CHAPTER 5 CASE STUDY

Transcription

1 90 CHAPTER 5 CASE STUDY 5.1 INTRODUCTION SAM A spinning and weaving textile mill situated in South India has been considered for this work. SAM is a part of the Pioneer Asia Group, a private sector company, established in The company manufactures high quality yarns from top quality cotton and focuses special attention to meet the expected standards of the buyers or customers in all over the world. The products of SAM are exported to the countries of South-East Asia, Europe and so on. The top domestic buyers are its regular customers. Designed with flexibility, SAM is able to supply a wide variety of products like cotton, synthetic and so on. The special feature maintained in this mill is its flexible manufacturing system which means that a wide variety of products can be produced with a short lead time as per customer s requirement. 5.2 FIBERS Different types of fibers are used to make yarn. These fibers fall into two categories, natural and synthetic. Natural fibers are obtained from a plant or an animal and used in weaving textiles. The most abundant and commonly used plant fiber is cotton, gathered from the cotton boil or seed pod when it is mature. In fact, cotton is the best selling fiber all over the world. Fibers taken from the plant leaf or stern are generally used for rope. Other plant fibers include acetate (made from wood pulp or cotton linters) and linen, made from

2 91 a vegetable fiber. Animal fibers include wool, made from sheep hair, and mohair, made from angora goats and rabbits. Silk is a protein extruded in long, continuous strands by the silkworm as it weaves its cocoon. Natural fibers i.e. cotton, silk, and wool represent the major fibers available to ancient civilizations. The earliest known samples of yarn and fabric of any kind were found near Robenhausen, Switzerland, where bundles of fibers and yarns and fragments of plain-weave linen fabric, were estimated to be about 7,000 years old. Cotton has also been cultivated and used to make fabrics for at least 7,000 years. It may have existed in Egypt as early as 12,000 B.C. Fragments of cotton fabrics have been found by archaeologists in Mexico (from 3500 B.C. )., in India (3000 B.C. ), in Peru (2500 B.C. ), and in the south western United States (500 B.C. ). Cotton did not achieve commercial importance in Europe until after the colonization of New World. Silk culture remained a specialty of the Chinese from its beginnings (2600 B.C.) until the sixth century, when silkworms were first raised in the Byzantine Empire Synthetic fibers did not appear until much later. The first synthetic, rayon made from cotton or wood fibers, was developed in 1891, but not commercially produced until Almost half a century later, nylon was invented, followed by the various forms of polyester. Synthetic fibers reduced the world demand for natural fibers and expanded applications. Synthetic fibers are made by forcing a thick solution of polymerized chemicals through spinneret nozzles and hardening the resulting filament in a chemical bath. These include acrylic, nylon, polyester, polyolefin, rayon, spandex and triacetate. Some of these fibers have similar characteristics to the natural

3 92 fibers without the shrinkage problems. Other fibers have special properties for specific applications. Denes et al (1984) presented static and dynamic methods for natural and synthetic fibers to impart new qualities for supporting the materials under cold plasma conditions. 5.3 YARN MANUFACTURING PROCESS Various varieties of cotton are mixed to get homogeneous blend of cotton for uniform quality and shade of yarn. The raw cotton is opened and cleaned for supply to carding in the form of lap in blowroom. Before precomber drawing process, it has been converted into sliver form by carding and collected in cans. After passing through pre-comber draw frame, delivered sliver is converted into a lap form by lap former machine. The comber machine separate longer to form sliver in can and feed it to finisher. Finisher-draw frame converts the collected synthetic fibers into a uniform linear density of sliver by doubling and drafting. Final yarn to market is made with the use of Autoconer by passing through electronic yarn cleaner to clear yarn fault. Packing of individual cone of yarn is carried out in suitable mode (Bag, Carton or Pallet) by confirming its quality and weight as per customer requirement. Lord (2003), Grosberg & Iype (1999) presented various techniques and guidelines in yarn manufacturing. The flow sequence of yarn manufacturing process is illustrated in Figure 5.1. The step by step manufacturing process involved in each stage is described below.

4 93 Raw Materials Mixing and Preparation Blow room Carding Pre comber drawing Lap former Comber Finisher drawing Simplex Spinning Auto coner Packing Finished products Figure 5.1 Flow sequence of yarn manufacturing process

5 94 RAW MATERIAL MIXING AND PREPARATION BLOW ROOM CARDING PRECOMBER DRAWING LAP FORMER COMBER FINISHER DRAWING SIMPLEX SPINNING AUTO CONER PACKING FINISHED PRODUCTS Figure 5.2 Yarn Manufacturing -Machines and Stages

6 Raw Materials Generally used raw materials in a spinning mill is cotton since it is having the quality characteristic of fiber properties like fiber length, strength, fineness, Maturity and moisture content. Spinning mills are receiving the raw materials in the form of highly compressed bales. Variety wise bales are laid as per the laying plan and they are opened manually and laid on the floor layer by layer Mixing and Preparation Mixing and Preparation is generally meant as the mixing of raw materials which is an essential preliminary step in the production of yarn. During this process, conditioning of mixed raw materials is an important one and for ensuring satisfactory conditioning, the mixed raw materials are kept exposed for a particular time. In hand mixing, contamination present in the raw materials is removed effectively. After conditioning, the material is ready for processing in the blow room Blow Room Blow room is the starting of the spinning operation where the fiber is opened cleaned, mixed, micro dust removed and evened thus passed to carding machine without increasing fiber rupture, fiber neps, broken seed particles. The basic function of blow room is opening, cleaning and dust removing, blending and evenly feeding the material on the card. The functions of Blow Room are described as follows Opening Opening is the first operation within the Blow Room in which the goal is always a high degree of openness of material with gentle treatment and

7 96 a fiber loss as less as possible. Opening is the first operation it means, tearing apart the compressed and the matted cotton until it is very much loosened and separated into small tuffs with a gentle treatment, and a fiber loss as small as possible. Opening is also related to cleaning as where is opening there is also cleaning Cleaning Cotton contains up to 18 percentage trash in most cases point to clean the material it is unavoidable to remove as much fiber as much waste. Hence it is necessary to measure the amount of the waste removed and its composition. As it is of high importance also called cleaning efficiency. The cleaning efficiency always has to be optimized and not maximized, since the fiber quality (short, neps) as well as fiber loss is always negatively affected by maximum trash removal Dust removal To extract the contamination in the cotton such as leaf, stone, iron particles, jute, polypropylene, colored feather and foreign material from cotton by opening and beating. An often under estimated task of the blow room line is the removal of dust and impurities. De-dusting in the blow room happens by air suctioning only, either between the machines, e.g. By dust cages, dust extractors, etc., are within the machine by normal air separation. Every blow room machine must be capable of extracting the dust so that special de-dusting machines should be needed. The efficiency depends not only on the devices but also on the size of the flocks. The smaller flocks, the higher is the efficiency.

8 Carding Carding is a mechanical process that cleans and mixes fibers to produce a continuous sliver suitable for subsequent processing. This is achieved by passing the fibers between differentially moving surfaces covered with card clothing. It breaks up locks and unorganized clumps of fiber and then aligns the individual to be parallel with each other. Attenuation of individual fiber is the main object of carding. In this machine input material is Blow room lap and the output material is called carding sliver having coiled in the plastic cans. The impurities present in the lap are dropped down as waste through the carding machine process. Uniform linear density of the sliver, perfect compactness of coiling and minimum no. of entangled fiber is the important quality requirement of card sliver. Carding plays a crucial role in all spinning cycles particularly in the woollen spinning cycle, in which it incorporates different function, all essential in order to obtain the level of quality required to the product Pre Comber Drawing Drawing is the process where doubling of slivers and drafting takes place. The chord slivers are being fed into the pre comber drawing machine in which the fiber parallelization takes place. By processing through the precomber drawing uniformity of sliver will improve. Drawing is the first process in yarn manufacturing that employs roller drafting. In drawing, practically all draft results are from the action of rollers. Containers of silver from the carding process are staked in the creel of the drawing frame. Drafting occurs when silver is fed into a system of paired rollers moving the sliver by drafting at different speeds.

9 98 Drawing straightens to make parallel to the axis of the silver. Parallelization is necessary to obtain the properties desired when they are subsequently twisted into yarn. Drawing also produces a sliver that is more uniform in weight per unit of length and helps to achieve greater blending capabilities. They are produced by the final drawing process, called finisher drawing are nearly straight and parallel to the axis of the sliver. Weight per unit length of a finisher drawing sliver is too high to permit drafting into yarn on conventional ring spinning systems Lap Former The main objective of lap former is converting slivers into sheet with more uniformity. This is a key machine in the combing process. Lap former is the machine meant for converting pre comber drawing sliver to lap for feeding to comber. There are two layers of sliver. First layer fed from back row and the second layer fed from front row of the machine. Both the layers are slightly drafted uniformly and laid one above the other. Lap Former Machine is used for lapping cotton and forming compact lap from drawn sliver by drawing and drafting to feed the combing machine. The lap is wound on to bobbin and cotton wool. The lap former machine is not use in the carded yarn process because it is used for lapping yarn. Former meaning make laps of various counts for carding machines of textile industry Comber Comber is the machine meant for combing the lap sheets and removes non spinnable fiber and makes all the cotton fiber parallel. Eight laps are fed into the comber. After combing, waste will be collected separately and sliver will be condensed on the table of comber. The sliver will be doubled

10 99 together and drafted to single sliver and coiled in can. Neps removal is enabled by combing the lap sheets from top portion by top cone and bottom portion by combing segment. The raw materials delivered by the carding machine are not suitable for combing both as regards form and fiber arrangement. If card sliver were feed to the comber, then true nipping by the nipping plates could occur only on the high points, with the risk that the nippers could not retain the less strongly compressed edge zone of the slivers. These could be pulled out as clumps by the cylinder combs. Hence a sheet with greatest possible degree of evenness is required as in feed to the comber. A good parallel disposition of within the sheet is a further pre requisite. If the fiber lies across the stand even long are presented to cylinder combs as they were short and they are eliminated as such. This represents unnecessary loss of producing best yarns. Combing is a process which is introduced into the spinning of finer and high quality yarns from cotton. The carded materials (sliver) contain certain amount of short, neps, fine kitty and leaf particles. Short is a hindrance to spinning of finer counts where the number of fiber in the cross section of the yarn is less. The short cause thick and uneven places in the yarn length and the yarn look hairy. Apart from this, short do not contribute anything to yarn strength. Short below a certain pre-determined length can be easily separated out by using comber Finisher Drawing Combed sliver is processed in finisher drawing by doubling and drafting. Fiber parallelization and uniformity of sliver improvement are takes place in this finisher drawing preparation. Auto leveling systems are supplied with auto levelers for producing high quality spinning yarns to meet export market.

11 Simplex In yarn manufacturing system, simplex frame is situated after the finisher drawing machine. The sliver which is produced from the drawing machine is thicker and it is not suitable to feed into the ring frame directly to produce yarn. For this reason, drawn sliver is treated before entering into the ring frame. The commonly used simplex machine for cotton is flyer frame or speed frame. There are three basic steps in the operation of the roving frame drafting, twisting and winding. These three basic steps are exactly the same as the basic steps required in spinning. The machine where the sliver is subjected to one or more attenuating process and the attenuated sliver receives a small amount of twist and is then wound on bobbins suitable for crewing at next process. In this process drawn sliver is input and fine roving is output. The roving is feed into ring frame for yarn production. It is noted that, simplex is essential for the production of cotton yarn Spinning In yarn manufacturing process spinning is the final stage wherein roving is drafted, twisted and wound. Drafted stand after inserting sufficient twist will be wound on empty cop through traveler. The traveler is running above the highly polished steel ring for maintaining better working performance of spinning each machine is provided with overhead traveling cleaner and effective humidification plant Autoconer Yarn produced in ring frame in the form of cop contains much kind of yarn faults. In order to convert the cops to full package of cone or cheese with electronic yarn cleaner, Autoconer is employed.

12 101 Cone or Cheese size will be varied according to customer requirement by optimizing winding parameters and electronic yarn cleaner setting, the best quality yarn of high and continuous length cones or cheese can be supplied to the customer. There are various attachments available in the Autoconer to produce cones without any kind of unwinding problem. Every Autoconer contains drums. Individual drums are having separate monitoring and measurement uniform cone weight can be maintained. Electronic yarn cleaner is versatile. It is possible to set the machine as per our requirement. Also individual yarn will be monitored and recorded. Autoconer is also very reliable quality monitoring and controlling process Packing Packing is one of the process to pack the finished products in Cone or Cheese in safe after ensuring the quality of each package. In packing each and every cone will be subjected to ultra violet lamp checking. After ultra violet lamp checking, Cones or Cheeses will be carried to checking table provided with extra light fan and compressor air nozzle. Individual cone will be cleaned by using compressor air, Then check all sites of cones or any kind of defect or stain. After ensuring, individual cones are wrapped by polythene bags. As per the packing instructions, number of cone or cheeses will be packed in a bag or carton. Disc provided inside the cone will prevent the cone from collapsing during transportation. Individual bag or carton will be weighed and recorded in the separate register provided for control. As per the requirement of customer some of the products will be packed in the form of pallet.

13 Finished Products of yarn. Finally the finished products are in the following different varieties i) Single yarn ii) Double yarn iii) Ply yarn(3ply,4ply,5ply) iv) Open end yarn v) steam conditioned yarn vi) TFO yarn vii) Cotton yarn combed or carded or hosiery viii) Polyester yarn ix) Tinted color polyester yarn x) Gassed yarn xi) Singeing yarn 5.4 PROBLEM DEFINITION Since the yarn manufacturing process involves the usage of number of machines and equipments at variety of stages, it is quite important to find out the optimal flow sequence of different form of cotton through these machines. The setup and arrangement of machines for yarn manufacturing process resembles the structure of flow shop scheduling. Hence the yarn manufacturing process is termed as a flow shop scheduling problem.

14 103 The flow shop scheduling problems can be formally described as follows (Engin & Döyen 2004): Machines are arranged into s stages in series; in each stage k (k=i,.,s) there are m k identical machines in parallel; job j, j=i,.,n, has to be processed on any machine at each stage and job j has finite processing times in each stage (p 1j, p 2j,., p sj ). It is assumed that all jobs and machines are always available during the scheduled period and the preemption is not allowed. The objective is to find a schedule which minimizes the maximum completion time (make span), mean flow time and machine idle time with bi-objective and tri-objective function value. Depending on the count of yarn the raw materials are put into process and time also calculated from this point to the end of production cycle. Every process has to be performed consecutively in order to complete a cycle and hence the total time required for completion of a production cycle is taken for consideration. In order to minimize the make span and bi-objective function value, the modified improved genetic algorithm is used and presented in this work.