MOTION IN WEAVING (Side fork motion & center fork motion )

AUXILIARY MOTION (WEFT STOP MOTION):-

Weft stop motion:-

Here is another type of weft stop motin which are normally used in every power loom and automatic loom. They are;

A) Side fork motion or weft break motion.

B) Center fork motion or weft break motion.

SIDE FORK MOTION OR WEFT BREAK MOTION:-

The side fork motion is an auxiliary loom motion. The main objective of side fork motion is to stop the loom immediately in case of weft insertion failure during weaving. The side fork motion is mounted at the starting handle side of the loom. Since the mechanism gets mounted at the one side of the loom so that this mechanism is called side fork motion. This side motion helps to improve both quality and productivity.

Fig.side fork motion.

Structure and working of side fork motion:-

A grid is mounted between one end of the shuttle box. The race board has grove just opposite of the prongs of the fork, the prongs get operated in this grove of the race board. The grid gets parallel to sley and infront of the prongs of the fork F. The fork F is fulcrummed at fulcrum point G. The fork is mounted on the weft fork lever K. The fork has prongs at one end and a tail hook H at another end. The weight of the tail hook side is greater than the side of the prongs. Normally the tail hook H of the fork F rests on the hammer lever notch J just because of the higher weight of the tail hook H. The knock-off lever L is mounted just behind the wef fork lever K. The other end of the knock-off lever gets touched to the starting handle M. A cam B is mounted on the bottom shaft A of the loom . The greyhound tail lever D and the hammer lever I are connected to each other and they are fulcrummed at the joint of both levers. A bowl C is mounted at the end of the greyhound tail lever D . Bowl C touches cam B.

WORKING:-

When the bottom shaft rotates , the cam B mounted on the bottom shaft also rotates with the bottom shaft. The cam impart up and down movement to the bowl mounted at the end of the greyhound tail lever. Since the greyhound tail lever and hammer lever are connected to each other and get fulcrummed at the joint of both lever, so that the cam imparts to and fro motion to the hammer lever.

The side weft fork motion performs it’s work when the sley moves to the front dead centre position. The prongs of the fork push the weft present in the shed in a normal running position of the loom. When prongs of fork strike the weft yarn , the tail hook of the fork lifts up and the loom gets to continue to running position. The cam makes one round when crank shaft makes two rounds.

If the weft yarn gets absent due to any reason during loom working, the tail hook of the fork falls down on the hammer lever. Since the hammer lever makes a to and fro motion, the hammer lever notch carries the weft fork lever with it . The fork lever pushes the knock-off lever in this situation. The knock-off lever strikes the starting handle and the starting handle gets disengaged. In this way the loom is stopped in a weft break situation.

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CENTER WEFT FORK MOTIONS OF LOOM , STRUCTURE AND WORKING:-

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

Image of center fork Mechanism. Ref by fiber2fashion

Working process of center fork motion:-

This motion has been designed to feel the weft thread every pick and stop the loom in case the weft threads breaks or run out , not matter which the shuttle is running at that time. The shuttle can be housed in any one box .

image of center weft fork motion ref by fiber2fashion.

The figure shows the center fork motion where;

A=Weft fork.

B=Lever.

C=Connecting rod.

D=Knock of arm.

E=Cam.

F=Projecting stud.

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 stop before the beat-up action take place . It does not necessary that the shuttle should always be in the starting handle side for affecting the loom stop. Therefore this device will not allow two missing picks before the loom stop. This device is useful for the loom weaving pick and pick colored weft. If there are two different colored pick weaving alternately and if one colored thread is broken , it is necessary to stop the loom immediately before another colored of the second pick is inserted in the shed. It is also helps to weave fualt less 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 in 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 marks on the cloth . Center fork motion is , therefore suitable for weaving fabrics made from filament yarn e.g. polyester, nylon , blended and yarn made out of other delicate fibers.

Though several types of center fork motions are designed the basic principle remains the same. A channel is cut in the race board , at or near the center depending upon the length of the weft from the shuttle eye to the fork also on certain attachment like pirn changing and box changing. The weft fork with prongs is fulcrummed on a bracket fixed to the front of the slay. When the sley moves towards the back center, the fork tilts upwards through the warp for enough to allow the shuttle to pass underneath and the weft laid under the fork. During the forward movement of the sley the fork drops downward upon the weft and is held moving futher down in the channel by the grid effect of the warp threads belonging to the bottom shed, supporting the warp thread against the light pressure of the fork. In this condition the weft fork holds the knock-off aim away from the knock-off lever. The fork is pulled out of the shed just before the 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 center weft fork motion 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 motion 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 threads to act a preventive device to knock-off the loom.

The center fork motion shown in the 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 , brake lever, the rod that connects the mechanism to the shipper lever all attached unde 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 them 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 raised and during the forward movement its drops down. The projecting stand F mounted under the breast beam has a knock-off lever G on one side and first pick shield in 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 of 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 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 to it rise the above the the top of the knock-off lever G. When the loom is started after the repaire of broken pick , the flat spring is moved away from the lever N but the shield F stays in positions owing to the dwell in 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.

Problem of center weft fork motion:-

1. Weft curls in the middle of the cloth .

Causes:-

(1) The prongs of the fork press the weft through the bottom shed.

(2) Early or strong picking.

(3) Irregular loom speed.

REMEDIES:-

(a) Correct tensioning of weft in shuttle. Shortening the prongs a little in case of rayon weft.

(b) A longer setting for the prongs in case of nylon weft.

2. Loom stopping constantly although weft has no broken.

Causes:-

Slack warp , slack weft, fibrous or hairy warp.

Remedy.

Correct tensioning of warp and weft.

Ref:-https://www.fibre2fashion.com

Ref:-https://www.textiladviser.com