· RING and TRAVELLER COMBINATION:
· The following factors should be considered
- materials of the ring traveller
- surface charecteristics
- the forms of both elements
- wear resistance
- smoothness of running
- running-in conditions
- fibre lubrication
· For the rings two dimensions are of primariy
importance. 1.internal diameter 2. flange width.
· Antiwedge rings exhibit an enlarged flange
inner side and is markedly flattened on it upper surface.This type of profile permitted to use travellers with a lower centre of gravity and precisely adapted bow(elliptical travellers), which in turn helped to run the machine with higher spindle speeds. Antiwedge rings and elliptical travellers belong together and can be used in combination.
· Low crown profle has the following advantage.
Low crown ring has a flattened surface top
and this gives space for the passage of the yarn so that the curvature of the traveller can also be reduced and the centre of gravity is lowered.In comparison with antiwedge ring, the low crown ring has the advantage that the space provided for passage of the yarn is somewhat larger and that all current traveller shapes can be applied, with the exception of the elliptical traveller. The low crown ring is the most widely used ring form now.
and this gives space for the passage of the yarn so that the curvature of the traveller can also be reduced and the centre of gravity is lowered.In comparison with antiwedge ring, the low crown ring has the advantage that the space provided for passage of the yarn is somewhat larger and that all current traveller shapes can be applied, with the exception of the elliptical traveller. The low crown ring is the most widely used ring form now.
· · The ring
should be tough and hard on its exterior. The running surface must have high
and even hardeness in the range 800-850 vikcers. The traveller hardness should
be lower (650-700 vickers), so that wear occurs mainly on the traveller, which
is cheaper and easier to replace. Surface smoothness should be high, but not
too high, because lubricating film can not build up if it too smooth.
· · A
good ring in operation should have the following features:
- best quality raw material
- good, but not too high, surface smoothness
- an even surface
- exact roundness
- good, even surface hardness, higher than that of the traveller
- should have been run in as per ring manufacturers requirement
- long operating life
- correct relationship between ring and bobbin tube diameters
- perfectly horizontal position
- it should be exactly centered relative to the spindle
· In reality, the traveller moves on a
lubricating film which builds up itself and which consists primarily of
cellulose and wax. This material arises from material abraded from the
fibres.If fibre particles are caught between the ring and traveller, then at
high traveller speeds and with correspondingly high centrifugal forces, the
particles are partially ground to a paste of small, colourless, transparent and
extremely thin platelets.
The platelets are continually being replaced during working. The traveller smoothes these out to form a continuous running surface.The position, form and structure of lubricating film depends on
The platelets are continually being replaced during working. The traveller smoothes these out to form a continuous running surface.The position, form and structure of lubricating film depends on
- yarn fineness
- yarn structure
- fibre raw material
- traveller mass
- traveller speed
- heigh of traveller bow
Modern ring and traveller combination with good fibre
lubrication enable traveller speeds upto 40m/sec.
· 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.
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.
· · 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 traveller
- to the traveller mass
- to 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.
· 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 hte 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.
· SHAPE OF THE TRAVELLER:
· The traveller must be shaped to match exactly
with the ring in the contact zone, so that a single contact surface, with the
maximum surface area is created between ring and traveller. The bow of the
traveller should be as flat as possible, in order to keep the centre of gravity
low and thereby improve smoothness of running.
· However the flat bow must still leave
adequate space for passage of the yarn. If the yarn clearance opening is too small,
rubbing of the yarn on the ring leads to roughening of the yarn, a high level
of fibre loss as fly, deterioration of yarn quality and formation of melt spots
in spinning of synthetic fibre yarns.· WIRE PROFILE OF THE TRAVELLER:
· Wire profile influences both the behaviour of
the traveller and certain yarn characteristics, they are
- contact surface of the ring
- smooth running
- thermal transfer
- yarn clearance opening
- roughening effect
- hairiness
· The traveller should generate as little heat
as possible quickly distribute the generated heat from the area where it
develops over the whole volume of the traveller transfer this heat rapidly to
the ring and the air be elastic, so that the traveller will not break as it is
pushed on to the ring exhibit high wear resistance be less hard than the ring,
because the traveller must wear out in use in preference to the ring
· In view of the above said requirements,
traveller manufacturers have made efforts to improve the running properties by
surface treatment. "Braecker" has developed a new process in which
certain finishing components diffuse into the traveller surface and are fixed
in place there. The resulting layer reduces temperature rise and increases wear
resistance.
· · Traveller
mass determines the magnitude of frictional forces between the traveller and
the ring, and these in turn determine the winding and balloon tension. Mass of
the traveller depends upon
- yarn count
- yarn strength
- spindle speed
- material being spun
· When the yarn runs through the traveller,
some fibres are liberated. Most of these fibres float away as dust in to the
atmosphere, but some remain caught on the traveller and they can accumulate and
form a tuft. This will increase the mass of traveller and will result in end
break because of higher yarn tension. To avoid this accumulation , traveller
clearers are fixed close to the ring, so that the accumulation is prevented.
They should be set as close as possible to the traveller, but without affecting
its movement. Exact setting is very important.
· · Specific
shape of the cop is achieved by placing the layers of yarn in a conical
arrangement. In the winding of a layer, the ring rail is moved slowly but with
increasing speed in the upward direction and quickly but with decreasing speed
downwards. This gives a ratio between the length of yarn in the main (up) and
cross(down) windings about 2:1.
· · The total
length of a complete layer (main and cross windings together) should not be
greater
than 5m (preferably 4 m) to facilitate unwinding. The traverse stroke of the ring rail is ideal when it is about 15 to 18% greater than the ring diameter.
than 5m (preferably 4 m) to facilitate unwinding. The traverse stroke of the ring rail is ideal when it is about 15 to 18% greater than the ring diameter.