7.The Sizing Process.pdf

Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The Sizing Process The process of coating the warp sheet with starch and other ingredients is called as the sizing process. The sizing process is the most important weaving prepa...

Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The Sizing Process The process of coating the warp sheet with starch and other ingredients is called as the sizing process. The sizing process is the most important weaving preparatory process and is considered as the heart of weaving. Main purpose of the sizing process is to provide additional strength to warp yarns to enable them withstand stresses and strains of weaving. Proper sizing enables the yarns to be woven at a higher speed with greater efficiency. Prepared By: Shakeel Ahmad Paracha Page 1 of 16  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Objectives of the Sizing Process To increase the strength of yarn. It is increased up to 20 - 30 % of original yarn strength. To cover the surface of the yarn with starch and other ingredients to withstand various forces during weaving. To reduce the hairiness of yarn (decrease the number of protruding fibers, which cause breakages due to tangling). To provide elasticity to the yarn to compensate the additional length required in the formation of the shed (minimum elongation of sized yarn should be 65 - 75 % of original yarn, unsized yarn elongation is 8 - 10 %, and it should not reduce below 4 % as it will cause breakages on slight stresses). To save the yarn from bacteria when it is stored in the weaving shed, particularly when the yarn has cellulosic nature. To give additional weight to the yarn when it is very thin or weak (for finer count it is required to increase the weight so enough strength of yarn may be achieved). To avoid or eliminate static charges as synthetic fibres develop static charges during weaving because of friction with the reed. To improve the abrasion of yarn. There is always friction between metallic parts, so abrasion of yarn is increased up to 200 - 300 %, by binding the yarn and by using good quality of softener. To make the yarn smooth and pliable (thick and thin places are covered), it is treated with certain chemicals during the sizing process. To get the required number of ends. The total number of ends necessary to weave a particular fabric is combined from warp beams on to weaver’s beam. If there is more than one warper’s beam, then they are also combined during the sizing process. To improve the appearance of the fabric in its loom state. For this purpose, whitening agents are used. Sizing Materials Following materials are used during the sizing process: o Starches o Softener o Other chemicals Starches Starch is the main sizing ingredient. It is used to give strength to the warp sheet. Starches used in sizing process are obtained from various sources. Prepared By: Shakeel Ahmad Paracha Page 2 of 16  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Softeners The starch used in the sizing process makes the yarn hard and brittle which cannot be used in weaving. In order to make it soft and pliable, we use softening agents. Softeners are also called as lubricants. Softeners also make the yarn extensible and flexible. Different types of softeners are used in the sizing process. The most used softeners or lubricants are: o Oils o Natural & synthetic fats o Glycerin o Soaps o Japan wax Other Chemicals Additional/optional chemicals that can be used in the sizing process include: o Humectants [to maintain min. moisture (8.5 %) in the sized warp sheet after drying] o Antiseptic agents (to prevent the warp sheet from the bacterial attack) o Weighting agents (to increase the weight of warp sheet in case of fine count) o Antistatic agents (to eliminate the static charges) o Defoamers (to restrict the formation of foam in the sizing solution) o Starch thinning agents (to make the starch thin) Quality of Sizing Material The sizing materials that are used during the sizing process should possess the following qualities: o They should give the fewest yarn breakages during weaving. o They should give the least exfoliation in the dry state. o They should be easily de-sized. o They should give good fabric characteristics. o They should be compatible with the machinery used. o They must not be hazardous to health. o They should not cause degradation of the textile material. o Minimum quantity of the sizing materials should yield the required results. Composition of Sizing Material The composition of sizing materials varies from machine to machine. It also depends on the nature of the yarns. General composition is as follows: o Starch → 9 parts by weight (90 %) o Softener → 0.9 parts by weight (9 %) o Other chemicals → 0.1 parts by weight (1 %) However, the exact size recipe is developed based on years’ experience and by hit and trial. Prepared By: Shakeel Ahmad Paracha Page 3 of 16  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Percentage Sizing Material (S %) The percentage sizing material (S %) is defined as the weight of oven-dry size material expressed as a percentage of oven-dry weight of the unsized yarn. Mathematically: Oven - dry weight of size material S % = x 100 Oven - dry weight of unsized yarn Percentage Size Concentration (C %) The percentage size concentration (C %) is defined as the weight of oven-dry size material expressed as a percentage of the amount of water used. Mathematically: Oven - dry weight of size material C% = x 100 Amount of water used Quantity of Sizing Material Preparation of Sizing Solution The sizing solution is normally prepared in an entirely separate area away from the sizing machine. The sizing ingredients are mixed with water in a vessel called sizing cooker and sizing solution is cooked until the required viscosity is achieved. After the sizing solution is prepared, it is transferred to the sizing machine with the help of a pump and piping system. Valves are used to control the flow of sizing solution in the machine as per requirement. Prepared By: Shakeel Ahmad Paracha Page 4 of 16  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Some important terms related to the Sizing Process Size Liquor Concentration It is the mass of solid contents in the size paste. It is the amount of solid size contents expressed as %age of the total volume of size liquor. Size Take-up It is the mass of paste pick up in the size box (wet pick up) per unit weight of oven dry un- sized yarn before drying. Size Percentage It is the mass of dry size material stored on the yarn and expressed as the % age of unsized yarn weight. Size Box Occupation It is used to determine the yarn spacing on different rollers in the size box. It should be less than 50 % for better sizing. Prepared By: Shakeel Ahmad Paracha Page 5 of 16  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The Sizing Machine Line diagram of a Sizing Machine Prepared By: Shakeel Ahmad Paracha Page 6 of 16  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Sections of the Sizing Machine A sizing machine is typically divided into following portions: o Creel section o Sizing section o Drying section o Leasing/separation/splitting section o Winding/headstock section o Cooking section The creel consists of a metallic frame which holds the warp beams, arranged in such a way to accommodate a greater number of beams in less space. Sizing section is the most important part of sizing machine. Size box contains the sizing liquor to be applied on the warp sheet. In drying section, the wet sized warp sheet is dried rapidly, thoroughly and uniformly either by drying cylinders or chamber. Splitting section has several leasing/splitting rods which split the sized warp sheet into its constituent back beam sheets. Headstock is the section of sizing machine, having motors to rotate the beam to wind the sized warp sheet on weaver’s beam. Cooking section consists of a cooker for the cooking of the sizing liquor. It is also provided with a storage tank to store the cooked size liquor. Creel Section It is the portion of the sizing machine on which the warp beams are loaded. It helps in the proper unwinding of the warp sheet. The beam arrangements in creel are usually of two types, as shown in figure: o Staggered, two-tier arrangement o Groups of 2, 4, 6 or 8, one to four tiers. Prepared By: Shakeel Ahmad Paracha Page 7 of 16  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Catwalks between individual groups ensure safe and convenient access to the warp beams. It also helps to insert the splitting laces on warp beams. The let-off of the yarn is negative, i.e. the beams are not directly driven by motors. The brake system consists of a leather belt which is passed over the ruffle of warp beam and connected to a pneumatic cylinder. The braking force is actuated pneumatically. Prepared By: Shakeel Ahmad Paracha Page 8 of 16  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Guide rollers are present to guide the warp sheet towards the size box. The creel capacity of sizing machine ranges from 16 - 36. The beams are loaded on the creel with the help of a mono-rail. Mono-rail It is a small crane having a capacity of 2 - 3 tons. It is fitted with two motors, one for vertical and other for horizontal movement. Mono-rail moves on H-type girder fitted in the roof in the horizontal direction. The speed range of mono-rail is 10 - 15 m/min. Sizing Section Sizing section consists of: o Pre-wetting o Size box Pre-wetting It is the treatment of spun yarns with hot water before impregnating in size solution. It improves the specific adhesive force of size on the surface of warp yarns. The hot water partially dissolves waxes, dust and other material loosely held by fibres. Prepared By: Shakeel Ahmad Paracha Page 9 of 16  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) In conventional two box-sizing machine, first size box may be used for pre-wetting with hot water (90 °C) to wash out pectin from cotton yarns. Two immersion and two dip rollers are used in pre-wetting as shown in above figure. Two basic technologies of pre-wetting are used: o Pre-wetting in a separate compartment with two dips and two squeezes. o Combined pre-wetting and size box. The first squeezing action holds back the dirt and expels air from yarns to increase the water absorption during second immersion. Generally, high squeezing pressure is required to ensure adequate pre-wetting and avoid dilution of size liquor in the size box. The advantages of using pre-wetting are: o Improvement in surface adhesion of the size to the yarn as the outer surface is wetted with size and the core is wet with water due to pre-wetting. o It allows the size add-on to be reduced by up to 30 - 50 %. o Better adhesion to the surface increases yarn strength by 15 - 20 %. o It also helps to reduce the hairiness of yarn. Size Box Size box is the most important part of sizing machine where warp sheet passes through the sizing liquor. The sheets of the yarn coming from the individual warp beam are dipped into the bath with the help of an immersion roller. The yarns pick-up the required quantity of size solution and the excessive solution is squeezed-off by squeeze rollers. By altering the pressure of squeeze rollers, the amount of sizing material applied on the yarn sheet is controlled. Multiple size boxes, single or double immersion rollers and single squeeze or double squeeze can also be employed depending on the size material, warp quality and density. Prepared By: Shakeel Ahmad Paracha Page 10 of 16  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The major parts of the size box are: o Feeding or drag roller o Immersion rollers o Squeezing rollers o Size tray o Size circulation pump o Perforated steam pipe o Size feed pipe & valve Drying Section The drying portion of the sizing machine is used to dry the wet warp sheet that is coming from the sizing box. Three types of drying methods are used on the sizing machines: o Hot air-drying o Cylinder drying o Infra-red drying Cylinder drying is the most used method of drying. The drying section of the sizing machine consists of: o Cylinder dryers o Condensate trap o Temperature sensors Prepared By: Shakeel Ahmad Paracha Page 11 of 16  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) o Ventilator o Mini cylinders Waxing Device It is a device used to apply wax over the sized yarn to cover hairiness and to improve strength. It is mounted at the beginning of the splitting section. It consists of: o Waxing roller o Can for wax o Wax tray o Heating arrangement o Drive arrangement for wax roller Prepared By: Shakeel Ahmad Paracha Page 12 of 16  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The wax roller is fitted in the box & is dipped into waxing solution. The solution is kept under constant temperature by steam heaters, temp. = 65 °C. The wax is added in the can according to the requirement. The sized warp sheet touches the roller surface and wax is applied over the sized yarn. Wax application is controlled with the help of roller movement which is controlled through the driving mechanism. Higher the speed of wax roller more will be the wax application. The %age of wax application varies from 0.2 - 0.3 % on the weight of sized yarn. Leasing Section It separates the warp sheet to avoid crossing or entanglement of warp threads before comb. The separation is carried out with the help of leasing rods. Lease rods are highly polished to reduce the friction b/w yarn & rods. Number of lease rods = Number of warper’s beams – 1 The diameter of the first leasing rod is greatest, and diameter of the last rod is least i.e. the diameter reduces from first to last. 1st lease rod is called burst rod. Leasing may be done in two ways: o Asymmetric leasing Higher yarn stresses. Less separation of the sheet. Uneven distribution of sheets. Prepared By: Shakeel Ahmad Paracha Page 13 of 16  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) o Symmetric leasing Fewer yarn stresses Better separation of the sheet Equal distribution of sheet Winding/Headstock Section Individual warp yarns separated by leasing rods are further separated individually by passing each individual yarn through an individual dent of the expandable comb. At the headstock section, weaver’s beam is driven by motor so that separated warp yarn sheet is wounded on the weaver’s beam. As the entire length of the warp sheet is wounded on the weaver’s beam, the full weaver’s beam is doffed and replaced by a new empty one. The weaver’s beam is prepared according to required number of ends & width of cloth with specific winding & pressing tension. Headstock consists of the following major parts: o Expandable comb o Measuring roller o Drag roller or carriage roller o Tension roller o Guide rollers Prepared By: Shakeel Ahmad Paracha Page 14 of 16  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) o Pressing roller o Weaver’s beam Cooking Section Cooking section includes: o Size cooker o Size storage tank o Limit switches on storage tank o Temperature sensors o Agitator (stirrer) The maximum capacity of size cooker is 1250 litres. The agitator ensures homogeneous liquor. It also helps to break the starch granules. A motor is used to pump the sizing liquor to the storage, located some 8 feet above the ground level. Storage tank is also supplied with stirrer and steam to ensure homogeneity and temperature maintenance. Pressure transducers are located at the top and bottom of the storage tank to check the size level. Cooking Procedure Quantity of water and cooking time is fed on the panel of the sizing machine. The water supply button of size cooker is pushed on. The water is added at normal temperature (35 – 40°C). PVA is added in this water and stirred for 10 – 12 min. Required amount of starch is added and stirred again for 5 min. Add acrylic and stirred for 5 min. Steam it for 25 – 30 min. at 90°C. Add wax and heat for 2 – 3 min. Prepared By: Shakeel Ahmad Paracha Page 15 of 16  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Sizing Production Calculations Production by Length Calculated Production yds = Sizing Rate( yds / min) x 60 x th Sizing Rate( yds /min) x 60 x th x Eff. Actual Production yds = 100 Production by Weight Sizing Rate( yds / min) x 60 x th x ES Calculated Production lbs = 840 x Ne Sizing Rate( yds / min) x 60 x th x ES x Eff. Actual Production lbs = 840 x Ne x 100 Where, th = Time in hours ES = Number of Ends of weaver ' s beam Eff. = Machine Efficiency for the said time period in hours Ne = English Count Actual Production Efficiency % = x 100 Calculated Production Q. Calculate the calculated , and actual production of a sizing machine in Length and Weight , if Sizing Rate = 1200 mtrs / hr., Efficiency = 90% , English Count ( Ne ) = 30 S , Time = 8 Hours , Total Ends = 9000 1200 x 1.0936 Sizing Rate = yds / min 60 Sizing Rate = 21.872 yds / min Calculated Production yds = Sizing Rate( yds / min.) x 60 x th Calculated Production yds = 21.872 x 60 x 8 Calculated Production yds = 10498.56 yds Sizing Rate( yds /mins.) x 60 x t h x Eff. Actual Production yds = 100 21.872 x 60 x 8 x 90 Actual Production yds = 100 Actual Production yds = 9448.704 yds Sizing Rate( yds / min) x 60 x th x ES Calculated Production lbs = 840 x Ne 21.872 x 60 x 8 x 9000 Calculated Production lbs = 840 x 30 Calculated Production lbs = 3749.485 lbs Sizing Rate( yds / min) x 60 x th x ES x Eff. Actual Production lbs = 840 x Ne x 100 21.872 x 60 x 8 x 9000 x 90 Actual Production lbs = 840 x 30 x 100 Actual Production lbs = 3374.537 lbs Prepared By: Shakeel Ahmad Paracha Page 16 of 16