WARP TYING OR KNOTTING PROCESS:
The process of warp tying or knotting can be performed in two ways:
• Manual warp piecing.
• Automatic warp tying or knotting.
MANUAL WARP PIECING:
In this method of warp piecing, all the actions of the process are performed manually. A well-trained person does this job. Very high skill is required to perform this job. When the existing warp beam is exhausted, this warp beam is required to change with a new warp beam. First of all, the lease is inserted in the warp sheet of the loom before unloading the empty warp beam. The empty warp beam is unloaded from the loom and a new beam is loaded on the loom. Now piecer makes the temporary piecing stand with the help of aluminium pipes and wooden blocks. The warp sheet of the new warp beam is passed over the aluminium pipe. The ends of leases of the new warp sheet and warp sheet of the loom are tied on both sides of the temporary piecing stand. The piecer stands between the whip roller and the aluminium pipe. He takes a bunch of each warp ends from both warp sheets from one side of the machine. Now the piecer ties these bunches on his waist. He selects one end of the new warp beam and one end of the warp sheet of the loom by hand. He cut both ends as per the requirement with the help of a sharp knife. Now both the ends are twisted together to make a joint. This action is repeated again and again till the completion of piecing. The lease helps to separate the ends in the correct sequence and prevents the crossing of ends to each other.
DISADVANTAGES OF MANUAL PIECING:
Manual piecing has many disadvantages, which are given below:
• Manual piecing is a highly time-consuming process.
• The end’s joints are not too strong, the twisted joints are opened during pieced warp pulling.
• The warp tension is not equal on both sides of the warp sheet after piecing.
• High-end breakage occurs due to uneven warp tension when the loom is restarted.
• Loom efficiency is reduced.
• Extra-person may be needed to draw broken ends.
• There may be chances of wrong drawing or wrong denting.
• There may be pattern mistakes in the warp.
• High-end breakage during pieced warp pulling can cause the end crossing.
AUTOMATIC WARP TYING OR KNOTTING:
The warp tying or knotting machine is a very important machine in the weaving shed when a style or fabric design is repeated for a long time on a loom. When the design is repeated, fresh drawing-in of warp is not required. The ends of the new warp beam are joined with the ends of the warp sheet of the loom with the help of automatic warp tying or knotting machine.
The warp knotting is completed in two following steps:
DRESSING OF WARP SHEET:
The empty beam is unloaded from the loom and is replaced with a new warp beam. Now knotter sets the knotting stand behind the loom. First of all, the warp sheet of the new beam is taken over the knotting stand then the ends are spread out on the stand. A brush roller holds the warp sheet temporarily. Now the lease rods are inserted into the warp sheet and the ends are tightened by a rotating brush roller. When all the ends of the warp sheet get tension properly, the tail of the warp sheet is clamped by clamping stripes. Now knotter separates all the ends with the help of a dressing brush. The brush roller is rotated after each ends separation. The process of ends separation is repeated till the completion of proper end separation. Now the ends of the warp sheet are brought to their proper place with the help of a half reed (comb). When all the ends get their proper places, the warp sheet is fixed on the stand with the help of the sheet fixing clamp. Now the lease rods are replaced by harness strings and these are tied on both ends of the stand.
Now knotter takes the warp sheet of loom over the stand and the same process is repeated as mentioned above. Now the dressing process of the warp sheet is completed and the knotter starts the next step which is called knotting.
Knotter mounts the knotting machine on the stand. he fixes the machine by locking the gears with a toothed rack. Now the lease strings are passed through the lease pipe and are tied on the right side of the stand. The power supply of knotting machine is connected to the supply point. Knotter starts the machine by pushing the start button. The machine automatically joins the ends of both warp sheets.
Structure and working of knotting:
The common components and working of knotting machine are given below:
An electric motor is mounted inside the machine. The toothed pulley is mounted on the motor rotter shaft. The motion is transmitted to the mechanism by a toothed belt. It is a D. C. motor. 180 volt A.C. supply is used to run this motor. A voltage stabilizer is used to supply constant voltage to the motor. This A.C. supply is converted into D.C. automatically by a voltage convertor in the machine.
All the functions of knotting machine are controlled electronically. The speed of the machine is increased or decreased by rotating a knob mounted on the top of the machine. If a machine fails to select the end of the top or bottom layer, feelers send a signal to the control unit and stop immediately. Start, stop and inching push buttons are mounted on the top of the control unit card. All the machine operations are initialized by these push buttons.
A knots counter is mounted on the top of the machine, which counts the number of knots completed during the process.
Machine travelling gears:
These gears are mounted in the bottom of the machine. When the knotting machine is kept over the stand, these gears are engaged with a toothed rack of stand by pressing the gear locks. When the lock is pressed, the travelling gear comes downward and is engaged with the teeth of the rack. The toothed rack is fixed. When the machine becomes started, the gears also rotates. The machine travels on the rack with the help of rotating gears on a toothed rack.
It is a very important part of the knotting machine. Two needles of the same size are used during the process. The main function of the selection needle is to select a single end from each layer of the warp sheet. The top needle makes a selection of ends of top warp layer and bottom needle makes the selection of ends of the bottom warp layer. These selection needles are needed to change when warp count changes. Different sizes of selection needles are put in reserve according to various types of warp counts to be used.
The function of the feeler is to send the confirmation of the selection of ends to be knotted. If proper selection is not performed, the control unit stops the machine immediately. In the knotting machine, two feelers are used, one for the bottom layer and the other for the top layer. These feelers move by the the pressure of yarn.
The main function of the yarn carrier is to carry the selected ends in between the yarn grippers. When the selection process happens, the top selection needle pushes the end downward and the bottom selection needle pushes the end upward. At the same time, the yarn carrier starts to move toward the yarn grippers. The top and bottom hooks of the yarn carrier catch the selected ends and carry them into the yarn grippers.
The main function of yarn grippers is to hold the selected ends during knotting. Two grippers are used in the knotting machine. The top gripper holds the end of the top layer and the bottom gripper holds the end of the bottom layer. The pushing springs are used to create enough gripping pressure between the gripping plates of the yarn gripper. The gripping pressure can be adjusted with the help of a screw. There is a need to change gripping pressure when warp count is changed.
The function of the main cutter is to cut the tails of the end after the gripping of the ends by the gripper. There are two cutters used in the knotting machine. These cutters work positively. The top cutter cuts the tail of the top end and the bottom cutter cuts the bottom end.
When the extra length of both ends is cut, the knotter hook starts to rotate. It wraps both the ends together with it and makes a loop.
Knotting needle: The knotting needle is fitted in the hollow pipe of the knotter hook. It makes in and out movement during operation. When the loop is formed, the needle comes out and catches the ends. Now the knot is completed.
When the knotting is completed, knotted ends have extra tail length. It is very difficult to pass these knotted ends through the eye of heald wire and dent of reed. It needs to cut the extra length of tail. The waste cutter performs this job.
The lease pipes are used to select the ends according to the sequence. The lease pipe makes up and down movement and separates the ends according to the sequence.
PRECAUTIONS OF KNOTTING PROCESS:
Knotting or tying is a very delicate process. Any negligence in the process may be dangerous in weaving. Following precautions should be taken during the process:
• The dressing of both warp sheets should be done perfectly.
• All the ends should have enough and equal tension.
• There should be no crossing ends when the warp sheet is being clamped.
• Each warp layer should be clamped properly. There should not be any slippage between clamp and yarn.
• The tension on the warp sheet should be according to requirement.
• The length of the tail of knotted ends should be adjusted properly by adjusting the main cutter.
• The knot should be fully tightened to prevent its slippage. If a knot is loose, the length of knotting needle should be adjusted by making a slight band in it.
• The gripping pressure should be adjusted properly.
• The edges of the main cutter should be enough sharp to cut the ends.
• The selection needle should choose precisely. Incorrect selection may cause double selection of ends or selection failure.
• The waste cutter should work properly. Improper working of it may cause to break the ends.
• The quality of knots should be checked manually after a regular interval of time.
• Cutting action of the main cutter should be clean. If there is any fibrous part at the tail of the end, it may be caught by grippers.
• Yarn feelers should work properly.
• Machine should be cleaned with kerosene oil. The machine should be run in a tub filled with kerosene oil for half-hour.
• The oiling of the machine should be properly. For the oiling of the machine, it should be run in the tub filled with sewing machine oil (22 number oil) for half-hour.
• Machine should be cleaned with compressed air before knotting each time.
• Moving parts of the dressing stand should be oiled properly.
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