After sizing, the sized warp beam is prepared to be placed on the weaving machine. High fashion fabrics generally have high density which increases the demand on the quality of shed opening. As a result, warp leasing is becoming more popular. Different lease combinations can be selected with the automated leasing machines.
Drawing-in is the entering of yarns from a new warp into the weaving elements of a weaving machine, namely drop wires, heddles and reed, when starting up a new fabric style. Tying-in-the new warp ends to the depleted warp is done when a pattern is not required.
A drop wire is a narrow metal sheet that that is hung in the air by the tensioned warp yarn. If the warp yarn is broken or slacken(loose), then the drop wire drops and touches a metal bar that extend along the width of the machine. This contact between the drop wire and metal bar closes an electrical circuit and shuts down the machine immediately. There is drop wire for each warp yarn.
Pinning machines are used to pin open drop wires on warps. Since the pinning speed is high (up to 200 wires per minute), these machines are economical for more than 3000 warp ends.
After drop wire, the warp yarn goes through the heddle eye (there is only one warp yarn per heddle eye). This is done according to a plan called drawing-in-draft. Then the yarn is threaded through the reed spaces. A reed space is the opening between two dents (metal) in a reed. In general, one, two or three warp yarns are passed one reed space. The reed plan specifies the number of yarns per reed spaces. The number of yarns depends on the diameter of the yarns and the dent opening; each yarn should be able to move freely up and down in the reed space independent of the other yarns.
Schematic of Drawing-in
In the manual mode of drawing-in, one person sorts the warp and the other draws it through from the other side. The sorting step can be automated by a reaching machine.
Today, the drawing-in and tying-in processes are fully automated. Drawing-in is done using robot-like machines. A special type of heddle is needed for automated drawing-in. The warp ends, taken from the warp sheet, are fed individually to the drawing in element; heddles are separated from the stack and brought to the drawing-in position; a plastic knife opens a gap in the reed and a hook draws-in the warp end through the heddle and reed in one step.
Fully automated Drawing-in machine
Automatic drawing-in increases speed, flexibility and quality in weaving preparation compared to manual drawing-in. A drawing-in rate of 50,000 warp ends per 8 hours (200 ends per minute) is possible.
Changing style means producing a new fabric style, weaver’s beam changing means going on weaving the same fabric style just replacing the empty beam with a full beam of same type.
Drawing in consists of threading the warp yarns through the drop wires, the healds and the reed. Depending on the styles of the produced fabrics and on the company’s size, this operation can be carried out manually, by drawing-in male or female works.
Tying-in:
After the depletion of a warp beam on the weaving machine, if there will be no change in design, then the drawing-in process needs not be repeated. The ends old warp beam (now a fabric beam) are cut and the ends of the of the new warp beam are tied to the corresponding ends of the beam which is called tying-in process. Then, the warp ends are pulled through the heddle eyes and reed until the knots are cleared.
A small portable robot is used on or off the weaving machine for tying-in. A typical warp typing machine can knot single or ply yarns from 1.7 to 80 Ne (340-7 tex.). They knot cotton, wool, synthetic and blend warp yarns as well as yarns of different thickness. Typical knotting of a knotter is from 60-600 knots per minute.
With a continuous filaments and bulky yarns, a non-slip double knot is recommended which can handled by knotting machine. Some automatic tying machine can knot extremely short tails of yarns (5mm). Tape yarns and monofilaments requires a slightly different typing machine. Tape yarns up to 8mm width can be tied. The knotting speed is typically 60 to 450 knots per minute. The number of warp ends to be tied together can be preprogrammed; once this number is reached, the knotter stops automatically. A dual knotting system is used on a double beam weaving machine; the knitters work from left to right and from right to left simultaneously.
The warp welding machine is used to weld the warp end layer with a plastic foil after drawing-in which provides simple insertion through the weaving machine. This results in time saving at the
machine startup. After drawing-in with a brush beam the ends protruding from the reed are aligned parallel and stretched evenly. An approximately 5cm wide plastic foil is placed on top of the lower welding bar and a longer piece of plastic foil is placed on the warp yarns above the lower piece of plastic foil. By moving the upper welding bar down, the plastic foils are welded together with the warp yarns in between.
Several points should be considered during drawing-in typing-in. Improper splicing and / or knotting can become critical to good weaving performance. The straightness of individual warp yarns and their freedom to act independently as they pass through a weaving machine are important for quality weaving. Yarns that are crossed and tangled cannot proceed without excessive stress and yarns that r restricted or influenced by drop-wire activity, heddle spacing, harness interference or reed spacing will not weave at top performance.
B.Sc. in Textile Engineering
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