MINISTRY OF SCIENCE AND TECHNOLOGY - DOC

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					                    MINISTRY OF SCIENCE AND TECHNOLOGY
       DEPARTMENT OF TECHNICAL AND VOCATIONA EDUCATION
      GOVERNMENT TECHNOLOGICAL COLLEGES AND INSTITUTES
                    DEPARTMENT OF TEXTILE ENGINEERING
                    Promotion Examination for B.tech.Year 1 (2006)
 18-10-2006 (Wednesday)                                           8:30 a.m-11:30 a.m
                TE 03023 Weaving Technology I (Sample Answer)


1. Fully explain the five methods of winding yarn on twister bobbins.
ANS
(a) Wrap wind- spool or straight-no tapers,
(b) Wrap wind- accelerated top-partial top taper,
(c) Wrap-wind-Dwight-taper at top only,
(d) Filling wind.
(a) Spool or Straight
       The warp wind is much like that used in spinning, where the ring rails traverse
nearly at full length of the bobbin for every layer. Wrap wind with no trappers, a
double-headed bobbin, or spool, is used. All the traverses are the same length. This
produces a cylindrical package of ply yarn, which completely fills the space between
the bobbin heads. It is commonly used for course yarns.
(b) Accelerated Top
        A doubled-headed bobbin is used, but the top head is considerably, smaller
diameter than the bottom head. Each traverse is the full length of the bobbin, but the
ring rail is moved more rapidly at the upper end of the traverse. The acceleration lays
the yarn more openly and the upper end of the bobbin does not build up as rapidly as
the rest. The top of the package is built up to the diameter of the small head by the
time the bottom of the package is the diameter of the bottom head. It is used for
medium and course yarns.
(3) Dwight Wind
       The bobbins used for this wind have a head at the base only. The first traverse
of this wind is the full length of the bobbin and each successive traverse is shortened
of the top. This produces a cylindrical package fitting close to the bottom head, with a
conical top end. It commonly used and is suitable for all but the very course yarns. It
is used in traverse, with the shortest traverse wound first and successive traverses


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continually lengthened. It is used to avoid snarling which sometimes results in
winding the regular Dwight wind. Reverse Dwight wind is also used for fine yarns
which require a long time to fill a bobbin.
(4). Regular Wind
         This wind is made on bobbins with bottom heads or no heads. The first
traverse is that full length of the bobbin and successive traverses use shortened at both
ends as in spinning. It is usually the taper of the top end is steeper than that at the
bottom end. It is used mostly for fine yarns. It may also be revered with the shortest
traverse being wound first to avoid snarling in unwinding and keep the early layers
clean.
(5). Filling Wind
         It may use a headless bobbin. Some of these bobbins have conical bases to
ease the traveler tension when starting a new set of bobbins. This wind is a series of
short conical layers wound progressively upward on the bobbin. It is used for fine
yarns and to unwind the yard over the end of the bobbin when desired.


2. Write short notes on the two common types of twister creels.
   ANS
Pin Spool and Beam Creels
         They are designed to hold yarn on spools or tubes. It consists of a series of
horizontal slats or bars on either side of the frame old projecting pins about 6 inches
long. The bars are mounted on cast-iron stands so that the outer ends of the pin are
included slightly upward. This prevents the spools from sliding off the pins as they
turn. The pins are arranged in vertical lines, but in others they are arranged to form a
small angle with the vertical. As the base of each pin there is a small up washer which
prevents the spool or tube from rubbing on the slats and keeps friction at a minimum.
The number of slats and bar varies as required up o as many as 16 and is controlled by
the number of piles being twisted. The disadvantage of high creeks is in the need of
steps to change bobbins in the creel, when there are many rows of pins. The heavy
load of material from the large number of spools also is disadvantage for pin creels.
Recent developments in the design of pin creels provide creels to hold cones or
cheeses. With these creels, the package does not turn because the yarn is drawn-off
over end. Usually, some form of yarn tensioning device is used between the package
and the rolls to give a controlled, uniform tension on each single yarn..


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(2) Bean creels
       It consists of cast-iron strands in the top of which are semi-circular notches of
the right size to hold section beam shaft from a regular warper. They are
recommended for twisters running yarns produced from a large number of single ends
and for heavy duty work. They are placed at regular intervals along the twister. With
careful preparation, each end drawn from the section beam is under equal tension, a
necessity in producing evenly twisted yarns. This form of preparation makes creeling
a short process and reduces to a minimum time lost from end breakage.


3. (a) Write down the names of materials used in size mixing. Why are the softener
used in size mixing?
       ANS
       The names of materials used in size mixing are
                 Stiffeners
                 Softeners
                 Emulsifiers
                 Lubricants
                 Humectants
                 Deliquescent
                 Preservatives
                 Fillers or weighing materials
       Softeners are used to give a softer feel to the sized yarn. They also impart
elasticity and pliability to the starch film, thus preventing shedding, brittleness and
other related difficulties. Glycerol is an example of a softener that has no lubricating
action and mineral oil is a lubricant but has no softening action. Japan wax is a good
softener and is easily emulsified and incorporated into the size mix. Soaps have some
softening action but are useful mainly as emulsifier to incorporate other softeners and
lubricants.


2.     (b) Mention the three main types of shedding mechanism.
     ANS
The three main types of shedding mechanism are tappet, dobby and jacquard. In the
simplest type of tappet shedding motion, the shedding cams are mounted on the



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bottom shaft, and the motion is suitable only for weaves repeating on two picks. By
mounting the tappets on a counter shaft driven by gearing from the bottom shaft at the
appropriate speed, the repeat can be extended up to eight or ten picks. Bobbies are
much more versatile and usually control at least sixteen, and sometimes as many as
36, head shafts. Since the lifting of the shafts is controlled by some form of pattern
chain, there is virtually no limit to the number of picks per repeat. Jacquard machines
are made in a wide variety of sizes to control from 100 to 2000 or more ends per
repeat. A common size controls 600 ends, which, in a cloth with 30 ends/cm, gives a
repeat 20 cm wide within which the designer has complete freedom. The lifting of the
ends is controlled by a chain of punched cards or by a loop of punched paper.


4. What are the four main types of conventional picking mechanism? Discuss fully
about the cone under pick motion with the help of diagram.
   ANS
       The four main types of conventional picking mechanism are
   (1) The cone- over pick
   (2) The cone- under pick
   (3) The side- lever mechanism, and
   (4) The side- shaft mechanism.
(2) The cone- under pick motion
       In cone under pick looms, the picker is usually fixed to the picking stick, and
the picking spindle is eliminated. It is then necessary to vary the height of the pick
fulcrum at the bottom of the picking stick during the pick in order that the picker may
follow a straight, horizontal path. The two common ways of achieving this
substantially horizontal movement of the picker are
       (a) the parallel pick
       (b) the link pick as shown in figure.
       In parallel pick method, a curved shoe fixed to the bottom of the picking stick
sides on the horizontal plate fixed to the slay sword, the shoe being kept in contact
with the plate by gravity and party by spring pressure. It is also necessary to prevent
the shoe form sliding along or across the plate. The link pick gives positive control of
the movement of the picker and is satisfactory at speeds considerably in excess of
those commonly used.
           Draw the Figure of the Parallel Pick and the Link Pick


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5. (a) Find the power required for picking in a loom with the following data;
       P is the loom speed in picks min
       R is the width of the warp in the reed in m
       L is the effective length if the shuttle in m
       Ө is the number of degree of crankshaft rotation available for the passage of
       the shuttle, and
       m is the mass of the shuttle in kg.
ANS
                          mv 2
       Energy/pick=            J
                           2
       v = velocity in m/s
       Power = 1 W = 1 J/ s
                                   mv 2   P    1
       Power for picking =              ×   ×     kW
                                    2     60 1000
       Time for the passage of the shuttle = t
                        60   
       t=            ×      =    sec
               360        p   6p
       Distance moved by the shuttle = d
             Rl
       d=             m
             100
       Average speed of the shuttle = v
             R  L 6p   6 p( R  L)2  104
       v=         ×   =                     m/s
             100                
                                   mv 2   P    1
       Power for picking =              ×   ×
                                    2     60 1000
            18mp 3 ( R  L) 2  104
        =
                2  6  10 4
            3mp3  ( R  L) 2  108
        =                              kW
                         2
5. (b) What is meant by the weft-stop motions? Discuss fully about the side-weft-
       fork motion with the help of diagrams.
   ANS
       The importance of stopping a loom immediately after a weft break is probably
greater than is the case after a wrap break, it is necessary before restarting the loom to


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adjust the position of the cloth fell if the shuttle has traversed the loom without
inserting a pick.
   Side-weft-fork motion
       The side weft fork is situated at the straight handle side of the loom, which is
invariably the left- hand side on modern automatic looms, and the weft fork will
operate as they slay comes forward to beat- up the pick after the shuttle has entered
the left- hand box. If a trial of weft extends from the sledge to the shuttle in the box,
it will be supports against the grid and the fork will be tilted about its fulcrum so that
the loop of the fork is clear of the knock- off mechanisms as shown in figure. When
the weft breaks, the fork passes through the gaps in the grid and remains undisturbed.
                        Draw the Figure of A Side Weft-Fork Mechanism




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