used for sizing of warp of high-speed loom. Good quality of fabric results with this adhesive. Maximum efficiency can be achieved by using this adhesive. This is much expensive so that it is used in the sizing of a fine count of warp yarn only.
Binding agent:
It is used to make the adhesive film enough strong. The adhesive film has brittleness. When it passes through various kinds of abrasive actions and jerks during weaving, the adhesive film becomes cracked and end breakage results during weaving. The binding agent provides strength to the adhesive film and prevents becoming a crack. There are many types of binding agents that are being used in sizing at present time. The widely using binding agents in today’s sizing are given below:
• Guar gum
• Carboxymethylcellulose (C.M.C.)
• Polyvinyl alcohol (P.V.A.)
• Polyester binder(R- bind, bilbind PS, eco size)
• Acrylic binder (rainscel)
Above binding agents are used individually or within combination according to requirement, quality and the warp count is always taken into consideration before the selection of binding agents.
Softening agent:
It is used to make the adhesive film more soft and flexible. As we know that the warp yarn passes through different angles so that the adhesive film becomes cracked due to the bending movement of the yarn. This problem necessitates that the adhesive film should be soft and flexible. The softening agent provides enough softness to the adhesive film. It also makes the yarn surface smooth. Following types of softening agents are used now these days:
• Vegetable fats (dalda, refined oil)
• Animal fats (mutton tallow)
• Synthetic softener (R-soft, textile wax)
A little amount of softener is used in the sizing liquor. It does not affect the cost of the sizing process on many scales.
SECONDARY SIZING INGREDIENTS:
The secondary sizing ingredients of sizing agents are given below:
Antistatic agent:
It prevents the generation of electrostatic charge in the warp yarn during weaving. When the warp makes up and down movement during weaving, the ends rub to each other and generate an electrostatic charge in the warp. These electrostatic charges cause warp breakage during weaving. A very little amount of antistatic agent is used in the sizing liquor. The types of antistatic agents are given below:
• Sepcostate
• LV-40
• PAA-40
Antiseptic agent:
It is used to prevent bacteria or mildew formation in the sized beam or fabric woven from a sized warp. When the sized warp or fabric remains unused, there are chances of bacteria or mildew formation in humid conditions or rainy seasons. Some antiseptic agent is added to the sizing liquor to avoid this problem.
• Salicylic acid
• Zinc chloride
• Phenol
• Emulsifier
• Copper sulphate
Hygroscopic agent:
The main role of the hygroscopic agent in the sizing liquor is to improve the moisture absorption capacity of warp from the air. Since we know that the strength of cotton increases by increasing moisture percentage when the warp absorbs the moisture during weaving, the warp breakage rate is reduced. The majorly using hygroscopic agents are given below:
• French chock
• China clay
BASIC REQUIREMENT OF SIZING INGREDIENTS:
The basic requirements of sizing ingredients are given below:
• It should be that which gives the least exfoliation.
• It should be easily washable i.e. permits easy desizing.
• It should give good fabric characteristics.
• It should be compatible with the machinery & associated parts.
• It should not cause any degradation of the textile material.
• It should not cause any health hazard.
• It should be cheap.
• Size ingredients should be neutral.
• It should be available.
STRUCTURE AND WORKING OF SIZING MACHINE:
The common parts and working of sizing machine are given below:
• Creel
• Sow box
• Liquor circulation system
• Drying unit
• Yarn separator and its platform
• Headstock
• Adjustable reed
• Beam winding system
• Beam pressing system
• Drive
• PIV boxes
• Control panel
• Automatic speed and moisture control system
• Length measuring system
• Stretch control system
• Cooking unit
• Liquor storage
Warper's beam creel:
Creel is a very important portion of the sizing machine. The warper’s beams are mounted on the creel. The beam mounting capacity of the creel depends upon the total number of ends required in the weaver’s beam. Each beam rotates in between two rollers nips. The rollers are able to move freely.
A braking system is attached to each pair of rollers. Beam tension is adjusted by loosening or tightening the handwheel. The alignment of the beam is also done with help of this handwheel. The yarn guiding rollers are fitted in the creel which guides the warp of each beam. Zigzag or vertical creel is used in the sizing machine. Zigzag creel occupies more space than vertical creel.
Sow box:
It is the most critical and important portion of the sizing machine. Mainly it is responsible for size pick-up percentage in the warp during. The common parts and function of a sow box are given below:
Stainless steel tub:
the sow box has a stainless steel tub. The sizing liquor is filled in this tub.
Guide roller:
it is mounted just before the immersion rollers, it guides the warp sheet during the process.
Immersion rollers:
the warp sheet passes under the immersion rollers. Two pairs of immersion rollers are used in a sow box, immersion rollers help to immerse the warp sheet into the sizing liquor. The warp sheet first passes under one pair of immersion rollers then between the nip of stainless steel and squeezing rollers. Now warp sheet again passes under another pair of immersion rollers and finally warp sheet passes between the nip of other stainless steel and squeezing rollers.
Stainless steel rollers: There are two stainless steel rollers in a sow box. Its function is to lift sizing liquor and to apply it on the yarn surface. When a very low amount of size pick-up needs, only stainless steel rollers are used to apply the sizing liquor on the yarn surface. The yarn is not immersed into the sizing liquor in case of a very low size pick-up.
Squeezing rollers:
When the warp immerses into the sizing liquor, it has an excess amount of sizing liquor with it. There is a need to eliminate this excess amount of sizing liquor from the warp. The warp coming out of immersion rollers passes between the nips of the squeezing roller, which is mounted just over the stainless steel roller. Two squeezing rollers are used in a sow box. The squeezing roller applies the pressure on the warp sheet and eliminates the excess amount of sizing liquor from it.
Perforated steam pipe:
This is mounted in the circulation box or tub. It is perforated and connected to the steam line. The main function of this perforated steam pipe is to maintain the temperature of sizing liquor in the sow box. A steam valve is fitted in the steam line which regulates the temperature of the sow box.
Pneumatic cylinders:
The pneumatic cylinders are fitted at both ends of squeezing rollers. These cylinders perform up and down movement of squeezing rollers. The squeezing pressure is maintained by these cylinders. The compressed air is supplied continuously to these pneumatic cylinders.
Pressure gauge:
A pressure gauge is fitted between the pneumatic cylinders and the air supply line. This pressure gauge reads the pressure during the process.
Pressure regulator:
An air pressure regulator is used to control the squeezing pressure. By rotating the air regulator valve the squeezing can be increased or decreased according to requirement.
Temperature sensor:
The temperature sensor is immersed in the sizing liquor. This sensor senses the liquor temperature and sends the signal to the control panel.
Liquor circulation system:
The main function is to perform the mixing of sizing liquor in the sow box and to prevent the formation of a thick layer of sizing liquor in the sow box.
The circulation system mainly consists of a geared feeding pump. When the tub of sow box is filled with sizing liquor, it begins to fall into the circulation box. The liquor from here passes into the inlet of the feeding pump. The outlet of the pump is connected to a sow box. The feeding pump continuously circulates the sizing liquor.
Drying unit and steam supply:
The main function of the drying unit is to dry the warp sheet after coming out of squeezing rollers. The Teflon coated steam cylinders are used in the drying unit. The steam is supplied to the drying cylinders which helps to heat the cylinder. When the wet warp sheet passes over the heated surface of drying cylinders, the moisture present in the warp sheet is evaporated from it and the warp sheet becomes dry. A main steam supply valve located in the main steam line can start or stop the supply of steam in the whole drying unit. In the sizing machine,
some drying cylinders are driven negatively. These cylinders are revolved due to warp tension over the cylinder. The last three or four cylinders are driven positively. A steam trip is mounted on each cylinder which releases an excess amount of steam pressure. The steam valve fitted with each cylinder regulates steam pressure in the cylinder. The temperature sensors fitted with each cylinder reads the temperature of the cylinder and send the signal to the control panel.
Yarn separator and its platform:
After the drying unit, a long platform is fitted just before the headstock of the machine. The yarn separator brackets are mounted on this platform. The yarn separators are kept on these brackets. The main function of the yarn separator is to separate the ends from each other. When the dry warp sheet
comes out from the drying unit, the ends are stuck to each other. The yarn separators are inserted into the warp sheet in a definite sequence. The number of yarn separators depends upon the number of warper’s beams to be used. The number of yarn separators is always one short of a number of warper’s beams. The yarn separators are fixed on their brackets. The warp sheet moves toward the headstock of the machine. This movement of the warp sheet helps to separate the ends from each other.
Headstock:
This portion of the machine is located at the last of the machine. It consists of a drag roller, which is rubber-coated. It drags the warp sheet. There are two pressure rollers used to provide sufficient grip of the drag roller on the warp. The warp sheet first passes over the pressure roller, then it is passed under the drag roller.
The warp sheet again passes over another pressure roller. The pressure of these rollers is controlled by pneumatic cylinders. These cylinders also help to lift upward the pressure rollers. A metallic cover is mounted over the drag rollers which prevents to fall off any foreign material between the pressure roller and the drag roller. A protection grid is mounted just in front of the drag roller which protects the operator’s hand.
Adjustable reed:
This reed is mounted just before the first pressure roller of the headstock. This is a zigzag reed. It fixes the number of ends per inch in the weaver’s beam. This is an adjustable reed. Its width can be increased or reduced within the tolerance limit. A mechanism attached to this reed performs the adjusting of the action of this reed.
A handwheel is used to reduce or increase the reed width. The width can be adjusted by rotating the handwheel in a clockwise or anticlockwise direction. There is another mechanism attached with this reed that helps to move it left and right direction.
Beam winding system:
When the warp sheet comes out of the drag roller, it is wound on the weaver’s beam. The pins of beam adapters are inserted in the holes of the beam driving mechanism. The beam is driven from one side. A winding motor transmit motion to a reduction gearbox, which is connected to the beam driving shaft. The surface speed of the weaver’s beam is kept a little higher than that of the surface speed of the drag roller. This speed difference maintains the tension on the warp during beam winding.
Beam pressing system:
The beam pressing system mainly consists of a pair of pressure rollers, two pairs of conical rollers, an iron beam and a pneumatic cylinder. The pneumatic cylinder is mounted in the trench under the weaver’s beam. The piston of the pneumatic cylinder is connected to the iron beam. A pair of conical rollers are fitted at each side of the iron beam. These conical rollers move free on their pin and bearings. The beam pressing rollers mounted on these conical rollers. When a machine is in operation, the pneumatic cylinder lifts the pressure rollers. The pressure rollers touch the surface of the beam. When the air pressure in the pneumatic cylinder increases, the pressure rollers start to press the beam. The air pressure in the pneumatic cylinder is regulated by the air pressure regulator valve. The compactness of the beam is controlled by pressing rollers. It also levels the surface of the warp beam. The pressure rollers perform other work of beam loading and unloading.
Drive:
An electric motor is used to drive the machine. This motor transmits the motion to the reduction gearbox. A vertical shaft is connected to the reduction gearbox. All the moving parts receive the motion through this shaft by means of chain sprocket and gears. In modern sizing machines, sow boxes, drying cylinders, drag rollers and beams are driven by individual motors. These motors are controlled by individual A.C. drive. The speeds of all the sections are synchronized accurately.
PIV gearboxes:
When the machine is driven by a vertical shaft, PIV gearboxes are used to vary the speed of different sections. PIV boxes synchronize the speeds of various sections to each other. The sow box, drying cylinder and drag rollers have PIV boxes to adjust their speeds. The PIV box consists of a chain, two pairs of variable diameter toothed pulleys and a diameter adjusting handwheel.
The one flanged toothed pulleys connected to the gear transmission system and the other end is connected through a chain sprocket to the receiving device. When the diameter of driver pulleys is increased, the diameter of driven pulleys reduces simultaneously. Therefore the speed of the motion receiving device is increased. When the diameter of the driver is reduced, the speed of the motion receiving device is decreased. The diameter adjustment is achieved by rotating the handwheel.
Control panel:
It is the electrical panel that controls all the electrical operations of the machine. There are many electrical contactors, relays, and printed circuit boards used in this panel. These devices switch on and off the supply according to signals received from various sensors located at different parts of the machine.
Automatic speed and moisture control system:
This system is very important for the efficient and accurate working of the sizing machine. In this system moisture percentage to have remained in the sized warp, the sheet is fed in the system. The main steam valve is opened and the temperature of different drying cylinders is adjusted manually. When the machine is running continuously, the speed of the machine varies automatically according to the moisture percentage fixed in the system. The machine speed is lowered to keep the moisture percentage constant when the steam pressure is reduced. When the steam pressure increases, the speed of the machine also increases to keep the moisture percentage constant.
Length measuring system:
The machine is equipped with a digital length measuring meter. A metallic pin is mounted on the flange of the pressure roller of the headstock. This pin passes just in front of the proximity sensor during each rotation. Thus proximity sensor sends the signal of completion of each rotation of the pressure roller to the digital meter. The diameter of the pressure roller is fed into the digital meter. The digital meter converts the rotation into the metres. The required warp length can also be fed into the meter. When the required warp length reaches completion, the machine stops automatically. The operator cuts the beam and replaces it with a new one.
Stretch control system:
The ratio of difference of delivered length and feeding length to feeding length expressed in the term of percentage is called stretch percentage. The stretch percentage always appears in the display of the control panel. It ranges between 1 – 2 %. If it is not ranging between this limit, the tension between the sow box and drying cylinder, the tension between the drying cylinder and the drag roller is adjusted.
Cooking unit:
This is a vessel in which the sizing liquor is cooked. This is made of stainless steel and is capable to bear high pressure. A stirrer is fitted in the bottom of this vessel. This stirrer revolves with the help of an electric motor. An airtight door is mounted on the top of the vessel which is used to drop the sizing ingredients into this vessel. A water supply pipe is fitted in this cooking vessel to supply the water in the vessel.
Steam is used to maintain the temperature in the vessel. A temperature meter and pressure gauge are fitted in this cooking vessel to reed temperature and cooking pressure. Normally the volume of the cooking vessel is 1000 litres. One inch height of the cooking vessel contains 20 litres of the volume of liquor.
Liquor storage:
A liquor storage vessel is used to store the cooking liquor. A stirrer is fitted to the vessel to stir the liquor. Steam supply maintains the liquor temperature.
PRECAUTIONS OF SIZING PROCESS:
Following precautions should be taken during the sizing process:
• Tension on the beams should be as minimum as possible.
• The alignment of beams should be done properly.
• Temperature of sow box should be 80 – 85 degrees Celsius.
• The condensation percentage of steam in the sow box should be determined. It should be as minimum as possible. High condensation percentage of steam can badly affect the refractometer value of sizing liquor and can dilute it.
• The level of sizing liquor in the sow box should be proper to maintain the continuous circulation of liquor.
• The viscosity of liquor should be as minimum as possible.
• The temperature of the first cylinder should be higher and the last cylinder should be lower.
• Water eliminator in the steam line of the sow box should always be used.
• The squeezing pressure should be set properly to avoid an excessive amount of sizing liquor.
• Stretch percentage should be as minimum as possible.
• Moisture percentage in the sized warp sheet should be 8 – 9 % approx.
• During the sizing process, the machine should not be stopped for a long time otherwise the sizing liquor marks may be created on the warp sheet which causes end breakage during the process.
• Warp cover of 60 – 65 % in the warp sheet gives better sizing performance. If it is more than this value double sow box should be used in the machine.
• Division of warp sheet into two parts before passes over the drying cylinder reduces end breakage in the sizing process.
• The yarn separators should be inserted correctly and carefully. If it is inserted wrongly, the end breakage rate and sticking ends are increased badly.
• The denting of ends should be done correctly, the cross ends in the dents of reed badly increase the end breakage rate.
• The drag roller should be cleaned properly, any stone particle present on the surface of the drag roller can rupture the warp ends.
• The operator should not sit on the top cover of the drag roller with shoes on their feet.
• The operator should be used a table to reach the broken ends to repair them.
• When the broken end is repaired, it should be put in the same dent where it was before breakage.
• The beam winding tension should be proper. High tension causes end breakage and low tension soft beam which creates problems in weaving.
• Beamwidth should be set precisely. Improper adjustment of beam width results in the form of loose or tight selvedges of the beam.
• The sizing liquor should be cooked properly. It is cooked up to 135 degrees Celsius, then the steam supply is stopped. Now the liquor is kept for one hour at this temperature. Thus liquor is ready to use.
• The moisture content of sizing ingredients should be taken into consideration before deciding the amount of water to dissolve the ingredients.
• The sizing ingredients should be used according to the quality and count of yarn.
• The operator should always be kept close watch over the reed during operation. Little negligence of the operator can be dangerous for a beam to be produced.
• The concentration of sizing liquor in the sow box should be checked with the refractometer after every hour.
• The lapped end should be repaired carefully.
• The pressure of the beam pressure roller should be proper.
PROCESS CONTROL IN SIZING:
The process control programme in the sizing process is a very important aspect. If it is not followed properly and continuously, the quality and productivity are affected badly. The proper monitoring and follow-up of the process control programme greatly improve the quality and productivity. The following points should be checked and controlled regularly as per schedule:
Size recipes and size pick-up:
This is a very important factor in the sizing process. The selection of correct recipes plays a decisive role in the quality of sizing. The quality parameters of warp yarn are tested before making a selection of size recipes. Mainly a number of imperfections per kilometre of yarn (thick places, thin places, neps, unevenness %), tensile strength, elongation at break and R.K.M.( tenacity in grams per tex) are tested properly. The warp having poor tensile strength needs more quantity of binders, the yarn having more thin places also need to increase more binders in sizing liquor. Thus yarn properties directly affect the selection of sizing liquor recipes. The size pick-up is also selected according to warp yarn properties. The poor yarn needs more pick-up than strong yarn.
Preparation of sizing liquor:
The sizing liquor is prepared very carefully to achieve the best process performance. Every step of the preparation of sizing liquor is performed properly and precisely. First of all the required amount of water in litres is taken in the cooking vessel. It is measured accurately with the help of a long graduated metallic scale in terms of inches then the volume of water in litres is calculated according to the level of water. Now the required sizing ingredients according to size recipes are weighed with the help of physical balance precisely. These ingredients are added to water in a definite sequence. The adhesives are added first then binders are added into the water. Other ingredients are mixed at last. The softener is added in the storage of sizing liquor to avoid its evaporation. It should always be noted that the stirrer is moving continuously during the period of liquor preparation. Now the cooking of liquor is carried out. When the temperature reaches to definite point (135 degrees Celsius), the steam supply is stopped in the vessel. The liquor is kept at this temperature for 1 to 1.5 hours then it is transferred into the storage vessel. The viscosity of liquor is checked precisely, the concentration of liquor is measured accurately before using the liquor. If there is found any deviation in parameters, corrective steps are taken.
Size pick-up percentage:
The amount of sizing ingredients picked up by warp yarn expressed in the term of percentage is called size pick-up. It is the most important factor in the sizing process. Required size pick-up is decided according to yarn count, quality ends per inch and picks per inch in the fabric to be bobbin. Poor and fine count yarn needs higher size pick-up. The less size pick-up than the required amount causes higher-end breakage in the sizing and weaving while more size pick-up than the required amount causes an increase in sizing cost and end breakage during sizing too. There is not any method to check size pick-up on the spot accurately. The concentration of sizing liquor is kept 2% less than the required size pick-up percentage. The squeezing pressure is kept 0.5 to 1.0 kg per inch square. The strength of the sized warp is judged manually by breaking the end. The slippage of fibres in the yarn during breaking is seen. If there is minimum slippage of fibres after breaking the sized end the quality of the sized warp is supposed to be better quality. The size pick up is analysed in the laboratory by desizing the warp yarn. This method is not much reliable. The most reliable method of analysis of size pick-up is to find the weight of all empty warper’s beam and with warp yarn thus the weight of warp before sizing is obtained. Now the weight empty weaver’s beam is found. The weight of the weaver’s beam is found after sizing with sized warp yarn. The weight of a sized warp is found. The size pick-up % is calculated as follow:
Stretch percentage:
The elongation in the warp yarn occurred during sizing expressed in the term of percentage is called stretch percentage. It is kept as low as possible in the sizing process. if it increases more than the limit, it is too dangerous to the warp yarn. It should be ranged between 1 – 2%. The setting of warp tension between different parts of the machine is performed accurately to minimise the stretch percentage. It is calculated just after the sizing of 100 – 200 metres of warp. If the value of it is found more than the limit, the tension between different parts of the machine is reduced to control the stretch percentage. The strength percentage is calculated as follow:
Moisture content: Moisture content in the warp after sizing is necessary. If a sized warp has less moisture, there will be much end breakage during weaving. If it contains more moisture, there will be excess end breakage during the sizing process. The value of moisture content in the sized warp ranges between 7 – 9 %.
Quality of beam: The quality of the beam depends on the extent of the required sizing parameters during the process. If all the required parameters are achieved precisely and successfully, the best quality sized beam results. Minimum end breakage, stretch percentage, correct size pick-up, moisture content, give improved quality of the sized beam. If the machine stops repeatedly due to any reason, the quality of the sized beam is affected. The variation in steam supply pressure results in the form of poor drying of warp which causes warp breakage. The surface of the cylinder catches a layer of sizing liquor, which goes with the warp and causes end breakage.
Machine speed:
The speed of the sizing machine depends upon the collective achievement of various sizing parameters. The steam supply, size pick-up, viscosity of sizing liquor, stretch percentage, moisture content, quality of warper’s beam, sizing operator skill and quality of warp yarn to be sized are the factors that directly influence the speed of the sizing machine.
VARIOUS SIZING FAULTS, CAUSES AND THEIR REMEDIES:
The various kind of sizing faults and their causes are given below:
Short ends: When the broken end is wrapped on the warper’s beam, stainless steel roller, drying cylinder or drag roller, the short end results in the sized beam. The wrapping of the end mainly occurs due to the un-mend warp end in the warping. This fault can be controlled up to a maximum extent by controlling short ends in the warper’s beam.
Sticking ends: When there is high-end breakage in the sizing, the broken ends become out of yarn separators. These ends lie without separation in the beam. These broken ends stick to each other. This is a very serious fault in the sizing process. The sticking ends can be controlled by reducing end breakage up to the optimum level. It is necessary to control all the parameters related to end breakage.
Sagging ends: The ends in the sized beam having less tension than normal are called sagging ends. Sagging ends occur due to uneven tension on the ends in the warper’s beam. The sagging ends can be avoided by putting equal warp tension on each end.
Cut marks: When the broken end is wrapped on the squeezing roller, stainless steel roller or drag roller, the pressure at that particular place on the warp sheet increased, which causes cut marks in the warp sheet. Any uneven surface of stainless steel roller, squeezing roller or drag roller also cause cut marks in the sized beam.
Sizing liquor marks: When the machine stops for a long time to repair any problem, deep size marks occur in the beam. These are objectionable marks that also appear on the fabric surface. The warp ends are displaced from their position. When there is a need to stop the machine for long period, the machine is inched after regular intervals of a short period to prevent deep size marks. If the inching of the machine is not possible, the size marks are washed with water before drying.
Uneven size pick-up: Size pick-up is always even throughout the width of the warp sheet. If there is a difference in warp pick-up between the middle and edges of the warp sheet, this is called uneven size pick-up. There may be two causes of uneven size pick-up. One cause is the difference between squeezing pressure of the left and right sides of the roller due to improper working of the pneumatic cylinder. The second reason is the different diameters of stainless steel roller and squeezing roller between middle and edges. When the machine is worked, the extreme edges of these rollers are left unused. The middle portion of these rollers is rubbed into the yarn and the diameter of these rollers is reduced gradually in the middle portion. Thus the diameter of edges remains unchanged and the diameter in middle is reduced beyond the tolerance limit. Uneven squeezing pressure results on the warp sheet so that uneven size pick-up results. To avoid this fault, the working of the pneumatic cylinder should be check regularly. The grinding of stainless steel roller and squeezing roller should be carried out when the diameter difference between the middle and edges becomes beyond the tolerance limit.
Over drying: Overdrying of warp sheet enables the moisture content in the sized warp sheet to be too low. It creates excessive-end breakage in weaving. To prevent this fault, the sizing speed should be selected precisely and increase if needed. When there is no possibility to increase the machine speed, the steam pressure in the drying cylinder should be reduced.
Under drying: If the sized warp sheet contains more moisture percentage than the standard amount, this is called under drying. It causes end breakage in sizing and creates the possibility of bacteria development while the sized warp beam remains unused.
Streaks in beam: When the distribution of ends in the beam is not even the streaks in the beam result. It occurs due to uneven denting of warp ends in the reed.
Loose selvedges: when the beam width is slightly greater than the reed width, the selvedges of the beam become loose. It creates tension problems in weaving.
Tight selvedges: When the beam width is slightly less than the reed width, the beam selvedges become tight and ends breakage on the selvedges results.
Loose winding tension: If winding tension is less than required, the beam becomes loose and results in the form of warp tension variation in weaving.
High winding tension: When the winding tension is more than required, the beam becomes more compact. The yarn losses its elongation and results in the form of high-end breakage in weaving.
Cut selvedges: Cut selvedges occur due to the rough edges of the weaver’s beam flanges. To avoid this problem, the edges of the flanges should be smooth.
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