Textile & Fashion World

Brake: A brake is a device by means of which artificial frictional resistance is applied to moving body in order to stop the motion of a loom.

Loom Brake

Types of Brake:
Through there are many types of brakes, the following are commonly used in looms:

i) Shoe brake
ii) Band brake

Band Brake:
The brake stops the loom immediately whenever required. The weaver uses it to stop the loom to repair broken ends and picks.

A band brake consists of a flexible band of leather, or steel lined with friction material, which embraces a part of the circumference of the dram shown in figure. One end is fixed at the point and other is fixed with a spring loaded collar. When force is applied to the lever hence the brake is applied. The friction between the band on the drum and the drum provides the braking force as lateral movement of leaver creates a pressure on the brake band. 

Read more: http://textilelearner.blogspot.com/2012/09/loom-brake-system-types-of-loom-brake.html#ixzz2OCVVcYw4

Experiment name: Study on beating-up mechanism .

Objects:
1.To know about the construction of the mechanism.
2.To know about the drive of the beating-up mechanism.

Introduction:
The beating-up is the third primary motion of weaving. It consists in driving the last pick of weft to the fell of the cloth. This is accomplished with the help of a reed fixed in the sley. The sley is given a sudden and quick movement towards the fell of the cloth by the cranks in the crankshaft. The sleywood runs from one shuttle box to another, and when at its backward movement, the shuttle travels over its race.

Main parts:
1.Crankshaft 
2.Crank 
3.Crank arm 
4.Reed cap   
5.Reed
6.Sley race
7.Sley

8.Sleysword

Description:
The crankshaft gets drive from motor via motor pulley and m/c pulley. The crankshaft has two cranks. These cranks transform the rotary motion into swinging motion. The reed cap is connected by crank arm to crank of the crankshaft. Again the reed is connected between reed cap and sley. There is sleysword under the sley that is bolted to the rocking shaft. There is also shuttle box on the sley. Now the crank gives the swinging motion to the sley by crank arm. When the sley is moving towards the healdshaft at certain position the shuttle passes through warp shed. Again when the sley is coming towards the front rest at last position the reed pushes the last pick to the previous pick of cloth. This is the beating-up motion and the cloth increases in lengthwise in this way.

Conclusion:
To make a woven fabric interlacement of warp and weft yarns is the main condition. That’s why beating-up mechanism is a very essential motion for weaving. Proper setting and adjustment should be taken for this motion. This practical helps me to know about beating-up motion. I think this will help me in my future career. 

 

http://textilelearner.blogspot.com/2012/02/beat-up-mechanism-study-on-beating-up.html#ixzz2OCSEPklJ

Experiment name: Study on over picking mechanism.

Introduction:
Picking is the second primary motion in weaving. The action of inserting weft yarn through the warp yarns is called picking. 

The functions of picking mechanism are:
1.To deliver the shuttle along the correct flight length.
2.To throw the shuttle at a predetermined speed.

Main Parts: 
 

Over picking

Features of Over Picking Mechanism:
1.Picking arm is over shuttle.
2.Suitable for narrow loom.
3.Higher picks per minute.
4.Less power required.
5.Works more smoothly.
6.Shortening the picking strap and changing the shape of the cam can increase picking force.

Mechanism of Over Picking:
Over picking mechanism is used on cotton and jute loom. It is robust and easy to adjust and maintain. The spindle is situated over the shuttle box and is essential to guide the shuttle along the correct path. It is normally set slightly up and slightly towards the front of the loom and its inner end.

The back end of the shuttle will thus receive a similar lift at the end of the stroke, so that its leading end will receive correct delivery down and into the shed. A flexible leather-picking strap is used to control the picker, which has tendency to stretched slowly in use, and vary with regard to its elastic property.

The cone over pick motion consists a vertical shaft placed either inside or outside the loom framing. The shaft serves as fulcrum of the picking arm, it is held against the loom frame. There is a spiral spring at the picking shaft, which causes the picking arm and picker to move back after the delivery of the pick.

At the two end of the bottom shaft, two picking cams are fixed. In revolving its nose the tappet strikes the cone shaped ant frictional roller strut, positively rotates the shaft and causes the pick to move inward with sufficient velocity to drive the shuttle across the loom. The timing of the picker begins to move can be attend by turning the picking tappet on its boss.

How to Increase PPM:
1.By increasing motor speed.
2.By setting the cone stud nearer to the picking tappet.
3.By decreasing the picking strap.
4.By altering the position of picking arm towards the centre of the loom.
5.By decreasing the length of the stroke of picking tappet.

Uses:
This is used for narrow and fast running looms, weaving light and medium weight fabrics and for many narrow and wide looms for weaving heavy fabrics.

Conclusion:
The over picking motion is negative one; the exact amount of power is required to drive a shuttle. By this experiment we learned about the over picking mechanism and how it works. This experience will help us in our future practical life.

http://textilelearner.blogspot.com/2012/02/picking-over-picking-mechanism-how-to.html#ixzz2OCRlMxEd

A loom in which the weft yarn is propelled through the shed by means of a jet of air.
OR .
A shuttleless loom capable of very high speeds that uses an air jet to propel the filling yarn through the shed.
OR .
A loom using a jet of air to carry the yarn through the shed.

U.S. Pat. No. 4,606,152 illustrates a method and apparatus for grinding or buffing a metal reed of an air jet loom by manually moving a buffer along the tunnel while the reed is positioned on the loom.

U.S. Pat. No. 4,640,316 illustrates another apparatus for treating an air jet loom reed while on the loom wherein air measuring apparatus is manually moved in sliding motion along the top of the loom reed.

Heretofore there was no method or apparatus available which would uniformly and consistently permit measurements of air flow and at the same time provide a means to make indicated adjustments to the loom reed to meet requirements as to air flow performance. Accordingly, objects of this invention include analysis and regulation of air flow for different types of filling with reduction in air consumption of the loom.

Another object of the invention is to permit the correction of problems associated with filling insertion and to assist in speeding up the loom while providing higher quality of cloth with fewer loom stops.

It has been found that a method and apparatus may be provided for optimizing air flow characteristics of an air jet loom by removing the reed from the loom and positioning same in a frame where a carriage is provided for rolling contact according to a predetermined path for measuring the air flow characteristics and for altering the physical nature of the air tunnel to accommodate improved air flow.

FIG. 1 is a perspective view schematically illustrating a frame for positioning a loom reed in inverted position remote from the loom together with a driving apparatus for moving the carriage;

FIG. 2 is a transverse sectional elevation taken on the line 2--2 in FIG. 1 with a carriage illustrated as being positioned upon the loom reed;

FIG. 3 is a plan view of the carriage taken on the line 3--3 in FIG. 2; and 

FIG. 4 is a plan view illustrating an apparatus for positioning a buffer for altering the loom reed in accordance with the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

The drawings illustrate a method and apparatus for enhancing air flow characteristics in an air jet loom reed broadly designated at 10. The reed 10 has a tunnel 11 and a bottom channel 12. The air jet loom reed is first removed from an air jet loom (not shown). The air jet loom reed is then positioned in a mounting frame A in a fixed preferably inverted at least partially upright position. In inverted position the bottom channel 12 is at the top, with a top channel 13 on a lower guide rail 14 of the frame A. The rail 14 of the frame A is opposite an upper frame rail formed by a channel 15.

A carriage B driven by a pulley C is illustrated for driving a buffing device D and an air measuring device E at a predetermined speed along the reed. The carriage is illustrated as being suitably supported as by a wheel F which rolls on the bottom channel 12 of the loom reed. Thus, the path of the buffing device relative to the tunnel of the air jet loom reed is located with respect to an upper portion of the loom reed when fixed in the inverted position.

The frame A is carried by a tubular base support 16 and the lower guide rail 14 is supported by a bracket 17 while the channel 15 is carried by posts 18. A bar magnet 19 is provided to hold the reed 10 in position upon the frame A. Rolling contact of the carriage is maintained by the rollers G (FIG. 2) with the respective reed channels 12 and 13. A roller 15a is provided for positioning the carriage in respect to the channel 15.

Thus, FIGS. 1 and 2 illustrate a universal mounting frame A which can be used for all known air jet reeds of a tunnel variety of varying lengths, heights and locations of air jet tunnel relative to top or bottom channel of the reed. The reed is held in place in the frame by the lower guide or alignment rail 14 and the magnetic bar holder 19 together with the gravity effect of the weight of the reed.

The drive pulley C together with a nylon coated cable 20 provide uniform or other predetermined motion to the carriage along the reed. The pulley is driven by a motor 21. It is important to note in the drawings that the top channel 13 of the reed 10 (as mounted in the loom) is located along the bottom of the frame and the bottom channel 12 of the reed 10 (as mounted in the loom) is located exposed at the top of the frame (e.g. This is the reverse of the arrangement in the air jet loom).

This is important because it exposes the bottom of the reed channel for exact and uniform rolling motion of the carriage along any type of reed. All types of loom reeds have critical reed dimensions which are referenced from the bottom of the bottom channel and from the front of the bottom channel to the sides of the tunnel and to the bottom of the tunnel. Dimensions to and from the top channel of the reed are considerably less critical and in fact can vary from one reed to another within limits without effecting the function of the reed in the weaving process.

Universal adjustment of the air measuring device E, illustrated as a Pitot tube within the air jet tunnel 11, is provided by the mounting which also provides universal adjustment of the buffing or grinding wheel D in and around any and all sections of the air jet tunnel. Various types of buffing or grinding wheels designed for different buffing purposes may be utilized. Any such device or operation for altering the surface as configuration of the tunnel is referred to herein as a buffer or buffing. A universal mounting 23 (FIG. 3) for an air jet nozzle as illustrated at 24 is provided at any desired location relative to the tunnel and at a variable distance from the Pitot tube. The carriage B may be variable in width to permit extensive changes of the distance of the Pitot tube from the nozzle and also permit use of multiple nozzles if this is desirable. This feature is useful because at present the location of the nozzles on the loom relative to the tunnel are fixed. This is true in the case of each type of loom. This capability provides for a means to determine the optimum nozzle location for different types of filling materials depending on count, denier, twist, etc.

An air cylinder 25 and a potentiometer 26 are illustrated in FIG. 4 connected in relationship to the buffing mechanism universal mounting 22. The buffing mechanism having the wheel D is located by moving it in or out of the desired position. A desired pressure of the buffing wheel may be applied to any selected part of the tunnel. Further, by means of the potentionmeter the speed of the wheel D is regulated providing for a constant surface speed during its motion across the air jet reed and accommodating any wear in the buffing wheel. Since the Pitot tube E also has a universal mounting capability both up and down and in and around of the air jet reed tunnel air flow, i.e. pressure drop, measurements may be made in any locations in the profile of the air jet tunnel.

A nozzle 27 of vacuum system is located in the carriage. It is moved into position automatically when buffing is performed, and out of the way when measuring is performed. Its purpose is to clean the reed and constantly remove any particles created during the buffing process. Thus, apparatus has been provided for measuring air flow for all types of air jet reeds for all known air jet looms.

The measuring of air flow by pressure drop from a known pressure can be performed anywhere in the cross section of the tunnel and at any distance from the Pitot tube to the nozzle. A variety of nozzles can be used and the nozzle location is variable relative to the tunnel and the Pitot tube. The number of nozzles is also variable.

Air pressure to the nozzles can be set at variable pressures. Once air flow measurements are taken with potentially a variety of methods, the air flow can be recorded in any suitable way. Adjustments in air flow throughout the cross section of the air jet reed tunnel and over the full length of the air jet reed tunnel are possible. Variations in air flow can be produced in both cross sections and over the length of the air jet reed to accommodate optimum filling stop arrangements, different fillings, air consumption and resulting power conservation, loom speed as measured in picks per minute, and cloth quality. These adjustments are accomplished by removing or creating slight burrs on the metal profile dents, varying the surface finish of the metal profile dents, modifying the shape of the metal profile dent to increase or decrease air flow and to increase or decrease turbulence, varying nozzle location relative to air jet tunnel, and changing nozzle design.

While a preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.

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Different Parts of a Loom

Short Description of Loom is Given Below:

Heald/Heddle: Wire or cords with eyelets that hold warp yarns in a place.

Function:
1. It helps in shed formation.
2. It is useful in identifying broken ends.
3. It determines the order or sequence of the warp threads.
4. It determines the warp thread density in a fabric.

Heald shaft/Harness: A wood or metal frame that holds the headl/heddles in position in the loom during weaving. It is usually more than one.

Shuttle: This is a vehicle for weft & passes through the divided warp for the interlacement of the warp & weft.

Shuttle box: Compartment of each end of the sley of a shuttle loom used to retain the shuttle between picking motion.

Picker: It is a piece of leather or other metal placed in grooves or on a spindle inside a shuttle box.

Beams: A cylindrical body with end flanges on which a multiple of warp ends is wound in such way to permit the removal of these yarns as a warp sheet.

Front rest: It is a fixed roller placed in front of the loom above the cloth beam & act as a guide for the cloth to wind on to the cloth beam.

Lease rods: The division of warp yarn into one & one, two & two, & so on is termed as lease. The two rods passed between the two successive divisions of warp yarns are called lease rods.

Slay: It is the portion of loom that carries the reed and oscillates between the harness & the fell of the cloth.

Reed: A comb like wire or device used to separate yarns on a loom & to beat up the filling during weaving.

Treadle: The treadle is a paddle or lever under a loom with which a thread is connected by means of cords.

Temple: Roller device on a loom that hold the cloth at a proper width to prevent it from being drawn in too much by the filling.

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A tappet is given a rotary motion so that it depresses a follower and a lever, known respectively as the anti-friction bowl and the treadle arrangement, by means of which the heald shaft is operated.

Construction
Figure 2 shows a negative tappet shedding mechanism. A pair of tappets A and B are fixed to the bottom shaft C at 180 degrees to each other. Two treadle levers D and E are connected to the loom back-rail by a bracket F.

The bracket acts as a fulcrum for the levers. The two treadles have teeth to carry the lamb rods G and H respectively. Two heald shafts J and K are connected to the lamb rods. A top reversing roller shaft Q carries two rollers of different diameters. The roller of small diameter N is connected to a leather strap L to which the front heald shaft J is connected. The roller P of large diameter is connected to a leather strap M to which the back heald shaft K is connected. The tappets A and B touch the anti-friction bowls or followers R and S respectively, which are fixed to the treadle levers.

Working
When the bottom shaft is rotated in the clockwise direction as shown in the figure, the tappets are also rotated. The tappet will depress the anti-friction bowl and the treadle. Being fulcrumed at one end, the front portion of the treadle moves down. This action is transferred to the lamb rod, the heald shaft and the leather strap. So one heald shaft is lowered and the threads connected to this heald shaft are lowered and form the bottom layer of the shed.

The leather straps attached to the reversing rollers are connected in opposite directions, i.e. when leather strap is pulled down, it is unwound from its roller. The shaft therefore rotates in the clockwise direction and the other leather strap is wound on to its roller. The heald shaft is raised and therefore the lamb rod and treadle lever are also raised. The threads connected to the heald shaft are also raised and form the top layer of the shed.

For the next shed, the other tappet works with the other set of bowl, treadle, lamb rod, heald shaft, strap and roller and the other heald shaft is lowered. The first heald shaft is raised by the top reversing rollers, and the positions of the healds shafts are thus interchanged. Thus, for one rotation of the bottom shaft, two sheds are formed.

In this type of tappet shedding therefore, one tappet depresses the concerned treadle and the corresponding heald shaft is lowered. But the other heald shaft is raised by means of the top reversing rollers. So this type of shedding mechanism is known as “negative tappet shedding mechanism”

Timings and settings
1. Turn the crank to the top centre position.
2. Fix the anti-friction bowls to the treadle levers; they should move freely in the slots.
3. Fix the treadle levers with a bracket to the back rail of the loom.
4. Set the grid and grid bracket to the front rail of the loom in the slots of the grid.
5. Make sure that the tappet with the lower throw is fixed to the bottom shaft at the starting handle side.
6. Fix the top reversing rollers to the top reversing roller shaft to be equidistant from the ends and at the same time ensure that the connecting screws of the rollers are symmetrical about the central axis of the shaft when the heald shafts are at the same level. The roller of smaller diameter is always connected to front heald shaft.
7. The heald shafts are connected to the top reversing rollers by means of cords and leather straps. The leather straps are connected to the rollers, such that when one of them winds on its roller the other strap unwinds from its roller and vice versa.
8. Lamb rods are connected to the heald shafts by cords.
9. Adjust the tappets on the bottom shaft and make sure of the following points :

i. The tappet with a bigger throw should be connected to the back heald shaft.
ii. The bowls should have perfect contact with the tappet surfaces.
iii. The treadles should be at the same level and parallel to each other at the top centre position.
iv. Heald shafts : The hook of the lamb rod of the front heald shaft should be connected to the first notch of the treadle lever while that of the back heald shaft should be connected to the third notch. If the depth of shed is altered, the connections of the hooks to the treadle levers can be changed.

Points to be observed
1. Turn the crank shaft through two revolutions and make sure that the bowls are always in contact with the tappets.
2. The heald shafts should not touch the side frames or the sley.
3. Turn the crank shaft to the bottom centre and check the size of shed. The bottom line of warp sheet or the heald eyes of the lowered heald shaft should have a clearance of 1 mm from the race board and the top.

Introduction:
Picking is the second primary motion in weaving. The action of inserting weft yarn through the warp yarns is called picking. 

The functions of picking mechanism are:
1.To deliver the shuttle along the correct flight length.
2.To throw the shuttle at a predetermined speed.

Main parts:
1.Picking arm 

 2.Picker  
3.Picking cam  
4.Picking bowl 
5.Race board  6.Shuttle 
7.Bottom shaft
8.Treadle lever
9.Angular lever
10.Crank shaft 

Features of under picking mechanism:
1.Picker arm is placed under the race board.
2.Suitable for wider loom.
3.Under picking works less smoothly.
4.More direct action.
5.Rough in action.
6.More clean mechanism.
7.Consumes more power.
8.Used for heavy weight fabrics in silk and rayon looms.

Under picking mechanism:
In under picking mechanism a race board is situated over picking arm. Under picking is controlled by picking cam which is fixed on the bottom shaft. At first the motion comes from motor and m/c pulley.

Then the motion comes in to the bottom shaft and thus picking cam. When picking cam rotates and its nose portion comes in contact with treadle lever and pushes it then the treadle lever pushes the angular lever. The picking arm gets motion from angular lever which is connected with picking arm.

A picker is placed in the picking arm which pushes the shuttle. When shuttle gets motion by picking arm then shuttle begins to move to and fro on the race board. Thus picking is done.

A spring is situated which causes the picking arm and picker to move back after the delivery of the pick. At the two end of bottom shaft, two picking tappets are fixed. By increasing nose length picking speed may be increased.

How to increase PPM:
1.By increasing motor seed.
2.By increasing the nose shape of picking tappet.
3.By decreasing the length of picking arm.

Uses:
This mechanism is used in all non-automatic cotton looms. It is also used in jute looms.

Conclusion:
This picking mechanism is very important for loom. In the loom under picking is directly done by picker and picking arm. Again under picking is necessary for weft yarn insertion. So we should learn about this mechanism very carefully. 

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An apparatus for making fabric by weaving yarn or thread. A loom is a device used to weave cloth. The basic purpose of any loom is to hold the warp threads under tension to facilitate the interweaving of the weft threads. The precise shape of the loom and its mechanics may vary, but the basic function is the same.

Shuttle Loom: The shuttle loom is the oldest type of weaving loom which uses a shuttle which contains a bobbin of filling yarn that appears through a hole situated in the side. The shuttle is batted across the loom and during this process, it leaves a trail of the filling at the rate of about 110 to 225 picks per minute (ppm). Although very effective and versatile, the shuttle looms are slow and noisy. Also the shuttle sometimes leads to abrasion on the warp yarns and at other times causes thread breaks. As a result the machine has to be stopped for tying the broken yarns.

Classification of Modern Loom:

Shuttle less loom: Many kinds of shuttle less looms are used for weaving such as Projectile Looms; Rapier Looms; Water Jet Looms; and Air Jet Looms.

Projectile Loom: It is sometimes called missile loom as the picking action is done by a series of small bullet like projectiles which hold the weft yarn and carry it through the shed and then return empty. All the filling yarns are inserted from the same side of the loom. A special tucking device holds the ends of the wefts in place at the edge of the cloth to form the selvage. This loom needs smooth, uniform yarn which is properly sized in order to reduce friction. Projectile loom can produce up to 300 ppm and is less noisier then the shuttle loom.

Rapier Loom: Rapier loom comes in many types. Early models of it use one long rapier device that travels along the width of the loom to carry the weft from one side to the other. Another type of rapier loom has two rapiers, one on each side of the loom. They may be rigid, flexible or telescopic. One rapier feeds the weft halfway through the sheds of warp yarns to the arm on the other side, which reaches in and carries it across the rest of the way. Rapier looms are very efficient and their speed ranges from 200 to 260 ppm. These looms can manufacture a variety of fabrics ranging from muslin fabric to drapery fabrics and even upholstery fabrics.

Water Jet Loom: In it, a pre measured length of weft yarn is carried across the loom by a jet of water. These looms are very fast with speeds up to 600 ppm and very low noise. Also they don't place much tension on the filling yarn. As the pick is tension less, very high quality of warp yarns are needed for efficient operation. Also, only yarns that are not readily absorbent can be used to make fabrics on water jet looms such as filament yarn of acetate, nylon, polyester, and glass. However, it can produce very high quality fabrics having great appearance and feel.

Air Jet Looms: In the air jet weaving looms, a jet of air is used to propel the weft yarn through the shed at speeds of up to 600 ppm. Uniform weft yarns are needed to make fabrics on this loom. Also heavier yarns are suitable for air jet looms as the lighter fabrics are very difficult to control through shed. However, too heavy yarns also can't be carried across the loom by air jet. In spite of these limitations, air jet loom can produce a wide variety of fabrics.

Circular Looms: These looms are particularly used for making tubular fabrics rather than flat fabrics. A shuttle device in it circulates the weft in a shed formed around the machine. A circular loom is primarily used for bagging material.

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Basic Mechanisms in a Plain Power Loom
In order to interlace warp & weft threads to produce a fabric, the following weaving mechanisms are necessary on any type of loom:

Primary Mechanism
These are fundamental or essential mechanisms. Without these mechanisms, it is practically impossible to produce a fabric. The primary motions can further be divided as shedding, picking and beat up motions. The shedding opens the warp sheet into layers to facilitate passage of shuttle. The picking motion causes the shuttle carrying weft to be propelled from one end of loom to another. The beat up motion lays the previously laid weft to the fell of the cloth.It is for the reason that these mechanisms are called “Primary mechanisms”. The primary mechanisms are 3 in number.

1. Shedding mechanism
2. Picking mechanism
3. Beat-up mechanism

Secondary Mechanism
These mechanisms are next in importance to the primary mechanisms. If weaving is to be continued, these mechanisms are essential. The secondary motions comprise of take up and let off motions. The take up motion helps to wind the cloth on to the cloth roller and also influences the pick density in the cloth. The let off motion helps to let the warp from the weaver’s beam at an uniform rate thus maintaining the warp tension constant throughout the weaving process.So they are called “Secondary mechanisms”. They are

1. Take-up motion
2. Let-off motion

Auxiliary Mechanism
To get high productivity & good quality of fabric, additional mechanisms, called “Auxiliary mechanisms” are added to a plain power loom. The auxiliary mechanisms are useful but not absolutely essential. The auxiliary motions consist of the warp stop motion, weft stop motion and warp protector motion. The warp stop motion is used to stop the loom in the event of warp breakages. This is necessary to prevent fabric defects such as missing ends and floats. The weft stop motion is used to stop the loom in the event of weft exhaustion or weft breakages. This is necessary to prevent missing weft threads called cracks, in the fabric. The warp protector is used to prevent multiple warp thread breakages in the event of shuttle getting trapped in the middle of the warp sheet. These are listed below:

1. Warp protector mechanism
2. Weft stop motion
3. Temples
4. Brake
5. Warp stop motion 

 

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Side weft fork motion check the presence of weft in every two picks. It is situated at the side of the reed. It is used for producing medium and heavy fabric. Basically, it is used in modern automatic loom. 

 

The basic principle of the side weft fork lies in the fork and grate. A metal grate is placed between the end of the reed and the shuttle box mouth on the starting handle side as shown in the figure. A weft fork made of light metal which has three prongs bent at right angles is situated in front of the grate. The complete weft fork motion is illustrated at figure.

Side weft fork motion

Where,
A= weft fork
B= weft fork holder
C= Fulcrum
D= knock over lever
E= Hammer lever
F= greyhound tail lever
G= Weft fork cam
S= Starting handle

A weft fork A with a single tail hooked at the end is held by a weft fork holder B at C. the other end of the holder is held by knock-over lever D, which is in contact with the starting handle when the loom is running.

The tail end of the fork is slightly heavier than the forked end. A hammer lever E fulcrummed at X is connected to a greyhound tail lever F, the bottom end of which is resting on a weft fork cam G which is fixed on the bottom shaft. During the rotation of the bottom shaft the cam raises the greyhound tail lever on every two picks and causes the hammer lever to rock towards the loom front.

A channel is cut in the wooden raceboard H opposite the weft fork so that when the sley comes forward to beat-up position the weft fork prongs will remain below the raceboard level until it is touched by a weft thread lying across the channel from the selvedge to the shuttle.

In this case the shuttle should be on the starting handle side. If the weft thread is not broken or missing, it will push the weft fork prongs, thus lifting the hooked tail clear of the hammer lever E. At the same time the rotation of the cam G makes the hammer lever move towards the front rest. In case the weft is absent either through breaking or from running out, the weft fork remains horizontal and the prongs pass freely through the bars of the grate. Then the hook tail of the fork is caught in the notch of the hammer lever E as shown in figure and when this lever moves towards the front rest it carries the fork along with its holder resulting in the weft fork lever D pressing against the starting handle S and knocking off the loom.

One fault in the mechanism described early is that the weft fork lever and the holder move in an arc of a circle because of the fixed fulcrum of the weft fork lever. This sometimes causes the prongs of the fork to hit against the side wall of the channel in the raceboard and cause damage. In the British made Northrop looms this arc of movement does not exist since the weft fork acts directly upon the starting handle with a straight backward push.

In the mechanism illustrated in figure the weft fork A is mounted on a sliding bracket B which slides forward and backward in a fixed bracket C. As usual the hook tail of the fork is caught in the notch of the hammer lever on weft failure and backward movement of this lever will push the knock-over lever D, thus the releasing the starting handle E. The spring S returns the sliding bracket B to its original position.

Mechanism of Side Weft Fork Motion

1. The weft fork must be a possible source of weft cutting if it protrudes too far through the weft fork grate.

2. The grate must be smooth.

3. The weft fork prongs, during the forward movement of the reed, should not touch the grate wires or any part of the grate or raceboard groove.

4. The weft fork prongs protrude neither too less nor too far through the grate.

5. The clearance between the hook tail of the fork and the notch of the weft fork hammer is very important. If the clearance is too wide the weft thread may not keep the hook tail raised till the tail is clear off the weft fork hammer notch. This will result in unnecessary knock off of the loom even though the weft has not broken. On the other hand if the clearance is too close the hammer notch might prevent the hook tail from lifting when the weft thread applies pressure on the prongs.

6. The fork must be properly balanced so that the tail end is slightly heavier than the forked end.

7. An accumulation of fluff at the base of the grate will unnecessarily press the prongs of the fork thus raising the tail end when no weft is present. This will make the loom run without the presence of weft.

8. The side-play in the rocking rail and sley might cause the grate foul the fork. Sometimes, loose cranks might also cause this trouble.

9. Weft thread catching on the prongs because of inadequate tension will cause the loom to run on.

10. Bent prongs, binding of the fork through rust on the fulcrum pin, fork fulcrum worn out etc. might affect the good working of the mechanism.

11. Faulty timing of the hammer lever may cause the loom running even after the failure of weft.

12. Weak or late picking from the off side of the loom may cause the shuttle to strike the prongs and damage it.

13. Insufficient tension in the weft fail to lift the fork sufficiently causes the loom stoppage.

14. If the hammer lever begins to move too soon before the weft has had time to lift the fork tail clear, the loom will keep stopping.

Disadvantage of Side Weft Fork Motion:
Since this mechanism is situated only at the starting handle side of the loom, the stopping is affected only when the shuttle reaches the starting handle side. This will result in missing a maximum of two picks when the weft breaks or exhausts as soon as the shuttle leaves the starting handle side.

In case such a device is to be provided on both sides of the sley the cost factor and the complicated knocking off arrangement has to be thought of. 

 

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The main function of the heald shaft is as follows:

(i) It helps in shed formation
(ii) It is useful in identifying broken warp threads
(iii) It maintains the order or sequence of the warp threads
(iv) It determines the order of lifting or lowering the required number of healds for a pick. In other words it helps in forming the design or pattern in a fabric.
(v) It determines the warp thread density in a fabric, i.e. the numbers of heald wires per inch determine the warp thread density per inch.

2 .Sley or lay
It is made of wood and consists of the sley race or race board, reed cap and metal swords carried at either ends. The sley mechanism swings to and fro. It is responsible for pushing the last pick of weft to the fell of the cloth by means of the beat up motion. The sley moves faster when moving towards the fell of the cloth and moves slower when moving backwards. This unequal movement is known as ‘eccentricity of the sley’. It is needed in order to perform the beat up and also to give sufficient time for passage of shuttle to pass through the warp shed. The beat up of the lastly laid pick of weft is accomplished through a metal reed attached to the sley.

3 .Shuttle
It is basically a weft carrier and helps in interlacement of the weft with the warp threads to form cloth. The shuttle which is made of wood passes from one end of the loom to the other. It travels along the wooden sley race and passes between the top and bottom layers of the warp sheet. The shuttle enters a shuttle box fitted at either ends of the loom, after passing through the warp shed. A shuttle normally weighs about 0.45 kgs.

4 .Shuttle Box
It is the housing for the shuttle and is made of wood. It has a spindle and a picker. It may also accommodate the picker without spindle. The top and side of the box towards the sley race are open. The shuttle dwells inside the box for the intermediate period between two successive picks.

5 .Picker
The picker is a piece made either of leather or synthetic material. It may be placed on a spindle or grooves in the shuttle box. It is used to drive the shuttle from one box to another. It also sustains the force of the shuttle while entering the box.

6 .Reed
It is a metallic comb that is fixed to the sley with a reed cap. The reed is made of a number of wires and the gap between wires is known as dents. Each dent can accommodate one, two or more warp ends. The count of the reed is decided by the number of dents in two inches. The reed performs a number of functions which are enumerated as follows:

(i) It pushes the lastly laid pick of weft to the cloth fell
(ii) It helps to maintain the position of the warp threads
(iii) It acts as a guide to the shuttle which passes from one end of the loom to the other.
(iv) It determines the fineness of the cloth in conjunction with the healds.
(v) It determines the openness or closeness of the fabric. 

There are various types of reed such as ordinary reed, gauze reed, expanding reed, V reed etc.

7 .Warp Beam
This is also known as the weaver’s beam. It is fixed at the back of the loom. The warp sheet is wound on to this beam. The length of warp in the beam may be more than a thousand metres.

8 .Back Beam
This is also known as the back rest. It is placed above the weaver’s beam. It may be of the fixed or floating type. In the first case the back rest merely acts as a guide to the warp sheet coming from the weaver’s beam. In the second case it acts both as a guide and as a sensor for sensing the warp tension.

9 .Breast Beam
It is also known as the front rest. It is placed above the cloth roller at the front of the loom and acts as a guide for the cloth being wound on to the cloth roller. The front rest together with the back rest helps to keep the warp yarn and cloth in horizontal position and also maintain proper tension to facilitate weaving.

10 .Cloth Beam
It is also known as the cloth roller. The woven cloth is wound on to this roller. This roller is placed below the front rest. It is also known as the cloth roller. The woven cloth is wound on to this roller. This roller is placed below the front rest. 

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Identification of End (Warp) & Pick (Weft) :
Warp and weft yarns have different demands placed on them and may differ in their structure or fiber type. Thus, a fabric may not have the same performance characteristics for warp and weft. The warp must withstand the high tensions of the loom and the abrasion of weaving, so the warp yarns are stronger and more uniform with higher twist. Filling yarns are more often fancy or special-function yarns such as high-twist crepe yarns, low-twist napping yarns, or boucle yarns. We can define end and pick in the following way.

End:
1. An individual warp yarn. A warp is composed of a number of ends. 2. An individual sliver, slubbing, roving, yarn, thread, or cord. 3. A short length or remnant of fabric.

Warp (End) and Weft (Pick)

Pick:
In a woven fabric, the yarn running from selvage to selvage at right angles to the warp. Each crosswise length is called a pick. In the weaving process, the filling yarn is carried by the shuttle or other type of yarn carrier. The picks interlace with the warp ends to form a woven fabric.

Identification of End & Pick: 

Differentiating between warp and weft is possible by carefully examining both the fabric and the length-wise and crosswise yarns.

1. Most fabrics have lower elongation in the warp direction.
2. The warp yarns lie straighter and are more parallel in the fabric because of loom tension.
3. Fancy or special-function yarns are usually in the filling direction.
4. Fabric crimp is usually greater for weft yarns since they must bend or flex over or under warp yarns due to the way the loom operates.
5. Fabric characteristics may differentiate between the warp and weft directions. For example, poplin has a weft rib and satin has warp floats.
6. The selvedge always runs in the lengthwise (warp) direction of all fabrics.
7. Warp yarns tend to be smaller, are more uniform in structure and appearance, and have higher twist.

Warps Protector Motion

To protect the warp yarn/reed/shuttle in case of trapping the shuttle in the shed is the function of warp protector motion. The shuttle failure or the shuttle trap inside the warp shed may cause many broken ends during the forward movement of the sley. In order to prevent this from occurring a device is necessary to stop the loom whenever the shuttle fails to reach the shuttle box.

Types of Warps Protector Motion.
Warp protector are two types

1. Loose reed warps protector
2. Fast reed warp protector

Now, we discuss only Loose reed warps protector .

Loose Reed Warps Protector:
The principle of the mechanism is that the reed is forced out of its support whenever the shuttle is trapped in the shed and this backward inside movement of the reed will cause a knock off device to act and stop the loom.

The reed A is held at the top of the slotted reed cap B. the bottom part of the reed is held firmly against the raceboard C by the reed case D which extends the whole width of the reed. This reed case is connected to a stop rod S by means of several brackets. The stop rod also extends the width of the sley and it is fixed to the sley below the raceboard. There are two, three or four frogs E, depending upon the width of the loom, mounted on the stop rod. In front of each frog there is a heater F fixed by means of a bracket to the breast beam.

Loose reed warps protector

Where,
A= Reed
B= Reed cap
C= Race board
D= Reed case
E= Frog
F= Heater
G= Bowl
H= Bow spring
J= Stop rod finger
S= Stop rod
K= Serrated bracket
L= Starting handle

During the normal working of the loom there are three devices to keep the reed firm:

• Frog E engaging the heater F.
• Bowl G riding the bow spring H.
• A light spiral spring I.

Frog and Heater:
When the sley moves forward the frogs slide under the heaters thus locking the reed firmly for a good beat up of weft.

Bowl and Bow Spring:
During the backward movement of the sley the bowl G rides on the flat bow spring H and keeps the reed firm to enable the smooth flight of the shuttle during it traverse from one box to another.

Spiral Spring:
The light spiral spring keeps the reed case tensioned all the time. A stop rod finger J is also mounted on the stop rod, and facing this finger is a serrated bracket K fixed to the starting handle L. When the shuttle is trapped in the warp shed it presses against the base of the reed during the forward movement of the sley, with the result the reed swung backwards turning the stop rod S through the reed case. When the stop rod is turned all the frogs and the stop rod finger are raised. During further forward movement of the sley the frogs ride over their respective heaters and the stop rod finger hits the serrated bracket and stop the loom. The frogs riding over the heaters will enable the reed case to move backwards easily.

The loose reed motion is only intended for light and medium weight fabrics. It is therefore necessary that the spiral spring I should only be strong enough to prevent the reed case from vibrating during running of the loom. If it is too strong the shuttle has to exert a greater force to push the reed back, which means more strain on the warp threads. Delicate warp used for light weight fabrics will not stand such strains with the result more warp breakage will occur. 

 

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Center weft fork motion check the presence of weft in each pick. It is situated at the middle of the reed. It is used for producing high quality fabric. Basically, it is used in modern conventional loom.

Working Process of Center Weft Fork Motion
This motion has been designed to feel the weft thread every pick and stop the loom in case the weft thread breaks or runs out, no matter which way the shuttle is running at the time. The shuttle can be housed in any one of the boxes. 

 

Center weft fork motion

Where,
A= Weft fork

B= Lever

C= Connecting rod
D= Knock off arm
E= Cam
F= Projecting stand
G= Knock off lever
J= Flat spring

It is for this reason the mechanism is situated in the center of the race board. The loom is brought to a stop before the beat-up action takes place. It is not necessary that the shuttle should always be in the starting handle side box for effecting the loom stop. Therefore this device will not allow two missing picks before the loom stops. This device is useful for looms weaving pick and pick colored wefts. If there are two different colored picks weaving alternately and if one of the colored thread is broken, it is necessary to stop the loom immediately before another colored thread of the second pick is inserted in the shed. It also helps to weave faultless cloth free from pick finding marks or broken picks. With effective braking system, the loom can be stopped dead on the broken pick. In addition a device is incorporated to turn back the loom, opening the previous shed with a broken pick laid inside, so that the weaver can rethread without making any bad mark on the cloth. Centre weft fork motion is, therefore, suitable for weaving fabrics made of filament yarns, e.g. polyester, nylon and yarns made out of other delicate fibers. Though several types of centre fork motions are designed the basic principle remains the same. A channel is cut in the raceboard, at or near the centre depending upon the length of the weft from the shuttle eye to the fork and also on certain attachments like pirn changing and box changing. The weft fork with prongs is fulcrummed on a bracket fixed to the front of the sley. When the sley moves towards the back centre, the fork tilts upwards through the warp far enough to allow the shuttle to pass underneath and the weft is laid under the fork. During the forward movement of the sley the fork drops downwards upon the weft and is held from moving further down in the channel by the grid effect of the warp threads belonging to the bottom shed, supporting the weft thread against the light pressure of the fork. In this condition the weft fork holds the knock-off arm away from the knock-off lever. The fork is pulled out of the shed just before the reed reaches the fell of the cloth for the beat up of the weft. If, however there is no weft underneath the fork as the sley moves forward, the fork drops into the channel in the sley and the knock off arm D is moved into contact with the knock-off lever G thus stopping the loom. One important device which is necessary in all the centre weft fork motions is to enable the loom to restart after the weft replenishment without the presence of a weft thread across the shed. This means that the knock-off arm should be made ineffective for the first pick without the help of the weft thread.

A shield has been provided in all such motions to enable the sley to move forward, on the first pick, without stopping the loom. On successive picks the shield moves out to enable the weft thread to act as a preventive device to knock-off the loom.

The center weft fork motion shown in figure has two important parts. The first part, the weft fork, is attached to the sley and moves with it. The second part consisting of, cam, knock-over lever, brake lever, the rod that connects the mechanism to the shipper lever, all attached under the breast beam, which is stationary.

The weft fork A is pivoted in a stud and is connected to a lever B pivoted in a bracket on the lower end of the stand by a connector rod C. An adjustable knock-off arm D which is connected to the lever B slides over the face of the cam E projecting from the breast beam assembly. The knock-off arm D is held against the cam face by a special spring S on the opposite end of the lever.

During the backward movement of the sley the fork is raised, and during the forward movement it drops down. The projecting stand F mounted under the breast beam has a knock-off lever G on one side and a first pick shield M on the other. The knock-off lever projects above the lug stop of the stand F. If the weft thread is not holding the fork from falling down in the sley channel, that is the absence of the weft, the knock-off arm D will follow the cam E during the forward movement of the sley and engage the knock-off lever G. When the knock-off lever is pushed back by the knock-off arm, a round bracket on the lower part of the lever will press a brake tube lever, turn the brake and stop the loom.

Immediately the loom is knocked-off, a flat spring J clamped to the shipper shaft pushed back the first pick shield through an intermediate lever N. Since the shield M is held by pins that follow the curved shape of the cam slots, a push at the back will enable it to rise above the top of the stand F and also above the top of the knock-off lever G. When the loom is started after the repair of the broken pick, the flat spring is moved away from the lever N but the shield F stays in position owing to the dwell in the cam slots. On the first pick the advancing knock-off arm, strikes the end of the cut out O in the shield pushing it forward into the normal position.

Problems of Center Weft Fork Motion:

1. Weft curls in the middle of the cloths.

Causes:

a) The prongs of the forks press the weft through the bottom shed.
b) Early or strong picking.
c) Irregular loom speed.

Remedies:

a) Correct tensioning of weft in the shuttle.
b) Shortening the prongs a little in case of rayon weft.
c) A longer setting for the prongs in case of nylon weft.

2. Loom stopping constantly although weft has not broken.

Causes:

a) Slack warp.
b) Slack weft.
c) Fibrous or hairy warp.

Remedies: Correct tensioning of warp and weft. 

 

Read more: http://textilelearner.blogspot.com/2012/04/center-weft-fork-motion-working-process.html#ixzz2OCX58ewR

Weaving Resistance:
When warp and weft are interlaced in a fabric then they oppose to each other due to static electricity or other factors. This opposition or resistance is called weaving resistance. Weaving resistance or its counterpart, beat up force, is at the center of the relationship between pickspacing, yarn properties and loom settings. 


Factors Affecting Weaving Resistance:
In case of pick spacing requires a larger beat up force or, for a given spacing, a thicker weft requires a larger force. It is suggested that a discontinuous relationship between pick spacing and weaving resistance but that has not been confirmed by experiment - possibly because irregularities in yarn properties would smooth the discontinuities. Loom settings are also known to influence the relationship. 

Weaving resistance

 There are some factors which affecting weaving resistance are given below:

• The effect of warp tension
• The effect of shed balance
• The effect of shed timing
• The effect of cloth fell distance and beat-up force
• The effect of weave

The Effect of Warp Tension:
There seems to be general agreement that increasing warp tension increases weaving resistance. Theoretically increased tension increases inter yarn forces and hence the effect of friction. . However, the influence seems to be fairly small, both indicating a rise of about 10% in weaving resistance for a doubling of the basic or average tension.

The Effect of Shed Balance:
They show a very significant effect of tension ratio in the two warp sheets on weaving resistance. It had earlier been reported by Bramma21 and Snowden8 that an unbalanced shed was helpful in achieving high setts. Jederan22 considered the effect on weaving resistance and, according to the English abstract of his Hungarian paper, found that "contrary to what is generally accepted" no reduction resulted. Mallah20 had reported that peak warp tension was reduced when the shed was unbalanced and both Yehia11 and Leung in their limited experiments, from which the present study has evolved, showed a significant reduction in beat up force when the shed was unbalanced. Yehia's work suggested that the effect was influenced by shed timing. Leung used a crude method of unbalancing that avoided Ito's "kinematic" effect and was incidentally independent of shed timing; he inserted a heavy roller like a lease rod in the warp so that each of the slacker and tighter sheets was always composed of the same threads. With the more normal arrangement, using a raised back rail to unbalance the shed, each yarn is alternately in the slack and tight sheet of the open shed; but when the shed is closed, i. e. crossing, it is by definition also balanced.So it would be expected that the timing of the shed relative to beat up would affect the weaving resistance.

The Effect of Shed Timing:
In view of what has already been said, it is not surprising to find contradicting statements about shed timing. Greenwood said the effect was so small that its significance must be doubted. Badve found a difference but not all his results show the effect consistently. Yehia's results suggested a "normal" timing gave least resistance. to a small extent. Theoretical studies suggested that it was not so much the effect of timing (and hence shed angle at beat up) on the actual beating up that mattered, but its effect in opposing slipping back. In industry it seems generally to be accepted that an early timing enables picks. to be beaten more closely. So a confused picture emerges and it is clear that a more detailed and more precisely defined range of settings should be used than the "late", "normal" and "early" often adopted.

Cloth Fell Distance and Beat-up Force:
Although cloth fell distance is not a basic or independent parameter (except when it is set at the start of a period of weaving) it is a visible feature that forms an important link in the relationships between other variables and so has received some attention. Badve set out to measure c. f. d. in order to test Greenwood's equations and pointed out that in developing the beat up force it is not the fell displacement in absolute terms that is related to beat up force, but the displacement relative to that which would occur due to shedding, back rail movements, etc., in the absence of beat up. When he had developed a means of measuring that relative movement, the modified c. f. d. or, as he termed it, the "interference" between reed and fell, was still often greater than seemed necessary for the force, even when true load/extension curves were used instead of constant moduli in the relationship. These results led him to suggest slipping back of picks might be responsible, so that the cloth fell was not clearly defined but was rather a region that was neither warp nor cloth. Greenwood found some evidence that c. f. d. was influenced by loom speed being slightly increased when the speed was reduced. That might be explained in the elastic moduli being slightly lower for slower rates of strain but it could also be an effect of fell movement rather than displacement by the reed.
 

The Effect of Weave:
For given yarns it seems obvious that, just as maximum possible sett depends on the density of intersections in the weave, so weaving resistance would also depend on that density. Galuszinski, working on plain weave derivatives, claims to show a direct simple relationship between weaving resistance and setting formula. Chen Jui-lung had previously reported similar results but expressed in less precise terms.