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 (C)</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 (D)</p> Signup and view all the answers

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

<p>Direct relationship (A)</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° (B)</p> Signup and view all the answers

What defines the maximum displacement of the heald frame?

<p>Lift or throw (A)</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. (A)</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. (D)</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 (B)</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. (A)</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. (C)</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. (C)</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. (B)</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. (A)</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. (B)</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. (C)</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. (B)</p> Signup and view all the answers

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

<p>Bottom position. (B)</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. (A)</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. (D)</p> Signup and view all the answers

Why might dobby shedding mechanisms lead to fabric faults?

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

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

<p>One double hook (C)</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 (A)</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 (B)</p> Signup and view all the answers

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

<p>Double lift format only (C)</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 (D)</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 (A)</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 (C)</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. (B)</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 (D)</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 (B)</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 (D)</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 (A)</p> Signup and view all the answers

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

<p>Bottom shaft rotation (A)</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. (A)</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. (C)</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 (C)</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 (A)</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) (D)</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) (B)</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 (D)</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 (C)</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 (A)</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 (A)</p> Signup and view all the answers

Flashcards

Tappet shaft speed reduction

The speed of the tappet shaft needs to be adjusted based on the number of cams used. For example, a 3/1 twill requires a 1/4 speed reduction from the main shaft, and 8-thread sateen needs an 1/8 reduction.

Cam construction factors

Cam design is influenced by the weave type, the heald frame's movement duration (dwell period) and range (stroke), and the treadle bowl's diameter and contact point.

Dwell Period

The time the reed stays stationary at its extreme position, or the time taken for the heald frame to return to its original position. It is related to machine width and inversely related to speed.

Treadle bowl

A lever that moves up and down, driven by the cams, to control the up-and-down movement of the heald frames.

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Cam lift/throw

The distance a cam displaces the heald frame. It expresses the vertical movement.

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Cam repeat size limitations

Cams typically handle 8-12 picks per repeat due to increasing cam slope with more cams. More cams produce greater stress and force required for movement.

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Cam follower arrangement

There are different ways of configuring the mechanism that makes use of cams to move other parts of the weaving machine.

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Cam shaft angle

To distribute the cams evenly, they are configured at a 45 degree angle to distribute force. More cams means a smaller angle for each cam.

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Cam Contour

The shape of the cam's surface, which dictates the motion produced.

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Excessive Force (Cams)

A large amount of force generated by cams, leading to wear and tear.

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Negative Tappet Shedding

Shedding mechanism where frames move (up/down) but return due to external forces (springs).

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Positive Tappet Shedding

Shedding mechanism where frames are raised/lowered by double cams.

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Reversing Media

The mechanism (e.g., springs, pulleys) that returns the frames to their original position.

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Tappet Cams

These cams control the motion of the heald frames.

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Bottom Shaft

The shaft driving the tappet cams.

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Heald Frames

The frames in a loom that raise/lower to create the shedding motion.

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Dobby Shedding

A versatile method of creating a shed, commonly designed to handle up to 32 heald frames. It allows for complex weave patterns like stripes, checks, and geometrical designs.

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Dobby Shedding Location

Dobbies are typically mounted at the bottom of the loom, except in water jet looms where they are mounted in the upper position to avoid water contact.

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Dobby Shedding Advantages

Dobby shedding offers several advantages, including a variety of designs, unlimited picks per repeat, easy design changes, and convenient settings.

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Dobby Shedding Disadvantages

Dobby shedding is more complicated, costly, prone to fabric faults, and slower compared to simpler shedding systems like crank or cam systems.

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Shed Opening Adjustment

The shed opening can be increased by moving the fork lever upward with the clamp screw, and decreased by moving the lever downward.

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Shed Height Adjustment

The shed height can be increased by extending the link rods with the lock screw, and decreased by shortening them.

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Dobby Shedding Classification

Dobby shedding systems can be classified based on various factors, allowing for differentiation and understanding of their specific characteristics.

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Dobby Shedding Limitations

Although dobby shedding offers flexibility, it has limitations in terms of speed and complexity, making it less suitable for high-speed production of simple fabrics.

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Hattersley Dobby

A type of dobby that uses reciprocating knives and is classified as a double lift positive dobby.

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Keighly Dobby

A reciprocating dobby similar to the Hattersley dobby, but it's a double lift negative type.

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Push Bars

Rigid components attached to the knives in a Hattersley dobby that move back and forth with the knives.

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Stop Bars

Fixed bars located opposite the push bars in a Hattersley dobby, used to stop the baulk.

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Locking Bars

Bars that engage or disengage hooks (H1 and H2) to hold the baulk in place during the weave selection.

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Rotary Dobby

A newer type of dobby that operates through rotation, allowing for much faster speeds compared to reciprocating dobbies.

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Dobby Shedding Speeds

Reciprocating dobbies have a maximum speed of around 500 rpm, while rotary dobbies can reach speeds of 1000 to 1500 rpm.

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Double Lift Principle

The method used by Hattersley and Keighly dobbies, where two knives are used to lift the heald frames.

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Harness Movement

The up-and-down motion of the harness in a loom, controlled by a double pulley system and knives.

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Double Acting Knives

Knives that can move both up and down, connected to hooks that determine the harness position.

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Retaining Hooks

Hooks that can latch onto the moving hooks, preventing them from moving further.

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Solenoid

An electromagnet that controls the retaining hooks, determining whether they catch or release.

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Harness Lowered

The state where the harness is at the bottom position, meaning no shed is created for the shuttle to pass through.

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Harness Lifted

The state where the harness is at the top position, creating a shed for the shuttle to pass through.

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Pick Cycle

The complete sequence of raising and lowering the harness to create a shed and allow the shuttle to pass through.

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Weave Design

The pattern of interlacing warp and weft threads that determines the fabric's structure.

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Vincenzi Jacquard

A type of Jacquard machine that uses hexagonal cylinders to facilitate high-speed operation.

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Verdol Jacquard

A type of Jacquard machine that uses a single cylinder and can be either single lift or double lift.

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Double Lift Verdol Jacquard

A type of Verdol Jacquard that uses a single double hook for each harness and two sets of opposing knives to create a semi-open shed.

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Selection Method of Verdol Jacquard

This method uses a continuous plastic pattern on the cylinder, selection needles, auxiliary needles, and a swing board to determine which hooks are lifted for weaving.

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Auxiliary needle

A needle in the Verdol Jacquard that is attached to a selection needle and can fall down or be pushed to the right, controlling the hook movement.

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Swing board

A board in the Verdol Jacquard that moves right and pushes auxiliary needles, determining whether a hook is lifted or not.

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Supplementary hook

A hook attached to the bottom of a double hook in a double lift Verdol Jacquard, working with a supplementary knife to create a semi-open shed.

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Supplementary knife

A knife carried by the fixed griffe in a double lift Verdol Jacquard that works in conjunction with the supplementary hook to create a semi-open shed.

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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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