Weaving Mechanisms Overview
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Questions and Answers

How much must the speed of the tappet shaft be reduced for a 3/1 twill weave?

  • By 1/2 of the main shaft
  • By 1/8 of the main shaft
  • By 1/3 of the main shaft
  • By 1/4 of the main shaft (correct)

    • What is the dwell period of the heald frame?

  • The time for which the reed is stationary at rear most position (correct)
  • The time for which the reed is in motion
  • The duration of one full cycle of the heald frame
  • The time for which the reed is stationary at maximum position

    • Which factor does NOT affect the construction of the tappet cam?

  • Dwell period of heald frame
  • Stroke of heald frame
  • Dia. of treadle bowl
  • Speed of the machine (correct)

    • What does the lift or throw of a cam refer to?

    <p>The distance a cam can displace a heald frame</p> Signup and view all the answers

    What happens as the number of cams increases in a cam shedding system?

    <p>The slope of the cam contour increases</p> Signup and view all the answers

    What is the relationship between the width of the machine and the dwell period?

    <p>Direct relationship</p> Signup and view all the answers

    At what angle are 8 cams installed on the counter shaft for a weave design of 8 picks per repeat?

    <p>45°</p> Signup and view all the answers

    What defines the maximum displacement of the heald frame?

    <p>Lift or throw</p> Signup and view all the answers

    What is the primary advantage of using the Hattersley dobby over pegged lattice systems?

    <p>It is more accurate in selection.</p> Signup and view all the answers

    What is a key distinguishing feature of the Hattersley dobby compared to the Keighly dobby?

    <p>It operates on a positive double lift principle.</p> Signup and view all the answers

    What is the maximum speed a rotary dobby can achieve according to the information provided?

    <p>1000 to 1500 rpm</p> Signup and view all the answers

    What role do the locking bars L1 and L2 play in the Hattersley dobby mechanism?

    <p>They prevent the frame from moving down until the next weave selection.</p> Signup and view all the answers

    What is the main principle behind the operation of the Hattersley dobby?

    <p>Reciprocating knives without return springs.</p> Signup and view all the answers

    How do the push bars operate in the Hattersley dobby mechanism?

    <p>They are attached to the knives and reciprocate with them.</p> Signup and view all the answers

    What is the significance of the stop bars S1 and S2 in the Hattersley dobby?

    <p>They assist in executing the locking mechanism.</p> Signup and view all the answers

    What innovation did the rotary dobby introduce in terms of weaving speed?

    <p>Ability to maintain a high speed of 1000 to 1500 rpm.</p> Signup and view all the answers

    What happens when the fork lever is moved upward with the clamp screw?

    <p>The shed opening increases.</p> Signup and view all the answers

    Which is a disadvantage of the dobby shedding mechanism compared to crank or cam systems?

    <p>It runs slower than crank and tappet/cam shedding.</p> Signup and view all the answers

    What is a key improvement of dobby shedding systems over cam shedding systems?

    <p>It allows easier changeover of the weave design.</p> Signup and view all the answers

    What is the typical position for mounting dobbies in most looms?

    <p>Bottom position.</p> Signup and view all the answers

    What classification feature is associated with dobby shedding mechanisms?

    <p>They can handle an unlimited number of picks per repeat.</p> Signup and view all the answers

    Which of the following is NOT an advantage of the dobby shedding system?

    <p>Higher complexity than crank systems.</p> Signup and view all the answers

    Why might dobby shedding mechanisms lead to fabric faults?

    <p>Their complexity increases the likelihood of errors.</p> Signup and view all the answers

    What types of patterns can be produced using the dobby shedding mechanism?

    <p>Fancy weave designs like stripes and checks.</p> Signup and view all the answers

    What is the purpose of the auxiliary needle (A) in the Verdol jacquard mechanism?

    <p>To interact with the swing board and determine hook movement</p> Signup and view all the answers

    How many hooks does the double lift Verdol jacquard utilize for each harness?

    <p>One double hook</p> Signup and view all the answers

    What shape are the cylinders of Vincenzi Jacquards made to enhance performance?

    <p>Hexagonal shape for stability in high speeds</p> Signup and view all the answers

    What happens if there is no hole for the selecting needle (S) in the Verdol jacquard mechanism?

    <p>The swing board will miss its target, pushing the hook away</p> Signup and view all the answers

    Which format of the Verdol jacquard is commonly used in modern applications?

    <p>Double lift format only</p> Signup and view all the answers

    What role does the supplementary hook (H) play in the double lift Verdol jacquard?

    <p>It works in conjunction with the supplementary knife</p> Signup and view all the answers

    What allows the hook in the double lift Verdol jacquard to move appropriately during the action?

    <p>The presence of holes corresponding to the selecting needle</p> Signup and view all the answers

    How does the knife K1 contribute to the lifting of the harness in the mechanism?

    <p>By slightly lowering the harness while allowing K2 to engage</p> Signup and view all the answers

    What happens to the force in the system as the slope of the cam contour increases?

    <p>The force increases.</p> Signup and view all the answers

    What is the maximum number of cams typically installed on a counter shaft to avoid excessive force?

    <p>8 - 12 cams</p> Signup and view all the answers

    In which type of Tappet Shedding are the heald frames returned by an external device?

    <p>Negative Tappet Shedding</p> Signup and view all the answers

    What is a reversing media in the context of Tappet Shedding?

    <p>The component that brings back the frames to their original position</p> Signup and view all the answers

    What type of mechanism is used to lower the heald frames in Negative Tappet Shedding?

    <p>Single cams and reversing media</p> Signup and view all the answers

    What drives the motion of the tappet cams in the described mechanism?

    <p>Bottom shaft rotation</p> Signup and view all the answers

    What is the role of the treadle lever in the Tappet Shedding mechanism?

    <p>It serves as a fulcrum for the heald frames' movement.</p> Signup and view all the answers

    What occurs when the tappet cam presses the treadle lever according to the mechanism described?

    <p>The first frame moves up and the second moves down.</p> Signup and view all the answers

    What is the purpose of the knives (f) and (g) in the loom's mechanism?

    <p>To move the hooks in conjunction with the harness</p> Signup and view all the answers

    At what point does the harness remain in the bottom position?

    <p>When knife (g) reaches the top while knife (f) is at the bottom</p> Signup and view all the answers

    What happens when the right-hand solenoid (H) is energized?

    <p>The retaining hook (e) does not catch hook (c)</p> Signup and view all the answers

    Which component is responsible for lifting the harness in the next pick cycle after it was previously lowered?

    <p>The left side of solenoid (H)</p> Signup and view all the answers

    What configuration occurs when both knives (f) and (g) reach their respective limits at point (3)?

    <p>The harness remains stationary and cannot move</p> Signup and view all the answers

    What continues to happen after the harness reaches the top-most position at point (5)?

    <p>The retaining hook (d) catches hook (b) for continuity</p> Signup and view all the answers

    Which of the following accurately describes the initial state of the system?

    <p>Hook (b) is up while hook (c) is down</p> Signup and view all the answers

    What is the role of retaining hooks (d) and (e) in the loom mechanism?

    <p>To ensure hooks catch at the right moments based on the weave design</p> Signup and view all the answers

    Study Notes

    Weaving Mechanisms

    • Warping yarns are divided into two layers:
      • Top layer is the top shed line
      • Bottom layer is the bottom shed line
      • The gap between layers is the shed
    • Objectives of shedding motion:
      • To raise and lower the heald frames carrying the warp yarns.
      • To create an opening for picking media.
      • To change the position of warp and weft yarns as needed for the desired weave design.
    • Types of sheds:
      • Bottom closed shed
      • Semi open shed
      • Centre closed shed
      • Fully open shed
    • Types of shedding mechanisms:
      • Crank shedding
      • Tappet shedding
      • Dobby shedding
      • Jacquard shedding
    • Jacquard shedding:
      • Makes use of individual harnesses to lift individual warp yarns.
      • Can be fitted to different loom types
    • Positive Shedding:
      • Raising and lowering of the heald frames is done using double cams
    • Negative Shedding:
      • Raising or lowering of heald frames is done by a mechanism that is returned by another external device, like springs.
    • Crank Shedding:
      • Simplest shedding mechanism
      • Suitable for plain weaves
    • Tappet Shedding:
      • Simple, uses cams
      • Inexpensive and easy to maintain
      • Suitable for plain weaves
    • Dobby Shedding:
      • Versatile mechanism for creating a shed
      • Handles 12, 16, 20, 24, 28, or 32 heald frames.
      • Suitable for creating intricate weaves
    • Electronic Shedding:
      • Uses electromagnets to lift or lower heald frames.
      • The lifting order is received electronically from computers.
    • Cam:
      • A specially designed rotating or sliding metal piece.
      • Converts rotating motion to reciprocating motion.
      • Works with a cam follower to transmit the drive.
    • Dwell Period:
      • The time taken by the heald frame to be stationary at a rare most position
      • Directly linked to the width of the machine.
    • Throw or Lift of a Cam:
      • Distance by which a cam can lift a heald frame
    • Repeat Size Limitations of Cams:
      • Practical limit of 8-12 picks per repeat
      • Related to increasing slope of cam contour and force
    • Shed Settings:
      • Adjusting the opening of the shed
      • Increasing the length of link rods to increase shed height.
    • Objectives of Shedding Motion
      • To raise and lower the heald frames which carry the warp yarns.
      • To make an opening for the passage of picking media.
      • To change the position of warp yarns to interlace the warp & weft as per weave design.
    • Various types of Tappet Shedding:
      • Negative
      • Positive
    • Tappet Shedding - Basic Information:
      • Heald frames are lowered by single cams and raised by reversing media.
      • The rotary motion of the tappet cams converts to up and down motion of the heald frames.
      • It gets its drive from the bottom shaft
    • Shedding Motion - Additional Information:
      • Shed opening and height can be adjusted.
      • The shed position is related to the loom speed and picking media passage.
    • Jacquard Harness:
      • Suspended from the ceiling above the loom.
      • Connected to the loom by a harness system of cords, heald eyes, and lingoes.
      • Transmits the movement of jacquard hooks to individual warp yarns.
      • Comber board is placed below the jacquard mechanism.
    • Jacquard Capacity:
      • Determined by the number of hooks in a row multiplied by the number of rows.

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    Related Documents

    Weaving Mechanisms PDF

    Description

    Explore the intricacies of weaving mechanisms, including the types of sheds and shedding mechanisms. Learn about the objectives of shedding motion and the specific functions of Jacquard shedding. This quiz covers essential terms and concepts crucial for understanding weaving.

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