Shed Geometry

Shed Geometry & Different Possible Shed Geometries. ?Elements Of Shed Geometry. ?Shed Geometry Classification:- “Shed Symmetricity “Shed Vibration “Shed Staggering “Shed Clearance ?Its Characteristics, Effect & Applications. ?On a weaving loom, warp yarn are divided into two half to make up a shed.This division makes up a specific geometry of divided warp yarns, called “Shed Geometry”. ?Shed Geometry plays vital roll in controlling warp yarns, “Tension “Elongation and “Friction between them. ?Resultantly this helps in controlling, “Weft Density of Fabric “Warp and weft yarn breakages and loom stoppages, hence machine efficiency “And also help to control/avoid fabric faults produced due to these. “Different Possible Shed Geometries: “Elements Of Shed Geometry: ?Components that may part of the Shed Geometry of may contribute to it are: “Frame Height “Frame Depth “Cloth Support (front rest) Height Back Rest (and Deflecting Roller) Height and Depth “Virtual Shed Dividing Line “Dropper Box adjustment and droppers movement. “Frame Height:- ?It is the distance between two reference points, one is fixed and is on loom’s stationary structure and other is on heald frame, as advised by the loom manufacturer. ?It is usually measured when all the frames at same level i. e. at machine leveling position. “Frame Depth (Lever Height): ?It is distance between the a frames maximum height position to its lowest height position. ?As it is adjusted by fixing lever joint on shedding system lifting levers, sometimes also said as Lever height. Cloth Support (Front Rest): ?It is the most forward part of loom frame structure that is closest to the reed when it beats up and it is exactly beneath the cloth fell. It supports the fabric stay above as just filling is inserted into warp shed. ?Its height directly and most intensively effects the Shed Shape and Shed Geometry. ? “Back Rest (Deflecting Roller): ?It is the rear most roller from where warp yarns start making the warp shed. ?It is most frequently used element of the shed geometry to control and divide the warp tension, hence the pick density of the fabric being produced. Virtual Shed Dividing Line: ?It is a line that divides the shed made at frames equally and is parallel to the machine horizontal. Types of Symmetric Sheds: “Symmetric Shed: “Characteristics: ?Whip roller height almost zero. ?Cloth support and whip roller are at same height with respect to each other. “Application: ?For Very light fabric such as voile, gauze i. e. fabric design in which longer float of warp and weft with almost 50% warp and 50% weft is apparent on both sides of the fabric with low fabric cover factor. ?Yarns with little or no elongation. ?Very weak yarns. ?Handkerchief fabrics. Effects: ?The threads in the upper and bottom shed have roughly the same tension, therefore the adjustment is very kind to warp ends. “Note: ?With this setting there is no rocking action, consequently the fabric can take fewer picks. ?It looks flatter and appears less closed. ?Accordingly this adjustment should be used only if the machine runs better with it. “Slightly Asymmetric Shed: “Characteristics: ?Cloth support is at normal height, back rest is slight above the zero position. “Application: ?May be employed as proven basic setting for all light to medium weight fabrics. Effect: ?With slightly asymmetric shed the bottom shed is tensioned more while the upper shed is slacker. ?A slight rocking effect results. ?The fabric can take more picks, it has more closed look and its handle and appearance are improved.”Strongly Asymmetric Shed: “Characteristics: ?Cloth support is raised quite above normal, back rest is raised to a very high position. “Application: “For very heavy fabrics with high warp densities, such as denim, sailcloth (such as cotton canvas), awning fabrics, etc. also poplins on account of appearance. “Effect: Due to the extremely height adjustment of the cloth supporting plate and whip roller the bottom shed is very strong rocking action results from this. At the beat up of the read the weft thread are pushed over each other somewhat very high weft densities can be attained in this way. “With this extremely slack upper shed, more attention must be take warp breakage. “Reverse Asymmetric Shed: “Characteristics: ?Cloth supporting plate is at normal position while back rest is below than normal zero position.”Application: ?Jacquard fabric. ?Satin weave. ?Dobby Weave. “Effect: With this adjustment the upper shed is tensioned and the bottom shed relieved. ?Since with one sided fabric the heavy lift is always woven at the top, a more even distribution of the tension force results between the two halves of the shed. ?Moreover jacquard harness and rubber return motions are treated better. “Shed with Staggered Timing: “Characteristics: ?With staggered timing the shed closure of the individual shaft pairs is displaced in time, to avoid all shafts crossing at the same time. “Application: ?Staggered Timing is purposeful only where “Very high warp densities are used. “Hairy yarn that separate badly are being woven. Fixed Height (Clear) Shed: “Characteristics: ?An ideal shed the ends of the upper and bottom sheds each form an ideal, closed sheet. ?A slight staggering in height may be observed in the bottom shed, that can be tolerated. “Application: ?For filament yarn fabrics, such as linings. ?For lightweight fabrics whose ends part well. ?For non-elastic fabrics like glass-fiber. ?For polyethylene and polypropylene ribbons. ?For twills woven from staple fabric. “Effects: “This adjustment is inadvisable for dense warp sheet, poor parting warp ends. “There are chance of end cut in case of projectile loom.

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