Dobby Shedding Mechanism | Classification | Types | Working

• To know regarding the various elements shaped this shedding.
• To learn the mechanism of dobby shedding.What is Dobby and Dobby Shedding?Dobby may be a compact, electronically or automatically guided shedding motion. Dobbies unremarkably area unit capable of getting up to twenty-eight shafts.Dobby may be a shedding mechanism placed on the highest of the loom so as to supply patterned patterns by victimization sizable amount of healds than the capability of a tappet. Dobby is additionally called a “witch or “wizard”. Dobby shedding is additional advanced and versatile shedding motion.
  
  Fig: Dobby shedding in loomDobby shedding is 2 types; negative dobby shedding and positive dobby shedding.

  Scope of a Dobby:
  The scope of dobby is restricted between a lever and a jacquard. the quantity of shafts which will be motivated by a dobby varies between half dozen and forty. in theory dobby will management forty eight shafts (maximum). However, much it will management thirty six shafts just in case of wool and allied fibers. Again, for cotton and allied fibers, it will management most twenty four heald shafts. In these case healds area unit operated by jacks and levers.

  Main elements of Dobby Shedding:

• Bottom shaft
• L-lever
• Upright shaft
• T-lever
• Upper draw knife
• Lower draw knife
• Upper hook
• Lower hook
• S-lever
• Bulk lever
• Thumb lever
• Jack lever
• Heald shaft
• Returning spring
• Motor
• Crank shaft
• Pattern cylinder
• Pattern chainClassification of Dobby:
  
  INTRODUCTION: –Dobby is a shedding device connected to loom to augmented the coming up with capability. The dobby unremarkably controls twelve to twenty four hold shafts the dobbies area unit classified as negative or positive, single raise, double raise, crank driven, cam driven etc.
  The dobby forms bottom closed, center closed, semi open and open style of shed. The dobby is additionally classified as left and mitt.
  The right-hand dobby is one that is placed at the left-hand facet of the left. It gets drive from left finish loom.
  The left-hand dobby is one placed at mitt facet of left-hand loom. left dobby gets its drive from right finish of the loom.Climax Dobby

  The Climax Dobby  is double acting machine controlled from bottom shaft ,  it forms the open shade.  The lifting of heald is finished by lifting of jacks. The healds area unit lowered as a result of  of springs used on the lowest facet. It has a pair of jacks. Dobby runs at 0.5 the speed. within the mitt dobby,  cylinder rotates in dextral direction. within the left Dobby, cylinder rotates in anticlockwise direction.

  Working

  Dobby gets its drive from the lowest shaft through rod.  The T- lever  gets oscillation  and thereby knives move forward and backward within the framing machine slot. once the knives area unit towards the set of  hooks  selection of engagement hook and knife is formed feller.  The feelers  are activated attributable to wood pegs. once the hooks and knives area unit engaged, then the hook is force, whereas the another hook and also the lever rest on the stop bar. currently the heald is upraised up.

  Timing and setting of Climax Dobby:

• 1- At 270 degree  The heald shaft is levelled,  knives area unit middle approach position.2- The T- lever is horizontal.  At sixty to a hundred and twenty degree is that the dwell amount of the dobby
• Heald area unit writing paper
• shed shed is open3- At ninety degree,  one arm  of the t— lever is outside and another is within.4- The bottom shaft is at prime or on bottom center .At a hundred and twenty To  360 degree To sixty degree is that the amendment amount of the heald  shaft.Settings:1-  The driving rod connecting to the crank connected to the lowest shaft off the loop and T-lever should  be set to applicable length.  If the rod is simply too short or long,  one set of the hook can cosmopolitan then additional distance than the opposite.

  2-  The length of driving rod is adjusted such T-Lever  is horizontal once the crank connected to the lowest shaft is in horizontal plane either within the front or back of rotary its stroke.

  3-  Crank and T-lever area unit unbroken within the horizontal position and currently 2  knives area unit  Adjusted by draw bolts, in order that they’re equidistance  from their slots. The pattern cylinder is turned by wheel.  Cylinder is turned by 1/8th revolution for each a pair of decide.  the cylinder is command steady purchase flat steady star wheel. The detent  regulate through of the star wheel. The T-lever  is lifting knives area unit extreme  position there ought to be a qurter in.  clearance between the tip of the detent and also the teeth of the cylinder ratchet.

  For mitt Dobby visible outer feeler that operate bottom drawer hook , pattern cylinder rotate dextral. In the left Dobby, the primary feeler may be a straight feeler  acts on the highest hook. In pegging,  the higher row of holes within the lug represents initial decide.

  Cross Border Fabrics:

  Many materials wants border within the warp yet as within the woof approach.  for making the woof approach border style. the quantity of pegleg needed area unit high. therefore to make a border style,  special cross border Dobby is employed.  the materials which require the cross border area unit sarees, carpets ,Chadar, tapestries,  handkerchiefs,  table covers.

  Cross border Dobby

  Cross border Dobby is employed once 2 different weaves are needed to plain woven victimization same variety of healds.Cross border Dobby eliminates high variety of wood legs that area unit needed in traditional dobbies.

  Types of cross border dobbies:

  1-    2  cylinder cross border Dobby

  2-   3  cylinder cross border Dobby

Dobby Faults:

The common problem in the dobby is Jack missing. The heald shaft is not lifted when required and weft floats across the warp end giving rise the fabric effect called stitching.

Stitching is sometimes caused by shuttle flying. Warp thread get break occur because of shuttle fly causing a major fabric defect.

The causes of Jack missing (Heald not lifted) are:

1) Bent wooden peg in a lag.

2) Wooden peg is worn out due to frequent use.

3) The spacing between the lag should be uniform and cylinder should be positioned below the feeler in the perpendicular manner. if the lags are not spaced properly more feelers may be lifted causing lifting of improper jack.

4) The pattern barrel in which wooden lag rotate should not move laterally.

5) Needle operating hook may get stuck and jack is missed, good oiling is necessary.

6) Wooden peg will be broken and therefore jack is missed.

7) The hook may come off from the knife in the middle of stroke, causing missing jack.

Ruti Cam Dobby:-

The ruti cam dobby is negative in action i.e the heald are lowered because of the spring in this dobby. The knives are pushed forward by the pair of cams. The knive will come back and always in the contact with the cams because of the spring. Here dwell of about 1/3 pic is achieved. The selection of the hook are made by paper pattern instead of wooden pegs.

Dobby Shedding Mechanism:

Fig: Diagram of Dobby Shedding Mechanism

Here a climax dobby is described to explain the dobby shedding mechanism. Climax dobby is a double lift double jack-lever negative dobby. Here two jack levers are operated by a single bulk lever. They are joined with the bulk lever by a timber lever and a link. The double lever is fulcrum med at a point and is connected with S-lever. The S-lever controls two hooks, one upper hook and one lower hook. The hooks are controlled by feelers. One hook is controlled by hooked feeler and other by a connecting needle. The two hooks control two knives that are joined with a T-lever. The T-lever is fulcrum med and is controlled by an upright shaft and an L-lever. They get motion from motor and machine pulley. When the feeler comes in contact with a peg and when it is not in the contact it goes down.

Fig: Dobby peg plan

Dobby loom is important for its use. We can use 8-12 heald frame in tappet loom but if we want to use more heald frame for more decorative design then we should use dobby loom. This practical helps me to know about the dobby loom and its mechanism. I think this will help me in my future life.

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