What is Yarn Twist?
The traditional staple yarns are strengthened by means of twisting the bundle of fibers. “Twist” could be elaborated as the spiral disposition of the components of a thread as a result of the relative rotation of the two ends. The presence of twist in a yarn binds the fibers together and helps to keep them in their corresponding positions. It provides coherence between the fibers and adequate strength to the yarn. Twist is also imparted to create different effects that are highly visible when fabric is manufactured from this yarn. The effects are attained by combining yarns with different twist levels and twist directions in the fabric. Twist is usually expressed as the number of turns per unit length of yarn, for example, turns per inch or turns per meter.
Effect of Twist on Yarn Strength:
Short staple yarn:
Twist is imparted into a staple yarn to bind the fibers together and provide coherence to give strength to the yarn. Firstly, with the increment of twist, the lateral force holding the fibers also increases, which allows more fibers to contribute to the yarn strength. But secondly, when twist increases from the optimum level, the angle of fibers made with the axis of the yarn also increases, which makes the fibers contribute less to the yarn strength. The influence of increasing twist on the strength of a staple spun yarn is shown in Figure-1.
Continuous filament yarns:
In the case of filament yarns, a small amount of twist is needed to hold the filament fibers together. Therefore increase in twist will decrease the strength of filament yarn. This is due to the fact that the filaments are stronger than short staple fibers, so less twist is needed to impart strength in the case of filament yarns. Theoretically the maximum strength of a continuous filament yarn is possible when the filaments are oriented parallel to the axis of the yarn. Since the filaments are of variable strength, so the primary function of twist is to provide support to weaker filaments thus resulting in an increase in the yarn strength. The influence of increasing twist on a continuous filament yarn is shown in Figure-2.
Effect of Twist on Yarn and Fabric Properties:
The twist level has an effect on the properties of yarn as well as fabric. The following parameters are affected by twist:
- Hand feel
- Moisture absorption
- Wearing properties
- Aesthetic effects
- Moisture wicking
- Air permeability
- Luster
Twist Directions:
Twist may be performed in the following two directions known as S (clockwise) and Z (anticlockwise) twists (Figure-3). These S and Z twist are described below.
S-twist:
When a twisted yarn is held vertically and the individual filaments appear as the diagonal in the letter “S,” then it is called an “S–twist.” Similarly, when several yarns are combined and given an S-twist, then the individual yarns appear as the diagonal in the letter “S.”
In another way, a single yarn has ‘S’ twist if, when it is held in the vertical position, the fibers inclined to the axis of the yarn conform in direction of slope to the central portion of the letter S. S and Z twisted yarns are shown in Figure-3.
Z-twist:
When a twisted yarn is held vertically and the individual filaments appear as the diagonal in the letter “Z,” then it is called a “Z–twist.” Similarly, when several yarns are combined and given a Z-twist then the individual yarns appear as the diagonal in the letter “Z.”
In another way, a single yarn has ‘Z’ twist if, when it is held in the vertical position, the fibers inclined to the axis of the yarn conform in direction of slope to the central portion of the letter Z.
As can be seen from the diagram of twist directions (Figure-3), by holding the yarn upright, the slope of the middle of the yarn should flow in the same direction as the slope of the middle of the letters S or Z. The majority of single yarns are Z, but the direction does not really affect the property of the yarn. However, in a plied yarn, the direction is important because the single yarn should be in one direction but when two yarns are combined to make the ply it is running in the opposite direction; this ensures that the yarn holds together.
For example, 2 x S single yarn + Z ply = stable, smooth, firm, tight and durable yarn suitable for weaving; worsted yarns often possess a high-angled twist.
2 x Z single yarn+ S ply = stable, soft, bulky yarn suitable for knitting. It often has a low-angled twist.
2 x S single yarns + S ply = an unstable yarn that will snag and curl.
2 x Z single yarns + Z ply = unstable yarn that will snag and curl.
The amount of twist added into a yarn will determine the property of the yarn in terms of durability, flexibility, resilience and strength. A high-twist yarn may offer a hard and relatively stiff yarn, whereas a low-twist may give a weak yarn that is more flexible. Finer yarns have more twists in them than coarser ones, and warp yarns have more twists in them than weft yarns. Fabrics with a soft surface, e.g. peach effect, have a slack twist called soft-twist, which allows fiber ends to be pulled to the surface. Fabrics with smooth surfaces have a higher amount of twist, which offers extra strength and some crease resistance, whereas textured surface fabrics, such as crêpe, are given a maximum twist.
Types of Fabrics with Respect to Different Types of Twist:
Soft surfaced fabrics have slack twist:
- Smooth surfaced fabrics have optimum twist. This stimulates strength, smoothness, and elasticity.
- Crepe fabrics have the maximum number of twists.
- Poplins have two single yarns that are Z-twisted individually and plied together using an S-twist.
- Sewing thread has three S-twisted single yarns, which are then Z-twisted together. Tear-resistance of this thread will be higher.
References:
- Advanced Textile Testing Techniques Edited by Sheraz Ahmad, Abher Rasheed, Ali Afzal, and Faheem Ahmad
- Fibers to Fabrics by Bev Ashford
- The Substrates – Fibres, Yarn and Fabric by Mathews Kolanjikombil
- Theory of Structure and Mechanics of Yarns By Bohuslav Neckář and Dipayan Das
- https://textilelearner.net/yarn-twist-types/
You may also like:
- Relationship between Yarn Count and Twist | Principles of Twist Measuring Methods
- Mechanism of Twist Insertion to the Yarn in Ring Spinning
- Calculation of Twist, Twist Constant of Ring Frame
- Calculation of Twist, Twist Constant of Roving Frame or Speed Frame Machine
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.
