Ring Spinning

-->

Ring Spinning 

The ring spinning could be defined, the process of manufacturing yarn with flying ring.

The ring spinner is made up of the following parts: 

Ring spinning 

1. Spools on which the roving is wound 

2. A series of drafting rollers through which the roving passes 

3. A guiding ring or eyelet 

4. A stationary ring around the spindle 

5. A traveler-a small, V-shaped clip on the ring 

6. A spindle 

7. A bobbin 

The roving is fed from the spool through the drafting rollers. The rollers elongate the roving, which passes through the eyelet, moving down and through the traveler. The traveler moves freely around the stationary ring. The spindle turns the bobbin at a constant speed. This turning of the bobbin and the movement of the traveler impart the twist to the yarn. The yarn is twisted and wound onto a bobbin in one operation. 

Bobbins must be removed from the machine when full. From here, bobbins are transported to a winding machine where yarn is wound onto packages. Automated systems for doffing and winding have been developed and are widely used. Winding is considered an important step. It provides an opportunity to condition yarn that is, to bring the yarn into equilibrium with the moisture in the atmosphere, and to add wax or other coatings that will facilitate weaving. Winding also allows the identification of flaws in the yarn and formation of larger yarn packages than the spindles on the ring spinning frame. 

1. The value and character of a yarn are determined by 

• Kind and quality of fibers 

• Amount of processing necessary to produce fineness. 

• Amount of twist, which increases tensile strength in the finished yarn. 

2. The purpose of the yarn must be anticipated, as this determines the number and kind & many manufacturing operations. 

3. The formation of yarn from staple fibers by shinning becomes possible when they have surfaces capable of cohesiveness. This quality is exemplified by the natural twist of the cotton fibers, which enables them to entwine around each other, the roughness of the linen fibers, which cause them to cling together, and the scale on the surface of the wool fibers, which cause them to graph each other. 

4. Flexibility permits the fibers to be twisted around one another. 

5. Uniformity & staple give yarn a required evenness & improve the quality. 

Yarn Twist due to ring spinning:

The amount of twist is an important factor in finished consumers’ goods. It determines the appearance as well as the durability and serviceability of a fabric. Fine yarns require more twist than coarse yarns. Warp yarns, which are used for the lengthwise threads in woven fabrics, are given more twist than are filling yarns, which are used for the crosswise threads. To retain the twist in the yarns and prevent any tendency to untwist or kink, the yarns are given a twist-setting finish with heat or moisture, depending upon the kind of fiber used. The direction of twist may be observed by holding the yarn in a vertical position. If the spirals conform to the direction of the slope of the central part of the letter S, the yarn has an S twist; if they conform to the slope of the letter Z, the yarn has a Z twist. 

Yarn Count maintain with ring spinning:

In the spinning process, there is always a fixed relation between the weight of the original quantity of fiber and the length of the yarn produced from that amount of raw material. 

This relation indicates the thickness of the yarn. It is determined by the extent of the drawing process and is designated by numbers, which are called the yarn count. 

The International Organization for Standardization (ISO) fixed relationship between the weight and length of all yarns: one tex equals 1 gram (g) per kilometer. The greater the weight, the thicker the yarn, and consequently the higher the tex number Because of the speed limitations in ring spinning, researchers concentrated on developing techniques for inserting twist into yarns that would permit more rapid production. A result of this search was the introduction, in the 1960s, of the open-end spinning machine, which operated at higher speeds but produced a yarn with slightly different characteristics than conventional ring-spun yarns with ring spinning.

-->

Rotor spinning; Open-End Spinning

-->

Self twist spinning or Open-End Spinning 

Open-end spinning omits the step of forming the roving. Instead, a sliver of textile fibers is fed into the spinning machine spinner by a stream of air. The sliver is delivered to a rotary beater that separates the fibers into a thin stream. It is carried into the rotor by a current of air through a duct and is deposited in a V-shaped groove along the outer edge of the rotor. Twist is provided by the turning of the rotor. 

Fibers fed to the rotor are incorporated into the rapidly rotating “open end” of a previously formed yarn that extends out of the delivery tube; hence, the name open- end spinning. As the fibers join the yarn, which is constantly being pulled out of the delivery rube, twist from the movement of the rotor is conveyed to the fibers. A constant stream of new fibers enters the rotor, is distributed in the groove, and is removed at the end of the formed yarn, becoming part of the yarn itself. 

The fineness of the yarn is determined by the rate at which it is drawn out of the rotor relative to the rate at which fibers are being fed into the rotor. In other words, if fewer fibers are being fed in while fibers are being withdrawn rapidly, a thinner yarn will result, and vice versa. The twist is determined by the ratio of the rotor turning speed to the linear or withdrawal speed of the yarn (that is, the higher the speed of the rotor, the greater the twist). 

Theoretically, a variety of different means may be used to form the yarn and insert twist. These have been divided into the following categories: mechanical spinning (of which rotor spinning is an example), electrostatic spinning, fluid spinning, air spinning, and friction spinning. Of these, only rotor and friction open-end spinning machines have been commercialized and most of the open-end spinning machines now in use are of the mechanical rotor spinning type Friction open-end spinning machines are also available. 

Friction spinning systems use friction to insert twist. A mixture of air and fibers is fed to the surface of a moving, perforated drum. Suction holds the fibers against the surface while a second drum rotates in the opposite direction. Twist is inserted and the yarn begins forming as the fibers pass between the two drums. The newly forming yarn is added to the open end of an already formed yarn, and the completed yarn is continuously drawn away. 

The advantages of open-end spinning are that it increases the speed of production, eliminates the step of drawing out the roving before spinning, and permits finished yarns to be wound on any sized bobbin or spool. As a result, it is less expensive. It produces yarns of more even diameter than does ring spinning. Yarns are more uniform in diameter, bulkier, rougher, more absorbent, and less variable in strength than are ring-spun yarns. 

Fabrics made from open-end spun yarns compared with ring spun yarns are more uniform and more opaque in appearance, lower in strength, less likely to pill, and inferior in crease recovery. A number of sources indicated that they are more subject to abrasion. 

Neither friction nor rotor spinning will produce yarns as fine and strong as ring- spun yarns, although recent advances have extended the range of yarn sizes possible. Open-end spun yarns have a handle that has been characterized as “harsh.” Some of the kinds of products that seem to be especially well suited to the use of open-end spun yarns are in filling yarns for fabrics where yarn strength is not a factor, toweling pile yarns, denim, and heavier weights of bed sheeting. The yarns even surface makes them desirable as base fabrics for plastic-coated materials. On the other hand, the more acceptable feel of ring-spun yarns has led knitwear manufacturers to prefer them, and they are better for fine blends of polyester and cotton.

-->

PRINTING METHDOS AND PROCESS MODIFICATIONS

PRINTING PROCESS MODIFICATIONS 

-->

Heat Transfer Roller Printing 

Like traditional roller printing, heat transfer printing is done by passing the fabric around a central drum or cylinder where it contacts a roller for transferring the design. The roller is followed by a heating zone to effect the sublimation of the dye. Since all colors are applied to the fabric at the same time, 

however, the operation is simpler with lower processing costs and fewer personnel required. Production can change rapidly from one design to another simply by changing the design paper, whereas in roller or screen printing, each separate roller or screen moved from the machine and the machine set up for a new design with different rollers or screens. Short runs are feasible, fast deliveries are possible, given shorter time for processing, and companies need not keep costly inventories of fabric in stock. On the other hand, heat transfer printing is slower than is either roller or screen printing. 10 to 15 meters of printed fabric are produced per minute in transfer printing operations. 

Heat transfer printing has proved especially successful in printing knitted fabrics. Knitted goods are less dimensionally stable than are woven fabrics. Manufacturers using conventional screen and roller printing techniques on knit fabrics experienced difficulties in making multicolor prints in which the segments of the print must fit together accurately. In transfer printing, all parts of the design are applied at once, eliminating the problem of fabrics stretching as they move from one roller to another. 

Losses of fabric through faulty printing are substantially lower during heat transfer printing than are losses in conventional roller printing. Energy requirements are also lower. Garments and garment pieces can be printed, and precise placement of decorative motifs on a completed garment is possible 

Transfer Printing 

Literally moving a design from one surface to another is known as transfer printing. A typical well-known technique is that of iron-on prints of emblems and decorations, which are generally made of pigments in a paraffin or thermoplastic base that can be melted and bound by heat and pressure onto a fabric surface. These pigment transfers are not very satisfactory because they make the cloth stiff and are not fast to laundering or light. A more sophisticated and effective method of transfer printing is that of transferring a design intact by vaporizing it from the paper to a fabric. There have evolved two principal processes: dry heat transfer and wet heat transfer 

Heat Transfer Printing 

Heat transfer printing, or sublimation printing, is a system in which dyes are printed onto a paper base and then transferred from the paper to a fabric. The transfer of colors takes place as the color vaporizes or “sublimes.” Transfer printing is achieved by rolling or pressing the paper and the fabric together under pressure and at high temperatures (424°F or 200°e). Sublimation printing achieves a sharpness and clarity that other types of printing cannot match. One disadvantage of heat transfer printing, however, is off-grain printing. Some dyes used on nylons and acrylics have displayed variations in shade depth and, in some cases, problems with fastness to laundering. Heat transfer printing also consumes a large quantity or print paper that cannot be reused and may present a disposal problem. Transfer printing can also be used to apply designs to garments such as T-shirts and jackets. Often the design is comprised of pigment colors on a paper sheet. When this is placed on the textile item and a hot press is applied the pigments adhere to the fabric in the design pattern. The design area is usually somewhat stiffer than the rest of the fabric. 

Initially, heat transfer dyes were disperse dyes mostly effective on nylons and polyesters. Disperse dyes can also be used on acrylics, triacetates, and polyester and cotton blends where the proportion of polyester is relatively high. In the early 1990s development of several alternative processes have extended heat transfer printing to silk, cotton and other cellulosic fabrics, and wool.

-->

Textile Printing methods; Methods Of Direct Printing

Block Printing Methods
The oldest method of printing designs on fabric is block printing by hand. It is not commercially important today because it is too slow––printed fabric cannot be produced inexpensively in large enough quantities by the hand block method. To make blocked prints, the design must first be carved on a wooden or metal block. The dyestuff is applied in paste form to the design on the face of the block. The block is pressed down firmly by hand on selected portions of the surface of the fabric, imprinting the carved design as many times as desired on a specific length of cloth. To obtain variation of color in the same design, as many additional blocks must be carved as there will be additional colors. The portions of the design that will appear in different colors must be separately imprinted by hand before each design is complete. The more colors used, the more valuable and expensive the blocked print will be, because of the enhanced beauty of design as well as the labor involved in the hand printing.

Roller Printing Methods
Roller printing is the machine method of printing designs on cloth by engraved rollers. It turns out color-designed fabrics in vast quantities at the rate of 1000 to 4000 yards (914-3658 m) an hour. This method of producing attractive designs is relatively inexpensive when compared with any hand method. It is a machine counterpart of block printing. In roller printing, engraved copper cylinders or rollers take the place of the hand carved blocks. Just as there must be a separate block for each color in block printing, so must there be as many engraved rollers in machine printing, as there are colors in the design to be imprinted. With each revolution of the roller, a repeat of the design is printed. Engraving is frequently done by pantograph transfer. Separate photographs on individually sensitized copper plates are taken for each color of the design. An artist then paints the appropriate color of the pattern on each plate. The engraver traces the outline of the design on the plate with one arm of a pantograph, plate which simultaneously cuts the design (with a diamond needle on its other arm) into the curved surface of a copper roller. Next, a chemical resistant is coated over the areas of the roller that will print the color, and the roller is treated with acid. The acid etches the unprotected areas, which form the design pattern to be used for color printing.

Each roller is polished for uniform smoothness so that the dye will spread evenly on the raised areas. They are then locked into precise positions on the machine for proper registration (alignment). The number of rollers used depends upon the number of color in the design, and as many as sixteen rollers can be employed.

Each of the engraved rollers first comes in contact with a companion roller that has been submerged in the dye paste to be used for its part of the design. A sharp blade, called the doctor blade, scrapes the excess dye from the surface of the roller. As the fabric passes between the engraved rollers and smooth cylinder rollers, the dye from the shallow areas is passed on it.

Behind and along with the fabric being printed is another fabric, called the back gray, which absorbs the excess print paste and multi color roller printing prevents it from striking through and staining the smooth rollers


The printed cloth is immediately passed into a drying chamber and then into a steam chamber where the moisture and heat sets the dye. The back gray is eventually washed out and reused.

Duplex Roller Printing
Duplex printing is done with rollers on a special machine that imprints designs on both sides of the fabric at the same time. Most often, the same design is printed on opposite sides, although different designs can be printed on each side. The resulting fabric looks like fabric with a woven design. This process is seldom used now, as it is almost as expensive to create duplex prints as it is to weave designs.

Rotary Printing Method
A printing machine that utilizes seamless cylindrical screens made of metal foil was originally developed in Holland. This process is called rotary screen-printing. The machine employs a rotary screen for each color, as in flat screen-printing, and the design for each rotary screen is made in a manner similar to automatic flat screen-printing. As the fabric to be printed is fed under uniform tension into the printer section of the machine, its back is usually coated with an adhesive, which causes it to adhere to a conveyor-printing blanket. Some machines use other means of gripping the cloth firmly in place. The fabric passes under the rotating screens through which the printing paste is automatically pumped from pressure tanks. A squeegee in each rotary screen forces the paste through the screen onto the fabric as it moves along, at rates of up to 100 yards (91 m) per minute.

Rotary screen-printing combines the advantages of roller and flat screen-printing techniques. Rotary metal screens are lightweight in contrast to the heavy copper rolls, and they cost less. They give color depth that is similar to or as good as that of flat screens. Prints of various types and intricate designs with shades of up to twenty colors can be obtained with a high degree of accuracy and sharpness.

Stencil Printing
Stencil printing originated in Japan. Its high cost limits its use and importance in the United States. In stencil printing, the design must first be cut in cardboard, wood, or metal. The stencil may have a fine, delicate design, or there may be large spaces through which a great amount of color can be applied. A stencil design is usually limited to the application of only one color and is generally used for narrow widths of fabric.

Screen Printing Method
Originally, this technique was referred to as silk-screen printing because the screens were made of fine, strong silk threads. Today, they are also made of nylon, polyester and metal. Screenprinting is done with the use of either flat or cylindrical screens.

Flat bed screen printing
Flat bed screen-printing is done commercially on long tables 9 to 60 yards in length. The roll of fabric to be printed is spread smoothly onto the table, whose surface has first bee coated with a light tack adhesive. The print operators then move the screen frames by hand successively along the whole table. Printing one frame at a time, until the entire fabric is printed. Each frame contains one color of the print. The rate of production ranges from 50 to 90 yards per hour by this method. A substantial amount of commercial hand screen-printing is also done on cut garment parts. In printing cut garments, an apparel manufacturer arranges by contract with screen printers Greige Carpet Needle Belt Magnet Color 2 specializing in this service. Customized or unique patterns are printed on garment parts before the pieces are sewn together.

Such items as printed beach towels and novelty printed aprons, draperies, and shower curtains are also printed by hand screen methods because it is possible to make large screen frames for large design repeats.

Hand screen-printing is also used for printing limited-quantity, high-fashion couture as well as for printing small-quantity runs to market-test a design. Flat-bed Zimmer carpet printing machine lays down each color separately form printing paste applied by means of two magnetic roller squeegees. Pressure is controlled by the selection of heavy or light squeegees and by varying the current going to the electromagnet. Endless belts fitted with needles assure a positive drive for good register.

Printing Methods; Methods of textile printing

-->

Methods of Printing 

There are three basic approaches to printing a color on a fabric. Direct, Discharge and Resist. Transfer Printing is comparatively a new method which is also gaining popularity Direct Printing. The most common approach for applying a color pattern is direct printing. It may be done on a white fabric or over a previously dyed fabric, in which case it is called overprinting. The dye is imprinted on the fabric in paste form, and any desired pattern may be produced. The dyes are usually dissolved in a limited amount of water to which a thickening agent has been added to give the necessary viscosity to the print paste. 

Direct Printing Method

The principle of direct printing is creation of a colored design by applying a dye or pigment directly onto a textile substrate (yarn or fabric). Discharge Printing. Another approach for applying a color pattern is discharge printing. The fabric is dyed in the piece and then printed with a chemical that will destroy the color in designed areas. Sometimes the base color is removed and another color printed in its place, but usually a white area is desirable to brighten the overall design. When properly done, discharge printing gives very good results; however, the discharged areas may literally fall out of the fabric if the goods are not thoroughly washed after printing (a rare situation today). The usual method of producing discharge prints is to print the design, such as polka dots, with a paste containing a reducing agent. A steaming follows and then there is a good washing to remove the by-products of the reaction. Resist Printing A third approach to obtaining a color pattern is resist printing. Bleached goods are printed with a resist paste––a resinous substance that cannot be penetrated when the fabric is subsequently immersed in a dye. The dye will affect only the parts that are not covered by the resist paste. After the fabric has passed through a subsequent dyeing process, the resist paste is removed, leaving a pattern on a dark ground. Their are several other methods also for printing textiles. Two are of significant commercial importance: the screen print method and the roller print method. A third method, heattransfer printing is a comparatively new concept & less significant. Other printing methods rarely used in commercial production of textiles are block, batik, ikat, and resist printing. Many textile printers print fabrics in both screen and roller methods. Most heat-transfer printing is done by printers that specialize in this method. 

Batik 

Batik cloth is made by a wax-resist process. The name batik originates in the Indonesian Archipelago, where resist printing has become an important art form. Wax is applied to the areas that the printer does not want to dye. In Indonesia a small, spouted cup with a handle called a tjanting is used to apply the wax. Melted wax is poured from the tjanting onto the cloth. When it hardens, the wax coats the fabric so that the dye cannot reach the fibers. 

If several colors are to be used, the process becomes somewhat more complex. For example, if a fabric is to be colored white, red, and blue, the artisan begins with a creamywhite cotton cloth. Those areas that are to remain white and those that are to be red are coated with wax. The fabric is now subjected to a blue dyebath, and the exposed areas take on the blue tint. The wax is boiled off and reapplied to cover the blue and white areas. When the fabric is placed in the red dyebath, the color penetrates only the uncovered areas of the design. After dyeing is complete, the fabric is treated with a fixative (a mordant) to make the colors fast, and a final rinse in hot water removes all traces of wax. For faster production a technique was devised whereby the wax could be printed onto the surface of the fabric with a device called a tjap. The design is carved on a tjap block, the block is 

-->

PRINTING

-->

Textile Printing

Printing has often been described as dyeing in a localized area to create patterned design. Creating design interest in fabrics can be accomplished in several ways, including yarn variation (novelty yarns). Weave variation (dobby and jacquard), and color effects in weaving. An additional color design can be created through the process of printing design shapes onto previously woven, knitted, or non-woven fabrics. 

Textile printing uses the same dyes or pigments applied to produce dyed fabric. The same principles of specific dye classes having select fiber affinities and the general fastness characteristics apply equally to printing and dyeing. 

The designs for printed fabrics are an important element of the printed fabrics industry. A continuous supply of new designs are required for this highly fashion oriented segment of the textile industry. 

Dyes or pigments used in dyeing are usually in a water bath solution. When the same dyes or pigments are used for printing, they must be thickened with gums or starches to prevent the wicking or flowing of the print design. The thickened solution, about the consistency of heavy buttermilk, is called the print paste. Some dyes cannot be used in printing pastes for reasons such as insufficient solubility and low color yield. 

The application of a pattern to fabric by the use of dyes, pigments, or other colored substances may be effected by a variety of hand or machine processes. Freehand painting of designs on fabrics is probably the oldest technique for applying ornament, but hand painting is a time-consuming procedure. Furthermore, it does not always result in a uniform repeat of a motif that is to be used more than once. If a design is transferred to a Bat surface that can be coated with a dye and then stamped onto the fabric, the same design can be repeated many times over simply by pressing the decorated surface against the fabric. This process is known as printing. Over many centuries a variety of techniques for printing designs have evolved. Printing can be applied to warp yarns, to fabrics, or to apparel pieces-for example, slogans or pictures on T-shirts. 

In general, printing is a cheaper way of creating designs on fabric than weaving or knitting with different colored yarns. Printing can be done with dyes or pigments. For pigments it is necessary to use an adhesive to bind the colored substance to the fabric. Different methods for applying designs can be combined with a number of printing tools or machines to provide the printer with a variety of processes. 

Methods of Printing 

There are three basic approaches to printing a color on a fabric. Direct, Discharge and Resist. 

Direct Printing 

The principle of direct printing is creation of a colored design by applying a dye or pigment directly onto a textile substrate (yarn or fabric). Discharge Printing. Another approach for applying a color pattern is discharge printing. The fabric is dyed in the piece and then printed with a chemical that will destroy the color in designed areas. 

Batik 

Batik cloth is made by a wax-resist process. The name batik originates in the Indonesian Archipelago, where resist printing has become an important art form. Wax is applied to the areas that the printer does not want to dye. 

Methods Of Direct Printing 

Block Printing

The oldest method of printing designs on fabric is block printing by hand. It is not commercially important today because it is too slow 

Roller Printing 

Roller printing is the machine method of printing designs on cloth by engraved rollers. It turns out color-designed fabrics in vast quantities at the rate of 1000 to 4000 yards (914-3658 m) an hour. This method of producing attractive designs is relatively inexpensive when compared with any hand method. 

Rotary Printing 

A printing machine that utilizes seamless cylindrical screens made of metal foil was originally developed in Holland. This process is called rotary screen-printing. 

Screen Printing

Originally, this technique was referred to as silk-screen printing because the screens were made of fine, strong silk threads. Today, they are also made of nylon, polyester and metal. Screen printing is done with the use of either flat or cylindrical screens. 

Heat Transfer Roller Printing 

Like traditional roller printing, heat transfer printing is done by passing the fabric around a central drum or cylinder where it contacts a roller for transferring the design. The roller is followed by a heating zone to effect the sublimation of the dye. Since all colors are applied to the fabric at the same time, 

Other Printing Techniques 

Photographic Printing 

Photographic printing is done in a manner similar to the photochemical preparation of screens for screen printing. A photosensitive dye is coated on the fabric, a negative is placed over the fabric, light is applied, and a photographic type of printing takes place. 

Electrostatic Printing 

Electrostatic printing is an experimental process in which a plate with an electrostatic charge is placed behind the fabric. A stencil in the form of the pattern is placed over the fabric. Special powdered inks that can be attracted by the electrostatic charge are passed over the surface fabric, and the inks are attracted into and color the fabric in the open areas of the stencil. 

Flock Printing 

By imprinting an adhesive material on the surface of a fabric in the desired pattern, and then sprinkling short fibers over the hesive, a flocked print may be created.

-->

TEXTILE ECONOMICS; Product Costing Methods, Job Order Costing System and Process Costing

Product Costing Methods 

The Basic methods of product costing are: 

Job Costing: allocates costs to products that are readily identified by individual units or batches, each of which is independently identifiable. When using the job cost system, costs are accumulated for each individual unit produced, or each separate order of products. This method is especially useful when producing something that is unique or custom-made. Job order costing would be used bya caterer, a garage, a helicopter manufacturer, a construction company and a textbook publisher, 

Contract Costing: a subset of job costing which is applied to relatively large cost units which take a long time to complete, typically over a year (e.g. civil engineering projects, ship building, building and construction etc). A separate account is maintained for each contract. Contract accounts involve: 

• determination of cost of sales 

• annual comparison of value of work certified as a proportion of the contract value and the costs to date as a proportion of total costs as a means of assessing the profit that should be recognised 

• record of payments received on account 

• records future expenses and accrued expenses 

Guidelines for Determining Profit to Date on Contracts No Profit is taken if contract is at an early stage. Reliability (prudence) concept is applied and losses are recorded as incurred or anticipatedIf the contract is near completion a proportion of the profit should be recognised having regard to work certified and costs to date 

Process costing: is applied when goods or services are produced from a series of repetitive or continuous processes or operations and the costs of processing are charged to the process as a whole before being averaged out over the units produced during the period. Process costing is used in a variety of businesses including distilling, water distribution, textiles, paint mixing and glass manufacture. 

Job Order Costing System 

The basic records maintained in a job-costing system include: Job-cost sheet (also called job-cost record or simply job order): records all costs for a particular product, service or batch of products are recorded on the job-cost sheet from: 

Materials requisitions: detail materials and components drawn from stores for particular jobs are priced and summarised, and entered as direct material costs on the job-cost record. Labour time records: show the time a particular direct worker spends on each job and are summarised to give direct labour cost on ‘the job-cost sheet. The manufacturing overhead will often be based on these labour hours or otherwise separately calculated and entered on the job cost sheet separately 

Actual rate vs. predetermined rate (normal) costing system 

Job-costing systems uses actual costs of direct labour and materials to determine the cost of individual jobs. However, a problem arrives with overhead costs, which are dependent on what is happening to the other jobs that are in process at the same time and can only be known after the event. Actual rate costing is a method of job costing that traces indirect costs to a cost object by using the actual indirectcost rate(s) times the actual unit of absorption base (direct labour, machine hours etc.), Predetermined rate (normal) costing systems use estimated amounts (at a normal level of activity) for the manufacturing overhead costs that are applied to each job and estimated amounts for the absorption base to calculate a predetermined overhead rate. This rate is based on the total estimated overhead costs for the period and the estimated usage of the absorption base (e.g. machine/labour hours). 

General Approach to Job Order Costing 

The following seven-steps approach is used to assign actual costs to individual jobs 

l Identify the chosen cost object(s) 

2.Identify the direct costs of the job 

3.Select the cost-absorption base(s} 

4.Identify the indirect costs associated with each cost-absorption base 

5.Compute the rate per unit of each cost absorption base to allocate indirect costs to jobs 6.Compute the indirect costs allocated to the job 

7.Compute the cost of the job by adding all direct costs assigned to it 

Process Costing 

Process costing (a.k.a. continuous operation costing) is a method that is applied when goods or services are produced from a series of repetitive or continuous processes or operations and the costs of processing are charged to the process as a whole before being averaged out over the units produced during the period. ‘A process costing system involves the costs of producing similar items being accumulated and allocated to the products by averaging costs over large number of nearly identical products. The average cost per unit is calculated by dividing the total production cost by the number of units produced. Process costing would be used by businesses such as food processors, household product manufacturers, chemical processors and oil refiners.. 

General approach to process costing 

I. collect cost data for the period on production cost report; 

2. prepare statement of physical flows and equivalent units of output for the period; 3. ascertain the total costs to be accounted for this period; 

4. calculate the cost per equivalent unit; 

5. apportion cost between finished output and work-inprogress; and 

6. check that all costs accounted for 

Similarities between process costing and absorption costing 

Both track the same manufacturing cost elements: DMs, DL, 

DEs and Mfg OhdsBoth involve WIP, FG and COGS 

Differences between process costing and job costing 

• No. of WIP accounts: PCS have many WIP accounts whereas 

JCS have one WIP account 

• Documentation to track costs 

JCS = job cost sheet 

• PCS = production cost report for each process 

• Point at which costs are totaled 

JCS - mfg costs totalled on completion 

• PCS - mfg costs totalled at fixed time intervals 

• Unit cost computation 

JCS - total job costs/no of units produced 

• PCS - total period costs/units produced in the period 

WIP and EQU/V ALENT UNITS 

Processes rarely deal with solely with completed units and therefore we need ‘to deal with output in terms of completed units and those still in the process at various stages of completion in the process. The notion of Equivalent Units enables work in process to be expressed in terms of completed output. 

Equivalent units may be defined as: A notional quantity of completed units substituted for an actual quantity of incomplete physical units, when the aggregate work content of the incomplete units is deemed to be equivalent to that of the substituted quantity of

TEXTILE ECONOMICS; Cost Terminology, Classification and Basic concepts

Cost and Cost Terminology: 

Cost is a resource sacrificed or forgone to achieve a specific objective. It is usually measured as the monetary amount that must be paid to acquire goods and services. A cost must not be confused with an expense, that is that part of costs of the goods or services that has been used up in the process of generating revenues. Actual Cost is the cost incurred (a historical cost) as distinguished nom budgeted costs. 

Cost Object is any activity, product, service or other item for which we can make a separate cost measurement. Examples would include a product, sales area, TV advertising campaign, employee, delivery van etc. 

Costs Classification 

Costs may be analysed into: Manufacturing costs (factory/ production) - Direct: labour, materials and variable overhead Indirect: manufacturing support Non-manufacturing costs - Selling and Marketing, Distribution, Research and Development Finance, General & Administrative 

Handout: Cost classification 

There are two basic stages of accounting for costs: 

1) Cost Accumulation: the collection of cost data in some organised way based on some natural classification such as materials or labour, using an accounting system. 

2) Cost Assignment: involves 

(a) tracing accumulated costs to one or more cost objects; and 

(b) allocating/apportioning accumulated costs to one or more cost objects such as activities, departments, products, customers etc. 

Handout: Basic cost concepts: 

Cost Assignment Methods

Traceability is the ability to assign a cost directly to a cost object in an economically feasible way using a causal relationship. Tracing is the assignment of costs to cost objects using either an observable measure of the cost object s resource consumption or factors that allegedly capture the causal relationship. “ Drivers are factors that cause changes in resource usage, activity usage, costs and revenues. Resource drivers measure the demands placed on resources by activities and are used to assign the cost of resources to activities by allocation and apportionment. 

For example, factory rates apportioned by floor space or supervisor time allocated to different production departments. 

Resource drivers also allocate/apportion service activities to production activities. Activity drivers measure the demands placed on activities by cost objects and are used to assign the cost of activities to cost objects. For example, the number of inspection hours used to assign the cost of inspection to individual products, or machine hours as a basis for absorbing departmental indirect costs. 

Direct tracing is the process of assigning costs to cost objects based on physically observable causal relationships (direct materials and labour). 

Driver tracing is assigning costs using drivers, which are causal factors. Often this means that costs are first traced to activities using resource drivers and then to cost objects using activity drivers. The driver approach relies on identification of factors that allegedly capture the causal relationship. 

Handout: Functional cost classification 

All costs can broadly be classified into manufacturing and non-manufacturing costs. Manufacturing costs include all costs of converting raw materials into completed products and non-manufacturing costs are all costs other than manufacturing costs. Manufacturing costs can further be divided into direct costs and indirect costs. 

• direct costs of a cost object are those that are related to a given cost object (product, department. etc.) and that calibe traced to it in an economically feasible way. Direct costs can be divided into direct materials and direct labour (and possibly direct expenses). 

• indirect costs are related to the particular cost object but cannot be traced to it in an economicallyfeasible way instead the costs are allocated to cost objects. 

Identifying product costs for a manufacturing firm 

There are typically two major cost elements: 

• Direct costs 

• Indirect overhead Cost 

The direct costs include direct materials, labour and expenses. 

The overhead costs include indirect material, labour and expenses split between: 

• Establishment costs (expenses incurred in providing the product or service environment [factory overheads] 

• Selling and Distribution costs (all costs of marketing and distributing the product); Administration costs (all costs of directors, managers and administrators and their associated expenses in terms of office overheads) 

• Finance costs (all costs of borrowed capital including interest and expenses incurred in raising funds) For product costs we are concerned with direct costs and establishment costs. 

Direct vs. indirect materials 

The cost of those materials and components that can be directly and conveniently traced to a unit of product are called direct materials (e.g. steel, windscreen-wipers or gearbox In a car). _Materials not directly traceable, and those extremely small in monetary value, are typically called indirect materials (e.g. dishwasher detergent in a fast-food restaurant, oil for production equipment, rags for cleaning or screws in a furniture factory) 

Direct VS. indirect labour 

The costs of production labour that can be directly and conveniently traced to a unit of product are called direct labour (e.g. workers on an assembly line, or chef in a restaurant) is direct labour, while labour costs that are not directly traceable, or those extremely small in monetary value, are typically called indirect labour (e.g. storekeepers, foremen, or secretaries) 

Production/factory/manufacturing overheads 

All costs related to the manufacturing operations, except for direct materials and direct labour, are called production/factory/ manufacturing overhead. Examples of such costs include, factory rent, factory rates, factory heating and lighting, depreciation of plant and equipment, insurance of the factory, and store costs.

Water Pollution Reduction in the Textile Industry

-->

Why was the project undertaken? 

During the 1970’s Hammarsdale was being developed as an industrial Hub to provide employment in KwaZulu. The textile industry in particular was being attracted to the area. The Department of Water Affairs and Forestry constructed the Hammarsdale Waste Water Treatment Works (HWWTW) to service the new industrial hub. There was poor environmental planning for the expanding Hammarsdale Hub. Because of this the quality of water in the Sterkpruit River was declining and the organic capacity of the HWWTW was at its limit. The effluent discharged by companies to the HWWTW was in certain circumstances highly corrosive and in one instance led to sewerage pipes being damaged and requiring replacement. Inlet screens designed to remove excessive materials were producing 25 cubic meters of waste per week that had to be disposed of at a low hazard waste disposal site. 

The high strength organic coloured effluents from the textile industries together with that arising from a chicken abattoir overloaded the works thus resulting in the colouration of the Sterkspruit River. This pollution was exacerbated since the treatment works was not designed to remove salts from the textile industries, which passed directly through the works into the River. Unfortunately the salt issue remains a problem but two companies, Gelvenor and Dano Textiles are investigating recycling their effluent and implementing cleaner production technologies to reduce the load. 

In 1982 Umgeni Water took over the HWWTW who assisted the University of Natal to deal with the issue of capacity by involving the Hammarsdale Industrial Conservancy in a campaign to persuade industry to reduce industrial waste loads. These efforts to minimise waste and encourage cleaner production resulted in energy, water and effluent treatment savings, but still there was little improvement in the quality of effluent delivered to HWWTW. At this stage Umgeni Water was applying an effluent tariff at a flat rate, which did not account for effluent strength. As a result there was no legal or financial incentive to reduce effluent loads. 

What Processes were undertaken? 

The incorporation of Hammarsdale and the nearby township of Mpumalanga into eThekwini Municipality and the Water Services Act of 1997 were significant factors leading to the reduction of effluent load. The Water Services Act stipulated that Municipalities were to become Water Services Authorities. Etekwini Municipality chose to own and operate Hammarsdale WWTW and having by-laws to support the collection of sewerage rates and to levy an additional charge for high strength effluent. 

The by-laws required that companies discharging to the Hammarsdale WWTW were permitted. A cooperative agreement between the Norwegian Pollution Control Authority and eThekwini Municipality led to the development of a five year integrated pollution control permit. The permit set targets for effluent colour. The permit also placed stress on waste minimisation / source control techniques which would reduce the salinity and therefore the electrical conductivity (a unit used for the measurement of the salt content of water) of discharged effluent. 

This approach to tariffs and pollution control permits was the innovative spark which led to the accelerated development of waste minimisation / source control techniques which could ensure that the effluent from the textile industry was at an acceptable standard. 

The development of the waste minimisation / source control technology, which was installed at Gelvenor, was funded by the European Union and the Water Research Commission. Gelvenor was identified since it was an ISO 14001 compliant company and, together with the potential trade effluent incentives was the most likely to succeed. This was an important decision, as the area needed a successful example to market the idea of cleaner production and better environmental controls. 

Project Description This project has two main components. The first is the five-year integrated pollution control permit, which sets targets for effluent colour, electrical conductivity and places stress on waste minimisation / source control techniques. 

The second component was the development of the waste minimisation / source control technology, which could benefit companies through reduced tariffs. In Gelvenor’s case this led to a reduction of chemicals, water and electricity in the production processes, and the discolouration of water was addressed through coagulation and settlement of the dyestuff in its effluent. 

What Positives have resulted from this project? 

Positives Hammarsdale Industrial township is now on the road to becoming more economically and environmentally sustainable. This has happened for various reasons. 

Firstly, the cost of utilities has been reduced to companies. Once cleaner production technology has been installed in the textile industry this can lead to reduced water use because consumption can be reduced if the treated effluent is recycled. For example, recycled water can be used in cooling towers and in air conditioning plants and this could lead to a savings of 40% on water. Further uses for the recycled water will be for dying, in toilets and for cooking. 

Because the quality of the effluent has improved, Gelvenor is being charged at a lower tariff, which can lead to a savings of R100, 000 per month. Using the same incentive scheme Rainbow Chickens also reduced its wasted load by 50%. This means that there is 25% less waste to treat at the works and therefore eThekwini, does not have to extend HWWTW with massive savings. The use of the cleaner production technology has released capacity at HWWTW, which can now be used to extend sanitation to approximately 8500 households in nearby Mpumalanga. 

The financial and environmental sustainability of certain companies has improved due to reduced water bills and effluent disposal costs yet improving environmental controls. These savings would more than finance the cleaner production technology at a rate of R4.5 million per annum. Gelvenor’s profit margin would increase after paying off the equipment cost over five years but Rainbow would recoup its costs in less than two. 

Because water effluent is cleaner the ecosystems of the Sterkspruit River and the Shongweni Dam will automatically improve. This will also improve the sustainability of farming in the immediate area and nature reserve surrounding Shongweni Dam will also have cleaner water input. 

Negatives: 

The only negative is that it is difficult to address the salt issue since technology for salt removal from water is extremely expensive. Two companies however are investigating the salt removal and re-use of the water. 

What were the most important lessons learnt in this project? 

Co-operative governance really works. Because of the shortage of skills national and local government teamed up with international experts, local academics and parastatal organizations in order to address a common goal. No action by an individual organization would have succeeded on its own. Stakeholder collaboration need not be on a formal basis provided that the goal is clear, but does require a champion. 

Stakeholder collaboration can extend the use of the technology. 

-The University of KwaZulu-Natal is researching with Water Research Commission funding the re-use of saline effluents from textile mills. 

-Dano Textiles is investigating cutting-edge technology using nitrogen blankets in its dye-baths to reduce the quantity of sodium hydrosulphite and thus the salt content of its effluent. 

-Dye-bath effluent treatment trials have been launched using excess anaerobic sludge digestion capacity at Mpumulanga wastewater works. 

The cost of technology can be prohibitive. De-salination technology, despite major strides still remains a prohibitively expensive means of treating textile mill effluent. Farming still remains a problem because of salinity issues but the aesthetics and the organic contamination from Hammarsdale would improve.

-->

Warp Knitting, Production of warp knitted fabric

-->

Knitted fabrics are divided into two general types: (1) those produced by weft knitting, where one continuous yarn forms courses across the fabric; (2) those produced by warp knitting, where a series of yarns forms wale’s in the lengthwise direction of the fabric. 

Warp Knitting 

This form of knitting is very different from standard hand knitting; the earliest warp knitting machine was Crane’s tricot machine (England), built about 1775. In warp knitting, a yarn is fed to each needle from the lengthwise direction. A bar guiding the yarns to the needles can move from side to side, or to the front or back of the needle, so that the loops can be interlocked in a zigzag pattern. Very wide (over 400 cm, nearly 170 in.), flat fabric can be produced by warp knitting, at speeds in the order of 1,000 courses per minute, giving almost 3 m2/min (3.6 sq. yds./min). The two main machine (fabric) types are tricot and raschel. 

Diagram of simple warp knit fabric. 

Tricot warp knitted fabric: Tricot is a machine with one needle bar (spring beard type) and one to three guide bars, +0 3++most are two-bar or three-bar. The spring beard needle, accepting mainly filament yarns, has limited the depth of texture that can be achieved in tricot fabrics; some fine spun tricot, produced on machines with hybrid needles, was introduced many years ago, but does not seem to have taken hold in the market place. Tricot does not ravel, can curl somewhat, and has almost no stretch or “give” lengthwise but a little crosswise. 

Raschel warp knitted fabric: Raschel is the other main warp-knitting machine. Fabric from these machines may be of any weight or thickness from lace to carpet; the one feature they share is a pillar-and-inlay effect; Wales like hand crochet chains forming the “pillar” with other yarns laid in to form patterns or the main body of the fabric, usually making up the right side. Raschel machines have one or two needle bars (usually latch, but may be spring beard), set horizontally on wide or narrow machines with 1 to over 30 guide bars. The multi guide bar types are used mostly for laces; most of our moderate-priced laces are knit on this type of machine. They do not have the depth of texture that the twisted Leavers laces or the embroidered Schiffli laces have. Powernet, knit on the raschel machine, incorporates elastomeric yarn to give one- or two-way power stretch for contour fashion Variations on raschel-type machines include crochet, ketten raschel, and Cidega machines. The latter, similar to raschel, can knit various fabrics side by side, and so is used for many narrow trims called “braids,” such as gimp and ball fringe. 

Minor Warp Knits: Simplex is a machine with two horizontal needle bars and two guide bars, producing a double tricot type of warp knit in a fine gauge, with two threads to each loop. The needles in one bar are directly behind those in the other, in much the same way that needles in the weft knit interlock are aligned; like interlock, simplex looks like plain-stitch jersey on both sides. The fabric is very firm and stable, used for its greater firmness in lounge wear, uniforms, and gloves.

-->

Weft Knitting, Produce weft knitted fabric

-->

Weft Knitting 

There are three fundamental stitches in weft knitting: (1) plain knit stitch, (2) purl stitch, (3) rib stitch. Novelty stitches are variations of these three stitches. The hand method of knitting is weft knitting. On a knitting machine, the individual yarn is fed to one or more needles at a time 

1. Plain-knit Stitch: The plain knit is the basic form of knitting. It can be produced in flat-knit or in tubular (or circular) form. The flat knit is also called jersey stitch because the construction is like that of the turtleneck sweaters originally worn by English sailors from the Isle of Jersey; it is sometimes called balbriggan stitch after the hosiery and underwear fabrics made in Balbriggan, Ireland. Plain flat knits may be shaped or full-fashioned. The knitting is done with a row of latch or beard needles arranged in a linear position on a needle plate or in a circular position on a cylinder. All the needles are evenly spaced side by side and are moved by cams, which act on the needle butts. The spacing of the needles is referred to as the gauge, gage, or cut. As applied to many flat knits and some circular ones, gauge refers to the number of needles in 11/2 inches; for example, a 60-gauge machine would have 40 needles per inch. 

2. Purl Stitch: This construction is also referred to as the link-sand links stitch after the German word “links,” or on the left). It is made on flat-bed and circular machines by needles using hooks on both ends to alternately draw loops to the front of the fabric in one course and to the back in the next course. It is a slower and more costly technique. The fabric looks the same on both sides and resembles the back of the plain knit. Like the plain knit, the purl knit will run up and down if a loop is broken. But a purl knit fabric will not curl at the edges. 

3. Rib Stitch: Rib-knit fabrics have alternating lengthwise rows of plain and purl stitches constructed so that the face and back of the fabric appear alike. This may be produced either on a flat rib machine or a circular rib machine. In the flat rib machine, one set of needles is placed opposite the other set of needles is placed opposite the other set of needles in an inverted V position of 45 degrees to the horizontal; in the circular rib machine, one set of needles is placed vertically in a cylinder and the other set of needles is placed horizontally on a dial. In both machines, one set of needles pulls the loops to the front and the other set pulls the loops to the back of the fabric. Each set of needles alternately draws loops in its own direction, depending upon the width of the rib desired. 

For example, rib stitches can be 1 x 1, 2 x 2, 2 x 1, 3 x 1, and so on. A combination of 1 x 1 and 2 x 2 is called an accordion rib. Rib construction is costlier because of the greater amount of yarn needed and the slower rate of production Rib knits are made on a two-bed machine with one set of needles forming the loops for one wale and the other set of needles forming the alternating wale.Rib knits have greater elasticity in the width than in the length. They are stable and do not curl or stretch out of shape as do the jersey knits. For this reason, they are often used to make cuffs and necklines on weft knitted garments. Rib knits are reversible unless the number of stitches in the alternating wales is uneven, as in a 2 X 3 rib.

-->

Knit Fabric; Different types and classification of knitted fabric

-->

Single Jersey Knits Fabric  

Knitting Machines with one needle bed and one set of needles are called jersey machines or single-knit machines. With one set of needles used for knitting and one needle bed, all needles face the same direction; all stitches are pulled to the same side of the knitted fabric. As a result, single jersey fabrics have a smooth face with a vertical grain on the right side of the fabric and a width wise grain on the back side. The knittig loops formed by the jersey machine are formed in one direction only, which gives a different appearance to each side of the fabric. The basic knit fabric produced by this knitting machine is known alternately as a plain, single knit, or jersey. The terms are interchangeable.Jersey stretches slightly more in the crosswise than the lengthwise direction. If one stitch breaks, the fabric may ladder, or run. Jersey fabrics tend to curl at the edges and are less stable than are some other types of knits. This is the result of the pressures exerted during knitting. In addition jersey knits may twist or skew after laundering, as the twisting tensions imposed during the knitting process are relaxed. 

Special finishing techniques are used to overcome these tendencies and maintain fabric stability; the principal ones use starches, gum mixtures, polyvinyl acetate emulsions, and resins. 

A great many items of hosiery, sweaters, and other wearing apparel are made from plain jersey knits. Consumer Brief 16.1 highlights one of the common uses of jersey knit fabrics: Tshirts. Plain knit fabrics can also be made into designs of two or more colors by use of a patterning mechanism that controls the selection and feeding of yarns and types of stitches to create jacquard knits. 

Double Jersey Knit Fabrics 

The term double knit is generally applied by consumers to fabrics that are, technically, double jersey fabrics. Double jersey fabrics are also made on two-bed knitting machines, but the arrangement of the needles is different from that for knitting rib fabrics. The layers of loops alternate from one side to the other, locking the two layers together. Double knit fabrics have the same appearance on both sides of the fabric, that is, exhibiting the appearance of the face or outer side of a single knit on both sides. Twice as much yarn is incorporated into double knit fabrics as into comparable single knits 

Interlock Knit fabric

Interlock knits are produced on a special machine that has alternating long and short needles on both beds. Long and short needles are placed opposite each other. Long needles knit the first feeder yarn; short needles knit the second feeder yarn. The fabric created is an interlocking of two 1 X 1 rib structures. The resulting fabric, like double knit fabrics, is thicker than single knit fabric, and more stable in the width wise direction. Interlock fabrics have been traditionally used for underwear. They are produced more slowly than are other rib knits and are generally made in plain colors or simple patterns because the addition of pattern slows down the manufacture even further 

High Pile Fabrics 

High-pile fabrics, such as imitation furs and plushes, are usually knitted by a jersey machine. While the knitting is taking place, a sliver of staple fiber is fed into the machine. These fibers are caught in the tight knit and are held firmly in place. Although any staple fiber can be used for the pile, the greatest quantity of these fabrics are made with acrylic and modacrylic fibers in the pile. By using staple fibers of varying lengths, adding color through fiber dyeing or printing on the surface of the pile, and by shearing or brushing the pile, an enormous variety of effects can be achieved. The use of knitted pile fabric ranges from excellent imitations of furs, such as leopard, tiger, mink, or mouton, to colorful pile outerwear, coat linings, or pile carpet fabrics.

-->

Gauge and Quality; Knitting machine element to produce knit fabric

-->

Gauge and Quality 

The size of the needle and the spacing of the needles on knitting machines determine the number and size of the knit stitches and their closeness those are known as knitting element. Each wale is formed on one needle. The number of needles is equal to the number of Wales. The closeness of the stitches determines whether a knit fabric will be lightweight and open or heavier and more dense. The term gauge is used to describe the closeness of knit stitches. Gauge is the number of needles in a measured space on the knitting machine. Higher-gauge fabrics (those with more stitches) are made with finer needles; lower gauge fabrics are made with coarser or larger needles. 

The term cut is also used to designate the number of needles per inch in the needle bed of a circular weft knitting machine. To describe the stitch density of a single or double knit fabric, the fabric may be designated as an 18-, 20-, 22-, or 24cut fabric. The higher the cut, the closer the stitches; the lower the cut, the coarser the fabric. 

Varying types of knitting machines measure gauge over different distances on the machine. For example, circular knit hosiery measures the number of needles in 1.0 inch, fullfashioned knitting in 1.5 inches, and Raschel knits in 2.0 inches. 

Because of these differences, it is best to keep in mind the generalized principle that the higher the gauge, the closer the stitches. 

The quality of needles used in manufacturing knit goods is related directly to the quality of the fabric produced. Needles of uneven size and quality will produce knit fabrics with unevensized stitches and imperfect surface appearance. 

In warp knits, those knits in which the yarns interlace in the long direction, one or more yarns are allotted to each needle on the machine, and those yarns follow the long direction of the fabric. For weft knits, those in which the yarns interlace crosswise or horizontally, one or more yarns are used for each course, and these yarns move across the fabric. In weft knits, one yarn may have from twenty to several hundred needles associated with it. To summarize, weft knits can be made with one yarn, but warp knits must have a whole set of warp yarns, that is, one or more for each needle. 

Once the basic distinction between warp and weft knits has been made, further subdivisions of knit classifications are usually based on the types of machines used in their production. The majority of knit fabrics are named after the machines on which they are constructed. For this reason, the discussion of knitted fabrics that follows is organized around the types of machines used in manufacturing knit fabrics and the types of knit fabrics made on these machines. 

1. Flat or circular jersey, or single knit, machine: one needle bed and one set of needles. 

2. Flat or circular rib machine: two needle beds and two sets of needles. 

3. Flat or circular purl, or links-links, machine: two needle beds and one set of needles.

-->

Loop Formation in knit fabric structure

Loop Formation 

The spring beard needle is formed from one piece of thin wire. One end of the needle is drawn into thinner dimensions and is curved to form a hook. The flexible outer side of the hook can be pressed against the stem of the needle to close the hook for sliding a formed loop off and beginning a new loop. In 1847 Matthew Townshend invented a different type of hook known as the latch needle, which has come to be the most widely used type of needle. Its operation s similar to that of the spring beard needle, except that instead of having to mechanically press the flexible wire of the needle closed so that the forming yarn loop will not slide off, a latch closes to hold the yarn in place. 

1. The old loop is held on the stem of the needle. The latch is open (a). 

2. The hook grasps the yarn to begin forming a new loop (b). 

3. The needle falls, the old loop rises, closing the latch of the needle (c). 

4. The old loop is cast off (d and e). 

5. The needle tises, and the new loop slides down to the stem of the needle, pushing the latch open again, and the needle is ready to repeat the cycle (f).

Loop formation in knit fabric

Yet a third type of needle, the compound needle, is used almost exclusively for warp knitting. The compound needle has two components, a tongue and a hook Its motion is as follows: 

1. The old loop encircles the hook; the tongue is in such a position as to leave the hook open. 

2. Both tongue and hook rise; a new yarn is fed to the hook. 

3. Both tongue and hook descend, but the tongue descends more slowly, thereby closing the hook. 

4. As the needle descends, the held loop slides off, forming a new loop. 

5. The needle returns to its initial position, the hook ascending more rapidly, thereby opening the hook again. 

For weft knitting with either needle type, a cam system provides the action for lifting the needles as the yarn is fed in. A small projection called a butt is located at the bottom of the needle. The butt is held in a groove formed by a system of cams or shaped pieces. The movement of the butt in the grooves between the cams causes the needle to rise and fall. 

The engaging by the needle of a new piece of yarn is called feeding. Devices called feeders are located to introduce the yarn to the needles. The number of feeders can vary, but obviously the more feeders a machine has, the higher will be the speed of fabric forming on the machine, since each needle produces a loop each time it is activated and if many needles are activated more frequently, many courses can be formed at the same time. 

Another important element of some knitting machines is the sinker. The already formed fabric may need to be controlled as the subsequent knitting action takes place. A thin steel device called the sinker may be used to hold the fabric as the needle rises, support the fabric as the needle descends, and push the fabric away from the needle after the new loop has been formed. Sinkers are generally mounted between the needles. Some machines, however, do not use sinkers but instead use the tensions placed on the completed fabrics for control.

Construction of Knit Fabric

-->

The construction of knitted fabrics is evaluated by the number of stitches or loops. When the interlocking loops run lengthwise, each row is called a wale. A wale corresponds to the direction of the warp in woven fabrics. When the loops run across the fabric, each row is called a course. A course corresponds to the filling, or weft. Thus, a knitted fabric having 40 loops or stitches in 1 inch of width, and 50 loops in 1 inch of length, is said to have 40 Wales and 50 courses.

Construction of Knit Fabric

The major difference between knitted and woven structures lies in the way the yarns are interconnected geometrically. In weaving, two sets of parallel yarns are interconnected by interlacing them at right angles. Different woven structures are produced by varying this basic principle In knitting, the yarns are initially formed into loops, and then these loops are interconnected in order to produce a textile structure. The term interlooping is used to describe this technique of forming fabrics. Based on this principle, a textile fabric is produced by using only one set of yarns. Thereby, a horizontal set of yarns (weft) could be interlooped to produce a weft knitted fabric, and a vertical set of yarns (warp) could be used to produce a warp knitted fabric. As a result of this interlooping of yarns, the surface of a weft or a warp knitted fabric is more open when compared to the surface of a woven fabric. Due to this interlooping of yarns a knitted fabric could be stretched more than a woven fabric, even when a small force alone is applied. 

Once this force is eased the fabric slowly returns to its original dimensions. In fact, weft and warp knitted fabrics have higher elongation values than woven fabrics due to their structure, and their elastic behaviour generally exceed the elastic properties of the yarns used to knit the fabric. 

Yarns have poor bending and tensional properties compared to their longitudinal elastic properties, and so once a knitted fabric is stretched and then released, it would slowly go back to its original state. The absolute elongation and the elastic behavior of the fabric are both determined by the knitted structure and the mechanical properties of the yarns used to knit the fabric. Due to the structure and good elastic behaviour of knitted fabrics, garments made of knitted fabrics (knitted garments) are comfortable to wear. The air trapped in the loops of a knitted garment insulates the human body against cold. At the same time the relatively loose and open structure helps the perspiration process of the human body, especially when the knitted fabric is made of yarns spun from natural fibers. Due to the interlooping of yarns, the knitted fabrics also have better crease recovering properties compared to fabrics woven from similar yarns. 

The term binding can be used to describe the connection of one or more yarns in a textile fabric. The structure of a knitted fabric can be evaluated by studying how the yarns in weft and warp knitted fabrics are bound or interconnected, and this can be illustrated using stitch (loop) diagrams (charts). The actual interlooping of yarns in order to produce knitted structures depends on the knitting principle that was adopted to produce the structure, i.e. weft or warp knitting, and on the patterning elements. Knitting is the process of making cloth with a single yarn or set of yarns moving in only one direction. Instead of two sets of yarns crossing each other as in weaving, the I single knitting yarn is looped through itself to make a chain of stitches. These chains or rows are connected side by side to produce the knit cloth” (American Fabrics and Fashions Magazine 1980, 370). The interlocking of these loops in knitting can be done by either vertical or horizontal movement. When the yarns are introduced in a crosswise direction, at right angles to the direction of growth of the fabric, and run or interlock across the fabric, the knit is known as a weft knit. (Some sources may refer to these knits as filling knits, but the term weft knit is used in the knitting industry.) 

When the yarns run lengthwise or up and down, the knit is known as a warp knit. In knitting terminology, the rows of stitches that run in columns along the lengthwise direction of the fabric are known as wales. This corresponds to the warp direction of woven fabrics. Crosswise rows of stitches or loops are called courses. The direction of the courses corresponds to the filling of woven goods. 

Both warp and weft knits are made by machine. Knitting machines may be either flat or circular. The flat-type knitting machine has needles arranged in one or two straight lines and held on a flat needle-bed. The cloth is made by forming stitches on these needles. The resulting fabric is flat. Machines with flatbeds are used to make both warp and weft knits. 

The circular knitting machine has needles arranged in a circle on a rotating cylinder. The resulting fabric is formed into a tube. Circular knitting machines produce weft knits almost exclusively. For nearly two hundred years after its invention in 1589, Lee’s machine was used without further improvement. Using a spring beard needle, Lee’s machine produced flat knitted fabrics by mechanically passing one loop of yarn through another.

-->