Production and Properties of Core Spun Yarns
Production and Properties of Core Spun Yarns
Production and Properties of Core Spun Yarns
1.0 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.
2.0 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.
1. Conventional core spinning attachment with ring spinning systems
2. S.R.R.C Core wrap spinning method
3. A.R.S. Patterned Spinning system
4. Core-twin spinning system
5. Composite electrostatic spinning system
6. Rotor spinning system
7. Friction spinning system and
8. Air jet spinning system
2.1 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.
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 cottonsided core twin spun yarn; when the core yarn inserted periodically in the both strands, this
yarn is called migrated core twin spun yarn.
It was noted that the width of the filament spread over decreased with increase in the roller
speed. At 0.33% antistatic fish on core with positive top electrode appeared to give largest
spreading effect. Incase of 0.15 %antistatic finishes on the core with negative top electrode give a
better filament spread .C.V% of measurements found to be large due to migration during the
coating or drying out in the processes and variation in the feed tension.
It was reported that filament spread improved as the potential difference of the applied voltage
between the electrodes increased, due to intensified electric field. The yarn produced by this
system has sufficient twist to prevent the surface fibers from sliding along the filament core.
7.1.1 Doubling
Two or three ends are twisted together to make sewing thread. This twisting process improves
the cotton covering of the core-spun yarn. Disadvantages of the single core yarn are that the
outer cover of staple fibers may rather be easily removed from the core filament by abrasion,
this is not recommended for sewing thread, since thread ism severally abraded against the
needle during the sewing. It requires higher resistance to abrasion. The doubling together of two
or more single core-spun yarn effectively overcomes this problem by binding with the structure
fibers more firmly with the structure.
7.1.2 Heat setting
Fibres and filaments used for the spinning core yarns having different characteristics and the
resultant yarn may shrink differently, so to achieve balance and set of these yarns, heat setting
has to be done. Setting of twist is done by steaming the yarn in an auto calve with steam
pressure of 0.6 kg/cm2 for 30-60 minute. Temperature of the steam has to be maintained with
100-105X C. The steaming time is decided on the basis of twist level in the doubled yarn. The
heat-setting leads to stabilization and equalization of the elongation properties of the thread and
it prevent the snarling. Polyester and Nylon threads required high pressure steaming and the
industrial sewing threads needed low pressure steaming.
7.1.3 Hot stretching
Hot stretching is a process of heating the thread to pre determined and controlled temperature
in the range of 180-240X Centigrade with tension and length control. Heat setting operation
causes a decrease in the modulus and increase in the extensibility of the thread. Consequently
when high modulus thread requires subsequent stretches. This hot stretching improves the
thermal stability and reduces the extensibility. The sewing thread length improved 4. -6%. The
specific tenacity improved to 3-5%. This helps to get improvement in dyeing and kink free
sewing thread.
7.1.4 Wet processing
After heat setting threads has to be converted in to hank form for required wet processing
treatments. High color fastness and precise shade matching are the key factor requirements for
Core-spun sewing threads. Normally to get uniformity, cross wound packages with high
pressure equipments used.
7.1.5 Lubrication
Gliding and cooling effect on the needle could be done with effective lubricants. Good lubricant
must not clogs on the needle eye or causes stain. The lubricant must allow the thread to unwind
evenly from the package. The friction between the abrading surface should be minimized with
lubrications inexpensive lubricants will be preferred.
12. Proper yarn number calculation and core content determining method should
be properly adopted
13. While producing core yarn polyester / Cotton yarn will be drafted and filament
should be processed through front Roller region.
14.For good blended, we should provide guide in between cradle and front top
roller.
15.Proper piecing method should be implemented in spinning to avoid improper
core yarn.
16.Traverse motion should not be utilised for producing good core yarn.
17.Precaution should to be taken for keeping the drafting zone clean. Cots, apron
condition, should be fluff and fly free.
18.Buffing should be done for every 30 days for producing Good yarn.
19.Traveller should be changed once in week. Special creel attachment should to
be provided for creeling Filament yarn.
20.Optimum unwinding tension of core filament is to be ensured for quality core
yarns
21.Another major factor influencing the quality is the selection of traveller. It is
essential that round cross section travellers are selected in order to ascertain that
the cover is not disturbed (peeling off).
22.Yarn balloon is to be closely monitored to ensure that it does not touch any
parts like separators, empties and gets disturbed.
23.Spindle speeds must be reduced to an extent that breakages are maintained
well below 101000 spindle hour.
Special Training to workers highlighting probable reasons detrimental to quality is
a must.
24. Core filament should not be missing at any place in the yarn to provide
necessary stop motions for the same
25. Yarn splice quality should be good.
26. Cops should be taken out from ends down spindles and keep the cops
separately
and remove the yarn till the core yarn comes to spring action, which is the
indication for Lycra content.
27.Set CA, CCA Setting in Autoconer as 6% to ensure Lycra missing
28. Piecing hands and fingers should be free from dirt and oil