Stop Marks, Starting Marks and Setting Shed in Weaving

Stop Marks, Starting Marks and Setting Shed in Weaving

Dario Paredes Vásquez
Textile Technician
Lima, Perú
Email: darioparvas4@hotmail.com



Is important to start by explaining that the stop marks and starting marks are common defects in the weaving, the difference, which can be an advantage or a disadvantage, is due to the characteristics of the fabric that makes these defects are more notorious or less notorious.

The intention of this publication is to explain the main criteria to control and repair these defects, the textile adjustments made must first seek to reduce or eliminate machine stoppages, warp stop and weft stop, then eliminate or attenuate stop or starting marks.

starting marks
Fig: Starting marks
First, we must recognize the types of defects that can occur in the fabric for a stop mark or a start mark:

1. Open Marks:

It occurs when one or more picks are separated leaving a horizontal line open. This failure usually occurs in fabrics with low cover factor.

Open Marks

2. Dense Marks:
It occurs when one or more picks are together leaving a closed horizontal line. This failure usually occurs in light-weight fabrics.

Dense Marks

3. Wavy Marks:
It is produced when more than one picks is superimposed, one above the other, leaving a horizontal band that is uneven and closed. This failure occurs in heavy fabrics, twills or satins with high cover factor and always at machine start-up.

Wavy Marks

The next step is to determine what type of defect is occurring and if it is generated at machine stoppage or startup. For this, there is a simple procedure for testing stop and start marks:
  1. Cause a stoppage of the loom, by warp and by weft.
  2. Insert a color yarn approximately 10 to 20 cm in front of the last inserted picks.
  3. Wait for one to three minutes.
  4. Start the loom.
  5. Check the type of defect, open or dense, and if this defect occurs before or after the color yarn used as a mark; this way, we determine if the failure occurred at stoppage or at machine start-up.
  6. To realize various tests with different regulations, minimum 20 cm distance between one and another test.

Basic Controls:
Is necessary to ensure the correct state and operation of the mechanical and electronic parts of the loom to rule out possible open and / or dense by default of machine, for example:

1. Mechanical function of let-off and take-up
  • Bearings
  • Gears
  • Transmission chains
  • Supports / joints
  • Covering of sand beam and pressure rollers.
2. Temple, wear and type of rings according to the fabric.
3. levers: transmission of the shed former, wastage of the bearings
4. Drive and brake of machine, pulleys and transmission belts.

There is also the possibility that the fabric presents open or dense defects during the weaving process, but these are attributed to defects of some mechanical or electronic component. This report will not review these defects, which correspond to preventive and / or corrective maintenance.

Main Causes:
We will review three main causes that generate the stops marks and starting marks and that in modern looms we have the option to control and regulate.

Machine stop times:

The start marks are more notorious depending on the time that the loom is stopped waiting for its intervention, the longer the stoppage, more severe is the failure; this reason is basically a work method. It must be sought to reduce machine stop as much as possible; with textile adjustments to avoid machine stop or with timely attention; For example, if there is a warp stop on a loom and a filling stop on another loom, the filling stop should be repair first since it is faster to intervene and repair next the warp stop.

Nominal speed:

It is the adjusted maximum speed of a loom during its working process and it differs accordingto the load or the slow motions of the loom. Here it is important to understand three concepts:

Braking angle: When a machine stop occurs, it does not stop instantly; it has a brake slip depending on the type of drive or the machine speed. This can be from 40 ° to approximately 200 °. It is important to know this information, since it allows us to know how the last picks inserted pass was completed. If this last was during the beat-up moment, it is possible that a open mark is generated; since it will be less than its nominal speed (less force beat-up).

Stop position: After the machine stop has been produced, it is positioned in a specific adjusted degree. The conditions of the position of stopped will depend on the type of insertion of the loom, the ligament and the stopped type; for example, it is recommended, when working a fabric plain, to regulate the stop position at the moment of the shed crossing when a filling stop occurs to avoid stretching the warp during the stop time, until the operator arrives to look for the correct picks and start the loom; similarly when a warp break occurs, adjust a stop position that allows the operator to easily insert the warp through the needles and the reed without the need for additional manual movements.

Start position: After the operator makes the repair or correction of the stop, the machine goes to a starting position degree. The criterion here is to seek that the first inserted picks is beat-up as close to its nominal speed, depending on the machine rpm, the nominal speed is reached only at the third or fourth picks. For example, when the first inserted pick leaves a open mark at the start, what we have to regulate is the position farthest from the finishing point; So we give you more time to reach your nominal speed.


In some modern looms, for example the Picanol loom, is possible to have the option of regulating empty picks (ASO value), in this way, it is possible to achieve that the first inserted picks is beat-up at its nominal speed.


It also has other electronic options to correct stop o starting marks with adjustments in the let-off and take-up system.

In the following image we show an interactive screen for adjusting the start and stop marks of a PicanolOmniPlus 800 loom and on the scale how movements are generated according to the setting made for "others


Warp tension difference:
The difference in tension that affects the stop and start marks is determined by the correct adjustment of the shed. The shed is the tunnel that is formed with the movement of the warps that go up and down according to the design of the fabric through which the weft is inserted and that we will detail some types of adjustments later on.

To regulate a correct shed it is necessary to know some conditions of the style or fabric:

The cover factor: It is a value that indicates the covering property of a fabric, the maximum capacity of warp or weft in a specific space. This will help us determine if the fabric to be worked is a heavy item (> 85% tupidity) or light weight (<65% tupidity) and in this way regulate the appropriate posterior shed.

The following are the formulas for calculating the warp, weft, and total coverage factor.

cover factor

For example, if we have a fabric with a weave plain (1/1) with a total cover factor of 31.5, with the maximum cover for 37, then we say 31.5 / 37 is equal to 85% of tupidity; This fabric can be considered heavy style.

The warp density: It is important to know the amount of warp per reed, if the style has 2 warps per tooth, 3 warps per tooth or more. Also, it is important to know the number of teeth per centimeter. This information will help us to know with what ease or difficulty the warp will crossing in their movement to form the shed. This will help us to regulate the previous shed appropriate to the weave or fabrics.

warp density

Weave of fabric: Knowing if the fabric is plain, twill, satin or dobby; also if it is a light, heavy or neutral weave will help us to regulate the appropriate posterior shed.
Weave of fabric

In addition, the shed must have certain important basic characteristics to achieve a "clean" shed that allows a correct separation and movement of the warp and a correct insertion of the weft.

Shed angle: You should start working with the lowest possible opening angle to prevent stretching the warp so much. It must be understood that the more shed opening is regulated; it will require more time to recover the elongation that suffers during the movement of the frames and the movements of slow motion during the stop and start of the machine.

Shed height: It will be restricted or limited according to the type of insertion (air, rapier or projectile). Similarly, what is sought is that during the beat-up of the weft is made as soft as possible. Also, to help warp layers can be individualized and to help separate them easily.

Symmetry: Depending the ligament and the cover factor, different variants of sheds can be adjusted to allow the best work (efficiency) and the lowest incidence of stop marks and / or starting marks (quality).

Gap: Depending the warp density, that is, the ease or difficulty of the warp to separate from each other during the shedding movement, different degrees of gap can be adjusted to help the warp pairs cross at different times allowing a better separation, the best gap frame is achieved in cam motion shed former, because makes the separation at the crossing shed moment.

Tension: According to the yarn title, the type of material, the amount of yarns, the preparation conditions, among other factors, the appropriate warp tension must be adjusted.

The Anterior Shed:
The separation of yarns formed between the beat-up and the needle (frame) is called "anterior shed". As an initial basic adjustment, you should seek for the smallest possible shed angle, sufficient for a clean weft insertion. For an adjustment it will be necessary to control the shed from the beginning of the insertion to the end of it, being at 180° after the crossing of the shed a maximum position that will show us the appearance or formation of the shed. There are two types of anterior shed:

Anterior shed symmetrical: The yarns of the upper shed and of the lower shed form closed lines. To form a shed symmetrical angle the opening of the frames is increasing, therefore they have different tensions.

Applications:

  • Filament fabrics, warp with little hairiness.
  • Lightweight fabrics, easily separated warp.
  • Fabrics with a low density of warp.
Anterior shed asymmetrical: The yarns of the upper shed and / or the lower shed form different layers (different lines)

Applications:

  • Fabrics with warp hairiness difficult to separate.
  • Fabrics with a high density of warp per comb tooth.
Is possible to regulate different variants of shed asymmetric:

1. With shed height:

Used in basic fabrics (taffeta, twill, satin) to separate in different layers.

Example:
• In ligaments with four frames
1st frame = basic adjustment+ 0 mm
2nd frame = basic adjustment + 1 mm or 2mm
3rd frame = basic adjustment + 2 mm or 4mm
4th frame = basic adjustment + 3 mm or 6mm

• Taffeta of four frames
1st frame = basic setting
2nd frame = basic setting
3rd frame = basic adjustment + 2 mm or 4mm
4th frame = basic adjustment + 2 mm or 4mm

2. With shed angle (opening):
Used in special fabrics that combine ligaments with different elongation points, it consists of giving different angles according to the ligament.

Example:
The frames that correspond to the twill that has more elongation should be given less opening than the frames that correspond to the taffeta that has less elongation. In this way it is about compensating or equaling warp tensions; remember that having more opening this warp stretches more and needs to recover this elongation.

3. With shed crossing:
Used only in cam motion, mainly in articles with high warp density and difficult separation in needle and reed, by giving different shed crossing the pairs of frames will cross at different times, having a better separation.


Example:
Frame 1 and 2 cross to 320 °
Frame 3 and 4 cross to 310 °
Frame 5 and 6 cross to 300


It is possible to use combinations of these three variants according to the complexity or need, taking care that one of them does not negatively influence the other, so that it decrease or cancel the obtained advantage.

Effects of Shed Crossing:
(reference of degrees for a loom with beat-up 0°)

1. Early Crossing: 290° - 310°

  • The filling is dragged with more friction and less tension in front of the reed, this allows it to better accommodate the beat-up.
  • The filling has less contraction.
  • Is favorable in heavy fabrics and wavy marks problems.
  • It does not favorable fabrics with hairiness yarns since having more friction creates more pilosity.
  • Presents a more closed aspect of the fabric.
2. Standard Crossing: 310° - 320°

3. Delayed Crossing: 320° - 350°

  • The inserted filling is dragged without creating any tension as it is softer dragged to the front beat-up.
  • We take better care of the filling.
  • Does not favor heavy fabrics.
  • The filling loses some of its tension, favorable for weak and hairiness warp.
  • It can cause vertical reed marks, rapier guides, projectile or relay nozzles.
  • The fabric has greater force the beat-up.
The Posterior Shed:
Posterior shed symmetrical: The support of the fabric in the anterior shed is the temple profile. This forms a line with the feeler roll.


In this way a symmetric line is obtain; here the warp of the upper shed and the lower shed have the same tension. So the warp are better taken care.


It can be used as a basic adjustment for light fabrics with low density, low cover factor, fabrics with weak warps, with loops warp.

Posterior shed symmetrical

Posterior shed asymmetrical:

Upwards: The height of the feeler roll adjusted above the point of symmetry.

With this adjustment, the lower shed have more tension and the upper shed have less tension. Thus, a beat-up effect is produced, higher weft densities can be possible obtain since the filling are placed one on top of the other achieving a more closed appearance of the fabric.

It can be used as a basic setting in heavy fabrics such as denim, canvas, awnings, etc., as well as in poplin to improve the striped appearance of the fabric.

When working with cam motion, it is possible to achieve this effect using asymmetric eccentrics with the longest position down, so we do not need to give a lot of height to the feeler roll, favoring ergonomics.

Posterior shed asymmetrical

Down: The height of the feeler roll adjusted below the point of symmetry.

With this adjustment, the upper shed have more tension and the lower shed have less tension. It can be used in fabrics where the highest load is woven upwards and is favorable for the best distribution and separation of the warps.

When working with cam motion, it is possible to achieve this effect using asymmetric cams with the longest position upwards; in this way we do not need to lower so much the height of the feeler roll.


Posterior shed short:
The back rest adjusted in position as more close to frames.

In this position the warp tension is bigger because the distance is shorter; a better separation of the warps is obtained in a way that favorable in hairiness warps.

It can be used in heavy fabrics and up to 8 frames since more frames can cause the action of the shed to raise the forks on their rails causing false stop warps or damaging the rails.

Posterior shed intermediate:
The back rest adjusted in intermediate position. Is possible obtain a better care of the warps since the distance to be controlled is greater.


It can be used as a basic adjustment in lightweight fabrics of 4 to more frames, in weak warps and with little elongation.

Posterior shed long:

The backrest adjusted in position farthest from the frames.


With this shed is possible to compensate better the warp tensions caused by warps with different ligaments, since the distance to be controlled is much greater.

It can be used on fabrics with weak warps and special fabrics with different elongation points.


Other Adjustment that Influence in the Posterior Shed:

Warp stop adjustment:
The influence of the profundity and height of the Warp stop,is also important for a good shed and a good appearance of the fabric.

Warp stops Profundity:

1. If we adjust the warp stop profundity more close to the weaver (forward):
  • The warps are separated more easily, favorable for hairiness warps.
  • Improves the warp tensions in both layers of warps achieving a cleaner shed formation.
  • When working with 6 or more frames, it can happen that the warps raise the forks causing damage to the warp rails and the warp yarns. This movement of the forks also causes tension differences, producing an uneven effect most notorious towards the selvedges.
2. If we adjust the warp stop profundity more farther from the weaver (back):
  • It is used for weak warps and of different tensions, to better care and control the warp, reduces the formation of specks and hanged warps.
Warp stop height:
  • In lightweight fabrics, care must be taken that the support of the warp stop does not deflect the warps, causing tension variation, since this may cause starting marks.
  • In weak warps or low sizing, the height of the warp stop be adjusted to reduce or eliminate the friction of the yarn.
Use the deflection cylinder:
It is used to lighten the load of the feeler roll when we work heavy fabrics, with a high cover factor.

The deflection cylinder can be adjusted in two different positions, according to profundity and height. It must be said that the deflection cylinder withstands most of the warp tension.

When working light fabrics, weak warps that produce breaks, it is preferable to remove the deflection cylinder, in this way the warp tension is better controlled.


Warp tension:
A correct warp tension is important for the formation of a good shed and as a consequence obtains a good efficiency and quality.

This tension will depend on the amount of warps, title, material, sizing quality, height and angle frame adjustments, and fabric density.

It is difficult to define a standard tension, due to the influence of different factors mentioned above, in practice and with the knowledge of said factors, the correct warp tension will be that which does not cause warp breaks (high tension), nor cause loops warp or fillingstop due to tangled or warp breaks during insertion in rapier or projectile looms (low tension), as well as their influence on the appearance of fabric (beat-up, edge ​​strength, edge formation) or starting marks.

The correct analysis of the defect presented and the appropriate adjustment according to the criteria explained will eliminate and / or attenuate the effect of the observed quality failure.
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Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.


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