Sizing

SIZING

The weaving process requires the warp yarn to be strong, smooth and elastic or extensible to a certain degree. To achieve these properties on the warp yarns, a protective coating of a polymeric film forming agent (size) is applied to the warp yarns prior to weaving; this process is called slashing or sizing. This size material is later on removed in the finishing operation called desizing.

The main purposes of slashing are:

· To strengthen the yarn by causing the fibres to adhere together .

· To make the outer surface of the yarn smoother so that hairs protruding from one yarn in the warp should not become entangled with hairs protruding from a neighboring yarn .

· To lubricate the yarns so that there is less friction when they rub together in the weaving process . Lubrication also reduces the friction between the yarns and the loom parts . The reduction of friction reduces the forces acting on the yarns during weaving .

The ultimate goal of sizing is to eliminate or reduce warp breaks during weaving. Warp breaks are caused either by high tension or by low strength in the yam. High tensions in the warp are caused by large shed openings, lack of proper tension compensation, high beat- up force and inadequate let-off. Knots, yarn entanglement and high friction also cause tension buildup.

It is important that the size film must coat the yarn surface without excessive penetration into the body of the yarn, because if the size material is penetrated deep in the yarn, complete desizing would not be possible. Therefore, only enough penetration should occur to achieve bonding of the size film to prevent removal during weaving. The following terms are used related to sizing:

· Size concentration: the mass of oven dry solid matter in size paste

· Size take-up (Size add-on): the mass of paste taken up in the size box per unit weight of oven dry unsized yarn

· Size percentage: the mass of oven dry size per unit weight of oven dry unsized yarn

There is an optimum level of size add-on that d minimum warp end breakage as shown in figure. Excessive size makes the yarn stiffer and less extensible; yarns with too little size will not be strong and smooth enough for weaving. Therefore, too little or too much sizing causes an increase in warp end break. Optimum size add-on gives the best results for weaving.

Other points to consider in slashing:

· Slasher creel tension control is critical especially with open-end yarns. Maximum tension should not exceed 5% of breaking strength (15—20 g for ring spun yarns and 12—15 g for open-end yarns). With coarse yarns, sometimes 30 g is allowable.

· The amount of size picked up is affected by the viscosity of the size mix as well as the yarn structure. The viscosity of the mix is controlled by the recipe, amount of solid content in the size liquor and the type of sizing product, mechanical mixing level, temperature and time of boiling. Flat filaments, textured and spun yarns pick up size differently.

· Yarn spacing at the slasher size box and on the drying cylinders is very important.

· The choice of size for staple yarns is usually based on cost. For filament yarns, the size material is chosen based on the compatibility with the fiber.

· Running the slasher at creep speed, which is sometimes necessary, generates a very undesirable condition for proper sizing and should be minimized in every way possible.

· Stretch of warp yarns during slashing should be controlled accurately to maintain residual elongation in the yarn which is needed for good weaving. Back beam— size box stretch should not exceed 0.5%.

· Guide rollers should be kept free from scratches and sharp edges. They should be sanded/polished frequently.

· Pre-wetting yarns prior to sizing can reduce the amount of required size add-on for the same performance, especially for cotton yarns.

Main parts of sizing machines are :

· Beam Creel

· Size Box

· Dryer

· Yarn Splitting System

· Head Stock

Beam Creel

Beam arrangements in the creel are usually two types:

a) Groups of 2, 4, 6 or 8, one to four tiers

b) staggered, two-tier arrangement

SIZE BOX

Main parts of the size box are

– Immersion Roller

– Squeezing Rollers

– Steam Heating Pipes

• Immersion Roller

Position of the immersion roller depends on the quantity of the size required to apply . If heavy size is required then the roller is required to apply .

• Squeezing Rollers

The purpose of these rollers are to remove the extra amount of size chemical from the yarns by squeezing them

among two rollers .The squeezing rollers should be placed above the size box so that the extra size chemical should fall in the box .

• Steam Heating Pipes

The temperature of size box is maintained with the help of Steam Heating Pipes and the steam flow is regulated to control the temperature .

Explantion:-

The size box is probably the most important section of the sizing machine. During the sizing process, the sheet of yarns is passed through the size box which contains the hot water solution or mixtures of sizing agents. The yarns pick up the required quantity of size solution in the size box, any excess size is squeezed oft as the yarns pass through squeeze rolls. Depending on the size material, warp quality and density, single and double immersion rolls and single squeeze and double squeeze configurations are used. Multiple size boxes can also he employed. In general, single box sizing machines have two squeezing rollers and two box machines have a single roller in each box. It is important that the rollers provide uniform squeezing pressure. The squeezing system determines the degree of size pick up to a large extent. While providing size consistency, the roll pressure should be adjusted to get around 125—130% wet pick up for cotton yarns, 110—115% for poly/cotton and 95—105% for polyester. On average, open-end yarns pick up around 10—15% more wet size than a comparable ring spun yarn. Therefore, about 10% more water should be added to get the same add-on. The bottom rollers are usually made of steel and the top rollers are rubber coated.

The critical parameters to watch in the sizing process are size homogeneity, constant speed of the sizing machine, constant size concentrations and viscosity. Flooding or dry zones should be prevented in the size box. Temperature of the size box is important for proper size pick up. For 100% polyvinyl alcohol (PVA) sizing, a temperature of 70 – 75 °C is recommended. Constant size temperature can be obtained in two ways:

1. Direct heating in which steam is injected into the size.

2. Indirect heating in which steam flows in pipes around the double walled size box.

A cooker is used to prepare the size; powdered size is metered into weight stations and then transferred to the cooker. Size mix is also called size liquor. Liquor concentration and the amount of water absorbed by the warp after the squeezing rollers are measured using a microwave measuring head, which enables the degree of sizing to be calculated. The degree of sizing can be calculated as the absolute degree of sizing or as a relative value. If the measured degree of sizing is different than the set data, then the squeeze pressure in the box is changed with a controller. The squeeze pressure is also adjusted according to speed of the system.

Rotor cooker is normally used for size preparation, in a rotor cooker, the size is prepared without pressure. The ingredients are added cold and mixed with a rotor and raking agitator. Additional breaking elements can be used to obtain high shearing effect. The size ingredients are automatically fed-in to the size box.

• DRYER

The different drying techniques used in sizing are as

under :

– Cylinder Type

• Two Cylinder Type

• Multi Cylinder Type

– Hot Air Drying

– Infra-red Drying

After the size box, the yarns go through the dryer section. The wet yarns are dried by using hot air, infrared radiation or cylinder drying. Cylinder drying is done using steam heated hot rolls which are called drying cylinders. Sometimes, a combination of drying methods is used on the same machine.

The drying temperature is critical; excess temperature increases the penetration of size into the yam, which can lead to excessive hairiness and even yarn breakage. The typical temperature range is 80 – 105°C. In cylinder machines, the evaporation rate can be calculated as the mass of water evaporated per unit contact area between warp and drying cylinder per unit time. A typical evaporation rate in a modern slasher is around 13 kg/hr/m². The maximum recommended machine speed is 120 m/min.

Splitting the warps after sizing and separate drying reduces the risk of adjacent yarns sticking together which reduces the number of yarn breaks. For air-jet weaving, a minimum of 75% open space on the dry cans is recommended for any type of yarn.

Sizing machines are classified based on the method of drying (cylinder, hot air or infrared) or according to the method of yarn supply (single end, direct and indirect). In single – end slashers, yarns are fed to the size box directly from the supply packages. This type of creel is generally used for a small number of yarns and textured yarns. In direct sizing, yarns are fed to the size box from a single creel beam or warper’s beam. In indirect sizing, several warper’s beams (“section beams”) are combined sheet to sheet, forming a final beam for weaving (weaver’s beam)

• YARN SPLITTING SYSTEM

Main parts involve in this section are :

– Lease Rods

– Lease Reed

YARN SPLITTING SYSTEM Lease Rods

· The function of the lease rods is to separate the individual yarns which are stuck together because of the drying of the size film in the drying section .

· To achieve this a series of lease rods , with one large diameter busting rod are used .

· These rods are generally chrome plated hollow cylindrical bars flattened at both ends .

· The yarn sheet emerging from the drying section is divided into two sections by one large lease rod and each section is further subdivided into two subsections by successive lease rods

YARN SPLITTING SYSTEM Lease Reed

• The function of the lease reed is to align the yarns to ensure uniform winding of the warp on the weaver’s beam .

• A V comb reed is used to help in providing an even distribution of the warp yarns and for avoiding abrasion

among yarns .

HEADSTOCK

• This is a take-up unit supporting the weaver’s beam and necessary drive gears .

• The drive equipment imparts necessary beaming tension for compact and straight winding of the warp yarn .

• Winding system is equipped with a positively driven roll commonly known as delivery roll or draw roll .

• This driven roller is placed between two heavy chrome plated nip rolls to assure that the yarn sheet being drawn is wrapped well around the draw roll .

SIZING INGREDIENTS

• For a size formula to approach perfection in a given application it should have several basic characteristics which will serve to eliminate warp breaks during weaving . For the size film to accomplish its primary tasks one would have to consider the following .

Tensile Strength Uniformity

· Adhesiveness Stability in Storage

· Flexibility Viscosity

· Elongation and elasticity

· Abrasion Resistance

· Penetration

· Uniformity

· Stability in Storage

· Viscosity

Base Materials

Since the prime function of sizing is to produce weavability in the warps the essential part of the size formula is the film forming ingredients . Base materials are the film forming ingredients or binders

Additive Materials

Additives are usually required to modify the base by increasing ( or decreasing ) one or more of the desirable properties .

Base Materials

Natural Base Materials

• Flour

– Maize Flour

– Rice Flour

– Wheat Flour

• Starches

– Rice Starch

– Wheat Starch

– Corn Starch

– Potato Starch

• Gum

• Dextrine

• Amylose

• Gelatin

Synthetic Base Materials

•Polyvinyl Alcohol ( PVA)

• Carboxylmethyl Cellulose ( CMC )

• PolyAcrylates

• Lubricants

Used to reduce friction and abrasion between adjacent yarns and the reed ,frames , drop wires

• Softeners

Used to give soft handle to the warp and the size film and to decrease the brittleness of the film

• Electrostatic Agents

Used to solve the static problem

• Deliquescent Substances

A small amount of hydroscopic agent or deliquescent in the size will prevent the size film from drying completely (Bone Dry ) and help the fibre to regain normal moisture after drying .

BASIC COMPONENT OF LOOM

1. Beam

2. Back rest roller

3. Drop wires

4. Motor driving the warp let-off

5. Healds

6. The motor driving the fabric take up

7. Slay

8. Reed

9. Take-down roller

10. Cloth beam

Loom:-

Loom is the machine that is used for this purpose. In the beginning, hand looms were used to produce cloths through weaving, at a commercial scale. These looms made use of a shuttle for the insertion of weft. The weaver had to throw a shuttle by hand from one side and catch it with the other hand at the other side. Then, after several developments and after the invention of electricity, power looms were came into being. The power looms were used for centuries, with the same element for weft insertion, the shuttle. The shuttle looms seemed to fail to meet the requirement of the modern, fast and quality conscious world. This led to the invention of the looms, which could insert weft into the fabricthrough any other means. Such looms are termed as shuttleless looms, which can give the desired quality and production. The looms were invented many years ago, but they came across the commercial success, about 35 years ago.

The production of a loom is generally measured by its speed in picks per minute. However, the correct way for the purpose is to figure out the weft insertion rate. After the commercial success of the shuttleless looms, the speed has been increased by up to 300-400% depending on reedwidths. The common projectile and rapier looms have similar speeds, which are at least 80% above the speeds of the best shuttle machines of similar width, and the air-jet machines have weft insertion rates 80-150% above those of the projectile looms.

When projectile weaving machines were successfully introduced three decades ago, they were running barely 50% faster than shuttle looms. The few rapier machines in use were slow and cumbersome, and jet machines had only just reached the prototype stage. The complete eclipse of the shuttle loom since then is mainly due to the reduced amount of labour required to operate the newer machines and the improved quality of the cloths produced on them. Greater production per machine and per unit of space reduces operating costs, but still greater advantages were obtained from the use of a supply of nearly continuous weft, smaller sheds, lighter sleys operating independently of the weft insertion unit, and the use of fewer, lighter, and better engineered components requiring less maintenance.

In recent years, the incorporation of microprocessors, for machine control and automatic adjustment, has resulted in further substantial increases in weft insertion rates.

WARPING

It is practically not possible to place hundreds or thousands of cones before a loom for the sake of providing warp to the fabric, so warping is used. Warping is basically the process of winding a part of the total ends of warp in full width on to a beam.

What Warping Should Do?

· To form from a predetermined single end packages, such as cones or cheeses, a continuous sheet of yarn of specified length and width.

· The individual ends of the sheet should be spaced uniformly across its full width.

· All the ends in the sheet should be wound at almost uniform tension.

· The density of wound yarn beam should be uniform across the width and from start to end of winding the sheet.

What Warping Should Not Do?

· Attempts should not be made to remove the yarn faults during the process of warping; the yarn breaks during warping should be as minimum as possible.

· Density of the beam should be controlled not by increasing yarn tension but by adjusting the pressure roll on the beam in case of spindle driven beam.

· The yarns should not get damaged during warping --- this can happen if the drum surface is not smooth and/or the parts in the yarn path have cut marks.

· The yarn sheet or the beam should not have faults, such as missing ends, cross ends, slack ends, fluff or wild yarn, high variation in tension between ends, damaged flanges etc. that will cause end break or defects at subsequent processes.

TYPE OF WARPING

Beam Warping

· Yarn is directly wound from cone onto the beam.

· This process is suitable for single color weaving

· The end product is called warp beam and must sent to the sizing department for further process .

Types of Beam Warping Machine

The warping machines are classified according to the 'package drive'; there are two basic types of the warping machines:

1. Direct driven or the spindle driven, in which yarn winding speed on to the beam increases as the diameter of the beam increases. Beam size is therefore limited due to the increase in yarn winding tension.

2. Surface driven; in which beam gets its motion while in contact with a drum, revolving at fixed r.p.m. In this case yarn winding speed remains constant through out the build of the beam.

Section Warping

· Yarn is wound firstly wound onto a drum and then wound onto the beam

· This process can be used for both single or multicolour weaving .

· The end product is called Weavers beam and can be directly installed onto the weaving loom

Ball Warping

· Ball warping is an intermediate process for storing yarn for transport , dyeing or reserve .

· It does not produce a beam .

· The usual form is a cross wound cheese in which multiple ends are wound at the same time in a ribbon which contains perhaps 50 or a 100 ends.

Description of the Warping Machine

Warping machine consists of:

(i) Head stock or winding head.

In itself it consists of the following:

a. Main driving gear which may be a fractional cone - clutch arrangement or it may be direct motor driven.

b. Adjustable reed to regulate the width of warp.

c. Yarn length measuring device.

d. Adjustable back reed for even distribution of warp threads.

e. Arrangement to detect thread breakage.

(ii) Creel

It is an arrangement where packages are placed on pegs. Single threads are taken from the packages passed through a tensioner, a guide and then on the front winding head. Function is to place all the threads in a sheet form so that whenever a thread breaks it can be easily traced out. The number of packages in a creel must be decided on the economic merit of any given situation with warper's bobbin its capacity is from 400 --600 packages; while with cones and cheeses the range is wider, i.e., 600 -- 1000 packages. In deciding about creel size, weight of yarn on supply packages, floor space available and number of beams required must all be considered.

Creel Types

There are four main types of creels

· Truck Creel

· Magazine creel

· Reversible Creel

· Duplicate Creel

Truck Creel

· The yarn packages are placed on a moving stand know as truck in a preparation area .

· A number of trucks are required per creel .

· At the end of the run the yarn of is broken between the package and the guide . The truck are then wheeled out from the centre of the creel to be replaced by the pre-loaded trucks .

· It is then necessary to tie up the yarn from each end to the correspond end in the creel .

There are a great many variants of the truck creel system but the principle is to use 'trucks', or mobile package carrier units, each consisting of a number of columns and tiers on either side so that when inserted on the axis of the creel frame it becomes a part of the creel. The side members carrying the tension units in positions corresponding to the packages on the mobile unit when correctly installed in the frame, can be moved outwards to provide working space between the tension device and the expended packages prior to running them out. The trucks have varying numbers of columns and tiers, generally in the range 6x9 per side, depending on the package size to be used and the corresponding creel gauge, which generally varies from 200 to 300mm.

The trucks are creeled-up away from the warper, frequently at the winding machine to avoid double handling, provided sufficient trucks are made available. This is not a low cost solution as many reserve trucks arc essential and these are not inexpensive units. If double handling is accepted the trucks can be reduced to one set in the creel and one complete reserve set, but this sacrifices some of the flexibility of the system. A truck creel with the trucks being loaded to the running position. Some of the more highly developed truck creels have a chain loading device, which pulls the trucks into the creel, correctly locates them sequentially, and with draws them from the back of the creel when a replacement is indicated. This type of creel is frequently used for very large creel package applications, which make trucks difficult to maneuver. Two arrangements are possible. The creel can be loaded from outside with inside draw-off or vice versa. The former arrangement is preferable as it not only provides a straighter thread-path but also is easier to load. They both can be arrange automatically.

Magazine creel

· Each package position is duplicated with one package in the running position and the other in the reserve position tied nose to tail.

· The package holders swivel to enable the empty cones to be removed and new cones tied to in nose to tail to the running package whilst the machine is in operation

· Drawback – it is normally a very long creel which greatly increased m/c stoppage time per break.

It is desired to avoid the knots in the body of the warp and thus preferable to rewind the yarn left on cones owing to the uneven yarn count from one cone to another.

OR

· This creel allows the tail of yarn from the package that is supplying yarn, to be tied to the leading end of the yarn , of the new package .

· Both packages are mounted on the spindles, which are aligned with the same guide, and the transfer of the feed from one package to the other is automatic.

· Although the space required for the creel is greatly increased

· The system is ideal for mass production.

Reversible Creel

· This creel allows the position of the old packages and the new ones to be reversed at he end of a run .

· The vertical racks of packages are arranged in sections which can be turned inside out .

· Or they are placed on a chain which carried the new packages from the creel’s inside position to

· the outside , from where the yarn is fed tot the headstock .

· The creel sides are arranged in a V-form , which leaves plenty of room for re-creeling in the inside position while the machine is running .

The two wings of an acute angled creel are each served by an endless chain, which moves the columns of yarn package holders, and tension units round an endless track, transferring the expended packages from the running position outside the creel wings to the creeling position inside the creel and the creeled packages into the running position. Creel changes inside cycle can be completed using such a system in less than; 15 minutes. A ‘creel’ is being transferred from the creeling position to the running position. The pegs shown as empty will normally carry cone residues from the running position to the creeling position where they are replaced by full packages for the next creel. There is considerable storage space within the creel for storage of creel trolleys.

Duplicate Creel

· There are 2 creels per headstock and at the end of each run they are moved sideways so that a full creel is quickly positioned behind the headstock .

· It is possible that one of the reverse creel positions could be behind the running position of

· the creel . However it is more usual for the headstock to move sideways as this requires less

· space .

· It is always necessary to re-thread the warp at the beaming headstock before commencing

· the new run .

Automatic Creels

The Schlafhorst ‘automatic’ creel Z25 is one of the most highly currently available. It is essentially a truck creel with automatic chain unloading and with two features to reduce creel change time. The creeler yarn from the package simultaneously through tension device break detector and collects all the ends from one tension column and twists them together before locating them in a holder on the threading truck. As the truck is pushed forward it automatically threads and separates the ends according to creel tiers and-columns.

The carriage stands at the rear of the creel during beaming, and is released when the running yam packages are almost expended. As the carriage moves along the creel every end is cut between package and tension device, the ‘live’ end being secured in a clamp. When the knotter carriage reaches the front of the creel, the operative operates the chain conveyer and removes the creel trucks from the creel. The creel trucks are designed with special pegs with clamps at their extremities so that when each cone is loaded the end is located in the clamp. This precludes the use of closed end cone shells. The knotter carriage has a separate knotter head for each tier on each side of the creel, so a six tier creel will have twelve knotter heads on the knotter carriage. When the full creel trucks are correctly assembled by the convener chain, the knotter carriage ties one column on each side simultaneously.

The creel incorporates other advanced features. These include a tension unit, which is set to minimum tension on each end of a column at the back of the creel, and this tension is matched on every end on the front column of the creel. All the intermediate columns are then calibrated by a scale so that all ends have equal tension as they reach the headstock. Once the basic setting has been made, uniform simultaneous adjustment can be made to all the ends by a single hand wheel. A traveling blower keeps the tension units and yarn packages free from 'fly' and a dust suction unit with stripping device is located at the base of the creel.

Effects of Poor Performance

The performance of the warping process is judged mainly by the end breakage rate at this process.

The operation cost of an end break in warping has been estimated to be about 700 times of that in automatic winding. An end breakage in warping, besides causing stoppage of the production from all the packages (400 - 600) put in the warping creel, reduces substantially the production efficiency of the warping machine. Besides the steep fall in productivity, an end break in warping is also likely to deteriorate the quality of the beam preparation due to three reasons:

1. When the machine stops with the broken end passed on to the beam, there is a possibility of incorrect mending --- taking the broken end from the beam in cross with the neighboring ends, bad knot, slack end--- which can lead to the formation of lapper in sizing or a stoppage in the loom shed;

2. The shortage caused in the length of the broken end during mending leads to high loss in extensibility of that end during unwinding of the beam at sizing or rebeaming and by that increases the probability of its breakage in sizing and weaving; and

3. Potential hazard to all the ends in the sheet due to rubbing of the beam yarn with the drum which stops abruptly at the time of machine stoppages.

Productivity

The productivity in warping is governed by the machine speed, the number of ends on the beam and the machine efficiency. The speed is mainly governed by the type of warping machine and to some extent depends upon the type of yarn and its count. The number of ends per beam depends on the creel capacity and the requirement for the set. The machine efficiency is influenced besides the machine speed, by the end breakage rate, time to mend a break, number of ends per beam, set length, length of yarn on the supply package, beam doffing time, creel change time etc.

In general terms, warping is transferring many yarns from a creel of single-end packages forming a parallel sheet of yarns wound onto a beam or a sectional beam. The warp beam that is installed on a weaving machine is called a weaver’s beam. A weaver’s beam can contain several thousand ends and there are several types of warping processes that can be used depending on the purpose.

Direct Warping

In direct warping, the yarns are withdrawn from the single-end yarn packages on the creel and directly wound on a beam. Direct warping is used in two ways:

a) Direct warping can be used to directly produce the weaver’s beam in a single operation. This is especially suitable for strong yarns that do not require sizing such as continuous filaments and when the number of warp ends on the warp beam is relatively small. This is also called direct beaming.

b) Direct warping is used to make smaller intermediate beams called warper’s beams. These smaller beams are combined later at the sizing stage to produce the weaver’s beam. This process is called beaming. Therefore, for if the weaver’s beam contains 10,000 warp ends, hen there would be – say – 10 warper’s beams of 1,000 ends each. If this weaver’s were to be made a one stage, the creel would have to have 10,000 yarn packages, which is impossible to manage.

Indirect Warping

In indirect warping, a section beam is produced first. The section beam is tapered at one end. Warp yarn is wound on the beam in sections starting with the tapered end of the beam. Each section has multiple ends and this kind of warping is generally useful for colored yarn warping.

Another type on indirect warping is ball warping. Ball warping is mainly used in manufacturing of denim fabrics. The warp yarns are wound on a ball beam in the form of a tow for indigo dyeing. After dyeing the tow is separated and wound on a beam.