Loom Break Mechanism

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

Picture: Electrical Break Mechanism (Picanol Delta Air-Jet Loom)

Clutches:

A clutch is a form of connection between a driving & a driven member in the same axis. It is so designed that the two members in the same axis. It is so designed that the two members may be engaged or disengaged at will either by a hand operated device or automatically by the action of some power driven device. The common types of clutches which are used in weaving machines are:

1. Friction Clutch
2. Electromagnetic Clutch

Friction Clutch:

A friction clutch is used in the transmission of power of shafts & machines which must be started & stopped frequently as in the case of weaving machines. The force of friction is used to start the driven shaft from the rest & gradually brings up to the proper speed without excessive slipping of the friction surfaces. In operating such a clutch the following care should be taken.

• The friction surfaces should engage easily & gradually bring the driven shaft up to a proper speed.
• The proper alignment of the bearings must be maintained & it should be located as close to the clutch as possible.
• The heat generated due to friction should be rapidly dissipated & tendency to grab should be at a minimum.
• Lateral displacement of the frictional clutch involves forces of high magnitude resulting in wearing of main shaft bearings. This can be avoided by using expanded clutches.
• The surfaces should be backed by a material stiff enough to ensure a reasonably uniform distribution of pressure.

The friction clutches are of the two types;

1. Disc or Plate Clutches
2. Cone Clutches

Disc or Plate Clutches:

In a disc or plate clutch as shown in fig.12.4 the driver A is rigidly keyed to the driving shaft B by means of a sunk key C & feather key E, so that it can move along the shaft. The driven member is faced with a friction lining F & is held against a driven member by means of axial pressure provided by a spring. The axial pressure exerted by the spring provides a frictional force in the circumferential direction when the relative motion between the driving & driven members tends to take place. If the torque due to this frictional force exceeds the torque to be transmitted, then due to this frictional exceeds the torque to be transmitted, then no slipping takes place & the power is transmitted from the driving shaft to driven shaft H.

Cone Clutch:

A cone clutch has a conical friction surface as shown in fig.12.5. The driver which is keyed to the driving shaft by a sunk key has an inside conical surface or face which exactly fits into the outer side of the conical surface of the driven member. Like the plate clutch, the driven pulley is mounted on the shaft with a feather key & the two conical surfaces can be engaged or disengaged by means of starting handle through levers. The contact surfaces of the clutch may be metal to metal, but more often the drive pulley is lined with felt or cork.

Electromagnetic Clutch:

With the conventional looms, the drive to clutch is usually controlled by means of a starting handle through a train of levers. The knocking of the starting handle should be done in such a manner that the loom is stopped with the shuttle in the starting handle side & the headls are at top centre in the event of a warp breakage or between bottom & back centre in the event of a weft breakage. With the high speed looms, it is very difficult to judge when to knock-off.This difficulty can be overcome by using an electrically controlled clutch unit which is controlled by means of a push button.

Because of the following advantages, it has gained wide acceptance for high speed looms.

• No physical strain is required to handle the weaving machine.
• Electric power transmission enables the controls to be operated anywhere on the weaving machine. The control pluses given by the stop motions & safety devices of the weaving machines are easy to connect. Thus when the weft breaks or stop motion button is pressed, the loom is stopped at the back centre position, but when the warp breaks, it is stopped at the top centre so that drawing-in can take place without any further adjustment of the loom.
• It ensures a quick & accurate start.
• The loom can be run at a normal speed, or slow speed (inching) to a predetermined position. There is a provision to reverse the loom. The reversing motion takes the loom to the back centre for starting. Further, reversing can be done for a few picks for the purpose of pick finding. It may be mentioned that majority of the shuttles-less weaving machines cannot be operated in the reverse direction because they are equipped with unidirectional cams.
• Variation in the loom speed during picking is less. The principle of working of electromagnetic clutch drive (2) is explained with reference to fig.12.7.
• When the loom is to be started the pressing of starting button completes an electric circuit & energizes clutch solenoids so that the plate which is fixed on the main shaft spline is attracted to the driven fly wheel. This will result in rotation of a planet gear through the main shaft gear & thus the loom driving pinion will be rotated.
• When the loom is to be stopped, the clutch solenoid is de-energized & the brake solenoid is energized & the break solenoid is energized so that the plate is taken away from the fly wheel on to the fixed motor casing. The timing is such that the loom is brought to rest exactly at the desired crank position depending upon the cause of stoppage.
• When the loom is to be reserved, reversing solenoid is energized. Instead of the fly wheel gears driving a shaft gear with an additional tooth to given a forward drive, the shaft position is adjusted & the drive occurs on a gear with one tooth less so that the loom will run in reverse.