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.