RINGS And TRAVELLERS
In most cases, the limit to productivity of the ring spinning machine is defined by the traveller in interdependence with the ring, and yarn. It is very important for the technologist to understand this and act on them to optimize the yarn production.
- The following factors should be considered
- materials of the ring traveller
- surface charecteristics
- the forms of both elements( ring and traveller)
- wear resistance
- smoothness of running
- running-in conditions
- fibre lubrication
Traveller imparts twist to the yarn. Traveller and spindle together help to wind the yarn on the bobbin. Length wound up on the bobbin corresponds to the difference in peripheral speeds of the spindle and traveller. The difference in speed should correspond to length delivered at the front rollers. Since traveller does not have a drive on its own but is dragged along behind by the spindle.
High contact pressure (upto 35 N/square mm)is generated between the ring and the traveller during winding, mainly due to centrifugal force. This pressure leads to generation of heat. Low mass of the traveller does not permit dissipation of the generated heat in the short time available. As a result the operating speed of the traveller is limited.
Heat produced when by the ringtraveller is around 300 degree celcius. This has to be dissipated in milliseconds by traveller into the air.
Parts of a traveller:
Height of bow: It should be as low as possible for stable running of traveller. It should also have sufficient yarn pasage.
Yarn passage: According to count spun the traveller profile to be selected with required yarn passage.
Toe gap : This will vary according to traveller number and flange width of the ring
Wire section: It plays an important role for yarn quality, life of traveller.
Ring contact area: This area should be more, uniform, smooth and continuous for best performance.
Inner width: This varies according to traveller profile and ring flange.
SALIENT FEATURES OF A TRAVELLER:
- Generate less heat
- dissipate heat fastly
- have sufficient elasticity for easy insertion and to retain its original shape after insertion
- friction between ring and traveller should be minimal
- it should have excellent wear resistance for longer life
- hardness of the traveller should be less than the ring
When the spindle speed is increased, the friction work between ring and traveller (hence the build up) increases as the 3rd power of the spindle rpm. Consequently if the spindle speed is too high, the traveller sustains thermal damage and fails. This speed restriction is felt particularly when spinning cotton yarns of relatively high strength.
If the traveller speed is raised beyond normal levels , the
thermal stress limit of the traveller is exceeded, a drastic
change in the wear behaviour of the ring and traveller ensues.
Owing to the strongly increased adhesion forces between ring and
traveller, welding takes place between the two. These seizures
inflict massive damage not only to the traveller but to the ring
as well.Due to this unstable behaviour of the ring
and traveller system the wear is atleast an order of magnitude higher than during the stable phase. The traveller temperature reaches 400 to 500 degrees celcius and the danger of the traveller annealing and failing is very great.
The spinning tension is proportional
- to the friction coefficient between ring and aveller
- to the traveller mass
- toto the square of hte traveler speed
and inversely proportional
- to the ring diameter
- and the angle between the connecting line from the traveller-spindle axis to the piece of yarn between the traveller and cop.
- In order to maintain the same friction or spinning tension with different coefficients of friction, different traveller weights must be used. The coefficient of friction is determined by the fiber lubrication and is subject to fluctuation. Dry cotton means higher coefficient of friction. For manmade fibres depending upon the manufacturer, lower to medium coefficient of friction.
The coefficient of friction with fiber lubrication can vary from 0.03 and 0.15.
R = Co ficeint of friction x N
R - traveller friction in mN
N = Normal force >= (Fc x ML x V xV)/(R)
Fc - centrifugal force
ML - mass of the traveller in mg
V - traveller speed in m/s
R - radius of the ring (inside)
- The yarn strength is affected only little by the
spinning tension. On the other hand the elongation
diminishes with increasing tension, for every tensile load
of the fibres lessens the residual elongation in the fibres
and hence in the yarn. Increasing tension leads also to
poorer Uster regularity and IPI values.
- If the spinning tension is more, the spinning triangle becomes smaller . As the spinning triangle gets smaller, there is less hairiness.
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