05-10-2012, 04:53 PM
PRODUCTION AND PROPERTIES OF CORE SPUN YARNS
PRODUCTION AND PROPERTIES.docx (Size: 85.88 KB / Downloads: 77)
Introduction
Definition: Core-spinning is a process by which fibres are twisted around an existing yarn, either filament or staple spun yarn, to produce a sheath– core structure in which the already formed yarn is the core.
Core-spun yarns are two-component structure with Core and sheath. Generally continuous filament yarn is used as core and the staple fibres used as sheath covering. The core-spun yarn used to enhance functional properties of the fabrics such as strength, durability and stretch comfort.
Methods for production of Core spun yarns
The production of Core-spun yarns done successfully by many spinning systems. Each system has its own features .The conventional ring spinning is simple and economy but the core positioning in the centre is difficult and major strip back problem may arise during subsequent process and the core filaments get twisted. In Dref III the core positioning can be set accurately and used to produce the industrial and conductive yarns. Probable methods of core-spun yarn production are discussed below.
Conventional Core spinning attachment in Ring frame
A core spinning attachment in ring spinning is shown in Fig.1. The attachment consists of metal plate (Bracket) bent to a shape. One end of the device is fitted on the roving traverse guide bar such that the relative position of the roving and the core filament may be kept constant all the time. There is a provision to vary the position of the device if required. The other end of the plate is fitted with a porcelain guide that feed the core filament at a precise position behind the front drafting rollers. This devise is fitted with a pre-tensioner and is kept in a horizontal plane. Varying the number of tension discs may vary the input tension of the core filament. The package containing core filament material is suspended from a bar such that they could rotate easily, thus avoiding any tendency to stretch the filament before it is fed to the tensioning device.
S.R.R.C. Core wrap spinning system
Southern Regional Research Center has developed a core spinning system [1] is shown in Fig. 2. In conventional core-spinning system yarns are merely a ply twisted and does not have good core coverage, strip back problem may arise during subsequent mechanical processing. The core wrap yarns produced by the SRRC core spinning system consists of a central core of a particular filament or staple fiber and core material is almost coaxially and totally wrapped with cotton on any other staple fiber. It is claimed that a high degree of coherence is obtained between the constituent fibers. The core-wrap assembly is used as twist breaker, which helps the sheath fibres to cover the filament.
Core Twin Spun Yarn
Harakawa [2 ] has developed and patented a Core twin spun yarn system as shown in Fig. 4. The figure is a schematic illusion for the core twin spin yarns. In the spun silk ring spinning frame the drafting part was equipped with an apron device for cotton fibers, because they were shorter then the silk fibers. The continuous filament core-spun yarn passes through a control disc inserted directly behind the front roller in a drafted strand of either cotton or spun silk via a core yarn guide. The drafted spun silk and cotton strands and the scoured silk continuous filament core yarns were twisted together as they emerge from the front rollers.
Usually the core yarn guide remains at a fixed position and also possible to move them by moving the position rollers. When the rollers change the position of the guide, the core yarns migrate periodically from the spun silk to cotton and from cotton to spun silk. When scoured silk core yarn is inserted in the spun silk strand only, this yarn was called ‘silk –sided’ core twin spun yarn; when the core yarn is inserted in the cotton strand only, this yarn is called ‘cotton-sided’ core twin spun yarn; when the core yarn inserted periodically in the both strands, this yarn is called ‘migrated –core’ twin spun yarn.
Composite yarn by Electro static filament charging method
Smith & others [3] developed a method for producing with the mixed construction of staple and filament fibers involved with use of the frictional contact methods by using electro static system and short comings with this system was only hydrophobic fibers can be handled, and often filaments tend to break and wound around the rotating components. This system prone to safety problems because of the high voltage required and a water supply required for imparting the electrical conductivity to the continuous filament yarn.
Another electrostatic filament charging method [4] shown in the figure.5 uses two electrodes to separate the multifilament yarn. The filament charging device is described which is based on the principle of two electrodes system; this was employed to separate a multi filament yarn. The separated filaments were then mixed with the staple fibers of roving at the roller nip on the ring spinning system as illustrated in the figure5. The blended ribbon was subsequently twisted to form a yarn. This is an effective measure for resolving the strip back problem.