Warp protector motion
The function of the warp protector motion is to stop when the shuttle fails to reach the shuttle box during picking. 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. The causes for such a failure might be due to: slack ends, improper opening of the warp shed, wrong shed, wrong timing of picking, mechanical failure of parts such a broken picking straps, loose or badly worn picking tappets, picking shaft springs broken, faulty pickers, odd sized shuttles, shed too low and stop rod brackets loose.
There are two types of warp protector commonly available for shuttle looms.
o Loose reed warps protectors.
o Fast reed warps protectors.
On high speed shuttle looms, electromagnetic warp stop motions are used.
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.
During the normal working of the loom there are three devices to keep the reed firm:
o 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.
Fast reed warps protector:
Fast reed warp protector is used for heavier fabrics because it works on the principle of fixed reed and the protector mechanism is operated by the shuttle box swell that reacts directly through the stop rod dagger to knock off the loom. Also, for heavier fabrics the beat up of weft by the sley should be very firm.
The stop rod A which runs beneath the sley has two fingers B fixed to it; one finger on each side of the shuttle box. These fingers with adjustable nuts are kept pressed against the swell C. To the same stop rod are fixed two daggers D, one each side of the shuttle box. The daggers face a sliding frog E mounted on the side frame. The sliding frog on the starting handle side carries the brake lever F at the rear and at the front it contacts the adjustable bolt that knocks of the starting handle. When the shuttle enters the box at either side, it passes the swell which makes the daggers rise above the frogs and the loom continues to run. If the shuttle fails to reach the box or if it rebounds owing to insufficient checking, then the swell will not be pushed back sufficiently to rise the daggers clear off the frogs with the result the daggers will dash against the frogs and push it backwards. Then the sliding frog will knock off the starting handle and the loom will stop. At the same time the brake lever F pulls the brake close on the brake drum to an almost instantaneous halt of the loom. The shock of the sudden stoppages taken by the two strong vertical springs S which are connected to the frog through a bolt G.
While setting the frogs with respect to the distance from the daggers, it is better to set so that the sley comes to a halt before the crank has passed the top centre. The sudden impact of the dagger on the frog is commonly known as bang-off. Sometimes frequent bang-off will cause the parts that are taking such force of the shock to fracture.
Electromagnetic warp protection:
The mechanism consists of a magnet in the end of the shuttle opposite to the shuttle eye. A coil B is mounted slightly off the centre position in the sley. As the shuttle passes over the coil, a pulse generated which is fed to an electrical control unit G. a second pulse is generated by a coil C and magnet D mounted on the disc E on the bottom shaft F and this occurs at a fixed time in each loom cycle. Under normal working these two pulses synchronize. A late passage or non-passage of the shuttle causes a break in the sequence of the two pulses. The solenoid then activate and then knock lever I will then be positioned in the knock off and catch and the loom will be brought to rest. The position of the knock-off catch depends upon the width of the loom, loom timings, speed of loom.
Advantages:
- Banging-off shock is eliminated since there more time is available for stopping of the loom.
- Unlike loose and fast reed methods of warp protection, there is no possibility of damage to the fell of the cloth since the loom is stopped before shuttle trapping can occur.
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