TYPES OF FANCY YARNS(Boucle, loop,stripe, cover):-

Types of fancy yarn:-

BOUCLE YARN:-

The boucle yarn is very similar in construction to the gimp yarn. It requires a minimum of three component yarn, a core, effect, and binder, and it is produced in two stages. The yarn construction illustrated in Fig. 7 . The main difference between a boucle yarn and gimp yarn is that the way projection of the boucle yarn surface are further away from the yarn body ,  a result of greate over feeling of the effect yarn during the first twisting stage. On the account of greater overfeed, the effect spirals very loosely around the core following the first twisting stage.The way projections can be more easily distorted during the second twisting stage leading to more variable yarn appearance.

Fig. 7 image of boucle yarn.

LOOP YARN.

Loop yarn are characterised by circular projections formed by the effect yarn. They are typically formed by atleast four components yarn:- two cores, the effect and the binder. Two cores are required to form a stable triangular space in which the over feed effect yarn can be accumulate to produce the loop during the first twisting stage shown in fig. 8

Fig . 8 loop yarn.

The first stage must be further processed by a reverse binding process to fix the loops on to the core yarns because in the first twisting stage , the core and effect  yarn simply twist around each other and the loops are not trapped by the cover yarns. The effect yarn is usually overfeed 200% or more relative to the core yarns. To produce uniform and staple loops, it is important that the effect yarn is made elastic and pliable fibers mohair and is not twist lively . Roving of long staple fiber may be used as effects to produce loose fiber loops.

Although the loop size is obviously depends on the effect overfeed ratio, it can also be controlled by the spacing of the core yarns, the twist level used during the first twisting stage , and the yarn tension. Controlling the twist level is easiest way to alter the loop size , as it does not require the change of any of the spinning machine parts. The reverse binding process also affords the opportunity to readjust the final yarn twist so that the yarn is overly hard. 

STRIPE YARN:-

A stipe yarn contains alternately elongated knop , revealing a separate core. The section of yarn between the knops take on the appearance of a multi threaded marl yarn.

image of stripe yarn.Ref by Amazon.

COVER YARN:-

A cover yarn is one in which a yarn at the core is completely covered by fiber or yarn wrapped around it. It is familiar to embroideries because my any metallic embroidery threads take the form of a cote threads with a metallic thread filmor flat ribbon wraped around it , but the method is the most commonly used to cover elastomeric yarns , which would othereise be extremely eccentric "bubble gum yarn" ,which consists of a core of filaments surrounded by a bubbled forth of resin, could also be described a cover yarn. 

image of cover yarn ref by Trade India

SNARL YARN:-

Snarl yarns are made in exactly the same way as loop yarns , except that the effect yarn is twist lively instead of stable . Due to the twist liveliness , the loops formed by the effect yarn collapse under the influence of the untwisting stress in the yarn and form kinks . An example is shown in Fig. 9 . To enhance the formation of the snarls, the effect yarn over feed usually higher than that used for loop yarn.

image of snarl yarn and structure.

KNOP YARN:-

A knop yarn contains section, with only the effect yarn being visible as shown in Fig. 10 . These section on knop are fromed where the core yarn is stopped momentarily while the effect yarn feeding continues. The excess effect yarn wraps around the core yarn at the same spot , forming these bunches . Between the knop sections the yarn resembles a normal plied yarn. For all the other yarns described previously, the effect yarn overfeed , when used is constant during production for knop yarn is , the overfeed is controlled. The feeding device for the core yarn must therefore be able to change speed during production. The formation of the knop can be controlled by a device called knopping bar or a control bar. The extent of the knop can be spread by the movement of the knopping bar, producing elongated knop or stripes. The core yarn and the effect yarn may be stopped at the alternately intervals, leading to a yarn showing alternately  sections of one of the component yarns. This type of yarn is also called cloud yarn.

fig.9 knop yarn.

Ref:-https://textilelearner.