System of imparting twist in roving:
Cross-sectioning of yarn will reveal many fibers. The fibers in the yarn lie side by side. Similarly, in roving, the fibers lie side by side. If the roving is not given a twist, the fibers will come loose from the roving. So the fibers are held in the roving by twisting them in a right-to-left or left-to-right pattern along the axis of the roving. However, roving provides relatively less twist than yarn. The imparting of twist facilitates winding on the roving bobbin, facilitates the transfer, and also eases use in the next machine i.e. spinning frame. https://bdfabric.com/importance-and-factors-of-twist-in-roving-frame/
Types of twist imparting in roving:
The type of twist depends on the direction of the twist. That is, depending on the direction in which the fibers are rotating with the axis of the yarn, the type of twist is differentiated. Depending on the direction of the twist it is divided into two categories:
In this case, the fibers rotate clockwise with the yarn axis to form a twist called S-twist. The English letter (S) is named as the stomach bends in the same way that the eyes bend with the axis of the thread.
In this case, the fibers turn left along the axis of the yarn and turn counterclockwise to form a twist, called Z-twist. So named because the fiber twists along the axis of the thread in the same way that the belly of the English letter Z bends. The roving is usually given an S-twist.
System of imparting twist in roving. In yarn production by roving, a draft is provided in the ring frame in 2 zones — a front zone and a back zone. The very little draft is provided in the back zone. The draft provided in the back zone is also called the break draft. That is, the slight twist imparted to the roving from the roving frame needs to be removed as it feeds into the ring frame. Otherwise, it is not possible to provide the required amount of draft in yarn making. The slight draft provided in the back zone of the ring frame to remove the roving twist is called the break draft.
Hence, a twist is provided in the roving, which is easily removed in the back zone of the ring frame. The roving twist usually depends on the roving hook and the twist multiplier.
The necessity of twist in roving:
Roving has given a twist for the following reasons:
1. The fibers in the roving hold each other together.
2. The roving needs to be twisted so that it does not tear easily from the bobbin.
3. Twisted roving facilitates the latter process.
4. The roving is easily transferable.
5. For the convenience of retaining shorter fibers in roving.
6. To give a yarn-like shape to the roving.