LOOM FAULT:-

LOOM FAULT:-

Weaving Fault:-

A loom must be correctly set and before weaving. A faulty loom always produce a faulty cloth . Weaving faults or defect are generally grouped under two heads:-

(1) Loom faults or Mechanical defects, and

(2) Cloth faults or Fabric defecys.

Mechanical Defects or Loom Faults:-

The common loom faults or mechnical defects msy be summed up as following:-

(1) Reed marks.

(2);Shuttle flying-out.

(3) Shuttle trapping in the warp shed.

(4) Loom banging-off.

(5) Loom stopping.

(6) Weft cutting.

(7) Bumping and

(8) Cop knocking -off or splitting.

Adjustments of Looms Parts.

By systematic observation of different motions and by correct adjustments of loom parts, a supervisor or a jobber can readily trave the source of trouble in a loom . Having a systematic plan, He can gain a better weaving result and a higher efficiency of loom productions. It is essential to check up the moving parts in the loom before actually starting it to work.

(i) A general tightening of nuts , bolts, setscrews ,straps , picking cam, etc. will reduce vibration and wear & tear of loom parts. In case of banging-off or frequent stopping of a loom , the lug strap requires tightening and the protector blade requires proper adjustment. Dobbies and Jacquards should also be repaired, cleaned and oiled before starting the starting the loom with a new warp.

(ii) The setting and timings of a loom should be set to standards, as any departure may often be the source of trouble.

(iii) The loom consist of certain Positive and other negative motions. The chief non-positive or negative movment is the shuttle. It should always be seen that the shuttle passes through the shed smoothly and in due time. Inspite of the best attention various causes , including deficiency in shed, broken cam, obstruct the movement of the shuttle.

(iv) The emery ( sand)roller, the reed holder and gears should also be carefully examined.

It is sometimes found that one cause goes to create diverse loom faults ,as for example, shuttle rebounding may cause loom banging-off, stitching, cops knocking-off , black pick, weft cutting, etc. Sometimes of the causes remedies of loom faults are discussed below.

(1) Reed Marks and Cover of Cloth:-

Reed marks are cause in the fabrics due fo damaged reed, bent reed wires, wrong denting eyc. If a coarse reed is used in weaving a finer sort, reed marks will also be apparent all over the fabric.

The position of warp line in s loom has an important effect on the production of cloth, since the height of top and bottom lines from the central line of the shed governs the relative strains pit upon the warp ends. If the warp threads move equal distance at the top and at the bottom lines from tje center , the strain on both the lines of shed will be equal. If this measure is adopted in a plain weave , the warp threads will lie in pairs in the order of denting, causing a hard and reedy appearance in the cloth showing this appearance is a 'bare cloth' . This is a serious defect in plain cloths.

COVER OF CLOTH:-

(i) To remedy reed marks in the cloth , the back rest is raised without altering the position of healds. The top line of shed will then be smaller and slack , and the bottom line is shed is bigger and strained . This method of alternate slackening and tightening the warp ends in succession picks is termed 'troughing the shed’. By this it will spread the warp yarns that form the top line of shed at the time of beating-up. The ends will be evenly distributed and the cloth will be soft and smooth. This appearance of the cloth is known as 'cover '. It should be remembered that the warp line cannot be raised beyond a certain limit, because the increased strain on the bottom line of shed will cause them to break. Secondly , too slack top shed will obstruct the passage of the shuttle and will cause 'stitching' defect in the cloth and shuttle flying out. Troughing the shed is sometimes adopted for twill and sateen weaves to make the effect more prominent when the method of ‘troughing the shed' is adopted in looms.

(ii) With a plain weave, beating-up with a crossed shed and producing a slack top line and a tight bottom line to obtain good ‘covered cloth’, it becomes necessary to make the shed early, so that no reed mark will be noticeable. In tappet looms for plain weave a shed is full open when the crankshaft is 30° passed the front centre, that is, long before the pick is effected, which takes place while the crank is on the bottom centre. The dwell of tappet is for one-third of a pick it more to suit the weave and for distribution of warp threads. These are done so that no reed mark is noticeable on the cloth .

(iii) 'A tugger cord or strap' runs from the front lease rod to the top of the reed cap cover the healds and lifts the warp to slacken the top line and to tighten the bottom line of warp threads at time beat-up for equidistribution. Thus a tugger cord, an increased dwell of tappet and an early shedding spread and fill between two warp threads and give good 'cover' to a plain cloth.

(2) Shuttle flying-out;-

In a negative picking, a shuttle is mot positively controlled , when travelling over the sley race at a high speed through the divided warp. A slight defect in the shuttle or on the box or on the race board or any obstruction will therefore, deflect the shuttle from its normal course of journey and may cause it flying-out of the loom. One point must be remembered that the size of the shed must be suitable and large enough for the passage of the shuttle without any obstruction. The bigger the shuttle, the bigger will be the depth of shed required. Again the bottom line of shed must be resting on the race board to minimise the cause of shuttle flying upwards. A careful attention must be given to fibrous yarns, long knots, small sheds , uneven sley race , worn pickers slack warp, high bottom shed line, position of swell etc. to minimise the risk of a shuttle flying-out of the loom.

(3) Shuttle Trapping in Warp.

(1) The warp threads , smashed on shuttle trap signify breakages of a large number of warp ends and occur due to an accident in the loom. The various causes shuttle trapping in the include a broken shuttle, shuttle tonge flowing up, broken picks , faulty protector blade, tight warp , large shuttle etc.

(2) The amount of damage in warp ends depends on various conditions, such ad, strength of warp , tension and the sort of cloth . On a fast reed loom , a smash may occur , if for any reason the stop rod and frog failed to arrest the sley, while the shuttle was still in the shed . On a loose reed loom, a smash would happen , if the reed failed to wing outwards when the shuttle was in the shed. In either of these causes, the reed will come forward and will come forward and ends will be broken probably for a width equally the length of the shuttle. A shuttle trapping in the shed causes a loom banging-off.

(3) Loom Banging-off:-

The shuttle fails to reach the opposite box when it receives an obstruction in its journey, orb motion imparted to it is insufficient. Consequently, the stop rod tongue or blade engages with the frog to stop the loom and the brake is applied to the crankshaft. A sudden stoppage of the loom by the application of a safety device, either in the fast reed or in the loose reed type, is commonly known as 'banging-off’' . But this fault is more frequently experience in fast reed than loose reed looms.

The shuttle fails to reach the opposite box when it receives an obstruction in its journey, orb motion imparted to it is insufficient. Consequently, the stop rod tongue or blade engages with the frog to stop the loom and the brake is applied to the crankshaft. A sudden stoppage of the loom by the application of a safety device, either in the fast reed or in the loose reed type, is commonly known as 'banging-off’' . But this fault is more frequently experience in fast reed than loose reed looms.

(a) Weak or short picking.

(b) Faulty shedding.

(c) Incorrect timing .

(d) Defect in safety motion, and

(e) Defect in shuttle.

(a) Weak or Short picking:-

This occurs due to sticky or slack driving belt: fluctuation of power: slipping on the pulleys at the time of picking: picking stick set too far backward or forward; loose driving wheels on crank and bottom shafts: picking shaft loose on its bearings or on worn out : worn out or incorrect setting of picking nose: loose or worn out picking bowl: or set too high or low.

(b) Faulty shedding.

Insufficient shedding for the passage of the shuttle, shedding , tappet getting loose on the shaft , and too tight warp threads and an unequal shedding stopping the progress of a shuttle through the shed may also cause loom banging-off.

(c) Incorrect Timing.

The loom bang off owing to driving gears insufficiently meshed: late or early or strong picking: picking boss or nose getting loose; bowl set too far: early or late shedding : or timing of shedding and picking motion not being harmonies.

(d) Defsct in Safety motion.

Although the Loomis working alright the following defect in the safety devices will cause it to work prematurely:-

finger loose on the stop rod: wide box; weak, worn out broken swell not giving forward: finger set too far back on the stop rod: stop rod tongue set too low: and stop rod bearing worn.

(e) Defect in Shuttle.

Light , narrow or worn out shuttles, shuttle rebounding in box crooked shuttles and worn swell pin are likely to occasion banging-off. 'Knocking off or banging-off' has already been discussed.

(5) Loom Stopping :-

The main cause of loom stopping are the broken warp , broken or exhausted weft in the pirn and faulty movement of shuttle, or shuttle flying-out and shuttle trapping in the shed.

(6) Weft cutting:-

Some of the various causes of weft cutting weaving are the following:-

(1) In each pick the shuttle leaves and enters the box with high velocity. A little rubbing between the trailing weft in the shuttle and any part of the shuttle box will , therefore damage or cut the weft. The weft cutting generally happenes in the off-side of a loom , nearest to the picker. Yo prevent weft cutting, ad the shuttle is being forced out of the box,is to make both the box fronts slope at the same angle at the shuttle front. Again in a side weft fatk motion the contact of the prongs with the grate when changing the cop in the shuttle, cuts the weft.

(2) The causes of weft cutting are: Too tight box, narrow shuttle box entrance: shuttle running crooked : picker binding the shuttle tightly against box front at the time of picking : unpolished sley, shuttle box or shuttle: shuttle peg chafing the weft: and shuttle running up in the box as it enters on account of faulty shedding.

(3) 'Ballooning ' or flying of the weft up and down , when the shuttle passes over the sley race , is another cause of weft cutting. To prevent ballooning of weft , fur, or flannel may be used on the side walls of shuttle for pulling a drag on weft, or specially shaped shuttle with less space in the middle may be used .

(4) Early or late picking and shedding , and loose shedding tappet cause weft cutting, aa the shed obstructs the shuttle, when it enters the shuttle bic. Weft cutting may also be caused if the temples come in contact with the reed, or if the weft fork far enters into the grid, or too thick selvedge ends ars employed, or if different selvedge and ground weaves are adopted.

(7) Bumping:-

Sometimes,inspite of proper tension on warp, the cloth continues to bump , that is , slackened considerably at the time of beat-up and becomes thin or short picks. The fault is more prevalent in heavy-wefted fabric owing to:- (i) sand roller not gripping the cloth or turning properly(ii) or the warp turning round the weaver’s beam.

Remedy:-(i) To remedy the former defect , the cloth roller is to covered a fresh and set to move uniform space with the weaver’s beam:and ,(ii) in case of the latter defect , additional weights on let-off lever to increase the the warp tension msy cure bumping.

(8) Splitting or Cops Knocking-off:-

(1) Splitting fault lies in cop winding either in the spinning or in the Preparatory department. The soft and slack-wound cops cannot withstand the recurring movements of the shuttle from one shuttle box to another and weft comes off in lumps .

(2) Splitting defect also arises due to bably pieced-up weft, or due to rough handling of weft or Cops.

(3) A high speed loom stopping abruptly, new pickers, uneven driving due to slipping belts, uneven or fluctuating speed will cause cops knocking-off or splitting. These defects may also cause a shuttle trap which is s serious fault in the loom and cause excessive wastage of materials. However, most of the faults for splitting occur before the cops are supplied to the weaving shed.

Ref:-Weaving Mechanism Book Vol.II by Pro. N. N. Banerjee.